Car alternator guide by expert mechanic

An alternator is that part of the car that doesn't get enough credit for its functionality/impact in the car. We've all gotten so used to having cars around that we're over the innovation that was put in place to power such a strong machine.

The alternator is one of such innovations that often gets overlooked by the average car owner. This is rather unfortunate as an alternator's function in the overall workings and performance of your automobile cannot be understated. Hence there's the need to be schooled on the car alternator.

  • What then does the alternator do in the car?
  • How can you detect a defective alternator
  • What's the impact of a faulty car alternator?

This article answers these questions and more.

Alternator overview

Alternator in a car

What does an alternator do?

The car is made of various parts and components that are involved in what is seemingly the simple act of transporting yourself from one place to the other. The car of course needs to be able to generate enough energy to power its various components.

Ideally, this should be the job of the car battery unfortunately, the car battery can only generate so much energy. In no time, other components of the car will use it all up causing the car to go off or even worse. This much strain on the battery can cause permanent damage. This is where the alternator comes into play.

In reality, the alternator is responsible for generating most of the energy your vehicle will need for all its basic functions. Mostly, all the battery does is start the engine or provide electricity to the car when the engine isn't running.

Then what specifically is the alternator? The alternator is a sort of generator that produces enough electricity to power and distribute electricity to the car while also charging the car battery.

Car alternators are about the size of a hockey hall. They are mounted to the front of the car's engine and they have a belt running through them. It's with the movement of this belt that they're able to create mechanical energy which is then transformed into electrical energy. For such a small device, you would probably think the alternator is negligible.

However, Car alternators are a critical piece they play an important role in the overall functioning of the vehicle. That's why a faulty alternator can be detrimental to the car's performance. And while it's an exceptionally durable device (lasting up to ten years or more) it's prone to damage.

What are the signs and symptoms of a bad alternator?

No car owner can afford to risk having their car alternator faulty. The car alternator is responsible for supplying electricity to the car battery which powers the car. Such a device developing a fault will be of great detriment to the overall performance of your vehicle.

To make sure your alternator is working at peak performance, you can always test it by following this extensive guide explained in this article. Or you can watch out for the following signs and symptoms:

Dashboard indicator

The battery indicator on the dashboard due to a bad alternator

One of the most glaring signs of a faulty alternator is the check battery indicator will clearly turn on on the dashboard. The car alternator is not only bolted right in front of the car battery, it's entire function is to supply the car battery with enough electricity to power the entire vehicle.

That's why when a problem associated with the alternator arises, it's usually the car battery that is first to show signs of wear before the rest of the car gets affected.

Weakened or dead car battery

Bad  Car battery

Another clear sign that you're dealing with a faulty alternator is a weakened or dead battery. Often when car owners notice that their car battery is becoming weak, they're quick to fix it. They do this without seeing the need to check if the problem is actually from the alternator.

The alternator after all is responsible for supplying the car and the car battery with power. In a situation whereby the alternator goes bad, all the responsibility of supplying your car with power will fall on the battery will lead to the ultimate damage of your car battery.

Instead of being too hasty about changing your car battery, you should check out your warranty or how long the car battery should last you can check out this how-to article which will tell you everything you should know about car batteries specifically the Ford Fusion car batteries.

Odd sounds

The alternator is comprised of mechanical parts that convert mechanical energy to electrical energy. If you're driving your vehicle and you hear weird sounds like whining or grinding noises, it is an indication that your alternator is going bad and should be checked immediately.

A grinding sound can be an indication of a worn-out bearing while a whining sound can be because the voltage regulator is sending messages to the alternator to generate more energy than your vehicle actually needs. Either way, these are clear indications that you should check your alternator as soon as possible.

Flickering headlights

When your car alternator goes bad, other important functioning of the car will start to malfunction as well. One of them being your car headlights. You might start to notice that when you put on your car's headlights, it will either grow dimmer or start to flicker.

This happens especially when you either increase or decrease your car's speed. No matter what the speed, your headlights should always be working well if your alternator is not faulty. Thus why headlights and dashboard lights can be great indicators of alternator health.

Problems starting your vehicle

The battery is in charge at the initial start of the car. Usually, when there's an issue with starting your vehicle, the battery is always checked first before anything else. (Check to see how long a car battery lasts).

However, in a situation whereby the battery has been given the clear, the next culprit would definitely be the alternator. Most vehicles have an indicator to show when the alternator isn't working properly. But you can still carry out inspections by following the guidelines highlighted in this in-depth article.

Electrical problems

The alternator is the primary source of electricity/power in your car and any fault can severely affect it. Electrical problems as a result of a faulty alternator can present themselves in several ways; one of them is your windows or windshield wipers will be operating slowly.

But you can never be too certain until you test them. You can do this by calling for the services of a professional. Or you can test it out yourself by following the instructions laid down in this article.

Bad alternator problem

 Bad alternator

The alternator is such an essential component of any vehicle that means any problems associated with a faulty or bad alternator will affect the car's overall performance. Here are some common areas that a bad alternator will affect and how they are affected

Car headlights

The car alternator provides voltage to the entire vehicle and when it goes bad or becomes faulty, the Voltage that is being supplied will become inconsistent. This inconsistent supply of voltage into the car will cause systems and accessories of the car that need electricity to start malfunctioning.

What that would look like is either too much performance or an underwhelming performance. The car headlights for example will either start going dim or it would flicker a lot especially when you alternate the speed of your car.


A bad alternator can also cause the end of your battery. Of course, this isn't always the case that's why you should know the warranty of your battery. However, in a situation where the alternator is bad, it would fall on the car battery to provide the car with voltage without receiving support or charge from the alternator. This of course can cause the battery to die out on time.

Ignition system

The car battery is responsible for the initial ignition of the car. And as we've already mentioned, a bad alternator can greatly affect the performance and general well-being of your car battery.

This is because the battery is receiving support from the car's alternator and it's affecting most of the car's system. Of course, this isn't always the case but you must run some tests on the alternator just in case.

Car sounds

When your car that used to run as smooth as butter starts developing strange sounds like a grinding or whining noise coming from the hood, it can be a sign of a bad alternator. These unusual sounds can be because the belt of the alternator has been misaligned or because of the bearings of the alternator. Whatever might be the case, it's worth checking out.


Car dashboard showing alternator problem

Your car's dashboard is there to warn you if anything is amiss. With a faulty alternator, you might notice the battery indicator would be highlighted. But other parts of the car that have started to get affected by the faulty alternator can also be highlighted.


If you ever perceive the smell of burning rubber coming from your car's bonnet, it might be a sign that parts of the alternator ie the belt have started to wear out and should be replaced as soon as possible. The alternator is especially at Risk of frayed ends or wear and tear not only because of how much work it does but due to its proximity to the car's engine which causes it to generate lots of heat.

Can you drive with a bad alternator?

If you have a bad alternator, it's advisable to replace it as soon as possible as it can cause greater damage to other parts of your vehicle. That being said, it's still very much possible to drive even with a bad alternator. Depending on the car or how old that particular model is, your car can cover anywhere from a couple of miles to a few feet.

But in a situation whereby you're driving your car at night with a bad alternator, then the car isn't expected to last more than a couple of minutes. This is because of the use of other electronic accessories such as headlights that put even more strain on the car battery.

How fast will a bad alternator kill a new battery?

If you're lucky you can get over an hour or even up to two hours before your car battery dies. That's why it's important to replace your alternator as soon as you notice it's going bad.

How long can you drive with a bad alternator?

There is no specific time frame regarding how long you can go with a bad alternator because there are factors at play. If you turn off every other accessory In the car, you can buy yourself a couple of minutes extra before your car caves in. So you can drive with a bad alternator anywhere from 30 minutes to 2 hours.

Do you have to replace the battery when replacing an alternator?

Replacing the car battery with the alternator isn't necessary at all. Of course, there are instances where the car battery dies with the bad alternator. This is because the car battery deteriorates faster with a fail alternator. In this case, then you'll need to change the car battery as well.

What causes an alternator to fail?

Bad diodes are a very common cause of a bad or failing alternator. In the case that it's just a few diodes that have gone bad, there's still the possibility of your car alternator being able to generate enough voltage to meet the car's basic needs. However, it still won't be enough and it will affect your car battery. Other common causes of a bad alternator are:

  • Wiring problems
  • Computer problems
  • A broken belt

What does a bad alternator sound like?

Cars are known for making distinct noises but a faulty alternator will generate some peculiar sounds of its own. Some of these sounds can be a whining sound or a grinding sound coming from the hood of the car.

The grinding sound can be an indication of a more mechanical problem e.g worn-out bearing. The whining sound can be because the Voltage regulator is sending signals to the alternator to generate more power than is needed.

How do I know if  I need a new alternator?

 Testing an alternator

But if you notice your car isn't running as smoothly as it used to e.g flickering lights, check car battery is indicated, or a strange noise coming from the hood, it can be a clear sign that you need a new alternator. Still performing a simple test can confirm the state of your alternator.


For such a small device, the alternator is pretty much the backbone of the electrical system in the vehicle. That's why as soon as there's a possibility that your alternator is going bad, you should get it checked immediately. Hopefully, this article has helped you in knowing all the signs and symptoms you might want to watch out for.

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