CAUTION
On 24 volt systems, use only a carbon pile
specifically designed for 24 volt use. A 12-
volt carbon pile could be damaged if used
in a 24 volt circuit.
1-25. THE BASIC HEAVY-DUTY ELECTRICAL SYS-
TEM.
Today’s basic heavy-duty electrical system
(See Figure 1-1) consists of batteries (usually 3 or 4
connected), a starter, an alternator, a magnetic switch,
an ignition switch, a pushbutton switch and the
required wiring. The batteries provide the high current
required by the starter. The magnetic switch controls
the battery current to the starter solenoid. The ignition
and pushbutton switches activate the magnetic switch
which in turn energizes the starter. If all functions work
properly, the engine will crank.
1-26.
The mechanical energy of the running engine
provides the power for the alternator. The alternator
creates the electrical energy needed to recharge the
batteries and power the vehicle’s electrical accessories
and loads.
1-27.
How well the electrical system components are
matched will determine in a large part how effectively
and efficiently the system will operate. Another
important factor in system design is to ensure that
system wiring is adequate to carry the current required
by each circuit.
1-28. HEAVY DUTY SYSTEM BATTERIES.
The
battery, or more common batteries, in the heavy duty
electrical system, are devices for storing energy. They
convert chemical energy into the electrical energy
needed to operate the starter. With the engine running
the alternator supplies electrical energy to the batteries
which they convert into chemical energy and store for
later use. Three basic types of batteries may be
encountered in heavy-duty electrical systems:
1-6
Figure 1-14. Digital Ohmmeter
EXAMPLES
DIGITAL
DIGITAL
2.3
.450
0.00
OL
DIODE
COIL
DP-1014
Figure 1-15. Carbon Pile
DP-1015
new diagnostic manual 4/5/05 9:47 AM Page 1-6
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