Type of Electric Motors

The motor's bearings

Allow for low-restriction rotation of the rotor. They help reduce friction and the heat generated by the motor's moving and rubbing parts and surfaces.

Motors

Are rated with two different current ratings, full-load or rated-load amperes (LRA) or rated-load amperes (FLA or RLA).

Motor slip%=

Calculated motor speed-actual motor speed/calculated motor speed x 100

S (rpm)=

Frequency * 120/ number of poles

Motor Slip

Represents the difference between the motor's calculated and actual speed.

Is not wired to the power source like the stator is

Rotor

The Starting and Running Characteristics

Two major considerations of electric motor applications

Magnets

are known to have two different electrical poles, north and south. Unlike poles attract each other, and like poles repel each other.

Electricity and magnetism

are used to create the rotation in an electric motor to drive the fans, pumps, and compressors.

Excessive motor slip

can be an indication of improper motor lubrication, defective motor bearings, poorly adjusted belts (too tight), or an improperly selected motor for the desired application (overload)

Capillary Tubes Applications

can typically use compressors with low starting torque as a the system pressures can equalize during the off cycle.

Single-Phase Motor

has two run windings and one start winding. The two run windings have the same resistance and the start winding has a high resistance.

Start Windings

have more turns than the run windings and are wound with smaller diameter wire.

Motor Housing, End Bells, and Base

hold the motor components in place and provide a means for securely mounting the motor itself.

The Stator

is a winding that, when energized, will generate a magnetic field-because there will be current flowing through it.

Typically, the LRA for a motor

is about 5 times the FLA/RLA.

The Motor Shaft

is connected to the rotor; therefore, when the rotor turns, so does it.

Start Winding

is in the circuit only for as long as it takes the rotor to get close to its rated speed and it then is electrically disconnected.

Slip

is often expressed in percentage.

Locked-rotor amperage

is often referred to as inrush current.

RPM

is rotation per minute.

Starting Torque

is the power to turn the shaft from the stopped position.

The Rotor

is the rotating portion of the motor and is made of iron or copper bars bound on the ends with aluminum.

Synchronous speed

is the rpm of a motor without a load.

Torque

is the twisting power of the motor shaft.

Start Winding

is wound next to the run winding but is a few electrical degrees out of phase with run winding.

When a motor is still

it takes a great deal of torque to get it turning, particularly if the motor has a load on start-up.

Split-Phase Motors

many have fours poles and run at 1800 rpm.

Some Motors

must have a great deal of starting torque and to turn the motor at the stopped position but do not need a great deal of torque to maintain speed.

A motor applied to a refrigeration compressor

must have a high starting torque, it must be able to start under heavy starting loads.

The Motor

must have enough torque to operate with the load of the application.

Some TXV systems

require greater starting torque as there may be a pressure differential across the compressor even when the compressor is not operating.