TM 55-6115-491-40
Caution
Do not touch the commutator surface after the final finish is obtained. Fingerprints
may prevent a uniform commutator film which is necessary for satisfactory operation.
Repeat sanding, if necessary, to remove fingerprints.
3-18. Reconditioning Slip Rings.
b. Take the lightest possible cut with a fine feed and
3-19. Use the same procedure for reconditioning slip
check to see if the first cut cleans up the slip ring
surface. If not, repeat the operation until the entire slip
rings as used for finishing the exciter commutator. Set
ring surface has been renewed.
the rotor in a lathe as described in paragraph 3-17a and
Caution
The slip rings, when new, have a diameter of 2.186 inches. If the turning process
reduces this diameter to less than 2.030 inches, replace the rotor.
3-20. Balancing The Rotor.
lamp lights, the coil being tested is grounded and the
3-21. Before the rotor is reassembled in the generator,
complete housing and stator assembly should be
replaced.
subject it to a balancing check. Balancing of the rotor is a
b. Using an ohmmeter {table 2-2}, test the
precise operation requiring the use of suitable balancing
exciter field winding for continuity and short circuits.
equipment and milling machines. The rotor must be
With one lead of the ohmmeter connected to terminal F1
balanced to within 5 grain-inches. Correct the balance
and the other lead to terminal A-, resistance should be
as required by milling the retaining bands on either end
9.6 ohms to 13.1 ohms. A resistance reading of less
of the alternator field (0.040-inch maximum depth for full
than 9.6 ohms indicates a short circuit, and a reading
width of bands) and by milling the retaining bands on
above 13.1 ohms indicates either and open circuit or a
either side of the armature (0.25-inch diameter by 0.025-
loose connection. (See figure 1-2.) Replace stator if
inch maximum depth). On the exciter armature, two
shorted or open.
grooves may be milled in the band closest to the
c. Check dielectric strength of stator winding
commutator, and one groove may be milled on the band
insulation by applying 875 volts (RMS) phase-to-phase
farthest from the commutator. The fan may contribute to
and phase-to-ground for one minute. There shall be no
the overall balance of the rotor and the rim of the outer
indication of insulation breakdown. Replace if
flange may be filed as necessary. When removing stock
breakdown is indicated.
from the fan, remove metal from outer rim only and do
3-23. Capacitor.
not extend the cut below the rim lip.
3-22. Stator Windings And Housing.
3-24. Use a capacitor tester to check capacitor (4, the
capacitor. The capacitor tolerances are10 figure 3-2).
a. Test the AC generator stator windings and
the exciter stator windings for ground by using the test
The capacitances shall be as shown in figure 3-
lamp circuit described in paragraph 3-16. Place one test
3.Terminal designations are indicated on percent for the
6.0 f element and20 percent for the 0.001 and 0.022
lead against a pole shoe in the housing and touch the
other test lead to each of the stator connections. If the
f elements. Replace the capacitor if capacitances are
not within limits.
3-14
