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Chapter 3 REPAIR OF GENERATOR SET
Up
TM-5-6115-440-34 Generator Set 7.5 Kw 28V DC GED Air Cooled 2 Wheel Mtd Pnematic Tires Manual
Next
Figure 3-1. Control box components, removal and installation.
(6) Increase the speed slowly to 8000 rpm and
(b) If hipot equipment is available, test the
turn the pile screw slowly. The regulated voltage
coil insulation to the spool at 600 volts for one
will at first rise and then drop slightly. Set the pile
second.
screw approximately in the position shown in figure
e. Repair or Replacement. With the exception of
3-5. The coil current (at no-load, 8000 rpm) should
cleaning pitted or blackened surfaces as described
be about 0.65 ampere. If the current is high, turn
in d (1) and (5), defective parts cannot be repaired
the magnet core in. Tighten the locking screws
and must be replaced.
uniformly. If the current is low, loosen magnet
f. Reassembly. The regulator can be reassembled
locking screw and turn magnet body out.
by reversing the disassembly procedures being
careful to make connections in accordance with
( 7 ) Allow the regulator to come up to
figure 3-3. Observe special instructions described
operating temperature by operating at 3500 rpm
for ten minutes.
below:
(1) If the magnet core has been removed,
(8) A pair of earphones connected as shown in
screw it up until 10 mils under flush, measuring
figure 3-4 can be used to check the stability of the
regulator. A stable regulator produces a humming
from the raised rim on the hole of the magnet plate
noise or steady roar. A rapid series of popping
and stop (46, fig. 3-2).
noises indicates instability. Listen carefully at high
(2) When replacing the armature in the
housing, the terminal on the armature should be
speeds when shocking (applying and removing full
load) the regulator  to detect instability. An
near the upper left tapped hole.
oscilloscope may also be used to check stability.
(3) Insert the magnet plate with chamfered
outer edge in.
When using an oscilloscope, instability is indicated
by low frequency, high-amplitude discontinuous
(4) The magnet assembly should be securely in
place before inserting the carbon pile.
oscillations, usually off scale on the screen. Do not
confuse with the higher frequency commutator
(5) When inserting the carbon pile hold the
regulator with the glass tube in a vertical position to
ripple.
minimize carbon breakage. While in this position
(9) The exact position of the pile screw should
the pile screw should be turned in to apply slight
be obtained by checking the full load and no-load
pressure to the pile.
regulated voltage at 8000 rpm. The full load
(6) Replace parts  should be sprayed or
voltage should not vary more than plus or minus
brushed with a moisture or  fungus-resistant,
0.1 volt from the no-load voltage. The coil current
varnish (Military Specification MIL-V-173A, Type
must be between 0.645 and 0.655 ampere. At 3500
I, or equivalent). Do not apply varnish to terminal
rpm, the full-load voltage should not be more than
boards, resistors, or rheostats.
0.5 volt lower than the no-load voltage. Adjust the
g. Test Procedure. It is preferable to use the same
magnet body as described in g (6). Recheck the
type of generator that the regulator will be used
pile screw setting and coil current until both voltage
with in service. The rpm values in the text below
and current requirements are satisfied.
refer to a generator with a speed range of 3000-
(10) Record the no-load voltages at 3 5 0 0 ,
4500, 6000, and 8000 rpm, also read voltage at
8000 rpm. These values will be different for other
ratings.
10,000 rpm, no-load, without shocking. The
regulated voltage should remain between 27.5 volts
(1) Mount the regulator on the test stand and
make connections shown in figure 3-4.
and 28.3 volts for all readings. If the voltage does
not remain between these limits, turn the pile screw
(2) The regulator should be wired in ac-
in slightly and recheck para g(9).
cordance with figure 3-3.
(3) Resistance values for checking the coil
(11) Increase the speed from 3500 to 8000
rpm without shocking and record the voltage at
windings, resistors and rheostat are given in d (11).
(4) Set the rheostat at its midposition. Make
8000 rpm. Shock several times at 8000 rpm and
sure that the magnet locking screws are tight.
note the voltage. The difference between the two
readings should not be greater than 0.3 volt. If it is
(5) Turn the pile screw out (counterclockwise)
until pressure on the carbons is relieved. Do not
greater, replace the carbon disks and check the
back out pile screw too far as end carbons may
insulation tube for cleanliness and cracks.
become dislocated and will break when the pile
(12) With the regulator operating, close the
equalizer switch and adjust the voltage drop across
screw is turned in (clockwise). Start the generator
the equalizer coil at the regulator terminals to 0.25
and note the voltage. It should be less than 10 volts.
If it is not, the carbon pile is too long and one
volt. Make sure the polarity is as shown on figure 3-
4. Read the voltage with the switch open at 5500
washer should be removed. The voltage should
rpm (no-load). Close the switch and again read the
start to rise when the pile screw is turned in (clock-
voltage. The voltage should drop between 2.25 and
wise).
3-2

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