TM 5-4310-384-13
1-15.
OPERATION OF THE ELECTRIC MOTOR.
a.
The electric motor is a single phase dual voltage induction motor. The operation of a single phase dual voltage
induction motor depends on two basic parts, the stator or stationary windings and the rotor.
b.
The rotor does not have windings, but has metal bars pressed into its frame which act as conductors of
electrical current. The rotor does not have any external connections.
c.
Electric power is connected across the terminals, which causes current to flow in the stator windings and
produce a rotating magnetic field.
d.
This magnetic field cuts across the conductors in the rotor, inducing currents in the conductors. This causes a
repelling force between the conductors and the magnetic field and causes the rotor to turn.
Electric Motor Schematic
1-16.
OPERATION OF ELECTRIC MOTOR CONTROLS.
a.
The electric motor controls consist of the on/off switch, the reset button, the pressure switch, and the motor
starter. These controls make the operation of the air compressor fully automatic.
NOTE
The overload (OL) in the diagram stands for the melting alloy device that opens when too much current is drawn by the
motor such as an OL condition.
b.
Power from the main switch comes into the starter at L1 and L2. Connections to the motor are at T1 and T2.
c.
Normal operation pressure below 160 psi: when the on/off switch is turned on and the pressure in the tank is
below 160 psi, the pressure switch contacts will be closed. Current will then go through the coil. The coil then pulls the
normally open contacts E1 and E2 closed. The circuit to the motor is completed and the motor starts.
d.
Normal operation pressure above 190 psi: when the pressure goes above 190 psi, the contacts of the pressure
switch open and stop the current through the coil. Contacts E1 and E2 open and the motor stops.
e.
Overload Condition: If the motor draws too much current, overload relay OL heats up and the normally closed
contacts in series with the coil open up. This stops the current through the coil and contacts E1 and E2 open. This stops
the motor and prevents it from burning out. The relay has to be manually reset before the motor can be started again.
This is accomplished by pushing the reset button which manually closes the overload relay contacts.
1-9
