The working principle of car generator

working principle

The working principle of the overall alternator

　　When the external circuit energizes the field winding through the electric brush, a magnetic field is generated and the claw poles are magnetized into N pole and S pole. When the rotor rotates, the magnetic flux alternately changes in the stator windings. According to the principle of electromagnetic induction, it can be known that alternating induced electromotive force is generated in the three-phase windings of the stator. This is the power generation principle of an alternator.

The DCexcited synchronous generator rotor is driven by the prime mover (i.e. engine) to rotate at a speed of n (rpm), and the three-phase stator winding induces an AC potential. If the stator winding is connected to the electric load, the motor will have AC power output, which will be converted into DC power through the rectifier bridge inside the generator and output from the output terminal.

Alternator is divided into two parts: stator winding and rotor winding. The three-phase stator windings are distributed on the shell according to the electrical angle difference of 120 degrees. The rotor winding is composed of two pole claws. When the rotor winding is connected to direct current, it is excited, and the two pole claws form an N pole and an 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 winding will cut the magnetic lines of force, generating a sinusoidal electromotive force with a 120 degree electrical angle difference in the stator winding, that is, three-phase alternating current, which is then converted into a direct current output through a rectifier element composed of diodes.

When the switch is closed, the battery first supplies current. The circuit is:

battery positive → charging indicator light → regulator contact → excitation winding → grounding → battery negative. At this time, the charging indicator light will light up due to current passing through.

But after the engine starts, as the generator speed increases, the generator terminal voltage also increases. When the output voltage of the generator is equal to the battery voltage, the potentials of the generators "B" and "D" are equal. At this time, the charging indicator lamp goes out because the potential difference between the two ends is zero. It indicates that the generator is working normally, and the excitation current is supplied by the generator itself. The three-phase AC electromotive force generated by the three-phase winding in the generator is rectified by the diode, and then outputs DC power to supply power to the load and charge the battery.