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.