HVACR317 - Refrigeration

1. HVACR317 - Refrigeration Motors, Shaded Pole

2. 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.

3. Parts of a Motor

4. 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.

5. Magnets Diagram “Like” poles of a magnet will repel each other. “Unlike” poles will attract each other.

6. 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.

7. 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.

8. Start and Run Windings Diagram

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. Shaded Pole Motor Diagram

18. 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.