Make the resultant magnetic field an elliptical rotating magnetic field, possibly even close to a circular rotating magnetic field. The electric motor thus obtains a starting torque. The motor using the resistance phase separation method is cheap. For example, the secondary winding can be wound with a thinner wire, but the phase separation effect is poor, and the resistance consumes energy. After this kind of motor starts and reaches a certain speed, the secondary winding is usually automatically cut off by a centrifugal switch mounted on the motor shaft to reduce the loss on the resistance and improve the operation efficiency. Generally used in occasions with low starting torque requirements, such as small lathes, small refrigerators, etc., the disadvantage is that the speed cannot be adjusted.