AC heat dissipation fan uses alternating current to supply power: single-phase AC motor has only one winding.

When the single-phase sinusoidal current passes through the stator winding, the motor will produce an alternating magnetic field. The strength and direction of the magnetic field change with time sinusoidally, but it is fixed in spatial orientation. So it is also called alternating pulsating magnetic field. The alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with the same rotating speed and opposite rotating direction. When the rotor is stationary, the two rotating magnetic fields produce two equal-sized and opposite-directional torques in the rotor, which make the composite torque zero, so the motor can not rotate. When we use external force to make the motor rotate in a certain direction (such as clockwise rotation), the motion of the cut magnetic line between the rotor and the rotating magnetic field in the clockwise direction becomes smaller, and the motion of the cut magnetic line between the rotor and the rotating magnetic field in the counterclockwise direction becomes larger. In this way, the balance will be broken, the total electromagnetic torque generated by the rotor will no longer be zero, and the rotor will rotate in the direction of propulsion.