What is the principle of starting the capacitor?

The single-phase current flowing through a single-phase motor cannot generate a rotating magnetic field, and a capacitor is needed to separate the phases, so that the current in the two windings produces a phase difference of approximately 90°, to generate a rotating magnetic field.

Capacitive induction motors have two windings, the start winding and the running winding. The two windings are spatially different by  90°degrees. A large-capacity capacitor is connected in series on the starting winding. When the running winding and the starting winding pass through single-phase alternating current, the current in the starting winding is advanced by  90°degrees from the current of the running winding due to the action of the capacitor. Maximum value. Two identical pulsed magnetic fields are formed in time and space, so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, an induced current is generated in the rotor of the motor, and the current interacts with the rotating magnetic field. The electromagnetic field torque causes the motor to rotate.

In order to make the single-phase motor rotate automatically, we can add a starting winding to the stator. The starting winding is 90° degrees out of phase with the main winding. The starting winding must be connected in series with a suitable capacitor so that the current with the main winding is The phase is approximately 90°degrees out of phase, the so-called phase separation principle. Such two currents that differ by 90 degrees in time into two windings that are spatially different by  90°degrees will spatially produce a (two-phase) rotating magnetic field. Under the action of this rotating magnetic field, the rotor can be started automatically. After starting, when the speed rises to a certain value, the starting winding is disconnected by means of a centrifugal switch or other automatic control device mounted on the rotor. In normal operation, only the main winding jobs. Therefore, the starting winding can be made in a short-time mode of operation. However, there are many times when the starting winding is not broken. We call this kind of motor a capacitive single-phase motor. To change the steering of this motor, it can be realized by changing the position of the capacitors in series.