I just charged some AA NiMh Titaniums, when I removed them from the charger I almost got burned! I measured the temp of the freshly charged batts, got 130 F, or 50 Celsius! They where to hot to hold! Havent had this happen before, Is this normal? I have had a few of them leak on me before (not the ones I charged), but never get this hot!
should they get so hot?
- Thread starter FlashSpyJ
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How long did you leave them in the charger to charge?
You typically only charge them till they are full and not over charge them.
Are you using a cheap charger? If so, then cheap chargers can't tell if the battery is full or not. So they just keep charging and the battery gets very hot. Hot batteries mean these are already fully charged but are still being charged.
You need to either get a smarter battery charger that can tell when batteries are fully charged and shuts down automatically
or
Watch the charger and touch the batteries every so often. Once you feel the batteries getting hot, stop charging as that means the batteries are fully charged.
SilverFox
Flashaholic
Hello FlashSpyJ,
We need some additional information...
What capacity are they?
Was this the first charge on them?
What is your chargers charge rate?
Did you happen to check their voltages before charging?
Tom
We need some additional information...
What capacity are they?
Was this the first charge on them?
What is your chargers charge rate?
Did you happen to check their voltages before charging?
Tom
The battery's capacity are 1800mAh, I think that it was their third or forth charge. The charger is a 4 bay AA/AAA rapid charger, charging current 2A max.
I have two exact same chargers, in one I charged two batts, and 4 in the other. All of them got hot, around 130F. I just dont remember if they got that hot in the first charges. When removing them from the charger, just after the leds on the charger turns green, you almost cant hold them.
I have two exact same chargers, in one I charged two batts, and 4 in the other. All of them got hot, around 130F. I just dont remember if they got that hot in the first charges. When removing them from the charger, just after the leds on the charger turns green, you almost cant hold them.
I didn't measure the voltage before I charged them, I use them in my 2D mag ROP, I run the high bulb, and I think it just started to dim a little when I took them out to charge.
I never leave home either when charging batteries. Had the charger on my desk beside my computer, sat there the whole time, didnt take more than an hour to charge them. I touched them periodically to feel if they got hot. But didnt feel the heat fully before I removed them from the charger.
I never leave home either when charging batteries. Had the charger on my desk beside my computer, sat there the whole time, didnt take more than an hour to charge them. I touched them periodically to feel if they got hot. But didnt feel the heat fully before I removed them from the charger.
SilverFox
Flashaholic
Hello FlashSpyJ,
My thought was that they might be new cells that have been in storage for some time. If this were the case, the electrolyte may have migrated slightly within the cell, causing hotter than normal temperatures during charging.
If you have the capability, you may consider doing a discharge, followed by a 0.1C charge for 16 hours. If you can't do that, you will have to get some cycles on the cells. Keep an eye on the last few minutes of the charge and pull the cells when they start to heat up.
If they are older cells, heat usually means higher internal resistance, so they may be wearing out, however, this does not sound like it's the case here.
At any rate, for the time being you will have to become "smarter" than your charger. If your charger had an option of different charge rates, you could select a little slower rate, but that does not seem to be an option.
Be advised that until you get this straightened out, you should limit the use of the cells to around 80% of the usual runtime. Until the cells can go through a full recharge cycle without getting too hot, you run the risk of your cells being out of balance with each other. In a multi cell application, cells that are out of balance run the risk of reverse charging.
Tom
My thought was that they might be new cells that have been in storage for some time. If this were the case, the electrolyte may have migrated slightly within the cell, causing hotter than normal temperatures during charging.
If you have the capability, you may consider doing a discharge, followed by a 0.1C charge for 16 hours. If you can't do that, you will have to get some cycles on the cells. Keep an eye on the last few minutes of the charge and pull the cells when they start to heat up.
If they are older cells, heat usually means higher internal resistance, so they may be wearing out, however, this does not sound like it's the case here.
At any rate, for the time being you will have to become "smarter" than your charger. If your charger had an option of different charge rates, you could select a little slower rate, but that does not seem to be an option.
Be advised that until you get this straightened out, you should limit the use of the cells to around 80% of the usual runtime. Until the cells can go through a full recharge cycle without getting too hot, you run the risk of your cells being out of balance with each other. In a multi cell application, cells that are out of balance run the risk of reverse charging.
Tom
RoyJ
Enlightened
Silverfox, do you know how much damage would have been done in such a case?
I over-charged an 8-AA pack using a complete dumb charger - 12V 1000ma adapter (guess I wasn't that smart either). The end result was similar - cells hot to touch and a voltage of 11.59V. Normally, when I keep a close eye on things, it'll reach about 12.05V or so before I shut it down.
I've done 3 cycles since, and the pack refuses to charge over 11.7V. It'll just peak around there and get hot. I'm assuming I've lost about 40% of the capacity permanently.
Since then, I've bought a "universal smart charger" off ebay, but it's not here yet.
I over-charged an 8-AA pack using a complete dumb charger - 12V 1000ma adapter (guess I wasn't that smart either). The end result was similar - cells hot to touch and a voltage of 11.59V. Normally, when I keep a close eye on things, it'll reach about 12.05V or so before I shut it down.
I've done 3 cycles since, and the pack refuses to charge over 11.7V. It'll just peak around there and get hot. I'm assuming I've lost about 40% of the capacity permanently.
Since then, I've bought a "universal smart charger" off ebay, but it's not here yet.
SilverFox
Flashaholic
Hello Roy,
The only way to determine how much damage has been done is to compare discharge graphs of before and after. Sometimes capacity will remain the same, but the voltage under load will be reduced. Other times both will drop off. Finally, in some cases the self discharge rate will increase.
Tom
The only way to determine how much damage has been done is to compare discharge graphs of before and after. Sometimes capacity will remain the same, but the voltage under load will be reduced. Other times both will drop off. Finally, in some cases the self discharge rate will increase.
Tom
