Lithium battery overcurrent protection.household energy storage battery

　　Overcurrent protection

　　Due to the chemical characteristics of lithium-ion batteries, the battery manufacturer has specified that the maximum discharge current should not exceed 2C (C=battery capacity/hour). When the battery discharge current exceeds 2C, the conventional battery will cause permanent damage to the battery or cause safety problems.

　　During the normal discharge of the battery to the load, when the discharge current passes through two MOSFETs in series, a voltage will be generated at both ends of the MOSFET due to the conduction impedance of the MOSFET. The voltage value U=I * RDS * 2, RDS is the conduction impedance of a single MOSFET, and the "V -" pin on the control IC detects the voltage value. If the load is abnormal for some reason, the circuit current will increase, When the circuit current is large enough to make U>0.15V (the value is determined by the control IC, and different ICs have different values), its "DO" pin will change from high voltage to zero voltage, so that V1 will turn from on to off, thus cutting off the discharge circuit, making the current in the circuit zero, and playing the role of overcurrent protection.

　　There is also a delay time between the time when the control IC detects the occurrence of overcurrent and the time when it sends off the V1 signal. The length of the delay time is determined by the internal or external delay capacitance of the IC, usually about 13 milliseconds, to avoid misjudgment due to interference.

　　Note: The battery used for mining should be less than 10 milliseconds, because the spark generated by large current during contact can cause gas explosion!

　　It can be seen from the above control process that the magnitude of its overcurrent detection value depends not only on the control value of the control IC, but also on the conduction impedance of the MOSFET. When the conduction impedance of the MOSFET is larger, the overcurrent protection value of the same control IC is smaller.

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