| |
Back
Operational Testing | Up
Construction Mechanic Advanced - Construction methods and practices | Next
Rectifiers |
CHAPTER 4
TROUBLESHOOTING ELECTRICAL SYSTEMS
In the early days of the automobile, only its ignition
system depended on electricity for operation. However,
in today’s automobile and construction equipment,
electricity operates the ignition, lighting, and starting
systems and many accessories, such as control units on
automatic transmissions and overdrives, choke controls,
emission controls, and air conditioning.
Storage batteries, generators, regulators, and other
units are required to provide an adequate source of
electrical current for construction and automotive
equipment. The Construction Mechanic is responsible
for maintaining the parts and units of the electrically
operated systems and accessories on this equipment.
Electrical repairs and adjustments, however, are special
tasks that require the know-how of an expert-a person
trained for this kind of work; in other words, an
automotive electrician.
As a CM1, when you supervise mechanics who
perform these special tasks in the shop or garage, you will
need automotive electrical testing equipment. For
example, in troubleshooting batteries and generators you
save time and reduce damage to equipment by using
ammeters and voltmeters instead of hit-and-miss methods.
All units in an automotive electrical system
operate on the basic principles described in this
chapter. You can find more on automotive electricity
in Construction Mechanic 3 & 2 and U.S. Army
TM-9-8000, Principles of Automotive Vehicles. This
chapter includes the techniques of troubleshooting the
charging, cranking, ignition, and lighting systems,
and other electrical accessories.
AC CHARGING SYSTEMS
The output requirements of automotive electrical
generators have increased considerable y in recent years
because of the growing popularity of current-consuming
electrical accessories, such as two-way radios and
radiotelephones for communications, heavy-duty
heaters, and air-conditioners.
A conventional dc generator built to produce the
required amount of electricity at both high- and
low-speed ranges requires an increase in size which
limits application. An ac generator (ALTERNATOR) has
been developed that can be used with a rectifier bridge
to produce enough current to fulfill almost any need over
a speed range that varies from idle-to-top engine speed.
ALTERNATORS
The small size of the alternator makes it adaptable
to almost any application. It is mechanically constructed
to withstand extreme heat, vibrations, and top speeds
met in normal service.
A review of Construction Mechanic 3 & 2 will
show that the alternator and the conventional dc
generator operate on the same basic principles. The rotor
assembly in the alternator does the same job as the field
coil and pole shoe assembly in the dc generator. The
stator assembly in an alternator has the same function as
the armature in a dc generator while in a fixed position.
The stator maybe either Y or delta connected to fit the
application. (See fig. 4-1.) Normally, the delta-
connected alternator is found where lower voltage, but
Figure 4-1.-Types of alternator internal windings.
4-1
|
