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 TM 55-1905-222-14
1-22
ELECTRICAL SYSTEM
a.
The electrical system is a 24 VDC two-wire ungrounded system. Normal source of electrical distribution for
power, lighting and IC (interior communication) systems circuits is supplied by two engine driven alternators. When the
engines are shut down, electrical distribution for power, lighting and IC circuits is supplied from two 12 volt series
connected storage batteries.
b. The prime purpose of the batteries in the vessel's electrical system is to provide a source of electrical power for
starting the engines. (Note that the power is applied to the control valves for hydraulic starting and not directly to the
starting motors). The batteries also act as a stabilizer to the voltage in the electrical system. They can, for a limited
time, furnish current when the electrical demands of the LCM-8 exceed the output of the alternator After the engines are
running, the alternator is intended to supply all of the electrical requirements of the LCM-8, plus additional power to
replace the charge taken from the batteries to start the engines.
c.
The belt-driven alternators convert mechanical and magnetic energy to alternating current (ac) and. voltage
by the rotation of an electromagnetic field (rotor). The three phase, full wave rectifier system contained within the
alternator converts the ac into direct current (dc). The six silicon rectifier diodes will pass current from the alternator to
the batteries or load, but will not pass current from the batteries to the alternator. Hence, no cut-out relay is required. A
fuel pressure switch, installed In each engine fuel system, disconnects the alternator field when the engine is shut down.
Each alternator assembly Includes a starting field resistor, a voltage regulator and a voltage protector. The function of
the voltage regulator is to maintain constant system output voltage under all speeds and load conditions. This is
necessary because excessive voltage will damage electrical components and Instruments. The electronic voltage
regulator functions like a solid state switch which constantly monitors system voltage. When the voltage tends to drop,
the switch closes and energizes the alternator field winding to increase the output. When the system voltage tends to
rise, the regulator switch opens and de-energizes the field circuit to decrease the voltage. The voltage protector protects
the alternator from high voltages under certain conditions. For instance, if the batteries are inadvertently disconnected
while the alternator is operating, unusually large output voltages could destroy the alternator
d.
A control and distribution panel is provided to supply groups of loads located in close proximity to each other.
The control and distribution panel is located. In the pilothouse Junction boxes are provided in the pilothouse, and stuffing
tubes are used where cables pass through watertight bulkheads. A circuit breaker enclosure is installed on the engine
room aft bulkhead with a breaker designed to protect the battery or alternators against short circuit. A safety switch is
also Installed on the aft bulkhead to protect the IC circuits. Circuits supplied from the control and distribution panel are
protected by 10A and 20A. fuses. Refer to Foldout-3 for a schematic diagram of the electrical system.
e.
Individual switches for fans, windshield wipers and engine room receptacles are located on the control and
distribution panel. The receptacle circuits are fuse protected. Two overhead white lights and eight overhead white lights
provide illumination in the lazarette and engine room respectively. The marine sanitation device compartment has one
overhead. white light. The stowage compartment has one over- head white light. Two bulkhead mounted red lights are
installed In the cargo well, aft. Panel lighting is provided, port and starboard, for the pilothouse console instruments. The
lights are controlled by a DPDT switch on the control and distribution panel, and protected with a 10A fuse. Each light
group is controlled by a separate switch.
1-32
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