SYSTEMS OPERATIONTM 5-3805-258-24-1OPERATOR’S STATIONINDIVIDUAL CIRCUIT DESCRIPTIONSTART SYSTEMWhen the main disconnect switch is closed, power is sent:1. To the starter relay,2. To the main power relay, and3. 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 sentthrough diode A of the 2V9473 Diode Assembly to activate the main powerrelay.When the main power relay is activated, its contacts close and sendcurrent to the cab and accessories.When the key switch is turned from the ON to the START position, the sameconnections that were made in the ON position are kept. Power is also sentthrough diode A of the 1V9633 Diode Assembly to activate the starter relay,which activates the starter solenoid, to start the engine.RIGHT SIDE BATTERY1. Battery (right side).LEFT SIDE BATTERY2. Battery (left side).When the engine starts and the key is released, the key switch goes back to theON position and no power is sent to the starter relay. The starter relay contactsopen and no power is sent to the starter solenoid.When the engine is in operation, the “R” terminal of the alternator sendspower through diode B of the 2V9473 Diode Assembly to the main powerrelay, to keep it activated when the key switch is turned OFF. This keeps thebattery load on the alternator. If the main power relay were to open as soonas the key switch was turned OFF, the battery load would be removed fromthe alternator while it still had a high output. This could cause damage tothe electrical system.Diode A of the 2V9473 Diode Assembly and diode A of the 1V9633 DiodeAssembly do not let the main power relay and the starter relay activate if thebatteries are connected backwards. This prevents reverse polarity damage tothe alternator.Diode B of the 1V9633 Diode Assembly is a “free wheeling” (see section ondiodes) diode across the coil of the starter relay for the protection of the keyswitch.3-168
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