# NiMH and voltage depression



## ChrisA (Jan 12, 2006)

i did a search on that topic, but found nothing. so please forgive me if this is common knowledge.

well, most of us use nimh cells from day to day to power their flashlights, digital cameras, mp3-players and so on... and most of us, at some point looong ago , have fallen for the low prices these cells are going for over the net. at least that's how i got these nice aaa's:







as you can see, these are supposed to hold 700mAh of charge and were made in china. i got 8 of them and paid ~10 USD including shipping. after a couple of charge/discharge-cycles none of them made it past 500mAh on my charger, so i figured that this was a 10 dollars lesson learned. so, after another unsatisfactory discharge i pulled them and was decided on trashing them.

out of curiosity i checked one cell with a dmm: open circuit voltage was ~1,1V, slowly declining to 0,9V if put under load with a 50 mOhm resistor. that's the point, the charger will stop the discharge cycle and starts recharging the cell. so far so good. but if you let the cell rest for a couple of minutes, it would recover to 1,1V



.

that's where voltage depression comes into play. the cells still contained a fair amount of charge, but would not release it fast enough. this phenomenon is caused by Ni-use in rechargeables. NiCad's suffered double from that problem and when NiMHs were developed, we only got rid of one part of it. it has to do with the way the Ni is disposed in the cell and the way it will form crystals that won't break up as easily (btw - crystal forming will benefit from slow charging, so fast chargers are better suited for NiMH chemistry, if they reliably detect a full charge). 

anyway, the charger would not let me discharge the cells completely, since the load it put on the cells would cause a voltage depression, after which the charger sensed an empty cell and started recharging. so i put the supposedly empty cell in an arc aaa and it would start out bright, but within 30 seconds it's output would decrease until completely dead in about two minutes. but turning it off and on again would work over and over - not a good way to deplete the cell...



so, what to do ?

individual NiCad cells can be discharged to 0V without ill effects. that's what the rc-guys do, if their battery-packs show signs of aging. just connect both poles with a resistor and let the cell sit for a couple of hours (that's for individual cells only, so for battery packs they used a device called "nagelbrett").

NiMHs will be harmed by deep-discharging them, so a simple resistor is not suitable to get rid of the lazy battery effect. diodes to the rescue:






that's a 2.7 Ohm resistor and a 1N4001 diode in series, connected to both poles of the cell (and a nice example of a bad soldering job - but it works nevertheless  ). the 1N4001 has a breakdown voltage of ~0.7V. it will let current pass through, unless the voltage sags under 0.7V. cost of materials is about one dollar and assembly may take three minutes (if your skills with a soldering iron are as bad as mine



).

i let it sit for a day:






that brought open cicuit voltage down to 0.88V and following charge/discharge-cycle got 0.62Ah from that cell



. i will repeat the process a couple of times to see wether it will gain even more capacity. anyway, that's close enough to 700mAh for the price i paid.

so, before you trash old or supposedly crappy cells, it may be worth to give it a try... (i doubt it will work on suspiciously cheap 2.800mAh Tamiyas though  )

chris


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## wptski (Jan 12, 2006)

Well, voltage depression isn't a certain voltage, it's when you discharge part of the cells capacity and recharge, repeatedly to the same point! Ni-MH do suffer from this but not as bad as Ni-CD, it takes longer to happen and it can be solved with a complete cycle or two.

RC guys don't discharge Ni-CD to zero volts. Why would they want to lose power or control in mid-flight? Besides, try putting a zero volt cell in a smart charger, it'll tell you, no cell!!


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## ChrisA (Jan 12, 2006)

> Well, voltage depression isn't a certain voltage, it's when you discharge part of the cells capacity and recharge, repeatedly to the same point!



okay, here's how i understand "voltage depression": a cell using Ni chemistry forms large crystals during charge (which happens if cells are overcharged, not cycled constantly and stored over a longer period of time) which will lead to a "reduced" capacity during discharge. that's because the larger crystals won't break up easily, so that the voltage of the cell drops, although there's still plenty of reactive material left...

if you do a cell analysis, a charger like the bc-900 will discharge the cell to ~0.9V and then starts recharging. if the cell is "damaged" due to the large ni-crystals it will sag under 0.9V even if there is still reactive material in the cell and capacity is "lost".



> RC guys don't discharge Ni-CD to zero volts. Why would they want to lose power or control in mid-flight?



hm, you got me wrong... a buddy of mine is into rc-boats. he "revives" low voltage nicad packs by discharging each cell down to 0V (not during use of course). because he does not want to disassemble the pack, he uses a thing called "nagelbrett"... the shrink wrapper is punctured by nails, so that each cell can be discharged completely.



> Besides, try putting a zero volt cell in a smart charger, it'll tell you, no cell!!



he uses a special charger (like the schulze charger tom mentions from time to time) that will recognize the battery pack even if completely depleted.

chris


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## wptski (Jan 12, 2006)

No, voltage depression or memory effect is from repeated partial charges. I have a Schultze and it's very picky about what it likes! It will do a non-timed, non-termination charge, if that's what he means.

I neglected some brand new AA Ni-MH and some read zero volts. I tried all tricks, some survived and some didn't!!


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## ChrisA (Jan 12, 2006)

> I neglected some brand new AA Ni-MH and some read zero volts.



i read that post and it was very informative, thank you. that's what the diodes are for - they will prevent the NiMH cell from discharging beyond 0.7V, since this will likely cause damage (IIRC there's a sanyo twicell article about that). the 0V-method works for NiCds only.

chris


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## wptski (Jan 12, 2006)

I'm refering to a self-discharge to zero, not with a load.


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## BentHeadTX (Jan 12, 2006)

Back in the day,
We had to discharge 144V NiCad battery packs used in portable X-Ray units and we discharged the packs to 0.000 volts. Attached a large bank of lights to them and let them run 24 hours past the point of no glow on the filament. Then we took the packs apart and attached shorting bars to each cell and let them sit for 24 hours dead shorted. Recharged the packs and repeated it every 6 months. We replaced the packs every 5 years and never had any problems.


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## lamperich (Jan 12, 2006)

The diode is a nice idea!

Voltage depression is how Duracell describes the memory effekt.
http://www.sanyo.com/batteries/pdfs/twicellT_E.pdf
http://www.duracell.com/oem/rechargeable/Nickel/voltdep.asp
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiMH_Overview.pdf

I´am not convinced in discharging NiMH down to an open voltage <1,1V.
As you already said the voltages drops under load. There is NO benefit in discharging them under 1V.
http://www.ife.ee.ethz.ch/~zinniker/batak/ideal/index.html

But yes it´s a interessing question...
I want to know more about that.



@ BentHeadTX 

I own a portabel screwdriver since 2001
The unit use NiCd Sub-c. unbelieveable how strong they are.

Do you already have expierence with NiMH in similar applications?


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## ChrisA (Jan 13, 2006)

@bentheadTX - 144V packs ? wow, that must have been an impressive battery pack ! would be interesting to know the loads, these were discharged at... 

the packs my buddy uses for his rc-boat are only ~7V but current draw will peak at ~50A



. that's why he still uses nicads, since nimhs aren't capable to deliver currents that high.

@lamperich - thanks for the very informative links ! i just read the duracell paper and this is what i found:

"The voltage drop occurs because only a portion
of the active materials in the cell is discharged and
recharged during shallow or partial discharging. The
active materials that have not been cycled change in
physical characteristics and increase in resistance.
Subsequent full discharge/charge cycling will restore the
active materials to their original state."

that's basically what i said above. anyway, the duracell paper goes on:

"The extent of voltage depression and capacity
loss depends on depth of discharge and can be avoided by
discharging the battery to an appropriate cutoff
voltage. Voltage depression is most apparent when the
discharge is terminated at higher cutoff voltages, such as
1.2 volts per cell. A smaller voltage depression and
capacity loss occurs if the discharge is cut off between
1.15 volts to 1.10 volts per cell. Discharging to 1.0
volts per cell should not result in significant voltage
depression or capacity loss during subsequent discharges."

well, that's the interesting part. according to duracell, it's sufficient to cycle the cell a couple of times to get back to full capacity. that's what i tried with the cell i mentioned above.

the chargers i mostly use (akkutrainer 1 and 3) will discharge a cell down to 0.9V and then start recharging. four full charge/discharge cycles brought the e-cell close to 500mAh, but that's all i got. after discharging it through the resistor + diode the same cell got 620mAh. that's quite an increase and i guess it's due to some reactive material being "reactivated" by the slow discharge to 0.7V








chris


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## VidPro (Jan 13, 2006)

"""it will sag under 0.9V even if there is still reactive material in the cell and capacity is "lost""".

yup, it sure will, the speed of discharge at the low end will be slow.
and dropping it a bit further for real, minus the huge drop that hits when using these "smart" chargers, is missing cycling the end.
good stuff.

Silver reported some manufacture saying it was Ok to drop to .4v slowly. i would think that would achieve the best attempt at cycling them, when they arent speedy at the bottom end.

i like to drop further than spec during a Cycling discharge, if i am going to crank them right back up again. IF i am having to specifically cycle to get it alive.
your method looks easy, now why didnt they bother to put a "feature" for doing a fuller deeper discharge in the "smart" chargers.

i have 2 old RS charge discharger things, that held 4 batts, might be a good place to put in that method.

i still dislike AAAs for recharging, because they are so puny and practially useless, and they get hurt easily. any improvement to them would be valuable.


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## ChrisA (Jan 13, 2006)

> your method looks easy,...



it's not "my" method  - i just added a diode to the resistor to prevent deep discharge. otherwise this technique is used on nicads for quite some time with good results.



> ...now why didnt they bother to put a "feature" for doing a fuller deeper discharge in the "smart" chargers.



i guess it just takes too long...  the cell i tested took 24h to drop down to 0.88V open circuit voltage, since current through the resistor will drop to a couple of mA when the V "cut off" of the diode is reached.



> i still dislike AAAs for recharging, because they are so puny and practially useless, and they get hurt easily. any improvement to them would be valuable.



you're absolutely right. it's really easy to overcharge them. that's why i prefer a fast charger and monitor the time - at ~1C they give a decent cut off signal, otherwise i pull them after 1:20h. the accutrainer 1 will run into timer cut off with 600+ mAh AAA cells, because the rate is too low and it doesn't sense the charge peak. that way, i ruined two nice sets of sanyos 

chris


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## lamperich (Jan 13, 2006)

ChrisA said:


> the chargers i mostly use (akkutrainer 1 and 3) will discharge a cell down to 0.9V and then start recharging. four full charge/discharge cycles brought the e-cell close to 500mAh, but that's all i got. after discharging it through the resistor + diode the same cell got 620mAh. that's quite an increase and i guess it's due to some reactive material being "reactivated" by the slow discharge to 0.7V
> 
> 
> 
> ...



that is a very interesting observation

The AT1 usually discharge to a lower level ;-)
http://www.digicamfotos.de/index3.htm?http://forum.penum.de/showthread.php?id=25821


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## wptski (Jan 13, 2006)

>>>
A smaller voltage depression and
capacity loss occurs if the discharge is cut off between
1.15 volts to 1.10 volts per cell.
>>>

I wonder how manys devices really do this? I know that a Fluke 189 DMM doesn't!


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## ChrisA (Jan 13, 2006)

> The AT1 usually discharge to a lower level



in case of my at1 (i got the older model from conrad, about 2 years ago) the cell will recover to a higher voltage, as soon as you pull it from the charger. the above e-cell recovered to 1.1V. and that's exactly what i try to understand.

the open circuit voltage of a depleteted cell should be ~0.9V. so i guess a cell that is "force" discharged to 0.9V (or even to a lower voltage) isn't really empty, since it will recover over time. that seems to indicate, that there is still reactive material in the cell which might be bound into structures that need longer periods of time to break up... otherwise i don't understand, why there's such a jump in capacity





chris


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## wptski (Jan 13, 2006)

ChrisA:

The same point came up another thread and SilverFox ran tests discharging cells all the way down to .5V. The cells always recovered to over 1V.


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## VidPro (Jan 13, 2006)

i dont think of it as a increase in capacity, because i think that the capacity is THERE, its just that the chemicals are slow to "spring" back.
the reasons we get a TESTED increase in capacity, is because were always stopping at some set voltage, when testing.
were not really completly depeating the cell to deadness, to get the SAME test, we use specific machines or stop points.

if the battery is still pushing juice out Quickly (speed) at the low end of the discharge (about 1v), then it will display that it has more capacity, but did the ACTUAL capacity change, or was the cell just vibrant enough at the low end, to KEEP the voltage up there, by keeping the flow going.

IMO if you cycle it THERE also (at the low end), then it is speedier there.
SO
if you were discharging a 5mm led with 3 of them, it will keep plugging away, because the 5mm led will only be pulling 2ma. Eventually you will get all possible capacity out of it. (mabey kill it, but you get it all)

but general use of things is that your trying to get a lot of current (for its total) out of them, the faster they discharge at the end , the more capacity the average device will give you, before it cuts out due to lack of "voltage".

we put rechargables in things that we need juice quickly, not because a alkaline would do the job  so general use of them a speedier discharge at the neer end of its discharge cycle, can be a fair ammount of time longer.


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## lamperich (Jan 13, 2006)

ChrisA said:


> in case of my at1 (i got the older model from conrad, about 2 years ago) the cell will recover to a higher voltage, as soon as you pull it from the charger. the above e-cell recovered to 1.1V. and that's exactly what i try to understand.
> 
> the open circuit voltage of a depleteted cell should be ~0.9V. so i guess a cell that is "force" discharged to 0.9V (or even to a lower voltage) isn't really empty, since it will recover over time. that seems to indicate, that there is still reactive material in the cell which might be bound into structures that need longer periods of time to break up... otherwise i don't understand, why there's such a jump in capacity
> 
> ...



iam not convinced in discharging a NiMH to an open voltage of 0,9V!
but it´s a very interesting question.


Can you trust the capacity showen by the BC900 or AT3?

Can you measure Ri ? 
http://www.elv.de/shopping/ArtikelD...Referenz=471-35&Stufe=2&Gruppe=ME-BA&Menue=Ja
if link doesn´t work search for "Rim 1000" on www.elv.de


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## ChrisA (Jan 13, 2006)

@vidpro - so it's not capacity that changes, but voltage during discharge (called "Spannungslage" - i don't know the correct english term). hm, that makes sense



.

chris


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## lamperich (Jan 13, 2006)

@chris


---
As with Ni-Cd batteries, the charge voltage of nickel-metal
hydride batteries may show signs of swinging
(pseudo -.V) when they have been kept standing
for a long time or when they have discharged
excessively, etc. The initial delay timer is needed
to prevent charge from stopping (to prevent
malfunctioning) due to this pseudo -.V.
---
http://panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiMH_ChargeMethods.pdf

The question is: What is "excessively discharged"?

i don´t know it.


If you only have a charger like the Akkumanager10 or 20 or AT1 you should not be surprised if you also get a short runtimes like Quickbeam get with his first NiMH Runtimeplot in a Streamlight 4AA.
https://www.candlepowerforums.com/threads/103445

Quickbeam didn´t store the old runtimeplot. but i did.





in Digicam you get pretty soon pretty short runtimes.
BUT 
This coud be pretty dangerours for example in a Fenix 2AA.
Remebers this regulator also works with only 1 battery nearly as bright as with 2!

THAT`S exactly why i don´t like NiMH´s anymore.
The risk that we user abusing them without knowing it is pretty high. 

also read this posting made by bitcharger.
You can find there an ugly "spannungslage" http://forum.penum.de/showthread.php?id=24293&eintrag=60


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## VidPro (Jan 13, 2006)

ChrisA said:


> @vidpro - so it's not capacity that changes, but voltage during discharge (called "Spannungslage" - i don't know the correct english term). hm, that makes sense
> 
> 
> 
> ...



ya thats it, the Spannangslage effect. i knew sombody would finnaly name it, so we can put a scope on it and test it 

i have an idea that it works, because i will use light bulbs for discharge, which dont cut out at 1v , but they sure do dimm.
and i still get better results with my light bulbs than with the machine, BUT the machine is easier, and i only deep discharge when needed.

i never thought about using a diode that stops at a specific voltage, which would be more protective.

the problems that will come from explaining the Spannangslage effect, is some nutcase with a SERIES rc pack, will discharge the PACK reverse charging some of the cells in a pack, and say, Hey that was stupid 

well mabey it is stupid, and that is why were HERE, and why others can test it, on slow moving cells, and see what they come up with. if a cell is only putting out 550ma, ya wouldnt have anything to LOSE from trying, then we get more data.


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## ChrisA (Jan 13, 2006)

> Can you trust the capacity showen by the BC900 or AT3?



if it's measurements are false, they are false for both measurements - the first and the second. so, at least they give me an indication, wether the cell is gaining "capacity" or not...

i don't think give too much about the actual numbers though. they might very well be false.




> Can you measure Ri ?



no, if you need an apparatus like the one in your link, then i can't. sorry.

chris


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## VidPro (Jan 13, 2006)

""This coud be pretty dangerours for example in a Fenix 2AA.
Remebers this regulator also works with only 1 battery nearly as bright as with 2!""

yup anything with a driver like that, with no warning, no change, and would depleat a cell beyond 0, would not be a good place for a cell that didnt like to be abused.

but also dont forget that them 60$ flashlights might not look so good with a Leaking dead alkaline in them either  hmm ruin the cell, or ruin the light, choices choices .

as far as battery manufactures, well who is gonna believe them? they told us that ni-mhy doesnt have any "memory effect" while they indeed don't have memory effect, what people were REFERRING to as far as memory, the ni-mhy still does have a self dicharge, and loss of vibrancy from lack of use.
so them manufacturers tried to cheat us, and make believe these batteries would not need cycling ever.
so who cares what they say, they lied


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## SilverFox (Jan 13, 2006)

Hello Chris,

It is my understanding that charging has to do with crystal formation and during discharging those crystals are broken up giving off energy.

At the low end of voltage, there is very little capacity to be gained. When you measure the capacity you get from discharging from 1.0 volts to 0.9 volts, even at very low currents, it is not much at all. On the other hand, there is some "measurable" capacity in the 1.15 - 0.9 volt range.

I believe what the Duracell paper was referring to is that many battery operated devices will shut off at 1.15 volts to eliminate the sudden shut off that would accrue if they went lower. Repeating this discharge cycle will end up with large crystal growth that effects capacity and internal resistance.

When I select automatic discharge on my Schulze, it discharges NiMh cells to 1.0 volts per cell. It starts out at 1.0 amp discharge, then when it has reached 1.0 volts per cell, it switches to 0.5 amps discharge. When it reaches 1.0 volts per cell again, it then switches to 0.25 amps discharge. Upon reaching 1.0 volts per cell again, it ends the discharge and, according to Schulze, the cells are ready for storage. Schulze goes on to state that to properly store the cells, they should be put through an automatic charge/discharge cycle every 30 days.

An interesting side note is that on automatic charge, the Schulze does a similar thing. It starts off charging at a slow rate, ramps up to a high rate, then near the end of the charge, it steps down the rate several times.

I am aware of at least one other discharger/conditioner that discharges NiMh cells at a rapid rate, then discharges at a very slow rate to complete the discharge cycle. Cells end up at a resting voltage of around 1.0 volts.

I am under the impression that some of the "no name" cells may be old stock that was purchased from warehouses and re-labeled. What you observed with your AAA cells is similar to what I see with "old" cells. 

They start off performing very poorly, then through repeated cycles, begin to improve. Sometimes the improvement takes big jumps, other times it just inches up a little bit at a time.

To restore "old" cells, or "form" new cells, a slow charge is used to equalize the chemistry within the cell and eliminate any "starved" areas. I am under the impression that this slow forming charge actually produces large crystals that are effective in spreading out the chemistry uniformly within the cell. After the forming charge, several cycles are needed to bring the cells up to full capacity.

Cells usually show a noticeable amount of increase in capacity over the first 5 cycles. I have noticed that cells that are provided for critical use will often state that maximum performance will not be realized until 10 cycles of use. I have a set of 2400 mAh AA cells that started out at 800 mAh of capacity, and it has taken 58 charge/discharge cycles to get them up to normal performance (2340 mAh). I believe Sanyo produced a graph that showed that the capacity actually increases a small amount over the first 100 cycles.

The bottom line is that I think your results are from cycling and not from discharging to a lower voltage... although perhaps it is a bit of both. 

Tom


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## ChrisA (Jan 13, 2006)

> If you only have a charger like the Akkumanager10 or 20 or AT1 you should not be surprised if you also get a short runtimes like Quickbeam get with his first NiMH Runtimeplot in a Streamlight 4AA.



@lamperich - well, why ? the at1 is considered to be a pretty good charger, isn't it ? anyway, i got 4 chargers: at1 (everyday charger), at3 (cell analysis), varta 30 min charger (charging aaa's) and a voltcraft p-100 (does prismatic cells).

i built some more of these discharge holders and will go through my nimh pile. hopefully it'll bring back some of the older, less frequently used cells. if it works, then this might be a good thing to do every now and then - just discharge the cell, place it in the holder and let it sit for a day... pretty convenient 

chris


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## VidPro (Jan 13, 2006)

SilverFox said:


> Hello Chris,
> 
> 
> Cells usually show a noticeable amount of increase in capacity over the first 5 cycles. I have noticed that cells that are provided for critical use will often state that maximum performance will not be realized until 10 cycles of use. I have a set of 2400 mAh AA cells that started out at 800 mAh of capacity, and it has taken 58 charge/discharge cycles to get them up to normal performance (2340 mAh). I believe Sanyo produced a graph that showed that the capacity actually increases a small amount over the first 100 cycles.
> ...



Hi Silver.
so my question is, would a deeper discharge of that SAME (58 cycle) battery, mabey had "recovered" it faster than 58 cycles?
see
you say tomoto, i say TomAto.

i will never know if a battery with 58 cycles will improve it  after about the 5th, its going in the trash. you DID do some low discharge testing didnt you?
and got zip for results? i wish i could see more expert analisis of this, and YOU the expert .


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## ChrisA (Jan 13, 2006)

> I am under the impression that some of the "no name" cells may be old stock that was purchased from warehouses and re-labeled. What you observed with your AAA cells is similar to what I see with "old" cells.
> 
> They start off performing very poorly, then through repeated cycles, begin to improve. Sometimes the improvement takes big jumps, other times it just inches up a little bit at a time.



that might very well be. maybe the jump from 500 mAh to 620mAh is just luck in the last cycle. i don't know. i just gave it a try, since it works pretty well for nicads (without the diode)...

chri


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## wptski (Jan 13, 2006)

Tom:

Speaking of Schultze! When your speaking of Ni-MH, exactly what? Cells or wired packs?

I had just emailed them about problems using good spring type cell holders. AutD program on eight AA cells works but none of the AutC do as the current drops so low that the maximum time of four hours is met! A wired/soldered Ni-MH pack or a DeWalt 14.4V Ni-CD works just fine.

Matthias Schultze answered either use a soldered pack or clamp the cells. I was asking about some DuraCell 2300mAh A cells made in China. He went on in lenght to say that these new high capacity cells are a different chemistry and have very high internal resistance that chargers have problems calculating current. He said that Sanyo doesn't list the internal resistance of this new breed in it's specs because of this! He said that if you want to use these cells charge at 1C because voltage detection is difficult on them!


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## lamperich (Jan 13, 2006)

ChrisA said:


> @lamperich - well, why ? the at1 is considered to be a pretty good charger, isn't it ? anyway, i got 4 chargers: at1 (everyday charger),




yes of course 
but you don´t recognize different charging times
because of the pseudo -deltaU caused by the big questionmark "excessively discharged" ;-)


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## SilverFox (Jan 13, 2006)

Hello VidPro,

While I have been accused of being an expert before... I consider myself a babe, just learning to walk. 

Tom


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## SilverFox (Jan 13, 2006)

Hello Chris,

I don't think you will damage your cells, but I seem to be observing that battery chemistry seems to be more stable when it is not at the extreme ends of the reactions. Keeping cells at low voltage for an extended amount of time sometimes results in vent failure that allows the chemistry to leak out.

I have done a lot of testing to lower voltages, but never let the cells remain at that low state of charge for any length of time.

I would recommend that you do your discharging in an area that can contain any possible leakage from your cells. You should also plan to charge the cells back up after your deep discharge, rather than storing the cells in a deeply discharged state.

Tom


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## SilverFox (Jan 13, 2006)

Hello Bill,

I was referring to NiMh cells. I don't use spring holders because I have found that they are not capable of handling the 5 A charge rate the Schulze tries during the automatic charge function.

Interesting news on the new formulation of the Sanyo cells.

Tom


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## wptski (Jan 13, 2006)

SilverFox said:


> Hello Bill,
> 
> I was referring to NiMh cells. I don't use spring holders because I have found that they are not capable of handling the 5 A charge rate the Schulze tries during the automatic charge function.
> 
> ...


Tom:

If you don't use spring type, how do you hold them? Just stopped at Sears and bought this hugh adjustable clamp that will hold eight AA cells! Just have to figure out how to hold them in line while I do that?  Might take a few of my neighbors!


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## wptski (Jan 13, 2006)

SilverFox said:


> Hello Bill,
> 
> I was referring to NiMh cells. I don't use spring holders because I have found that they are not capable of handling the 5 A charge rate the Schulze tries during the automatic charge function.
> 
> ...


Tom:

If you don't use spring type, how do you hold them? Just stopped at Sears and bought this hugh adjustable clamp that will hold eight AA cells! Just have to figure out how to hold them in line while I do that?  Might take a few of my neighbors! 

Wonder why they don't make holders similiar to the contacts used in AA chargers?


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## SilverFox (Jan 13, 2006)

Hello Bill,

Just get yourself a length of 5/8" diameter PVC pipe. It does a good job of keeping them in line.

Tom


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## wptski (Jan 13, 2006)

SilverFox said:


> Hello Bill,
> 
> Just get yourself a length of 5/8" diameter PVC pipe. It does a good job of keeping them in line.
> 
> Tom


Tom:

That's exactly what I was thinking about too! One about 7" or so for four cells and around 15" for eight cells. I'm also going to drill a bunch of holes along the lenght for cooling too. I might have a piece out in the garage.


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## ChrisA (Jan 16, 2006)

a small update about my testing so far.

i cycled the cell another 2 times with resistor + diode and capacity remained at 0.6Ah. i guess, that's max for that cell. the ones i cycled with the at-3 remained at ~0.4Ah, so these are going through the resistor + diode procedure right now.

anyway, since i built some more of these discharge holders i did cycle a set of old panasonic 1600mAh cells that where neglected for some time (charged sporadically, never discharged completely => held ~1400mAh after a reconditioning cycle on the at-3). after a 24h discharge to 0.7 (under 2.7 Ohm load; 0.9V open circuit) once, these seem to be back to full capacity (1.62, 1.59, 1.55, 1.58).

with fresh and well cycled cells, this method seems to have only a small impact on capacity (@VidPro - or on spannungslage  ) if anything at all, since i did test two 2300mAh sanyo cells and they did not improve (tested 2.21, 2.25 before and 2.23, 2.23 afterwards). 

so, my findings so far:

1. this method seems to be a pretty good way to revive lazy cells without occupying various chargers for several hours

2. i need a charger that features a computer interface to plot charge/discharge graphs






chris


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## SilverFox (Jan 16, 2006)

Hello Chris,

I ended up with a Schulze charger because I also wanted computer interface abilities...

While it seems that battery chemistry is still a bit of a mystery, your tests are very valuable and add to our knowledge base. Thank you.

Tom


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## krautracer (Jan 22, 2006)

Hello Chris

When you put the resistor and diode together with the battery holder, do you put the cathode side on the positive or negative side of the battery. 
I haven't tried this yet but I need a cheep discharger for my batteries. 
Do you need a 2.7 ohm resistor or would something around that work? 
Thanks Brett.


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## Wolf Lonesome (Oct 1, 2014)

Has anybody else tried this method?
Any success with increased capacity?
What charger should I use after 24 hour (2.7 Ohm resistor and 1N4001 diode).
What about the WildFlyer way to recover ni mh batteries?


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