Figure 3-19. Alternator and Brackets (RMP-J/1-10G)

TM 5-4110-217-14

If a battery

is being installed, make

certain that

the negative terminal is

connected to

ground. Reverse polarity

will destroy

rectifier diodes in the

alternator.

Test Equipment Required.

(1) Volt-ampere tester such as the Sun

Electric Model VAT-20 or equivalent with meter ranges

shown below:

DC ammeter

0-60 ampere

DC ammeter

0-5 ampere

DC voltmeter

0-16 volt

Rheostat

40 ohm, capable of handling

3 amps

Carbon pile

45 ampere

(2) In-circuit diode tester (Sun Electric Model

Screw

11.

Regulator, voltage

RDT or equivalent).

Washer, lock

12.

Screw

(3) Test lamp-12 volt DC.

Bracket, adjusting

13.

Pulley

(4) Ohmmeter-Any

commercial

type-not

Nut

14.

Nut

absolutely necessary but can be helpful.

Screw

15.

Washer, lock

c. Isolation Diode Test. If it is suspected that the

Washer, lock

16.

Capacitor

battery is being discharged with the ignition switch OFF,

Nut

17.

Clip

the cause could be a shorted isolation diode.

Bracket, mounting

18.

Screw

(1) Make sure that the regulator is connected

Belt, alternator drive

19.

Washer, lock

to the alternator.

10.

Alternator

20.

Nut

(2) Measure the voltage appearing at the

auxiliary terminal. With the ignition switch OFF, the

Figure 3-19. Alternator and Brackets (RMP-J/1-10G)

voltage should not exceed 0.1 volts. A voltage in excess

of 0.1 volts indicates excessive leakage, and the diode

the field rotates and the generating windings (armature)

should be replaced. Refer to direct support unit for

are stationary. The field current necessary to control the

replacement of the diode.

output of the alternator is supplied from the alternator.

d. Alternator System Test. This test checks the

The regulator controls the current fed to the field via the

current output of the alternator to determine if the system

brushes and rotor slip rings.

(alternator and voltage regulator) is functioning properly.

a. Testing Precautions.

(1) With the engine off, disconnect output

(1) When making the "Alternator System

cable from alternator output terminal and connect an

Test, " the battery must be in good condition and fully

ammeter with a range of 0-60 amperes in series with

charged so that the alternator output current can be

output terminal and output cable (negative terminal of

completely controlled with an external load.

meter to positive terminal of battery).

(2) DO NOT under any circumstances, short

(2) Connect a carbon pile load to the negative

FIELD terminal of alternator to ground.

side of ammeter and negative battery terminals.

(3) DO NOT disconnect voltage regulator

(3) Connect a voltmeter to alternator output

while alternator is operating.

terminal and negative ( - ) battery terminal.

(4) DO NOT disconnect load (alternator

(4) Start engine (allow about 5 minutes for

output lead) from alternator while the alternator is

temperature stabilization), slowly increase load with

operating.

carbon pile until minimum is reached (10 amperes). The

(5) DO NOT remove alternator from unit

voltage at the output terminal should be at least 13 volts

without first disconnecting the negative ( - ) battery cable.

but not more than 15 volts.

If battery must be removed, disconnect negative cable

(5) If voltage exceeds 15 volts at rated

first.

current output (35 amperes), replace or check voltage

regulator (para 3-47).

CAUTION

(6) If the rated output cannot be obtained at

proper engine speed, check fan belt for proper tension.

3-26