TM 5-3810-306-20
ELECTRICAL SYSTEM
General
The electrical system is 24-volt operation, consisting of an alternator and four lead-acid batteries, series-parallel
connected. The system is the single wire ground return, utilizing the crane’s superstructure as ground.
Batteries
The 12-volt batteries are located in a box on the left side of the machine behind the rear axle. Two batteries are
connected in parallel to make two parallel sets. Both parallel sets are connected in series to provide the necessary 24-
volts for the system.
Starter
When the start button is depressed, the coils in the solenoid are energized creating a magnetic field. This field pulls in the
plunger which causes the shift lever to push the drive assembly in mesh with the ring gear in the engine. At this time the
plunger closes the circuit between the "BATTERY" terminal and the field coil.
The current passes through the field coil, then through the brushes until it reaches the armature. The current forms
counteracting magnetic fields around the field coil and the armature, causing the armature to turn. The armature turns the
drive assembly which cranks the engine through the ring gear.
When the engine starts, the start button is released. This causes the magnetic field in the solenoid to collapse and a
return spring forces the plunger back to its original position. As this happens, the shift lever disengages the drive
assembly from the ring gear teeth. The contact from the "BATTERY" to the field coil is also broken by the returning
plunger, which causes the armature to stop turning.
Alternator
The alternator is mounted on the engine and is belt driven. It is a 65 amperage alternator with a 24-volt output terminal.
The 24 volts from the alternator is supplied by a transformer rectifier unit mounted on the end frame of the alternator.
When the engine is running, the 24-volt terminal supplies the voltage to recharge the batteries and maintain them at a full
state of charge.
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