In order to achieve a phase shift between the start and run windings of a single-phase motor, it is common practise to use the usage of a capacitor. This phase shift is essential for the successful starting and continued operation of the motor.
Why is a capacitor required for the single-phase motor?
To start spinning, single-phase motors need to have a starting torque applied to them in order to overcome the rotor’s inherent inertia. Unfortunately, a single-phase system’s voltage is not stable, and as a result, the windings of the motor are subjected to voltage variations, which result in the windings’ reduced ability to create torque. This issue is made worse by the fact that the start windings and the run windings are connected in series with one another, which further lessens the amount of torque that is accessible.
A capacitor is added to the start winding circuit to create a phase shift between the start and run windings. This phase shift produces a rotating magnetic field that provides the necessary starting torque to overcome the rotor’s inertia and get the motor started. Once the motor is up to speed, the capacitor is no longer needed, and it is disconnected by a centrifugal switch or other means.
In summary, a capacitor is required for a single-phase motor to provide the necessary starting torque and to overcome the voltage fluctuations in the single-phase power supply.