# Charging NIMH Batteries - Getting HOT in Charger



## reviewum (Jun 20, 2005)

Friends,

My brother and I've got a Vanson "speedy box" charger. We notice that sometimes while charging our AA and C batteries that they start to get warm and then REALLY REALLY hot in the charger. A few questions:

1) Why is this happening?
2) Does this mean that the batteries and/or charger are bad?
3) Should I toss the batteries after this happens?
4) I thought all these "smart chargers" were suppose to eliminate these types of issues with all their circuitry and other snazzy stuff.

Thanks in advance for your help!


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## Archangel (Jun 20, 2005)

You may be charging them too fast (read: at too high of a current). What is the mAh rating of the batteries and how many mA are you putting through them? There's no problem with them getting warm, but REALLY REALLY hot will definitely shorten their life.


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## Sub_Umbra (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

<rant>
Even at relatively low charge rates my NiMHs charge *hot.* This is a pet peeve of mine. All of this talk about how quick NiMHs charge doesn't add up in my book. I bought an AC2020 mainly because I felt that it would be somewhat gentle with my cells. It is a smart charger with one channel per cell. It is only capable of charging a D cell at 700 mA or *less.* The cells charge hot. Don't even think about closing the door of an AC2020 while you're charging NiMHs!

On the other hand, the higher priced Ansmann unit jams 1 AMP into each NiMH D cell. Geeze, those must get hot, too. Of course, IIRC Ansmann didn't even bother to put a door on their charger!

I've got NiMH D cells from two different manufacturers that are bulging at the negative poles and *not one of them* has ever been charged at a rate over 700 mA. What gives here? I've got a charger that takes over 24 hours to charge a NiMH D cell and half of the cells are bulging. 

Don't get me wrong, I love to USE the cells. I'm just seriously wondering how mature this NiMH technology is. How much do I have to spend for a NiMH D cell that works as advertised? If I've got to pop $23 each, we're talking $138 just to run my $125 cd boombox!!! And oh ya, since it's going to take 2.5 days to re-charge those pigs I should probably have another whole set. OK, so thats over $250 (even with quantity deals) to run my $125 boombox on NiMH cells. Green may be beautiful but that's stupid.

I'm temped to buy a bunch of Nicad Ds before the Green NAZIs make them a black market item. At least it's a mature chemistry and I could score quite a few Ds for $100.
</rant>


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## VidPro (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

how would you describe it, without a thermal probe?
if you can still touch them, it might be normal, if you can not even touch them (burn ya), then it might be charging to fast for them to last many many cycles.

if they are bulging, then that is bad.


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## Lynx_Arc (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

I have a rayovac 1hr charger that makes batteries pretty hot, so much I put a cpu fan on top of them when charging to wick the heat away from them when I have to fully charge them. Topping them off usually doesn't heat them up near as much though just a 1/2 to full charge does it. Perhaps chargers will have to have freon cooling for the batteries if they ever break the 5 minute barrier to keep from melting the cases of them.


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## reviewum (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Friends, thanks for the posts! 

I just wish I knew if it was a battery issue or a charger issue. I'm leaning toward battery issue because it doesn't seem to happen to all my batteries. I should do some experiments to see if it is a function of how discharged the batteries are when I put them in, age of the batteries, etc.

I dont' have a lot of things that use anything other than AAA or AA batteries. For the few items I do have I'm thinking about trying to use those AA to C to D converters and just use AA for everything. Sure the batteries won't work in everything and won't last as long, but per the issues stated above (price, charge time, and price) for the C and D cell NIMH I'll take my chances with AA converters.

Now if I can just keep these batteries from heating up so much... I'm sure it wouldn't be a good thing if they blew up.


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## Archangel (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Sub Umbra- What cells are you using that charge hot to the touch (as opposed to "merely" very warm)? Even high-capacity AAs should be able to handle 1A. Oh, and you shouldn't ever close the battery case, even when you charge slow.


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## Sub_Umbra (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Powerizer 9500mAH Ds (from Batterystation)

DIGI-USA Hitech 9000mAH Ds (from CCrane)

I think that on a *really* quiet night...you can hear my D cells suck...from any location on earth...


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## Sub_Umbra (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

I'm not having any trouble with AAs.

The surface to mass ratio on AAs is completely different than that of Ds. If a D cell (with all of its mass and very little surface area, compared to a AA cell) feels hot to the touch on the surface, there's no telling how hot it is on the inside. The idea of putting a fan on charging D cells is repugnant to me for two reasons, A) I bought a 'smart charger' for a reason, and that reason *was not* so I could put a fan on it because it was actually designed as a 'stupid charger' that needed auxilary cooling that the charger manufacturer was too asleep at the wheel to provide, and B) I am not at all convinced that removing a tiny anount of heat from just the surface of a charging NiMH D cell accomplishes anything in the real world.


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## VidPro (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

i charge my D cells really slow. but the ones i have are rated very slow.
4400 and 4500 ni-cads rated at 440ma
the 9000 are rated for 900ma, and are just fine at 220ma and 440.
because i bulged, and exploded from overcharge a 9000, i am sceered to even do them at 900 now. but they have so much juice that taking 16-30 hours to charge is no big deal.

seems like when they put a LOT of capacity in them, they are not as capable of being abused , (less plates , more electrolyte) but the one that blew, had very capable plates, and a minimum of electrolyte.

OOPS, corrected one rate in there.


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## Gene (Jun 20, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

This has been a mystery to me since I started using NiMH's a couple of years ago. I also have a Vanson and some AA's, C's and D's get hot, (especially the C and D's), some don't. Same thing using a MAHA 401. Some do, some don't. I gave up being concerned about it and just let them do their thing until I get the green. So far, no problems. You want to feel HOT, charge some AA or AAA's on a 401 using fast charge. Yikes!

Whenever the full line, (N, AAA, AA, C and D), of rechargeable, protected Li-Ions come out, these NiMH's will be gone. I like NiMH's okay but they're slow to charge and lose their charge too rapidly.


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## reviewum (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Hmmm... I guess then I should not only keep the lid open, but also remove it from the drawer that I have it in while charging. Whoops!


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## VidPro (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

[ QUOTE ]
*reviewum said:*
Hmmm... I guess then I should not only keep the lid open, but also remove it from the drawer that I have it in while charging. Whoops! 

[/ QUOTE ]

(Sinefield impression) Yes, Yes Please do. /ubbthreads/images/graemlins/wink.gif

don't know why they put a lid on them things, but the directions usually point out to not have the lid down when charging. i guess it keeps the dust out when your not using it.


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## VidPro (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

[ QUOTE ]
*Gene said:*
This has been a mystery to me since I started using NiMH's a couple of years ago. I also have a Vanson and some AA's, C's and D's get hot, (especially the C and D's), some don't. Same thing using a MAHA 401. Some do, some don't. I gave up being concerned about it and just let them do their thing until I get the green. So far, no problems. You want to feel HOT, charge some AA or AAA's on a 401 using fast charge. Yikes!

Whenever the full line, (N, AAA, AA, C and D), of rechargeable, protected Li-Ions come out, these NiMH's will be gone. I like NiMH's okay but they're slow to charge and lose their charge too rapidly. 

[/ QUOTE ]

its not as big a mystery to me, but still compared to li-ions the ni-??? sure do heat up, which shows that the energy going in is being wasted.

and, the few that i have (nextcell) that get VERY hot, are doing so because they are garbage now. they still work but they have low capacity, and a discharge curve that looks more like a alkaline.
because they were used directally alongside other brands, that still work great , i am assuming they were just poorly made to begin with.
amazingly enough, the "radioshack" ones of various types are still doing great. a battery pack maker once told me that them and sanyos are great. and time told that he was not kidding, even if i would have prefered to aquired them elsewhere.


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## blr (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Heat from overcharging is a main concern in 90% of the so-called "smart" chargers. The sour truth is that most of these chargers overcharge to some extent. It is also true that some cells get hotter than others because their voltage curve during charging makes it more difficult for the charger to detect full charge and turn off the high charge current. If I were you, I'd get some high quality AA cells like Sanyo/Energizer 2500 mAh and use AA-D adapters. My Vanson Speedy Box charges at 700 mA some older batches charge at 500 mA. This is not too much providing that the end of charge could be detected accuratelly. In my charger AA cells get moderately warm to about 42-45C. This is still within the safe limits although some small overcharging occurrs. If you want quick and safe charging for AA cells get Lenmar Mach1 Gamma. This is really fast and cool charger


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## VidPro (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Hey BLR
i was just reading your post on the Ni-Mhy thread, i think it is very well said/done.

this one 
From BLT
-----------------------
The most important factor determining cycle life is charging. Any amount of overcharge will shorten cycle life. Sanyo writes in their technical papers on NiMH cells that charging with -dV termination will shorten cycle life by about 20% compared to charging with 0dV (peak voltage detection). This is providing that the voltage drop that will triger shut-off is 10 mV per cell or less. Many chargers are not sensitive enough to detect this and will continue charging until 20-30 mV per cell is detected. Depending on the current you are chargin at this can cause excessive heating and increase of internal pressure. I estimate that the average fast "smart" -dV charger charging at something like 1000 mA with -dV termination shortens the cycle life by at least 30-40%. Many people don't care about it. Indeed the cells are more likely to be replaced by newer higher capacity ones before the end of their life. For heavy everyday users it may matter however. The problem is that some cells cannot take the abuse of a typicall fast -dV charger as we could see from Koala's pictures. I wouldn't consider something that heats my cells to 50C and above safe. Venting not only destroys your cells but is potentially very harmfull. See this electrolyte leaking. This is a very concentrated hydroxide solution. It causes burns upon contact with skin 
------------------------

I have always had personal issues with computerized chargers that detect a Vdrop myself. and that charge to fast.
BUT
the variation in Vhigh, or a maximum charge voltage, can be reduced capacity or overcharge too :-( 
different cells sizes , capacities, brands, cycle ammounts, cycle type, cycled often or not, and age, act sooo different .

what can you do /ubbthreads/images/graemlins/smile.gif other than manually determine which p.o.s. charger will do the best job fo the cells ya happen to have /ubbthreads/images/graemlins/grin.gif
oh well, at any rate, they pay for themselves 10X over.


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## MrAl (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Hi there,

My RS charger makes the cells get pretty hot too.

I've also done careful monitoring of cells while they
were being charged and i can see that the temperature rises
as the cell approaches it's minus delta V point, which means
that the minus delta V technique (which many chargers use)
overcharges the cell somewhat each time it is recharged.

There is a way around this, and it's not 'that' hard, but
requires a small purchase and some means of mechanically 
mounting small thermistors, preferably one to each cell.
You can then monitor the resistance of the thermistor and
convert it to temperature, or use a circuit to do this.
If you monitor with a simple ohm meter, you'll note that
a given temperature is going to always mean the same
resistance so you'll always know when to stop charging.
The hard part is mounting the thermistor to some kind of
spring loaded arm or something so that it always makes good
contact with the cell, or perhaps you can come up with 
a better mounting method.

Once the temperature rises to a certain point, you can stop
charging and know that you've extended your cell's life 
span.

Please post results and techniques here if you do this.


Take care,
Al


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## VidPro (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

doesnt your RS charger have 8 Cell slots. they are all wired in series, so they are all getting the same blast, but then you still (somehow) have to temp monitor 8 batteries. because they are all imbalanced , so they will all heat different, because they are not all charged yet.

I have a charger that does the vdrop and charges each of 10 cells seperate, shutting each off as they are (alegeldy) charged. it would need 10 seperated curcuits.

which brings up another pet peeve, and that is series charging, even 2 cells in series charging, never get "rebalanced" making thier out of balance further off.
UNLESS they are slow overcharged. (or discharged prior)

with very SLOW overcharging, series charging in 2x chargers, and 8x chargers , or Best example, power tool chargers, they can re-balance the cells.

I have good luck with a charge rate that is so slow, it is speced for the overcharge rate (or lower). at that slow charge rate, i dont get bulge, overheat, or venting.
so is the worlds stupidest charger, the best one?
(if we cant make the worlds smartest)

BUT, trickle charging isnt the best, to reassemble the plates, and get the stuff out of the electrolyte, a HARD FAST charge for the first 80% is best (if you can ALWAYS prevent ANY overcharge of any sort, and dont overheat).
AND
slow long permanent trickle, or overcharging , is not so good either, I might choose it over the Vdrop method (and its flaws and misses), but its not great either.

then PULSE charging, can get the elements back into place, without boiling the cell. hard hitting, without heating.

so to ME a ultra smart charger, will:
1) work with single cells (lots of them, as seperate units)
2) blast them at first (but only if discharged)
3) never overcharges (but always fully charges)
4) slow down at the end (it could do this with a Vhigh) 
5) always pulse charges
6) fully top off SLOWER 
7) after full charge does short burst Slow rate pulses, at long pause intervals, to maintain charge without trickle.
8) temp watch (to late)
9) battery pressure watch (to late)
10) Vdrop (to late)
11) can cycle them (discharge) if ever needed.

it is to late to see the pressure rise, because your already bubbling then, after all what is the pressure from.
it is to late to get the temp rise , because the internal temps are already higer than the external, and probes dont make great contact. (burned batteries are brown in thier tight interior)
internal temps on Large cells, can be WAY different than the external temps.

I would bet temp RISE, might totally occur BEFORE pressure and vdrop (boiling), and is still the best bet (like Big Al said). but some temp rise is normal, and batteries that are not so good but usable , will temp rise higher (ok toss them). sounds like the best plan, if you can calibrate it, just like the Vdrop, but before Vdrop occurs.

all of the above "indicators" can represent Damage, so the only flags were using , other than Vhigh are a cell being damaged. and Vhigh can vary also, so we might not be fully charged, or it might never reach it.

another fatal flaw in smart chargers:
Topping off by re-applying to the charger, the smartest chargers in the world, become the stupidest when you just want to top off a bunch of cells. 
there they go again, torture testing them. If the power goes out, or you mix the cells up, or put them back on the charger, or move to a different charger , or different human touches them, or you put them in something ,or you dont know how much or if it was used (its still fully charged) , etc etc.

so they must be able to detect a Vhigh loosly at least when first placed on the charger, then work FROM there,
to completly top off the battery.
if its high, just SLOWly top it off, if its low, then charge it normally, till it reaches Vhigh.
that leaves only one thing again, Slowly pulse overcharging it, after some set Vhigh.
WHY
because they arent going to heat up , pressure rise, or vdrop , before they are being damaged. 
and each time you put them back on the charger (or power goes back on), the charger is again braindead, and they are cool. so all the charger can do is find the flags again. 

did you ever notice, that the protection and charge Specifications for a LI-Ion is about the same thing you would want to do with these? 
why does the li-ion get personally singularly babied, and the ni-mhy tortured?
a good Li-ion charger would also, pulse charge them quick without heating, taper off near the end (a specific voltage) , and stop charging before there is any buildups of pressure or heat.

Oh oh i rambled again, and i couldnt afford the ultra charger anyways /ubbthreads/images/graemlins/smile.gif


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## Sub_Umbra (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

GEEZE, you guys have given me much more to worry about!


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## VidPro (Jun 21, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

[ QUOTE ]
*Sub_Umbra said:*
GEEZE, you guys have given me much more to worry about! 

[/ QUOTE ]

would we all be better off, if we just lost a little capacity here and there, and bought into the newest latest capacity and speed technology, as the others get old anyways?
Surely my 1600s and 1800s have paid for themselves many times over. and the D cells saved me from having to go through another set of Gell Cell lead acid things, that wouldnt make 10 good high powered deep discharges.

they did thier job, and then some, even with the deficiencies in the human (me) and the chargers.


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## koala (Jun 22, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Regarding the thermistors, has anyone here seen one that works? How does a thermistor mounted underneath a layer of plastic(charger body) able to correctly measure the temperature of a cell? My point of view being these thermistors 'trip' only when the cells temperature are way over the limit.

I recently posted a picture of a NiMH cell cooked in a Sony charger. The heat not only destroyed the cell's plastic sleeve but also melted the charger's charging bay. The termistor did not work or perhaps the intelligent charger did not even have one.

I guess the way manufacturers can sell more rechargeables is to build 'hot' chargers that cook cells so normal consumers would have to buy new cells frequently. Looks like new technology creating more landfill. Well, at least each rechargeable cell is reused a couple more times than primaries.

-vince.


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## Lynx_Arc (Jun 22, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

I would *guess* the thermistors are connected thermally to one of the metal charging tabs as this would be the best way to measure temperature of a cell.


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## MrAl (Jun 22, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Hi again,


Vidpro:
My charger has four slots, but each pair of cells are individually charged.
Yes, i'd have to monitor 4 cells i guess.
And yes, they dont charge evenly in this stupid charger i have 
The temp rise is usually chosen to actually be a 'change' in temp, like
say 40 deg C or something, above ambient.
The reason Li-ion can be handled differently is because the charge regimen
is very different. Using a current limit, the voltage detemines when the
charge is to be dropped, and this is very easy to measure. The delta Vf
is much harder to measure because it involves only a couple tens of mv
of change.
I have to agree that with all the problems they still work for some things
very well. I've said that about the Rayovac rechargeable alkies too.

Sub_Umbra:
Dont worry, be happy, and be prepared to buy more cells when needed /ubbthreads/images/graemlins/smile.gif

koala:
Yes, there are lots of thermistors that work.
Heat travels across short distances very well, so it doesnt take much
to get through thin plastic. I'd prefer to mount the thermistor on
top however, with some moderate but firm pressure, right in the middle
of the cell. I envision a small, wide arm with a thermistor installed
in a cutout indentation in the bottom of the arm so it can contact
the cell directly when the arm comes down, or perhaps through a tiny,
thin piece of metal for protection. The cell placement has to be just
right so it has to be constructed carefully to allow for variations
in cell diameter or whatever.
As Lynx had mentioned, it might be a good idea to mount it at one end
of the cell instead.

Any method that involves NiMH cells is *supposed* to be backed up by
a timer that shuts off after the longest possible required charge time.
This shows that 'none' of the methods are 100 percent reliable.


Russ (aka Lynx):
Yes, that's probably a good idea.


Take care,
Al


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## VidPro (Jun 22, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

MR AL
""The delta Vf 
is much harder to measure because it involves only a couple tens of mv 
of change. 
""

i never realized it was such a SMALL drop that they were trying to read, untill i read about those Controllable Computerized chargers.
i am really tempted to buy the one that does the 4 seperate channels with the LCD display in it, as it sounds totally cool.

and trying to stick with the temp high idea, there is also temp "breakers" and temp "fuses" i have seen them pasted into packs of both types. 
a temp fuse blows if the cells were getting to hot, and the pack becomes useless, but then again, chances are the cells in it were useless anyways 
i assume that uses a tiny spring type thing, in there that gets releaced when the solder melts that holds it in. various melting temperatures of solders make various temperatures of thermal fuses?

and 
a temp breaker which disconnects when the temps get to high, then reconnects when it goes back down.
i assume they use dissimilar metals that flex the contacts away when the temp gets to high.

of course both of those are for catastrofic failures.
BUT
what if we can get hold of a specific temperature thermal breaker , and use that, and a locking logic curcuit, or locking relay. so when it goes open the first time, the curcuit doesnt reconnect.
Always trying to find the EASY way out of the situation /ubbthreads/images/graemlins/smile.gif

course the prefered
a microcontroller, that watches temp rise on a minute basis, and when temp rise is to a certian level it starts to watch for a fast increase in temps.

still wont work for cold cells, that are charged, but stuck back in the charger anyways. or weird thermal changes in ambient temps.

do you have any ideas how long the temp has gone very high, before the normal cutoffs (besides timer) kick in?

and how MUCH higher it gets when it has gone from charging fast, to overcharging.

Ohhh Silverfox /ubbthreads/images/graemlins/smile.gif


a thought on the tab temperature reading.
that would read the "center" of the battery better, and be GREAT designed into the charger itself, no thermal probe to deal with, just stick the battery in.
BUT :-(
there can be a GAP between the electrolyte roll thing , and the tabs. so it would still read off the metal, but it might have less thermal contact to the part were trying to measure.
on the other hand, the anode wire is right behind the top tab (often) and it comes from the center of the cell ???

oh hey, how about a FOAM at the bottom of the battery tray, with the themister attached, the foam will keep the thermister tight against the battery, and no action from the user required. as sort of spring loaded thermister holder.


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## lasercrazy (Jun 22, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

2 of my 2400mah titanium batteries get really hot and can sometimes take 7-10 hours @500-700mah to show charged. Seems kind of odd and dangerous, not to mention sever overcharge and reduced life. This happens in both my vanson and ansmann chargers.


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## VidPro (Jun 22, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

[ QUOTE ]
*lasercrazy said:*
2 of my 2400mah titanium batteries get really hot and can sometimes take 7-10 hours @500-700mah to show charged. Seems kind of odd and dangerous, not to mention sever overcharge and reduced life. This happens in both my vanson and ansmann chargers. 

[/ QUOTE ]

when they have been on the charge for 7+ hours, and you measure the current (WITH a SEPERATE meter) , is it still 500+ ma?

there is some waste, meaning you do have to put in more than you get out.
and a primo charger might be slowing down, or stopping temporarily if it saw heat.

do you have a way to put a sepearte meter in there to read the actual current the battery is getting?


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## MrAl (Jun 23, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

HI again,

VidPro:
The 'time' it takes to get hot isnt quite as important
as the fact that it does get hot...because this time
depends on the cell capacity, cell size, and charge rate.
For a 2000mAh AA cell at 1 amp it probably takes about 5 mins
to reach a temp where it's getting hot (after full charge
has been reached) but at 2 amps it gets hot much faster.

A tiny thermistor should work the best because it doesnt
take much heat energy to raise it's temperature.
I thought if it was on top it would work best because
heat rises. This doesnt mean it cant be on the 'bottom'
when the cell is installed in the charger, then turn the
charger upside down.

Foam has elastic properties that cause it to deform
permanently over time so i'd use a spring or something.


Take care,
Al


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## VidPro (Jun 23, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

but if the charger is upside down, then the heat rising wont get off of the batteries as quickly. it might be reduced slightly. unless the batteries are suspended in air (hmm another idea)

heat rises in air, which could negativly effect the thermal probe with turbulent convection currents, heat isnt going to move upward in the battery as well as it does in the air. 
the top shouldnt be hotter than the bottom, even if the heat from the bottom is going past (via convection) the top to get out.
usually the top of the cells are cooler, because the air gets to them most (i sometimes roll them over)

Reverse that, and the bottom or the lower part of the batteries wouldnt want to be even hotter because some thermal probe was blocking convection and normal airflow.

(just tell me to shut-up anytime 

so its a toss up, IF you were going to use the themal probe to not only discover the cutoff, but somehow also use it for thermal managment, then it wouldnt matter how much you blocked heat flow, you could even manage the temps for ANYTHING the user did with it, putting the cover on, putting it in a drawer, the sun blasting it from a window, or high ambient temperatures. 
course i wouldnt want to be the one who had to do the programming 

if you wanted to see more heat, it seems to occur where the most blockage of the air is, on some of my stuff the cells lay FLAT (horizontal) and the bottom is plastic already touching the cells, the top is more exposed and cooler.
(no big heat loss in sticking a probe there)

do we want to read the hottest place, or the coolest place on the battery? umm probably the coolest, because when it does the overcharge heating , that place will get just as hot as the other, and have the largest thermal change.
(so the probe should be on the top, when the bottom is a heat trap)

isnt there foam on the thermal probes for batteries already, to insure good contact with the battery, and reduced exposure to the ambient air?
the only thermal probes i have seen, have 2 sides to them, not that it made that much difference that the heat was only on one side. 
to me, the probe needs to make excelent contact to the battery only, and insulated to anything else.


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## lasercrazy (Jun 23, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

[ QUOTE ]
*VidPro said:*
[ QUOTE ]
*lasercrazy said:*
2 of my 2400mah titanium batteries get really hot and can sometimes take 7-10 hours @500-700mah to show charged. Seems kind of odd and dangerous, not to mention sever overcharge and reduced life. This happens in both my vanson and ansmann chargers. 

[/ QUOTE ]

when they have been on the charge for 7+ hours, and you measure the current (WITH a SEPERATE meter) , is it still 500+ ma?

there is some waste, meaning you do have to put in more than you get out.
and a primo charger might be slowing down, or stopping temporarily if it saw heat.

do you have a way to put a sepearte meter in there to read the actual current the battery is getting? 

[/ QUOTE ]

I have no way to put a meter between the cell and charger since I don't have a meter anymore. It's only those 2 that do it, no matter which bay on either charger I put them in.


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## VidPro (Jun 23, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

do you know the "time" cutoff for the charger? is it ending only after time, and missing the Vdrop thing?

do the still have all thier capacity?

it sounds like they are overcharging, and might be total toast by now. BUT only somebody with one of those chargers would know for sure.

the vanson is that 10x single charger? is its rate that hign? my knockoff version of a 10x is slow, takes 10-12 hours to FULLY charge 2300-2500s.


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## SilverFox (Jun 24, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Hello Reviewum,

Keep in mind that it usually takes a few "conditioning" cycles to bring NiMh cells up to the point where they will charge properly.

The first charge on a NiMh cell should be a timed charge (ideally at 0.1C). You need to determine the charge rate of your charger and the capacity of the cells you are charging and keep track of the charge time. When the time is up, pull the cells from the charger. Don't wait for the green light.

By the third cycle, the cells should be "conditioned" and the charger should be able to be "trusted" to properly charge the cell.

Tom


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## SilverFox (Jun 24, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Hello Sub Umbra,

I noticed your comments when you first posted about the problems you were having with bulged cells. It slipped my mind to comment on your problem.

Recently I have re-discovered that the end of charge signal is difficult to determine at low charge rates. 

The best charge rate to determine the end of charge signal is 0.5C - 1.0C. That means you would need a charger capable of about 5 amps per cell...

Your 700 mA charge rate works out to about 0.08C. At that rate, you may want to consider it a "timed" charge and terminate the charge after a certain time has passed.

By the way... It was really quiet yesterday and I was wondering what the sucking noise was... /ubbthreads/images/graemlins/evilgrin07.gif /ubbthreads/images/graemlins/smile.gif 

Tom


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## SilverFox (Jun 24, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Hello Al,

The information I have on charging NiMh cells suggests terminating the charge when the cell reaches a temperature that is 20F to 40F above ambient. This is for a charging rate of 1C.

This comes from the RC people.

Tom


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## STEVENT6 (Jun 24, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Months ago I could have went insane trying to figure out what would be a decent charger. After a lot of reading I concluded that the Accupower20 would be pretty good all around charger. Right?? So may I ask what is a good charger that doesn't damage cells? In other words one that charges them properly to get a good life span?


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## vcal (Jun 24, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

I've used a charger from CCRane ($35.) for many years. It has _never_ made batteries so hot as what's been described in the above posts. There are quite afew chargers (above $20.) that don't mistreat batteries.

My rule: if any charger is making batteries so hot that I can't hold them in a closed fist comfortably, I get rid of it! /ubbthreads/images/graemlins/icon15.gif


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## MrAl (Jun 24, 2005)

*Re: Charging NIMH Batteries - Getting HOT in Charg*

Hello again,

VidPro:
Yes turning the charger upside down might cause other 
problems which would have to be dealt with no doubt.
I was going to try a flip up arm with a thermistor
mounted underside.

Silverfox:
Ok thanks. I might end up trying the thermistor method
at some point because i really dont like the charger i 
have now.


Take care,
Al


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