JRP3
Hyperactive Member
No, balancing is actively managed by the BMS. Basically they either bleed off charge from higher voltage cells through a resistor or they use charge shuttling and bleed off charge from higher cells and send it to lower cells. I think with the NCA chemistry the charge slope is steep enough that they could balance anywhere along the charge slope but I think it makes the BMS unnecessarily complex to do so. In the DIY community those who top balance use a BMS that is set to bleed off charge at a specific voltage using specific circuitry for that voltage. Because of the flat middle SOC of LiFePO4 cells there is no point in trying to balance in the middle since two cells at the same voltage can have different SOC. With NCA voltage has a close correlation to SOC through the entire charge curve. My guess is that Tesla felt an occasional balancing near the end of a full charge would be enough since cell drift should not be that significant with good quality closely matched cells.