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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.