Following production of 100AH battery packs, we have found a number of latent 'features' that appear to be related to the cell balancing within the BQ78PL116 management chip. The cell balancing seems to terminate on some packs prematurely, often when the cell voltage differential increases beyond 400mV, thought his varies between packs. This condition often leads to a cell over voltage during charge, and always appears to occur on cell 2 or 3 of a four cell stack. At the time of the balancing termination,there are no active warnings or safety conditions. As far as the pack parameters are concerned:
- The cell imbalance fail voltage is set to 1000mV and disabled (time set to 0).
- The cell balancing algorithm is set tot the default open circuit balancing.
- The cell chemistry used is LiFePO4.
- Typical charge / discharge current: 6 / 15A
We have noticed that even when idle following the cessation of charging and the clearing of safety flags related to the over voltage condition, cell balancing does not resume.
Is there a reason that balancing would stop prematurely?
Is there a reason that cells 2 and 3 appear to always be the cells that are at a higher state of charge?
Which pumping algorithm performs best with the LiFePO4 cell chemistry?
Given the capacity of the cells, what pumping current is recommended?