Odd Charging Behavior - LGABB41865

bglaplante

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May 3, 2021
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Hi, I'm working on building up a larger pack from some medical packs which are 3S2P with LG LGABB41865 cells. The packs physically look new. Typically the cells are at 2.5 volts or better. To check them out I've connected my Liitokala tester so that it is charging / testing 1 cell pair at a time. Since we have two 2600 mah rated cells in parallel, we'd expect around 5000 + mah on the fast test mode (where the tester tests the current required to charge.

the odd thing: very quickly the cells go up in voltage, and will exceed 4.1 volts while having only accepted about half the rated charge. In fact I'll see around 2600 mah, and 4.2 volts. BUT, it continues at a steady 4.2 volts and then comes up to near the rated to total storage! I've never seen so much current be absorbed with so little of a voltage increase. Oh, I'm using the 1000 mA setting.

I'm concerned as for my purpose I'll cap the max voltage to 4.1 ...

Why would I see this odd behavior? I'm seeing this on 3 different cell pairs on two different packs (100% consistent so far).
 

floydR

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Aug 23, 2017
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1,062
Are the packs disassembled down to 2p units?
later floyd
 

bglaplante

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May 3, 2021
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No, they are still welded up as 3S 2P, but the BMS has been removed. So no way I can see that the extra cells "hanging off the end" would have any effect.
 

Wolf

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Sep 25, 2018
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That my friend is the purpose of CC/CV. You see as long as the cell sits at ≈4.2V and accepts a certain amount of amperage it will continue to push that current. As the voltage tries to increase the charger will cut back on the current to maintain the voltage threshold and I believe the LiitoKala has a termination current of ≈100mA.
Wolf
 

bglaplante

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May 3, 2021
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Right... if there is substantial internal resistance the voltage will quickly go up the voltage limit. i wouldn't expect substantial internal resistance with two cells in parallel. Unless cells that have been sitting for a long time have higher internal resistance on the first charge?
 
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