Analysis of the passive and active balancing methods of lithium battery protection board and the principle of protection board balancing

Passive equalization and active equalization methods of lithium battery protection board 1. Passive equalization Passive equalization generally discharges lithium batteries with higher voltage through resistance discharge, and releases electricity in the form of heat to gain more charging time for other batteries. In this way, the power of the entire system is limited by the battery with the least capacity. During the charging process, lithium batteries generally have a charging upper limit protection voltage value. When a certain string of batteries reaches this voltage value, the lithium battery protection board will cut off the charging circuit and stop charging. If the voltage during charging exceeds this value, which is commonly known as overcharge, the lithium battery may burn or explode. Therefore, lithium battery protection boards generally have an overcharge protection function to guard against battery overcharge. The advantages of passive balancing are low cost and simple circuit design; the disadvantages are that balancing is based on the lowest battery residual capacity, and the capacity of the battery with less residual capacity cannot be added, and 100% of the balanced power is wasted in the form of heat. 2. Active balance Active balance is balanced by means of power transfer, with high efficiency and low loss. Different manufacturers have different methods, and the equalizing current also ranges from 1 to 10?A. At present, many active equalization technologies appearing on the market are immature, leading to over-discharge of the battery and accelerating battery degradation from time to time. Most of the active equilibrium in the market adopts the principle of voltage transformation, relying on the expensive chips of chip manufacturers. In addition to the equalization chip, this method also requires expensive transformers and other peripheral components, which are larger in size and higher in cost. The benefits of active equalization are obvious: high efficiency, energy is transferred, and the loss is only the loss of the transformer coil, which accounts for a small proportion; the equalization current can be designed to be large, reaching a few amperes or even 10A, and the equalization takes effect quickly. Despite these benefits, active balancing also brings new problems. The first is the complex structure, especially the transformer method. How to design the switch matrix for dozens or even hundreds of batteries and how to control the drive is a headache. At present, the price of BMS with active balancing function will be much higher than that of passive balancing, which also somewhat limits the promotion of active balancing BMS. Passive balancing is suitable for lithium battery packs with small capacity and low number of strings, and active balancing is suitable for power lithium battery packs with high number of strings and large capacity. For BMS, in addition to the balance function is very important, the balance strategy behind it is even more important. Commonly used equalization charging techniques for the equalization principle of lithium battery protection board include constant shunt resistance equalization charging, on-off shunt resistance equalization charging, uniform battery voltage equalization charging, switched capacitor equalization charging, step-down converter equalization charging, inductance equalization charging, etc. When charging a group of lithium batteries in series, ensure that each battery is charged in a balanced manner, otherwise the performance and life of the entire group of batteries will be affected during use. During the charging process of lithium batteries, each lithium battery is equipped with an equalization circuit. During charging, the voltage of each battery is controlled by the equalization circuit of the lithium battery protection board to keep each string of batteries in the same state to ensure the lithium battery’s Performance and longevity. If the regulated power supply set by the equalization circuit of the lithium battery protection board is 4.2V, when the lithium battery does not reach 4.2V, each lithium battery is continuously charged, the equalization circuit is useless, and the charging current continues to pass through the lithium battery: when the lithium battery When one reaches 4.2V, the equalization circuit starts to work, it will stabilize the voltage to 4.2V, that is, the charging current will no longer pass through the lithium battery. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Lithium battery explosion mechanism