Lithium battery charge and discharge requirements

　　1. Lithium battery charging: According to the structural characteristics of the lithium battery, the maximum end-of-charge voltage should be 4.2V, and it cannot be overcharged. Otherwise, too much lithium ions from the positive electrode will be taken away and the battery will be scrapped. The charging and discharging requirements are relatively high, and a dedicated constant current and constant voltage charger can be used for charging. Normally, the constant current charge to 4.2V/cell will switch to constant voltage charge. When the constant voltage charge current drops to less than 100mA, the charging should be stopped.

　　Charging current (mA) = 0.1 to 1.5 times the battery capacity (such as a 1350mAh battery, the charging current can be controlled between 135 and 2025mA). The normal charging current can be selected at about 0.5 times the battery capacity, and the charging time is about 2 to 3 hours.

　　2. Discharge of lithium battery: Due to the internal structure of the lithium battery, all lithium ions cannot move to the positive electrode during discharge. Some lithium ions must be retained in the negative electrode to ensure that lithium ions can be inserted into the channel smoothly during the next charge. Otherwise, the battery life will be shortened accordingly. In order to ensure that some lithium ions remain in the graphite layer after discharge, it is necessary to strictly limit the minimum discharge termination voltage, which means that the lithium battery cannot be over-discharged. The final discharge voltage is usually 3.0V/cell, and the minimum should not be lower than 2.5V/cell. The length of battery discharge time is related to battery capacity and discharge current. Battery discharge time (hours) = battery capacity/discharge current. Lithium battery discharge current (mA) should not exceed 3 times the battery capacity. (Such as 1000mAH battery, the discharge current should be strictly controlled within 3A) Otherwise, the battery will be damaged.

　　At present, the lithium battery packs sold on the market are equipped with matching charge and discharge protection boards. Just control the external charge and discharge current.

　　Charge and discharge protection circuit for two lithium batteries. It is composed of two field effect transistors and a dedicated protection integrated block S-8232. The overcharge control tube FET2 and the overdischarge control tube FET1 are connected in series in the circuit, and the battery voltage is monitored and controlled by the protection IC. When the battery voltage rises to 4.2V , The overcharge protection tube FET1 is turned off and charging is stopped. In order to prevent malfunction, a delay capacitor is generally added to the external circuit. When the battery is in a discharging state, when the battery voltage drops to 2.55V, the over-discharge control tube FET1 is cut off and stops supplying power to the load. Overcurrent protection is to control FET1 to cut off and stop discharging to the load when a large current flows through the load. The purpose is to protect the battery and the field effect tube. Overcurrent detection uses the on-resistance of the field effect tube as the detection resistance, monitors its voltage drop, and stops discharging when the voltage drop exceeds the set value. A delay circuit is generally added to the circuit to distinguish between surge current and short-circuit current. The circuit has perfect functions and reliable performance, but it is highly professional, and the dedicated integrated block is not easy to buy, and it is not easy to imitate by amateurs.