Charging electric vehicles with charging piles is actually charging the battery in the electric vehicle. Charging principle is the battery discharge, with direct current and discharge current in the opposite direction through the battery, so that it restores the ability to work, this process is called battery charging. Battery charging, battery positive and power supply positive connection, battery negative and power supply negative connection, charging power supply voltage must be higher than the total electromotive force of the battery. Generally speaking, the charging pile has two charging methods, respectively, constant current charging and constant voltage charging.

Constant-current charging method: constant-current charging method is to adjust the output voltage of the charging device or change the series resistance of the battery, to maintain the charging current strength of the charging method. Control method is simple, but due to the battery's ability to accept current is with the charging process and gradually decline, to the late charging, charging current is used for electrolysis of water, generating gases, so that the gas is too much, therefore, often choose the stage charging method.

Constant voltage charging method: the charging power supply voltage in all charging time to maintain a constant value, with the gradual increase in battery terminal voltage, the current is gradually reduced. Compared with the constant current charging method, the charging process is closer to the optimal charging curve. Fast charging with constant voltage. Because of the low electric potential of the battery at the beginning of charging, the charging current is very large, and as charging proceeds, the current will be gradually reduced, so only a simple control system is needed.