Shaded-Pole Motor

The shaded-pole motor is the original type of AC single-phase induction motor, dating back to at least 1890. A copper ring or bar surrounding part of each stator pole delays the phase of the magnetic flux passing through the shaded section, producing a weak rotating field that causes the rotor to spin from the unshaded toward the shaded side of each pole. The design uses a single winding and needs no capacitor, but has low starting torque relative to its running torque and an efficiency of only around 26 percent, so it is generally limited to small loads up to about a quarter horsepower such as fans, electric clocks, phonograph turntables and electric shavers.