The shaded pole motor is electrically simple,
since it has no start winding, starting
switch or capacitor. Its speed can be
controlled by varying the voltage, or by a
multi-tapped winding, as shown. A
continuous copper ring is wound around a small
segment of each motor pole. This
"shading" causes magnetic flux in that
segment, to lag the flux field in the un-shaded
segment. The reaction between the two,
causes the rotor to rotate. The
benefits of the design are low cost, easy to
manufacture motors for many
applications. There are some drawbacks to the
design. Low starting torque, as low as
25% to 75% of running torque. High slip,
meaning the motor speed will slip back as much
as 7% to 10%. They are also
inefficient, sometimes as low as 20% efficient.
These motors are typically applied in fan
applications with low starting torque
requirements.