Hobart 120CU20, Operation And Maintenance Manual With Illustrated Parts List

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OM-2228 / Operation and Maintenance Manual
120CU20 / Series 500120 / 400 Hz. Generator Set
October 15, 2013 Chapter 2-3
Page 3
b) Operational Test Procedures
(1) Start the engine according to the instructions in Section 1-3.
(2) Check operation of engine instruments; voltmeter , coolant temperature indicator, oil pressure
gauge and hour meter (all shown in Figure 1).
(3) Check engine idle speed. Should be 1000 +/- 25 RPM.
NOTE: A stroboscope may be required for this check.
(4) Again, check for oil, fuel, and coolant leaks and correct any leaking condition.
(5) Position switches and controls for automatic voltage regulation and power delivery as follows:
a Place regulated-diagnostic switch (Figure 7) in “ REGULATED ” position.
b Place EF Bypass switches (Figure 3) in “ BYPASS / OFF ” position.
c If the output voltage coarse adjustment potentiometer on the voltage regulator has been
disturbed, place the knob at mid-range position.
(6) Bring the engine up to rated speed, which also energize the generator, by pressing the “ ENGINE
START ” push button switch a second time. If the engine comes up to rated speed and a 115 V
voltage value appears on the voltmeter, the engine ECM and excitation circuits are functioning.
(7) After generator overhaul or repair, the Regulated/Diagnostic switch must be placed in the
“ DIAGNOSTIC ” position for 3 to 5 seconds to re-magnetize the exciter. Then return the switch to
the “ REGULATED “position after voltage has built-up.
(8) Observe frequency meter. If engine speed is properly set, frequency should read 400 Hz.
(9) Observe voltmeter. Use output fine voltage coarse adjustment potentiometer (Figure 7) to adjust
voltage to 115 V AC.
(10) Check adjustable voltage range.
a Observe voltmeter and turn output voltage coarse adjustment potentiometer to full clockwise
position. Maximum voltage should be 134 volts or higher.
NOTE: If voltage should decrease when regulator potentiometer is turned clockwise, it indicates that
internal wiring in the voltage regulator is incorrect. Replace complete voltage regulator assembly.
b Observe voltmeter and turn regulator potentiometer knob to full counterclockwise position.
The minimum voltage should be 95 volts or lower.
(11) Position load bank switches, etc., to apply a light load to the generator.