Kohler 27EFOZ, Service Manual

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TP-5936 7/04 28 Section 7 Generator Troubleshooting
7.3 Separate Excitation
By separately exciting the generator to determine the
presence of a faulty voltage regulator, it is possible to
determine if a running fault exists in the rotor and/or
stator. A generator component that appears good while
static (stationary) may exhibit a running open or short
circuit while dynamic (moving). Short circuits can be
caused by centrifugal forces acting on the windings
during rotation or insulation breakdown as temperatures
increase.
1. Disconnect all of the leads from the voltage
regulator.
2. Disconnect the P6 (F1, F2) connector.
3. Connect separate excitation circuit as shown in
Figure 7-2. Connect an ammeter and a 10 amp
fuse in series with F1.
Note and record the
ammeter reading.
4. The approximate ammeter reading should be
battery voltage divided by the specified exciter
resistances (cold). Disconnect the resistor leads
and determine the exciter current value using an
ohmmeter. See Section 1, Specifications, for the
normal values.
Example:
12 Volts (Battery Voltage)
0.5-amps
Exciter Current
=
22.7 Ohms
Exciter
Resistance
5. Start the engine and check that the ammeter
remains stable. An increasing meter reading
indicates a shorted exciter field or inoperative F1
resistor. A decreasing meter reading to zero, or
unstable reading, suggests a running open in the
exciter or F1 resistor. If the ammeter is stable,
continue with step 6.
6. Check for AC output across the stator leads and
compare it to the values in Section 1,
Specifications. If the output varies considerably
from those listed, a faulty stator, rotor, rectifier
module, or armature is likely.
If the AC output is not within specifications, the voltage
regulator is probably inoperative.
If there is no
generator output during normal operation, but output is
available when the generator set is separately excited,
the voltage regulator is probably inoperative.
Note: See Section 1, Specifications, for the stator
output
voltages (with separately excited
generator). These specifications are based on a
battery voltage of 12. Should the battery voltage
vary (11--14 volts), the resulting stator output
values will also vary.
+ —
+ —
F1 F2
P6
1
2
3
4
5
6
7
8
TP-593653
1. Voltage regulator
2. 10-amp fuse
3. DC ammeter
4. Battery
5. Ground to generator frame
6. Exciter armature
7. Exciter field
8. P6 connector
Figure 7-2 Separate Excitation Connections
7.4 PowerBoost V Voltage
Regulators
The generator set is equipped with a PowerBoost
t
V
voltage regulator. See Figure 7-3. The PowerBoost
t
V
voltage regulator monitors output voltage magnitude to
control the current to the generator exciter field. The
voltage regulator has an underfrequency unloading
feature that is referred to as volts-per-Hz (V/Hz). To
determine if the voltage regulator is functioning, reduce
the engine speed (Hz) and watch for a corresponding
drop in the AC voltage. The AC voltage should remain
constant until the engine speed drops below 57.5 Hz on
60 Hz models or 47.5 Hz on 50 Hz models.
When the frequency drops below either 57.5 or 47.5 Hz,
the AC voltage should decline. Perform the following
test to check the regulator output.