Onan UF Series Instruction Manual And Parts Catalog page 72

14
M A I N T E N A N C E
across the segments of the commutator.
b. At some point around the com-
mutator a spark should occur as the
blade contacts the two adjacent segments.
If a spark occurs, the circuit is complete
(not open) between those two segments.
Then it will be necessary to rotate the
armature just enough to test the next two
segments.
Continue the rotating and testing until the
commutator segments have been tested FIG. 5 - OPEN CIRCUIT TEST
completely around. A good spark should
occur between all adjacent segments when those segments and windings
attached to them are in the correct position in the growler magnetic-
field. If no spark occurs, the winding between those two segments is
open circuited. (There is a possibility that a short circuit of a windingl
might prevent the sparking, but then the armature would also be mag-
netized as described in the following paragraph.)
TESTING THE ARMATURE FOR SHORT CIRCUITS. - Place the arma-
ture in the growler
(see figure) which is connected to alternating current. Hold a steel blade
(or old hack-saw blade) 1/4 inch from the armature laminations. If the
steel blade is attracted to any magnetized armature laminations, either
the armature windings or commutator is short circuited. Do not test
for magnetism at just one point of the
armature laminations, but test all of
the armature laminations from one
side over to the other side (along the
dotted line on figure). After testing
the armature in one position, revolve
the armature about 1/8 revolution and
test for magnetism again. Continue
the revolving and testing until the arma-
ture has been tested completely around.
BUPE
GPOWLEZ— •
TO A.C
SOUXCE-
6 - SHORT CIRCUIT
TEST
F I E L D WINDINGS, OPEN CIRCUIT. - A
test
lamp set can be used to test field windings
for an open circuit. Place one test prod on FIG.
one of the terminal ends of the field windings,
and the other test prod on the other terminal
end of the winding. The test lamp should light. If it does not, an open
circuit is indicated. Check carefully to see that the open circuit is not
at the terminal leads or a loose terminal. An open circuit due to a
broken lead or loose terminal is easily repaired. An open circuit with-
in a coil requires replacement of the set of coils.