The difference of passive balance and Active balance

Passive balancing

The passive balancing method is relatively simple and straightforward. The battery is discharged through a dissipative bypass route. This bypass can be integrated externally or externally to the integrated circuit (IC). It’s cost-effective. Thus, this approach is beneficial for low-cost system applications. However, 100% of the excess energy from higher energy batteries is dissipated as heat, which makes passive balancing method less desirable during discharge as it has a noticeable effect on battery runtime. This technique limits balancing to high SOC platform and can only be performed during charging.

Passive balancing currents are relatively small, so multiple cycles may be required to equalize a battery pack. Usually, the BMS comes with 200mA~500mA balancing current. If the current is too large, the heat generated may be too high. The battery pack is prone to overheating.

Active balancing

Active balancing, which utilizes capacitive or inductive charge shuttling to deliver energy where it is most needed with minimal loss. It is significantly more efficient cause energy is diverted to where it is needed, rather than being consumed. Of course, the trade-off for this improved efficiency is the need for additional components at higher cost.

Therefore, it is more preferable for efficiency-conscious designs and applications where providing maximum runtime is a priority.

Active balancing can happen during any battery operation - charging, discharging or rest. Compared to passive cell balancing, almost no energy is lost as heat. It extends battery life by maximizing the capacity of the battery pack, ensuring that all its energy is available.