What is the primary disadvantage of passive cell balancing compared to active cell balancing?

The primary disadvantage of passive cell balancing compared to active cell balancing is its inherent energy inefficiency, as it dissipates excess energy from stronger cells as heat rather than transferring it to weaker cells. Cell balancing is necessary in battery packs to ensure that all cells operate within their safe voltage limits and to maximize the pack's overall capacity and lifespan. In a battery pack, cells can have slight differences in capacity, internal resistance, and self-discharge rates due to manufacturing tolerances or variations in operating conditions. These differences can lead to voltage imbalances during charging and discharging, where some cells become fully charged or fully discharged before others. Passive cell balancing addresses these imbalances by using resistors to dissipate excess energy from the stronger cells (cells with higher voltages) during charging. When a cell reaches its maximum voltage, a switch is activated to connect a resistor in parallel with the cell. The resistor dissipates the excess energy as heat, preventing the cell from overcharging. While passive cell balancing is simple and inexpensive to implement, it is inherently energy inefficient. The energy dissipated by the resistors is essentially wasted, reducing the overall efficiency of the battery pack. For example, if a cell has 100 mWh (milliwatt-hours) of excess energy that needs to be dissipated to balance the pack, that energy is lost as heat. In contrast, active cell balancing transfers energy from stronger cells to weaker cells, rather than dissipating it as heat. This can significantly improve the energy efficiency of the battery pack. Active cell balancing uses various techniques, such as capacitive or inductive energy transfer, to move charge from high-voltage cells to low-voltage cells. This allows the weaker cells to be charged more fully, increasing the overall capacity and energy utilization of the pack. While active cell balancing is more complex and expensive to implement than passive cell balancing, its superior energy efficiency makes it a preferred choice for high-performance battery packs, such as those used in electric vehicles and energy storage systems. The energy wasted by passive cell balancing can be particularly significant in large battery packs with substantial cell imbalances, leading to reduced range, increased operating costs, and a shorter lifespan. Therefore, the energy inefficiency is the primary disadvantage of passive cell balancing compared to active cell balancing.