ARMY TM 9-6115-639-13
AIR FORCE TO 35C2-3-386-51
MARINE CORPS TM 10155A-13/1
1-18. ALTERNATING CURRENT SYSTEM. (Figure FO-1)
a. The power for the alternating current electrical system (Figure FO-1) is provided by the permanent
magnet generator (G1). The power converter (A8) converts this AC power electronically to 120 / 240V, 60 Hz
or 400 Hz power.
A8 is not waterproof. Water in the A8 can cause the A8 to short out, thereby creating
a catastrophic failure.
b. In generator set model MEP 831A (60 Hz), a duplex convenience receptacle (Jl) provides power for
common 120VAC appliance or tool loads. A ground fault circuit interrupter (CB3) protects both the
convenience receptacle circuitry and the connected appliance should a ground fault occur.
c. Once the generator set reaches normal operating voltage (114 to 126 V for 120 V connection, 228 to
252 V for 240 V connection), the CIRCUIT INTERRUPTER switch (S5, located on the control panel) is placed
in the CLOSED position. The AC circuit interrupter (Kl) closes, applying power converter output voltage to the
output load terminal board (TB2, terminals Ll, L2, and N). Placing CIRCUIT INTERRUPTER switch (S5) in
the OPEN position opens AC circuit interrupter, removing power converter output voltage from load terminals.
d. Voltage adjustment is accomplished using the VOLTAGE ADJUST rheostat (Rl), located on the
control panel. Output from the power converter is displayed on a LOAD meter (M2) and a VOLTAGE meter
(M1). Both meters are located on the control panel.
e. In generator set model MEP 831A (60 Hz), two thermostatically controlled AC ventilation fans (B2
and B3) are mounted in the generator set enclosure assembly. These fans provide internal cooling of the
generator set under high temperature operating conditions. The fan temperature switches (S20 and S21) are set
to turn on fan B2 when internal air temperature reaches 85F (29C), and fan B3 when internal air temperature
reaches 110F (43C).
1-19. GENERATOR. (Figure FO-1)
a. The AC generator (G1, Figure FO-1) is a direct coupled, permanent magnet generator. The rotor and
fan are dynamically balanced at all speeds up to 125 percent rated speed to minimize vibration. The windings
and coils in the stator assembly use Class H insulating material. Temperature rise of the windings is limited to a
change of 221F (105C) (max.).
b. The generator produces voltage by rotating permanent magnets in the rotor past a stator winding. The
magnetized poles of the rotor have alternate north and south polarity. The magnetic flux lines leave each north
pole of the rotor, pass through the stator, and return to the adjacent south poles of the rotating field.
The power inverter / converter (A8) converts generator output to a 120 / 240V, 60 Hz
or 400 Hz output, regardless of engine speed. The electric governor varies the engine
speed in proportion to the kilowatt load on the generator set.