Kohler 27EFOZ, Service Manual

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TP-5936 7/04 32 Section 7 Generator Troubleshooting
F+
F--
AC
AC
AC
1
2
3
4
5
6
TP-5936510
1. Main field (rotor)
2. Stator windings
3. Rectifier module 4. Ohmmeter
5. Armature
6. Exciter field
Figure 7-8 Exciter Armature Ohmmeter Test
F+
F--
AC
AC
AC
1
2
3
4
5
6
7
TP-5936511
1. Main field rotor
2. Stator windings
3. Rectifier module
4. Megohmmeter 5. Shaft connection
6. Armature
7. Exciter field
Figure 7-9 Megohmmeter Connections on Exciter
Armature
7.7 Exciter Armature
The exciter armature supplies excitation current to the
generator main field through the rectifier module. Test
the exciter armature as described in the following steps.
Exciter Armature Test Procedure
1. Disassemble the alternator. Refer to Section 9.
2. With the alternator disassembled, disconnect the
armature leads from the rectifier module AC
terminals. Refer to Section 9.
3. With an ohmmeter on the R x 1 scale, check the
resistance across the exciter armature leads. See
Figure 7-8. See Section 1, Specifications, for the
armature resistance. No continuity indicates an
open armature winding. If the resistance test is
inconclusive, perform a megohmmeter test on the
exciter armature as described in the next step.
Note: Consider the exciter armature good if the
resistance reading (continuity) is low and
there is no evidence of a shorted winding
(heat discoloration).
4. Check the exciter armature winding for a short to
ground condition. Use a megohmmeter to apply
500 volts DC to either armature lead and the
armature frame.
Follow the megohmmeter
manufacturer’s instructions for using the
megohmmeter. See Figure 7-9. A reading of
approximately 500 kOhms (1/2 megohm) and
higher indicates the exciter armature is good. A
reading of less than approximately 500 kOhms
indicates deterioration of the winding insulation
and possible current flow to ground. Replace the
exciter armature.