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JBD Cell Reading Spike

Seifer

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Jan 2, 2021
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Hey Guys, having an issue with my JBD 120A 4S. When charging one cell reads higher than the others, genrally around 0.02 amps when charging at less than 10a. However when charging at higher than 15a cell #3 takes off to the point where its constantly hitting the over charge limit (3.55v). As soon as it hits the limit charging stops and the cell drops back to 3.35ish with the rest of the cells (at rest theres no difference). When charging resuems the cycle continues. Thinking it could be a dud cell I tried swapping around cells, and bus bars; bascially changed up the pack however its the same #3 position cell on the BMS that spikes which leads me to think its the BMS and not the cells themselves. Tried replacing connector on the #3 cell but no difference in reading. ANy ideas on what else I can check before binning the BMS? Ive got no other BMS's to test the pack with.
 
When charging one cell reads higher than the others, genrally around 0.02 amps when charging at less than 10a.
Do you mean 0.02 amps or 0.02 volts?

However when charging at higher than 15a cell #3 takes off to the point where its constantly hitting the over charge limit (3.55v).
The HVD should be set to 3.65 volts.

As soon as it hits the limit charging stops and the cell drops back to 3.35ish with the rest of the cells
Hopefully that is with a load on the cells.

ANy ideas on what else I can check before binning the BMS? Ive got no other BMS's to test the pack with.
What cells do you have? Did you parallel top balance them?
 
Yep meant volts.
Ok regarding the HVD, but largely irrelevant as the cell shouldnt be anywhere near that level in the time its taking to get there (a few minutes of charge), or even 3.55 for that matter.
That's with no load.
Lishen 272, theyre top balanced. Again the issue isn't with the cells, it doesnt matter in what order I put them, the cell thats in position 3 is always the runaway cell leading me to believe its a BMS issue, not a cell issue.
 
Have you verified the cell voltage with an independent voltmeter? I understand what you're saying about the problem sticking to the BMS balance lead #3, but the check with the voltmeter is needed to confirm what the BMS is reading.

If you can check the voltage at the connector where the balance leads plug into the circuit board that would help eliminate the wire as the problem.

Otherwise, it does sound like a bad BMS.
 
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