DRESSTA TD-25M EXTRA, Service Manual

Page: 320 / 595

SECTION 8
ELECTRICAL
Page 44
TD-25M EXTRA DRESSTA
CRANKING MOTOR 42 MT
e. No-Load Test (Fig. 8.14)
BAT.
S
M
1
2
3
4
5
6
7
8
Fig. 8.14. No-Load Test Circuit
1. Battery
2. Ammeter
3. Switch
4. Voltmeter 5. Cranking Motor
6. Solenoid
7. RPM Indicator
8. Carbon Pile
Connect a voltmeter from the motor terminal to the motor frame, and use an [RPM] indicator
to measure armature speed. Connect the motor and an ammeter in series with a fully charged
battery of the specified voltage, and a switch in the open position from the solenoid battery terminal
to the solenoid switch terminal. Close the switch and compare the [RPM], current, and voltage
reading with the specifications in this Section. It is not necessary to obtain the exact voltage
specified in these specifications, as an accurate interpretation can be made by recognizing that if
the voltage is slightly higher the [RPM] will be proportionately higher, with the current remaining
essentially unchanged. However, if the exact voltage is desired, a carbon pile connected across
the battery can be used to reduce the voltage to the specified value. Connect the carbon pile to
only one of the 12-Volt batteries. If the specified current draw does not include the solenoid, deduct
from the ammeter reading the specified current draw of the solenoid hold-in winding. Make
disconnections only with the switch open. Interpret the test results as follows:
f. Interpreting Results of Tests
1. Rated current draw and no-load speed indicates normal condition of the cranking motor.
2. Low free speed and high current draw indicate:
a. Too much friction-tight, dirty, or worn bearings, bent armature shaft or loose pole shoes
allowing armature to drag.
b. Shorted armature. This can be further checked on a growler after disassembly.
c. Grounded armature or fields. Check further after disassembly.
3. Failure to operate with high current draw indicates:
a. A direct ground in the terminal or fields.
b. "Frozen" bearings (this should have been determined by turning the armature by hand).