How Does an Alternator Function

You may be wondering, as I do, what an alternator is and what does it do. But the fact that you opened this post and you are reading it you will orient yourself on this particular auto part.

There was a time when I heard about it but I could not figure out how does it look, where is it located and what does it do in the performance of the engine.


What an alternator does-alternator


Where is it located

The alternator is located at the drive belt end of the engine. It is conspicuous and is accessible from under the hood.

What does an alternator do-alternator location 1


As you can see here in this model, the alternator is located in the upper right side of the engine. In other models, it is located on the left side.

In the image below you will see how the alternator is placed or attached to the left side end of the engine.

What does alternator do-alternator engine left side


What does the alternator do?

There are two functions of the alternator in the engine operation. It charges the battery and it helps in the power booster brake system.

Charging the battery

When the engine is started and ran the alternator starts to work in charging the battery. The charging output of the alternator must be 14.2 V to 14.5 V as measured right across the battery posts.

When the alternator charge output is more than 14.5 V when revved, it will overcharge the battery in the long run and the battery cell will not last long.

Alternator Boosts Brake System

As the alternator is run by the engine it does not only produce current to charge the battery but it also produces air supply to the brake vacuum booster. In that way, the air that circulates in the brake vacuum booster is compressed to help push the brake piston when the pedal is pressed making it convenient for the feet for it doesn’t need much effort to apply a brake pressure whether you are driving a huge vehicle or a small car.

Signs of a Failing Alternator

Dim headlight-when the alternator starts to fail you will notice that the headlights are dimming or it may even flicker.

Dying battery-meaning your battery will gradually weaken because it is not being charged. All electrical parts that needed to work when you needed them are now failing too. Flashers, stoplights or brake lights, and fans will no longer function normally.

Difficult to start the engine-this is because of a weak battery. The more you crank the engine and it doesn’t start the more the battery will become weak.

Engine Stall-a time will come that your engine will stall because the battery is consumed and the alternator produces no current, no fire that ignites the petrol inside the combustion chamber.

It’s Time for Repair or for Replacement

When everything else fails your only alternative is to bring it to a technician for repair. Usually, repairs will cost you 350 to 400 pesos when no parts are for replacement. However, it will cost you more if you buy for replacements of parts but it is more costly if you will replace the alternator itself.

If the technician advises you to buy a piece of parts for more than three thousand it would be better to buy a brand new alternator. than to spend more than the half price of the brand new one.

In Case You Need an Alternator

Alternators and Generators for

Toyota, click here

Mitsubishi, click here

Honda, click here

Suzuki, click here

Trucks and SUVs, click here

Thank you for reading this short post and I hope it enlightened and helped you. If you deem this article can be beneficial to others please share it using the share buttons. In doing so you help me improve this site to be a home for everyone.


12 thoughts on “How Does an Alternator Function”

  1. I don’t know much about cars but your article was very informative. I am happy to say that I now know that an alternator has many functions within a vehicle, I did not realize that it can affect so many other things such as the battery, headlights, and engine stall. Thank you

    • The alternator does two things: charge the battery, and helps in the brake booster.

      The thing is that even if you have a defective battery as long as you have a good alternator you can run your engine. However, even if you have a good battery if you have a defective alternator you will run out of the current and you cannot crank your engine once it stalls.

  2. Hi,

    Thanks for this great article about what does an Alternator do. I didn’t have any knowledge about Alternator and how its work. But after reading this article I have learned so much that I can’t explain. I drive a Toyota Yaris. Sometimes I face some problems which I couldn’t recognize, though I love this brand. I know Toyota is most easy to use the car and have a low maintenance cost. But I got a problem with engine stall. After reading this article I can understand how it could be the Alternator problem. So I will definitely go to check it out. Thanks again. 

    • Yes, Nazmun, I’m not sure if the cause of your engine stall is the alternator. If your battery isn’t being charged maybe your problem is the alternator.

      If you have the tools to check and measure the charging voltage of your alternator you will know it. However, if you don’t have the tools there’s no other option than to bring it to the shop or call a technician to check.

  3. The first thing that comes to mind is alternator alternate blah blah blah but doesn’t really know what it is about. While the way you went about it with pictures has been helpful, I would have appreciated it more if you had used some arrows to point to the right point. I kind of lost my way in locating it in the subsequent pictures. 

    I’m just inexperienced with the car engine so thanks for the indicators on the alternator failure………learnt something here 🙂

    • Thanks, Derr for your comment and your love to learn about the alternator. You said you were lost in identifying the alternator and you suggest there should be an arrow to point to it. I will include that in the future update.

      However, for this time you can go back and see the image of the alternator at the beginning of the post and whatever identical image attached to the engine is unmistakably the alternator. The looks, the form, regardless of size will tell you what an alternator is.

  4. hello jimmy,

    i have got a dodgy alternator on my motorbike which is why I found myself looking up your site.A few more basic ideas I thought your readers may benefit from

    – it is driven around by the motor

    – it generates electricity (alternating current hence the name)

    – sometimes different model cars will use the same alternators

    – like any electric motor/generator they can be rebuilt from the inside out if you can find a good auto electrician who knows what they are doing


    • Thanks, Remy. I can see you are an inventor because you can creatively produce light for your motorbike and maybe for other purposes.

      You are right, even different models can use the same alternator. The conversion is in the hands of the technician. You only have to spend more money because they have to make adjustments and more work to do.

  5. Hello

    Very interesting topic

    I don’t know much about car mechanics
    but your article with pleasure because i can understand almost all parts of the car

    A Transducer is a machine very important to the car engine not only for the engine operation but also for the power brake system.

    The four unwanted alternator trimming marks that you mentioned a lot

    I recently serviced my car and changed the alternator because I had trouble starting the engine

    Thanks a lot for this interesting post

    • Thank you for adding your experience on the discussion. You did it, we did it and we know the importance of an alternator and how it works.

      I hope you love and enjoy doing the things on your car.

  6. Great information. I am a layman when it comes to what goes on under the hood. Your insights are done in a way even I can understand. what might help in you 3rd picture you could circle the alternator. I am still not sure where it would be on my own car.

    If your alternator is failing do you need a new battery as well? Or vice versa, if your battery is failing do you need a new alternator?

    • Thanks, Peter for joining the discussion. I’m sure you know what an alternator is but I will include your suggestion in the future updates.

      If your alternator is failing do you need a new battery? 

      No. Not necessary. Maybe the battery is good so you have to bring the alternator to the technician for repair if not for replacement.

      If your battery is failing do you need a new alternator?

      No. Not necessary. The alternator may be good so you have to bring your battery to the service center for reconditioning or for replacement. 

      Does your battery retain the current when charged? Try to disconnect from the engine when not in use for at least overnight or 24 hours then check the voltage if it’s still the same from the time it was disconnected. If the current dissipated your battery has a problem.


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