Cell always out of Balance

[Jaco Slabbert]

I have a 15 cell battery less than 1 year old. One cell is out of balance. At the top end, if the other cells is above 3.5, that cell will only reach 3.45. On the lower end, if the other cells is still above 3v, the problem cell is already on 2.5 volt and the BMS shuts down.

The pack is rated at 100 Amp Hour, but I only get 87 Amp hour. I already send it back to the supplier. They send it back and said nothing wrong.

Please advice.

 

[time2roll]

If the battery can be opened... that individual cell could be boost charged to match the others.

Otherwise the BMS has to balance the cells and could take a long time. To speed the process increase the charging voltage to reach 3.60 on the highest cell and hold the voltage for an hour each day.

If a solid 100 AH is needed for the system a second battery is the immediate solution.

 

[MisterSandals]

At the top end, if the other cells is above 3.5, that cell will only reach 3.45.

If possible, maintain the voltage at this level so the 3.45V battery can absorb and catch up.
(14 x 3.5) + 3.45 = 52.45V

Is there a reason in particular why you made a 15S battery and not the standard 16S battery?
What charger do you have that accommodates this voltage?

 

[mikefitz]

Your supplier is avoiding the issue. You have a problem cell with reduced capacity compared to the others. Any attempt to top balance will not improve things much. The battery capacity is limited by the low capacity cell.

 

[Lt.Dan]

Is this a LiFePo4 battery, or a different flavor of Li-Ion? Could make a huge difference

 

[Jaco Slabbert]

Is this a LiFePo4 battery, or a different flavor of Li-Ion? Could make a huge difference

Lifepo 4. It is now returned to the supplie. They agreed to replace the faulty cell.