Post on 18-Dec-2015
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HVACR317 – Core for Refrigeration
MotorsSplit Phase
PSCCSIRCSCR
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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