Control Box Assembly; (A) Resistors; (B) Generator Output Monitors (Meters) 1-1 - Hobart 6921 Series Operation And Maintenance Manual

OM-2040 / Operation and Maintenance Manual
90D20 / Generator Sets
A rectifier with six diodes is mounted on the exciter rotor and converts exciter AC output to DC for
excitation of the generator revolving fields. The exciter DC output to the generator fields, and
consequently, the generator output is controlled by the amount of DC voltage supplied to exciter
fields by the static voltage regulator. A centrifugal, radial-blade fan, which is part of the hub and
coupling assembly, draws cooling air over all internal windings. Air enters at the exciter end and is
discharged at the drive end. The complete generator is bolted to the engine flywheel housing.
e. Control Box Assembly
The control box (Fig. 8) is a sheet metal enclosure which houses and provides mounting facilities for
generator and engine controls and monitoring equipment. The box is equipped with two, drawer-type
trays which contain generator output control devices and monitoring instruments. Trays slide in and
out on nylon rollers for easy access to internally mounted components and are easily removable by
disconnecting an "Amphenol" connector, unlocking safety latches.
Two, shielded, instrument panel lights are mounted on top of the control box front panel to illuminate
controls and instruments within the trays.
(1) Generator control tray (see Figure 9)
The generator control tray contains instruments and controls for monitoring and controlling the
generator output.
a. Resistors
Two, 20-ohm, 100-watt, ballast resistors (2) are connected in series in the generator exciter
DC field circuit.
A variable resistor (1) is connected in series between the manual control rectifier (14) and
rheostat (13) . Its purpose is to adjust the DC voltage to the rheostat and thus determine the
voltage range through which the rheostat can control generator output voltage.
February 28/94
Revised
Control Box
Figure 8
Chapter 1-1
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