Case Study: Setting up the MAX17205G fuelgauge evkit with the GUI, customer observed after some cycling of the two cell battery pack, they were not getting cell balancing.
Analysis:
Cell balancing only works when end of charging is detected. This requires VFSOC > FullSOCThr, and current < ICHGTerm * 1.25. In the logs, I can see VFSOC only reaches ~50% and FullSOCThr is 80%. In this setup, it will never balance.
The intention of the function is to keep battery cells balanced when they start close to each other. In this setup, one cell is near 50%, and the other is near 100%, and in such a setup, the pack should be declared dead, and not charge any more.
Please ask the engineer to only have ~5-10% difference in the battery cells and repeat the test.
For cell balancing to occur, the following two conditions must be met;
- The voltage fuelgauge state of charge (VFSOC) > FullSOCThr
- 4x ICHGTerm<AvgCurrent<0xFFF8
Based on the register pictures the customer sent, VFSOC is lower than expected. If this value never gets above 80%, this could explain why cell balancing is not occurring.
In order to debug the VFSOC register, you will need the data log from the EVKIT. The software can log all the register values into a CVS file. The customer can find this feature under File->Start Data Log.