WMD
GENERATOR
TROUBLESHOOTING
2. Check the generator with a Hertz meter:
No-Load
Hertz
61-61.5 (51-51.5)
No-Load Voltage 130-132 volts (generator cold)
No-Load Voltage 126-130 volts (generator hot)
3. Test the Bridge Rectifier. The bridge rectifier may be
faulty and should be checked asiollows:
The field excitation rectifier is a full-wave bridge rectifi-
er.
This type
of
rectifier has four terminals: two AC, a
DC
positive, and a
DC
negative. The rectifier is tested
in
the following manner: Connect one ohmmeter lead to the
positive
DC
terminal, and the other lead to each
of
the
AC
terminals
in
turn. A high or low resistance reading
will be obtained. Reverse the meter leads, and
an
oppo-
site reading should be observed. Now check from the
negative terminal
to
each
of
the AC terminals, using the
same procedures as above. Check each terminal to the
case, and no resistance reading should be observed.
If a battery-powered test light is used, follow the
proce~
dures described above. If the rectifier is good, the light
will come on,
in
one direction only.
If the rectifier fails any
of
the above tests,
it
should be
considered defective and replaced.
TESTING
THE
BRIDGE
RECTIFIER
B~ACK
H
--"';;;;::;:~~:b
TEST
lEAD
4. Check the field coil resistance as per the following speci-
fications:
FIELD
COIL
RESISTANCE
(TOTAL)
Aluminum
Windings
14.2
ohms
::t5%
WMD
11.0
KW
(3.5
ohms
per
coil)
and
12.5
KW
Copper
Windings
22.6
ohms
::t5%
(5.65
ohms
per
coil)
5. Insufficient cooling
of
the generator. Ambient air entering
the generator should not exceed
104°F (40°C). Operating
efficiency
of
the generator decreases as the ambient air
temperature entering the generator endbell increases
above
104°F. Generators
in
confined areas may require
the ducting
of
cool outside air into the compartment,
directed toward the inlet at the generator endbell.
6. Check the condition
of
the brushes for wear and contact
with the slip rings on the armature. Ensure that the brush-
es are not sticking
in
the holders.
7. Condenser Testing. Condensers are built into the genera-
tor circuit to minimize radio interference during opera-
tion.
If
a condenser shorts out,
it
shorts the generator out-
put.
To
determine whether a condenser is shorted, stop
the generator, disconnect the lead wire from the brush
holder to which the condenser
is
connected, start the gen-
erator and check the output. If the generator then pro-
vides power, the condenser was at fault and should be
replaced.
(If
the generator did not provide power after the
lead wire was disconnected, the problem was not caused
by that condenser.) Reconnect the lead wire.
NOTE:
There should be no continuity found between the
lead end from the condenser and the metal case
of
the
condenser.
If
so,
the condenser is shorted.
HIGH
VOLTAGE
OUTPUT
1. Verify the voltage at the generator output leads.
No-Load Voltage
126--130 volts (generator hot)
61.5-62.0 hertz
2. Check the internal wiring
of
the generator leads attached
to
the brush rig and the leads from the brush rig feeding
AC
to the bridge rectifier. One connection is from a hot
brush rig and the other must be from a neutral brush rig.
SOLENOID
WITH
THROTILE
LINKAGE
The solenoid plunger must move smoothly and rapidly into
the solenoid when the solenoid is electrically energized,
drawing with
it
the engine throttle arm into the set speed run
position. Failure
of
the solenoid plunger to bottom
in
the
solenoid will result
in
a failed solenoid.
THROTIlE
.
ADJUSTMENT
LINKAGE
FUEL
SOLENOID'
Engines & Generators
82
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