GENERATOR ASSEMBLY REPAIR INSTRUCTIONS
a. The main generator is a brushless type con-
sisting of a stationary three-phase armature and a
rotating salient pole wound field. The exciter,
mounted integrally with the main generator, con-
sists of a three-phase rotating armature mounted on
the shaft with the generator field and a stationary
salient pole field.
The exciter has ten poles.
b. A full wave bridge rectifier containing six
diodes is mounted on the shaft. Access to test or
replace the rectifiers is through the access hole on
the end of the endbell assembly. Access to the ex-
citer stator and rotor, and inspection of the main
generator armature and field, require disassembly
of the generator.
c. The generator shaft is directly driven by the
engine shaft through flexible metal disk coupling.
The flexible coupling compensates for misalignment
between the two shafts to eliminate injurious stress
on the connecting components.
d. The main generator stator is installed in the
stator frame and is fastened to and spaced by longi-
tudinal ribs which are part of the frame. An eye
bolt on the stator frame provides a means of lifting
the unit. The exciter stator is mounted in an end-
bell which positions on the stator frame rabbit.
e. The rotor is supported at one end by a single
healing in an endbell bolted to the stator frame. The
opposite end of the rotor is provided with a blower
assembly and coupling disk which bolts directly to
the engine flywheel.
The rotor is skewed to improve
generator output voltage waveform.
f. The bearing is a double-seal type ball bearing,
packed with grease conforming to Specification MIL-
G-23827. It provides a minimum of 5000 hours of
service at continuous loads.
9-2. Generator Removal and Disassembly.
a. Insulation Resistance. To test insulation resis-
tance, use a megohmmeter to measure the resistance
between a winding and ground. The insulation resis-
tance of each of the windings should be at least 1 meg-
ohm at 75°F.
If this value is not met, clean or dry
out the winding and repeat the test. Replace if de-
Low insulation resistance may be caused
by dirt or excessive moisture. Insulation
failure may be caused by wrong voltages,
induced voltages caused by opening field
circuits too quickly, oil and grease, high
temperatures or excessive vibration.
(1) Generator Stator- Disconnect all leads to
voltage regulator and all other points to completey
isolate the winding before meggering.
(2) Generator Rotor - Disconnect both field
leads from the rotating diode assembly before meg-
(3) Exciter Stator - Disconnect both field leads
from terminals 15 and 16 of TB16.
(4) Exciter Rotor - Check this only if other
windings have low insulation resistance as the leads
must be unsoldered from all diodes before meggering.
b. Electrical Malfunctions and Isolation. A mal-
function of the main generator is usually indicated
by low output voltage, or no voltage output. To iso-
late a malfunction to the main generator, proceed as
(1) Tag and disconnect the two top leads on
terminals 15 and 16 of TB16 (located on the current
transformer mounting plate). Connect one side of
a dc ammeter to one of the terminals (15 or 16) and
an adjustable dc voltage source to the other terminal
and the dc ammeter.
The adjustment shouId be set
to mint mum voltage.
(2) If the set is a 50/60 Hz set, select 60 Hz
and start the engine.
Bring the speed up to 1800 rpm
manually and turn on the adjustable dc power supply.
Adjust the dc voltage so that the output voltage (no
load) reads 208 or 416 volts (depending on low or high
The dc ammeter should read be-
tween 1.25 and 1.55 amperes to produce either 208
or 416 volts.
(3) If the set is a 400 Hz set, start the engine
and bring it up to 2000 rpm. Turn on the adjustable
dc power supply.
Adjust the dc voltage so that the
output voltage (no load) reads 208 or 416 volts, (de-
pending on low or high voltage connection). The dc
ammeter should read between 3.0 and 3.65 amperes
to produce either 208 or 416 volts.
(4) If the dc ammeter indicates incorrect in-
put exciter current to obtain rated voltage in steps
(2) or (3) above, the generator has failed. Proceed
with the following steps. If the output is as speci-
fied, the excitation system assembly has failed (re-
fer to paragraph 8-1).
The following steps are pre-
sented to enable isolation of the fault within the gen-
Only steps (5), (6) and (7) would normally
be done without some disassembly of the generator.
(5) Remove six bolts securing air intake grille
and remove griIle.
Remove screws, cover plate,
and gasket from generator endbell. See figure 9-1.
Remove bolts from the six diodes on the exciter
rotor frame, one at a time, replacing each diode
Test diodes per paragraph 14-12b.