what is the function of a run capacitor ?

Regardless of any of capacitor, it has a starting action at the beginning of the motor start.and what is the function of a run capacitor ? let us have a look

when the motor reaches about 75%of the rated speed, the starting capacitor is automatically disconnected by the centrifugal switch. As the name implies, the running capacitor continues to work with the motor. The process of starting the motor is actually the process of "column phase". Because the single-phase motor is different from the three-phase motor, there is no phase difference, and the rotating magnetic field cannot be generated. The function of the capacitor is to make the starting winding current of the motor in time and space, leading the 90 electrical angles of the running winding to form a phase difference. Among them, the operating capacitor also plays a role in balancing the current between the primary and secondary windings.

The starting capacitor is to make the starting coil of the single motor energize at startup, and cut off after starting. The running capacitor is to make the motor compensate for the capacitor during operation, so the starting capacitor can't be less, and the running capacitor can be used.

When the stator winding of a single-phase motor passes a sinusoidal current, the motor generates an alternating magnetic field. The strength and direction of the magnetic field change sinusoidally with time, but the orientation is fixed. This magnetic field is an alternating pulsating magnetic field. The alternating pulsating magnetic field can be decomposed into two rotating magnetic fields that are opposite to each other at the same rotational speed and rotation direction.

 When the rotor is stationary, the two rotating magnetic fields generate two equal-sized and opposite-direction torques in the rotor, so that the synthesis the torque is zero, so the motor cannot rotate. When we use an external force to rotate the motor in a certain direction (such as clockwise rotation), the movement of the cutting magnetic field between the rotating magnetic field of the rotor and the clockwise rotation direction becomes smaller; between the rotating magnetic field of the rotor and the counterclockwise rotation direction As the cutting magnetic field moves, the total electromagnetic torque generated by the rotor will no longer be zero and the rotor will rotate in the direction of the pushing. In order to make the single-phase motor rotate automatically, we add a starting winding to the stator. The starting winding is 90 degrees out of phase with the main winding. The starting winding is connected in series with a suitable capacitor so that the current with the main winding is in phase. Approximate 90 degrees difference is the phase separation. Such two currents that differ by 90 degrees in time into two windings that are spatially different by 90 degrees will spatially generate a (two-phase) rotating magnetic field, under which the rotor can automatically initiate rotation, then stand up.

The function of the running capacitor and the starting capacitor are exactly the same, except that the capacity of the starting capacitor is large, so the starting current is large, and a large starting torque can be obtained, but the long-term operation will cause the starting winding to generate heat. When the startup is completed, the centrifugal switch switches to a smaller capacity operating capacitor to maintain the rotating magnetic field and avoid heating of the starting winding.