Generator And Exciter Test; Diode Test - Hobart 60PL20 Operation And Maintenance Manual

4. Generator and Exciter Test

The generator fields may be tested with a "Kelvin" bridge. This is a double-bridge type instrument required
for the very low resistances encountered in this test. It is understood that 0 resistance indicates a SHORT
CIRCUITED condition. An infinite resistance reading indicates an OPEN CIRCUITED condition. See Fig.
11 below for resistance values.
NOTE: The equipment should be COLD or at normal ambient temperature when tests are made.
A. Disconnect generator stator leads at the power module panel.
B. Disconnect exciter leads from terminal board mounted on rear of engine control panel. Positive lead is
RED. Negative lead is YELLOW-BLACK.
C. Check resistances and compare to values given in Fig. 11.
TEST CONNECTION
GENERATOR STATOR
Phase A to N
Phase B to N
Phase C to N
NOTE: The two leads of a phase must be connected when test is made.
EXCITER A-B, B-C, A-C
Field (RED to YELLOW-BLACK)

5. Diode Test

Test values for diodes are not given here because they could be misleading. Test values may vary even
between diodes of the same part number, rating, and manufacturer. General instructions for testing di-
odes follows:
A. Disconnect diode lead (s).
B. Use a good quality ohmmeter. An instrument which indicates 50 ohms at the center of the scale is
preferable.
NOTE: Make certain the battery is in good condition and the pointer is adjusted to zero when the
test lead points are shorted together. Set the scale selector to RX1.
C. Hold one ohmmeter lead point on the threaded end of the diode. Hold the other lead point on the
wire terminal end. Observe and note the indicated resistance. Now reverse the lead connections on
the diode. Again observe and note the ohmmeter indicated resistance. Generally speaking, if an infi-
nite or very high resistance was indicated with the leads connected one way and a low, readable resis-
tance was indicated with the leads connected the opposite way, the diode may be considered good.
December 31/91 Revised
Generator and Exciter Stator Test Values
(70F Ambient Temperature)
Figure 11
NOMINAL RESISTANCE IN OHMS
0.008
0.008
0.008
0.1
7.23
OM-2053
2-3
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