A shaded-pole motor is a type of single-phase induction motor that uses a simple and inexpensive method to create a rotating magnetic field, which in turn drives the motor's rotor to spin. While more common induction motors require multiple phases to generate a rotating magnetic field, shaded-pole motors achieve this with a clever design that takes advantage of the interaction between a main winding and a shaded pole.
Here's how a shaded-pole motor works:
Main Winding: The motor's main winding is wrapped around a significant portion of the stator (the stationary part of the motor). This winding is connected to the power source and carries the single-phase AC voltage.
Shaded Pole: Adjacent to the main winding, there is a pole made of a material that's typically less conductive, such as copper or brass. This pole is known as the "shaded pole." It's called "shaded" because it's partially covered by a thin, usually copper, ring or sleeve that's placed on one side of the pole.
Phase Difference: When the AC voltage is applied to the main winding, it generates a magnetic field that alternates in polarity due to the changing current direction. This magnetic field is not uniform across the stator due to the presence of the shaded pole. The shading coil causes a phase difference in the magnetic flux between the shaded side and the unshaded side of the pole.
Starting Torque: Due to this phase difference, the magnetic field on the unshaded side of the pole lags behind the shaded side. This time lag causes a temporary imbalance in the magnetic field around the pole. As a result, a rotating magnetic field is created within the stator, even though the main winding alone would only produce a pulsating magnetic field.
Rotor Interaction: The rotor, which is typically a squirrel-cage rotor (similar to that used in other induction motors), is located within this rotating magnetic field. The rotating field induces currents in the rotor bars, generating a magnetic field in the rotor as well. The interaction between the stator's rotating field and the rotor's field results in a torque that drives the rotor to spin.
Motor Operation: The torque produced by the interaction of the rotating magnetic fields causes the motor to start rotating. However, shaded-pole motors are generally used in applications requiring low starting torque, such as small fans, toys, or other light loads.
It's important to note that shaded-pole motors are relatively simple and cost-effective, but they have limitations. Their starting torque is low, and they might not be suitable for heavy loads or applications that require precise speed control. However, for their intended uses, they provide a simple and reliable solution for creating a rotating magnetic field in single-phase induction motors.