Download
1 / 47
480 likes | 628 Views
HVACR317 - Core for Refrigeration. Motors. 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. Parts of a motor. Motors.
E N D
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.
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.
Magnets Like poles of a magnet will repel each other. Unlike poles will attract each other.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.
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 • 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 • The switch is normally closed when the motor is not operating.
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 • Residential Condenser fan motors and residential furnace blower motors are the primary use of PSC motors.
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.
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.
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 (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.
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.
CSCR Motors • This motor can be abbreviated to CSR. (Capacitor Start and Run).
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 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 • 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).
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).
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.
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.
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
CSCR Diagram R C S
Split Phase Diagram R C S
PSC Diagram R C S
