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HVACR317 - Refrigeration. Split Phase Motors PSC, CSIR, CSCR. 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.

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hvacr317 refrigeration

HVACR317 - Refrigeration

Split Phase Motors

PSC, CSIR, CSCR

split phase motors
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.
split phase motors1
Split Phase Motors
  • 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.
split phase motors2
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
split phase motor
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.
centrifugal switch
Centrifugal Switch
  • The switch is normally closed when the motor is not operating.
psc motors
PSC Motors
  • PSC stands for 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.
psc motor
PSC Motor
  • Residential Condenser fan motors and residential furnace blower motors are the primary use of PSC motors.
  • 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.
csir motors
CSIR Motors
  • CSIR stands for Capacitor Start and Induction Run motors.
  • CSIR Motors 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.
csir motors1
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.
cscr motors
CSCR Motors
  • CSCR stands for Capacitor Start Capacitor Run Motors. Can also be abbreviated to CSR (Capacitor Start and Run).
  • These 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.
cscr motors1
CSCR Motors
  • Once the motor has been started, the start capacitor must be taken out of the circuit using a switch or a relay.
  • These devices are called start components and will be covered in another section.
hermetic motors
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.
hermetic motors1
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
motors
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).
motors1
Motors
  • Once you know C, check between C and the other two terminals.
  • The one with the highest resistance is Start (or S).
  • The one with the lower resistance is Run (or R).
motors2
Motors
  • The best way 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.
motor speeds
Motor Speeds
  • Motor speeds are shown in RPMs (revolutions per minute).
  • This is a measure of how many times per minute the shaft rotates.
  • Sometimes you will need to figure out RPMs for a motor.
motor speeds1
Motor Speeds
  • To figure motor speed, first use the motor labels.
  • If there is no label, use this formula:

Speed (rpm) = (frequency x 120) / Poles

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