Worst cell lower voltage on top balance

[Delphinus]

I'm testing my batteries with a full charge and discharge and had this happening during absorption that I set to 55.3V I have an average of 3.466V per cell.

The worst cell reach 3.46V and start to drop voltagem during balance ending with 3.34V, since is the worst cell and has a higher voltage when balance start at 3.4V it discharges to increase voltage of the others but during the 1 hour absorption it should balance to the voltage of the others when their internal resistance increases.

The BMS is a JK and if I charge the cell independently with an RC charger it will go to 3.6V without problems.

Can anyone let me know what is happening? Do I have a bad BMS port or bad cell, already tested bus bars, balance cables and all are fine.



A normal cell has 3.48V do this during top balance set to 3.4V, voltage increases.

 

[Bob B]

We'd need to know what the other cells voltages and pack voltage while this is happening. It looks like it is simply drawing current off that cell to balance.
With an active balancer, another cell should be increasing.

 

[Delphinus]

I had an error in the voltage of cell 1, all other cells were arround 3.48V and the pack with 55.45V

My JK have an active balancer of 2A, the drawing current happens when the cell 5 pass 3.4V, and by the grafic absorption ends at minute 3H13 and from there 1H equalization starts, and during that time cell 5 should be the one who receive more A to increase voltage since is with 3.35V and others with 3.41V and the inverse happens.

I believe that the internal resistance of the cell is higher but I borrow my meter and can't test it.

In other packs the worst cells increase the voltage during equalization.

I would like to see in the market a BMS that balance by the higher voltage on charge and lower on discharge that will fully equalize the cells.

 

[Delphinus]

Just discharge the cell 5 the capacity was not far it's an EVE LF105 and from the 3.34V to 2.5V got 102.07Ah. Then I choose cell 5 that had 3.4266V and got 104.54Ah.

I fully charged this cell 5 five days ago and after fully charged by the inverter it accepeted 8.82Ah this means that overtime the delta will increase.

 

[Berseker]

How did you resolve this, seems am having a somewhat similar issue

 

[nikbok]

Any explanation on this problem? I'm having same issue with one cell in pack.