Kohler 27EFOZ, Service Manual

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TP-5936 7/04 33 Section 7 Generator Troubleshooting
7.8 Rectifier Module
The rectifier module converts the AC from the exciter
armature to DC, which magnetizes the generator main
field.
Test the rectifier module as described in the
following steps.
Rectifier Module Test Procedure
1. Disconnect the exciter armature and the main field
leads from the rectifier module.
2. Use an ohmmeter on the R x 100 scale to check the
resistance between the rectifier diodes as shown in
Figure 7-10. The ohmmeter should show a low
resistance in one direction and, upon reversing the
ohmmeter leads, a high resistance in the other
direction. Replace the rectifier module if any of the
diodes test differently than described.
7.9 Rotor
The generator rotor (magnetized by DC from the rectifier
module) rotating within the stator windings induces AC
in the stator windings. Test the generator rotor (main
field) as described in the following steps. Disassemble
the
generator prior to performing this test.
See Section 9.
Generator Rotor Test Procedure
1. With the generator disassembled, disconnect the
generator rotor (main field) windings the rectifier
module terminals F+ and F--.
2. Check the main field resistance by connecting an
ohmmeter across the main field F+ and F-- leads.
See Figure 7-11. See Section 1 for the resistance
reading. A low reading indicates an internal short
and a high reading indicates an open winding.
Repair or replace the main field if the ohmmeter
readings indicate the main field is inoperative. If
the resistance test is inconclusive, perform a
megohmmeter test on the main field as described
in the next step.
3. Check the main field for a short to ground condition
by using a megohmmeter. Apply 500 volts DC to
either field lead and the main field frame. Follow
the megohmmeter manufacturer’s instructions for
using the megohmmeter.
See Figure 7-12. A
reading of 500 kOhms (1/2 megohm) and higher
indicates the main field is good. A reading of less
than 500 kOhms indicates deterioration of the
winding insulation and possible current flow to
ground. Replace the main field.
TP-5936512
--
+
AC
AC
AC
3
1. Diode terminal
2. Diode terminal
3. Ohmmeter
1
2
Figure 7-10 Rectifier Module Test
F+
F--
AC
AC
AC
TP-593613
1
2
3
4
5
6
1. Main field (rotor)
2. Stator windings
3. Rectifier module 4. Ohmmeter
5. Armature
6. Exciter field
Figure 7-11 Ohmmeter Connections on Rotor
F+
F--
AC
AC
AC
TP-5936514
1
2
5
4
6
7
8
3
1. Main field (rotor)
2. Stator windings
3. Frame connection
4. Shaft connection 5. Rectifier module
6. Megohmmeter
7. Armature
8. Exciter field
Figure 7-12 Megohmmeter Connections on
Main Field