Re-Checking The Entire Unit After Testing; Generator Set Adjustment; Voltage Regulator Adjustment - Hobart 120CU20 Operation And Maintenance Manual With Illustrated Parts List

OM-2228 / Operation and Maintenance Manual
120CU20 / Series 500120 / 400 Hz. Generator Set
g) Re-checking the entire unit after testing.
(1) With the engine running at normal rated speed, check the entire unit for vibration and for any
parts that may have become loosened during the above checks. Tighten any loose hardware as
required.
(2) Check engine oil pressure at rated speed (2000 RPM). The oil pressure gauge should indicate at
least 44.9 psi (3.1 bar) when engine is hot. Also at rated speed, check the engine coolant
temperature. The temperature gauge should indicate in the range of 180° to 190° F (82º to 88º
C), depending upon operating conditions.
WARNING
If a metal sounding rod is used to detect bearing noises, exercise extreme care to
avoid injury from moving components.
(3) Check 400 Hz generator bearings. Use a stethoscope or metal sounding rod to listen for unusual
noises. If using a metal rod, place on end on the generator housing and hold the other end near
the ear. Hold the rod with three fingers and use the index finger and thumb to form a sounding
chamber between the rod and the ear. Do NOT allow the rod to touch the ear. Listen for grinding
or pounding sounds, which would indicate a defective bearing. An engine noise may be
telegraphed to the generator and misinterpreted as a generator noise. Contact the equipment
manufacturer if in doubt of bearing serviceability.

3) Generator Set Adjustment.

a) Generator Adjustment.
The 400 Hz generator is a brushless type requiring no adjustments of any kind.
b) Voltage Regulator Adjustment.
When a voltage regulator is first put into service, or when output (generator-to-aircraft) cables are
changed, the regulator may require adjustments of output voltage value and line-drop compensation.
For making these adjustments, the voltage regulator has three potentiometers shown in the figure
below:
•
A coarse output voltage potentiometer
•
A fine output voltage potentiometer
•
A line-drop compensation potentiometer
For the following adjustment, the generator set must be running at rated speed (2000 RPM), under
no-load conditions. Adjust the regulator as follows:
October 15, 2013 Chapter 2-3
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