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OM-2053
(c) Oil pressure gage and oil pressure switch
The oil pressure gage (10) is a bourdon tube type and indicates engine lubricating oil pres-
sure. It is graduated from 0 PSI to 75 PSI. An oil pressure switch is mounted in a tee fitting di-
rectly behind the gage. This switch connects 12-V DC power to the engine control system
and to the generator 12-V DC control system when the engine is running.
(d) Hourmeter
The hourmeter (6) is electrically driven from the 12-V DC battery system. The hourmeter
measures and records engine running time and will record up to 9999.9 hours on five revolv-
ing drums. The hourmeter operates only when the engine is running and the oil pressure
switch is closed.
(e) Fuel gage and blocking diodes
An electric fuel gage (2, Fig. 8) accurately indicates the quantity of fuel oil in the tank provided
for the generator set. A sending unit mounted in the trailer or truck mounted unit fuel tank sup-
plies the signal to the gage. Twelve-volt DC operating power is supplied to the fuel gage from
two sources. The gage functions when the engine is running, or when the instrument lights
are ON. Since two power sources are connected to the fuel gage system, a blocking diode is
required in each power source circuit. One diode prevents energizing the motor-generator
control circuit when panel lights are ON. Another diode prevents operation of the panel lights
by the engine-generator circuit when the engine is running. (See Connection Diagram in
Chapter 6 for location of these diodes). To check fuel quantity when engine is stopped, use
switch to turn on panel lights.
(2) Engine and generator controls
(a) Engine-generator control switch
The engine-generator control switch (5) (also identified as the "build-up-voltage, generate,
idle" switch) is a three-position toggle type. It is spring-loaded in one position, BUILD-UP-
VOLTAGE, and will automatically reposition to GENERATE position when released. In
BUILD-UP-VOLTS position it performs a dual function. First, it supplies power to the gover-
nor control box, which allows the engine to operate at normal governed speed; second, it mo-
mentarily supplies current for closing the excitation-deenergization relay (1, Fig. 7) contacts,
to make three-phase, 115-V AC power available to the voltage regulator, or to the regulated-
diagnostic circuit, for excitation of the generator exciter. In GENERATE position, power is
maintained to the governor control box and to the excitation relay (1, Fig. 7). When the switch
is placed in IDLE position, power is disconnected so that the engine returns to idle speed and
the exciter field is deenergized.
(b) Contactor control switch
This is another three-position, toggle switch (7, Fig. 8) identical to the engine-generator con-
trol switch. When placed in the spring loaded CLOSE position, it provides 115-V AC power di-
rectly to a rectifier which supplies DC power for closing the load contactor. When released it
returns to the normal ON position and continues to provide power to the rectifier, but in this
switch position, AC power must pass through the plug interlock and fuse interlock relays. In
OFF position the switch opens the AC circuit to the rectifier, thereby cutting off the source of
DC power to the contactor coil which allows the contactor to open.
(c) Instrument light and switch
A shielded, instrument panel light (1) is mounted at the left side of the control panel. It is con-
trolled by a toggle switch (3) , which also controls instrument lights on the control box.
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December 31/91 Revised
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Table of Contents
Troubleshooting
