A shaded-pole motor is a type of AC single-phase induction motor. It is
basically a small squirrel cage motor in which the auxiliary winding is composed
of a copper ring surrounding a portion of each pole. This auxiliary winding is
called a shading coil. Currents in this coil delay the phase of magnetic flux in
that part of the pole enough to provide a rotating magnetic field. The direction
of rotation is from the unshaded side to the shaded (ring) side of the pole. The
effect produces only a low starting torque compared to other classes of
single-phase motors. These motors have only one winding, no capacitor nor
starting switch, making them economical and reliable. Because their starting
torque is low they are best suited to driving fans or other loads that are
easily started. Moreover, they are compatible with TRIAC-based variable-speed
controls, which often are used with fans. They are built in power sizes up to
about 1/6HP or 125 watts output. For larger motors, other designs offer better
characteristics.
