LiFePo4 Balancing vs. Charge Rate

. Why Passive-Balancing LiFePO4 Batteries Have a .2C Recommended Charge Rate One of the most common misconceptions about LiFePO4 batteries is the belief that a battery’s advertised max charge rate and its balancing capability are the same thing. They’re not. A passive-balanced battery may be perfectly capable of accepting a 0.5C to 1C, charge rate from a safety standpoint. The cells don’t suddenly burst into flames because you charged them at 1C. In fact, many LiFePO4 cells are quite happy to accept high charge currents through much of their state of charge range. The problem begins when the battery approaches full charge hence the .2C recommendation. What does a Passive Balance Circuit look Like? This is what a typical 4S drop-in balance circuit looks like. This BMS balances at 30mA and each of the four balance circuits uses doubled up surface mount resistors. When the balance chip says a cell is getting too high a voltage, the mosfet switches turn on so the resistors can slow…