SYSTEMS OPERATION
TM 5-3805-258-24-1
OPERATOR’S STATION
INDIVIDUAL CIRCUIT DESCRIPTION
START SYSTEM
When the main disconnect switch is closed, power is sent:
1. To the starter relay,
2. To the main power relay, and
3. Through the 8 amp circuit breaker to the key (OFF-ON-START) switch.
When the key switch is turned from OFF to the ON position, power is sent
through diode A of the 2V9473 Diode Assembly to activate the main power
relay.
When the main power relay is activated, its contacts close and send
current to the cab and accessories.
When the key switch is turned from the ON to the START position, the same
connections that were made in the ON position are kept. Power is also sent
through diode A of the 1V9633 Diode Assembly to activate the starter relay,
which activates the starter solenoid, to start the engine.
RIGHT SIDE BATTERY
1. Battery (right side).
LEFT SIDE BATTERY
2. Battery (left side).
When the engine starts and the key is released, the key switch goes back to the
ON position and no power is sent to the starter relay. The starter relay contacts
open and no power is sent to the starter solenoid.
When the engine is in operation, the “R” terminal of the alternator sends
power through diode B of the 2V9473 Diode Assembly to the main power
relay, to keep it activated when the key switch is turned OFF. This keeps the
battery load on the alternator. If the main power relay were to open as soon
as the key switch was turned OFF, the battery load would be removed from
the alternator while it still had a high output. This could cause damage to
the electrical system.
Diode A of the 2V9473 Diode Assembly and diode A of the 1V9633 Diode
Assembly do not let the main power relay and the starter relay activate if the
batteries are connected backwards. This prevents reverse polarity damage to
the alternator.
Diode B of the 1V9633 Diode Assembly is a “free wheeling” (see section on
diodes) diode across the coil of the starter relay for the protection of the key
switch.
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