Checking amps between cells while top balancing yields interesting results

OM617YOTA

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May 27, 2021
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I'm top balancing my 280ah lifepo4 pack, and on a whim, thought to check the amperage between cells. Starting at the wire from the power supply and moving down the line, it was easy to see what cells were soaking up amps, and where the amperage dropped to essentially zero. Current between cells 1-4 was nil.

My thinking is that cells 1-4 are charged, and that cell 6 is nearly so. Does this seem reasonable?

I can't get my clamp meter around the bus bars to check the negative side, but if folks think it's worth the trouble, I'd be willing to make more wire jumpers so I could test them.
 

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time2roll

Photon Sorcerer
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Mar 20, 2021
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2,424
Good time to verify the voltage is equal between the cells. Measure direct on the cell terminal, not the stud, not the wire.
 

OM617YOTA

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May 27, 2021
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119
Voltage varies by about 1/10th of a volt while charging, higher among the higher numbered batteries, and evens out while resting and in parallel. I expect that to even out, including while charging, as the top balance finishes and they all get close to 3.65v.
 

Ampster

Renewable Energy Hobbyist
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May 3, 2020
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Kenwood, California
I would call those currents eddy currents that @OM617YOTA is measuring, That only happens initially when the SOC is uneven when in parallel. Once the cells were balanced my guess is the current should be the same throughout the pack if you staggered the negative and positive on opposite ends of the parallel pack. It should not be different between negative or positive.
 
Last edited:

Roswell Bob

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Dec 5, 2020
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Warner, NH
Have you connected the power supply wires at opposite corners? Red one corner black the opposite diagonal corner. If you connect them to one end you will see exactly what you are seeing. What Mr Ampster already said.
 
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