A shaded pole motor is basically a small squirrel cage motor in which the auxiliary winding is made up of a copper ring or bar that surrounds a portion of each pole. This one-turn auxiliary winding is called a shadow coil. Current induced in this coil by the magnetic field creates a second electrical phase by delaying the phase of magnetic flux changeover so that enough pole to provide a 2-phase rotating magnetic field.
The direction of rotation is from the unshaded side to the shaded side of the post. Since the phase angle between shaded and unshaded sections is small, shade loop motors produce only a small starting torque compared to full speed torque. Shadow motor poles of the asymmetrical type shown are only reversible by dismounting and pulling in the stator, although some similar-looking motors have small auxiliary coils of fine wire cuttable connection instead of copper bars of thickness and can be reversed electrically. Another method of electrical reversal involves four coils.
Usage of shaded pole motors
The common, asymmetrical form of these motors have a single winding, without starting capacitor or start winding/switch, making them economical and reliable. Larger modern types and can have multiple physical windings, although electrically only one, and a capacitor can be used. Because their starting torque is low, they are best suited for fans or other loads that start to drive easily.
They can have multiple delay lines near one end of the electrical winding, which provides variable speed and power through the selection of one tap at a time, as in ceiling fans. On the other hand, they are compatible with variable speed controls based on TRIAC, which are often used with fans. They are built in power sizes up to approximately 1/6 hp or 125 watts output. For larger engines, other designs offer better features.
This type of motors is used in specific cases, such as driving fans or blowers, which have very low power requirements. Its power range ranges from 0.0007 to 1/4 HP and most are manufactured in the range of 1/100 to 1/20 HP.
Advantages of these motors
Squirrel Cage Induction Motor: The most common type of shaded pole motor in the use of fractional power is squirrel cage induction motor. This has a rotor consisting of a rolled steel cylinder with conductive copper or aluminium rods longitudinally embedded in its surface, connected at the ends to each other.
The main advantage of these engines is their simplicity of construction, reliability and robustness, plus they have a low cost. Unlike other single-phase AC motors, split phase motors do not require auxiliary parts (capacitors, brushes, switches, etc.) or moving parts (centrifugal switches). This makes maintenance a minimum and relatively simple matter.