TM 5-2410-241-23-1
0008
ELECTRICAL SYSTEM CONTINUED
Starting System Components
0008
Refer to Table 2.
0008
Starting Solenoid
0008
The starting solenoid is an electromagnetic switch that performs the following basic operations:
Closes the high current starting motor circ it with a low current start switch circuit.
u
Engages the pinion for the starting motor with the ring gear.
The solenoid has windings around a hollow cylinder. A plunger capable of moving forward or backward with spring
pressure (core) is inside of the cylinder. When the start switch is closed and electricity is sent through the windings,
a magnetic field is created. The magnetic field pulls the plunger forward in the cylinder. This moves the shift lever in
order to engage the pinion drive gear with the ring gear. The front end of the plunger then makes contact across
the battery and motor terminals of solenoid. Next, the starting motor begins to turn the flywheel of the engine.
When the start switch is opened, current no longer flows through the windings. The spring now pushes the plunger
back to the original position. At the same time, the spring moves the pinion gear away from the flywheel.
The windings are called the hold-in winding and the pull-in winding. Both sets of windings have the same number
of turns around the cylinder, but the pull-in winding uses a wire with a larger diameter. The wire with a larger
diameter produces a greater magnetic field. When the start switch is closed, part of the current flows from the
battery through the hold-in windings. The remaining current flows through the pull-in windings to the motor
terminal. The current then flows through the motor to ground. The solenoid is fully activated when the connection
across the battery terminal and the motor terminal is complete. When the solenoid is fully activated, the current is
shut off through the pull-in windings. At this point, only the smaller hold-in windings are in operation. The hold-in
windings operate for the duration of time that is required in order to start the engine. The solenoid will now draw
less current from the battery, and the heat that is generated by the solenoid will be kept at an acceptable level.
0008-4
