TM 5-3805-290-23-1
THEORY OF OPERATION - CONTINUED
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ELECTRICAL SYSTEM
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1.
General.
a.
Electrical system is a negative ground system.
b.
Charging circuit operates when engine is running. Alternator in charging circuit produces direct current for electri-
cal system.
2.
Starting Motor.
a.
Starting motor turns engine flywheel. Rpm must be high enough to initiate a sustained operation of fuel ignition in
cylinders.
b.
Starting motor has a solenoid. When ignition
switch is activated, voltage from electrical sys-
tem will cause solenoid to move pinion toward
engine flywheel ring gear. Electrical contacts in
solenoid close circuit between battery and start-
ing motor just before pinion engages ring gear.
This causes starting motor to rotate. This type of
activation is called a positive shift.
c.
When engine begins to run, overrunning pinion
drive clutch prevents damage to armature caused
by excessive speeds. Clutch prevents damage by
stopping mechanical connection. However, pin-
ion will stay meshed with ring gear until ignition
427-B2155
switch is released. A spring in overrunning
clutch returns clutch to rest position.
3.
a.
Alternator produces three-phase, full-wave, rectified electrical output.
b.
Alternator is an electro-mechanical component driven by a fan drive pulley belt. Alternator charges storage battery
during engine operation.
c.
Alternator is cooled by an external fan mounted behind pulley. Fan forces air through holes in front of alternator.
Air exits through holes in back of alternator.
d.
Alternator converts mechanical energy into ac voltage by rotating a dc electromagnetic field inside a three-phase
stator. Electromagnetic field is generated by electrical current flowing through a rotor. Stator generates ac voltage.
e.
The ac is changed to dc by a three-phase, full-wave rectifier. Direct current flows to alternator output terminal.
f.
A regulator is installed on rear end of alternator. Two brushes conduct current through two slip rings, then to rotor
field. A capacitor protects rectifier from high voltages.
g.
Alternator is connected to battery through ignition switch; therefore, alternator excitation occurs when switch is set
to ON.
4.
Sensors.
a.
Fuel level sending unit provides input to machine ECM which sends data to dash panel cluster. Data will position
fuel gage accurately.
b.
Air filter restriction indicator provides information on air flow to dash panel cluster for indicator.
c.
Engine oil temperature sensor provides data for engine oil temperature gage.
d.
Engine speed sensor provides data to dash panel cluster.
e.
Transmission oil filter circuit contains a sensor which activates indicator.
