Feature: Power
Figure 2: Impact of impedance-mismatched cells during battery pack charging and discharging
is 5% of its capacity, then 200mAh needs to be equalised. Tis scenario is well suited for passive balancing, where a BMS designer can implement a 200mA passive balancing circuit to dissipate the charge in about an hour or a 100mA circuit to do so in two hours. Ultimately, the designer can tailor the passive balancing strategy based on the passive balancing current capability of the selected cell monitor IC and the cell capacity. In contrast, consider a 300Ah high capacity energy storage
cell where the balancing charge at 5% reaches 15Ah. Even with a 300mA passive balancing current – which is already quite high – it would take over 50 hours to complete balancing. In reality, this
time would be even longer, as continuous passive balancing on a single cell channel for extended periods could overheat and may damage the BMS chip. Terefore, active balancing is essential for high capacity cells. For instance, if an active balancing circuit can handle 15A of
charge transfer, the 15Ah imbalance can be corrected in about an hour. With 7.5A capacity, it would take about two hours, and so on. Unlike passive balancing, active balancing does not waste energy but rather redistributes it to other cells or packs, improving overall energy efficiency whilst easing the thermal management burden of the BMS.
Table 1: Advantages and disadvantages of passive and active battery balancing 28 November 2025
www.electronicsworld.co.uk
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