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 TM 55-1905-221-14-2
5-12.
ENGINE ELECTRICAL SYSTEM.
a. GENERAL.
The electrical system includes two 70-amp, 24-volt alternators; one alternator mounted on the inboard engine of each
propulsion unit. Four 6-volt batteries, connected in series to provide 24-volt current, are contained in the battery box
located aft in the engine room. The alternators and batteries provide electrical power to operate all lights and electrical
accessories on the landing craft and for the electric starters which are mounted on the outboard engines of each
propulsion unit.
b. ALTERNATORS
One 70-amp, 24-volt alternator is belt-driven from the inboard engine crankshaft pulley. The electrical circuit of the
alternator uses six silicon diodes in a full wave rectifier circuit. Since the diodes will pass current from the alternator to
the battery or load,. but will not pass current from the battery to the alternator, the alternator does not require the use of
a cutout relay. A voltage regulator is the only control required.
c. VOLTAGE REGULATORS
The all-electronic transistorized voltage regulator is an electronic device using no mechanical contacts or relays.
When the voltage supply is below a predetermined amount, the transistor conducts, acting like a closed switch between
the supply voltage and the field of the alternator. When the supply is above a predetermined amount the transistor is cut
off, acting like an open switch which removes the excitation from the field, reducing the alternator output.
d. ELECTRIC STARTING MOTORS.
Electric starting motors are installed on the outboard engines of each propulsion unit. The two electric starting motors,
model numbers 1108850 and 1108890, are identical except for direction of rotation. Model number 1108850 has a
clockwise rotation, viewing from the drive end, and is installed on the outboard engine of the starboard propulsion unit.
Model number 1008890 has a counter-clockwise rotation, viewing from the drive end, and is installed on the outboard
engine of the port propulsion unit.
e. See foldout located in the back for schematic.
5-151
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