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Help with one cell rising more than bms can keep up on a charge.

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brandonboosted

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Jul 30, 2021
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I just got my second 24v 280ah battery together and I am using a jibaba bms and cell “6” when charges just slowly keeps rising until it hit my bms max cell voltage. Also the cell it’s calling cell 6 is really cell 3 and measures to the over voltage the bms app is saying. Is my cell bad? Possibly a bad bms? It’s worth noting as well this bank is parallel with another 24v 280ah bank and I have tried to run the batteries separately and still have the same issue. Any help is appreciated, thank you.
 
Did you do a proper top balance as part of the commissioning process?
 
brandonboosted said:
Also the cell it’s calling cell 6 is really cell 3 and measures to the over voltage the bms app is saying. Is my cell bad?
Click to expand...
First I would double check your BMS and it's wiring before reaching any conclusions. Even if you quadruple checked connections something is not right. Can you unplug the BMS harness and sequentially step through the voltage at the connector? You may need a narrow probe like a paper clip or small wire.
 
FECFA967-92A1-4006-992F-5703BEB19732.png26.7, this picture it was discharging and when doing so the voltage evens out but as soon as any charge is applied cell 6 just creeps to 3.65
 
If it were me I would change the cell balance profile in I may even bleed off some by hand from that cell. I would also go through all the connections, buss bars and bms leads. Checking for pour connections. Maybe swap bms. Maybe swap cell. See if problem moves.
 
Hook a light bulb to the High cell to drain it down. 1156 automotive lamp. drain it down some. charge up the pack. when all are the same voltage drain the whole pack down to 20 SOC and see if that cell is lower than the rest. That's how I check them. If the cell is lower than the rest this would indicate a weaker cell. Does this make sense?
1156-gc.jpg
 
brandonboosted said:
Yes, also it’s worth noting I quadruple checked my connections
Click to expand...
It doesn’t appear that your top balance was as successful as you think it was.

Can you summarize the process you used?

Also, if you directly check cell voltages eith a multimeter measures directly on the aluminum cell terminals, how do those voltages compare to the voltages being reported by your BMS?
 
brandonboosted said:
I did that as well I’m not sure why it’s saying it’s cell 6 when the cell is 3 the app must have them ordered in reverse
Click to expand...
Do you happen to have a good pic of your battery wiring?

I would be wildly surprised that a BMS app would have them reversed.

You do know cell #1 is the negative end of the battery, right?
And wire/pin 1 comes from negative end cell, pin 2 from positive on negative end cell.
 
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Cell 6 reporting as cell 3 could just be looking at the problem from the wrong end.

As @740GLE suggested try moving the cell and see if that sheds any light on the subject?
 
Entirely possible that's a mismatched cell, too. My first pack was seven 230ah cells and one higher ah cell. Even after a top balance, that one cell didn't track with the others. OP may have one lower ah cell.
 
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