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HVACR317 - Refrigeration

Motors, Shaded Pole

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Motors

• Motors consist of a stationary part called the ‘stator’ that surrounds a rotating part called the ‘rotor.’

• One ore more windings are mounted on the stator.

• There are usually no windings on the rotor.

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Parts of a Motor

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Motors

• The rotor, or the center part of the motor, is not connected to any external source of voltage.

• When the winding on the stator is powered, it generates a magnetic field.

• As the A/C changes from a positive to a negative, this magnetic field will rotate.

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Magnets Diagram

“Like” poles of a magnet will repel each other.

“Unlike” poles will attract each other.

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Motors

• As you recall, ‘like’ poles of a magnet repel each other.

• As the magnetic fields of the stator windings change from positive to negative, it “chases” the rotor, because the poles on the rotor are positive and negative.

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Motors

• This constant changing of the magnetic field will keep a motor running.

• The problem comes when you are trying to start a motor. If the magnets are lined up evenly between poles, the motor will not start.

• This is the purpose of the start winding.

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Start and Run Windings Diagram

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Start Winding

• This is an additional winding in a single-phase motor that allows the motor to start when the poles of the stator and rotor are not in the correct position.

• The current applied to the start winding is slightly out-of-phase with that of the current applied to the run winding.

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Run Winding

• This is the winding on the stator that allows the motor to continue to operate.

• The run winding gets constant voltage until the motor shuts off.

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Shaded Pole Motor

• The shaded pole motor is the simplest motor.

• It has one winding surrounding a laminated core.

• It uses a shaded pole to determine its rotation.

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Shaded Pole Motor

• The shaded pole motor consists of a squirrel cage rotor, an iron core, and two or more rings (poles) with a coil and small copper inserts.

• The insert slows the buildup of the magnetic field just enough to cause rotation towards the magnetic field.

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Shaded Pole Motors

• The action provides for induced magnetism into the rotor.

• The rotor will then turn as if it is attracted by the magnetism.

• Movement of the rotor will continue as long as there is change of the polarity of the poles and the rotor.

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Shaded Pole Motors

• The action provides for induced magnetism into the rotor.

• The rotor will then turn as if it is attracted by the magnetism.

• Movement of the rotor will continue as long as there is change of the polarity of the poles and the rotor.

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Shaded Pole Motors

• If the motor stalls or if the bearings freeze, the motor windings will not usually burn out.

• When the motor is in a locked condition, the windings draw very little current.

• The direction of a shaded pole motor is towards the shaded pole.

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Shaded Pole Motors

• Shaded pole motors can be made multiple speed by inserting voltage taps into the motor winding.

• Shaded pole motors are low in cost, but have a very low starting torque and a very low power factor.

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Shaded Pole Motor Diagram

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Shaded Pole Motors

• Shaded pole motors are built for very small sizes and are used for light duty in small appliances.

• In refrigeration, shaded pole motors are frequently used for evaporator fan motors.