# Appropriate Charge Rate for NiMH Batteries



## Scooby Doo

I own the Maha MH-C9000 WizardOne battery charger and I would like to know the appropriate charge rates for the following batteries:

1. Duracell Rechargeable AA 2650 mAh
2. Energizer Rechargeable AA 2200 mAh
3. Rayovac IC3 AAA 800 mAh
4. Rayovac Rechargeable 1.2V AA
5. Rayovac Rechargeable IC3 1800 mAh


Thanks.


----------



## Marduke

0.5-1.0C is the proper charge current.

However I recommend not charging the IC3 cells, as they require a special charger and will quite possibly self destruct on any other charger.


----------



## Scooby Doo

For a charge rate of 1.0 C, how long would it take to charge the above batteries?

I read on other sites charging batteries for 1 to 2 hours is the best way for prolonging the batteries lives. Is this correct?

I also own the Energizer 15 minute charger. I used this charger, before owning the Maha charger, to charge some of the batteries listed above but the charger had damaged those batteries, would I be able to bring them back to life using the Maha charger? I assume the excessive heat had damaged the batteries.

Is Sanyo Eneloop batteries considered to be better than the above listed batteries?


Thanks.


----------



## tino_ale

All this is throughly explained in the charger manual IIRC


----------



## SilverFox

Hello Scooby Doo,

Welcome to CPF.

Charging at 1C takes just over 1 hour. Charging at 0.5C takes just over 2 hours. Charging at 2C is not recommended, but if you did it would take just over 0.5 hours.

When using a charger that uses -dV to terminate the charge, the strongest end of charge signal is generated when you charge in the range of 0.5 - 1.0C.

15 minute charging is quick and it has its place, but you pay for this convenience in reduced cycle life. Once a cell is damaged physically, there is nothing you can do to bring it back. If the performance of the cell drops due to uneven electrolyte distribution, you can revive the cell through using the Break-In function on the C9000. 

15 minute charge rates tend to damage the internal components of the cell as opposed to storage which can also involve damage to the internal components, but at first it usually be reversed. At any rate, the best way to try to improve your cells performance is to periodically run a Break-In function on them.

The IC3 cells terminate the charge by disconnecting the internal circuit when the cell internal pressure reaches a set value. A non-IC3 charger will think that you removed the cell at that point, and when the switch resets it will think that you inserted a new cell and begin charging all over again. If you are planning on charging IC3 cells on the C9000, you must remove them as soon as they first shut off.

Tom


----------



## travelinman

I charge all my Nimh cells at 200 mah. But then, I'm retired and my time is worth nothing and I have all day/week/month to wait. :nana:


----------



## Marduke

travelinman said:


> I charge all my Nimh cells at 200 mah. But then, I'm retired and my time is worth nothing and I have all day/week/month to wait. :nana:



That is actually really bad for the cells. Chances of missed termination, and hence cooking the cell is greatly increased.


----------



## TorchBoy

travelinman said:


> I charge all my Nimh cells at 200 mah. ... :nana:


Quite apart from the practice being bad if it's not terminated, NiMH cells have a capacity in mAh, and are charged in mA for a certain number of h.

:nana:

Yes Scooby Doo, Eneloops are great.


----------



## travelinman

Marduke said:


> That is actually really bad for the cells. Chances of missed termination, and hence cooking the cell is greatly increased.



I guess that all depends on which charger you are using. If your charger terminates at the appropriate time reliably then there's no problem. If you find that it terminates properly after "x" number of samples, then its OK to trust it.

You can even (and I have) checked the current flowing into the cell and compare that with the time it has been on the charger and calculate the amount milli amp hours sent to the cell on the cheaper chargers with no readout for that. I constantly check the readout on my 900 and it has never exceeded the cells safe capacity, therefore has always terminated properly.

I know some have found chargers that have done that at 200 ma, but I guess mine was not made on a monday or friday.


----------



## brted

It seems like you would want to charge them as slowly as you can, provided you don't risk missing the termination. Since there have been problems missing termination lower than 500 ma, then I charge my AA's at 600 ma. Charging at 0.5C to 1.0C seems to be fine, but the faster you charge a battery the more heat you get and heat is bad, right?

If a battery has less than 1200 mah (like AAA's) then I use 0.5C.


----------



## Marduke

If the cell is healthy, it will not get hot (just warm) when charged at the proper currents (0.5-1.0 C).

While you may think you are being kinder by charging them slower, you are actually putting your cells in an early grave.


----------



## jayflash

Yes, SilverFox and other sources have indicated a .5C - 1C is better for the NiMH chemistry and will result in better performance than a slow charge.


----------



## 45/70

Most sources agree that NiMH's are best charged at a 0.5-1C rate.

I think the misconception that a slow rate is good for NiMH's is a hangover from the days of NiCds. The simplest, and cheapest chargers were ones that approximated a forming charge or 0.1C hence, the 14-16hr chargers they used. NiCd's are somewhat tolerant of slow charging, but for example, Battery University states on their "Do and don't" page, that a fast charge is preferred over a slow charge for NiCds as well.

Dave


----------



## Mr Happy

45/70 said:


> Battery University states ... that a fast charge is preferred over a slow charge for NiCds as well


In fact I believe NiCd's can take even faster charging than NiMH, 2C or beyond.


----------



## alfreddajero




----------



## Turbo V6 Camaro

glad i searched 

I have been going off the c-9000 book at .3c to .1c i ahve been doing all my cells at 700mah charge and 350-500 discharge

should i step it up some?


----------



## Mr Happy

Turbo V6 Camaro said:


> glad i searched
> 
> I have been going off the c-9000 book at .3c to .1c i ahve been doing all my cells at 700mah charge and 350-500 discharge
> 
> should i step it up some?


Not 0.3C to 0.1C, 0.3C to 1.0C. In general, the highest rate your charger can do up to 1.0C is best. If your charger can't go that high, just use the highest it can manage.


----------



## J_C

Marduke said:


> That is actually really bad for the cells. Chances of missed termination, and hence cooking the cell is greatly increased.



Bad perhaps but I wouldn't say _really bad. _That rate is at or below 0.1C for most modern NiMH AA, cells that size can sit at 200mA current for many hours past being fully charged and you'll only lose maybe a dozen % of the lifespan in the long term, which can be an acceptable trade-off. Not ideal, but in the end we're talking about batteries costing a couple bucks a piece. Much commotion is made about idealisms in charging NiMH, but they really aren't all that picky to recharge providing they don't get excessively hot. Many batteries will be hotter at the end of a 1C rapid charge than they would get sitting at 200mA charge current for several hours past being fully charged.

There is insufficient evidence to conclude a rapid charge rate will result in better performance, more of an urban myth since we know a slow charge is completely capable of fully charging a battery, it just has to terminate not too soon and not too late which is the trickier part. What it will do instead is waste less power but if you're on the grid the difference won't matter.

On the other hand, I've 3 different cheap chargers that never have a problem sensing Delta-V cutoff when charging at about ~0.3C (700mA) with all the batteries I've put in them. Maybe charging circuits are getting better than they used to be, and since a basic level of features comes with even a $10 charger these days, not much reason to do without cutoff circuits in them unless it's a series pack being charged and so the charger either doesn't exist or is much more costly.


----------



## SilverFox

Hello J C,

I beg to differ...

There is enough evidence to support charging in the 0.5 - 1.0C range that the battery manufacturers actually recommend it.

Tom


----------



## J_C

See Sanyo's FAQ page, they clearly recommend against it.

http://us.sanyo.com/Batteries/FAQs



> Can I use a "Quick Charger" to charge an eneloop battery?
> 
> 
> Though it is possible to charge an eneloop battery in a "Quick Charger", it is not recommended. We recommend charging eneloop batteries in a NiMh charger that is 2 hours or more. Charging eneloop batteries in a "Quick Charger" can reduce the overall life of the battery.
> 
> 
> How long does it take to charge an eneloop battery in the eneloop 4-position charger?
> 
> 
> From 4 to 7 hours



(more on linked page)
Same is true of most battery manufacturers, they make several chargers with under 0.5C rate.


----------



## Marduke

J_C said:


> See Sanyo's FAQ page, they clearly recommend against it.
> 
> http://us.sanyo.com/Batteries/FAQs
> 
> (more on linked page)
> Same is true of most battery manufacturers, they make several chargers with under 0.5C rate.



I suggest you read the technical specs and not the dumbed down FAQ written for illiterate consumers. 

Sanyo recommends 1C charge...
http://us.sanyo.com/dynamic/product/Downloads/AA_4Pack-49579479.pdf 
http://us.sanyo.com/dynamic/product/Downloads/AAA_4Pack-35338904.pdf

Energizer recommends 1C charge (page 19)....
http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

Duracell recommends 1C charge...
http://www.duracell.com/oem/rechargeable/Nickel/methods.asp


Believe it or not, there is little correlation to what a company's chargers do (designed purely for cost/profit reasons), and what the best practices say to do (chosen purely for technical reasons). Until the day comes that the bean counters making the decisions are actually knowledgable about the products they sell (fat chance), there will always be a discrepency. However, we here has CPF as knowledgable consumers (usually) have the advantaged of knowing the proper methods, and knowing what equipment will give the best performance for the cells you choose.

Edit:
Panisonic also recommends 0.5-1C charge...
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiMH_ChargeMethods.pdf

Rayovac also recommends 1C charge...
http://www.rayovac.com/technical/pdfs/NM715_2100MAH.pdf 
http://www.rayovac.com/technical/pdfs/NM724.pdf


----------



## J_C

There's nothing profitable about their batteries not meeting their published specs. They do not stipulate you must use any one of the methods they recommend to achieve the specifications for their cells.

There are certainly things that shouldn't be done, but anything except 0.5C to 1.0C isn't one of them.

Again I will remind that there is a slight reduction in lifespan from some charge rates and overcharging, but they are $2 batteries not your long lost child or bars of gold. The more important factor is convenience which can lead to rapid charging in some scenarios or not in others. The majority of the planet does not rapid charge and proves the successful use of lower charge rates despite people who obsess about tiny differences and most of them with unscientific tests posed as "fact".

Take for example the crazy supposed facts about battery temperature rise opposed to voltage rise for Delta -V termination. The supposed facts ignore the constants.

If you take one battery 5% away from it's Delta -V threshold and put it into a charger, and compare it to another battery which had been fully drained and recharged up to 5% away from Delta -V, the latter battery is hotter than the former. Delta -V is not temperature dependent, it just happens that a change, a variable one, facilitates it which is a far different situation than predicting end of charge from an absolute temperature or rise over ambient temp.

So it goes with most studies. Only when you take all the information do you find the glaring holes in the research.

What all these battery companies do is guarantee their product when you use their chargers which operate below 0.5C charge rate. I don't make that guarantee, they do. It is not important to try and eek out the last % capacity or life from a battery, we got along fine with less performance for many years and in the years coming will have even more. 

Once again, the majority of the world has no problem carrying out their lifes, using myriad types of devices charging at a rate you don't like. Despite it being less than a hypothetically ideal rate, it is fine to use and the world stands constantly ready to prove that every moment.

There is no better proof than almost everything and almost everyone (manages to use their devices and batteries fine without a care in the world about some narrow charge rate).


----------



## Marduke

"That's how everyone is doing it" is not a valid reason for how something is supposed to be done. Lots of people do lots of things incorrectly, that doesn't make it right.

The point of the discussion here of what charge currents to use is not about what lots of people do (incorrectly, even by manufacturer standards), but what is BEST.

And as silverfox described, much of the world using slow charging DO have issues, they just don't know it. They think short life cycles and worsening performance are the norm and don't have the knowledge that the grass really is greener on the other side. 

Lots of people drink and drive and get away with it, speed, swim less than 30 minutes after eating, etc. But that doesn't mean any of those are good ideas either. 

There is no doubt, given the choice between the two, fast (1C) is better than slow, as proven by documentation above. 

Where is your proof of the opposite?


----------



## Marduke

As for you temperature dependance question, feel free to view the Energizer document in great detail.

Also, try artificially cooling a cell during charging at 1C and monitoring the temp and voltage. Whoops, the -dV signal just disappeared. So much for that theory....


----------



## sygyzy

Great advice. I wrote it all down. 

*What's the appropriate DISCHARGE rate?*


----------



## travelinman

You really do like to  don't you


----------



## clintb

travelinman said:


> You really do like to  don't you


I don't see Marduke as provoking in the least. On the contrary, he dug up plenty of factual information, and presented a distilled version of what the folks (mostly SilverFox) have discovered in actual tests. If you have some good test numbers to backup the one, consumer focused, document you've posted, then please, by all means, give more info.


----------



## wapkil

SilverFox said:


> Hello J C,
> 
> I beg to differ...
> 
> There is enough evidence to support charging in the 0.5 - 1.0C range that the battery manufacturers actually recommend it.



Can you (or someone else) direct me to the places or documents describing why fast charging is better than standard charging? I have read it many times that fast charging is recommended but I couldn't find any clear explanation why. 

It is obvious that if the charging current is too low for the charger to terminate correctly and it overcharges the cell it will be bad for the cell life. I think it may be the most important reason for fast charging current recommendations. 

If we assume though that the charging will be terminated correctly, I don't know why 0.1C can be worse than, say, 0.75C. As I understand, every charging is shorting the life of the battery. If fast charging is better it would mean that these negative effects are lower with higher currents. It may be true but it's counterintuitive for me - I would think that it's usually better to perform similar chemical reactions slower, not faster.


----------



## Mr Happy

wapkil said:


> If we assume though that the charging will be terminated correctly, I don't know why 0.1C can be worse than, say, 0.75C. As I understand, every charging is shorting the life of the battery. If fast charging is better it would mean that these negative effects are lower with higher currents. It may be true but it's counterintuitive for me - I would think that it's usually better to perform similar chemical reactions slower, not faster.


It's a bit of speculation, but here's a hypothesis for you. It is possible that higher charge currents reach more of the chemicals in the battery.

It is commonly observed that flowing things take the path of least resistance. For instance, if you have a trickle of water flowing down a river bed the water will follow a path down the middle and leave much of the channel dry. The reeds at the edge will not get watered. On the other hand if you have a large flow of water the whole river bed well be flooded right up to the edges.

It could be the same with charging an electrochemical cell. A full charge on the battery requires all of the electrode material to be reached by the charging current, but there is no guarantee that all of the paths through the cell have the same resistance. Small currents may follow the path of least resistance and overcharge some parts of the electrodes while leaving other parts undercharged. While larger charging currents may do a better job of flooding the cell and reaching every part of the electrodes.

As I said this is speculation and may be wrong, but it is something to think about.


----------



## TakeTheActive

wapkil said:


> ...It is obvious that if the charging current is too low for the charger to terminate correctly and it overcharges the cell it will be bad for the cell life. *I think it may be the most important reason for fast charging current recommendations*...


We also have the relationship between Charge Current and Crystal Size:
Low Charge Current encourages Large Crystals
High Charge Current encourages Small Crystals
Add to that, Self Discharge also encourages Large Crystals and we start heading towards Separator Damage. :thinking:


----------



## TakeTheActive

Mr Happy said:


> It's a bit of speculation, but here's a hypothesis for you. *It is possible that higher charge currents reach more of the chemicals in the battery*...


I was thinking just the opposite, as evidenced by a recent experiment by *Marc999* in the thread *Mh-C9000: R&A vs. Cycle* dealing with some *Storage Box Queens*:


Code:


Powerex 2700mAh AA [dated 07-08] |   #1    #2    #3    #4
---------------------------------+---------------------------
08/25/09 C9000 Break-In          | 2445  2415  2342  2204 mAh
08/21/09 C9000 Cycle5:  2000/ 100|    ?     ?     ?     ? mAh
08/xx/09 C9000 Cycle4:  2000/ 100| 2109  1917  2080  2281 mAh
08/xx/09 C9000 Cycle3:  2000/ 100| 2125  1960  2061  2298 mAh
08/xx/09 C9000 Cycle2:  2000/ 100| 2160  2022  2103  2316 mAh
08/xx/09 C9000 Cycle1:  2000/ 100| 2239  2168  2153  2351 mAh
08/xx/09 C9000 Break-In          |    ?     ?     ?     ? mAh

AFAICT, it appears that the slow Break-In Charge Current (08/25/09) allowed more of the chemicals (including the areas released by the newly-dissolved crystals) to accept a charge. :thinking:


----------



## TakeTheActive

sygyzy said:


> *...What's the appropriate DISCHARGE rate?*


Appropriate for what? 

I use:
*0.2C* for comparing Capacity
*1.0C* for evaluating vibrancy
*100mA* for dissolving crystals


----------



## wapkil

TakeTheActive said:


> I was thinking just the opposite, as evidenced by a recent experiment by *Marc999* in the thread *Mh-C9000: R&A vs. Cycle* dealing with some *Storage Box Queens*:
> 
> 
> Code:
> 
> 
> Powerex 2700mAh AA [dated 07-08] |   #1    #2    #3    #4
> ---------------------------------+---------------------------
> 08/25/09 C9000 Break-In          | 2445  2415  2342  2204 mAh
> 08/21/09 C9000 Cycle5:  2000/ 100|    ?     ?     ?     ? mAh
> 08/xx/09 C9000 Cycle4:  2000/ 100| 2109  1917  2080  2281 mAh
> 08/xx/09 C9000 Cycle3:  2000/ 100| 2125  1960  2061  2298 mAh
> 08/xx/09 C9000 Cycle2:  2000/ 100| 2160  2022  2103  2316 mAh
> 08/xx/09 C9000 Cycle1:  2000/ 100| 2239  2168  2153  2351 mAh
> 08/xx/09 C9000 Break-In          |    ?     ?     ?     ? mAh
> 
> AFAICT, it appears that the slow Break-In Charge Current (08/25/09) allowed more of the chemicals (including the areas released by the newly-dissolved crystals) to accept a charge. :thinking:



I'm not sure how the values were compared but if it's the comparison between the C9000 "cycle" charge and "break-in" charge results, I think it may not be easy to draw any conclusions from it. The C9000 undercharges good batteries with its strange 1.47V (IIRC) voltage termination but the break-in charge fully charges them.

Anyway, I also think that it's quite possible for the standard charge (0.1C) to provide higher charge levels than with the fast charging currents. I remember seeing the results confirming it but it's also what the data sheets suggest. The battery capacity is always given in accordance to the standard that uses 0.1C. If there was a way to get better charge with higher currents, the manufacturers would use a standard with this better method  I've read that batteries charged with 0.1C may have problems giving higher currents but with moderate currents their charge capacity should be higher.

It's still not clear for me how the standard and fast charge methods compare in relation to the cells longevity, assuming that no errors are made (overcharge, overdischarge, keeping batteries unused etc.). I think the separator damage you wrote about in the previous post is an example of such an usage error (letting the battery self-discharge for an extremely prolonged period). These errors are important but I wanted to start from discussing how the standard charge and fast charge rates compare in the ideal conditions.


----------



## travelinman

OK, I waited until today hoping my buddy would be at "coffee" and sure enough, there he was. The coffee is a gathering of ham radio types on Friday mornings at 10am. We sit around for an hour or so and talk electronics, and politics. 

This morning I raised the topic of "how best to charge Nimh cells" This one particular guy is the tech for the regional RCMP detachment, and is responsible (among other things) for the care and feeding of 250+ cells and packs of Nimhs used in a wide assortment of electrical devices daily.

There was no hesitation on his part, as he has made charging method comparisons over the last few years on several different types of packs, individual cells and manufacturers. All his individual cells are colour coded, and the packs are numbered for data gathering.

He now exclusively charges (16+ hours) at ~0.1C and does NOT depend on any of his chargers (even the so-called computer controlled "smart" chargers) to terminate properly at any voltage. He has found this method gives him the most capacity immediately after charging, the best longevity of cells, and the fewest malfunctions of cells. 

He is 100% positive that this method has saved his department thousands of dollars per year on replacement batteries.

I don't know how many of you out there have his breadth of experience, or how much the sale of new cells has influenced the manufacturer's data being quoted here, but I'm inclined to base my future charging on his advice.

Of course, everyone in our society is encouraged to their own beliefs. :twothumbs


----------



## Mr Happy

travelinman said:


> He now exclusively charges (16+ hours) at ~0.1C and does NOT depend on any of his chargers (even the so-called computer controlled "smart" chargers) to terminate properly at any voltage. He has found this method gives him the most capacity immediately after charging, the best longevity of cells, and the fewest malfunctions of cells.



_most capacity immediately after charging - _Yes, certainly. A 16 hour 0.1C charge is the gold standard for achieving a 100% full charge.
_
the fewest malfunctions of cells_ - Quite believable. This charging method is very fail safe for cells of all ages and conditions and for both packs and single cells.

_the best longevity of cells_ - On balance, maybe yes. It depends on many factors concerning the exact application of fast charging and the quality of the fast charger used. A fast charger only has to overheat your batteries a few times to undo the benefit that fast charging theoretically brings.

It's worth noting that industrial NiMH battery packs tend to use dT/dt charge termination rather than dV/dt since the batteries are so sensitive to temperature.

On balance, nice feedback.


----------



## wapkil

travelinman said:


> This morning I raised the topic of "how best to charge Nimh cells" This one particular guy is the tech for the regional RCMP detachment, and is responsible (among other things) for the care and feeding of 250+ cells and packs of Nimhs used in a wide assortment of electrical devices daily.
> 
> There was no hesitation on his part, as he has made charging method comparisons over the last few years on several different types of packs, individual cells and manufacturers. All his individual cells are colour coded, and the packs are numbered for data gathering.
> 
> He now exclusively charges (16+ hours) at ~0.1C and does NOT depend on any of his chargers (even the so-called computer controlled "smart" chargers) to terminate properly at any voltage. He has found this method gives him the most capacity immediately after charging, the best longevity of cells, and the fewest malfunctions of cells.
> 
> He is 100% positive that this method has saved his department thousands of dollars per year on replacement batteries.
> 
> I don't know how many of you out there have his breadth of experience, or how much the sale of new cells has influenced the manufacturer's data being quoted here, but I'm inclined to base my future charging on his advice.
> 
> Of course, everyone in our society is encouraged to their own beliefs. :twothumbs



I hope we don't have to rely on beliefs. Batteries may be somehow complicated but I'm sure there is enough demand for data and research about them to find the comparison of the standard and fast charge rates. Of course there may be no simple answer which one is better (it may depend on requirements and additional conditions) but some discussion and experimental data is probably available.

Has your buddy mentioned some research documents about the subject or was he working only by doing his own experiments? I don't doubt his results validity. In my previous posts I wrote that my gut feeling is that 0.1C charge rate should be better for longevity and moderate current applications. It would be even better though to see some hard, published data accompanied by a theory explaining it (even if it would require too much chemical knowledge for me to understand it).

BTW, I don't think it can be said that manufacturers recommend fast charge rates because they are "better". In most of the longer manufacturer's documents that I read this recommendation was prefixed by an explanation that it is because of the contemporary trend to charge batteries faster or because it reduces back to service time. I haven't seen anywhere an explanation that it is actually better for batteries...


----------



## J_C

Marduke said:


> "That's how everyone is doing it" is not a valid reason for how something is supposed to be done. Lots of people do lots of things incorrectly, that doesn't make it right.
> 
> The point of the discussion here of what charge currents to use is not about what lots of people do (incorrectly, even by manufacturer standards), but what is BEST.



Exactly, sort-of. It's not "incorrect" to not do what is absolutely best. It's not "supposed" to be done only one way, manufacturers don't claim it will "fry" or "cook" a battery to simply charge it at a lower rate. In most areas of life, every day we all do things which may not be hypothetically the "best" way possible, for various reasons and in the end we only care if the need was met, OUR need not your hypothetical about what we _should_ want or need.



> And as silverfox described, much of the world using slow charging DO have issues, they just don't know it. They think short life cycles and worsening performance are the norm and don't have the knowledge that the grass really is greener on the other side.



Short life cycles and worsening performance would be things that people do notice. Many people do not notice problems as suggested.

Further, worsening performance as a cell ages is typical with any charge method. Further, a common resolution for worsening performance is to leave a battery trickle charging once it had supposedly reached max capacity, resolving the pseudo-memory effect which is yet another myth many consumers repeat.



> Lots of people drink and drive and get away with it, speed, swim less than 30 minutes after eating, etc. But that doesn't mean any of those are good ideas either.



Hardly an equivalent example. How about lots of people eat different foods, not the same hypothetically "best" meal they possibly could every time. Lots of people accelerate and decelerate their automobile in a way that is not the hypothetically "best" way to get maximum fuel economy. Lots of people cook food in a way that is not the hypothetically "best" way to get best energy efficiency and lowest power bill.

Why? Because the difference between best and the rest isn't enough to matter relative to other factors. 



> There is no doubt, given the choice between the two, fast (1C) is better than slow, as proven by documentation above.



I never wrote that fast wasn't better. I wrote that slow isn't a problem (to reasonable people who do not have significant problems every day). You are incorrect and have now tried to twist the topic away from that into claiming I am against fast charging when I am not. It is not a problem if a $2 battery doesn't reach the ultimate heights of performance when the difference is usually quite small. If the slower charging rates people use weren't sufficient they would change the rate or the device but they don't in most cases because it JUST WORKS.

Battery manufacturers are well aware that the majority slow charge their batteries, if it were the problem you suggest they would strongly warn against it, even put the clear directions on the product package. The last thing a battery manufacturer wants is people becoming disenchanted with their product and avoiding it in favor of the competitors' product.


----------



## wapkil

J_C said:


> Battery manufacturers are well aware that the majority slow charge their batteries, if it were the problem you suggest they would strongly warn against it, even put the clear directions on the product package. The last thing a battery manufacturer wants is people becoming disenchanted with their product and avoiding it in favor of the competitors' product.



I'm not sure if it is correct. I think that for many years the recommended charge rate was the standard charge rate. In recent years fast chargers became more popular than they used to be. It seems possible to me than now the manufacturers are aware that fast charge rates are becoming more popular, hence their recommendations. Reading various manufacturers documents I had an impression that the recommendations for fast currents sounded more like "if they absolutely have to use fast charging, let's at least tell them to use an algorithm that shouldn't overcharge with 0.5C-1C".

I may be wrong of course. It is only my impression. Maybe there were some changes in the batteries technology that made fast charge rates better than the standard rate. I haven't seen though anything confirming it and the more I read, the more it seems that my impression may be correct.

EDIT: I meant that I'm not sure whether the majority still slow charges their batteries. I agree that the manufacturers would probably warn against the standard charging if it was bad, although I don't think they would warn against fast charging. It wouldn't look good and could scare off the people with "15min" chargers. BTW some manufacturers still put the text "standard charge rate XmA" on their batteries.


----------



## 45/70

travelinman said:


> Of course, everyone in our society is encouraged to their own beliefs. :twothumbs



I'm glad you're giving us a break travelinman. 

It doesn't really surprise me that your RCMP friend is using the 0.1C charge rate. Since I'm guessing most of the batteries they use are cells in packs, this is the best way to charge them. You run the risk of overcharging the cells in an unbalanced pack, when charging at a faster rate. The 0.1C rate also balances the cells as well, in a series pack. Most radio equipment and such that I'm aware of, that use nickel based chemistry batteries, use the 0.1C rate for these reasons.

Another thing I curious about, is if all the batteries and cells they're using are NiMH. A lot of the LEO and military equipment here in the States is still run on NiCD's. I remember reading an article here recently about the U.S. Navy trying out NiMH packs for their two way radios. The conclusion was that the NiCD's were less trouble, more tolerant to abuse, and lasted longer in the long run. Sorry, I don't have any links.......well, this one. 

Dave


----------



## VidPro

good point, them radios and stuff are in series, and while you can fast charge them in series using hobby chargers and other things like those super expencive charge racks that goverments might use, it still cant get it perfect, because whats the poor charger supposed to read.
without a perfected series charge alogrythm, series V-drops are just bad guesses, because some are going up while others are finished.

https://www.candlepowerforums.com/threads/187526&highlight=torture
as far as slow charging i did this test, which could be concidered far from slow, for over 300 hours, only the first few hours are in a time lapse video.
the battery still doesnt act squat different from the others, if i could just remember which one it was  because now i forgot how i marked it, and they all test out the same.

but this is NOT some digitally averaged 1000ma+ high pulse charge, it is stable same current. 
http://home.comcast.net/~trivalvid/ENLTor00-20hrDx.avi


----------



## wapkil

VidPro said:


> https://www.candlepowerforums.com/threads/187526&highlight=torture
> as far as slow charging i did this test, which could be concidered far from slow, for over 300 hours, only the first few hours are in a time lapse video.
> the battery still doesnt act squat different from the others



 It shows that a slow charge rate can be really dangerous. It first damaged your power supply and then even the mains power. If you have a nuclear power plant nearby, please don't perform any longer tests


----------



## Marduke

J_C said:


> They do not stipulate you must use any one of the methods they recommend to achieve the specifications for their cells.



In fact they do, and I specifically linked the reference documents above. 



wapkil said:


> BTW, I don't think it can be said that manufacturers recommend fast charge rates because they are "better". In most of the longer manufacturer's documents that I read this recommendation was prefixed by an explanation that it is because of the contemporary trend to charge batteries faster or because it reduces back to service time. I haven't seen anywhere an explanation that it is actually better for batteries...



They changed their tune over trends, but not quite how you assume. Back in NiCad days, slow chargers worked just fine, as NiCads were very tolerant of it. When NiMH consumer cells were introduced, the chargers did not drastically change. If you know the precise capacity of the cell in question, you can charge at a slow rate on a timer. Since it was easier to use the same chargers and just change the time, it was an easy assumption to simply assume consumers would recharge cells only when depleted. This is also when you started to notice more strong language to the effect of "use only our cells in our charger". Put a lower capacity cell in a charger meant for higher capacity, and you can damage the cell.

Eventually, it became evident that consumers wanted to be able to charge up their cells whenever they wanted, regardless of the state of capacity. Cells of varrying capacity also became prevelant. Charging a cell of unknown capacity at an unknown state of charge is much harder than when you knew exactly how much a cell stored and assumed it was empty.

That meant the charger had to become "smart". You know have to know eactly what the capacity is, and what the state of charge is to do a timed charge and not kill the cell. Obviously that is not easy. Second best method is to give the charger some brains so it can figure out on it's own when a cell is "done" charging. There are MANY different algorithims you can use to apply a charge to a cell and monitor it for completion, many of which are discussed in the above referenced documents. Of these, a method had to be chosen that was reliable, affordable, and easy for the consumer to do. That drove smart chargers to a -dV/dT condition to sense end of charge. But to sense this signal, the charger must be able to measure it. A typical NiMH cell will show this signal more prominantly >0.5C charge. Below that and the signal is VERY difficult to measure, or the cell may not even display one at all. Above 1C charge, you can get into other issues with charging the cell too fast. 

0.5-1.0C is a sweet spot where you can both measure a -dV/dT signal, and not overcharge the cell. If your equipment is capable of it, that is the current "best" method to charge NiMH cells of an unknown state of discharge.


----------



## wapkil

Marduke said:


> They changed their tune over trends, but not quite how you assume.
> 
> [...]
> 
> 0.5-1.0C is a sweet spot where you can both measure a -dV/dT signal, and not overcharge the cell. If your equipment is capable of it, that is the current "best" method to charge NiMH cells of an unknown state of discharge.



And of unknown capacity. I generally agree with you, although I'm afraid that all these "smart" methods have their problems. For example a supposedly advanced Maha C9000 charger uses the simple maxV termination at a too low voltage of 1.47V probably because they couldn't implement a smart algorithm that would work reliably with all "crap" cells that users may put inside.

I don't think anything you wrote contradicts my "assumptions" (actually more like impressions, I know too little to assume anything). I believe you explained quite well why smart chargers became popular. I wrote that my impression is that since they became popular, the manufacturers started to recommend the best methods for them. It means that these algorithms are probably best for smart chargers but it doesn't mean that they are better than a correctly performed standard charge.

I haven't read now the documents from the links that you provided but I saw all of them earlier. I may have missed something but I believe that in none of them it was written that fast charging is better for batteries. Some of the documents recommend fast charging but I'm not sure if this recommendation isn't simply based on user convenience. Especially when confronted with documents that actually advertise fast charging as more convenient for users but, even if they describe the standard charging procedure, don't offer any suggestions that fast charging is better for batteries.


----------



## VidPro

if a "fast" charger is looking for a V-drop, there better BE one.
if a "smart" charger is looking for a V-drop, there better BE one.
if a "digital" charger is looking for a V-drop, there better BE one.

anybody find me a "good" slow charger this week? i bought something that was timed and had slow specs (lies on a website), and when i tested it it was at 350ma. The front of the box should have said Betty crockers battery baker.

look at the rates on the dumb chargers manufactures are putting out in packaged kits, Not slow, but great for selling more batteries i guess.

all these digital pulse chargers AVERAGING a slow rate, not slow, hard pulses.

how do you Even DO a slow charge, if it wasnt for OLD backwards chargers from the 80s, which you can still find in the antiques section of E-bay.
some of my actually slow chargers timeout before 2000ma even

how do you TEST slow rates, on chargers that dont have them?
it is no wonder, with Lacross 900s and stuff like them , that the manufactures Dont recommend slow. it Cant be Done.
i know of like 2-3 units out there still sold that do a real in rate slow charge.


----------



## travelinman

Actually Randy (my rcmp tech buddy) deal with a lot of individual cells, such as flashlight cells etc. You're right, not all are AA, some are C as well.

As a matter of fact, he is researching going to Lithium Ion. He has a couple of his techs looking into high capacity Lithium for some of his uses. Don't know what kind, maybe only available to industry or something like that. I'll let you know more when I do.


----------



## wapkil

VidPro said:


> if a "fast" charger is looking for a V-drop, there better BE one.
> if a "smart" charger is looking for a V-drop, there better BE one.
> if a "digital" charger is looking for a V-drop, there better BE one.
> 
> anybody find me a "good" slow charger this week? i bought something that was timed and had slow specs (lies on a website), and when i tested it it was at 350ma. The front of the box should have said Betty crockers battery baker.
> 
> [...]
> 
> how do you TEST slow rates, on chargers that dont have them?
> it is no wonder, with Lacross 900s and stuff like them , that the manufactures Dont recommend slow. it Cant be Done.
> i know of like 2-3 units out there still sold that do a real in rate slow charge.



Once again I completely agree. For an average user and usage fast charge rates are more convenient, easy to get in current chargers, maybe even less prone to errors. I think no one is denying it.

As I understood though the discussion is about the best method in ideal conditions for someone who doesn't care about charging convenience. If I took my hobby charger (which I don't have) and took time to select all the parameters needed for the algorithm, would it be better for the batteries future performance (assuming moderate discharge current afterwards) to use the standard charge or some fast charge method. It still seems to me that the standard charge would be better in this case.


----------



## clintb

VidPro,

If you're not afraid to spend a little bit, here's a truly wonderful constant current charger with two channels. I've had one for years, and it's served me well.

http://www.acehobby.com/ace/ACE2528.htm


----------



## VidPro

clintb said:


> VidPro,
> 
> If you're not afraid to spend a little bit, here's a truly wonderful constant current charger with two channels. I've had one for years, and it's served me well.
> 
> http://www.acehobby.com/ace/ACE2528.htm


 
now thats old scool , even discontinued 


*When using the DDVC charger, you must keep in mind that it is not a peakdetect or automatic cut-off charger. You are the only one who can stop it. Don't forget about it, or you could damage your cells. *

so it had 2 otions i guess , the old 16 hour slow charge, or fast charging while holding battery in hand, terminate on "ok its warm enough".


----------



## VidPro

wapkil said:


> , would it be better for the batteries future performance (assuming moderate discharge current afterwards) to use the standard charge or some fast charge method. It still seems to me that the standard charge would be better in this case.


 
many good hobby chargers have nice slowdown alogrythms , like the triton silverfox has talked about. 
and most of them do really nice stuff of the proper CC/CV for li-ion.

and then a person can often adjust that V-drop detection, to very low, so the machine terminates sooner on a overcharging. 
and often you can put a temp probe ON the battery, and set very tight specs for that to bail out, which can be relative to the room temps your in and charge rate, so it would actually work, because of a manuel perfecting of it..
but
they cant single channel 4 or 8 ni-?? cells, like a consumer would want.


----------



## Marduke

wapkil said:


> And of unknown capacity. I generally agree with you, although I'm afraid that all these "smart" methods have their problems. For example a supposedly advanced Maha C9000 charger uses the simple maxV termination at a too low voltage of 1.47V probably because they couldn't implement a smart algorithm that would work reliably with all "crap" cells that users may put inside.



Well, there is more to that. The C9000 also has -dV/dT IIRC, but LSD cells and Eneloops in particular (the majority of CPF's use on the C9000), the cells terminate at a higher than typical voltage vs what the c9000 was designed for. "Regular" NiMH I believe have a good change of actually triggering the -dV/dT condition.




wapkil said:


> I haven't read now the documents from the links that you provided but I saw all of them earlier. I may have missed something but *I believe that in none of them it was written that fast charging is better for batteries. *Some of the documents recommend fast charging but I'm not sure if this recommendation isn't simply based on user convenience. Especially when confronted with documents that actually advertise fast charging as more convenient for users but, even if they describe the standard charging procedure, don't offer any suggestions that fast charging is better for batteries.



Duracell states for "optimum performance", use this method:


For fast charging and *optimum performance*, Duracell recommends a three-step procedure:
Charge at 1C rate, terminated by using dT/dt = 1°C (1.8°F)/minute
Apply a C/10 top-up charge, terminated by a timer after 1/2 hour charge (optional, not required)
Apply a maintenance charge of indefinite duration at C/300 rate
 
The recommended charge procedure should be used with a backup temperature cutoff of 60°C (140°F).
Duracell SPECIFICALLY recommends 6.3.1

Interestingly, Energizer states that "the charge acceptance efficiency for the NiMH cell is improved as the charging rate is increased." which tells us it really is more effecient to charge at 1C than at slower rates.


----------



## Bones

VidPro said:


> if a "fast" charger is looking for a V-drop, there better BE one.
> if a "smart" charger is looking for a V-drop, there better BE one.
> if a "digital" charger is looking for a V-drop, there better BE one.
> 
> anybody find me a "good" slow charger this week? i bought something that was timed and had slow specs (lies on a website), and when i tested it it was at 350ma. The front of the box should have said Betty crockers battery baker.
> 
> look at the rates on the dumb chargers manufactures are putting out in packaged kits, Not slow, but great for selling more batteries i guess.
> 
> all these digital pulse chargers AVERAGING a slow rate, not slow, hard pulses.
> 
> how do you Even DO a slow charge, if it wasnt for OLD backwards chargers from the 80s, which you can still find in the antiques section of E-bay.
> some of my actually slow chargers timeout before 2000ma even
> 
> how do you TEST slow rates, on chargers that dont have them?
> it is no wonder, with Lacross 900s and stuff like them , that the manufactures Dont recommend slow. it Cant be Done.
> i know of like 2-3 units out there still sold that do a real in rate slow charge.



I'm pretty sure the old Energizer CHM39 I use for cells that none of my other chargers will recognize is a true slow charger:

http://data.energizer.com/PDFs/chm39.pdf

Its output: 130mA x 2(AA) / 80mA x 2(AAA) / 23mA x 1(9V)

Granted, its a two channel, four place, timer controlled 14 hour charger; but given enough time, it eventually even things out at a slow enough rate to minimize concern.

It's also surprisingly well built and finished and actually may keep going and going...


----------



## VidPro

wapkil said:


> It shows that a slow charge rate can be really dangerous. It first damaged your power supply and then even the mains power. If you have a nuclear power plant nearby, please don't perform any longer tests


 
not to worry, it's just a nuclear and Bio warfare lab nearby  but they burn out more stuff than i do. A little tritium in the groundwater just makes it easier to get a glass of water at night  and 6fingers, the neighbor kid is going to be a great pianist someday if they can just do something about the wart problem, and that tail thing he has.


----------



## wapkil

Marduke said:


> Well, there is more to that. The C9000 also has -dV/dT IIRC, but LSD cells and Eneloops in particular (the majority of CPF's use on the C9000), the cells terminate at a higher than typical voltage vs what the c9000 was designed for. "Regular" NiMH I believe have a good change of actually triggering the -dV/dT condition.



I know, there is also a timeout and I think another condition. Nevertheless all the NiMH batteries I have (LSD and non-LSD) terminate on the maxV. I was really surprised when I found out this behavior. I believe that when the cells age other conditions may appear earlier, but it doesn't seem to happen for good cells.

I mentioned this to show the problems with "smart" algorithms. IIRC Maha lowered the maxV level after problems with missed terminations in earlier C9000 versions. It shows that at least for this particular manufacturer smart algorithms turned out to be not smart enough to rely on them.



Marduke said:


> Duracell states for "optimum performance", use this method:
> 
> 
> For fast charging and *optimum performance*, Duracell recommends a three-step procedure:
> Charge at 1C rate, terminated by using dT/dt = 1°C (1.8°F)/minute
> Apply a C/10 top-up charge, terminated by a timer after 1/2 hour charge (optional, not required)
> Apply a maintenance charge of indefinite duration at C/300 rate
> 
> The recommended charge procedure should be used with a backup temperature cutoff of 60°C (140°F).
> Duracell SPECIFICALLY recommends 6.3.1
> 
> Interestingly, Energizer states that "the charge acceptance efficiency for the NiMH cell is improved as the charging rate is increased." which tells us it really is more effecient to charge at 1C than at slower rates.



Duracell writes "For fast charging and optimum performance" you can interpret it any way you want. They also recommend an indefinite trickle charge. I think it means that the recommended algorithm is not dedicated to ensure the best cells longevity (but will ensure that the batteries will be always fully charged, hence the optimum performance).

I don't think we can really find the answer to the question about the best charging algorithm directly in manufacturers recommendations. They couldn't for example write "We recommend the standard charge for our batteries. It will take only 16h. Before charging make sure to test the battery actual capacity to select the appropriate current. The capacity will change so you have to test it periodically. You need a good charger (~$100 for a single channel version). If you want to charge more than a single battery at once, you'd need a separate single channel charger for each of them" 

The better charge acceptance efficiency at higher current is interesting but I don't know if it has any influence on batteries longevity or other performance factors.


----------



## Marduke

wapkil said:


> Duracell writes "For fast charging and optimum performance" you can interpret it any way you want. *They also recommend an indefinite trickle charge. *I think it means that the recommended algorithm is not dedicated to ensure the best cells longevity (but will ensure that the batteries will be always fully charged, hence the optimum performance).
> 
> I don't think we can really find the answer to the question about the best charging algorithm directly in manufacturers recommendations. They couldn't for example write "We recommend the standard charge for our batteries. It will take only 16h. Before charging make sure to test the battery actual capacity to select the appropriate current. The capacity will change so you have to test it periodically. You need a good charger (~$100 for a single channel version). If you want to charge more than a single battery at once, you'd need a separate single channel charger for each of them"



Unless you are seeing something I'm not, they ONLY recommend the 1C charge. They only present other options, but they are not recommended. Certain charge rate rages are specifically NOT recommended actually.


----------



## VidPro

sanyo has it figured, Just use our charger OK :nana: i dont even HAVE one of thiers, and i got like 8 now.

*Though it is possible to charge an eneloop battery in a "Quick Charger", it is not recommended. We recommend charging eneloop batteries in a NiMh charger that is 2 hours or more. Charging eneloop batteries in a "Quick Charger" can reduce the overall life of the battery. It is strongly recommended to use eneloop, GE/Sanyo or Sanyo NiMh battery chargers. We only warrant eneloop if used with an eneloop, GE/Sanyo or Sanyo NiMh battery charger. *

http://us.sanyo.com/Batteries/FAQs

their charge things they say in the faqs are 2-4hours and the other charger 4-7 hours


----------



## Mr Happy

It is true that modern NiMH cells are designed to withstand a 0.1C charge without damage when already fully charged. Therefore a 0.1C standard charge is in theory fine to use. Where this comes unstuck is that the charger cannot know what 0.1C actually is -- it relies on a human to enter that data into the charger. And most ordinary consumers and users of NiMH batteries do not know what the capacity is and do not want to enter it into the charger like they might have to do in the "complicated" MH-C9000.

So to build a slow timed charger, what charge rate should it use? Maybe 270 mA for 2700 mAh cells? Then it will overcharge and damage eneloops. OK, so maybe 200 mA for eneloops. But that will overcharge and damage 1600 mAh cells. Ah, then 160 mA. But that will overcharge and damage the new Sanyo Harmolattice cells (1000 mAh).

Therefore, to play it safe the universal timed charger should use a charging current of 100 mA, and should have a timer for 160% of 2700 mAh giving 43 hours. That's the design of the perfect consumer charger! Consumers will flock to buy it! Everyone will love to wait nearly two days for their batteries to charge


----------



## travelinman

Every time I hear the phrase "smart charger", I'm reminded of some movie or other that has the line....."strong like bull, smart like tractor" in it.


----------



## VidPro

i want mine to charge at a pulse 2amps 50-50 then drop to 1amp and .5amp and .1amp till full, and finish with very short pulses of .05 for final topping for an hour, all based on temperature or voltage.

ray-o-vac didnt care what you do they will work with anything , any charger you got, they dont care.

Here is energysers OLD speel http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

*Determining when overcharge has occurred is critical to charging schemes that*
*minimize the amount of time spent at high charge rates in overcharge. In turn, these*
*efficient charging techniques are a key to maximizing cell life, as will be discussed later.*
*Primary charge control schemes typically depend on sensing either the dramatic rise in cell temperature*
*or the peak in voltage*​ 
*Charge control based on temperature sensing is the most reliable approach to*
*determining appropriate amounts of charge for the nickel-metal hydride cell.*
*Temperature-based techniques are thus recommended over voltage-sensing control*
*techniques for the primary charge control mechanism.*
*Recommended Charging Rates*
*Today’s trend to faster charge times requires higher charge rates than the 0.1 to 0.3C*
*rates often recommended for many nickel-cadmium charging systems. Both Figures 18*
*and 19 indicate that fast-charge rates serve to accentuate the slope changes used to*
*trigger both the temperature and voltage-related charge terminations. A charge rate of*
*1**C **is recommended for restoring a discharge cell to full capacity. For charging schemes*
*that then rely on a timed "topping’ charge to ensure complete charge, a rate of 0.1**C*
*appears to balance adequate charge input with minimum adverse effects in overcharge.*
*Finally a maintenance (or trickle) charge rate of 0.025**C (C**/40) is adequate to counter*
*self-discharge and maintain cell capacity.*​ 
. . . there is lots more right under that too.

I wonder when they are going to tell the guy that wrote it , that none of the energyser chargers (cept the 15min) even followed any of it ​


----------



## travelinman

That's what happens when the head office is in Florida, the engineering is done in Romania, marketing is in London and manufacturing is in Taiwan!


----------



## VidPro

Mr Happy said:


> then 160 mA. But that will overcharge and damage the new Sanyo Harmolattice cells (1000 mAh).
> 
> Therefore, to play it safe the universal timed charger should use a charging current of 100 mA, and should have a timer for 160% of 2700 mAh giving 43 hours. That's the design of the perfect consumer charger! Consumers will flock to buy it! Everyone will love to wait nearly two days for their batteries to charge


 
43 hours , that sounds like fun. the harmolattice and other very robust lower capacity cells like even the eneloop cope with the "overcharge" rates (relative to capacity) better than the high capacity.

but that all makes BONES slow charger just about right.

one thing i dont understand is why people call the 12-14 hour chargers "Travel" chargers, when i got mabey 6 hours in a motel before the maid is turning the bed out on me. Checkout time :wave:, and at home i got all day.


----------



## Marduke

VidPro said:


> one thing i dont understand is why people call the 12-14 hour chargers "Travel" chargers, when i got mabey 6 hours in a motel before the maid is turning the bed out on me. Checkout time :wave:, and at home i got all day.



You plug in at home, go traveling, and they are done when you get back :nana:


----------



## clintb

VidPro said:


> now thats old scool , even discontinued
> 
> 
> *When using the DDVC charger, you must keep in mind that it is not a peakdetect or automatic cut-off charger. You are the only one who can stop it. Don't forget about it, or you could damage your cells. *
> 
> so it had 2 otions i guess , the old 16 hour slow charge, or fast charging while holding battery in hand, terminate on "ok its warm enough".


Uh, no. It's sole purpose is to output a user defined (in 5mA steps) current; that's it!

2 channels
1-10 Nixx cells on each channel
Each channel adjustable from 5mA - 500mA, in 5mA increments.
You supply the timer, or don't.

Outside of the LCD that displays current, the switch for changing channels, and the pots for adjusting current, there's nothing else on this guy. That's the beauty; it's dead simple! When I want to do a break-in on some AA cells, I'll load 'em up in the plastic cell holders, eight in each, and stick them on the DDVC, and it into a digital lamp timer. No need to tie up the C9000 with a break-in, unless I want to see the capacity from the break-in mode. I can do a 0.1C charge on 20 (TWENTY) cells at one time! How's that for efficiency?


----------



## TorchBoy

travelinman said:


> O... the care and feeding of 250+ cells *and* packs of Nimhs ... daily.
> ...
> He now exclusively charges (16+ hours) ...


Er, how many chargers does this guy have? :duh2:



45/70 said:


> Sorry, I don't have any links.......well, this one.


Aw, how cute.


----------



## wapkil

Marduke said:


> wapkil said:
> 
> 
> 
> Duracell writes "For fast charging and optimum performance" you can interpret it any way you want. *They also recommend an indefinite trickle charge.*
> 
> 
> 
> 
> Unless you are seeing something I'm not, they ONLY recommend the 1C charge. They only present other options, but they are not recommended. Certain charge rate rages are specifically NOT recommended actually.
Click to expand...


I'm seeing what you, and Duracell, wrote:



Marduke said:


> Duracell states for "optimum performance", use this method:
> 
> For fast charging and optimum performance, Duracell recommends a *three-step procedure*:
> 
> Charge at 1C rate, terminated by using dT/dt = 1°C (1.8°F)/minute
> Apply a C/10 top-up charge, terminated by a timer after 1/2 hour charge (optional, not required)
> *Apply a maintenance charge of indefinite duration at C/300 rate*



I think it is a good example why manufacturers recommendations cannot be taken literally and, without additional information, can not be trusted. I think the third step of the recommended procedure will shorten batteries life. The current is low so it won't be severe but I think it is still not good for batteries. This step is to compensate for self-discharge, it will ensure the batteries are fully charged so they decided to recommend it as "optimum performance". The problem is their optimum (keeping the cells fully charged) is not my optimum that we are discussing here.


----------



## Ny0ng1

hmm looks like quoting manufacturer's data sheet/specs is the best we can do without any real expert and theory on battery chemistry and physics behind it.
even when we have someone with that information, there are also differences between various generations of NiMH alone, and again, it has to be dissected and explained.
so take it easy guys, lets learn together 

After knowing the complexities of this supposedly simple activity of charging batteries, i think i prefer to become the 'average' user with a simple 'no-options' charger rather than tinkering with all various options in the smart charger to get the 'best' results on my batteries :green:
I guess thats because i dont have scores (hundreds or over) of batteries to maintain everyday and responsible for it . Oh, and i use lithium primaries on my lights :nana:

of course YMMV :thumbsup:


----------



## wapkil

Ny0ng1 said:


> hmm looks like quoting manufacturer's data sheet/specs is the best we can do without any real expert and theory on battery chemistry and physics behind it.
> even when we have someone with that information, there are also differences between various generations of NiMH alone, and again, it has to be dissected and explained.
> so take it easy guys, lets learn together



We could also quote more independent documents but I, for once, haven't yet even started searching for them  I have nothing against quoting the manufacturers' documents but I wanted to warn that they have to be frequently taken with a grain of salt. There used to be a time when there generally were useless marketing brochures and rather honest data sheets. Now it seems that many data sheets are written not to explain how things work but "why our product is better than competition, with good looking numbers and graphs". In case of charging recommendation I think they recommend the procedure that will please most users but not necessarily the batteries.



Ny0ng1 said:


> After knowing the complexities of this supposedly simple activity of charging batteries, i think i prefer to become the 'average' user with a simple 'no-options' charger rather than tinkering with all various options in the smart charger to get the 'best' results on my batteries :green:
> I guess thats because i dont have scores (hundreds or over) of batteries to maintain everyday and responsible for it . Oh, and i use lithium primaries on my lights :nana:
> 
> of course YMMV :thumbsup:



Fast charging has its place of course and I definitely won't resign from it - in many situations it is more convenient. The standard charge is much longer but the only thing it requires is the knowledge of the battery capacity. If it turned out it is better for batteries, I would prefer using it when I'm not in hurry.


----------



## Marduke

wapkil said:


> I think it is a good example why manufacturers recommendations cannot be taken literally and, without additional information, can not be trusted. I think the third step of the recommended procedure will shorten batteries life. The current is low so it won't be severe but I think it is still not good for batteries. This step is to compensate for self-discharge, it will ensure the batteries are fully charged so they decided to recommend it as "optimum performance". The problem is their optimum (keeping the cells fully charged) is not my optimum that we are discussing here.



C/300 is well below the threshold to harm a battery. As long as you didn't leave a cell on for days or weeks, you'd be fine. It's not really a "trickle CHARGE" per se.


----------



## wapkil

Marduke said:


> C/300 is well below the threshold to harm a battery. As long as you didn't leave a cell on for days or weeks, you'd be fine. It's not really a "trickle CHARGE" per se.



There is no point in recommending the indefinite C/300 charge if the battery is not left for days or weeks. This recommendation is for people who want to leave the batteries in the charger for months and have them fully charged when taken out. They will have a better performance then - the batteries will be fully charged while not trickle charged competition may already be empty. It's only a different definition of performance than the one we were talking about.


----------



## J_C

Marduke said:


> In fact they do, and I specifically linked the reference documents above.



In fact I have 2 Eneloop datasheets here that plainly state:

(AAA) "Single cell capacity under the following condition. 
Charge: 80mAx16h, Discharge: 160mA*E.V.=1.0V) at 25C"

(AA) "Single cell capacity under the following condition.
Charge: 200mAx16h, Discharge: 400mA(E.V.=1.0V) at 25C"

So not only do they find this an acceptable charge rate, it is the rate at which the capacity itself is guaranteed, not at any other rate.



> They changed their tune over trends, but not quite how you assume. Back in NiCad days, slow chargers worked just fine, as NiCads were very tolerant of it. When NiMH consumer cells were introduced, the chargers did not drastically change. If you know the precise capacity of the cell in question, you can charge at a slow rate on a timer. Since it was easier to use the same chargers and just change the time, it was an easy assumption to simply assume consumers would recharge cells only when depleted. This is also when you started to notice more strong language to the effect of "use only our cells in our charger". Put a lower capacity cell in a charger meant for higher capacity, and you can damage the cell.


You're simply backwards arguing towards a position supportive of your assumption. Your assumption was that if/when a battery manufacturer touts the ability to fast charge, that they are also suggesting it shouldn't be done any other way. If that were what they were suggesting, THEY would have stated it, not leaving ambiguity for 3rd parties to reinterpret.

They clearly list charge rates THEY use for their own testing which take 16 hours.



> ...That drove smart chargers to a -dV/dT condition to sense end of charge. But to sense this signal, the charger must be able to measure it. A typical NiMH cell will show this signal more prominantly >0.5C charge. Below that and the signal is VERY difficult to measure, or the cell may not even display one at all. Above 1C charge, you can get into other issues with charging the cell too fast.


So you keep claiming, but in fact the signal is not so difficult to measure, every single low-priced charger I've seen in recent years that has Delta -V detection, detects it just fine below 0.5C. ALL of them, so obviously what is difficult in your mind, is not so hard to do when a charger is designed to do this very thing. They not only detect Delta -V at lower levels, they do it successfully with only one cell having reached Delta -V if the cells were at different enough capacity that both did not reach Delta -V at an overlapping moment in time.

Certainly there is a charge rate low enough that Delta -V is too low to be detected, but once again (why is it necessary to keep repeating what chargers prove to be true?) if you look at the chargers, those which detect Delta -V, have a high enough charge rate to do so, they aren't making 200mA chargers that detect Delta -V for this reason, but are making chargers below 0.5C charge rate because it clearly works.



> 0.5-1.0C is a sweet spot where you can both measure a -dV/dT signal, and not overcharge the cell. If your equipment is capable of it, that is the current "best" method to charge NiMH cells of an unknown state of discharge.


I can put a 90% charged AA battery in a low end 5 year old 700mA rate charger and it Delta -V terminates just fine. What you claim is not supported except perhaps on the first generations of Delta -V capable chargers but as with most electronics, successive generations of product improved in performance.

The Delta -V change doesn't need to be as high or fast as possible, only enough that a charger can detect it which they do.


----------



## VidPro

not all of the Medium Speed chargers use V-drop, some dont Wait for that, and just bail out when the voltage is no longer continuing to increase.


----------



## Marduke

J_C said:


> In fact I have 2 Eneloop datasheets here that plainly state:
> 
> (AAA) "Single cell capacity under the following condition.
> Charge: 80mAx16h, Discharge: 160mA*E.V.=1.0V) at 25C"
> 
> (AA) "Single cell capacity under the following condition.
> Charge: 200mAx16h, Discharge: 400mA(E.V.=1.0V) at 25C"
> 
> So not only do they find this an acceptable charge rate, it is the rate at which the capacity itself is guaranteed, not at any other rate.



I recommend you look up what "Standard Charge" actually means. It does NOT mean that is the recommend charge scheme. That is the method by which the capacity is determined, NOT the typical recommended method.

If you look on the same data sheet, it recommend that the typical charge is 1C...


----------



## wapkil

J_C said:


> So you keep claiming, but in fact the signal is not so difficult to measure, every single low-priced charger I've seen in recent years that has Delta -V detection, detects it just fine below 0.5C. ALL of them, so obviously what is difficult in your mind, is not so hard to do when a charger is designed to do this very thing. They not only detect Delta -V at lower levels, they do it successfully with only one cell having reached Delta -V if the cells were at different enough capacity that both did not reach Delta -V at an overlapping moment in time.



I'm afraid it's not so simple. You are right that the chargers most of the time will detect the -dV condition with currents lower than 0.5C. The problem with this algorithm is that not always. There is really no good sensitivity level that you could set. If you set it high, there may be false peaks that will result in premature termination. If you set it low the voltage drop may be too subtle to detect and you will overcharge the battery. I believe this was the problem with Maha C9000 that I wrote about previously.

I think that -dV by definition slightly overcharges batteries - only when overcharged they produce this signal. In the documents that I read, if various fast charge termination methods were compared, the temperature based dT/dt was, I think, always recommended. It was described as the most reliable for fast charging and ending the charge just on time. The only problem is that you need to be able to closely monitor the cell temperature which is costly.

EDIT: here is the cycle life comparison from the Duracell document quoted earlier by Marduke:





This overcharging by the universally used -dV method and reduced cycle life is yet another reason why I think the standard 0.1C charge is better. Unfortunately I haven't seen a comparison similar to the one above with the standard charge included but I believe it does not reduce the cells life in the way -dV does.


----------



## J_C

Marduke said:


> I recommend you look up what "Standard Charge" actually means. It does NOT mean that is the recommend charge scheme. That is the method by which the capacity is determined, NOT the typical recommended method.
> 
> If you look on the same data sheet, it recommend that the typical charge is 1C...



LOL. You are actually suggesting they recommend against the very rate they use for their own testing? It is not believable, far more likely they use that rate because it gives their cells the max performance. Certainly they are not going to specify a testing parameter that isn't even a valid method to recharge them!

On the same data sheet, it does not recommend 1C charge rate, it merely specifies what rate someone wanting to do a fast charge would use so they don't exceed the maximum. 

Specifying a maximum alone never means there is no minimum or other capable value. Haven't you seen this on lots and lots of datasheets? On almost ALL datasheets for electrical/electronic components? For example a 3A, 40V diode is not recommended to run only at 3A & 40V exactly, that is only the upper limit.


----------



## wapkil

J_C said:


> LOL. You are actually suggesting they recommend against the very rate they use for their own testing? It is not believable, far more likely they use that rate because it gives their cells the max performance. Certainly they are not going to specify a testing parameter that isn't even a valid method to recharge them!



Unfortunately a single manufacturer can use for testing the method that would give the best capacity, recommend another method that they think the users will like the most and write in their own technical documents that the method they previously recommended is worse than another one that they didn't recommend (see Duracell above). As I wrote previously these documents are valuable but only if you can decide how to interpret them and which parts can be trusted...


----------



## J_C

wapkil said:


> I'm afraid it's not so simple. You are right that the chargers most of the time will detect the -dV condition with currents lower than 0.5C. The problem with this algorithm is that not always. There is really no good sensitivity level that you could set. If you set it high, there may be false peaks that will result in premature termination. If you set it low the voltage drop may be too subtle to detect and you will overcharge the battery. I believe this was the problem with Maha C9000 that I wrote about previously.



I suggest that most chargers don't set it high, or low, they use testing in the product development to set the most appropriate level possible, but one where there is still a short period of trickle charging needed to top off the cell.



> I think that -dV by definition slightly overcharges batteries - only when overcharged they produce this signal. In the documents that I read, if various fast charge termination methods were compared, the temperature based dT/dt was, I think, always recommended. It was described as the most reliable for fast charging and ending the charge just on time. The only problem is that you need to be able to closely monitor the cell temperature which is costly.



I could never want a temperature based termination. Put one 90% charged battery in a charger and one 10% charged battery in a 2nd identical charger. The 90% charged battery will be cooler when it reaches full charge than the 10% charged battery is.

I don't necessarily think it really costs much to implement a cell temperature circuit. They cheaply enough implement Delta -V, if it can sense voltage changes a typical thermal sensor would provide voltage changes also, so the remaining factor is a good conductive interface to the cell body, perhaps embedding it in a semi-flexible silicone pad the cell casing rests against.



> EDIT: here is the cycle life comparison from the Duracell document quoted earlier by Marduke:
> 
> 
> 
> 
> 
> This overcharging by the universally used -dV method and reduced cycle life is yet another reason why I think the standard 0.1C charge is better. Unfortunately I haven't seen a comparison similar to the one above with the standard charge included but I believe it does not reduce the cells life in the way -dV does.



I suspect it is more stressful to charge at 1C, such a high rate which is why it is often spec'd as the upper limit, but that at a lower rate the Delta -V detection is not subjecting the cell to as high a temperature. Unfortunately these come back to the issue of full charge and discharge cycles when personally my goal is to not run out of battery charge every time I use a device, that is the least desirable usage pattern to me, having run out of power, nor do I accept increasing wear by discharging a cell each time before recharging.

The rapid charge rate with higher initial capacity for ~260 cycles seems a fair tradeoff to make, especially when you don't have to wait as long but I think we are drifting off on a tangent again so I will restate my position.

I am not interested in getting every last cycle or every last mAH possible out of a $2 battery. I find most methods of charging entirely acceptable, except medium-current timer shutoff type dumb chargers with no other safety/shutdown circuitry as these really do have a tendency to regularly cook the batteries any time they weren't fully discharged, especially if the charger is newer than the batteries so it is optimized for a battery with higher capacity.

I'd much rather rotate aging batteries out of demanding applications into lesser applications on a periodic basis, and if 20% one way or the other mattered I'd have spare batteries along because as mentioned above, fully draining cells as the data generated assumes as the usage profile, is the opposite of the goal to chose rather than be forced to stop using a device.


----------



## Marduke

J_C said:


> LOL. You are actually suggesting they recommend against the very rate they use for their own testing? It is not believable, far more likely they use that rate because it gives their cells the max performance. Certainly they are not going to specify a testing parameter that isn't even a valid method to recharge them!
> 
> On the same data sheet, it does not recommend 1C charge rate, it merely specifies what rate someone wanting to do a fast charge would use so they don't exceed the maximum.




As I said, you obviously have no clue what "Standard Charge" actually means, and have absolutely no interest in educating yourself about it...


----------



## wapkil

J_C said:


> I suggest that most chargers don't set it high, or low, they use testing in the product development to set the most appropriate level possible, but one where there is still a short period of trickle charging needed to top off the cell.



As far as I know such a level simply doesn't exist. You either have a higher risk of overcharging or higher risk of premature termination. With the usual level there is probably non-negligible risk of both. Except the false positives or negatives the sensitivity doesn't change the moment of termination in any important way. The -dV overcharges the cells - if you apply the trickle charge afterwards they will be even more overcharged. 



J_C said:


> I could never want a temperature based termination. Put one 90% charged battery in a charger and one 10% charged battery in a 2nd identical charger. The 90% charged battery will be cooler when it reaches full charge than the 10% charged battery is.



dT/dt is not based on the temperature value but on the detection of the temperature rise rate. Please read the descriptions of appropriate algorithms if you are interested in comparing them.



J_C said:


> I don't necessarily think it really costs much to implement a cell temperature circuit. They cheaply enough implement Delta -V, if it can sense voltage changes a typical thermal sensor would provide voltage changes also, so the remaining factor is a good conductive interface to the cell body, perhaps embedding it in a semi-flexible silicone pad the cell casing rests against.



You may be right but the documents I read claim that it would be more costly to implement it correctly than to have a simple -dV. I tend to believe they are right here.



J_C said:


> The rapid charge rate with higher initial capacity for ~260 cycles seems a fair tradeoff to make, especially when you don't have to wait as long but I think we are drifting off on a tangent again so I will restate my position.
> 
> I am not interested in getting every last cycle or every last mAH possible out of a $2 battery.



I understand your position and sometimes it is more appropriate also for me. Nevertheless I am interested in finding out what are the results of using various available charging methods. Especially since there seems to be a popular impression that there exist a single best method that can be recommended to everyone and I think it is simply not true.


----------



## Bullzeyebill

Gentlemen, let us be nice to each other, no slights, or disparaging remarks here. This is about our fun hobby, and info should pass in good cheer.

Bill


----------



## travelinman

It's beginning to seem like a couple of posters are mistaking this for a fundamentalist religious argument.

We are only discussing opinions on how best to charge a cell, not run the rest of your life or whether a certain mode of living will get you into heaven. 

I'd guess some of the previous posters are having difficulty accepting that others can have different opinions than they have. This isn't a good thing for your blood pressure.


----------



## VidPro

travelinman said:


> It's beginning to seem like a couple of posters are mistaking this for a fundamentalist religious argument.


 
you have to Believe in the battery, , man.



travelinman said:


> I'd guess some of the previous posters are having difficulty accepting that others can have different opinions than they have.


 
its about different charge rates  the difficulty is only in the different Chargers :thinking: and the way people have seen them work, making thier opinions 100% valid.

if everyone had the same charger , of these guys , they would all have the same opinion  

if the manufacutures would follow ANY of thier own specs when selling thier chargers, if they would say the same thing in the data sheet that they do, or tell people to do. 
If all the chargers wern't so heavily varied in thier approaches, and if so many of them werent using cheap tricks.

The Dates people aquired thier information makes a big difference, the "Trend" has changed, even though the reality is basically the same.
The Machines have changed, which changes information anyone would even provide.

in reality everyone here is 100% correct, BUT only if your machine uses the alogrythm they are correct about.


----------



## Marduke

I think _some_ people have missed the entire point of the original question. Asking for the "Appropriate Charge Rate for NiMH Batteries" implies you have a charger which actually gives you a choice.

Obviously if you have a slower smart charger and that is all you have, that is what you use and make the best of it. However, if given the CHOICE using a good charger such as the BC-900, BC-9009, or C9000, the appropriate rate to CHOOSE would be 0.5-1.0C to ensure a reliable termination.

Since the OP has a C9000, his appropriate choice would be 0.5-1.0C for typical use. For basic charging, there is no reason to choose a slower rate, as it does not "give" you anything extra. It would take longer, and increases the chances of a missed termination.


----------



## VidPro

exactally, what marduke said. What charger if you only got One?
the 9000 maha
which does digital pulsing (PWM) to achieve different averaged currents, and if they have a later model of it, it slows down on voltage peaking.
and it has a seperate break-in method.

if it was a lacross, it is relying on a V-drop only then times out, and still uses an averaged PWM current method. and will melt into a pile of plastic blob on the floor if you miss one step 

while there are only tiny differences in the two models, what it can do, and does to batteries is entirely different. what it Cant do, might be even more important


----------



## Marduke

VidPro said:


> if it was a lacross, it is relying on a V-drop only then times out, and still uses an averaged PWM current method. and will melt into a pile of plastic blob on the floor if you miss one step



It has a temp sensor guard against that also.


----------



## VidPro

Marduke said:


> It has a temp sensor guard against that also.


 
the temp sencors being only emergency meltdown indicators, nowhere near capable of a temperature based inclusion in the charging alogrythm.
and stopping then restarting again, think about what the does to something trying to indicate a V-drop, its no wonder why its not part of the alogrythm.

meaning, if they were using temperature sencing , first they have to have the sencor on the Battery not hiding down in the case somewhere, then they have to include it into the charging alogrythm, they dont.
and if a battery is overheating when it gets close to a v-drop, and it pauses, then restarts again, then it can do that over and over again, never reaching the v-drop. that means it just keeps ramping the temps up and down like a yo yo.

its so many things to concider, it is no wonder why they dont concider them. poor little microcontrollers :-(
mine melted down because the microcontroller wasnt even running anymore, so much for it even being a emergency shutdown.


----------



## TorchBoy

VidPro said:


> the 9000 maha ... and if they have a later model of it, it slows down on voltage peaking.


Are you referring to the top-up charge (_after_ DONE is shown)?


----------



## VidPro

TorchBoy said:


> Are you referring to the top-up charge (_after_ DONE is shown)?


 
the maha "7th generation" (or whatever cute name) charge alogrythm, has included in it now, a voltage peak indication, when the voltage of the battery reaches some set point, they slow down. 
you can see this being said many times by people tracking the voltages on the 9000 itself , along with other newer model Maha chargers.

it is what is keeping the batteries cool(er), it keeps OLD cells with loose resistance from going crasy, and solves the problems of digital current controls and v-drop detection (which it also uses) and can keep meltdowns from happening.
but it also means that batteries are not usually heavily overcharged either. which is also indicated by the reduced charge capacity people get on a discharge tests. especially if they Pull before all the topping is done.

its in the book, i dont yet own the 9000, so me not being the one to talk  but i have the other Maha, and i should use a scope to see things even with it, because its got all kinds of complex stuff going on.

see now i have stepped out on a ledge of logic based only on hours of user data, it could be wrong. or you could just Believe


----------



## VidPro

try this, it might be better than believing 
http://www.google.com/search?hl=en&num=100&tbs=qdr%3Ay&q=allintext%3A+1.47v+maha&lr=lang_en&aq=f&oq=&aqi=

the voltage number they SAY isnt always the same, but it is very close, like some have called it 1.49v. if you have 3 meters you never know what time it really is


----------



## TorchBoy

VidPro said:


> see now i have stepped out on a ledge of logic based only on hours of user data, it could be wrong. or you could just Believe


Or you could be just smoking something, because that's what happens after the DONE is shown, because of the top-up charge. What model number is this "7th generation"?


----------



## VidPro

TorchBoy said:


> Or you could be just smoking something, because that's what happens after the DONE is shown, because of the top-up charge. What model number is this "7th generation"?


 
ok it says DONE when it goes into topping and isnt done, and . . . 

i dont know what you want in model numbers, the original first 9000 that people tested, is different than todays 9000 that people are usually buying. check out silverfoxes original thread on it.


----------



## VidPro

I think i see the problem here.
Let me restate it.

Many chargers have a high voltage termination, or just a voltage max (useless usually).
The high voltage termination on the 9000 is now set at a "lower" level than other chargers, including older version of the 9000.
Most of the chargers will do final topping after the initial charge termination anyway, so nothing changes there.

The 9000 though will slow down ON this high voltage, WHERAS many V-drop chargers (with high peak and max voltages) will not REACH their high voltage termination or max, and instead be in the overcharge state, then V-drop terminate, and then continue to finish up by slow topping.

The difference being, the 9000 is much more capable of terminating on high voltage (being lower), and much more likly to do so.
Slam a battery with different currents, averaged or not, and check the peak voltages reached.
The higher the input current the higher the battery voltages will reach. also dependant totally on the resistance of the cell. 
SO
With a lower "high voltage termination" level, and depending on the current, the Maha charger will Terminate a charge Earlier than other devices, prior to going on to topping.
This Can, in some situations at some charge rates, mean that the Maha charged batteries will not read as "full" capacity , as seen by a discharge on a SEPERATE discharger. even after full topping.

So the batteries are not always "fully" charged, and the batteries are also not overcharged as much (or ever), at fast rates especially where it is more important.
I see all this as a GOOD thing.
I am not knocking the charger, or its style , its great. keeping away from overcharging , treating bad cells better, and working at different currents without V-drop Only termination issues.

Given high rate, and a low resistance battery, it is likely that a battery charged in the 9000 will not be charged "as far" as it can be on other chargers, reguardless of final topping.

The voltage termination level is not changed or adjusted for different resistances or charge rates, it was just changed in the rest of the pages of code the microcontroller uses , to "improve" it. it is just one non-moving indicator, it is not a voltage "alogrythm" it is just "peak" voltage.

That is my analisis from the data provided by the users, and the manufacture themselves, and the many tests the users have shown data on.

Anyone with a 9000, could pull the cells "fast" charged, and after Full topping, and prove it by discharge on a different device.
then charging the cell in something else, or using a slower rate, or a break-in rate, and testing the same cell again.

What am i supposed to do when the data doesnt add up, put 2+2 together and make a logic choice on the shown data, then test it here, i have , i just dont have an actual 9000. 

notes: everything is just more likely or less likely , with so many possible variables, rate, temperature, resistance of battery, capacity of battery, there is no absolutes. so that is why i put in all the more thans and less thans.


----------



## wapkil

VidPro said:


> Most of the chargers will do final topping after the initial charge termination anyway, so nothing changes there.
> 
> The 9000 though will slow down ON this high voltage, WHERAS many V-drop chargers (with high peak and max voltages) will not REACH their high voltage termination or max, and instead be in the overcharge state, then V-drop, and then continue to finish up by slow topping.
> 
> [...]
> 
> What am i supposed to do when the data doesnt add up, put 2+2 together and make a logic choice on the shown data, then test it here, i have , i just dont have an actual 9000.



Am I correct that by "V-drop" you mean the -deltaV algorithm? Are you sure that most chargers will top off the batteries after it? -deltaV when finished will already overcharge the battery, topping off afterwards will make it even worse...

I have a C9000 and I believe your description of its behavior is generally correct. I think though that maxV at 1.47V doesn't make overcharging impossible. It makes it less likely but if I correctly remember as the cells age their peak voltage before overcharge gets lower. With old cells it may get below 1.47V and you'd have to trust -deltaV which is also not completely reliable.

From what I read -deltaV, although sometimes recommended by manufacturers, is definitely worse for the batteries life than dT/dt and probably worse than the standard 0.1C charge. 

The algorithm used by C9000 with many termination conditions still doesn't guarantee that the cell will not be overcharged (although it is usually unlikely).

I think that the standard 0.1C charge, if the correct capacity is supplied, guarantees that the cell won't be overcharged. It offers good charge level and prolongs the cells life. If the time is not a limiting factor (which would require a fast charging method) I think the standard 0.1C charge can be considered the best approach. I may be wrong but I still couldn't find any argument to the contrary.


----------



## VidPro

delta , i am not greek  yes same thing.
When hit really hard and the battery voltage (eventually) drops, that does not mean ALL the chemicals have converted over to the charged state.
because that can occur in a fast charge and it is just because MOST of the chemicals are already converted. Then it gets too complicated for me to repeat correctally. but the gas re-integration stuff cant occur as fast or whatever. The charge speed is to fast for the DESIRED chemical reaction. 
So there is room for more charge, even after the battery cant take any more at that speed.

On .1c charging I would tend to agree, there is NOT a problem with it and ni-mhy cells, but Silverfox is the expert, and if he says there is , then he has been right like 99.99% of the time, and when he wasnt he corrected it quick. you dont mess with those odds  Add to that a Pulsed 1000ma or 2000ma Averaged charge speed is NOT slow, so depending on the machine, there is no real slow. 
EX: If we try and get a Lacross to do 200ma it does 1000/5 not 200ma.

The question becomes, is long term slow charging worse than the slam of the overcharge V-drop (and respetive evil gasses and temperature)? I also want to form up the stuff for fast discharges even on slow discharges , because we want to keep the voltages up , and we want to knock the stuff back into Place on the plates and all. (we dont want pits in our metal, or whatever)

with the Maha stuff doing the voltage peak termination, we basically can have a nice fast initial charge and still not wack it so hard when it reaches overcharge. 

so that is why i say it Is a good thing, but any of this stuff is still doing cheap tricks. because really extensive multi sencing would be much better, and so much more problematic if it wasnt done correct. the Rate of charging Should (in a perfect world) match perfectally the ammount of charge acceptance, or chemicals that are ready to move.


----------



## VidPro

then the 1.47v , that must have been thought up by somone paying attention, because when Manually charging i have always thought that around there somewhere, is a beutifull place for a Voltage only type of alogrythm. at 1.47-9v that is about where i want my ramping pulse voltage based charger to be at .1c or less.

and i have tested that many times and it works better than these computers. even in series. . . well most of the time 

older cells usually have higher resistance, it is rare for them to have lower resistance , IN this chemistry , that means they are a more "open curcuit" to the voltage being poked at them. like many older (crap) cells V-drop terminate around 1.5-1.8v at high rate charges, like 1C if i remember right. so on these junk cells that have high resistance and would be heating up badly at high voltages, the voltage termination stops thier torture and further overheating.

then if your going really SLOW with the charging , the 1.47 might not be reached, BUT then again it is also probably going slow enough to handle the overcharge.

Tough, robust cells be they lower capacity or just low resistance dont V-drop as easily, and because of low resistance dont rise in voltage as high. so they might not make it to the 1.47v but they also can handle the rates easier. so it still keeps working out . . . most of the time


----------



## wapkil

VidPro said:


> On .1c charging I would tend to agree, there is NOT a problem with it and ni-mhy cells, but Silverfox is the expert, and if he says there is , then he has been right like 99.99% of the time, and when he wasnt he corrected it quick. you dont mess with those odds  Add to that a Pulsed 1000ma or 2000ma Averaged charge speed is NOT slow, so depending on the machine, there is no real slow.



Do you happen to remember where Silverfox described the problems with 0.1C? I've read a few of the discussions where he participated but I haven't seen such a description.

The standard 0.1C charge is of course not ideal. It is slow, requires you to know the cell capacity and it shouldn't be used on a partially charged cell (or alternatively you should use shorter time for a partially charged cell). You are also right that a pulsed charger does not perform the standard charge (although I don't know how different will be the results). While these factors may be inconvenient in some situations IMO none of them can be seen as a drawback of the 0.1C charge when the cells performance and longevity are considered.



VidPro said:


> older cells usually have higher resistance, it is rare for them to have lower resistance , IN this chemistry , that means they are a more "open curcuit" to the voltage being poked at them. like many older (crap) cells V-drop terminate around 1.5-1.8v at high rate charges, like 1C if i remember right. so on these junk cells that have high resistance and would be heating up badly at high voltages, the voltage termination stops thier torture and further overheating.



Heh, I remembered that the peak voltage moves but now when I read what you wrote, I admit that I'm not sure in which direction 

Interesting thing is that if, as you describe, the peak voltage becomes higher for older cells, it means that the C9000 will end up at 1.47 maxV no matter how old are the cells. It would be consistent with my measurements and other people tests but it would make other conditions rather useless for most.


----------



## VidPro

https://www.candlepowerforums.com/threads/178667
and your right, what silverfox said about slow charging cant be put into small sentances.


----------



## VidPro

*will end up at 1.47 maxV no matter how old are the cells.*

yes IF I also included the post termination TOPPING, so when reading along with what they are saying, there will also be something like "it floated up to 1.51 , then back down again after a few hours after it said Done"
meaning (to me) that on topping it doesnt have that restriction. (nor would it be needed).
and
most of the testers pointed out that on the break-in it did not seem to have the peak voltage termination, which is logical that on a "slow" charge it wouldnt be as critical.


----------



## 45/70

Wow, this thread is really getting deep!

There are a couple things I'd like to point out relevant to the discussion.

Concering NiMH cells, when a battery cell manufacturer or charger manufacturer refers to a "Standard Charge", this is a reference to the IEC 61951 standard for determining the capacity of NiMH cells, nothing more, nothing less. That is to say, it is not a reference as to how a NiMH cell should normally be charged, but rather an industry standard by which the capacity of NiMH cells is determined.

The other point I'd like to bring up is the Maha C-9000's "top off charge". All but the initial version of the C-9000 have this feature, which applies a 100mA charge for two hours after "DONE" when in charging mode. This rate is 0.1C or less, for all cells except those of <1000mAh capacity. It seems to me this is a good way to accomplish a full charge however the C-9000 terminates, whether it's -dV, by temperature, or the 1.47 Volt max V method. It's a way to in effect, finish the charge in a way that resembles a "Standard Charge".

As for Scooby Doo's original question, what is the appropriate charge rate for NiMH batteries, I think there may very well be more than one answer. As I've said elsewhere, part of the reason I changed over to NiCd's back in the early 80's (from alkalines) was their increased performance, yes at that time capacity suffered, but the performance was superior, ie. less voltage drop under load.

I used the 14-16hr chargers for 10+ years, that's pretty much all that was commonly available. Then the 4-6hr chargers showed up around the same time that NiMH chemistry did. Now we have chargers that will charge at a 4C rate (15min chargers). I've stayed away from the 4C chargers and after researching a few years ago, decided that the often recommended 0.5-1C rate was a good choice.

From the early days to now, one thing I've noticed is that with faster charge rates, cells seem not to develop voltage depression as often. In some cases over a period of time, the same batch of cells were charged both ways, some fast and some slow, so improvement in cell technology wasn't playing a part.

One aspect of faster charging that might be of significance, is that faster charge rates are known to retard large crystal formation in cells better than slow charge rates. Actually very slow rates, somewhere below 0.05C I believe, actually are a cause of large crystal formation in cells, although this may only happen when the cell is in a state of overcharge (trickle).

What I've seen in my cells may not be readily apparent, unless you frequently use your NiMH cells at 0.5-3C discharge rates. In most medium/low discharge rate applications it's possible you would not be aware that your cells were suffering from voltage depression.

I can only report what I've experienced personally. I find the discussion here of the ins and outs of charge rates interesting. I also suspect both sides are correct, in some ways, but for me, from a high performance aspect, I'm going to continue with the 0.5-1C charge rate, as it seems to work the best for me.

Dave


----------



## VidPro

I think Freddy and Daphney probably got scoobey out just in time
http://www.freewebs.com/scoobyrule/MYSTERY.WAV
http://www.freewebs.com/scoobyrule/BUMPS.WAV


----------



## jayflash

Good summation, 45/70. Your conclusions seem to be supported by my experience and, certainly, SilverFox's many explanations on this subject. The NiMH cells I've charged in this manner have not suffered voltage depression and have maintained their capacity. No over heating has occurred or missed termination - ever.


----------



## TorchBoy

VidPro said:


> i just dont have an actual 9000.


----------



## J_C

wapkil said:


> As far as I know such a level simply doesn't exist. You either have a higher risk of overcharging or higher risk of premature termination. With the usual level there is probably non-negligible risk of both. Except the false positives or negatives the sensitivity doesn't change the moment of termination in any important way. The -dV overcharges the cells - if you apply the trickle charge afterwards they will be even more overcharged.



... and I'm suggesting it doesn't necessarily overcharge, because they use a conservative termination with the idea that yes, it's a little undercharged, will finish charging with the trickle.



> dT/dt is not based on the temperature value but on the detection of the temperature rise rate. Please read the descriptions of appropriate algorithms if you are interested in comparing them.



... but this is even worse, in aforementioned example the 90% charged battery temp rise is much faster than the other. I am still of the opinion that dT is not so good unless only comparing two cells going through the majority of a charge cycle, and with similar impedance else you again have different temp rise.



> You may be right but the documents I read claim that it would be more costly to implement it correctly than to have a simple -dV. I tend to believe they are right here.



I can believe it is more costly to implement "correctly" because it would need a microprocessor to factor for several things in addition to just temperature change, like the amount of time and rate vs cell size. This is one of the reasons I feel Delta -V is at present still the reasonable method to use, but the higher the charge rate, the more important the charger have a safety temperature cutoff circuit, emergency type not just typical end-of-charge detection type. Often a circuit like this is quite simple, simply a resettable thermal breaker in series with the charging contact and of course as close to the battery tube as reasonably possible.



> I understand your position and sometimes it is more appropriate also for me. Nevertheless I am interested in finding out what are the results of using various available charging methods. Especially since there seems to be a popular impression that there exist a single best method that can be recommended to everyone and I think it is simply not true.



I think the best method is the most convenient one, that will vary per the situation.


----------



## Mr Happy

J_C said:


> ... but this is even worse, in aforementioned example the 90% charged battery temp rise is much faster than the other. I am still of the opinion that dT is not so good unless only comparing two cells going through the majority of a charge cycle, and with similar impedance else you again have different temp rise.


Actually, not so. The rate of temperature increase provides a very certain and predictable indicator of when the cell is fully charged. When the cell has capacity remaining most of the supplied energy is absorbed by the cell and stored, so the temperature rise is moderate. But as soon as the cell is fully charged and can store no more energy the whole of the applied power is converted to heat inside the cell leading to a rapid temperature rise. This temperature rise provides a certain signal that charging is complete and will be just as evident whether the cell starts out 0% full or 90% full.

You can see how it works in this test with an eneloop:







You can see the really sharp uptick in temperature at the end. This is what chargers look for when they are doing dT/dt control. If I had not stopped charging when I did the temperature would rapidly have gone off the scale.

The eneloop is a good quality cell. Here is a similar test with a "crap" cell:






Due to the poor cell performance the rate of temperature increase is higher during the normal charging phase here, but there is still an uptick when the cell is fully charged. As with the eneloop or any other cell, if I had not stopped charging at this point the temperature would have risen steeply off the scale and a charger would be able to detect this.

(Here is the original thread containing those pictures for reference.)


----------



## wapkil

Thanks for the graphs Mr Happy  

I'll try to write a longer paragraph describing how I understand some things related to charging. I'll need to find some time for it so probably later this week.

I think your graph with a "crap" cell demonstrates why I don't believe -dV or maxV can be universally relied upon. Here is mine:





The cell was charged with ~0.7C in Maha C9000 charge mode. At ~130min. it was already fully charged. The voltage at this point was ~1.44V. Apparently Maha measures when its pulsing is off, so it takes the lower "boundary" of the green voltage values. 1.44V is lower than Maha's 1.47V maxV so it happily continued charging. The problem was that -dV hasn't appeared (or was small enough to stay undetected). 

When the voltage finally reached the 1.47V maxV, the cell was seriously overcharged. I'd have to check but I think by ~15%-20%. You can see how the temperature skyrocketed. Maha stopped the fast charge but continued topping off an seriously overcharged cell. I let it continue for 5 minutes and stopped the torture.


----------



## 45/70

Interesting plot and result, wapkil. I'm curious, was the cell an AAA?

Dave


----------



## wapkil

45/70 said:


> Interesting plot and result, wapkil. I'm curious, was the cell an AAA?



No - an old AA. It already lost some of its capacity but I think it could still live and work many more cycles. Unless of course it is charged in the way depicted above that simply kills it.


----------



## 45/70

OK, thanks wapkil. I asked because I've noted that the C-9000 seems to work somewhat differently with AAA's. I'm not so sure it's as good a solution for them, as it is for AA's.

Dave


----------



## Mr Happy

wapkil said:


> No - an old AA. It already lost some of its capacity but I think it could still live and work many more cycles. Unless of course it is charged in the way depicted above that simply kills it.


Your cell reached 49°C. Mine went over 51°C. I think this is simply what happens when -dV/dt charge termination is applied. It could be argued that it's not a good system in terms of stress on the cells. Probably a lower charge rate and 0 dV/dt is kinder to the cells, but is also more expensive to implement.

To do a really good job of charging NiMH cells I think you need microprocessor control and some very clever programming.


----------



## J_C

Marduke said:


> I recommend you look up what "Standard Charge" actually means. It does NOT mean that is the recommend charge scheme. That is the method by which the capacity is determined, NOT the typical recommended method.
> 
> If you look on the same data sheet, it recommend that the typical charge is 1C...



No, it does not recommend, "recommend" is the word you apply rather than recognizing all they have done is suggested the maximum safe fast charge current.

That doesn't make it "standard" nor recommended moreso than any other, they just needed to list a maximum range they don't want people to exceed.

Again, this is something many component datasheets do, it does not in any way mean there is a problem with something other than the absolute max.

What you are suggesting is like seeing that an automobile tire is rated for 120MPH and thinking that everyone should only drive at 120MPH or else something bad will happen.


----------



## TorchBoy

"Recommend" is not just a word that has been applied by the users, even if it doesn't actually appear on the datasheet. The Twicell manual uses the word.


> When charging the Twicell, we recommend that you ensure precise charging control, and use constant current charging (quick charging) with a constant current of 0.5 It to 1 It,*** taking into consideration the various characteristics of the battery. Depending on the model of battery, charging at a constant current equivalent to 0.1 It is also possible.
> ...
> ... Set the charging current at a value between 0.5It and 1It,*** during quick charging.
> If charging is performed at a current less than 0.5 It, the voltage change and temperature rise that occurs when the battery becomes fully charged will not be sufficiently pronounced, making charging control difficult.
> ...
> ***···Maximum charge current for HR-4/3AU and HR-4/3FAU is 3.0A


----------



## J_C

TorchBoy said:


> "Recommend" is not just a word that has been applied by the users, even if it doesn't actually appear on the datasheet. The Twicell manual uses the word.



Ok, to that extent I am wrong if you really dig up some generic old document you do find the word recommend. However,

1) That manual is ancient in terms of NiMH and charger tech. Presumably back then, even they didn't have chargers that could cope which fell into consumer price-points but now they clearly do sell chargers at different rates.

2) A paragraph, maybe two or three before and after it mentions that cells can be charged at different rates and to contact a rep for details (meaning it can be done or else they'd just write "no"). 

3) This isn't even for the cells we're talking about it's for the old 4/3 A size used in multi-cell packs as the *** indicates.

Do you realize the significance of that? Back then, the volumetric (energy) density of cells was lower, it means that the temperature rise wasn't as high as it is with today's more energy dense cells. For example, if today's battery were exactly twice as energy dense w/same voltage, then it halves the "recommended" charge rate to 0.25 to 0.5C instead of their old recommendation.

4) They also use the word recommend liberally, stating things like that they don't recommend discharge above 1C but people do that too.

It's pretty clear cut, Sanyo sells several chargers WITH the batteries we've been talking about that do not charge at 0.5 to 1C. To think that is not a recommendation to use the charger with those batteries is a bit beyond bizarre. They even go so far as to state they don't warrant them if you don't use their charger on pages specific to the Eneloops *some* of us have been talking about.

In another topic we even have people advising about which of these chargers to buy... not to avoid all of them.


----------



## J_C

Mr Happy said:


> Actually, not so. The rate of temperature increase provides a very certain and predictable indicator of when the cell is fully charged. When the cell has capacity remaining most of the supplied energy is absorbed by the cell and stored, so the temperature rise is moderate. But as soon as the cell is fully charged and can store no more energy the whole of the applied power is converted to heat inside the cell leading to a rapid temperature rise. This temperature rise provides a certain signal that charging is complete and will be just as evident whether the cell starts out 0% full or 90% full.
> 
> You can see how it works in this test with an eneloop:
> 
> 
> 
> 
> 
> 
> You can see the really sharp uptick in temperature at the end. This is what chargers look for when they are doing dT/dt control. If I had not stopped charging when I did the temperature would rapidly have gone off the scale.



The chart illustrates my point. If only considering the graph of fully recharging a cell, not comparing against a cell (same cell...) that has a large % of charge already before being placed in a charger, it is not contrasting the other scenario.

When a cell starts with a large % of charge already, upon starting it is at room temp still, while the graph clearly shows the other cell has elevated temp when reaching the same amount of charge.

When you have two cells at the same charge level, supposing they have roughly the same waste energy being produced by charging, but one at a *pre-heated* state already because it's been sitting in the charger recharging for time as the graph shows, the pre-heated one has a higher difference between it and ambient temp compared to the cell which already had most of a charge before being placed in a charger.

The already charging cell's rate of temperature rise is then lower than that of the partially charged cell that just started to recharge, yet it's absolute temperature will remain higher until some point, possibly after the safe cutoff level from a rapid charge rate to avoid overcharging. You cannot then use rate of temperature change to terminate charge on both cells and end up with them both at the same charge (or overcharge) level, unless some elaborate calculations and data are added and used by the charger, probably requiring manual user input as well if we want to drift down the river of precision at any cost or effort. On the other hand, I am not certain using Delta -V would be accurate either but it is certainly simpler to implement *properly*.

If the already partially charged cell had a smaller difference in charge between it and the drained cell when both started to charge, then their final temps and rate of change would be approaching each other but this is contrary to the typical desires of users to be able to top off a cell at any point.


----------



## Marduke

I suggest you re-read both the Duracell, Rayovac, and Energizer docs above. Both RECOMMEND 1C, and do NOT state it as a maximum.

Also, the temperature termination being discussed is dT/dt, NOT dT/To as you are describing.


----------



## travelinman

The more I'm reading here, the more I'm tempted to go out and get a handful of LM317 variable voltage regulators, set one up with a scrap 12v wall wart, at a fixed 1.47v setting and feed it into a gutted AA charger body from the thrift store. (Maybe do all 4 bays in separate circuits)

I'll then put a 3v, 200 ma incan bulb in series with the circuit to limit current to 200 ma and plug the whole thing into a standard wall timer set for 16 hours. Whole thing should be available for under $5. Simple, failsafe, cheap.

That'll charge my AA eneloops safely and just the way I want it to.


----------



## J_C

Marduke said:


> I suggest you re-read both the Duracell, Rayovac, and Energizer docs above. Both RECOMMEND 1C, and do NOT state it as a maximum.
> 
> Also, the temperature termination being discussed is dT/dt, NOT dT/To as you are describing.



You don't accept that the slope is steeper if the cell starts out significantly cooler at the same charge level? 

You still haven't addressed that in fact, recomend does not mean "because it's not possible for another rate to work fine", when plenty of chargers, their designers, and battery manufacturers themselves seem confident enough in what they sell.

Picket these manufacturers to pull their chargers, THAT would at least be aligned with your supposed goal of keeping people doing what you assume to be the only correct way to charge NiMH.

<yawn>, I'm fine with us disagreeing since I get fine performance for my needs with chargers that don't do 0.5-1C. That pretty much makes more of this topic a waste of my time no matter how long someone else disagrees about it. The proof is in doing. Since I have chargers that DO it ok, text on the internet against it is a bit of fiction to me. 

Maybe I need to rebadge these magical chargers and sell 'em for $100 a pop as they must perform miracles, but till then I think this is pretty much...


----------



## Mr Happy

J_C said:


> You don't accept that the slope is steeper if the cell starts out significantly cooler at the same charge level?


It may be that it is, but even so it is a benefit rather than a problem. What the charger needs is a positive end of charge signal -- and if the slope is steeper the signal is more pronounced, not less. Since chargers traditionally have a problem detecting end of charge when faced with partially charged cells this more pronounced signal is a good thing.


----------



## Marduke

Again, YOU missed the entire point of his thread. It is not about what "will work" but what is BEST. As you yourself admitted several times, 1C is "best".

No one here (other than you) claimed we were saying there is only ONE way to do it, we were all discussing the BEST, and RECOMMENDED method.

Do whatever you want to your cells, but when someone asks for the "best" method of doing something you don't tell them to use inferior methods that offer ZERO benefits.


----------



## J_C

Marduke said:


> Again, YOU missed the entire point of his thread. It is not about what "will work" but what is BEST. As you yourself admitted several times, 1C is "best".
> 
> No one here (other than you) claimed we were saying there is only ONE way to do it, we were all discussing the BEST, and RECOMMENDED method.



BUT we totally disagree on why. I think it's best because it takes less time and is more energy efficient, and chargers aren't *necessarily* excessively expensive yet at that rate. Then again, I'd just as soon charge at 2C even if it got me only 80% capacity and 50% lifespan, IF chargers were reasonably priced. I'm never in such a hurry that I need a 15 minute charger though and wouldn't want to limit whether I can charge some of the older cells lying around at 4C.



> Do whatever you want to your cells, but when someone asks for the "best" method of doing something you don't tell them to use inferior methods that offer ZERO benefits.


People often ask a generic question with the word "best" in it, and then people answer what is best to them, because if there was only one "best" in all ways, there would only be one charger. 

That wasn't what was asked though, what was asked is what is an "appropriate" rate, to which the answer is there is a range that will work, it need not be 0.5C to 1C and if someone is not in a rush to charge or overly concerned about battery life, they are likely to put a little less wear on their battery at a little lower rate, or likewise to put a little less wear on their battery if they pick any rate fast enough their particular charger is able to sense a sufficiently low termination threshold if they were going to use an intermediate rate just a bit above a trickle but weren't likey to remember to manually terminate it.

The short answer is easy, but seldom enough or we wouldn't keep seeing discussions about charging.

... I haven't even mentioned yet that higher current through a charger will tend to wear it out faster, if not melt it, all else being equal.


----------



## J_C

Mr Happy said:


> It may be that it is, but even so it is a benefit rather than a problem. What the charger needs is a positive end of charge signal -- and if the slope is steeper the signal is more pronounced, not less. Since chargers traditionally have a problem detecting end of charge when faced with partially charged cells this more pronounced signal is a good thing.



If the charger is designed properly to terminate a cell charged from a fully depleted state (as it should be), a steeper slope could cause premature termination, depending on how the logic onboard is implemented. It typically seems an either/or/both, never a weighted combination of the two so temperature rate change, nor absolute temp alone isn't necessarily, unlike what a full charge graph suggests, a universal solution.


----------



## VidPro

The reason the .5C-1C rate is chosen has little to do with the speed of charge.
It comes from INSURING charge termination, on a device that seeks a V-drop termination method. on a "smart" computer, that is so stupid it will fail to terminate properly everytime with every cell at a lower rate.

Its all about the charger itself, and it's termination method. Just because the 9000 has ADDED in a (sort of) secondary method (voltage peak), it is still a V-drop termination charger.

The ONLY other possible "wise Recommendation" is to be slow enough that it is below the specs listed for an overcharge rate, and only if the charger can do that slow rate. 

WHEN your trying to get a stupid computer to try and terminate AND V-drop is it's method for doing so. a SLOW ramping down of the voltage drop on a battery that is being overcharged , over spec, can sometimes be missed because microcontrollers are not humans.
Computers have specific timings and specific sensitivites to the voltage. they dont Look back in hindsight and stop on thier own, till any timer function is reached.
It is a simple Program code set that loops moronically sencing things, it doesnt have 50KB of ram stored that it back compares sencor data to. 
Although it does hold a few hundred bytes of data in storage, for the user to glean over, its not that much different than other V-drop seeking chargers. 
Round and round they go when they stop the v-drop knows.

The advice for recommended was Solid, there are other choices, but there is a heck of a good reason that the rates selected were recommended, in the first of the thread. Specifically applied to THAT machine the 9000. Other rates that the charger has would usually work most of the time, but could still rarely cause a cell to continue to Overcharge, beyond overcharge specs, damaging it.


----------



## TakeTheActive

*C9000 Impedance Check Voltage on *CRAP* Cells...*



Mr Happy said:


> ...*Here is a similar test with a "crap" cell:*
> 
> ...Due to the poor cell performance the rate of temperature increase is higher during the normal charging phase here, but there is still an uptick when the cell is fully charged...





wapkil said:


> No - *an old AA.* It already lost some of its capacity but I think it could still live and work many more cycles...



What is the C9000 Impedance Check Voltage on these *crap* cells?



TakeTheActive said:


> ...
> 
> DISCHARGE them @ 100mA on the C9000.
> Post the voltage from an IMPEDANCE CHECK on the C9000:
> Individually, in Slot #4 (with all other slots empty):
> Insert a cell.
> Press ENTER twice.
> Post the first voltage displayed (GT 1.50VDC).
> *Reference: **Interpreting MH-C9000 Impedance Check Voltages*



Thanks!


----------



## wapkil

45/70 said:


> OK, thanks wapkil. I asked because I've noted that the C-9000 seems to work somewhat differently with AAA's. I'm not so sure it's as good a solution for them, as it is for AA's.



Maybe there is something similar in older, low capacity AAs and AAAs? I think the C9000 doesn't distinguish between AAs and AAAs and hits AAAs with 2.5C - 3C current. It is pulsed but I would have to read a really good explanation to believe that it can be harmless.



Mr Happy said:


> Your cell reached 49°C. Mine went over 51°C. I think this is simply what happens when -dV/dt charge termination is applied. It could be argued that it's not a good system in terms of stress on the cells. Probably a lower charge rate and 0 dV/dt is kinder to the cells, but is also more expensive to implement.
> 
> To do a really good job of charging NiMH cells I think you need microprocessor control and some very clever programming.



I don't think we should compare the absolute temperature values. I believe that it is not the temperature that harms the cell. The rapid temperature rise is only a side effect of the reactions that start to occur when the positive electrode is "overcharged" and starts producing oxygen. 

If the charge rate is slow, electrolysis that produces the oxygen will be reversed at the negative electrode and the additional current will do practically no harm. That's why with 0.1C we don't have to worry too much about overcharging. 

On my plot the charging wasn't slow. I believe it was fast enough for the oxygen generation far exceeding the recombination reactions speed. It started to oxidize the electrode alloy thereby deteriorating its capacity. This deterioration, with accelerating speed, lasted for ~20 minutes...

This is also the reason why I don't like fast charging. I think all the termination methods rely on the signals that are produced only when the cell is already overcharged and the negative electrode is deteriorating. I don't think that I saw a fast charge termination algorithm that, without knowing in advance the cell capacity, could prevent it.

I think the voltage plateau (0 dV) is extremely hard to use. It happens randomly during charging, not only at the end so relying on it can result in frequent premature terminations.



TakeTheActive said:


> What is the C9000 Impedance Check Voltage on these *crap* cells?



For mine it wasn't bad. I don't remember exactly but IIRC higher than 1.5V and lower than 1.6V.


----------



## 45/70

*Re: C9000 Impedance Check Voltage on *CRAP* Cells...*



wapkil said:


> Maybe there is something similar in older, low capacity AAs and AAAs? I think the C9000 doesn't distinguish between AAs and AAAs and hits AAAs with 2.5C - 3C current. It is pulsed but I would have to read a really good explanation to believe that it can be harmless.



Yes, I think you're probably on to something here.

With newer AAA cells (eneloops), I'm not seeing a problem. If you consider that AAA's have a higher IR than AA's when new however, (I assume because of their smaller configuration) and then add the rising IR of older cells, which is where I am seeing problems, it would seem something is going on here, similar to the AA you tested.

I don't use many AAA's, so my experience is limited. I do wish the C-9000 actually treated them differently than AA's. As it is, a lot of AAA's are rejected merely because of the impedance check, when, for an AAA, they're really still quite usable and in reasonable health. I'm guessing this more than likely all ties together somehow, so I thought I'd bring it up.

Dave


----------



## wapkil

J_C said:


> If the charger is designed properly to terminate a cell charged from a fully depleted state (as it should be), a steeper slope could cause premature termination, depending on how the logic onboard is implemented. It typically seems an either/or/both, never a weighted combination of the two so temperature rate change, nor absolute temp alone isn't necessarily, unlike what a full charge graph suggests, a universal solution.



Theoretically the temperature rise speed when the cell is overcharged should be ~5-10 times higher than when it is normally charging. It should make it possible to detect the dT/dt signal no matter what was the state of the cell when the charging started. Theoretically...

I'm not saying dT/dt is good. It isn't - I believe no method of fast charge termination is completely reliable and, to make things worse, even if the termination signal is detected some harm was already done.

Here is a strange (IMO) example for dT/dt:





It is an empty cell (the same as previously) charged with constant current (not Maha) ~0.15C. I have no idea why the temperature raised so dramatically at the beginning nor do I know why it suddenly dropped down after ~60 minutes. Nothing in the environment has changed, it's just how the cell decided to act this time. At ~600 minutes the charge was terminated so this temperature drop is normal.



VidPro said:


> The ONLY other possible "wise Recommendation" is to be slow enough that it is below the specs listed for an overcharge rate, and only if the charger can do that slow rate.
> 
> WHEN your trying to get a stupid computer to try and terminate AND V-drop is it's method for doing so. a SLOW ramping down of the voltage drop on a battery that is being overcharged , over spec, can sometimes be missed because microcontrollers are not humans.
> Computers have specific timings and specific sensitivites to the voltage. they dont Look back in hindsight and stop on thier own, till any timer function is reached.
> It is a simple Program code set that loops moronically sencing things, it doesnt have 50KB of ram stored that it back compares sencor data to.
> Although it does hold a few hundred bytes of data in storage, for the user to glean over, its not that much different than other V-drop seeking chargers.
> Round and round they go when they stop the v-drop knows.



I think you are unfair to the poor computer chips. With fast charging they are in a hopeless situation. Looking at the real charge graphs I also sometimes have no idea at what charge level the cell is. I can guess what happens when I know the cell capacity and how much charge it had left when inserted but usually no one tells it to the chip...

The reactions during a NiMH charging are ugly and unpredictable. The best I can do is to accept it, ignore them and use the timer and the 0.1C charge which, I believe, shouldn't harm the cell.


----------



## TakeTheActive

wapkil said:


> ...*I think the C9000 doesn't distinguish between AAs and AAAs and hits AAAs with 2.5C - 3C current. It is pulsed but* I would have to read a really good explanation to believe that it can be harmless...



What did you ever read to make you think otherwise?



wapkil said:


> ...For mine it wasn't bad. I don't remember exactly but IIRC higher than 1.5V and lower than 1.6V.



So, in the C9000's eyes, it's a low Internal Resistance (i.e. healthy, vibrant) cell. Are you equipped to measure Internal Resistance with a LOAD? 

*How Do You Measure Internal Resistance (w/Known RESISTANCE Load)? {TECHNICAL!}*


----------



## TorchBoy

J_C said:


> 1) That manual is ancient in terms of NiMH and charger tech. Presumably back then, even they didn't have chargers that could cope which fell into consumer price-points but now they clearly do sell chargers at different rates.


So you're saying they've changed their recommendation because consumer chargers are now available that can charge at 0.5C?  I had one that could when I downloaded that PDF.



J_C said:


> 2) A paragraph, maybe two or three before and after it mentions that cells can be charged at different rates and to contact a rep for details (meaning it can be done or else they'd just write "no").


So batteries can be charged at lots of different rates and it still works. So what?



J_C said:


> 3) This isn't even for the cells we're talking about it's for the old 4/3 A size used in multi-cell packs as the *** indicates.


I understand that footnote as referring only to those cells, which implies the recommendation itself is not only to those cells.



J_C said:


> Do you realize the significance of that? Back then, the volumetric (energy) density of cells was lower, it means that the temperature rise wasn't as high as it is with today's more energy dense cells. For example, if today's battery were exactly twice as energy dense w/same voltage, then it halves the "recommended" charge rate to 0.25 to 0.5C instead of their old recommendation.


How old do you believe cells of, say, around 2,000 mAh to be?



J_C said:


> 4) They also use the word recommend liberally, stating things like that they don't recommend discharge above 1C but people do that too.


And...? :shrug:


----------



## Bullzeyebill

A guy could go crazy thinking about which AA charger to buy. Not me, I will stick with my old 401F, and use my Triton for the 0.1C charges ever so often, when my cells get close to 1 volt.

Bill


----------



## wapkil

TakeTheActive said:


> wapkil said:
> 
> 
> 
> ...*I think the C9000 doesn't distinguish between AAs and AAAs and hits AAAs with 2.5C - 3C current. It is pulsed but* I would have to read a really good explanation to believe that it can be harmless...
> 
> 
> 
> What did you ever read to make you think otherwise?
Click to expand...


Nothing. I just haven't checked it and didn't want to make an impression that I know that it doesn't do it. Many simpler chargers distinguish between cell sizes (e.g. to be able to charge them with different currents) and the C9000 could and probably should do it as well.



TakeTheActive said:


> So, in the C9000's eyes, it's a low Internal Resistance (i.e. healthy, vibrant) cell. Are you equipped to measure Internal Resistance with a LOAD?
> 
> *How Do You Measure Internal Resistance (w/Known RESISTANCE Load)? {TECHNICAL!}*



I don't have a precision ohmmeter so I would have to rely on a (poor) accuracy of a resistor and the DMM resistance measurements. It would be sufficient though to see if the resistance is "high" or "low". I guess the reading should be something moderate, unless the cell decides to act funny also in this test. The battery still works rather well but I don't have access to it now. I could check it in the second half of the month.

EDIT: The C9000 was also discharging this battery without premature termination - another information suggesting that the internal resistance is not too high in this cell.


----------



## wapkil

Bullzeyebill said:


> A guy could go crazy thinking about which AA charger to buy. Not me, I will stick with my old 401F, and use my Triton for the 0.1C charges ever so often, when my cells get close to 1 volt.



The scary 401FS that managed to frighten SilverFox? You sir are a brave man :nana:


----------



## Bullzeyebill

wapkil said:


> The scary 401FS that managed to frighten SilverFox? You sir are a brave man :nana:



Yeah, the same one. I read Tom's concerns early on. Not so brave, as it has never failed me, and I get the same finishing voltage readings each channel. I have never done a discharge test after using it, but I have a feeling that the LDS cells I am using will show consistant discharge rates, as I notice that cells read the same voltage when I remove them from my lights. You know, you never see a problem till there is a problem, and I just go on using my cells.

Bill

Whoops, actually one channel did fail, me early on, and I don't use it. Gave me an incomplete charge. I never had it diagnosed, and three channels is fine with me.


----------



## clintb

wapkil said:


> The scary 401FS that managed to frighten SilverFox? You sir are a brave man :nana:


Eh, nothing wrong with the 'ole 401...as long as it's used on SLOW.


----------



## VidPro

wapkil said:


> I think you are unfair to the poor computer chips. With fast charging they are in a hopeless situation. Looking at the real charge graphs I also sometimes have no idea at what charge level the cell is. I can guess what happens when I know the cell capacity and how much charge it had left when inserted but usually no one tells it to the chip...
> 
> The reactions during a NiMH charging are ugly and unpredictable. The best I can do is to accept it, ignore them and use the timer and the 0.1C charge which, I believe, shouldn't harm the cell.


 
and not only that, but when the room temperature changes, the votage being metered on a CC slow charge seemed to change. there is huge quantities of "things going on" and for a microcontroller to even try and calculate all of them, and include all external anomolies too. it would have to have a level of sofistication well beyond the present. taken out of a Lab and put into thousands of different working situations, with undeterminate variations both internal and external, it is no wonder why they pick simple.

get a perfect temp alogrythm worked out, and somone in a igloo at the poles wants to know why it doesnt work right . or some person has it charging in thier car sitting in direct sun. Have a voltage alogrythm worked out and , someone wants to know why thier battery isnt fully charged. make a nice slow alogrythm and when a 3800ma cell actually exists somone wants to know why it doesnt get fully charged in the time alloted. Then include all sencing both internal and external and one breaches the desired point before the other, then you end up with layers of If Thens. 

Cool temp graph by the way on the old cell.


----------



## wapkil

VidPro said:


> and not only that, but when the room temperature changes, the votage being metered on a CC slow charge seemed to change. there is huge quantities of "things going on" and for a microcontroller to even try and calculate all of them, and include all external anomolies too. it would have to have a level of sofistication well beyond the present. taken out of a Lab and put into thousands of different working situations, with undeterminate variations both internal and external, it is no wonder why they pick simple.



This is true in general but I believe in practice it results in problems mainly for NiMHs. 

If you take a Li-Ion cell, everything you have to do is to first measure the voltage and then the current. If you miss the exact point you planed to switch to CV - no problem, the voltage will rise further and you'll see it. When you measure the current in CV, no problem either - you can finish at 10% or 3%, doesn't really matter. If you want to charge at 0.8C, good for you. If you prefer 0.1C, do as you please, only the CC phase will be longer and the CV shorter. This is how a nice chemistry should behave, it's the NiMHs behavior that makes things ugly


----------



## wapkil

clintb said:


> Eh, nothing wrong with the 'ole 401...as long as it's used on SLOW.



Yeah, nothing wrong with any charger as long as it's used close to 0.1C. That's the main point for me coming from this thread. Although if the 401 is not the real CC but a pulsed current similar to the C9000, I think I would prefer something else.


----------



## travelinman

And if you do have to use the 401 on high, so not use the clear plastic top so some of the heat can escape. (just like it says in the instructions). :twothumbs


----------



## Bullzeyebill

travelinman said:


> And if you do have to use the 401 on high, so not use the clear plastic top so some of the heat can escape. (just like it says in the instructions). :twothumbs



Right. I do not close the lid when using the high charge mode, per instructions.

Bill


----------



## wapkil

wapkil said:


> Unfortunately I haven't seen a comparison similar to the one above with the standard charge included but I believe it does not reduce the cells life in the way -dV does.



I still haven't seen a direct comparison but I just realized that for Eneloops there is something that can be useful:





What you see above is the result of using a fast 1C, -dV charge followed by a fast 1C discharge. They call it "accelerated cycle test" because it, as expected, accelerates aging. 

An Eneloop is advertised as a battery that you can recharge "1000 times and more". It is probably true for the standard 0.1Cx16h charge but not for fast charging. With fast charging you can get only 250-300 cycles before it deteriorates below 75% capacity and maybe 400 cycles before it completely dies. They advertise Eneloops as much better than standard NiMHs which on the graph perform even worse than that.

One could write that the cycle life would be longer in the battery rests longer, is subject to some clever methods to "heal" it and if it is discharged slower. I believe it is partially true - you would get a few more cycles but still far from the expected cycle life. As I see it, the main reason why on the above graph the batteries perform poorly is the fast charge and overcharging that it inevitably introduces.


----------



## VidPro

or they just LIED about the 1000 times :huh:
Hey mabey they could use the creative marketing term UPTO 1000 times.
then they could say costs as little as 2cents to buy.
then say it outperforms many cells on the market today in capacity
then say , it stays charged for UPTO 2 years.


----------



## wapkil

VidPro said:


> or they just LIED about the 1000 times :huh:
> Hey mabey they could use the creative marketing term UPTO 1000 times.



They did  "You may recharge eneloop up to 1.000 times and more". I love it how marketing uses numbers and makes them completely meaningless...

Nevertheless in a more scientific document about Eneloops I saw their claim that the batteries have the cycle life performance of 1000 cycles according to IEC standards.


----------



## clintb

Did anyone else catch the -dV of 10mV?! Jeebus, that's crazy high for NiMh. I've never seen anyone use a figure that high, most of the time it's 3-5mV per cell. If that's not a typo, it could be the reason those cells were toast after 250-300 cycles.


----------



## wapkil

clintb said:


> Did anyone else catch the -dV of 10mV?! Jeebus, that's crazy high for NiMh. I've never seen anyone use a figure that high, most of the time it's 3-5mV per cell. If that's not a typo, it could be the reason those cells were toast after 250-300 cycles.



10mV is what they use for Eneloops in all the data sheets. I think that for these batteries this termination signal may be stronger. 

It could be the reason why on this graph they perform so much better than standard NiMHs :devil: On the other hand, standard NiMHs are ~500 cycles according to IEC so probably Eneloops are better anyway.

EDIT: Nevertheless, interesting catch. It would be nice to know if Eneloop -dV chargers also use 10mV. If they do and people use them for standard NiMHs... Well, it would be an effective way to "prove" the users how much better Eneloops are :devil:


----------



## VidPro

clintb said:


> Did anyone else catch the -dV of 10mV?! Jeebus, that's crazy high for NiMh. I've never seen anyone use a figure that high, most of the time it's 3-5mV per cell. If that's not a typo, it could be the reason those cells were toast after 250-300 cycles.


 
and that would be because . . . . they would be more likly to be, hard overcharged for longer than 1/2 that or 1/3rd that?


----------



## Bones

wapkil said:


> 10mV is what they use for Eneloops in all the data sheets. I think that for these batteries this termination signal may be stronger.
> 
> It could be the reason why on this graph they perform so much better than standard NiMHs :devil: On the other hand, standard NiMHs are ~500 cycles according to IEC so probably Eneloops are better anyway.
> 
> EDIT: Nevertheless, interesting catch. It would be nice to know if Eneloop -dV chargers also use 10mV. If they do and people use them for standard NiMHs... Well, it would be an effective way to "prove" the users how much better Eneloops are :devil:



The only other manufacturer I've seen claim 'up to' a 1000 cycles is Duracell, and it's for a 1700mAh regular chemistry cell:





Incidentally, Rayovac used a negative delta-V of 8mV for their version of an 'accelerated' life-cycle test of their 2100mAh regular chemistry cell:

http://www.candlepowerforums.com ... post3064609
-


----------



## wapkil

VidPro said:


> and that would be because . . . . they would be more likly to be, hard overcharged for longer than 1/2 that or 1/3rd that?



I'm not sure if I understand your question but with standard NiMHs 10mV signal may never be generated. As I wrote previously -dV is unreliable and there is really no good level for this signal - some manufacturers recommend less than 10mV, some 5mV, some 2mV...

BTW, in old Twicell documentation Sanyo warns that if you use -dV the service life will be reduced about 20% compared to maxV. They don't write how much maxV is worse compared to the standard 0.1C charge. I think that when they started selling -dV chargers these warnings "accidentally" disappeared from newer documentation. At least in their chargers descriptions they still write that "the slow charging by using a low charge-current ensures a long cycle life".


----------



## SilverFox

Hello Wapkil,

Are you sure of the charge rate on the graph you showed charging at 0.7C? The amount of time for the charge seems to suggest that it was a charge closer to 0.5C.

The -dV of 10 mV is a standard NiCd termination value. When NiMh chemistry was introduced there were questions if NiMh cells could be charged on NiCd chargers. The answer is yes, but the cycle life is reduced.

This turned into an "in house" standard for accelerated life cycle testing.

The general belief is that the reduction in cycle life comes from the extra time spent in overcharge while the cell voltage is driven to the -10 mV. 1C charging is in the IEC cycle life standard, but capacity change is determined by a standard 0.1C 16 hour charge followed by a 0.2C discharge. This capacity check is done every 50 cycles. You end up with 49 1C charge cycles followed by a 0.1C charge to determine capacity.

The reason to use a -dV value rather than max V is because max V changes as the cell ages. When the -dV value approaches 0 mV the risk of premature termination increases. It is a balancing act to find a -dV value that minimizes overcharge yet is reliable through the life of the cell.

Tom


----------



## wapkil

SilverFox said:


> Hello Wapkil,
> 
> Are you sure of the charge rate on the graph you showed charging at 0.7C? The amount of time for the charge seems to suggest that it was a charge closer to 0.5C.



I think you may be right. I used in the calculations the capacity determined by Maha C9000 but I it doesn't perform the IEC capacity analysis (contrary to what the manual claims) and the actual capacity may be higher. I'll change the description to read "0.5C - 0.7C".



SilverFox said:


> The -dV of 10 mV is a standard NiCd termination value. When NiMh chemistry was introduced there were questions if NiMh cells could be charged on NiCd chargers. The answer is yes, but the cycle life is reduced.
> 
> This turned into an "in house" standard for accelerated life cycle testing.



Sanyo uses 10mV in all their graphs, including typical charge characteristics. I believe this is the sensitivity level that they find the best for all their batteries, including the newest Eneloops. 10mV is also what the general battery literature that I read recommended for NiMHs (as opposed to 10mV-20mV range for NiCads). The literature I saw may be outdated and it is possible that for modern high capacity cells made by some manufacturers lower levels are more suitable but I doubt it that 10mV has anything to do with testing accelerated aging.



SilverFox said:


> The general belief is that the reduction in cycle life comes from the extra time spent in overcharge while the cell voltage is driven to the -10 mV. 1C charging is in the IEC cycle life standard, but capacity change is determined by a standard 0.1C 16 hour charge followed by a 0.2C discharge. This capacity check is done every 50 cycles. You end up with 49 1C charge cycles followed by a 0.1C charge to determine capacity.



I don't have a copy of the standard but everywhere I saw it, the cycle life was tested as follows:





I think this is what the standard defines. Maybe there is some additional procedure for accelerated aging that uses 1C but I haven't seen it employed anywhere. 10mV sensitivity is a bit more severe than lower levels but I believe that no matter what level is chosen, -dV will always overcharge batteries.


----------



## TorchBoy

wapkil said:


> What you see above is the result of using a fast 1C, -dV charge followed by a fast 1C discharge. They call it "accelerated cycle test" because it, as expected, accelerates aging.





VidPro said:


> or they just LIED about the 1000 times :huh:


The MH-C9000 doesn't treat the cells so roughly, though, does it? Terminating short of the -dV signal would mean we should get a much longer cycle life even if we fast charge/discharge.


----------



## Mr Happy

TorchBoy said:


> The MH-C9000 doesn't treat the cells so roughly, though, does it? Terminating short of the -dV signal would mean we should get a much longer cycle life even if we fast charge/discharge.


Yes, I think so. I think stopping the charge short of the peak voltage like the C9000 does with most cells is a good thing.


----------



## Bullzeyebill

I can adjust the -dV signal on my Triton. Can I set it to stop charging just prior to the -dV signal?

Bill


----------



## Mr Happy

Bullzeyebill said:


> I can adjust the -dV signal on my Triton. Can I set it to stop charging just prior to the -dV signal?


I don't think so. I think you can only reduce the -dV to the smallest value the charger allows. The potential problem with that is that you might get false terminations where the charger stops charging too soon.


----------



## TorchBoy

Bullzeyebill said:


> I can adjust the -dV signal on my Triton. Can I set it to stop charging just prior to the -dV signal?


Can you? How would you (or it) know what's about to happen? (I have no idea if you can stop on max V or a particular value of V.)


----------



## wapkil

Mr Happy said:


> TorchBoy said:
> 
> 
> 
> The MH-C9000 doesn't treat the cells so roughly, though, does it? Terminating short of the -dV signal would mean we should get a much longer cycle life even if we fast charge/discharge.
> 
> 
> 
> 
> Yes, I think so. I think stopping the charge short of the peak voltage like the C9000 does with most cells is a good thing.
Click to expand...


I think it depends on the battery and, obviously, the voltage level. For new cells (like an Eneloop from Mr Happy's graph) the 1.47V level in the C9000 means that the termination will be before the cell is fully charged and thus it will be gentle. For older cells (like an old cell from the second Mr Happy's graph or my graphs) this level may be too high and the charge will be painful for the battery. I don't know why older batteries heat up (i.e. with fast charging start to overcharge) earlier than the new ones. I thought that in theory it should work the opposite way but it seems that's how it is. 



Bullzeyebill said:


> I can adjust the -dV signal on my Triton. Can I set it to stop charging just prior to the -dV signal?



I agree with the previous answers. For batteries you cannot predict the future. You can set lower -dV level and risk premature termination or set higher -dV level and risk that it will never happen and the battery will overcharge. It is possible though that for a hobby charger you could set many terminations signals to make your situation a bit better.


----------



## SilverFox

Hello Wapkil,

The section of the standard that deals with 1C charging for cycle life is section 7.4.1.2.3.

Tom


----------



## clintb

Bullzeyebill said:


> I can adjust the -dV signal on my Triton. Can I set it to stop charging just prior to the -dV signal?
> 
> Bill


As Mr Happy has already stated, you can't set it to stop prior to the -dV. You could, however, start out with a -dV of 2mV, do a charge on a discharged cell, and once it's done, turn around and do a low rate discharge to 0.9V to see what you get back out. If it's lower than the rated capacity, raise the -dV and repeat. This is where having a charger that outputs live views to a pc comes in handy; you can SEE the point at which the voltage starts to drop.


----------



## MarioJP

What I don't understand about NiMh batteries is the high self discharge. My duracells 2650 self discharge way too fast, you talking within a day they are very low. I only had these batteries for couple of months what gives??.

What do you guys think about these cells?. Are they trash?.


----------



## digitor

MarioJP said:


> What I don't understand about NiMh batteries is the high self discharge. My duracells 2650 self discharge way too fast, you talking within a day they are very low. I only had these batteries for couple of months what gives??.
> 
> What do you guys think about these cells?. Are they trash?.


If they self-discharge that quickly, yes. What charger are you using?

Cheers


----------



## wapkil

SilverFox said:


> Hello Wapkil,
> 
> The section of the standard that deals with 1C charging for cycle life is section 7.4.1.2.3.



Thank you for the information. When I'm back home, at the and of the month, I'll try to take a look at the standard.

As I wrote, I haven't seen the 1C charging used for cycle life estimations in any data sheet and I've seen dozens using the 0.1C/0.25 procedure. The manufacturers even call it the IEC standard, e.g: 





is called by Sanyo "a comparison of cycle life performance according to IEC standards".

It's not surprising for me that they are using this testing procedure. I believe it results in a few times longer cycle life than the 1C charges you described would.

Do you know what's the purpose of the procedure in the section 7.4.1.2.3 ? Maybe it is some accelerated aging test that no one seems to use?


----------



## wapkil

clintb said:


> As Mr Happy has already stated, you can't set it to stop prior to the -dV. You could, however, start out with a -dV of 2mV, do a charge on a discharged cell, and once it's done, turn around and do a low rate discharge to 0.9V to see what you get back out. If it's lower than the rated capacity, raise the -dV and repeat. This is where having a charger that outputs live views to a pc comes in handy; you can SEE the point at which the voltage starts to drop.



This is an interesting experiment but note that NiMH batteries are able to tolerate a limited number of discharges, especially deep discharges. It would be better for their life if you could estimate the charge level without unnecessarily discharging them (e.g. based on the charger output).


----------



## clintb

wapkil said:


> This is an interesting experiment but note that NiMH batteries are able to tolerate a limited number of discharges, especially deep discharges. It would be better for their life if you could estimate the charge level without unnecessarily discharging them (e.g. based on the charger output).


Agreed. I was coming at it from the angle of a sacrificial cell. You know, in the name of Science! 

As you stated, it really wouldn't be necessary to do this on a fully depleted cell; even one that's as low as 50% discharge, and even 75% discharged would probably work just as well. And we're only looking at, maybe, 5 cycles of this to find an appropriate -dV for that particular charger (Triton in this case.). I know for my iCharger 208B, a AA Eneloop is good on 2mV, possibly 3mV depending on the cells health.


----------



## SilverFox

Hello Wapkil,

The accelerated cycle life test procedure is used to "accelerate the test or to use cycling conditions approximating those in actual applications..."

Tom


----------



## MarioJP

digitor said:


> If they self-discharge that quickly, yes. What charger are you using?
> 
> Cheers



15 minute energizer charger. Though it actually takes 30 minutes to charge the 2650 and another 15 minutes to cool down as they get really hot to touch.


----------



## Marduke

MarioJP said:


> 15 minute energizer charger. Though it actually takes 30 minutes to charge the 2650 and another 15 minutes to cool down as they get really hot to touch.



And there is the true source of your problem. While occasional use is one thing, continued use of that charger will turn your batteries into mush.


----------



## wapkil

MarioJP said:


> 15 minute energizer charger. Though it actually takes 30 minutes to charge the 2650 and another 15 minutes to cool down as they get really hot to touch.



Ouch. I'm not familiar with this charger but no matter how clever they claim it to be, using a charger with 7.5A current is the best way to quickly kill your cells 

I don't know how the charger operates but if it does not slow down after ~15-20 minutes, after 30minutes it would not only damage the cells with its extremely high current but also severely overcharge them. Maybe someone with better knowledge of this charger could write if it's normal for it to charge for 30 minutes (I guess trickle charging in the last part).

To conclude - almost certainly the charger cooked your cells to death.


----------



## MarioJP

wapkil said:


> Ouch. I'm not familiar with this charger but no matter how clever they claim it to be, using a charger with 7.5A current is the best way to quickly kill your cells
> 
> I don't know how the charger operates but if it does not slow down after ~15-20 minutes, after 30minutes it would not only damage the cells with its extremely high current but also severely overcharge them. Maybe someone with better knowledge of this charger could write if it's normal for it to charge for 30 minutes (I guess trickle charging in the last part).
> 
> To conclude - almost certainly the charger cooked your cells to death.



I actually studied this charger. The way it charges the cell it slows down if it gets too hot individually, but then speeds up once its cool and back up to getting hot again. With only one LED status for 4 its hard to tell if each cell has been charged equally which is another problem i am starting to get annoyed.

One out of 2 cell would be flat dead while the other one has charge left in them. I would not be surprised if polarity reversal has happen. Batteries still charge but you better use them asap lol. That is what i am getting tired of. All i know this charger has caused me great deal of grief and the maintenance is taking its toll on me 

Another problem is that eventually this charger will refuse to charge after a month of use and just gives me the red flashing led. Once that has happen no matter what the state charge of the battery is it will not charge it period. And that is where i drew the last straw for this charger unfortunately. Not only does this charger causes high battery maintenance, only to find out all that hours spent was for nothing. It is also picky of the battery's condition state too.


----------



## wapkil

clintb said:


> As you stated, it really wouldn't be necessary to do this on a fully depleted cell; even one that's as low as 50% discharge, and even 75% discharged would probably work just as well. And we're only looking at, maybe, 5 cycles of this to find an appropriate -dV for that particular charger (Triton in this case.). I know for my iCharger 208B, a AA Eneloop is good on 2mV, possibly 3mV depending on the cells health.



Good point on using partially charged cells but I was referring to your recommendation to discharge the battery to check whether the charge terminated correctly. I thought that instead of discharging the cells when finished, one could estimate how well they were charged using the charging current and the time. If the cells were used normally, they would be discharged afterwards in some device so the experiment wouldn't put an additional load on them.

Another problem with estimating the "best" -dV value is that the situation is essentially random. I understand that your goal was to test for the lowest level (highest sensitivity) to prolong the cells life. When you find that during a test charge with 2mV the termination was correct, the only thing you know is that during this charge a random >=2mV voltage drop didn't happen. Unfortunately it may happen next time when you charge the cell...


----------



## wapkil

MarioJP said:


> I actually studied this charger. The way it charges the cell it slows down if it gets too hot individually, but then speeds up once its cool and back up to getting hot again. With only one LED status for 4 its hard to tell if each cell has been charged equally which is another problem i am starting to get annoyed.



It explains why it can take 30 minutes but it still isn't a good method to charge the batteries. Unless you agree to severely reduce their cycle life. I believe that when the charger slows down seeing that the cell overheats, the battery charged this fast already generated enough oxygen to oxidize the negative electrode and reduce its capacity.



MarioJP said:


> One out of 2 cell would be flat dead while the other one has charge left in them. I would not be surprised if polarity reversal has happen. Batteries still charge but you better use them asap lol.



This is another indicator of a dead cell. I believe even fresh cells can be charged to a higher than 100% charge level but they would soon self-discharge to ~100%. A dead cell can act in a similar manner but with the available capacity dropping to a much lower level.


----------



## Mr Happy

I tried the Energizer 15 minute charger on some older eneloops and it popped the vent on one of them. I really would not trust it as an everyday charger, but it is OK for a once-in-a-while emergency charge.


----------



## MarioJP

Mr Happy said:


> I tried the Energizer 15 minute charger on some older eneloops and it popped the vent on one of them. I really would not trust it as an everyday charger, but it is OK for a once-in-a-while emergency charge.



oh about that. the batteries that came included with the 15 min charger and i believe its the 2450 ones. It started to make popping noises on the positive terminal one one of the 4 cells and it got louder until i had to disconnect the charger. And even after the charge stopped it was still making the popping sound but eventually it stopped.

so much for my everyday charger. I later got the LaCrosse BC-9009


----------



## wapkil

Mr Happy said:


> I tried the Energizer 15 minute charger on some older eneloops and it popped the vent on one of them.



 I though that if it controls the temperature, at least it won't let the pressure go this high... 



Mr Happy said:


> I really would not trust it as an everyday charger, but it is OK for a once-in-a-while emergency charge.



I agree that it can be used if there is no other choice but I wouldn't call OK something that harms the cells so much and sometimes even makes them vent. On the second thought though, it is probably still a bit better than connecting the battery directly to the wall outlet


----------



## wapkil

Mr Happy said:


> I tried the Energizer 15 minute charger on some older eneloops and it popped the vent on one of them.





MarioJP said:


> oh about that. the batteries that came included with the 15 min charger and i believe its the 2450 ones. It started to make popping noises on the positive terminal one one of the 4 cells and it got louder until i had to disconnect the charger. And even after the charge stopped it was still making the popping sound but eventually it stopped.



It eventually let the generated gaseous oxygen out and the pressure inside lowered enough to close the vents.

Even for me it is disturbing that a battery manufacturer can sell such a charger. On the other hand, I'm sure that if the marketing department decides so, they will put this charge method as "recommended" in the data sheets


----------



## MarioJP

The only cells that actually withstand this kind of abuse is the duracell precharged. These batteries were severely abused by getting soo hot that it actually started to melt the paper wrapping a little. And i currently have these batteries and they show no or little signs of abuse.

Not only does it still hold their charge even after days sitting there. They last a long time when using them and don't show any signs of poor performance either.

wish I can say the same thing about the duracell 2650 which i only had them for 2 months and showing signs of degrading and its degrading very fast. The only problem with the duracell precharged is the 15 min energizer charger now refuses to charge them. Instead i am greeted with a blinking led. First it started with one cell and eventually 2 and now it wont even charge all 4 precharged cells. These batteries are rated 2000mah. this is why i bought the la crosse charger and these batteries still going strong despite how severely they were abused. More abuse than the duracell 2650.

The only damage to these LSD 2000mah cells is the paper wrapping comes off easily lol. But other than that it still performing like a champ.


----------



## Marduke

Your particular duracell precharged are probably rebadged Eneloops. 

I suggest getting a good charger, and some good cells, and determine how bad your existing cells are.


----------



## wapkil

The "precharged" or low self discharge batteries are built differently than standard NiMHs. I don't know much about them but for example Eneloops use a different alloy in the negative electrode that is said to be more corrosion (oxidation) resistant.

Like all other NiMHs also low self discharge ones have a "charge reserve" on the negative electrode. This excess capacity is first used up and the user doesn't see any battery deterioration. Of course the sooner it is consumed, the sooner the battery capacity will start to get lower.

I'm afraid that probably your precharged cells were also partially damaged. They were more resistant and the results may not yet show up but they will live shorter than they would without being abused by this charger.

EDIT: I read once again what you wrote - if the 15 minutes charger doesn't want to charge these cells, it probably means that they developed a high resistance. It shows that they also suffered during charging but this effect may be reversible. You could search CPF for the procedure that may help them (generally a slow 0.1C x 16h charge and a slow 0.2C discharge) although I don't know if it can help in this particular case.


----------



## MarioJP

the only thing i noticed is the 15 minute refuse to charge the precharge. Sounds like higher resistance has develop. So far the performance has not degraded at all by much. I suppose I can do a discharge test with the lacrosse charger now and find out. But from the device that i use it in last quite a good while.

This device happens to be a Mobile charger for my cell phone. It uses 2AA which i happen to use the precharged in. Even after the abuse i am able to charge my blackberry phone from 0 up to 85%. The 2650 ones lucky if it hits 30%.

Now i did another test with the 4AA mobile charger. The precharged was able to charge my phone from 0% to 100% and the led stays lit even after my phone is fully charged.

the 2650 ones. Unfortunately the charger turns off unexpectedly, I push the on button i see the blue led light up and 5 seconds later it turns off. I push it again turns on and turns off after 5 seconds and eventually it will not turn on.

Question I have should i stick with LSD batteries and forget the 2500 and up ones. I noticed the higher the milliamp the harder it is to keep them in good shape. Or is it because the 15 minute charger just wrecks any cell that it charges??.


----------



## wapkil

MarioJP said:


> the only thing i noticed is the 15 minute refuse to charge the precharge. Sounds like higher resistance has develop. So far the performance has not degraded at all by much. I suppose I can do a discharge test with the lacrosse charger now and find out. But from the device that i use it in last quite a good while.



I believe that if they work correctly for you, you don't have to worry about them. The resistance and the capacity are not directly connected. With higher internal resistance, the cell may be not able to work in high current devices but still work quite well, with its normal capacity, if the discharge speed is low. It won't hurt to perform a procedure similar to the Maha C9000 break-in on them but it is not necessary (or guaranteed to work) either.

I think we drifted somehow from the thread topic. The discussion has shown that LSD cells seem to be able to tolerate higher currents, without as much damage as it causes in standard NiMHs but recovering them seems a bit off topic 

EDIT: About the question that you added (also off topic but answering it in this edit shouldn't matter  ):



MarioJP said:


> Question I have should i stick with LSD batteries and forget the 2500 and up ones. I noticed the higher the milliamp the harder it is to keep them in good shape. Or is it because the 15 minute charger just wrecks any cell that it charges??.



Everything you wrote is true - the 15 minute charger will kill any cell and the LSD cells can, by definition, hold their charge better. High capacity cells are useful if you want to charge them and use soon (maybe a few weeks) afterwards - for example a Sanyo 2700mAh could give you ~1/3 more energy than an Eneloop. LSD cells, on the other hand, are more convenient if you don't want to worry about them. I have both types and use both.


----------



## MarioJP

Now as far as the charging rate goes 15-16hr that is kind of ridiculously, considering how a lithium cell charges in 2-3hr.

I know for a fact that the 15 minute charger pumps around 7.5A for AA and 3A for AAA. That is way too high and exceeds the rated capacity of a cell.

Now with this La Crosse charger I can see whats going on and so far it is showing some good results  

Now I don't want to charge them too slow as I keep hearing that slow charging can cause crystals to form, not to mention the heat generated could not be good for the cell either.

What i decided to do is I added a cooling fan. The La crosse charger does get quite hot and that kind of concerns me. I know by adding a cooling fan this requires that you keep an eye on the voltage and don't let the cell voltage skyrocket, as that is the indication that the battery is charged.

Once the cell voltage goes beyond 1.44V that is when it is nearing to its end charge cycle. But the fan makes sure the batteries are cool to the touch .

I don't want to go through that high maintenance again. That almost drove me to just go back to primary batteries lol.


----------



## wapkil

MarioJP said:


> Now I don't want to charge them too slow as I keep hearing that slow charging can cause crystals to form



I believe it can. I read though that you can break them with slow, deep discharge. If it's true, it should be sufficient to put the cells once in a while in a slow discharging (~0.2C) device. On the other hand, I agree that fast charging may be simply more convenient, even if it will make the batteries live shorter.

EDIT: As I understand it, unless these crystals grow extremely large (and I think it would need extremely long time without a deep discharge) they are also rather harmless. NiOOH crystals are always formed during charging and disappear during discharge. I think that the only thing the systematic 0.1C charge can really cause is a voltage depression (i.e. worse behavior in high current applications) and it should be curable by a deep slow discharge.



MarioJP said:


> not to mention the heat generated could not be good for the cell either.



The standard 0.1C charge is more gentle to cells. I believe they will be able to live longer with it. Their temperature will be actually lower than during fast charging but the main reason (and the problem) is not the heat. With slow charging most of the oxygen generated when the cell is almost fully charged will recombine at the negative electrode without doing any harm. With fast charging the recombination will be too slow and the negative electrode will oxidize. This is exactly what you saw with your 15 minutes charger, although with e.g. 1C it will be much less severe. I wrote a bit more about it previously in this thread.



MarioJP said:


> What i decided to do is I added a cooling fan. The La crosse charger does get quite hot and that kind of concerns me. I know by adding a cooling fan this requires that you keep an eye on the voltage and don't let the cell voltage skyrocket, as that is the indication that the battery is charged.
> 
> Once the cell voltage goes beyond 1.44V that is when it is nearing to its end charge cycle. But the fan makes sure the batteries are cool to the touch .
> 
> I don't want to go through that high maintenance again. That almost drove me to just go back to primary batteries lol.



You are right that you have to be careful with active cooling. If the charger as a primary method uses -dV termination (and I think it does) cooling the cell may hide the termination signal. It won't really help the cell during charging and will make the charger overcharge the battery.

The voltage when a cell is fully charged depends on many factors. I think that you cannot set it in your charger anyway. For Eneloops it will generally be higher than for standard NiMHs and I think 1.44V is too low for almost any cell. Maha C9000 uses 1.47V maxV and it undercharges almost all the cells that I used, except the strange one for which I've shown the graphs in this thread.

EDIT: To be clear, I don't think adding a cooling fan is a good idea in this case, unless you want to sit there watching your cells every time you charge them.


----------



## MarioJP

I meant to say 1.44-1.47 is that is where you have to watch it lol. This charger does has other methods. One of them if the voltage goes to high it will stop the charge. One time it got to 1.49 and stop at 1.5V. So it does has other ways of turning the charge off.

Now I was going to get the Maha C9000, but only one problem. It checks for high impedance. The la crosse charger just charges lol. When a cell resistance gets to a certain value, even slow chargers will refuse to charge them. As far as the slow charger goes there are some, where the power transformer is built right in. 

While it is charging the cell at a slow rate the power transformer can generate enough heat that it can actually get the cells too hot. 

So if slow charging is used make sure the charger itself does not get too hot, or have those type of charger that uses a AC adapter instead.


----------



## wapkil

MarioJP said:


> I meant to say 1.44-1.47 is that is where you have to watch it lol. This charger does has other methods. One of them if the voltage goes to high it will stop the charge. One time it got to 1.49 and stop at 1.5V. So it does has other ways of turning the charge off.



I believe that these other methods are set to the levels making them only safety backup. As I wrote, it depends on many things but I believe 1.5V will be generally good for Eneloops but can be too high for many standard NiMHs. 

If by using a cooling fan you make the charger miss -dV, it doesn't matter that the cooled cell won't heat up. If the battery will be overcharged, it will be partially damaged, even when cooled. This is why I wrote that I don't think a fan is a good idea.


----------



## MarioJP

that I know. This is so it wont overheat and trip the thermal sensors which i had that happen twice already. Cells with a high internal resistance generates more heat than a low resistance cell. Without the fan the charger and batteries gets really hot (only the high impedance cells). I know its not a good idea but, when voltages hit to 1.4 that is a sign that it is almost done. and when the voltage starts to climb up really fast that is when i pull the plug lol. Man Nimh is a beast isn't it? lol.


----------



## wapkil

MarioJP said:


> that I know. This is so it wont overheat and trip the thermal sensors which i had that happen twice already. Cells with a high internal resistance generates more heat than a low resistance cell. Without the fan the charger and batteries gets really hot (only the high impedance cells). I know its not a good idea but, when voltages hit to 1.4 that is a sign that it is almost done. and when the voltage starts to climb up really fast that is when i pull the plug lol.



Oh, I understand now. You may then try to simulate the Maha's break-in on your charger. If it cures the high resistance, it should remove the necessity to treat these batteries in a special way.

EDIT: I looked at the BC-900 manual and it seems that the best way to slowly discharge the cell would be to use a discharge mode, with 0.2C current but stop it before it starts charging the cell. You shouldn't charge the cell with 0.4C current and it seems that the charger doesn't know how to perform the 0.1C x16h charge. You may then charge the cell with 0.1C current and manually terminate it, or repeat it until 16 hours pass. You should probably repeat the whole procedure a few times. I'm not sure though if the 0.1C part can help with high resistance, maybe it sufficient to perform only the slow discharge and normal charge after it?



MarioJP said:


> Man Nimh is a beast isn't it? lol.



Yes, it is but I think most of your problems are the result of using the cells that were already damaged by the 15 minutes charger. You shouldn't experience them with good cells.


----------



## vali

I have a question too about the "recommended" charging rate relative to missing terminations.

Right now I almost allways use 0.6C to charge my cells. There are some eneloops, several "normal" NiMH and a few NiCads. After getting the C9000 I realized how crap the NiMH I had are (My dad used to buy the cheapest ) and will be tossed very soon, as those cells seem to degrade every charge, even for new ones (read it as not used, not recently purchased).

Some members reported missing terminations up to 0.5C but If I remember correctly, none of them were in LSD cells (Tried a search, but "eneloop" and "missing termination" are too generic ). Can it be eneloops need less current to get a proper -dV or they need the same as non-LSD ones?

I am asking this because the recommended charge seems to be to prevent overcharging those old, crappy and beated cells that almost all of us have around the house (well, except Silverfox, of course ) and eneloops are better built and robust and shouldnt have those kind of problems, at least if you take care of them.


----------



## MarioJP

the only batteries that i don't have to use a fan are the precharged ones. Those don't get too hot. But the high resistance ones gets way too hot in a short amount of time, Which will result charging being interrupted. Those cells are still good enough for low end use. But one thing for sure it craves a higher current to push the voltage as slow charging, the voltage just stays at a certain value for a very long time. Its like its eating the charge rather than storing it lol.

That is the side effect of high resistance nimh battery lol. Even at high current charging at 1.8C the voltage stays at 1.46 for awhile and barely could get it to 1.47. A normal battery will cause the voltage to just jump through the roof. And whats worst its getting harder and harder to get it at 1.46v. and the new low limit is now 1.45 If it gets too tough to even push it at 1.44 these batteries are getting tossed and recycled.

How high the impedance of the nimh develops i am sure it has to be a limit. Otherwise the resistance will be so high to the point that its just not going to charge at all and just eat the charge instead lol.


----------



## wapkil

vali said:


> I have a question too about the "recommended" charging rate relative to missing terminations.
> 
> Right now I almost allways use 0.6C to charge my cells. There are some eneloops, several "normal" NiMH and a few NiCads. After getting the C9000 I realized how crap the NiMH I had are (My dad used to buy the cheapest ) and will be tossed very soon, as those cells seem to degrade every charge, even for new ones (read it as not used, not recently purchased).



I would try to use the standard 0.1C charge on them (e.g. taken from the C9000's break-in procedure), using their real capacity. It may be possible that it won't degrade them so much.



vali said:


> Some members reported missing terminations up to 0.5C but If I remember correctly, none of them were in LSD cells (Tried a search, but "eneloop" and "missing termination" are too generic ). Can it be eneloops need less current to get a proper -dV or they need the same as non-LSD ones?



I don't know, it is possible but with fast charging I wouldn't rely on this assumption. I think that if someone wants to charge fast, he or she should use the recommended 0.5C-1C range (and probably it is a good idea to use something like your 0.6C, unless it results in missed termination). If the cell longevity is a priority, the standard 0.1C should be used.

This is a general recommendation though and everything depend on the charger and batteries. The C9000 uses 1.47V maxV and Eneloops terminate at a high voltage (~1.6V @1C). I think it is quite possible that an Eneloop will reach 1.47V before it fully charges, even with currents much lower than 0.5C. If it is true, it would mean that the C9000 will terminate this Eneloop charge at maxV before it is charged, no matter what the current was.


----------



## TorchBoy

Thanks for those graphs wapkil. Where did the data come from for them? (Did I miss that?)



wapkil said:


> Even for me it is disturbing that a battery manufacturer can sell such a charger. On the other hand, I'm sure that if the marketing department decides so, they will put this charge method as "recommended" in the data sheets


Energizer? Aren't they that *primary* battery maker? 



MarioJP said:


> Question I have should i stick with LSD batteries and forget the 2500 and up ones. I noticed the higher the milliamp the harder it is to keep them in good shape. Or is it because the 15 minute charger just wrecks any cell that it charges??.


What wapkil said, except I only buy Eneloop now. I regard non LSD cells as a waste of money for my uses. I don't absolutely need that extra 25% energy and I really can't be bothered with the fussy charge-then-use-immediately requirements.



MarioJP said:


> I don't want to go through that high maintenance again. That almost drove me to just go back to *primary* batteries lol.


Funny that.


----------



## wapkil

TorchBoy said:


> Thanks for those graphs wapkil. Where did the data come from for them? (Did I miss that?)



Uhm, which graphs you are asking about? I've put quite a few of them in this thread already, some from my measurements, some from different documents...


----------



## TorchBoy

Ah, I just found the last one (the slow charging cycle life) in a PDF on the LSD mechanism. What about the fast charging cycle life graph?


----------



## wapkil

TorchBoy said:


> Ah, I just found the last one (the slow charging cycle life) in a PDF on the LSD mechanism. What about the fast charging cycle life graph?



The one from #72? I wrote that Marduke linked to it earlier but it seems that I was wrong: http://www.duracell.com/OEM/Pdf/others/TECHBULL.pdf


----------



## MarioJP

As far as conditioning the cells. I use the combination of the charger's discharge feature and manually or the device that is in. ESPECIALLY IF THE CELL HAS A VERY HIGH IMPEDANCE. this not only affects how it performs but also the charging and charging rate as well.

When the battery gets too low where the current is at safer limits. I just use my dandy multimeter and measure not just the voltage but the peak current until the charge is around 100miliamp peak load (Voltage is probably around 0.50V). This is as flat you can get these batteries in. As long as the battery is able to build the charge up your good.

If the cell does not build the charge up after you remove the leads. Then that battery is tossed, unless it has been severely discharged for days and maybe you be able to bring it back to life if not then you toss it.

It actually did improve the battery's performance but just by tiny fraction lol.

Discharge rate for these chargers are around 500miliamp. But manually? around 2.5C and up lol. usually no more than 2c. Just make sure it does not get too hot.

High current discharge does break down the resistance as it is breaking down the crystals formation. This is the treatment for batteries with high resistance. If the resistance is too high. Discharge rate goes above 5C topping at a whoppin 8C to almost 10C!!! hitting the multimeter max amp capcity that it starts to beep and display flashing lol. This will for sure break this ridiculous internal high resistance. Currently there is no charger that discharge that fast. Sometimes you have to bend the rules a little to keep these batteries going LOL.


Now the 15 minute charger should not be used to charge batteries period. Especially when they are new. Charging current is just too much. I also heard that when the batteries are new it can give a false voltage drop which will terminate the charge too soon. It either the charger misses the -dv termination, overcharging it a little, or it cuts off too soon slightly undercharged. Is this true?

So based of what I have experienced. When the cells are new it is ok to charge them slow. But when you have these crystals forming around the separator it is time to condition the battery and amp up the current before this becomes permanent. Also does different brand of nimh makes a difference?. Like where it is made from as well? Most importantly Capacity of the cell?


----------



## TorchBoy

wapkil said:


> The one from #72? I wrote that Marduke linked to it earlier but it seems that I was wrong: http://www.duracell.com/OEM/Pdf/others/TECHBULL.pdf


Thanks for that, although I was thinking of the one in post 136.

Edit: And where is Tom's 15 minute charger cycle testing? Edit2: I think https://www.candlepowerforums.com/threads/114943 might have been it.


----------



## wapkil

TorchBoy said:


> Thanks for that, although I was thinking of the one in post 136.



http://www.eneloop.info/home/performance-details/cycle-life.html


----------



## wapkil

MarioJP said:


> When the battery gets too low where the current is at safer limits. I just use my dandy multimeter and measure not just the voltage but the peak current until the charge is around 100miliamp peak load (Voltage is probably around 0.50V). This is as flat you can get these batteries in. As long as the battery is able to build the charge up your good.
> 
> [...]
> 
> High current discharge does break down the resistance as it is breaking down the crystals formation. This is the treatment for batteries with high resistance. If the resistance is too high. Discharge rate goes above 5C topping at a whoppin 8C to almost 10C!!! hitting the multimeter max amp capcity that it starts to beep and display flashing lol. This will for sure break this ridiculous internal high resistance. Currently there is no charger that discharge that fast. Sometimes you have to bend the rules a little to keep these batteries going LOL.



Yeah, you really exercise your cells, although I'm not sure if they will be grateful for it. IIRC there was a similar procedure for NiCads. When they were starting to get lazy, people were shorting them out and leaving them this way for a long time. No one was officially recommending it and although NiCads are really hard to kill I'm not sure if I would risk it.

I believe that you may break the crystals this way but at the same time you are essentially overdicharging the cell. I think a slow, deep discharge should let you achieve the same benefit, without as much damage. EDIT: Although you may need a real constant current device to achieve it. I think that if it uses high current pulses (like the C9000 does) it may be much harder or even impossible to perform it correctly.


----------



## MarioJP

wapkil said:


> I believe that you may break the crystals this way but at the same time you are essentially overdicharging the cell. I think a slow, deep discharge should let you achieve the same benefit, without as much damage.



Actually not necessarily true. As the battery voltage begins to drop so does the current rate as well. A fully charged cell will push around 8C to 11C if no resistance is added to the circuit (don't want to do this on a new cell or a cell that are in good condition). When discharging it starts to gradually drop as i can see the readout on the multimeter. Eventually the voltage will be soo low that the peak current will be weak to overdischarge the cell.

Only way of doing this if you don't disconnect the leads and is left for hours or a day or so. Point is don't let the peak load current drop below 50milliamp (0.30V or less). Each cell behaves differently. Some are a pain to overdischarge and could take hours, while others just drops instantly. The ones that drops instantly are the ones that are going to have problems in the future. 

But most of the cells around 100milliamp and steadies there for a good while which can take couple of hours before peak load drops to 0. This will ensure a truly cycled battery. No charger discharges the battery that low. As long as the battery builds the charge back up the moment you disconnect the leads the battery is good. if it does not. you are looking at problems with that cell down the road.


----------



## 45/70

wapkil, MarioJP, I think you guys are confusing dendrites with crystals.

Dendrites are associated _only _with NiCd cells (among nickel based chemistry cells). (*EDIT*) Yes they can be treated with a high Amp charge, but in most cases, the damage is already done to the separator.

Large crystal formation is common to both NiCd and NiMH chemistries. It is dealt with by discharging at a very slow rate. We're talking about two totally different problems here.

Gotta go,

Dave

Edited the post for major errors. Reminder to self, don't skim and post in a hurry!


----------



## MarioJP

So to answer to this thread "appropriate charge rate for nimh batteries"

That all depends on the battery itself. If the battery is new it is ok to charge it at the industry standard charging rate. But when the cell ages and depending on usage will determine the charging rate ultimately.

Graphs are good way to start but does not end at a specific standard charging rate. The question is what is the ultimate charging rate??. Where is the sweet spot to balance good longetivity and waiting for the battery to charge?. 

For the most part Nimh batteries are flexible when it comes to charging rates. You can charge them slow or fast. Just not ultra fast or a charging current that exceeds the rated capacity of the cell.

Since I got this new charger I decided to set the charging rate closets to its rated capacity.

so if a cell is 2000mah i charge it at 1C. I am experimenting charging rate at 1.8C. If a cell was marketed for "high drain devices". 

What discharge rate is considered high drain??.

My mobile charger draws about 1C to charge my phone, my cordless soldering iron that takes 4AA draws about 1.8C to 2C. So wouldn't be almost the same to charge it at that 1C or 1.8C rate??. Of course the charger has to know when to terminate the charge. The only difference here is that it is easy to overcharge than overdischarge that is the only differences but the rest is practically the same.

So if these batteries are designed to be used in high drain application or is marketed that way. it should be able to handle 1C charging. Otherwise fast discharging that only last 2-3 hours vs slow 15-20 charging. Hmmm something is not right here. Correct me if i am wrong here, but isn't fast discharging is harmful to the batteries just as fast charging?? (exception of the 15min chargers) Lets keep the charging/discharging cycle balanced lol.


----------



## SilverFox

Hello MarioJP,

There are two basics that govern the ideal charging rate.

The first is the termination method used, and the second is the application the battery is going to be used in.

There are a wide variety of termination methods, but the most used are temperature, -dV, and time.

The battery manufacturers have run tests on this and suggest some charging rates. 

If you are trying to terminate on a change in the temperature profile, which is the best way to terminate according to the battery manufactures, you need to generate a strong signal for termination. The best charge rate over the life of the cell for this termination method is 1C. 

If you are trying to terminate using -dV, the best charge rate over the life of the cell is 1C, but they feel that an adequate signal can be generate over the charging range of 0.5 - 1.0C. 

If you want to charge at 0.1C, the best termination method is time. Overcharging at 0.1C is well tolerated by the cell, but there isn't a reliable -dV or temperature signal over the life of the cell. 

When you want to charge in the 0.1 - 0.5C range you run the risk of missed terminations. Also, these rates are high enough to do damage to the cell. Chargers that charge in this range usually are terminating on a back up method. The most common back up method of termination is maximum voltage. The problem with this is that the voltage of the cell changes over its life. When the cell is new, you may be overcharging it, and when it is aged, you will be undercharging it. Another common back up method with these chargers is time. Sometimes these chargers claim to use -dV for termination, but from the research and testing done we know that it is very likely that the -dV termination will be missed leaving the termination to the back up method.

The 15 minute chargers push things beyond the limits, yet all in all they do a pretty good job. Don't expect more than 125 - 150 cycles from a cell and you will be delighted with the speed of charging. Internal impedance causes heat when charging, so these chargers are very picky about the cells they will charge. One of the best uses of these chargers is to only charge for 10 minutes, but you can run into a balancing problem in a multi cell application.

The next piece of the puzzle involves how the cell is going to be used. 

If you application run time is 4 hours or longer, you can do very well with the 0.1C charge terminated with time. If you application run time is 1 hour or less, you are better off using a 1C charge rate. If the run time is between 1 and 4 hours, you are in a grey area and will need to do some testing to see what charge rate works the best.

To obtain a reasonable cycle life from NiMh cells, the charge rate should be limited to 1C. The RC people often push to 2C charging rates, but after some battery pack explosions the hobby charger manufacturers are suggesting dropping back to 1C charging as a maximum charge rate. 

Some of the hobby chargers allow for advanced charging algorithms and variable charge rates. The Schulze charger, for example, has a mode where it adjusts the charge rate based on the internal impedance of the cell. You can dial in a maximum charge rate, but the charger will determine if the cell is capable of receiving a charge at that rate.

As NiMh chemistry ages, it becomes less predictable. All chargers will miss charge termination signals, so the back up termination is very important. I think there are enough graphs floating around to demonstrate some of the odd behavior involved with charging these cells. The hobby chargers use maximum charge capacity as a back up, and that seems to be very effective in eliminating gross overcharging. The issue with the hobby chargers is that they cost more and they require user input to function properly.

Once you determine the appropriate charge rate, based upon the termination method used and the application, then things start to get a little more involved. If your application uses a battery pack, you need to make a provision to balance the cells in the pack. The best way to do this is to charge at 0.1C for an extended period of time. The temptation in this case would be to do all the charging at 0.1C, but if time is an issue the 16 hour charge time will not be well received. If the application is an RC vehicle in a race, the people who charge at 1C will out perform the people that charge at 0.1C.

I happen to think one of the best charging methods is utilizing the internal resistance of the cell to determine the charge rate. During the charge the impedance will change, so this ends up being a multi charge rate method of charging. I believe the termination used with this method of charging is -dV with the value set to 0 mV.

Tom


----------



## wapkil

45/70 said:


> wapkil, MarioJP, I think you guys are confusing dendrites with crystals.
> 
> Dendrites are associated _only _with NiCd cells. Yes they can be treated with a high or shorting discharge, but in most cases, the damage is already done to the separator.
> 
> Large crystal formation is common to both NiCd and NiMH chemistries. It is dealt with by discharging at a very slow rate. We're talking about two totaly different problems here.



I haven't yet read or tested enough about crystalsline formations but I wasn't writing about dendrites, which, btw, can appear in many battery types, not only NiCads, but I think don't appear in NiMHs.

The voltage depression, caused as I understand by forming large crystals can be cured by a deep discharge that would break these crystals. I think that what MarioJP is doing starts with a much too fast discharge rate, which I believe not only doesn't help but can damage the cell. Then it slows down, deep discharges the cell and breaks the crystals. Finally, even with constant resistance, it overdischarges the battery, once again damaging the cell. This is the reason why I wrote that even though it it may cure the voltage depression I believe the medicine is worse than the illness.


----------



## wapkil

Thank you for the summary, I have a few questions though 



SilverFox said:


> The next piece of the puzzle involves how the cell is going to be used.
> 
> If you application run time is 4 hours or longer, you can do very well with the 0.1C charge terminated with time. If you application run time is 1 hour or less, you are better off using a 1C charge rate.



Is this recommendation based on the fact that slow charging encourages larger crystal formations and voltage depresion? If it is, wouldn't it be sufficient to discharge cell fully (e.g. below ~1.1V @1C) or once in a while perform a slow, deep discharge to have a 0.1C charged cell perform well even in high current applications?



SilverFox said:


> I happen to think one of the best charging methods is utilizing the internal resistance of the cell to determine the charge rate. During the charge the impedance will change, so this ends up being a multi charge rate method of charging. I believe the termination used with this method of charging is -dV with the value set to 0 mV.



Do you know where I could read more about this method? Does it use the resistance or the impedance (or both, or maybe which one is not important for this algorithm)? Is "0mV -dV" the same as the standard voltage plateau (0dV)?


----------



## 45/70

wapkil said:


> I haven't yet read or tested enough about crystalsline formations but I wasn't writing about dendrites, which, btw, can appear in many battery types, not only NiCads, but I think don't appear in NiMHs.
> 
> The voltage depression, caused as I understand by forming large crystals can be cured by a deep discharge that would break these crystals. I think that what MarioJP is doing starts with a much too fast discharge rate, which I believe not only doesn't help but can damage the cell. Then it slows down, deep discharges the cell and breaks the crystals. Finally, even with constant resistance, it overdischarges the battery, once again damaging the cell. This is the reason why I wrote that even though it it may cure the voltage depression I believe the medicine is worse than the illness.



Gotcha, wapkil. I edited my previous post for a major error. Don't post when you're in a hurry! 

I'm not familiar with MarioJP's method. I confused it with the high amp "Zap" method of disconnecting dendrites, somehow. I agree his method sounds like the cure may be worse than the disease. That applies to zapping of dendrites in NiCd cells as well, although I used to do it.

I do think that most break up of large crystals occurs when the cell is nearly depleted though. With a fully charged cell, the energy is going to be drawn from the finer crystals first, regardless of the discharge rate, so the larger ones will be affected last. With that in mind, it makes sense to discharge the cell most of the way first, before implementing the slow discharge.

What I have done, after the cell is initially slow discharged, I give it a 5 minute charge at about 1C, and then do another slow discharge, repeating the process a few times. This saves time, and seems to work just as well.

I don't really do this much anymore, as most cell "rescue" operations seem to be in vain. I take pretty good care of my rechargeable cells, and when most are in need of rescue, they are years old and suffering from general degradation anyway. It was interesting to play with them though, and I felt I learned something.

Dave


----------



## wapkil

45/70 said:


> Gotcha, wapkil. I edited my previous post for a major error. Don't post when you're in a hurry!



I think you are looking at the wrong electrode:



45/70 said:


> Dendrites are associated _only _with NiCd cells (among nickel based chemistry cells).



What about NiZn? 



45/70 said:


> I do think that most break up of large crystals occurs when the cell is nearly depleted though. With a fully charged cell, the energy is going to be drawn from the finer crystals first, regardless of the discharge rate, so the larger ones will be affected last. With that in mind, it makes sense to discharge the cell most of the way first, before implementing the slow discharge.
> 
> What I have done, after the cell is initially slow discharged, I give it a 5 minute charge at about 1C, and then do another slow discharge, repeating the process a few times. This saves time, and seems to work just as well.



I also think this is how it works but still one shouldn't discharge with 10C or overdischarge to 0.5V or 0.3V (at minuscule current!) - this is what I, and I think you, didn't like in MarioJP's method


----------



## 45/70

wapkil said:


> What about NiZn?



Um, uh, OK, I have no idea! 



wapkil said:


> I also think this is how it works but still one shouldn't discharge with 10C or overdischarge to 0.5V or 0.3V (at minuscule current!) - this is what I, and I think you, didn't like in MarioJP's method



Yeah, as I said, I'm with you there. Now if we were talking NiCd, sure (not too sure about the 10C though) and when watched closely I know you can discharge an NiMH cell down to 0.6 Volt, but I don't remember the specific conditions.

Dave


----------



## wapkil

45/70 said:


> wapkil said:
> 
> 
> 
> What about NiZn?
> 
> 
> 
> Um, uh, OK, I have no idea!
Click to expand...


As far as I know, NiZn also develop dendrite formations. It is a serious problem for them and important changes were introduced in the chemistry to reduce it. Just an example to show that NiCads are not, as you thought, the only nickel based chemistry with dendrites


----------



## SilverFox

Hello Wapkil,

When I think of actual crystal formation, I think of NiCd chemistry. I am not sure that actual crystals are formed in NiMh chemistry, but the discharge behavior is so similar I wouldn't be surprised to find some crystals there.

If you research crystal formation you will find micro photographs of NiCd chemistry, but I have not been able to locate any examples in NiMh chemistry. Crystals are easier to visualize, but in NiMh chemistry I think it has more to do with the paths through the separator. It's like some of the paths are blocked and slow discharge rates open up those paths. There may be a crystal involved, but I have not been able to document that.

In slow charged/fast discharged applications the voltage is depressed and the cell temperature increased. The voltage depression is not great, but you can gain enough of an increase to give you an edge using fast charging. Fast charging tends to generate higher temperatures, but you make up for this during the fast discharge where the cell temperatures are actually lower than cells that have been slow charged. I am not sure of the theory on this performance, but actual testing demonstrates it.

The impedance charge method is propriatory to Schulze chargers. I don't know what the actual algorithm parameters are, but am "guessing" at what is going on after watching several hundred charge cycles. I believe voltage plateau is the same as using a -dV = 0 mV, but it is different than peak voltage, if that clears things up.

Tom


----------



## SilverFox

Hello Wapkil,

When I think of actual crystal formation, I think of NiCd chemistry. I am not sure that actual crystals are formed in NiMh chemistry, but the discharge behavior is so similar I wouldn't be surprised to find some crystals there.

If you research crystal formation you will find micro photographs of NiCd chemistry, but I have not been able to locate any examples in NiMh chemistry. Crystals are easier to visualize, but in NiMh chemistry I think it has more to do with the paths through the separator. It's like some of the paths are blocked and slow discharge rates open up those paths. There may be a crystal involved, but I have not been able to document that.

In slow charged/fast discharged applications the voltage is depressed and the cell temperature increased. The voltage depression is not great, but you can gain enough of an increase to give you an edge using fast charging. Fast charging tends to generate higher temperatures, but you make up for this during the fast discharge where the cell temperatures are actually lower than cells that have been slow charged. I am not sure of the theory on this performance, but actual testing demonstrates it.

The impedance charge method is propriatory to Schulze chargers. I don't know what the actual algorithm parameters are, but am "guessing" at what is going on after watching several hundred charge cycles. I believe voltage plateau is the same as using a -dV = 0 mV, but it is different than peak voltage, if that clears things up.

Tom


----------



## MarioJP

The reason why I do a high current discharge which I forgot to mention when a nimh cell has high internal resistance, which is another side effect that was not mentioned.

Due to the cell having a very high resistance. The cell acts like there is a resistor attach to the circuit.

What this means is when I do a short directly to the meter measuring peak amperage you guys are thinking instant 5C and higher right. 

Unfortunately reality is that it starts off way too low starting at 1C and gradually increases. In fact the resistance is so high that it takes couple of minutes to hit to 2C. If this was a real world scenario of having this battery in a high drain application. It will perform very poorly and might give a low battery warning due to voltage severely depressed from high internal resistance.

It can take 5 minutes before you can really see good performance during a constant high discharge. Slow discharge does not work for this type of condition, but then again its not a high drain device either.

A normal good cell I would not do this as this will harm the cell. If the current instantly jumps to 8C right away disconnect right away. This indicates a very heathy cell and no need for conditioning.

But a weakened cell I get readings only 1.8C even when fully charged but slowly increases. That is not good all of my 12X 2650 cells does that. No wonder my charger is having a hard time charging 

This means you no longer taking advantage of "high drain devices" anymore


----------



## 45/70

SilverFox said:


> When I think of actual crystal formation, I think of NiCd chemistry. I am not sure that actual crystals are formed in NiMh chemistry, but the discharge behavior is so similar I wouldn't be surprised to find some crystals there.



What? No crystal formation in NiMH's? 

OK, I'll go to my room now, but first.....



SilverFox said:


> If you research crystal formation you will find micro photographs of NiCd chemistry, but I have not been able to locate any examples in NiMh chemistry. Crystals are easier to visualize, but in NiMh chemistry I think it has more to do with the paths through the separator. It's like some of the paths are blocked and slow discharge rates open up those paths. There may be a crystal involved, but I have not been able to document that.



From B.U.



> In addition to the crystal-forming activity on the positive plate, the NiCd also develops crystals on the negative cadmium plate. Because both plates are affected by crystalline formation, the NiCd requires more frequent discharge cycles than the NiMH.


This seems to suggest that NiMH's do develop crystalline formation, but only on the positive plate.

This, also from B.U.



> The effects of crystalline formation are most pronounced if a _*nickel-based battery*_ is left in the charger for days, or if repeatedly recharged without a periodic full discharge.


Would seem to indicate the same.

I've seen this mentioned elsewhere as well, however I have no idea where, as it's been a year or two.

Dave


----------



## wapkil

I think a part of the problem with "crystals" is that sometimes all of them are treated here, at CPF, as something bad that should be eliminated. 

As far as I know (and the chemistry here is too complicated for me to understand it) this is wrong. Different nickel hydroxide crystalline formation are a normal part of a nickel-based battery cathode. Without them the battery wouldn't work. Both NiOOH (when charged) and Ni(OH)2 (when discharged) form crystal structures. To make things even more complicated, these structures have different variants that they transform into.

The questions may be how the way we charge the battery influences these crystals formation and how they, in turn, influence the battery performance during discharge. I think that this is a complicated research problem with ongoing discussion, although probably a chemist familiar with batteries chemistries could tell us much about what is already known.


----------



## wapkil

MarioJP said:


> The reason why I do a high current discharge which I forgot to mention when a nimh cell has high internal resistance, which is another side effect that was not mentioned.
> 
> Due to the cell having a very high resistance. The cell acts like there is a resistor attach to the circuit.
> 
> What this means is when I do a short directly to the meter measuring peak amperage you guys are thinking instant 5C and higher right.
> 
> Unfortunately reality is that it starts off way too low starting at 1C and gradually increases.



Well, now I don't really know what to say about your method or batteries, except that they seem to be in a really bad shape. If they put out 1C when shorted, it looks like their internal resistance is something like 10, maybe 20 times higher than normal. I think no matter what you do to them, they won't get much worse  

Such batteries can be really interesting to test. They behave in a completely different way than, in theory, new healthy ones should. I think not much documents are available describing this. You only have to be careful to not let them evolve in some alien chemistry form


----------



## VidPro

MarioJP said:


> What this means is when I do a short directly to the meter measuring peak amperage you guys are thinking instant 5C and higher right.


 
well no really i was thinking about how the stuff is connected internally and how cool it looks when it MELTS.


----------



## MarioJP

wapkil said:


> If they put out 1C when shorted, it looks like their internal resistance is something like 10, maybe 20 times higher than normal. I think no matter what you do to them, they won't get much worse



The worst just got even worst. I did another round with these 8 batteries. I can't believe what i saw in the readings. These 8 batteries were put in electronic piano so my sister can use the piano. Only to find out that the LCD would flicker sharply with the music. and the music from the speakers distort and sometimes the LCD would just blink off and come back on, and the Cells were fully charged too. I took them out of the piano, I did not even bother to measure the voltage. I was after the peak amperage instead. I measured again the Peak amperage load and wow.

all of the cells pushes 900milliamps now. One cell in particular pushed around 500milliamp. It took 10 minutes for that cell to gradually increase up to 2.5C. Wow talk about high internal resistance. This is how it went

at the beginning of direct short test out of one of the 8 cells.

start= 0.5C and climbing

5min= 0.9 and climbing

15min= 1.3C

30min= 2.2C

35min= 2.8-3C

at 40-45 minutes it peaked at 4.2C and then it started to decline sharply down to 100milliamp.

After these results, these cells have developed *critical* high internal resistance in a short amount of time since the last test that they are no longer useful and are going to get tossed. These are the duracells 2650. I did not bother to test all 8 since I already know where it was heading,and all 8 of them too!!. These batteries are not cheap 

I think this is the results of the 15 minute charger cooking the nimh chemistry to a high resistance state

I only have 4 of these 2650 left, which were also used in the 15 minute charger but not long enough since the new charger arrived. I did a direct 2 sec short test and it peaks around 8C. But the only problem is it self discharge way too fast. They are flat in 2 days .

I hope this will answer alot of questions about charging rates and logetivity of nimh cells.

Also makes me to believe that these duracells 2650 are poor quality considering that they can't even make their own precharged version instead of precharged duracell which is actually ray O vac hybrids or Sanyo Eneloops.


----------



## digitor

Hello Mario,

Please, do yourself a favour, and throw these cells (and your 15 min charger) in the bin, and buy some Eneloops! :twothumbs 

And maybe a C9000....

Cheers


----------



## MarioJP

Yes I did Not only did I tossed those batteries. I retired my 15 minute charger. I now have the Lacrosse BC-9009 with firmware version 35:thumbsup:.

Got it off at amazon. I like this charger, not only can you finally see whats going on with each and individual cell. You can actually see each cell voltages along with charging rate, which you can select. It also came with 4 C and D adapters with 4x Lacrosse AA 2600mah batteries, and 4x Lacrosse AAA 1000mah batteries.

The only issue with this charger it gets quite warm almost hot but as long as its not the 15 minute charger its all good.:twothumbs


----------



## clintb

digitor said:


> Hello Mario,
> 
> Please, do yourself a favour, and throw these cells (and your 15 min charger) in the bin, and buy some Eneloops! :twothumbs
> 
> And maybe a C9000....
> 
> Cheers


There is absolutely nothing wrong with the 15 min charger, as long as the operator is willing to accept reduced cycle life, or it is used in moderation. Having something with the safeguards, and rapid charging is quite convenient, should it be needed.


----------



## MarioJP

clintb said:


> There is absolutely nothing wrong with the 15 min charger, as long as the operator is willing to accept reduced cycle life, or it is used in moderation. Having something with the safeguards, and rapid charging is quite convenient, should it be needed.



The problem with the 15 minute charger though is that it starts to rejects cells, even at their beginning of their life cycles. This charger is very good for checking resistance which I can probably use it for as a impedance checking. As far as reliability goes. I really can't say about its reliability because of this.

There was a time when i was in a rush and i forgot to charge the batteries, I dish out the handy 15 minute charger thinking "no problem this will do the job in 15 minutes". Nope instead I was greeted with the "red flash of death" lol. 

I looked at the charger's manual and I did exactly what it told me to do. I even cleaned the contacts on the charger, and the battery itself. Nope still the red flash of death.

Another issue is, despite it having a cooling fan on the bottom that blows air to the batteries, they still get really hot to touch especially when the cells are new.

I do notice one pattern from the 15 min charger. When the cells are new it gets really hot. But after couple of charges in this charger, the cells do not get as hot as when they were first new.

You definitely are right about reduced life cycles. In fact so much that you be replacing them within a month give it 2 month tops lol.


----------



## SilverFox

Hello MarioJP,

That is not a "problem," but a "feature..."

The 15 minute chargers have a variety of safeguards built into them including checking for internal resistance. If it didn't check for this, the cells would burn up on the charger due to the high charge rates involved.

If the cells you are trying to charge have developed high IR, the charger will reject them. If they are marginal, they will tend to heat up during the charge, and subsequently develop high IR and will be rejected by the charger.

The best way to use these chargers is to limit their use to cells that have low IR. 

With good quality cells, you should be able to get somewhere in the 100 - 150 cycles from them using the 15 minute chargers exclusively for charging. I agree that this is not a great cycle life, but considering the fast rate of charging, I think this is actually pretty good given the circumstances.

On the other hand, with marginal cells you can totally kill them rapidly in just a few cycles.

You may find this thread informative.

Tom


----------



## 45/70

wapkil said:


> I think a part of the problem with "crystals" is that sometimes all of them are treated here, at CPF, as something bad that should be eliminated.
> 
> As far as I know (and the chemistry here is too complicated for me to understand it) this is wrong......



That is very true wapkil.

The anode and cathode are of a crystalline nature. The problem is when the crystals absorb electrolyte and become enlarged.

Dave


----------



## TorchBoy

digitor said:


> Please, do yourself a favour, and throw these cells (and your 15 min charger) in the bin, ...





MarioJP said:


> Yes I did Not only did I tossed those batteries.


In the recycling bin, I hope!


----------



## MarioJP

in the recycling bin it goes yes.

Update

I ordered Ansmann 2850 4pk cells off at Amazon. This time I am going to treat these cells with respect and won't even dare be charged in the 15 min charger ever again lol.


----------



## toddbailey

I have some old 1700 and 2500 ma nimh AA batteries. 
The makeshift charge I have is a Tektronix power supply with adjustable voltage and current.

I've made a 18 v battery pack and was wondering if charging at 20 v @100 ma is really going to take over a day.


----------



## Mr Happy

toddbailey said:


> I have some old 1700 and 2500 ma nimh AA batteries.
> 
> I've made a 18 v battery pack and was wondering if charging at 20 v @100 ma is really going to take over a day.



You can safely charge at about 0.1C, which would be about 200 mA for those batteries. The equation is then 1700 mAh / 200 mA + X%, where X% is about 20% or so. That would give, for example, 1700 / 200 = 8.5 h, +20% = 10 h. Normally you are looking at about a 12 h duration for a 0.1C slow timed charge.


----------



## toddbailey

Is there a desired voltage I should target?

The psu can go from 0 to 22, and as part of the configuration, I have both voltage and current being monitored via separate devices.

additionally is it ok to "trickle" charge nimh continously say at 10 to 20 ma at a few tenths of a volt above rated voltage?


loosly translated: Deeper, deeper, somewhere in the depth there is a light


----------



## Mr Happy

toddbailey said:


> Is there a desired voltage I should target?
> 
> The psu can go from 0 to 22, and as part of the configuration, I have both voltage and current being monitored via separate devices.
> 
> additionally is it ok to "trickle" charge nimh continously say at 10 to 20 ma at a few tenths of a volt above rated voltage?



NiMH batteries are usually charged with a constant current. You set the current to some appropriate value and then you monitor the cell voltage, the cell temperature, and the elapsed time to decide when charging should stop.

If you are using an adjustable power supply, there is usually one knob for the maximum voltage and another knob for the maximum current. To arrange for constant current charging you set the maximum current to your desired value like 200 mA and set the maximum voltage about as high as it will go. (The maximum voltage doesn't matter as it will never come into effect.)

What you now do is start the charging and watch the battery voltage (it will normally be displayed on the power supply front panel). The battery voltage will slowly increase as the charging proceeds. You should stop the charging when the battery voltage stops going up, or when the temperature of any cell starts to get uncomfortably warm, or after 12-16 hours. (You will expect the battery to be fully charged when the voltage per cell is somewhere in the region of 1.45 V to 1.60 V.)

If you are doing a slow conditioning charge at a charging current of 0.1C then you typically force the charge to proceed for 16 hours regardless of the cell voltage. You would only stop sooner than this if any cells started getting too hot.

It is of course burdensome to do this with a power supply as you have to set an alarm clock for the time and monitor the cells to make sure nothing bad is happening. A purpose designed battery charger will do the monitoring automatically and save you the trouble. However, if you have the power supply and don't mind baby-sitting your battery, it will work fine as a charger.


----------



## rwharold

wapkil said:


> I would try to use the standard 0.1C charge on them (e.g. taken from the C9000's break-in procedure), using their real capacity. It may be possible that it won't degrade them so much.
> 
> 
> 
> I don't know, it is possible but with fast charging I wouldn't rely on this assumption. I think that if someone wants to charge fast, he or she should use the recommended 0.5C-1C range (and probably it is a good idea to use something like your 0.6C, unless it results in missed termination). If the cell longevity is a priority, the standard 0.1C should be used.
> 
> This is a general recommendation though and everything depend on the charger and batteries. The C9000 uses 1.47V maxV and Eneloops terminate at a high voltage (~1.6V @1C). I think it is quite possible that an Eneloop will reach 1.47V before it fully charges, even with currents much lower than 0.5C. If it is true, it would mean that the C9000 will terminate this Eneloop charge at maxV before it is charged, no matter what the current was.



I've contacted Maha Technical Support and the confirm the 1.47 V cut-off rate. But ADD that you should leave the Eneloops in the C-9000 charger for an additional TWO HOUS for a top-off current of 100 mA to bring the Eneloops to a 100 % charge. After two hours, the charger goes into a 10 mA trickle charge state where your can leave the Eneloops in the charger as long as you like.


----------



## chili20001

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

Hi everyone, new poster so be gentle! 
I also have just bought a mh-c9000 and a load of Amazonbasics pre charged rechargeable NiMH which seem to have favourable reviews comparing them to the Eneloops at half the price.
The back of the AA batteries say a standard charge of 200ma is recommended but reading through this forum that sounds like it would not be good for them. So as a rule of thumb I was told to charge the batteries at A: half their Mah, so 1000ma for a 2000Mah rated battery and B: discharge them at a quarter of the Mah, so 200ma.
Am I right in using this rule for all NiMH batteries?


----------



## Yamabushi

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*



chili20001 said:


> So as a rule of thumb I was told to charge the batteries at A: half their Mah, so 1000ma for a 2000Mah rated battery and B: discharge them at a quarter of the Mah, so 200ma.
> Am I right in using this rule for all NiMH batteries?


The rule is OK but your arithmetic is a bit off ... a quarter of 2000mAh is 500ma.


----------



## Turak

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

Boy, the debate over the 'correct/appropriate/best' charge rates is still raging strong I see.

Tom (Silverfox), myself, and others have debated/discussed this many times over the years, especially early on when I too had just found this forum.

I have noticed throughout the discussions that many people seem to latch onto certain pieces of information or read a piece of literature and suddenly take it as the 'gospel' of how its supposed to be done. Even the battery manufacturers can't 100% agree on the rates. The best they can come up with is a .1C charge rate and a .2 c discharge rate to determine capacity. But even they CANNOT agree on the BEST charge/discharge rates.....because there IS NO 'BEST' RATE!

Tom and others seem to love to quote the 'recommended' rate is '.5C to 1C'. Others seem to latch onto the recommended rate from the battery manufacturers is 200mA or some fairly low rate. Guess what, BOTH are true from certain perspectives.

The REAL TRUTH......There is NO SINGLE BEST RATE!!!!

Mostly the debate goes between the 'slower charging rate' being the 'best/better' and the other end......the 'faster charging rate' is the 'best/better'.

Each rate has it's advantages and disadvantages.....but more importantly I think its better to understand where some of this is coming from.

Let's start with the '.5C to 1C' rate is the recommended/best rate. A battery company recommendation, in particular PowerEx. Yeah, others recommend it, but trace it back funny how it started being more strongly recommended slightly after the MH-C9000 appeared.

This really came to life when the MH-C9000 came out because MAHA couldn't get the charger to terminate reliably at the lower rates.

The first versions of the MH-C9000 truly terminated on -deltaV as their 'primary rate', but the batteries were coming off the charger way 'too' HOT. I guarantee this... I had one of the early revision 'F' chargers. Everyone wondered how come my Enloops after break-ins were about 100mA higher than theirs. Then we found out about the change between revision 'F' and revision 'G and above' chargers. They then lowered the maxV voltage so that it terminated at 1.47v. Now Enloops almost ALWAYS terminate because they hit the maxV instead of -delta V. So now, maxV of 1.47V is really the primary termination method that most batteries encounter when using the MH-C9000 charger. Yeah the other methods are there, but the battery will probably never use/hit them.

As for the battery manufacturers recommendations of 200mA or really low rates.

There are a few reasons for this.

One reason is its an older hold over from the days when there were not smart chargers and 'fast' charge rates. You basically timed the charge and did it at a really low rate so the battery didn't die right away or explode.

Another reason, it is fairly hard to damage a modern 2000 mA battery charging it at 200mA and below. I didn't say it couldn't be done, just that its not easy. The battery can take that level of a charge for days and still work fine. I have torture tested Enloops charging them at 200mA for 7 days straight...yes 168 hours....guess what. They still work fine. I did notice a 3-5 mohm increase in the internal resistance though.

Here is one of the best reasons that almost everyone seems to overlook....

*ALL NEW NiMH Batteries can miss their termination charge on the first few charge cycles....NO MATTER WHAT RATE YOU USE!!!!!*

It take 1-5 charges on a battery before the end of charge signal (-deltaV) becomes as strong as its going to get. On some new batteries, it can take 1 or 2 cycles before you even 'see' and end of charge signal! Yes, generally speaking a larger charge rate will produce a larger end of charge signal...but not always on the first couple of charges.

That is why you see brand new batteries charged at 1A still miss their termination charge. It is also why batteries charged at ANY rate can miss their end of signal charge the first couple of cycles. I see so many people blame the charger or a low charge rate for a missed termination on a brand new battery....probably wasn't either. It was the new battery itself. Run it through a few cycles and it will terminate just fine I bet on the lower rate...that is assuming you don't have a charger that is always unreliable at the lower rates.

So...battery manufacturers play it safe and go the 'charge it at a really low rate' safe method......1. Harder to overcharge/overheat the batteries and cause a problem. 2. Don't have to worry about missing a termination charge signal. 3. Generally always get a good, complete charge.

Now with all that said, back to what is the 'best' rate. Again it varies depending on ALOT of factors; personal preference, technical factors.

There are trade-offs with each method.

Through the years and with many discussions here with Tom and others, I have finally fallen into the following patterns.

I generally try to charge them at the highest rate I can that DOES NOT cause them to get hot. *Warm is ok HOT is NOT.*

With a brand new AA cell, that can be .500mA, 1A or even 2A. The point is are they getting HOT. *HEAT KILLS A BATTERIES LIFE (AMOUNT OF CYCLES).*

Now with that said, the higher the rate, the more heat generated, so the more cycles lost. It seems to be a bell curve, where it helps to a certain point, then after a certain point, it starts killing cycle life off the battery. So again, its a trade-off.

I have found that MOST NiMH batteries, as they age, develop a higher and higher internal resistance. This in turn causes the batteries to started heating up when charged at the higher rates. So, as they age a bit and develop a higher internal resistance, I lower the rate so again they are NOT getting HOT when charged.

Some might say well why not then always just use a low charge rate? Well, larger rates do produce a larger end of charge signal. So a cheaper charger or a charger that 'needs' this to work reliably would have a problem with the lower rates. It is possible to cook a battery charging it at 200mA if you leave it on a charger for WEEKS.

Another good, often overlooked reason that I have noticed,....while I won't go as far as calling it a memory effect. I have notice that if you continually discharge or charge a battery at the low rates, it will get to where it does not like charging/discharging at the higher rates. Generally you will find it has developed a higher internal resistance. It will perform poorly under high discharge rates and heat up under high charge rates. So here you see that a low charge rate can also cause the cycle life to decrease. You generally cannot 'fix' this type of problem once it occurs.

I generally charge them at the highest rate I can when new (.5A, 1A, or 2A) where they only get warm. I will mix in a few slow (200mA or .5A) charge/discharge cycles ever now and then on a battery that always charged/discharged at a high rate (1A or 2A). Like a high output flashlight. I also do the opposite. I throw in a high rate charge/discharge cycle (1A charge/.5A discharge) on batteries that are continually used in a slow discharge rate application. Like a travel clock).

Also as the battery gets older and develops a higher internal resistance, I lower the charge rate so that they are not getting HOT when charged. Usually you will also start to see a decrease in capacity. One the capacity gets to about 70-80% of the original, I dispose of/recycle the battery

Now even though I bashed the *MH-C9000 ...... I have 2 of them and find them to be one of if not the best NiMh AA/AAA Analyzer charger on the marker right now.* Yes, it has some features I do not like, but so do all the other charger/analyzers out there right now. I personally own 1 - CBA II, 2 - BC900's , 2 - MH-C9000's, BT-C2000, and a BT-C3100 on the way. Like them all, for various reasons. Can't beat the CBA II for discharge testing.... But I like the MH-C9000's the best right now for newer batteries, charging, and capacity testing. I like the BC900's for older batteries, cycling older batteries, and CAN"T BEAT ITS DISPLAY METHOD...all batteries at once!


----------



## Etsu

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*



Turak said:


> The first versions of the MH-C9000 truly terminated on -deltaV as their 'primary rate', but the batteries were coming off the charger way 'too' HOT. I guarantee this... I had one of the early revision 'F' chargers. Everyone wondered how come my Enloops after break-ins were about 100mA higher than theirs. Then we found out about the change between revision 'F' and revision 'G and above' chargers. They then lowered the maxV voltage so that it terminated at 1.47v. Now Enloops almost ALWAYS terminate because they hit the maxV instead of -delta V. So now, maxV of 1.47V is really the primary termination method that most batteries encounter when using the MH-C9000 charger. Yeah the other methods are there, but the battery will probably never use/hit them.



Interesting. I have a couple of smart chargers I use on Eneloops, and if I remove a cell just a few minutes before it would normally terminate (judging by the other cells I leave on it), the resting voltage is very close to 1.6 volts. Of course, it drops quickly, but it seems clear that Eneloops will get up near 1.6v before the -dV kicks in. Terminating at 1.47v would definitely result in an incomplete charge on an Eneloop.

Non-Eneloops don't seem to reach anywhere near 1.6v, so perhaps the 1.47v cut-off was designed for older NiMH cell types.


----------



## SilverFox

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

Hello Etsu,

If you leave the cells in the charger during the top off charge you will see Eneloop cells reach 1.59 to 1.60 volts during that top off period.

Tom


----------



## Turak

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

Hi Tom....

Hmmm I must be doing something right....

Out of the original 24 Generation 1 Eneloops I bought and put into service around 2007...

using capacity = 2000mAh.

18 = 90% or better capacity

5 = 80-89% capacity

1 = 78% capacity. (this one got left in a clock for over 5 years. Ran totally flat. Obviously it took a hit from it capacity wise.)


----------



## Mr Happy

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*



Turak said:


> I generally try to charge them at the highest rate I can that DOES NOT cause them to get hot. *Warm is ok HOT is NOT.
> 
> With a brand new AA cell, that can be .500mA, 1A or even 2A. The point is are they getting HOT. HEAT KILLS A BATTERIES LIFE (AMOUNT OF CYCLES).*



One other thing about this is that some chargers heat up the batteries from the outside. The charger electronics get hot and this heat is transmitted to the battery, making it hotter than otherwise.

This is why some people might say you can charge an AA cell at 1000 mA without it overheating, while others say that 1000 mA will make it sizzling hot. The difference is probably in the charger.

One reason I like the C9000 is that it has a lot of space between the charger electronics and the charging bay. The charger itself does not cook the batteries.


----------



## DT123

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

I tested recently a new charger. I can set charging current to 500/1000/1500/2000/Auto.
It claims that it sets the current automatically depending on the condition of the cell. In any case - the set current is the max current.
If I charge an empty LSD cell and set 1000 mA, then it starts with 500 mA and after about 1/3 of the charging time it is changing the current to 1000 mA.
Is there any benefit to start charging with a lower current?


----------



## SilverFox

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

Hello DT123,

Some advanced chargers set the charge rate according to the cells internal resistance. The issue with a higher charge rate is that sometimes a cell will give an end of charge signal early and you end up with a cell that is only partially charged. By starting a little slower that early signal may be eliminated.

Other chargers simply ignore the cell for the first part of the charge and then monitor it later on.

Tom


----------



## DT123

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

Thanks for that explanation. I didn't see something like that before so I was not sure whether this is a good feature or not.
But if I set 1000 mA and it will never increase from 500 to 1000 - isn't there a higher chance that the termination will be missed? 
That charger is decharging sometimes in a cycle 1200 mAh and charging 1800 mAh or more.
I never had that behaviour with the C9000 (same cells). When I discharged 1200 then I never expected to charge more than 1500.


----------



## TinderBox (UK)

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

Anybody know what these are, they are described as some sort of battery charger/regenerator. :thinking:

http://www.ebay.co.uk/sch/thomas.autark/m.html?item=172451488086&rt=nc&_trksid=p2047675.l2562

John.


----------



## Capolini

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

What is the BEST charging rate for AAA Ni-MH 750mAh Enloops?

I have seen .5C[1A] and 500mAh?

,Thanks,,,,,,Capolini


----------



## Atum62

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*



Capolini said:


> What is the BEST charging rate for AAA Ni-MH 750mAh Enloops?
> 
> I have seen .5C[1A] and 500mAh?
> 
> ,Thanks,,,,,,Capolini




Not quite following your notation here, 0.5C/1A would apply to 2000mAh (AA) cells. 

Assuming a charge rate between 0.5C and 1.0C, you're looking at 375mA to 750mA. Most likely settings would be 500mA or 700mA. AIUI, the faster charge is more likely to produce a stronger termination signal [-deltaV], so 700mA would be a good option for cells in decent condition.

HTH.


----------



## ChrisGarrett

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

I charge my Eneloop AAAs up at 400mA and have hit 500mA and my AAs up at 1000mA/1A and tried 2A, once.

That's just me.

Chris


----------



## Capolini

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

400mA to 500MA sounds good to me.

I do not have a specific Ni-MH charger. But I have a few where I can set it to 500mA. That has been what I have been charging them at for the last 4+ years and they are working and holding up well. 

I heard/saw on other threads and when I googled it that some people charged them at 1A. I think I will stick to what I have been doing,,,just was wondering if 1A was too much and would degrade the battery!


----------



## ChrisGarrett

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*



Capolini said:


> 400mA to 500MA sounds good to me.
> 
> I do not have a specific Ni-MH charger. But I have a few where I can set it to 500mA. That has been what I have been charging them at for the last 4+ years and they are working and holding up well.
> 
> I heard/saw on other threads and when I googled it that some people charged them at 1A. I think I will stick to what I have been doing,,,just was wondering if 1A was too much and would degrade the battery!



1A is only .5C for a standard Eneloop and less than .5C for a HiCap. Maha suggests .3C or above, to get the batteries hot enough to trigger dT and end termination. 500mA is only .25C.

When they wear out, they wear out and I get new ones. I don't want to trash my stuff, but I'm not going to spend extra time coddling them, either.

'Use me and abuse me,' is what she said.

Chris


----------



## Kurt_Woloch

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

The charging current doesn't matter that much regarding battery degradation. Here you can find a comparison of different charging / discharging currents:

http://aacycler.com/post/high-current-vs-low-current/

In this case, the nominal capacity is 2.1 Ah. A charge at 1.5 A (roughly 0.7 C) yielded 154 cycles when discharged to 0.9 V, and a charge at 0.5 A (roughly 0.23 C) yielded 180 cycles. So that higher charge current cost about 0.093% or 1/1066 of cycle life per cycle. This is with 0dV termination. You can also use higher charge rates if you terminate the charge properly, and much lower ones also work. I routinely charge my 8 Ah D cells at 0.5 A, which is 0.06 C, and they still works fine. I think a higher charging rate will mostly affect cycle life at the end of the charge when heat builds up since a higher charging rate generates more heat.

It really depends if you want to have your cells full fast or if you prefer a longer cycle life.


----------



## Capolini

*Re: Appropriate (dis)Charge Rate for NiMH Batteries*

^^^^

Thanks that makes sense to me. One of my chargers either at 500mA or 1000mA. It has been suggested by several people that some of my smaller cells[IMR 10440/16340] [Ni-MH AAA ENLOOP 750mA] should probably be charged at a lower current. 

My IMR 10440 are only several months old, however I have Three[3] IMR 16340 that are almost Two years old and they are still working well after being charged at 500mA.


----------

