Week 3 HVACR- Motors
Capacitor-start, Induction-run (CSIR) motors are available in either
120 V or 240 V and can produce up to 3 hp.
PSC motors operating voltages are either
120 V or 240 V. They are commonly used in blowers and fans where variable speeds are desirable.
Mircofarads
2650 X amps of the start winding/ voltage start winding= Mircofarads
Vacuum down to
29.92 ins of mercury
Start capacitor
A capacitor used only during motor start-up to provide initial starting torque. Only used for a fraction of a second.
Ac motor
A motor that runs on alternating current.
Capacitor-start, Capacitor-run (CSCR) motor
A single-phase induction motor that has a start capacitor and a run capacitor wired in series with the start winding, but the run capacitor is wired in parallel with the start capacitor.
Capacitor-start, Induction-run (CSIR) motor
A single-phase induction motor that has a start capacitor wired in series with the start winding. The start capacitor puts the current in the start winding out of phase with the current in the run winding. The electromagnetic flux of the two out-of-phase windings provides very high starting torque.
Most single-phase induction motors have two types of stator windings:
A start winding and a run winding also a common terminal.
Capacitor-start, capacitor-run (CSCR) motor use at least two capacitors.
All capacitors are in the start winding circuit, but only the start capacitor is controlled by a centrifugal switch or relay.
When a CSCR motor starts,
Alternating current flows through the whole stator circuit, which includes the run winding, the start winding, the start capacitor, and the run capacitor. The current through the run winding due to the start and run capacitors. This produces a high starting torque.
Induction motors
An AC motor that operate by using the magnetic field generated in the stator to induce current in the rotor.
Single-phase motor
An ac motor that runs on a single phase of alternating current. Single-phase motors are used in many residential applications because the power supplied by utility companies to residential homes is single-phase power. Most single-phase motors are rated for 120 V, 208 V, or 240 V power. Many single-phase motors can run either clockwise or counterclockwise.
Centrifugal switch
An electrical device mounted on the end of a motor shaft that disconnects the start windings from the circuit. It consists of weights that are held close to the motor shaft by the force of a spring. These weights hold a plate against a set of electrical contacts to keep them closed. As the motor shaft approaches its running speed, the weights overcome the spring's force and move away from the shaft due to centrifugal force. This pulls the plate away from the electrical contacts and opens the circuit.
In a CSCR motor a phase difference continues to exist between the run winding and the start winding as the rotor continues to spin.
As a result, a run capacitor improves a motor's power factor, making CSCR motors very efficient.
Terminals may be identified by their
Capitalized first letter on the motor.
Running terminal
Connects to the other end of the run winding.
Motor terminal box
Mounted on the outside of the frame. Where electrical connections are made to control and power the motor.
Motor nameplate
Mounted on the outside of the frame. Which displays essential motor information.
To calculate a motor's synchronous speed
Ns= 120 X f/p 120 X 60Hz/2 = 3600 RPM
Special cooling provisions must be made for hermetic and semi hermetic compressor motors using one of several methods.
One method is pressing the stator into a dome that has cooling fins. heat from the motor travels along the enlarged surface area of the cooling fins and dissipates quickly. Another method is using water flowing through a coil around the motor to dissipate heat while the unit is running. However, systems will more often pass cool suction line vapor and oil over the motor windings.
Run capacitor
Operates in the same way as a start capacitor, except it remains in the start winding circuit while the motor is running. It provides a signal that is out of phase for added torque during the motor's entire operation. Run capacitors are filled with oil and are designed to dissipate the heat generated by the high current used to run a motor.
End bells
Or plates, close the openings at either end of the motor frame. The end bells hold the bearings. When the motor shaft is mounted in the bearings, the end bells support the rotor.
Are normally closed (NC)
Potential relay also a starting relay
Rated load Amperage
RLA
Squirrel cage rotor
Rotor which is made of metal bars mounted on an iron core. The bars connect at each end of the rotor to form a complete circuit.
1 Pa means
Single phase
Induction motors can also be differentiated by their required input power:
Single-phase, two-phase, three-phase, and four-phase. Many small ac motors are single-phase, while many of the larger ac motors are three-phase.
The following single-phase motors are the most common.
Split-phase motor Capacitor-start, induction-run (CSIR) motor Capacitor-start, Capacitor-run (CSCR) motor Permanent split capacitor (PSC) motor Shaded-pole motor
Two types of capacitors used with ac motors:
Start capacitors and run capacitors
There is no difference between a permanent split capacitor motor's
Starting and Running modes. It operates the same way as a CSCR motor operates in its running mode. However, PSC motors often have multiple speeds.
Run windings
Stator windings that are energized during the entire operation of the motor. They provide the bulk of the magnetic force for driving the rotor.
The speed of an ac electric motor is determined by two variables:
The alternating current's frequency (measured in Hz) Number of magnetic field poles in the stator.
motors differ from each other by
The amount of starting torque and running torque that they generate.
Rotor
The axle-mounted unit that rotates as the polarities of the stator's field poles change. The stator can also be called the armature. It is composed of coils of wire surrounding an iron core.
Locked rotor amperage (LRA)
The current that a motor draws as power in first applied to start turning the rotor. This value may be two to six times higher than full-load amperage.
Slip
The difference between synchronous speed and rated full-load speed.
For hermetic units, the motor terminals that connect the motor windings to the power source are
always located outside of the compressor dome.
If a motor runs on a quarter horse but you are using 1/8 horse you will
burn the motor out because it is less horsepower has to do more work because its the same load.
In a motor with both start and run windings,
capacitors are added in series with start winding.
Permanent split capacitor (PSC) motors are sensitive to
changes in applied voltage because they do not have a start capacitor. A 5% to 10% drop in applied voltage will cause starting difficulty and overheating. To prevent damage, a thermal overload protector is used to open the circuit.
Motors are not 100% efficient because of
clearances, bearing friction, and imperfect windings.
The black lead on a voltmeter means
common
No thing as a
common winding
PSC motors applications are limited to
easily started loads and low-horsepower applications.
CSIR motor are commonly used in
hermetic compressors for refrigeration units.
A single unit run capacitor
hooks up to a single motor, and it is more commonly used in smaller HVAC systems, like small air conditioners.
Counter emf depends on the
speed of the motor. The relationship among applied voltage counter emf, and current tends to maintain the rotor at a constant speed. However, if a motor is slowed considerably by a heavy load, the current induced in the rotor increases greatly. Current flow increases because the rotor turns more slowly, which means counter emf and its resistance to current drops.
Split-phase motors are typically built using a
squirrel cage rotor and are available in either 120 V or 240 V.
If a hermetic compressor with an intact motor does not identify the terminals by letter,
take resistance measurements of the windings using an ohmmeter. Terminal identification can be determined by comparing ohmmeter readings taken between the terminals.
You have to check the pins of the compressor
to see if the compressor is damaged. Because if you measure from the wires they can be damaged.
motor is a device that
turns electrical energy into movement.
The rotor is mounted on a motor shaft that has
two bearings, one at each end. The bearing are accurately machined to provide the proper amount of endplay for the rotor.
Permanent split capacitor (PSC) motor
A single-phase induction motor that uses a single run capacitor in series with the start winding for the motor's entire operation. It does not use a centrifugal switch or relay to switch off any capacitors or windings. Current flows through the run winding, the start winding, and the run capacitor during the motor's entire operation.
Split-phase motor
A single-phase induction motor used in applications that operate in the fractional horsepower range. Small condensing units and fans that require up to 1/3 hp are often driven by this motor.
During the start-up of a CSIR motor, current passes through both the start winding and the run winding.
At about 75% of the motor's rated speed, a centrifugal switch or a relay in series with the start winding opens. This disconnects the start winding and start capacitor. The motor continues to run as an induction motor using only the run winding.
The three motor terminals on a single-phase hermetic compressor are
Common (C), Starting (S), and Running (R).
Common terminal
Connects to a single line that joins one end of the start winding to one end of the run winding.
Though PSC motors are very efficient, they have low starting torque.
If a PSC motor tries to start a compressor when a system's low-side and high-side pressure are not balanced, the motor will overheat.
The motor then operates on the run windings only.
If the start winding is left in the circuit, it may overheat.
Counter electromotive force (cemf)
In a running motor, the induced current flowing in the rotor generates a magnetic field. The rotor's magnetic field induces a voltage with a polarity opposite of the voltage applied to the stator. It's the oppositely polarized voltage.
Full-load amerage (FLA)
The electrical current level at which a motor's full-load torque and horsepower are reached.
on a capacitor 45/5 μF means
The first number indicates what the compressor requires and the second is for the fan.
Synchronous speed
The speed of the rotating magnetic field in the stator. If the rotor rotates at the same speed as the stator's rotating magnetic field, then the motor runs at synchronous speed.
Phase splitting
The start and run winding have different inductance values, the current flowing through the start winding is out of phase with the current flowing through the run winding. The means by which single-phase motors are started. The split phases create a rotating magnetic field in the stator, causing the rotor to start turning.
Torque
The work performed by a twisting or turning action, such as a rotating motor shaft.
After a Capacitor-start, Capacitor-run (CSCR) motor reaches 60% to 75% of its rated speed,
a centrifugal switch or relay opens the circuit between the start capacitor and the start winding. This drops the start capacitor out of the circuit, but leaves the run capacitor in.
In some cases, single-phase induction motors use capacitor to create
a much larger phase displacement to help start the motor.
If your would to ohm the 3 phase motor
all the terminals would equal the same.
Internal overload protectors are located
in the circuit of the common terminal
A dual run capacitor
incorporates two capacitors into a single unit. With a dual run capacitor, you can power two electric motors.
IO
internal overload
521
is your potential relays with start capacitor it can also be called a compossar savior.
The start winding may be of smaller diameter than the run winding because
it is only energized for a short time and is not required to handle a continuous current as the run winding must do.
Measure diameter on a fan with two poles
measure from end to end
Measure diameter on a fan with three or more poles
measure from the tip of the fan to the center than multiple by 2
Don't pull motor from the leads
or let it hang from the leads.
A split-phase motor uses the different inductance values of its start winding and run winding to
produce phase splitting and achieve initial rotation. As a result, the starting torque is lower than motors are use capacitors, which means split-phase motors must be used on systems with an easily starting load.
Capacitors are wired in
series
Field windings
The wires wrapped around the field poles of the stator. When current from a power source flows through the field windings, it creates a magnetic field around the field poles.
Starting terminal
Connects to the other end of the start winding.
Are normally opened (NO)
Contactor also a starting relay and current relay
High head pressure can be caused by
Dirty condenser, Too much heat load, Overcharged.
Rated full-load speed
Electric motors do not operate at exactly synchronous speed, they are not rated at synchronous speed. Instead, they are rated at their operating speed under a full load. Under actual conditions, a 3600 rpm motor operates at approximately 3450 rpm.
Field poles
Electromagnets whose polarities change as the flow of current alternates in the field windings.
The terminals on a capacitor are
Herm, Common, and Fan
Start windings
Stator windings that are used for motor starting and additional torque. For each run winding there is a start winding. Start winding coil is made of a smaller diameter wire and has more turns than a run winding coil.
All electric motors share two primary components:
The rotor and the stator.
Stator
The stationary part of a motor that is attached to the inside of the motor housing. The stator is sometimes called the frame. Parts of the stator also include field poles and field windings.
Capacitor-start, Capacitor-run (CSCR) Motor have enough starting torque to start heavy loads.
They generally come in 1/6 hp and larger and are often used in large hermetic compressors in commercial systems and on belt-driven blowers.
In a Permanent split capacitor (PSC) motor the additional wires connect at different points in the run winding.
To change the speed of a motor, switch the wire connections to the motor circuits. The shorter the winding is that the current must pass through, the faster the motor speed. More winding means less speed. Fewer windings mean more speed.
The capacitor on a CSIR motor is usually placed on
Top of the motor in a metal or plastic cylinder.
Unlike the stator, the rotor is not connected to a power source.
When current from a power source is applied to the field windings in the stator, it creates an electromagnetic field. This magnetic field induces current in the coils of wire or metal bars in the rotor. The current induced in the rotor also creates an electromagnetic field created by the stator. The interaction between the magnetic fields of the stator and the rotor causes the rotor to rotate.
Most of current in a single-phase induction motor is conducted through the run winding. When the motor is starting, however, current goes through both the start and run windings.
When the motor reaches 60% to 75% of its rated full-load speed, the start winding circuit is opened by a centrifugal switch or a starting relay.
Capacitors cause capacitive reactance in a circuit,
which is the opposition to the flow of current that causes voltage to lag behind current in an ac cycle
For capacitor
you can only go up in voltage but not down. if it is a 370 V you can't use lower, you can only use higher like 440 V.
On a motor it has a plug
you place it on the side that is facing up so liquid like rain will not go into the motor. The other side of the motor without the plug is so the liquid from the motor will escape so it won't damage the motor.
Mircofarads
μF. We measure in mircofarads for the capacitance
Built-up terminals
These are bolt to the compressor dome. Gaskets of synthetic material are used to make a leakproof joint. The advantage of using these is that it is easier for technicians to install replacement terminals if needed.
There are many different design of single-phase motors.
These motors differ based on the applications they are used in and the methods that are used to start and run them.
