TM 5-3895-382-24
When the start relay closes, coils (W) and (X) receive power.
Battery voltage is applied to test point (3), which is the start
terminal (S). Terminal "G" of the coil (X) is permanently
grounded to the ground post or the housing of the starting
motor. Grounding for the test point (4) of the pull-in coil (W) is
momentary. This ground takes place through the DC
resistance of the starting motor.
When the magnetic force increases in both coils, the pinion
gear moves toward the ring gear of the flywheel. Then, the
solenoid contacts close in order to provide power to the
starting motor. When the solenoid contacts close, the ground
is temporarily removed from the pull-In coil (W). Battery
voltage is supplied on both ends of the pull-in coil while the
starting motor cranks. During this period, the pull-in coil is out
of the circuit.
Cranking of the engine continues until current to the solenoid is
stopped by releasing the ignition switch.
Power which is available during cranking varies according to
the temperature and condition of the batteries. The following
chart shows the voltages which are expected from a battery at
the various temperature ranges.
Table 29
Typical Voltage Of Electrical System During
Cranking At Various Ambient Temperatures
Temperature
12 Volt
24 Volt
System
System
-23 to -7 C
6 to 8 volts
12 to 16 volts
(-10 to 20 F)
-7 to 10 C
7 to 9 volts
14 to 18 volts
(20 to 50 F)
10 to 27 C
8 to 10 volts
16 to 24 volts
(50 to 80 F)
The following table shows the maximum acceptable loss of
voltage in the battery circuit. The battery circuit supplies high
current to the starting motor. The values in the table are for
engines which have service of 2000 hours or more.
Table 30
Maximum Acceptable Voltage Drop In The
Staring
Circuit
12 Volt
24 Volt
System
System
Battery post "-' to
0.7 volts
1.4 volts
the starting motor
terminal "-“
Drop across the
0.5 volts
1.0 volts
disconnect switch
Battery post “+"
0.5 volts
1.0 volts
to this terminal of
the starting motor
solenoid “+"
Solenoid terminal
0.4 volts
0.8 volts
"Bat” to the solenoid
terminal “Mtr”
Voltage drops that are greater than the amounts in Table 30
are caused most often by the following conditions:
Loose connections
Corroded connections
Defective switch contacts
Diagnosis Procedure
NOTICE
If equipped with electric start, do not crank the engine for
more than 30 seconds. Allow the starter to cool for two
minutes before cranking again.
Never turn. the disconnect switch off while the engine is
running. Serious damage to the electrical system can
result.
If the starting motor does not crank or cranks slow, perform the
following procedure:
1.
Measure the voltage of the battery at the battery posts
with the multimeter when you are cranking the engine or
attempting to crank the engine. Measure the voltage
across the battery posts. Do not measure the voltage
across the cable post clamps.
2.
Battery voltage
a.
If the voltage is equal or greater than the voltage in
Table 29, then go to Step 3.
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