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HVACR214 – Electrical for Oil

Motors

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Motors

• 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.

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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

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

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Motors

• 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.

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Motor

• 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.

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Start and Run Windings

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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 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 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.

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Shaded 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.

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Shaded 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.

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Shaded 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.

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Shaded Pole Motor Example

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Shaded 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.

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Split 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.

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Split 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.

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Split phase motors

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

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Split Phase Motors

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Split 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.

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Centrifugal Switch

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

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Centrifugal Switch

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Permanent Split Capacitor Motors

• In order to increase the starting torque of a motor you can insert a capacitor in series with the start winding circuit.

• In a PSC motor this capacitor remains in series while the motor is operating. There is no switch or relay that removes this capacitor from the circuit.

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PSC Motor

• Residential Condenser fan motors and residential furnace blower motors are the primary use of PSC motors.

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PSC Motor

• PSC motors have moderate starting torque and intermediate running efficiency.

• These motors are used primarily for small compressors and direct-drive blower and fan applications.

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PSC Motor Example

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CSIR Motors

• CSIR are capacitor start and induction run motors.

• They use a start cap and a start relay.• Once the motor has reached 75% of its

rated speed the start capacitor is removed from the circuit.

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CSIR motors

• CSIR motors have a high starting torque and are used in residential and small commercial compressors.

• May see them in beverage coolers or small reach ins.

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CSCR Motors

• CSCR (Capacitor Start Capacitor Run) motors are the same as Permanent Split Capacitor motors except they have a start capacitor wired to them.

• A start capacitor is a high capacitance capacitor that will provide the motor with additional torque when starting.

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CSCR Motors

• Once the motor has been started it, the start capacitor must be taken out of the circuit using a switch or a relay.

• These devices are called start components and this is covered in the next section.

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CSCR Motors

• This motor can be abbreviated to CSR. (Capacitor Start and Run).

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CSCR Motor Example

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Hermetic Motors

• Hermetic motors are single phase up to about 5 hp (horsepower).

• Hermetic motors are those found inside the compressor shells.

• They are wired the same way as any other split phase motor, but the start components must remain outside the compressor shell.

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Hermetic Motors

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Hermetic Motors

• On the outside of the compressor shell there are three terminals. Most of the time these have some markings on them.

• They are labeled C, R, S– S = Start winding– C = Common– R = Run Winding

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Hermetic Motors

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Motors

• If the windings are not marked use your ohm meter and check resistance.

• Check between all three windings.• The winding measurement with the highest

resistance is between start and Run (S and R). The remaining terminal is Common ( or C).

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Motors

• Once you know C check between C and the other two terminals the one with the highest resistance is S (or Start).

• The one with the lower resistance is Run (or R).

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Motors

• Best way to do this is to write down C, S, R in a triangle on a piece of paper and make sure you write down each measurement.

• If you have any doubt - go back and do it again.

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Motor Speeds

• Motor speeds are shown in RPM’s• RPM is revolutions per minute. This is a

measure of how many times per minute the shaft rotates.

• Sometimes you will need to figure out RPM’s for a motor.

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Motor Speeds

• To figure motor speed first use the motor labels

• If no label is found use the formula:– Speed (rpm) = (frequency x 120) / Poles

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Shaded Pole Diagram

CR

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CSCR Diagram

C

S

R

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Split Phase Diagram

C

S

R

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PSC Diagram

C

S

R

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