11.1v Lithium Ion Battery Charger FOUR Stage Charging Principle And Requirement

- Jan 20, 2019-

11.1v Lithium ion Battery Charger FOUR Stage Charging Principle and Requirement

Taking a conventional lithium-ion battery as an example, the nominal capacity of 11.1v battery is 5000mAh, the nominal voltage is 11.1V (also on the market 12V), the discharge termination voltage is 8.25V, and the charge termination voltage is 12.6V.

The basic requirements of lithium battery charger are specific charging current and voltage, so as to ensure the safe charging of the battery. Adding other charging AIDS is to improve battery life and simplify the operation of chargers, including trickle charging for over-discharged batteries, battery voltage detection, input current limitation, switching off chargers after charging, automatic start-up charging after partial discharge of batteries, etc.

The charging mode of lithium batteries is voltage limiting and constant current, which is controlled by IC chips. The typical charging mode is to detect the voltage of the batteries to be charged first. If the voltage is less than 9V, the battery should be pre-charged first. The charging current is 1/10 of the set current. After the voltage rises to 9V, it enters the standard charging process.

The standard charging process is constant current charging with set current. When the battery voltage rises to 12.6V, it is changed to constant voltage charging, and the charging voltage is kept to 12.6V. At this time, the charging current decreases gradually, and when the current drops to 1/10 of the set charging current, the charging ends.

Four stages of charging lithium batteries are described:

Stage 1: Trickle current charging 

  - Trickle current charging is used to pre-charge the fully discharged battery unit (restorative charging). Trickle current charging is used when the battery voltage is less than 9V. The trickle current charging current is one tenth of the constant current charging current, i.e. 0.1C (for example, the constant charging current is 1A, the trickle current charging current is 100mA).

Stage 2: Constant current charging 

  - When the battery voltage rises above the trickle current charging threshold, increase the charging current for constant current charging. The constant current charging current is between 0.2C and 1.0C. The battery voltage gradually increases with the constant current charging process, which is generally set at 3.0-4.2V for a single battery.

Stage 3: Constant Voltage Charging 

  - When the battery voltage rises to 12.6V, constant current charging ends and constant voltage charging begins. According to the saturation degree of the core, the current decreases gradually from the maximum to 0.01C as the charging process continues. When the current decreases to 0.01C, the charging is considered to be terminated. (C is a representation of the current relative to the nominal capacity of the battery. For example, the capacity of the battery is 1000 mAh, and the charging current is 1000 mA for 1C.)

Stage 4: Charging termination

  - There are two typical charging termination methods: using the minimum charging current to judge or using a timer (or a combination of both). The minimum current method monitors the charging current at the constant voltage charging stage and terminates charging when the charging current is less than 0.02C. The second method counts the time from the beginning of the constant voltage charging stage and terminates the charging process after two hours of continuous charging.

It takes about 2.5 to 3 hours for the complete discharge battery to be charged by the above four-stage charging method. Advanced chargers also use more safety measures. For example, if the temperature of the battery exceeds the specified window (usually 0 to 45 degrees Celsius), the charging will be suspended. After charging, if the battery voltage is detected below 3.89V, it will be recharged.