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What is The Difference Between BMS Active balancing and Passive balancing?
By HY-MeganApril 17th, 2025522 views
BMS plays a vital role in the battery pack. It not only monitors the status of the battery, but also ensures the performance and life of each single cell in the battery pack through balanced charge and discharge control，to maintain cell consistency. At present, the BMS balancing technology for managing battery cell consistency is mainly aimed at the balancing management of battery cell SOC.Under ideal conditions, balancing technology can keep the SOC of each battery cell balanced, thereby ensuring that all battery cells reach the upper and lower voltage limits of charging and discharging synchronously, thereby improving the overall capacity utilization of the battery pack.BMS Balance management is divided into passive balance and active balance. 1.Working principle (1) passive equilibrium:By connecting a resistor in parallel to each battery cell in the battery pack, when the voltage of a battery is higher than the set value, the excess energy is released in the form of heat energy through resistor discharge, reducing the voltage and achieving the purpose of balancing. Taking a wooden barrel as an example, passive balance is similar to cutting the long board to make the length of the long board and the short board the same, so as to achieve the balance of the entire barrel. (2) Active equilibrium:By transferring the energy from the high-energy battery to the low-energy battery, the battery pack is balanced. Active balancing does not require the energy to be dissipated in the form of heat. Taking a wooden barrel as an example, active balancing is more like “cutting the long and filling the short” of the barrel, which is a more efficient and energy-saving balancing method.
2.Comparison between active and passive equalization (1) efficiency Passive equilibrium: Since energy is dissipated in the form of heat, the overall system energy utilization is low, and heat is generated during the balancing process, which may cause the battery pack temperature to rise. The balancing current is generally small, usually around 100mA, and the balancing speed is slow. Active equilibrium: The energy loss during energy transfer is small, the balancing speed is fast, and it is suitable for use in large-capacity battery packs. The balancing current is large, which can reach 1 to 10 amperes. (2) Cost Passive equilibrium: Due to the simple circuit design, the cost is low, suitable for small-capacity, low-string lithium battery pack applications. Active equilibrium: Due to the need for expensive chips and transformers and other peripheral components, the cost is high, suitable for high-string, large-capacity power lithium battery pack applications. (3) Application scenarios Passive equilibrium: Applicable to small-capacity, low-string lithium battery packs, for example, low-capacity battery packs (such as consumer electronics mobile phones, laptops, etc.), short-life or low-cycle scenarios (such as power tools and electric drills, etc.), low-cost energy storage systems, and small-scale systems with high-voltage platforms.which can release the energy storage capacity of each battery cell and maximize the utilization of power. Active equilibrium:Applicable to power battery packs (electric vehicles), large energy storage systems, high-value equipment (such as aerospace, medical equipment, etc.), low-temperature and high-rate scenarios.
BMS equilibrium charge and discharge control is an indispensable part of battery pack management. By real-time monitoring of the charge and discharge status of each single cell in the battery pack and adopting corresponding balanced control strategies, BMS can achieve balance within the battery pack and improve the performance and life of the battery pack.
