A single-phase resistance-start asynchronous motor has a stator with a primary phase winding and a secondary phase winding. These two windings are at a 90-degree electrical angle to the axis in space. The secondary phase winding is typically connected in series with an external resistor via a centrifugal switch, and then connected in parallel with the primary phase winding and connected to the power supply together.
When the motor starts and reaches 75%–80% of its synchronous speed, the centrifuge opens, the centrifugal switch contacts are de-energized, and the secondary phase winding is cut off, becoming a single-phase motor. In AC miniature geared motors, when AC current flows through the stator winding, an armature magnetomotive force is established, which has a significant impact on the motor's energy conversion and operating performance. Therefore, when single-phase AC current is applied to the single-phase AC winding, a pulsating magnetomotive force is generated. This magnetomotive force can be decomposed into two rotating magnetomotive forces with equal amplitude and opposite speeds, thus establishing forward and reverse magnetic fields in the air gap.
These two rotating magnetic fields cut through the rotor conductors, generating induced electromotive force and induced current in the conductors, respectively. Single-phase asynchronous motors have low power and are mainly manufactured as small motors . They have a wide range of applications, such as in household appliances (washing machines, refrigerators, electric fans), power tools (such as electric drills), medical devices, and automated instruments.
