Section 2. Description - Hobart Jet-Ex 4D Operation And Maintenance Manual

OM-2063 / Operation and Maintenance Manual
Jet-Ex 4D / Specs 7003A-3 and 7003B-3 / Generator Sets

Section 2. Description

1. General
The two Jet-Ex 4D units covered in this manual (Figure 1) are diesel engine driven, self-contained,
trailer-mounted generator sets manufactured by Hobart Brothers Company, Ground Power Division,
Troy, Ohio U.S.A. They are identified by specification numbers 7003A-3 and 7003B-3.
The basic generator set is designed to generate and deliver 28.5 volts DC power to an aircraft when its
on-board generators are shut down. In addition to providing continuous, regulated power to the aircraft,
the unit is designed for starting any fixed-wing aircraft or helicopter which is equipped with an external
28.5 volt DC power receptacle (see page 3 for complete Specifications and Capabilities).
The Specification 7003B-3 generator set is virtually identical to the Specification 7003A-3 generator set,
except that it has a Furnas contactor and a different air cleaner.
2. Special Features
The "Soft-Start" current limiting feature, recommended by most aircraft engine manufacturers, provide
the operator with controls to limit the inrush current to the aircraft engine's starter. When the operator
presets this control, the generator will provide constant voltage to the preset current value. As more
current is applied beyond the preset current value, the voltage will decrease to a minimum of 14 volts
DC, after which the voltage will remain constant as more current may be delivered beyond the preset
current value. Limiting inrush current is recommended by most engine manufacturers to protect the
aircraft engine's starter shear section. The current limiting control is continuously adjustable from 300
amperes, which is recommended for helicopter and small turbine starting, to 2000 amperes, required for
starting larger aircraft engines when the control is turned fully clockwise.
A four-wheel trailer is available to add mobility to the generator set. It is equipped with pneumatic rubber
tires, a drawbar for towing, and hand lever-operated, parking brake. It also includes fenders, bumpers
and cable trays. This option is available from Hobart Brothers as Part No.181000-1.
A water heater kit is installed inside the enclosure and is connected to the cooling system of the diesel
engine. Its purpose is to keep the coolant warm when the engine is shut down for extended periods of
time in cold weather and permit the engine to start quickly.
A fuel/water separator, attached to the side of the engine, replaces the standard prefilter. This special
filter removes water/condensation along with any solid contaminants from the fuel.
3. Orientation
The radiator end of the Jet-Ex 4D is the front. Right and left are determined by standing at the rear of
the unit, facing it. The control panel is located at the rear.
4. Identification
Each generator set has an Identification plate attached inside the hinged control panel door. This
nameplate lists the machines Model No. (Jet-Ex 4D), Specification No., Serial No., and electrical rating.
If any of the options described in paragraph 2.b. are included, they will be listed by name and part
number on a separate option nameplate located next to the Identification plate.
Dec 31/92 Chapter 1-2
Page 1