Battery Can not be charged

[Parsons]

I am a newbie and built a battery bank, 4X 3.2v 78ah Lifepo4 Lishen Prismatic with a JBD 4S 100A BMS. However, today, I noticed that it will take forever to charge my battery. The battery is charged at 1.3a, instead of 10a. btw, I am using NOCO GENIUS10, a 10A Smart Charger. Please see the screenshot here,
Any advice would be greatly appreciated. Thank you!

 

[time2roll]

Cell 2 is much higher on charge than the others. Need to use a resistor to bleed the voltage down from 3.491 to the lowest cell at 3.313 volts. Then restart charging.

Note the max charge says 9.87 amps so the NOCO-10 was operating fine and charging at max. The NOCO dropped to float when the BMS shut down the battery charging due to #2 cell high voltage.

An incandescent bulb. rated 6 or 12v can be used to bleed down the cell. Just clip it across cell #2. No need to disassemble.
A 3 ohm 5 watt resistor would work also. Or possibly attach an active balancer to speed up the process. The BMS is very slow and is made to fine tune the balance more than doing the bulk balance that is needed with these cells.

 

[Parsons]

Thanks for your quick reply. I really appreciate for your suggestions. btw, is the #2 cell bad? Do I need to replace this cell? or is there anything I can do on BMS settings to avoid this situation? Sorry for the questions. Thank you so much.

 

[rodrick]

The cell is probably fine just a higher state of charge bleed it down with the other like time to roll said and keep a eye on it for a while

 

[time2roll]

No I would not call #2 bad. The cell just arrived at a higher state of charge. Often cells are placed in parallel and charged to 3.650 volts to equalize them before assembling the battery with BMS and cells in series.

 

[Parsons]

Great. Nice to learn. Thanks!

 

[Parsons]

It looks really weird for me. When I was trying to discharge the battery, #2 cell showed very low voltage. Do I still need to bleed down the voltage? Thank you!!!

 

[rodrick]

No you have bleed the cell to low you need to get it to the same voltage as the others

 

[Parsons]

Thanks

 

[time2roll]

OK you went too far. Put the charger back on and again start bleeding the top cell to the lowest. Do not continue unattended. Do not discharge the high cell lower than the lowest. If you must step away stop the charger and stop the discharge of the high cell.

Need to use a resistor to bleed the voltage down from 3.491 to the lowest cell at 3.313 volts. Then restart charging.

 

[MisterSandals]

btw, is the #2 cell bad? Do I need to replace this cell?

Cell #2 appears to be lower capacity than the others. It will hit cell over volt first when charging and cell under volt first when discharging.

If top balancing does not "fix" this, you can choose to live with the narrowed voltage range (maybe acceptable?) or replace the cell.

You'd need to observe the battery voltage where cell 2 voltage starts to diverge (it will be a quick divergence and easy to see) and charge only to that battery voltage.
I'd guess ~13.6V which with sufficient absorb time will be mostly full.

 

[Parsons]

OK you went too far. Put the charger back on and again start bleeding the top cell to the lowest. Do not continue unattended. Do not discharge the high cell lower than the lowest. If you must step away stop the charger and stop the discharge of the high cell.

Need to use a resistor to bleed the voltage down from 3.491 to the lowest cell at 3.313 volts. Then restart charging.

When I stop charging, the cell voltage readings are very similar. Once discharging, #2 drops quickly.

 

[Parsons]

Cell #2 appears to be lower capacity than the others. It will hit cell over volt first when charging and cell under volt first when discharging.

If top balancing does not "fix" this, you can choose to live with the narrowed voltage range (maybe acceptable?) or replace the cell.

You'd need to observe the battery voltage where cell 2 voltage starts to diverge (it will be a quick divergence and easy to see) and charge only to that battery voltage.
I'd guess ~13.6V which with sufficient absorb time will be mostly full.

View attachment 151818

Yes Sir, that's what I saw so far.

 

[time2roll]

Was the battery able to charge with all cells above 3.450 volts? This would be very close to full charge.

Assuming this full charge was reached.... was it then the #2 cell dropped voltage very fast? Yes if that was the sequence that #2 is in poor shape.

 

[mikefitz]

You may have discharged the cell too much.
When 'bleeding down ' a cell, do thus with the battery under charge , ( cell volts higher than 3.4 volts) and monitor the cell volts. Apply the bleed load across the high cell initially for no more than several seconds whilst observing the drop in cell drop, they are small capacity cells so the voltage may drop quickly.
.

 

[Substrate]

One goal at a time! In this case actually finishing a top-charge and balance. -grin-

It takes TIME for those bms bleeder resistors to do their job on a bank with a large initial balance variance. - this can take many cycles and I noticed you have zero cycles tracked. Once that's achieved, then you can do your capacity measurements.