What is the purpose of a capacitor in a single-phase motor?

In a single-phase motor, the primary purpose of a capacitor is to provide starting torque. When the motor is stationary, it requires an initial push in order to begin turning. The capacitor creates a phase shift in the alternating current, which generates a rotating magnetic field. This helps in establishing a rotating motion and gives the motor the necessary torque to start. Once the motor reaches a certain speed, the capacitor may be disconnected from the circuit, or it may remain in the circuit depending on the type of single-phase motor being used.

While capacitors can play roles in noise reduction, increasing efficiency, or load balancing in certain electrical contexts, these functions are not the primary reason for their inclusion in single-phase motors. The critical starting torque they provide distinguishes them as essential components for the operation of these types of motors.