1

HVAC214 - Oil ElectricalHVAC214 - Oil Electrical

Motors Part 1

Motors Part 1

2

MotorsMotors

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

• One or more windings are mounted on the stator.

• There are no windings usually on the rotor.

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

• One or more windings are mounted on the stator.

• There are no windings usually on the rotor.

3

Parts of a motorParts of a motor

4

MotorsMotors

• 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.

• 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

MagnetsMagnets

Like poles of a magnet will repel each other. Unlike poles will attract each other.

6

MotorsMotors

• As you remember 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 as the poles on the rotor are positive and negative.

• As you remember 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 as the poles on the rotor are positive and negative.

7

MotorMotor

• 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 would not start.

• This is the purpose of the start winding.

• 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 would not start.

• This is the purpose of the start winding.

8

Start and Run WindingsStart and Run Windings

9

Start WindingStart 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 applied to the run 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 applied to the run winding.

10

Run windingRun 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.

• 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 MotorShaded 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.

• 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 MotorShaded Pole Motor

• The shaded pole motor consists of a squirrel care 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.

• The shaded pole motor consists of a squirrel care 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 MotorShaded Pole Motor

• 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.

• 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 MotorsShaded Pole Motors

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

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

15

Shaded Pole MotorShaded Pole Motor

• 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.

• 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.

16

Shaded Pole Motor ExampleShaded Pole Motor Example

17

Shaded Pole MotorShaded Pole Motor

• 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.

• 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.

18

Split Phase MotorsSplit Phase Motors

• Split phase motors are also called induction start - induction run motors.

• These motors use a current relay or a centrifugal switch to remove the start winding from the circuit.

• The start windings work on a phase shift principle.

• Split phase motors are also called induction start - induction run motors.

• These motors use a current relay or a centrifugal switch to remove the start winding from the circuit.

• The start windings work on a phase shift principle.

19

Split Phase MotorSplit Phase Motor

• The voltage from the start winding to the run winding is 10 degrees out of phase.

• Starting torque and running torque are relatively low in split phase motors because the phase shift is so low.

• The voltage from the start winding to the run winding is 10 degrees out of phase.

• Starting torque and running torque are relatively low in split phase motors because the phase shift is so low.

20

Split phase motorsSplit phase motors

• These motors are used for belt drive blower applications such as small appliances like:– Washers– Dryers– Dish washers– Some older furnace blowers

• These motors are used for belt drive blower applications such as small appliances like:– Washers– Dryers– Dish washers– Some older furnace blowers

21

Split Phase MotorsSplit Phase Motors

22

Split Phase MotorSplit Phase Motor

• The centrifugal switch removes the start winding from the motor circuit once the motor reaches around 75% of its rated speed.

• This is the part that most often fails when a motor is started and stopped many times.

• The centrifugal switch removes the start winding from the motor circuit once the motor reaches around 75% of its rated speed.

• This is the part that most often fails when a motor is started and stopped many times.

23

Centrifugal SwitchCentrifugal Switch

• The switch is normally closed when the motor is not operating.

• The switch is normally closed when the motor is not operating.

Centrifugal Switch