Komatsu 830E-AC Shop Manual page 206

Armature Servicing
If the armature commutator is worn, dirty, out of
round, or has high insulation, the armature (45, Fig-
ure 2-6) should be put on a lathe and the commutator
turned down. The insulation should then be undercut
0.79 mm (0.031 in.) wide and 0.79 mm (0.031 in.)
deep, and the slots cleaned out to remove any trace
of dirt or copper dust. As a final step in this proce-
dure, the commutator should be sanded lightly with
No. 00 sandpaper to remove any burrs left as a result
of the undercutting procedure.
The armature should be checked for opens, short cir-
cuits and grounds as follows:
1. Opens are usually caused by excessively long
cranking periods. The most likely place for an
open to occur is at the commutator riser bars.
Inspect the points where the conductors are
joined to the commutator bars for loose connec-
tions. Poor connections cause arcing and burn-
ing of the commutator as the cranking motor is
used. If the bars are not too badly burned,
repair can often be effected by resoldering or
welding the leads in the riser bars (using rosin
flux), and turning down the commutator in a
lathe to remove the burned material. The insula-
tion should then be undercut.
2. Short circuits in the armature are located by use
of a growler. When the armature is revolved in
the growler with a steel strip such as a hacksaw
blade held above it, the blade will vibrate above
the area of the armature core in which the short
circuit is located. Shorts between bars are
sometimes produced by brush dust or copper
between the bars. These shorts can be elimi-
nated by cleaning out the slots.
D2-16
3. Grounds in the armature can be detected by the
use of a 110-volt test lamp and test points. If the
lamp lights when one test point is placed on the
commutator with the other point on the core or
shaft, the armature is grounded. Grounds occur
as a result of insulation failure which is often
brought about by overheating of the cranking
motor produced by excessively long cranking
periods or by accumulation of brush dust
between the commutator bars and the steel
commutator ring.
Field Coil Checks
The field coils (46, Figure 2-6) can be checked for
grounds and opens by using a test lamp.
1. Grounds - The ground connections must be
disconnected during this check. Connect one
lead of the 110 volt test lamp to the field frame
(35) and the other lead to the field connector
(42). If the lamp lights, at least one field coil is
grounded and must be repaired or replaced.
2. Opens - Connect test lamp leads to ends of
field coils (46). If lamp does not light, the field
coils are open.
Field Coil Removal
Field coils can be removed from the field frame
assembly by using a pole shoe screwdriver. A pole
shoe spreader should also be used to prevent distor-
tion of the field frame. Careful installation of the field
coils is necessary to prevent shorting or grounding of
the field coils as the pole shoes are tightened into
place. Where the pole shoe has a long lip on one
side and a short lip on the other, the long lip should
be assembled in the direction of armature rotation so
it becomes the trailing (not leading) edge of the pole
shoe.
24 VDC Electric Supply System D02034