What is an alternator?

From the 1960s onwards alternators gradually replaced dynamos. They are lighter, cheaper, more rugged, and can provide useful charge at idle speed.

Dynamos produced direct current, but alternators produce alternating current. This is why they feature rectifiers and voltage regulators.

What does an alternator do?

Alternators are used in vehicles to charge the battery and to power the electrical system when its engine is running.

Technical details

Automotive alternators are normally belt driven at 2-3 times the speed of the crankshaft. The alternator rotates at a variable speed (which varies the frequency) since it is driven by the engine. This is not a problem because the alternating (AC) current is rectified into direct (DC) current.

Modern alternators are fitted with overunning decoupler pulleys which reduce wear and relieve the auxiliary drive system (damper pulley, air-con compressor bearings etc.). Pulley failure can result in wear of the internal spring and malfunction of the clutch mechanism. A damaged disengageable alternator pulley cannot properly absorb vibrations or transmit power to the alternator.

Malfunction symptoms:

- The alternator no longer charges and the warning light comes on on the instrument panel.
The problem probably comes from the brushes which have worn out in contact with the collectors.

- The alternator charges too much at full speed and may damage the battery.
This is a fault in the regulator, which should normally limit the voltage to 14V.

The alternator's decoupler pulley should give an impression of  free rotation in one direction and have a “spring feel” in the other direction

If this is not the case then it is defective.

Modern alternators are with integrated ventilation (the fan is inside instead of on the outside), which allows them to be more compact and achieve better cooling. But in a 4x4 they tend to get dirty faster and eventually fail.

Also remember to check your drive belts which may be worn or dirty.

How to repair an alternator?

We offer a range of alternator rebuild kits and other spare parts. 

Browse all these parts here:

What parts are replaced in a remanufactured alternator?

All components are disassembled, cleaned, checked and tested. Certain parts are zinc plated and others sand blasted then painted. Certain parts are replaced.


  • Bearings (parts #3 & #5 on diagram)
  • Rotor insulation (#4 on diagram)
  • Carbon brushed (#8 on diagram)
  • Regulator and defective diodes (#9 on diagram)

Remanufacturing process:

All parts are disassembled and all components are washed, except the rotor which is steel-brushed.

Bearings are replaced by new parts.

The rotor is electrically tested and painted to prevent corrosion.

After being washed, the stator is fully steel brushed to eliminate traces of corrosion then painted. The interior diameter is calibrated.

Pulleys are controlled, painted and chromed

Regulators are washed, dried and sand blasted. Brushes and springs are replaced.

The diodes of the rectifier bridge are tested and replaced if required.

Before final painting, all renovated components are reassembled and each complete product is tested. Once assembled, the alternator undergoes final testing.


Some examples of the alternators available at Euro4x4parts. 

You can choose between a genuine assembly, OEM quality, remanufactured (exchange) or aftermarket alternators.

We offer the widest range of alternators on the 4x4 market in Europe (over 600 references for nearly 40 brands of all-terrain vehicles). Our aftermarket parts come from well established manufacturers and our standard exchange alternators are refurbished with high quality parts.

Standard exchange is part of our policy for sustainable development. Standard exchange promotes recycling of main components and raw materials.

Here at Euro4x4parts we are firmly committed to reducing our ecological footprint by reducing the use of raw materials and energy consumption.

Our standard exchange products are renovated according to manufacturers' specifications and come with a full 2-year warranty.

Choose the right alternator for your 4x4:

Do it yourself, you'll be even prouder! To help you out, Euro4x4parts shares its know-how and expertise in mechanics through 4X4XPERT: new products, technical sheets, and personalized tutorials... You've got the keys!
And because we also learn from your experiences, your feedback is essential. Let us know your thoughts and suggestions by email: 4x4xpert@euro4x4parts.com

Check out our complete catalogue of 4x4 parts and accessories!

All the photos in our articles are taken on authorized roads or tracks, private land, or during supervised competitions. Let's all do our part to preserve the environment!

Please note: Euro4x4parts publishes this information to help its customers, but cannot be held responsible for the advice given here and their consequences when used.