Generac Power Systems IM Series - Manual (Page 6)

INTRODUCTION TO TROUBLESHOOTING
Introduction
A typical RV generator set does not have a large number
of parts. However, the parts are expensive. For that
reason, a parts replacement method of troubleshooting is
not cost effective. A basic understanding of generators is
essential to good troubleshooting, i.e., why they behave
or don’t behave as they should. This section will introduce
the technician to some of the fundamentals of
troubleshooting.
DANGER!: Recreational vehicle generators produce
extremely high and dangerous voltages. Use ex­
treme care when working on or around the gener­
ator. Contact with live wires and terminals will cause
extremely hazardous and possibly lethal electrical
shock. Only personnel who have been thoroughly
trained In the maintenance of RV generators should
attempt to troubleshoot, test, repair or service a gen­
erator.
Tools and Test Equipment
The generator service technician should have a well
stocked tool box having a good selection of common hand
tools. Such a tool box should contain wrenches in both
metric and english sizes. Also recommended is a good
nut driver set.
A
Volt-Ohm-Milliammeter:-An accurate volt-ohm-mil-
liammeter (VOM) is essential for the troubleshooting and
testing of generators. Simply having a VOM is not
enough. The technician must understand electricity, must
be familiar with electrical circuits, must be able to read
wiring diagrams/electrical schematics, and must know
how tio use the VOM.
B
Frequency Meter:- This test device permits the gen­
erator’s a-c ou^ut frequency, in HERTZ or CYCLES PER
SECOND, to be read. Measurement of frequency is re­
quired for precise adjustment of engine-generator speed.
Also see ROTOR ROTATIONAL SPEED.
C
Insulation Resistance Tester:- Also called a "Hl-
POT", this device permits generator Stator and Rotor
winding insulation to be tested for breakdown. Use the
Hi-Pot tester to test resistance between parallel stator
windings, between isolated windings, and the resistance
of all windings to ground. See also EFFECTS OF DIRT
AND MOISTURE ON GENERATORS.
NOTE: An electrical LOAD BANK Is also recom­
mended for generator testing and adjustment. The
Load Bank permits a known electrical load to be ap­
plied to the generator, for the purpose of testing/ad-
justlng unit operation under load.__________________
Rotor Rotational Speed
The generator’s revolving field on Series NP45G, NP55G
and NP65G generators is a 2-pole type, having a single
north and a single south magnetic pole. The Rotor is en
gine driven through a belt and pulley arrangenrient. Such
a 2-pole Rotor must be operated at 3600 rpm to supply
an a-c frequency output of 60 Hz. The belt and pulley ar­
rangement pro>4des a speed reduction, so that engine
speed can be reduced while driving the Rotor at its re­
quired operating speed. The following formulae apply