Shaded-pole motor

[2] When single phase AC supply is applied to the stator winding, due to shading provided to the poles, a rotating magnetic field is generated.

Shaded-pole motors of the asymmetrical type shown are only reversible by disassembly and flipping over the stator, though some similar looking motors have small, switch-shortable auxiliary windings of thin wire instead of thick copper bars and can reverse electrically.

[3] The common, asymmetrical form of these motors (pictured) has only one winding, with no capacitor or starting windings/starting switch, making them economical and reliable.

[4] A major advantage is that the motor's stall current is only slightly higher than the running current, so there is low risk of severe over-heating or tripping the circuit protection if the motor is stalled for some reason.

In more recent times, the use of variable frequency controls permits synchronous motors to start slowly and deliver more torque.