D2-18 24 VDC Electric Supply System D02023
Cleaning and Inspection
1. The drive (71), armature (45) and fields (46)
should not be cleaned in any degreasing tank,
or with grease dissolving solvents, since these
would dissolve the lubricant in the drive and
damage the insulation in the armature and field
coils.
2. All parts except the drive should be cleaned with
mineral spirits and a clean cloth.
3. If the commutator is dirty, it may be cleaned with
No. 00 sandpaper.
NOTE: Never use emery cloth to clean commutator.
4. Inspect the brushes (13, Figure 2-8) for wear.
a. If worn excessively when compared with a
new brush, they should be replaced.
b. Make sure the brush holders (10) are clean
and the brushes are not binding in the hold-
ers.
c. The full brush surface should ride on the
commutator. Check by hand to insure that
the brush springs (16) are giving firm contact
between the brushes (13) and commutator.
d. If the springs (16) are distorted or discolored,
they should be replaced.
Armature Servicing
If the armature commutator is worn, dirty, out of
round, or has high insulation, the armature (45)
should be put on a lathe and the commutator turned
down. The insulation should then be undercut 0.031
in. (.79 mm) wide and 0.031 in. (.79 mm) deep, and
the slots cleaned out to remove any trace of dirt or
copper dust. As a final step in this procedure, 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 con-
nections. Poor connections cause arcing and
burning of the commutator as the cranking
motor is used. If the bars are not too badly
burned, repair can often be effected by resol-
dering or welding the leads in the riser bars
(using rosin flux), and turning down the commu-
tator in a lathe to remove the burned material.
The insulation 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.
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 2-8) 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.
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