Generator; (A) Resistors - Hobart 90 C 20 Operation And Maintenance Manual

D. Generator
The 400-Hz generator is a brushless, revolving field, three-phase, alternating current type. The ro-
tor assembly is mounted by two, permanently lubricated, sealed, ball bearings. The front bearing
is supported by the fan housing; the rear bearing is mounted in the exciter housing. Both of these
housings are attached to the main generator stator housing. The front end of the rotor shaft ex-
tends forward beyond the rear bearing and into the exciter stator housing. The exciter rotor is
mounted on this shaft extension with a Woodruff key and is secured by a washer and 1/2"-13 thd,
cap screw. A rectifier with six diodes is mounted on the exciter rotor and converts exciter AC out-
put 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. 6) 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. Each
tray is easily removable by disconnecting an "Amphenol" connector, unlocking safety latches, and
sliding the complete tray assembly out of the control box.
A shielded, instrument panel light is mounted on the left side of the control box front panel, to illu-
minate controls and instruments in the trays.
(1) Generator control tray (See Figure 7)
The generator control tray contains instruments and controls for monitoring and controlling
the generator output.

(a) Resistors

Two, 10-ohm, 100-watt, ballast resistors (2) are connected in series in the generator ex-
citer 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.
April 30/96 Revised
OM-2031
1-1
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