Alternator: operation and parts

The alternator is the part of a car engine that is responsible for converting mechanical energy into electrical energy, which feeds the car’s electronic circuits and systems, while recharging and maintaining the battery’s condition. It is a very important accessory of the motor system, so it is important to understand its operation and its parts.

For all those users who do not know anything about mechanics, hearing about the engine and its parts can be disconcerting. Many times, this jargon may sound like Chinese; however, it is very important to know and know how to differentiate the different parts of a car engine, as well as to understand how they work. In this way, if there is ever a breakdown, it will be easier to know what is happening and how to solve it. 

Knowing what an alternator is can help you understand why your car has stopped starting. This could be because this part is not working properly and therefore is not converting the mechanical energy of the engine into electricity, so your car’s electrical systems have stopped working. 

The operation of an alternator is simple, since it is responsible for converting the mechanical energy, produced by the turns of the motor shafts, into electricity. In this sense, it is one of the most important parts of a car’s powertrain. This is because the alternators supply energy to the battery and to the circuits in charge of managing the electronic system of the car such as the windscreen wipers, the electric windows, the engine control system, the lights and the automatic ignition.

On the other hand, the electric alternator is also responsible for keeping the car’s battery in good condition. The surplus electricity from the electronic system passes to the battery, so it stays charged. In this way, we could say that these parts perform the functions of battery starters (check this link for some purchase options), preventing you from being left stranded and without power.

How does the car’s electric alternator work?

It works by turning a rotor with permanent magnets . This shaft, called the inductor element, is connected to the car’s crankshaft pulley and surrounded by a stator, which is the element against which the magnetic field reacts, generating a process that converts motor energy into electricity.

The parts of an alternator

The stator is one of the most important parts of this element. It is made up of a metal coil, which can be seen through the aluminum casing that covers the alternator. 

Surrounding the motor shaft are the alternator brushes, which are the ones that collect electricity through the stator and send it to the rectifier and voltage regulator. In this sense, the rectifier bridge is the piece in charge of converting the energy collected by the brushes, that is, the high voltage alternating current, into direct current, of low voltage and compatible with the electrical systems of the vehicle.

Next, the alternator regulator adjusts the output voltage and amperage, eliminating voltage spikes that could burn or damage the car’s internal circuitry. In more modern cars, this regulator has been replaced by an electronic control unit, which remains constantly connected to protect the car’s central computer. The entire assembly remains housed inside a casing that keeps the alternator elements protected from external corrosive agents such as dust or water.

Newer types of alternators also have a fan, which keeps moving to cool the alternator parts . These, due to electromagnetic induction, get very hot, so there needs to be an air current to keep them cool, avoiding overheating problems.

Finally, the alternator pulley, a rubber band that fits next to the crankshaft pulley. It is the connection of the alternator with the car and the one that is in charge of distributing the rotation from the engine to the alternator. Being connected, these two parts always rotate at the same speed and at the same time.

types of alternators

Now that you know what the car alternator and its parts are, let’s see what types exist.

First and second generation compacts

Made up of 12 poles, they were designed for vehicles with high energy demands, such as older passenger cars . The name of first and second generation, is because the second generation alternators were capable of generating and storing more electricity.

As part of the compact alternators, it is also possible to find liquid-cooled alternators, which are more expensive and difficult to maintain, but with greater power and less noise.


Very similar to the compact ones, but with a much higher turning power, capable of exceeding 20,000 revolutions per minute (RPM).

of intercalated poles

The most used and known. The magnetic poles are claw-shaped and, as the name suggests, they appear interspersed, favoring rotation.

of individual poles

This is a type of three-phase alternator used when very high power is required. They are equipment for vehicles with a consumption greater than 100 A, with a voltage of more than 24 V. 

with guide rotor

It is an alternator with a unique design, based on using as few parts as possible, thus reducing wear and increasing the useful life of the part. This alternator does not use bearings and is the most suitable for long-distance transport vehicles, as well as those that make great efforts, such as trucks or trailers.

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