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 ELECTRICAL
Figure 40.
Figure 39.
appear to be in good condition, the battery and external
circuit are found to be satisfactory, and the cranking
motor still does not operate correctly, make the following
tests:
1. No-load test: Connect the cranking motor in
series with a battery of specified voltage and an
ammeter capable of reading several hundred amperes.
Read the armature RPM in addition to the current draw.
2. Torque test: It is advisable to use in the circuit a
high current-carrying variable resistance, so that the
Figure 41.
specified voltage at the motor can be obtained. A small
variation of the voltage will produce a marked difference
a. Rated torque, current draw and no load speed
in the torque developed. (Fig. 41)
indicate normal condition of cranking motor.
3. Interpreting results of No-load and Torque Test:
b. Low free speed and high current draw with low-
developed torque may result from:
(1) Tight, dirty, or worn bearings,
B-80
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