Principle of single-phase AC motors

Using a single-phase capacitor motor as an example: A single-phase motor has two windings, namely the starting winding and the operating winding. The two windings differ by 90 degrees in space. A capacitor with a larger capacity is connected in series on the starting winding. When the operating winding and starting winding pass through single-phase AC power, the current in the starting winding is 90 degrees ahead of the current in the operating winding in time due to the action of the capacitor, reaching the maximum value first. Two identical pulse magnetic fields are formed in time and space, creating a rotating magnetic field in the air gap between the stator and rotor. Under the action of the rotating magnetic field, an induced current is generated in the motor rotor, and the interaction between the current and the rotating magnetic field generates electromagnetic torque, causing the motor to rotate.

There are several starting methods for 220V AC single-phase motors:

The first type is that the starting winding does not participate in the operation work, while the motor continues to operate with the running winding coil.

The second method is to turn on the centrifugal switch when the motor is stationary. After being powered on, the starting capacitor participates in the starting work. When the rotor speed reaches 70% to 80% of the rated value, the centrifugal switch will automatically trip, and the starting capacitor will complete the task and be disconnected. And the operating capacitor is connected in series to the starting winding to participate in the operation work. This connection method is generally used in places with high and unstable loads such as air compressors, cutting machines, and woodworking machines.

The third type, split phase starting, is assisted by an auxiliary starting winding, and its starting torque is not large. The operating speed remains roughly constant. Mainly used in electric fans, air conditioning fan motors, washing machines and other motors.

If a motor with a centrifugal switch cannot start successfully in a short period of time, the winding coils will quickly burn out.

Capacitance value: A dual value capacitor motor with a large starting capacitance and a small operating capacitance, with a voltage resistance generally greater than 400V.