CHAPTER 3 REPAIR OF ELECTRICAL SYSTEM

TM 10-3930-633-34

CHAPTER 3

R E P A I R OF ELECTRICAL SYSTEM

Section I. ALTERNATOR

3-1. General

together and the positive battery terminals

together.

The alternator is an A .C. (alternating current)

c. When connecting a charger to the battery,

generator which delivers relatively high output of

connect the charger positive lead to the battery

energy at low speeds. The physical characteristics

positive terminals and the charger negative lead

of the design are discussed below.

to the battery negative terminal.

a. Operation. The unit consists of a rotating

d. Never operate the a.c. generator on open

field coil, called the rotor, which is supported by

circuit. Make absolutely certain all connections in

bearings and rotates, being driven by the engine,

the circuit are secure.

inside an electromagnetic field generated by the

e. Do not short across or ground any of the

stator windings. The stator windings are attached

terminals on the a.c. generator or regulator.

to the alternator frame. Brushes in the unit pick

f. Do not attempt to polarize the a.c.

up the oscillating current from the rotor, and pass

generator.

it through a set of diode rectifiers in the alternator

g. Always disconnect alternator before doing

end frame to produce a D.C. (direct current)

any repair welding, to prevent reverse current

output. A voltage regulator is used with the

damage.

alternator to control the strength of the electrical

fields, and therefore the relative values of the

3-3. Maintenance

output .

a. While the a.c. generator is constructed to

b. Rotor. The rotor consists of one continuous

give long periods of service, a regular inspection

electrical winding on the rotor shaft. The shaft is

procedure s h o u l d be followed to obtain its

supported by a ball bearing at the drive end and a

maximum life. The frequency of inspection is

needle roller bearing at the brush end. The

determined largely by operating conditions. High

bearings are provided with grease reservoirs,

speed operation, high temperatures, dust, and

eliminating the need for periodic lubrication.

dirt all increase the wear on brushes, sliprings,

c. Stator and Frame. Stator windings are

and bearings.

assembled on the inside of a laminated core that

b. At regular intervals inspect terminals for

forms part of the frame. Six rectifier diodes are

corrosion and loose connections and wiring for

assembled into the slipring end frame and are

frayed or deteriorated insulation. Check

connected to the stator windings.

m o u n t i n g bolts for tightness and belt for

d. Brushes. Two brushes are used to carry

alignment, proper tension and wear. When

current from the regulator circuit, through the

tightening belt tension, apply pressure against

sliprings, to the rotor field coil. Brushes are extra

the stator laminations between end frames and

long for extended service.

not against either end frame.

3-2. Service Precautions

c. Noise from an a.c. generator may be caused

by worn or dirty bearings, loose mounting bolts,

Since the a.c. generator and regulator are

loose drive pulley, defective diode or defective

designed for use on only one polarity system, the

stator.

following precautions must be observed when

working on the charging circuit. Failure to ob-

3-4. Alternator Repair

serve these precautions will result in serious

a. General. If the a.c. generator is new but

damage to the electrical equipment,

suspected of being faulty, a generator output test

a. When installing a battery, always make

should be performed before removing the unit

absolutely sure the ground polarity of the battery

from engine. S e e TM 10-3930-633-12 for

and the ground polarity of the a.c. generator are

procedure. After extended periods of operation

the same.

however, or at time of engine overhaul, the

b. When connecting a booster battery. make

generator should be removed for a thorough

certain to connect the negative battery terminals

inspection and cleaning.

3-1