The difference between active and passive battery balancing

The battery management system BMS needs to have a balancing function to coordinate the inconsistency of the battery cells. Balancing is divided into passive balancing and active balancing. Simply put, active balancing is to transfer electric energy, and passive balancing is to release electric energy through resistance.

1. Passive balancing.

Passive balancing was applied earlier, with low cost and simple circuit. Passive balancing generally uses resistor discharge to discharge the battery with higher voltage, release energy in the form of heat, balance the voltage of the whole group, and gain more charging time for other batteries.

The disadvantage is that it wastes electric energy. At the same time, it is carried out in the form of heat dissipation. Considering safety, the balancing current cannot be set too large, otherwise the temperature of the battery pack will be too high. Generally, it is discharged with a small current of about 100mA, and the balancing speed is slow.

2. Active balancing

Active balancing is to transfer the high-energy battery cell to the single-cell low-energy battery in the form of power transfer, so as to balance the voltage of the whole group, and the energy loss during the transfer process is very small. Whether it is discharging, charging or static, balancing can be performed. Energy transfer will not generate heat like resistor consumption. Generally, active balancing currents of 1~2A are more common, and even reach 10A. The balancing current is large and the balancing speed is fast, which is suitable for use in large-capacity battery packs.

In summary, there are significant differences between active balancing and passive balancing of batteries according to the usage scenarios. Active balancing is more suitable for high-string and large-capacity power lithium battery pack applications. Such as electric vehicles, energy storage power stations, etc. Passive balancing circuits are simple and low-cost, and are more suitable for small-capacity and low-string lithium battery pack applications.