Shorted NiMH Battery damage - RCCanada - Canada Radio Controlled Hobby Forum
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Old 09-08-2004, 06:26 PM   #1
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Shorted NiMH Battery damage

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Battery is a NiMH 2300mah 7cell pack AA's

I have been given a brand new battery pack to test for damage from a fellow flyer. By brand new I mean this pack was soldered together by me and was then charged and used about 4 or 5 times. After being charged the last time the battery was unplugged from the charger by having the banana plugs pulled out of the chargers out puts and not disconnected from the chargers lead. It was left over night like this and in the morning was found to be very hot and the exposed ends of the banana plugs were touching together creating a short. The battery was very hot at the positive end of the pack or where the red positive wire is soldered to the positive end of the battery. The rest of the battery was warm but not anything like the positive lead location.

I have tried to discharge/charge the battery on my Triton charger and it will not take anywhere near the amount of mah it did before and on discharge it is not giving the voltage it should. Also the same location that was very hot after the short was very hot again.

I am about to disassemble the pack and try charging and discharging each cell. Is there anything else I should do to this pack before I disassemble it or after for that matter? How should I go about charging and discharging each cell? What charge and discharge rates?
I have never had to do something like this with a pack before. I expect that some of the cells will not be salvageable, but I am hoping that some will be able to be used to make another pack with some new cells. If some of the cells test out to be ok, then is it a good idea to replace the cells that have been damaged and make a new pack or are all the cells not reliable or useable regardless of the test results?

Just to avoid some of the comments that it was my soldering job that caused the problems or that the problems originate from a home built pack, I have soldered many packs together before without problems and this pack was functioning fine before the probable short. Not that my soldering is perfect but I do not think that in this case it has anything to do with the problems experienced.

Thanks in advance for the replies.
Ted LeBlanc
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Old 09-08-2004, 07:57 PM   #2
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As you have discovered, unplugging banana plugs to disconnect a battery from a charger is a bad idea. Leaving the banana plugs in and using an intermediate connector is much safer.

NiCds don't mind being fully discharged. NiMHs are a different story. They will probably all be degraded. I'm not sure it is worth trying to salvage cells out of your pack.

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Old 09-08-2004, 10:13 PM   #3
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Chances of any undamaged cells is slim, besides, the chances of new cells being a match for any survivors is even slimmer.
I think this pack is HISTORY
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Old 09-09-2004, 01:50 AM   #4
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Do you have a Wattmeter, be a good (see great! ) way to check each individual cell.

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Old 09-09-2004, 03:07 AM   #5
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Sorry about your pack. Like Rob mentioned, NIMHs don't like being fully discharged. You probably have degraded your pack. You could pull it apart and see if you can salvage anything but you could only make it into a smaller pack. Any new cells added to the pack wouldn't match very well with the older cells. More that likely it is RIP (Recycle it Properly)


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Old 09-09-2004, 06:53 AM   #6
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Thanks for the replies guys. Geof, I do not have a watt meter, however it is one of the next purchases I am going to make. How would a watt meter help me in diagnosing the damage to this pack?
Ted LeBlanc
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