How Split-Phase AC Induction Motor Works

The other name of split phase motor is an induction start/induction run motor. This motor has two windings : a start and a main winding. The start winding is made with fewer turns and smaller gauge, relative to the main winding to create more resistance, thus the start winding’s field is put in to the different angle than that of the main winding which causes the motor to start rotating. Because the main winding, the motor keep running until the rest of the time.

The starting torque is low. It’s typically only 100% to 175% of the rated torque. The motor draws high starting current approximately 700% to 1000% of the rated current. 250% to 350% of the rated torque are the maximum generated torque ranges.

Good application for split-phase motors include small fans, small grinders and blower and the other low starting torque applications with power needs from 1/20 to 1/3 hp. For any applications requiring high on/off cycle or high torque, we have to avoid using this type motor. [Circuit’s schematic diagram source: Microchip Application Note]