What is a car alternator? Seldom does any driver ask him/herself this question. Despite the fact that the alternator is one of the most important parts of the car.

In fact, the alternator is so important, that the evolution to today’s modern car we know and drive wouldn’t be possible without it.

In this article, we’ll try to shed some light on the whole subject and try to explain the most important things about the alternator.

Besides this, you can watch our video at the end of this article or on our YouTube channel.


The alternator is an electric generator that supplies electricity to the car while the engine is running.

It is the main supplier, besides the car battery, of all electric energy in the car.

Besides this, the alternator recharges the battery while the engine is running.

Electricity has a huge role in almost every vital car system like the ignition system, fuel intake system, steering system, and else.

This is why the alternator is so important.

If it stopped working for some reason, the car cannot function. The battery would give electricity for a short period and once depleted the car would stop.

Without the alternator, the car would be practically useless.



The alternator is an electric generator that turns mechanical energy provided by the engine into electric energy.

It’s driven by a serpentine belt (in older cars a v belt) that connects the alternator to the crankshaft pulley and other pullies also.

The alternator starts producing electricity almost immediately after the engine is started. Once the engine is working, it takes over the complete power supply of the car while simultaneously recharging the battery.

What else is important to know is that the alternator needs an initial electric input from the car’s battery to start working and producing electricity.

This is provided when you turn the ignition key to the first stage and the battery warning light on the dashboard appears.

The input helps create a magnetic field within the alternator which is crucial for creating electricity.

What is interesting about an alternator is that it’s a generator of alternate current instead of direct current.

Hence the name.


This is interesting because the whole installation on the car, by default is made for direct current.

What is the reason for this peculiar solution?

In the past, before the alternator, there was the dynamo machine which is a direct current generator. But it always had a fluctuating and pretty unstable power supply.

With the alternator, the car has a generator that has a much more stable and reliable power supply while having much better endurance and a longer maintenance interval.

This is a huge gain in the overall longevity and reliability of the car, not to mention the possibility of further improvement of the car itself.

So, here’s the basic principle of how the alternator works:

1. When the ignition is turned to the first stage, the alternator gets the initial input (this is when the battery sign on the dashboard appears)


2. This input energizes the rotor and creates an electric field within the alternator.


3. When the engine is started, the serpentine belt starts turning the pully with the energized rotor, and electricity is instantaneously produced.


4. The electricity is induced into the statorstator-on-alternator-energized


5. The electric current then goes through the rectifier which turns alternate current to direct current. The direct current then goes into the car installation and recharges the battery.



This is the basic principle. For a better and more thorough explanation click here to read a great article from Wikipedia.



This part of the article will state the main parts which are more or less the same for any alternator.

The first four are in charge of actually producing electricity while the other six have more of a mechanical function.

If you’re interested in alternator problems, click here to read a separate article on that topic.

Besides this, you have an article about the most common symptoms and solutions to alternator problems. Click here if you want to read it.

So, the main parts of almost any alternator are:



The rotor is the moving part of the alternator. As mentioned, it is in charge of energizing and creating a magnetic field within the alternator.

It consists of the shaft, finger poles (which look like opposed claws), copper spools of wire inside the finger poles, and two copper slip rings.

On the slip rings sit the brushes from the voltage regulator.

On each end of the shaft, there are two bearings.

Also, the rotor shaft holds the ventilator and pulley.



The stator is a stationary part housed in the rear bracket and you’ll recognize it by the thick, lacquered copper wires wound inside the stator bracket.

Once the rotor starts turning, a current is induced inside the stator. So, the stator sort of stores the electricity before it’s sent to the rectifier.



The induced alternate current goes from the stator to the rectifier. The rectifier then turns the alternate current to direct current using diodes or other electronic elements.

It is best recognized as a pretzel-shaped plate housed in the rear bracket and has screws or connectors coming from it.



The voltage regulator regulates the voltage output of the alternator.

It makes sure the output is stable and always the same since the alternator rotates at different speeds.

Without it, the alternator would produce higher voltage when the engine revs are higher and low voltage when the revs are lower.

In both cases, it would harm or damage the electric installation.

The voltage regulator is usually located in the rear of the alternator, next to the rectifier, bolted, or attached in some other way.



The front bracket holds the rotor, front bearing, and usually an anchor to hold the alternator in place.



In the rear bracket, you’ll find the stator, rectifier, voltage regulator, and rear bearing housing.

Also, it may have a rear anchor. But if the alternator has one main anchor on the front bracket, then there might not be one.



In the front of the alternator is the pulley. Its task is to provide leverage for the serpentine belt to be able to turn the rotor.

It’s tightened to the rotor usually with a bigger nut and washer.

Worth mentioning is that modern alternators have pulleys with a delaying mechanism.

This is installed to relieve tension on the engine caused by the alternator when starting the car.

On older cars, the pulley was one simple part that just held the serpentine belt or v belt.



To enable proper and easy rotation of the rotor, there are two bearings on each side of the rotor.

The usual displacement is that the front bearing is in the front bracket. The rear bearing is pressed onto the rear side of the rotor and sits in the rear bracket.



The ventilator has the task of cooling the inner parts of the alternator with air.

In older alternators, the ventilator was located outside, just behind the pulley. In modern versions, the ventilator is inside the housing between the front bracket and the rotor.



On some alternators, there is a rear protective cap. It’s usually made out of plastic and can be removed to access the voltage regulator and else.




We’ll mention two important types of connections for the alternator :

  • Electrical

The alternator is connected to the car’s electric installation through a set of wires (usually three).

The wires are connected with screws, nuts, plastic or metal connectors, or a combination of both.

Most important on this part is that the wires must be properly connected otherwise there can be huge damage to both the alternator and the car’s electric and electronic installation.

  • Mechanical

Mechanical connections are the ones that hold the alternator in place and to the engine.

It’s held, in most cases by two or three anchors located on the alternator brackets.

These anchors fit onto predefined engine mounts.

Through both the anchors and mounts go usually two (or more) bolts or screws for holding and tightening it in place.

So, the alternator has two, three, or even four holding points.



To sum up the topic of what is a car alternator: it is a marvelous invention, a mini generator, and a powerhouse with an outstanding reliability record.

Compared to its predecessor, the dynamo machine  (with all due respect to it also), it was a gigantic leap forward.

Mainly in terms of reliability, power output, and maintenance.

Know that without this invention a lot of the appliances and systems on the car that we use and enjoy today wouldn’t be possible if it wasn’t for the alternator.

Also, the era of electronics in cars probably wouldn’t be possible since all these systems are highly sensitive and heavily rely on a stable power supply.

Because of this and other reasons, a very big „thank you“ is in place. Both to the inventor of the alternator and also to all the other genius people who found a way to use it on the car.



Written by: Sibin Spasojevic


Former car technician, life-long car and DIY enthusiast, author for Despairrepair.com



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