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The role of the equalization function of the protection board of the lithium battery pack

by:dcfpower     2021-03-19

1. It is necessary to bring balance: when the battery pack is produced and stored for a long time, due to the different static power consumption of each circuit of the protection board and the self-discharge rate of each cell Different, the voltages of the battery strings in the entire battery pack are not consistent, so there is a significant pressure difference, but when the capacity is consistent, the equalization has the function of equalizing the voltage of the battery pack, so as to achieve the full charge and discharge of the battery pack capacity. The efficiency of the battery pack makes the battery pack play a big role.

2. The situation where the balance cannot be used: Many people think that the battery pack has a balanced use in the middle and later stages of use. In fact, when the battery pack is used in the middle and later stages, due to the capacity of each cell Different losses cause a difference in capacity. The balance of the protection board cannot compensate for the cell capacity. On the surface, the voltage of each string of the battery pack is the same, but due to the inconsistency of capacity, it is often a single string with low capacity during charging and discharging. Cells are protected against over-discharge and over-charge first, so the capacity of the battery pack is represented by a single string of cells with low capacity. Therefore, we should understand that the protection board balances the voltage, and the capacity cannot be supplemented.

3. The contradiction in the use of balance: balance generally has two elements: A: balance on voltage setting: the balance voltage setting is low, the protection board is turned on for a longer time, and the balance effect is more obvious, but The protection board will generate heat while equalizing. The longer the balance time, the more heat will appear, which will directly affect the performance of the protection board or the protection board will be damaged; the higher the balance voltage setting, the shorter the balance opening time, and the less obvious balance effect. B: Equalization current setting: The equalization current setting is large, the equalization effect is obvious, but the equalization is severe heat, which will damage the protection board; the equalization current setting is small, the equalization effect is not obvious, and the equalization time is short.

Currently, the two most common methods of lithium battery pack balancing are energy-consuming balancing and energy-transfer balancing.

pack energy-consumption equalization, as the name implies, is to use resistors to drain the excess power of a certain high-voltage battery in the lithium battery pack. The cost of this method of balancing is relatively low, and the design is relatively simple. It can play a certain role when the voltage between the single lithium batteries in the lithium battery pack pack cannot reach the same level, but relatively, this method is also more balanced. It is prone to failure, and the temperature emitted by the lithium battery pack is higher when it is balanced. And there is one thing, because the capacitance of each single cell in the lithium battery pack is not the same, so each time the battery is charged, the battery with a smaller capacity will quickly reach saturation. Because the battery with a larger capacity is still being charged, the capacity Smaller lithium batteries will be balanced, and the power will be consumed in a form similar to the amount of discharge. It will continue to cycle until the large-capacity battery is saturated. So you can imagine that the overall performance of the smaller-capacity battery will be greatly reduced over time. , This is the same reason as the performance degradation of our mobile phone battery for a long time. Therefore, energy-consumption equalization of lithium battery packs has great disadvantages.

The energy transfer equilibrium of the lithium battery pack pack is also well understood, that is, the higher energy lithium battery in the battery pack is transferred to the lower energy lithium battery. This kind of equalization is really practical at first glance. , But in actual situations, the current energy transfer balance is not very perfect, because this way of balance does not transfer energy by detecting the voltage of a single cell, but transfers energy by battery capacity. When a high-energy battery transfers energy to a low-energy battery, because the equalization current and charging current are fixed and uncontrollable, the low-capacity battery may reach overcharge during the transfer, and the lithium battery protection board is Will work to stop charging, so the entire cycle will be terminated.

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