Hobart 6824-1, Operation And Maintenance Manual, Page: 31 / 214

g. Fuse
A 10-ampere fuse (13) protects the 12-V DC engine control circuit, hourmeter, illuminating
light circuit, and 12-V DC system in the main generator protective system.
(3)
Air cleaner indicator
The air cleaner indicator (12) is mounted on the engine control panel for easy viewing. Its
function was explained in Para. 6, C, (3) (see Fig. 6).
(4) Test receptacle connector
This Amphenol connector (19) provides an attaching point for leads which are connected to
selected test points throughout the engine and generator electrical systems. Connections and
schematic diagrams indicate points at which the leads are connected. The receptacle connector
is designed to mate with a test box plug connector
(see Fig. 12).
(5) Charging circuit resistor
This 0.5 ohm, 100 watt resistor (20) is required on tractor-mounted units only. Its purpose is to
allow the battery charging alternator to maintain a near normal voltage in the electric governor
control box supply circuit when the TOW TRACTOR ENGINE is being started. Without this
resistor in the circuit, cranking the tow tractor engine can cause a sufficient voltage drop in the
system to influence operation of the electric governor control box and cause an overspeed
condition which will cause the overfrequency relay to operate and shut off power to an aircraft.
With the resistor in the circuit, alternator charging capability is limited to approximately 4
amperes at all times, and battery charging will be done mostly by the tow tractor generator or
alternator.
g. Voltage Regulator
The voltage regulator (Fig. 10) is located on the right side of the machine just back of the engine
compartment near the lifting yoke. On tractor and truck mounted units, or stationary units the
regulator is accessible for adjustment by opening rear doors on the right side. On tractor mounted
units, which have a large panel on the right side, the regulator is reached by removing the rear
hood-type vent cover on top of the canopy.
Depending on specification number, the regulator used in a generator set may be either a magnetic
amplifier type (Part No. 430391C) or a solid state regulator (Part No. 489812A). A seperate
regulator manual is supplied with the generator set for each of these voltage regulators in Chapter
6 of this manual. A brief, working description is given here of the magnetic amplifier (mag-amp)
regulator used with many Series 6824, Series 6824A, and Series 6824B GENERATOR SETS.
The voltage regulator is designed to provide 1% voltage regulation with .25second recovery time
for all loads up to 100% of rated load on a threephase, four-wire, 115/200-volt, 400-Hz, brushless
generator. This regulator provides field excitation power for the rotary exciter, and regulates
generator output voltage by varying the exciter field power as required to meet varying load
conditions. Thus, the generator output is held at a constant voltage. The maximum continuous
rating of this regulator is 4.0 amperes at 140 volts DC.
Any deviation of the generator output voltage from its set, regulated level is sensed by the voltage
detection and comparison circuits. A signal is fed from the comparison circuit into the transistorized
pre-amplifier, amplified, and used to drive the magnetic amplifier. The magnetic amplifier output
changes in response to this signal, changing the field power of the rotary exciter enough to return
the generator voltage to its regulated value. The voltage at which the generator is regulated may be
adjusted with the voltage adjustment rheostat
(2, Fig. 10) .
OM-499
May 31/94 Revised 1-1
Page 17