The car is equipped with two DC power supplies, battery and generator. All the electric equipment used in the car is connected in parallel with the DC power supply. Battery functions are :1. When the engine starts, power supply to the starter and ignition system; Electricity; 2. When the engine is running at low speed, it will be supplied power to electrical equipment and generator magnetic field winding. 3. When the engine is running at medium and high speed, the remaining electric energy of the generator will be converted into chemical energy and stored. When the generator is overloaded, assist the generator to supply power to the electrical equipment. 5. The battery is equivalent to a large capacitor, which can absorb the instantaneous overvoltage in the circuit, protect the electronic components, and keep the voltage stability of the automobile electrical system.