What is the principle of forward and reverse rotation of single-phase motor?

Forward and reverse wiring diagram for single-phase motor:

Principle of forward and reverse rotation for single-phase motor:

A single-phase capacitor motor has two windings, the start winding and the run winding. The two windings are 90 degrees apart in space. In the start winding in series with a larger capacity capacitor, when the run winding and start winding through the single-phase alternating current, due to the capacitor effect so that the current in the start winding in time than the run winding current ahead of the 90-degree angle, the first to reach the maximum value.

The formation of two identical pulsed magnetic fields in time and space, so that the air gap between the stator and rotor generated a rotating magnetic field, under the action of the rotating magnetic field, the motor rotor generates an induced current, the current and the rotating magnetic field interact with each other to generate electromagnetic field torque, so that the motor rotates.

Generally running winding (main coil) wire diameter is a little thicker, start winding (secondary coil) wire diameter is thinner, using a multimeter to measure the start winding than the running winding resistance value is a little larger.

Expanded information:

Single-phase motor starting principle points:

1, resistor start (refrigerator motor, etc.);

2, capacitor starting Type (woodworking electric planer motor, etc.);

3, capacitor operation (washing machine, electric fan, etc.);

4, capacitor start operation.

Capacitor start type motor in the motor after the start of the capacitor is disconnected, the principle of disconnection is a centrifugal switch on the motor shaft, to reach a certain speed switch is broken, if the break is not open to start the wire packet will be burned; capacitor running motor capacitor in the motor startup or normal operation of the motor are working, if the capacitance becomes smaller will cause motor startup difficulties, the fan rotates slowly, the wind speed reduces the failure.

Reference:

Baidu Encyclopedia: Motor Forward and Reverse