SOLUTION

SHADED-POLE MOTORS

The shaded-pole motor has the lowest starting torque of all the single-phase motors. It is relatively inexpensive and is used to turn very small fan blades connected directly to the shaft of the motor. The basic construction of this motor is very simple since no start winding is present. The imbalance in the magnetic field needed to produce rotation is obtained by shading a portion of the run winding with heavy copper wire or band.

When the motor is energized, the strength of the magnetic field is different in the area of the main poles than in the area of the shaded poles, allowing the rotor to turn.

The direction of rotation of a shaded-pole motor is determined by the orientation of the main poles and the shaded poles. The rotor will turn in the direction indicated by the arrows in Figure. Shaded-pole motors are used for very small applications and are rated in watts instead of horse-power. They normally range in size from 6 watts to roughly 35 watts. This is the equivalent of 1/125 horse-power to 1/20 horsepower. The direction of rotation is from the unshaded portion of the pole to the shaded portion of the pole.