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The term "shaded-pole motor" typically refers to one of the simplest alternating-current, single-phase induction motors used today. Typical configurations essentially consist of a rotor assembly and a stator pole. As an induction motor, this motor relies on electromagnetic forces to generate torque. The simplicity of this motor is both beneficial and limiting, making it efficient for a limited range of applications. There are many variations of a shaded-pole motor, though many of the principles used in their design provide the basis for other comparable motors.
The simplest shaded-pole motor consists of a rotor assembly and a stator pole and contains a series of shaded and unshaded windings. Shaded windings consist of copper conductors that typically produce a weak magnetic field once a rotor starts spinning. This magnetic field is often used to create an increased torque that can be altered to maintain and adjust rotor speed.
Generally, induction motors rely on the magnetic production of torque for much of their operations. A shaded-pole motor is a unique induction motor because the copper shade windings do not receive any direct electrical charge. Instead, it is the magnetic flux created by the interactions of the windings in the pole with the moving rotor that further increases the torque once started.
There are several benefits to using a shaded-pole motor and several limitations to what they can achieve. The configuration of these motors is often considered simple, which makes them more rugged and less expensive than many comparable designs. This simplicity, however, means the power that can be produced is weak compared to other motors. The low starting torque of these motors also means they are best suited to small electronic devices.
To use a shaded-pole motor, a device must have an easily started load, because of the low torque and power produced. Common applications include household fans, which typically require low torque and adjustable rotor speeds. Additional applications can include many low-power devices, such as hair dryers, humidifiers and some electronic toys. In many cases, this type of motor will be the most rugged and least expensive component of a household device.
Generally, a shaded-pole motor is defined by its size, horsepower, maximum torque and primary function. Variations typically stem from increasing or decreasing the amount of shaded and unshaded windings in the pole. Large box fans, for instance, are likely to have a more complex shaded-pole motor than small personal fans with much smaller fan blades.