Alternator
Checking the alternator
You will find useful information and important tips on the subject of vehicle alternators here.
The alternator supplies all electrical components in the vehicle with electricity. Should the alternator lose its full functionality, the electronics will fail after a certain period – the battery will no longer be charged, and the vehicle will no longer be roadworthy. In order that this does not happen, any faults should be detected in good time. We therefore provide you with various problem descriptions and detailed solutions in the following.
Important safety note
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.
TABLE OF CONTENTS
ALTERNATOR: BASICS
The task of the alternator is to supply all electrical consumers within the vehicle with energy while charging the battery at the same time. Three-phase alternators are generally installed in modern vehicles.
The alternator power, battery capacity and the total power requirements of the vehicle's electrical system are matched to each other.
DESIGN AND FUNCTION OF THE ALTERNATOR: FUNCTION
The alternator is usually composed of the following components:
- Housing
- Stator
- Alternator rotor
- Alternator regulator
The stator with three-phase winding is mounted in the alternator housing. Claw poles, excitation winding, fan and slip rings are mounted on the shaft of the alternator rotor. The pulley is mounted on the front of the external part of the shaft. The electronic control unit with carbon brush brackets is attached in the rear area of the alternator.
Function
Electricity is generated in the three-phase alternator on the induction principle. An electrical voltage is generated in the stator winding when the magnetic field within this winding changes. This change in the magnetic field is generate by the rotating alternating rotor. A sinusoidal alternating voltage is generated by the changing magnetic field with alternating north and south poles. This alternating voltage, which is unsuitable for the electrical system in the vehicle, is converted to direct-current voltage by the rectifier. The control unit adjusts the alternator voltage to the respective operating state of the motor and to the voltage requirements of all consumers in the system.
ALTERNATOR FAULTY: SYMPTOMS
The following symptoms may indicate a fault in the alternator:
- Charging indicator lamp lights up
- Starting difficulties due to insufficiently charged vehicle battery.
- Vehicle battery becomes hot due to overload
- The illuminance of the headlamp deviates in relation to the engine RPM
- Bulbs burn out more quickly than normal
CAUSES OF FAULTY ALTERNATORS: CAUSE OF FAILURE
An alternator malfunction can have different causes. The cause is not always due to an internal alternator fault, such as a faulty winding, rotor, rectifier or control unit. Before replacing the alternator, additional components should be considered as a cause of failure and checked.
- Prematurely aged or faulty vehicle battery
- Electrical connections on the alternator loose or faulty
- V-belt or V-ribbed belt loose or faulty
- Belt tensioner or free-running roller damaged
TESTING THE ALTERNATOR: TROUBLESHOOTING
When performing troubleshooting on the alternator, the following fundamental rules are to be observed:
- Do not disconnect, short circuit or mount battery or connection terminals when the engine is running or the alternator is in operation (voltage peaks can lead to damage)
- Never perform voltage or current measurements via short circuit (voltage peaks) - use a voltmeter or ammeter
A multimeter and a clip-on ammeter are required for troubleshooting. Please also refer to the technical info: "Ground (31)".
NOTICE
When performing welding work on the vehicle and when removing or installing the alternator, the battery must be disconnected.
Charging indicator lamp flickers.
| CAUSE: | REMEDY: |
|---|---|
| V-belt too loose | Tighten V-belt |
| Setting of the contacts incorrect or the control unit resistor burnt out (Only with contact control units) | Adjust contacts, replace resistor or control unit |
Charging indicator lamp lights with unchanged brightness at an increased RPM.
| CAUSE: | REMEDY: |
|---|---|
| Cable D+/61 has a short circuit to frame |
|
| Control unit faulty | Replace control unit |
| Check alternator and repair or replace if necessary |
Charging indicator lamp lights up brightly with the ignition switched on, but dims or flickers when the engine is running.
| CAUSE: | REMEDY: |
|---|---|
| Contact resistance in the charging current circuit or in the cable for the indicator lamp | Check cable and connections, and replace if necessary |
| Control unit faulty | Replace control unit |
| Alternator faulty | Check alternator, repair or replace if necessary |
| URSACHE: | ABHILFE: |
|---|---|
| Übergangswiderstände im Ladestromkreis oder in der Leitung zur Kontrolleuchte | Leitung und Anschlüsse überprüfen ggf. erneuern |
| Regler defekt | Regler austauschen |
| Generator defekt | Generator überprüfen, instandsetzen, ggf. erneuern |
Charging indicator lamp does not light up with the ignition switched on.
| CAUSE: | REMEDY: |
|---|---|
| Battery discharged or faulty | Charge battery, check, replace if necessary |
| Cables or connections damaged, loose or oxidized | Check cables and connections, attach, replace if necessary |
|
|
| Short circuit of a positive diode | Immediately disconnect battery or B+ (otherwise discharge in situ) and repair/replace alternator |
| Oxide coating on the slip rings, break in the rotor winding | Repair/replace alternator |
| Indicator lamp faulty | Replace indicator lamp |
Battery is not charged or charged insufficiently.
| CAUSE: | REMEDY: |
|---|---|
| V-belt too loose | Tighten V-belt |
| Cables or connections loose, damaged, or oxidized | Check cables and connections between battery and alternator and the respective ground connection, replace if necessary |
| Battery faulty | Charge battery, check, replace if necessary |
| Control unit faulty | Replace control unit |
| Check alternator, repair or replace if necessary |
How helpful is this article for you?
Not helpful at all
Very helpful