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How to check individual cell volts for NiCd or NiMh packs

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How to check individual cell volts for NiCd or NiMh packs

Old 06-18-2020, 05:45 AM
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Sti491
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Default How to check individual cell volts for NiCd or NiMh packs

Hi all. I have a battery checker that will tell me individual cell voltages for a LiPo, LiFe, etc., but I canít seem to find one that show a 4 or 5 cell NiCd or NiMh Packs individual cell volts. It only shows the total pack volts.

is there a tester that will show each cell?
Old 06-20-2020, 04:12 PM
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init4fun
 
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Originally Posted by Sti491 View Post
Hi all. I have a battery checker that will tell me individual cell voltages for a LiPo, LiFe, etc., but I canít seem to find one that show a 4 or 5 cell NiCd or NiMh Packs individual cell volts. It only shows the total pack volts.

is there a tester that will show each cell?
That is not possible unless the battery pack is specifically wired for monitoring each cell . You will notice that on your LIPO , LIFE , etc packs the balance lead has several wires or more depending on the number of cells , whereas the NIMH has only the two wires leading to it's power connector (with no separate "balance connector" to access each cell separately) . For someone who builds their own packs it would be a simple matter to provide the wires between the cells that would be needed , but as of yet I haven't seen any commercially available NIMH packs with the needed wiring .
Old 06-21-2020, 03:05 AM
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Thanks. After further research I believe the reason for this is nickel batteries self balance during charging better than lithium.
Old 06-23-2020, 02:09 PM
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Thanks. After further research I believe the reason for this is nickel batteries self balance during charging better than lithium.
No, they do not "self balance". No multi-cell battery pack (NiCad, NiMh, Li, PB - etc) "self balances".
The main reason there are no balance leads on a NiCad / MiMH pack is that NiMh or NiCad cells will not burst into flames if they are over-charged (like a Lithium cell will). They will heat up, but not catch on fire and burn down the house.
I've used NiCad for decades and wish they had balancer ports on them. The only way to gauge the health of a NiCad / NiMh pack is to put a volt meter on each individual cell in the pack every once and a while to make sure the cells are all within the same range.
You can easily have a 5 cell NiCad pack that reads an expected voltage on the main discharge lead while 1 cell in the pack is pretty much close to dead.

The death mode of NiCad / NiMH when being over-charged is to heat up to a certain point (hot to the touch but not to the point of combustion) where their internal chemistry starts to break down. As their chemistry breaks down, their internal resistance becomes so high, they stop passing charge current and cool off again. But, at that point, they are now dead.
You might say the NiCad "fail safe" is to get cold. There is no "fail safe" for LiPo.

Last edited by ticedoff8; 06-23-2020 at 02:21 PM.
Old 06-24-2020, 03:57 AM
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Appreciate the education. Makes sense. Thanks!

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