TM 5-3895-359-14&P
The hold-in voltage should be 10 volts and the hold-in
commutator bars for loose connections.
Poor
current 13-15.4 amperes. Use the carbon pile to
connections cause arcing and burning of the
decrease the battery voltage to 10 volts and compare
commutator bars as the cranking motor is used. If the
the ammeter reading with specifications. A high reading
bars are not too badly burned, repair can often be
indicates a shorted hold-in winding, and a low reading
effected by resoldering or welding the leads in the riser
excessive resistance. To check the pull-in winding
bars (using rosin flux), and turning down the commutator
connect from the solenoid switch terminal (S) to the
in a lathe to remove the burned material. The insulation
solenoid motor (M or MTR) terminal (Fig. 6).
should then be undercut except as noted above.
2. Short Circuits-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 eliminated by cleaning out the
slots.
3. Grounds-Grounds in the armature can be detected
by the use of a 1 10-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 starting 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 can be checked for grounds and opens by
Fig. 4 - Internal Solenoid Circuit. ("G" and "S"
using a test lamp.
Terminals Moved to Clarify Illustration).
Grounds-Connect one lead of the 110-volt test lamp to
the field frame and the other lead to the field connector.
If the lamp lights, at least one field coil is grounded
which must be repaired or replaced.
Opens-Connect test lamp leads to ends of field coils. 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 distortion
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.
Solenoid Checks
A basic solenoid circuit is shown in Fig. 4. Solenoids
can be checked electrically by connecting a 12 volt
battery, a switch, and an ammeter to the two solenoid
windings. h all leads disconnected from the solenoid,
make test connections as shown to the solenoid switch
terminal and to the second switch terminal, (G), to check
Fig. 5 - Checking Solenoid Hold-In Winding.
the hold-in winding (Fig. 5).
10-8-15
