A capacitor start motor is a type of single-phase induction motor that is designed to provide high starting torque and improved starting performance compared to standard split-phase induction motors. It's commonly used in applications where a higher starting torque is required, such as in compressors, pumps, fans, and other machinery.
The basic construction of a capacitor start motor involves the inclusion of an additional capacitor in the motor circuit. This capacitor is connected in series with the motor's auxiliary winding, which is also known as the start winding. The main winding, referred to as the run winding, is also connected in parallel to the capacitor and the start winding.
During the starting phase of the motor, both the start winding and the capacitor are energized. The capacitor helps create a phase shift between the currents in the start and run windings, which produces a rotating magnetic field. This rotating magnetic field results in a higher starting torque, allowing the motor to overcome inertia and start rotating more effectively.
Once the motor reaches a certain speed, a centrifugal switch is often used to disconnect the start winding and capacitor from the circuit. This is because the capacitor is mainly useful during the starting phase, and leaving it connected during normal operation could lead to inefficient performance and increased energy consumption.
In summary, a capacitor start motor is designed to provide improved starting performance by using a capacitor to create a phase shift in the currents between the start and run windings. This results in a higher starting torque and better ability to start under load.