Mitsubishi 380. Manual - part 245

16-2

CHARGING SYSTEM

GENERAL DESCRIPTION

M1161000100629

The charging system charges the battery with the 
alternator output to keep the battery charged at a 
constant level during varying electrical load.

OPERATION 

Rotation of the excited field coil generates AC volt-
age in the stator.
This alternating current is rectified through diodes to 
DC voltage having a waveform shown in the illustra-
tion above.
The average output voltage fluctuates slightly with 
the alternator load condition.

When the ignition switch is turned on, current flows in 
the field coil and initial excitation of the field coil 
occurs.
When the stator coil begins to generate power after 
the engine is started, the field coil is excited by the 
output current of the stator coil.
The alternator output voltage rises as the field cur-
rent increases and it falls as the field current 
decreases. When the battery positive voltage 
(alternator S terminal voltage) reaches a regulated 
voltage of approximately 14.4 V, the field current is 
cut off. When the battery positive voltage drops 
below the regulated voltage, the voltage regulator 
regulates the output voltage to a constant level by 
controlling the field current.
In addition, when the field current is constant, the 
alternator output voltage rises as the engine speed 
increases.

AKX00183

VOLTAGE

TIME

APPROXIMATELY

14.4 V

AB

06DB028A

ALTERNATOR

<3.8L ENGINE>

B

STATOR 

COIL

ALTERNATOR

MALFUNCTION

LIGHT

IGNITION 

SWITCH

BATTERY

FIELD COIL

+

–

S

L

VOLTAGE REGULATOR

CHARGING SYSTEM

ENGINE ELECTRICAL

16-3

CHARGING SYSTEM DIAGNOSIS

M1161000700427

TROUBLESHOOTING HINTS

Alternator malfunction light dose not go on when the ignition 

switch is turned to ON, before the engine starts.

• Check the bulb.

Alternator malfunction light dose not switch off after the engine 

starts.

• Check the IC voltage regulator inside the 

alternatoralternator.

Discharged or overcharged battery.

• Check the IC voltage regulator inside the alternator.

The alternator malfunction light illuminates dimly.

• Check the diode (inside the combination meter) for a 

short-circuit.

TROUBLESHOOTING GUIDE

The charging system troubleshooting guide is shown in the fol-
lowing steps.

STEP 1.

Q: Is the battery in good condition? (Refer to GROUP 54A, 

Chassis Electrical 

− Battery − On-vehicle Service − 

Battery Check 

P.54A-5

.)

YES : Go to Step 2.
NO :  Charge or replace the battery.

STEP 2.

Q: Is the alternator drive belt in good condition? (Refer to 

GROUP 00, General 

− Maintenance Service − Drive Belts 

(For Alternator, Power Steering Pump and Air 
Conditioning) (Check) 

P.00-39

.)

YES : Go to Step 3.
NO :  Adjust the belt tension or replace the belt.

STEP 3.

Q: Does the alternator malfunction light come on when the 

ignition switch is turned on?
YES : Go to Step 4.
NO : 

• Check the ignition switch. (Refer to GROUP 54A, 

Chassis Electrical 

− Ignition Switch − Ignition 

Switch 

− Inspection 

P.54A-44

.)

• Check for burnt-out alternator malfunction light.

• Check the alternator. (Refer to Charging System − 

Alternator Assembly 

− Inspection 

P.16-17

.)

• Check the alternator malfunction light-related 

circuits.

CHARGING SYSTEM

ENGINE ELECTRICAL

16-4

STEP 4.

Q: Does the alternator malfunction light go out after 

starting the engine?
YES : Go to Step 5.
NO :  Check the alternator (Refer to Charging System 

− 

Alternator Assembly 

− Inspection 

P.16-17

.)

STEP 5.

Q: Is an oscilloscope available?

YES : Go to Step 6.
NO :  Go to Step 7.

STEP 6.

Q: Does the oscilloscope show a normal wave pattern? 

(Refer to Charging System 

− On-vehicle Service − Wave 

Pattern Check Using an Oscilloscope 

P.16-11

.) 

YES : Go to Step 7.
NO :  Check the alternator. (Refer to Charging System 

− 

Alternator Assembly 

− Inspection 

P.16-17

.)

STEP 7.

• Engine: 2,500 r/min

• Headlight: ON (high beam)

• Voltage between alternator terminal B and the positive bat-

tery terminal
OK: 0.5 V or less

• Voltage between the negative battery terminal and 

alternator body
OK: 0.5 V or less

Q: Are the alternator output wire and ground wire in good 

condition?
YES : Go to Step 8.
NO :  Check the alternator output wire and ground wire.

STEP 8.

Q: Is the output current normal? (Refer to Charging 

System 

− On-vehicle Service − Output Current Test 

P.16-8

.)

YES : Go to Step 9.
NO :  Check the alternator (Refer to Charging System 

− 

Alternator Assembly 

− Inspection 

P.16-17

.)

CHARGING SYSTEM

ENGINE ELECTRICAL

16-5

STEP 9.

Q: Is the regulated voltage normal? (Refer to Charging 

System 

− On-vehicle Service − Regulated Voltage Test 

P.16-10

.)

YES : Go to Step 10.
NO :  Check the alternator (Refer to Charging System 

− 

Alternator Assembly 

− Inspection 

P.16-17

.)

STEP 10.

Q: Is the voltage drop in the alternator output wire normal?

YES : Alternator is normal. Check other systems.
NO :  Check the output wire.