(1) Constant current charging method
During the charging process, the charging current always remains the same, which is called constant current charging method, referred to as constant current charging method or isocurrent charging method. During the charging process, the battery voltage gradually increases and the charging current gradually decreases. In order to keep the charging current from decreasing due to the increase of the battery terminal voltage, the power supply voltage must be gradually increased during the charging process to maintain the charging current. The degree of automation of charging equipment is relatively high, and generally simple charging equipment cannot meet the requirements of constant current charging. In the constant current charging method, in the case of the maximum allowable charging current of the battery, the greater the charging current, the shorter the charging time. In terms of time, it is advantageous to adopt this method. However, if the charging current remains the same in the later stage of charging, since most of the current is used to electrolyze water, the electrolyte will have too many bubbles and become boiling. This not only consumes electric energy, but also easily causes a large amount of active material on the plate to fall off, and the temperature Excessive rise will cause the plate to bend, and the capacity will drop rapidly and be scrapped in advance. Therefore, this charging method is rarely used.
(2) Constant voltage charging method
During the charging process, the charging voltage always remains unchanged, which is called constant voltage charging method, referred to as constant voltage charging method or equal voltage charging method. Since the constant voltage charging starts to the later stage, the power supply voltage is always constant, so the charging current is quite large at the beginning of charging, which greatly exceeds the normal charging current value. But as the charging progresses, the battery terminal voltage gradually increases and the charging current gradually decreases. When the battery terminal voltage is equal to the charging voltage, the charging current is reduced to a minimum or even zero. It can be seen that the advantage of using the constant voltage charging method is that it can avoid the excessive charging current in the later stage of charging that causes the active material of the electrode to fall off and the loss of electric energy. But its disadvantage is that at the beginning of charging, the charging current is too large, and the volume of the electrode active material changes and shrinks too fast, which affects the mechanical strength of the active material and causes it to fall off. In the later stage of charging, the charging current is too small, so that the active material in the deep part of the plate cannot get a charging response, resulting in insufficient charging for a long time, which affects the service life of the battery. Therefore, this charging method is generally only suitable for special occasions where there is no power distribution equipment or the charging equipment is relatively simple, such as the charging of the battery in the car, and the charging of the small battery of the dry cell type 1 to 5 adopts the equal voltage charging method. When using the equal-voltage charging method to charge the battery, the required power supply voltage is about 2.4~2.8V for each single cell of acid storage battery, and about 1.6~2.0V for each single battery of alkaline storage battery.

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