Hobart 6921 Series Operation And Maintenance Manual Download

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f. Engine Control Panel

(Fig. 11)

The engine control panel is mounted into the side of the control box. The engine controls and
instruments and generator output controls are included. A plexiglass window in the engine control
panel door slants outward at the bottom to form an opening for access to controls when the door is
closed.

(1)

Engine Instruments

Engine operation is monitored by an ammeter

(4),

an oil pressure gage

(2)

, and an oil

temperature gage

(5)

. An hourmeter

(3)

records engine operating time.

a. Ammeter

The ammeter

(4, Fig. 11)

indicates the direction and value of current flow in the 12 VDC

electric system. Its graduated range is from - 60 A through 0 A, to +60 A.

b. Oil Temperature Gage

This gage (5) indicates engine temperature. Its graduated range is 150

to 300

(50

150

C).

c. Oil Pressure gage and oil pressure switch

The oil pressure gage

(2, Fig. 11)

is a bourdon tube type and indicates engine lubricating oil

pressure. It is graduated from 0 PSI to 75 PSI. An oil pressure switch is mounted in a tee
fitting directly behind the gage. The switch connects 12-V DC power to the engine control
system and 12-V DC control system to the generator when the engine is running.

d. Hourmeter

The hourmeter

(3)

is electrically driven from the 12 VDC battery system. The hourmeter

measures and records engine running time and will record up to 9999.9 hours on five
revolving drums. The hourmeter operates only when the engine is running and the oil
pressure switch

(2)

is closed.

(2)

Engine and generator controls

a. Fuse

A 15-ampere fuse

(16, Fig. 10)

protects the 12-VDC engine control circuit hourmeter,

illuminating light circuit, and 12-VDC system in the main generator protective system.

b. Engine-generator control switch

The generator mode control switch

(9, Fig. 11)

is a three-position toggle type. It is

spring-loaded in BUILD-UP-VOLTAGE position, and will automatically reset to GENERATE
position when released. The switch supplies power to the governor control box allowing the
engine to operate at normal governed speed. It also momentarily supplies current which
closes the excitation-deenergization relay,

(3, Fig. 9).

When the switch is in GENERATE position, power is maintained to the governor control box
and to the excitation relay. When the switch is in IDLE, power is disconnected so the engine
returns to idle speed and the exciter field is deenergized.

c. Contactor control switch

The engine start switch is a three-position toggle type

(15, Fig.11)

identical to the

engine-generator control switch. When placed in the spring loaded ON position, it provides
115-VAC power directly 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. 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, cutting off the
source of DC power to the contactor coil which allows the contactor to open.

OM-2040 / Operation and Maintenance Manual

90D20 / Generator Sets

Chapter 1-1

February 28/94

Page 16

Revised