17 Flashcards
Converts AC power to DC by use of phase-controlled rectifier or diode bridge
rectifier.
Dc converter
Electronic device in a motor circuit that is used to control motor speed for variable
speed motors.
Pulse Width Modulator
Single phase motor with a start and run winding that has a capacitor in series with
the start winding which remains in the circuit until the motor gets up to 75% of the motor’s rated speed.
Capacitor start motor
Assists in starting the motor using BEMF to cut out the start capacitor.
Potential relay
Used as a switch or as a device to amplify or increase an electrical signal.
Convert DC power to AC power.
Transistor
When the contacts between terminals 1 & 2 in a potential relay will be opened by
BEMF.
Pick up voltage
As temperature increases, resistance increases. Acts as an open circuit and stops
all current flow through a circuit.
PTC start device
Switching or transistor section of the variable frequency drive that produces an
AC voltage at just the right frequency for motor speed control.
Inverter
Induced voltage in the start winding that is used to open the switch in a potential
relay.
BEMF
Similar to a split phase motor but does not have a start capacitor. Used for low
starting torque applications.
PSC motor
Maximum EMF that the coil can tolerate continuously without overheating and
opening the circuit in a potential relay.
Continuous coil voltage
Single phase motor that has a start capacitor in series with the start winding that is disconnected after start-up and run capacitor in parallel that stays in the circuit while running.
Capacitor start capacitor run motor
Cycles per second of the electrical current that the power company supplies. Can
be either 50 or 60 Hz depending on geographical location.
Frequency
The speed at which power devices in the VFD switch on and off.
Switch frequency or carrier frequency
Used to control the capacity of small compressors. Can be considered as tow
motors in one housing.
Two speed compressor motor
Solid state device used with some motors to open the start windings after the
motor has started.
Electronic relay
The stator is the rotating part of an electrical motor. T/F
F
Synchronous motors have slip. T/F
F
If a three-phase fan rotates in the wrong direction, it will move only about half
as much air. T/F
T
The heavier the load on an operating motor, the greater the amount of slip. T/F
T
The centrifugal switch mounted on the shaft of a split-phase motor has a normally closed contact. T/F
T
_If the switch or the coil in a potential relay have a reading of “OL” when checking resistance, the potential relay is good. T/F
F
The microfarad rating of the run capacitor is lower than that of the start capacitor for any given motor. T/F
T
A permanent-split capacitor motor has a run capacitor only. T/F
T
The contacts in a potential type starting relay are normally open. T/F
F
A capacitor-start capacitor-run motor that is wired with a potential
relay will have the start winding energized when the relay’s contacts are open. T/F
T
Terminal S of a current relay is connected to the Start winding. T/F
T
The contacts in a current type starting relay are normally closed. T/F
F
Two speed compressor motors have more than three motor terminals to
operate its two motors. T/F
F
The difference between a split phase motor and a PSC motor is the split phase motor will have a run capacitor and the PSC motor will have a start capacitor. T/F
F
The full wave rectifier moves the negative portion of the sine wave to the
positive side of the sine wave thus converting AC voltage to pulsating DC voltage. T/F
T
The Service Factor (SF) on a motor data plate is 1.25. How many amps can the motor draw above its full load amp rating of 5A, for a limited time, without damaging the motor?
6.25 A
Motor A has a rating of 1800 pm, motor B has a rating of 1200 pm and motor C has a rating of 3600 rpm. Which motor has the most poles?
Motor B
motor that has 4 poles and is powered by 60 Hz voltage has a no-load speed of how many rotations per minute?
1800 rpm
What does it mean when a 3-phase motor is single phasing?
One of the phases dropped out
Switch, filter, or rectification
Transistor
Switch
Switch, filter, or rectification
Inverter
Switch
Switch, filter, or rectification
Silicone controlled rectifier
Rectification
Switch, filter, or rectification
Capacitor
Filter
Switch, filter, or rectification
Diode
Rectification
Switch, filter, or rectification
Choke
Filter
Switch, filter, or rectification
Pulse width modulation
Switch
List the steps you would take to check out a 3-phase disconnect for the proper voltage.
check above the fuses, the line side voltage.
Then check The load side going to the load.
Name four devices that may be used to remove the start capacitor from the motor
starting circuit.
Centrifugal switch, current relay, potential relay, electronic relay
You are checking the switch in a potential relay. What terminals do you place your probes on?
1 and 2
When voltage leads current
Inductive
When current leads voltage
Capacitive
What is the total capacitance going to the start winding circuit when the start
capacitor is 110 uf and the run capacitor is 10 uf in diagram A?
120
If Common to Run measures OL what is the expected resistance reading for Run to Start?
OL
Common to Start measures OL. Common to Run measures OL. Run to Start measures
5 Q. What is wrong with the compressor?
Open internal overload
When measuring the motor windings of an ECM motor, what is the expected resistance of all the windings?
All the same
