How does a capacitor start motor create starting torque?

A capacitor start motor creates starting torque by utilizing a capacitor to create an additional phase. In this type of motor, a capacitor is connected to the start winding, which generates a phase shift in the current flowing through it. This phase shift results in a magnetic field that is out of phase with the magnetic field produced by the main winding.

The interaction between these two magnetic fields—one from the main winding and one from the start winding—produces a net torque that helps to overcome the inertia of the motor at startup. Essentially, this additional phase enables the motor to initiate rotation more effectively than it would with a single-phase winding alone, providing sufficient starting torque to allow the motor to overcome friction and other loads.

Once the motor reaches a certain speed, a centrifugal switch or relay typically disconnects the start winding and capacitor from the circuit, allowing the motor to run on the main winding alone. This design is particularly beneficial for applications that require high starting torque, such as air compressors or refrigeration compressors.