How to equalization charge Lithium ion battery pack（Cell Balancing）

When the lithium-ion battery pack is produced and stored for a long time, due to the difference in static power consumption of each circuit of the protection board and the different self-discharge rate of each battery cell, the voltage of each string of batteries in the entire battery pack is inconsistent. Equalization charge has the function of equalizing the voltage of the lithium-ion battery pack, so as to achieve the full charge and full discharge of the battery pack capacity, so that the battery pack can exert its maximum effect.

How to equalization charge Lithium ion battery pack

Commonly used equalization charge technologies for lithium-ion battery packs include constant shunt resistor balanced charging, on-off shunt resistor equalization charge, average battery voltage equalization charge, switched capacitor equalization charge, step-down converter equalization charge, inductive equalization charge, etc. When a group of lithium-ion batteries is charged in series, each battery should be charged in a balanced manner, otherwise, the performance and life of the whole group of batteries will be affected during use.

1. Add a parallel equalization circuit to every single battery of the lithium-ion battery pack to achieve the purpose of shunting. In this mode, when a battery is fully charged first, the equalizer can prevent it from being overcharged and convert the excess energy into heat to continue charging the battery that is not fully charged. This method is simple, but it will cause energy loss and is not suitable for fast charging systems.

2. Before charging, each cell is discharged to the same level through the same load one by one, and then charged with a constant current, so as to ensure a more accurate balanced state between each cell. But for the battery pack, due to the physical differences among individuals, it is difficult to achieve completely consistent ideal results after deep discharge of each monomer. Even if the same effect is achieved after discharging, new imbalances will appear during charging.

3. Timely, sequentially, and independently detect and evenly charge the single cells in the lithium-ion battery pack. When charging the lithium-ion battery pack, it can ensure that each lithium-ion battery in the battery pack will not be overcharged or over-discharged, thus ensuring that each battery in the lithium-ion battery pack is in a normal operation state.

4. Using the time-sharing principle, through the control and switching of the switch components, additional current flows into the battery with relatively low voltage to achieve the purpose of balanced charging. This method is more efficient, but the control is more complicated.

5. Take the voltage parameters of each battery as the equalization object to restore the voltage of each battery to be consistent. During equalization charge, the capacitor is alternately connected to two adjacent batteries through the control switch, receives the charge from the high-voltage battery, and then discharges to the low-voltage battery until the voltage of the two batteries tends to be the same. This equalization method better solves the problem of battery pack voltage imbalance, but this method is mainly used in occasions with a small number of batteries.

6. The whole system is controlled by a single-chip microcomputer, and the single battery has an independent set of modules. According to the set program, the module manages the charging of every single battery separately and automatically disconnects after charging is completed. This method is relatively simple, but when the number of single cells is large, the cost will be greatly increased, and it is also not conducive to the reduction of the system volume.

Lithium-ion battery equalization charge principle

The number of single-cell lithium-ion battery protection chips is determined according to the number of lithium-ion battery cells, and they are used in series to protect the charging and discharging, over-current, and short-circuit states of the corresponding single-cell lithium-ion battery. At the same time as charging protection, the system realizes balanced charging through the protection chip to control the on-off of the switching device of the shunt discharge branch. This method is different from the traditional method of realizing equalized charging at the charger end and reduces the cost of designing and applying the lithium-ion battery pack charger.

The lithium-ion battery pack is composed of multiple single lithium-ion batteries connected in series. Due to the differences in the cells, when the terminal voltage rises inconsistently when charging in series, some cells will be overcharged and some cells will be undercharged. All batteries are connected in parallel during equalization charge and connected in series during normal charging and power consumption. During balanced charging, all batteries connected in parallel have the same voltage, which realizes the forced balancing of each battery.