Motor (section20)
Why is the frame number of a motor so important?
It gives all the physical data of the motor when you need to replace a motor
What is the maximum variation from motor nameplate voltage that can be tolerated without possible problems
+or- 10%
What does the motor horsepower rating indicate?
The amount of work that a motor can do
Describe the operation of a motor starter heater
The heater will begin to heat up substantially if its current rating is exceeded
What does a motor full load amp rating refer to?
The maximum amperage that the motor is designed to run at
What does a motor thermal protector actually sense?
The of the motor windings temperature
Describe the operation of a motor overload assembly
The overload is a spring loaded set of contacts held in place by a small ratchet cog The cod is soldered in place If the overload heater amp rating is exceeded the heater will heat hot enough to melt the solder and the cog will slip allowing the overload contacts to open After the overload cools a reset button can be used to reset the overload contacts
if the centrifugal switch has two sets of contacts, what is the purpose of the second set?
The second set serves as a safety device to disconnect a control circuit in a machine if the motor is not running
What is a motor stator?
The stationary part of the motor that holds the motor windings
What type of fuses must be used for motor applications?
Time delay
what is the purpose of an automatic reset thermal protector?
To protect the motor windings from overheating and failing
What is the function of motor brushes?
To provide the electrical power to the armature windings
What is the function of a centrifugal switch on a split phase or capactor start motor?
To remove the stan winding from the circuit when the motor gets to about 2/3 of its full speed
How long does the centrifugal switch remain closed when the motor is started?
Until the motor reaches about 213 of its normal speed.
What is the advantage of using a motor starter over other forms of motor protection?
Very close monitoring of overloads to protect the motor
When should you replace motor brushes?
When they wear down(I suggest replacing them when they wear to 50% or so of their normal length)
What are the four main types of sleeve bearing systems?
Wick oil cup, oil ring reserve, yarn packed, three felt wick
Do motor overload heaters ever weaken? Why?
Yes, especially if the ratchet cog is on the heater The ratchet can only reset so many times before it is weakened
What is the major advantage of DC motors in applications in the Foodservice industry?
can control and vary the speed of the motor without losing so much ofits torque
How does a capacitor start motor vary in design from a split phase motor?
capacitor is added in series with the start winding
What preventive motor maintenance is required for oDP motors to prevent bum out?
keep the vent holes clean and occasionally blow out the inside of the motor through the vent holes with compressed air or CO2.
How does the resistance of a start winding help to start a motor?
lf puts the current in one winding out of phase with the other to create more starting torque
How does a centrifugal switch work?
movable parts switch is mounted to The centrifugal force when the rotor gets up to a certain RPM is enough to overcome the spring tension the switch and open it in
Does a shaded pole motor have a start winding?
no
Does a shaded pole motor used a centrifugal switch?
no
what will happen if a run capacitor remains in the circuit too long?
nothing
Give four possible reasons for a motor to draw excessive amperage,
overloaded, low voltage, high voltage, tight motor bearings
What applications require the used of sealed ball bearings?
related equipment like pumps, disposers or grea fans
What is a commutator and what is its purpose?
segments located around the motor shaft on a Dc motor that are insulated from each other. It switches the pole from to on DC motors as the armature rotates
What does an ambient temperature rating of a motor refer to?
the maximum ambient temperature that it can operate in without problems
What is the problem with just using a normal branch line circuit breaker to protect a motor?
the size of the breaker is offten nowhere close to the fla rating of the motor
Describe an open drip proof motor
through the motor stator to cool the windings
Describe the torque characteristics of a three phase motor
very high start and running torque
Give the five minimum facts that you will need to get a replacement motor
voltage, speed, horsepower, frame number, and type of motor housing(open or TEFc)
When should a resilient motor mounting be used?
when vibration from the motor can be transferred, and quiet operation is desired
When should a manual reset thermal protector be used?
whenever a dangerous condition could exist if the motor restarted by itself
Do most motors operate at less than full load amperage?
yes
At what frequency are motors in this country designed to operate?
60 hertz
How should fuses used to protect motors be sized?
78 As close to the FLA rating as possible
What is the main problem with using only fuses to protect a motor circuit?
79 It is often impossible to find a fuse that is rated very close to the FLA rating so The size of the breaker is often nowhere close to the FLA rating of the motor
What is a permanent magnet DC motor?
A DC motor that has a field that is a permanent magnet
Give some applications for capacitor start motors?
Air compressors, large heavy wheel blowers. production machines
What is a split phase motor?
An AC motor having only a run winding and start winding
what is the starting current of a split phase or capacitor start motor?
Approximately 5-6 times the full load running current
What will happen if motor brushes are allowed to wear excessively?
Arcing will occur and the commutator will be ruined
What is the rotating part of a DC motor called?
Armature
if a fan has an adjustable pulley on it, what will happen to the motor as the pulley is adjusted to make the fan run faster?
As the speed of the fan is increased the motor amperage will increase
Why will good Dc motor preventive maintenance include cleaning the inside of the motor housing?
Because the as the brushes wear the carbon dust can eventually short the motor
why are some AC motors called induction motors?
Because the current is induced into the rotor by the windings in the stator
A standard general purpose motor will have what insulation class rating?
Class A
A heavy duty motor will normally have a insulation class rating of what?
Class B
What is an automatic motor starter?
Contains a contactor, overloads, and overload heaters in one unit
what applications require the use of shielded ball bearings?
Dusty or dirty environments ke kitchen exhaust
In what range of amp ratings are motor overload heaters assembly
Every few tenths of an amp in many cases
Which amp rating on a contactor must be used when sizing for a motor application?
FLA(Full Load Amps)
When can a ODP motor be used?
Fairly clean and dry environments.
PSC motors are normally used for what applications?
Fans and blowers often found in furnaces and air conditioners
Give some examples of applications where split phase motors are used
Fans, and light blowers
What of magnets have allowed permanent magnet motors to be manufactured smaller sizes?
Ferrite ceramic magnets
When is a TEFC motor needed?
Grease laden or moisture laden environments(Dishwashers, disposals, shortening filters)
When should ball bearing motors be used?
Heavy radial loads, or applications where the sleeve motor bearings are not likely to be
66 Class For H insulated motors are used in what applications?
High ambient heat applications
What applications are universal motors used for?
High speed applications blenders, power tools etc
What applications would need a capacitor start, capacitor run motor?
High start and run torque loads where energy is desired efficiency
Describe the torque characteristics of a capacitor start motor?
High starting torque, medium to high running torque
what type of lubricant is needed for high temp app
High temperature synthetic motor oils
How does a start capacitor differ from a run capacitor?
High to the microfarads in a run capacitor A start capacitor handle motor currents for more than a minute or so, where as the run capacitor handles current as long as the motor is running
What does the temperature rise rating of a motor refer to?
How hot the motor will run at full load above the ambient temperature
Where is the capacitor connected in a capacitor start motor?
In series with the start winding
How does a PSC motor differ from a capacitor start motor?
It has low starting torque compared to the high starting torque on a capacitor start motor It is more energy efficient lt uses a low uf run capacitor in the circuit all the time instead of the high uf start capacitor in the circuit for a short time
What happens to the speed of a universal motor as the load is increased?
It slows way down
If dirt or dust keeps the centrifugal switch contacts from making a good connection how will the motor act?
It will draw high amps, and sit there and hum until the overload opens the circuit
What will happen if a start capacitor remains in the circuit too long?
It will open up or short out
Describe a good preventive maintenance procedure for a motor
Keep the motor clean and lubricated if needed check the bearings for tightness, and always check the running current and voltage to ensure they stay within the nameplate limitations
What preventive maintenance is required for a TEFc motor to prevent chances of burnout?
Keep the motor housing clean of grease or other residue and the fan blade clear of obstructions and clean
Describe a manual motor starter
Like a manual switch with an overload protector to open the circuit if it senses a motor overload
Motors work from the principle of magnetic poles which states that opposite poles react how? like poles and opposite react how
Like poles repel, opposite poles attract
Describe the torque characteristics of a shaded pole motor
Low running and very low starting torque
Describe the torque capabilities of a split phase motor
Low starting torque, medium running torque
Describe the torque characteristics of a PSC motor
Low starting torque, medium running torque
When can sleeve bearings be used on motors?
Low to medium loads when the motor will be accessible to have the bearings oiled on a regular basis. and inexpensive
Why is a permanent magnet DC motor better for speed control than a wire wound motor?
More constant torque as the load and voltage changes
How often do ball bearings need to be relubricated?
Most are permanently lubricated, if you ran into an old motor will grease jerk fitting, follow the motor or equipment manufacturers lubrication suggestions
Describe a (TEFC) totally enclosed fan cooled motor
Motor housing is totally sealed An external fan blade attached to the back of the motor draws over the outside of the motor to cool it
Most electric motor burn outs are caused by what?
Motor overheating
Does a PSC motor use a centrifugal switch?
No
Does a three phase motor have a start winding?
No
Can a split phase motor be used for an air compressor? Why?
No, not enough starting torque
can all sleeve bearing motors be installed in any position or angle? Why?
No, those with a reservoir would dump the oil in some
What is a PSC motor?
Permanent Split Capacitor
What does the capacitor on a capacitor stan motor do to the electric current on the motor to increase its starting torque?
Puts the current in the start winding further out of phase with the run winding to create even greater starting torque
What is the major disadvantage of sleeve bearings?
Quiet
What does the service factor rating on a motor mean?
Relates to the motors ability to do more than its rated amount of work
What are the three most common types of motor mountings?
Rigid, resilient, and face mount
What is the rotating part of an AC motor called?
Rotor
what type of lubricant should be used on sleeve bearings for a normal motor application.
SAE20 motor oil wick
The difference between synchronous speed and nameplate rated speed is referred as what
Slip
Give some common applications for shaded pole motors.
Small fans and gear motors
What characteristic of a motor does frequency affect?
Speed
What is meant by the term synchronous speed of a motor?
Speed at ideal conditions
