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The working principle of lithium battery protection board and the balanced charging method

Lithium-ion battery protection board is used for the charge and discharge protection of series-connected lithium-ion battery packs. It ensures that the voltage difference between each individual cell is smaller than the set value when fully charged, achieving balanced charging of individual cells in the lithium-ion battery pack and effectively improving the charging effect in series charging mode. At the same time, it detects over-voltage, under-voltage, over-current, short circuit, and over-temperature status of each individual cell in the battery pack, protecting and prolonging the battery's service life. Under-voltage protection prevents battery damage due to over-discharge during discharge.

Working principle of lithium battery protection board

Lithium battery protection board commonly uses various balancing charging technologies, including constant current shunt resistor balancing charging, on-off shunt resistor balancing charging, average cell voltage balancing charging, switch capacitor balancing charging, voltage reduction type converter balancing charging, and inductor balancing charging, etc.

During series charging of grouped lithium-ion batteries, each cell should be balanced charged to prevent the performance and lifespan of the entire lithium iron phosphate (LiFePO4) battery pack from being affected. However, the existing single-cell lithium-ion battery protection chips do not include balancing charging control function, and the control function of balancing charging for multi-cell lithium-ion battery protection chips needs to be externally connected with CPU. This is achieved through serial communication with the protection chip, which increases the complexity and design difficulty of the protection circuit, reduces the efficiency and reliability of the system, and adds power consumption. The balancing principle of lithium battery protection board can protect and balance any structure and voltage level of power lithium-ion battery pack by changing the protection chip model and series connection number, and the power level of switch devices and energy-consuming components in the circuit.

Balancing charging methods for lithium battery packs

In the case of a long storage time after the production of a lithium-ion battery pack, the voltage inconsistency of each cell in the battery pack is caused by the different static power consumption of each protection board and the different self-discharge rates of each cell. Balancing has the function of balancing the voltage of lithium-ion battery packs, thereby achieving the full charge and full discharge of the battery pack and maximizing the effectiveness of the battery pack.

An additional parallel balancing circuit is attached to each individual cell of the lithium-ion battery pack for the purpose of diversion. In this mode, when a certain cell reaches full charge first, the balancing device can prevent overcharging and convert the excess energy into heat energy, and continue to charge the cells that are not yet fully charged. This method is simple, but it will cause energy loss and is not suitable for fast charging systems. Before charging, each individual cell is discharged through the same load to the same level, and then constant current charging is performed to ensure a relatively accurate balancing state between each individual cell. However, for battery packs, due to the physical differences between individuals, it is difficult to achieve a completely consistent ideal effect after deep discharge. Even if the same effect is achieved after discharge, new imbalances may occur during the charging process.

Perform individual testing and uniform charging of each individual cell in the lithium battery pack on time and in sequence. When charging the lithium-ion battery pack, it ensures that each individual cell in the battery pack does not overcharge or overdischarge, thereby ensuring that each cell in the lithium-ion battery pack is in a normal working state. By using the time-sharing principle and controlling and switching of switch components, extra current flows into the cells with relatively low voltage to achieve balanced charging. This method has a relatively high efficiency but is more complicated to control.

Balance the voltage parameters of each cell to restore the voltage consistency of each cell. During balancing charging, the capacitor is alternately connected to two adjacent cells by controlling the switches. It receives charging from the high-voltage cell and discharges to the low-voltage cell until the voltage of the two cells tends to be consistent. This balancing method solves the problem of voltage imbalance in the battery pack better, but it is mainly used in scenarios with fewer batteries.

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