The car alternator is the main power source of the car. Its function is to supply power to all electrical equipment (except the starter) and charge the battery at the same time when the engine is running normally. So how does it work?
      When the external circuit energizes the exciting winding through a brush, a magnetic field is generated, so that the claw poles are magnetized into N and S poles. When the rotor rotates, the magnetic flux alternates in the stator windings. According to the principle of electromagnetic induction, it can be known that an alternating induced electromotive force is generated in the three-phase windings of the stator. This is the principle of alternator power generation.
      The prime mover (ie, the engine) drags the rotor of the DC-excited synchronous generator and rotates at the speed n (rpm), and the three-phase stator winding induces the AC potential. If the stator winding is connected to an electrical load, the motor will have AC power output. The rectifier bridge inside the generator will convert AC power to DC power and output it from the output terminal.
      The alternator is divided into two parts: a stator winding and a rotor winding. The three-phase stator windings are distributed on the housing according to an electrical angle of 120 degrees from each other. The rotor winding is composed of two pole claws. When the rotor winding is connected with DC power, it is excited, and the two pole claws form N pole and S pole. The magnetic field lines start from the N pole, enter the stator core through the air gap, and then return to the adjacent S pole. Once the rotor rotates, the rotor windings will cut the magnetic lines of force, generating sinusoidal electromotive force in the stator windings with an electrical angle of 120 degrees from each other, that is, three-phase alternating current, which then becomes a direct current output through a rectifier element composed of a diode.