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Car Alternator: What is it and How it works?

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An alternator for a 1993 Chevy Silverado.
An alternator for a 1993 Chevy Silverado.

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Picture taken by Angelsharum.

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People say car runs on petrol. Well, they are definitely right.

But, we are missing something equally important and that is… electricity!

I’m not talking about the latest Tesla electric car model, but ALL cars have some form of electrical system.

If your car don’t have electricity,

  • Your car headlights and rear lights won’t light up!
  • No radio, no wipers, and none of your accessories will work.
  • All of the above don’t matter anyway. Because your car won’t start at all. Igniter needs electricity to spark the first explosion in your car engine.

So what makes all of these possible? Two things: our car battery and alternator.

If you are interested specifically in the car battery, we will discuss the car battery in a separate article.

For now, we are going to put a magnifying glass on the car alternator.

What is a Car Alternator?

Can you spot the alternator? It's the one at the centre of the engine, slightly to the left.
Can you spot the alternator? It’s the one at the centre of the engine, slightly to the left.

Car alternator first appeared commercially on the 1960 Chrysler’s Valiant.

It is a small, light-weight power generator that is about the the size of a coconut. You can always find it fitted close to your car engine.

Do you you still remember those wind turbine farms you see at the countryside (like in the movie)? They make electricity when the wind to turns its blades.

An alternator works the same way!

Except it generates electricity when engine belt drives the rotor of the alternator.

It converts the mechanical energy from the engine into electric energy that is eventually used to:

  • Charge your battery, and
  • Supply additional electric energy to power up your car’s electrical system.

Now you may be wondering…

A car battery supplies electricity too!

So why do we need an alternator?

Well, it’s because car battery only carry enough electrical charges to power up your car’s electrical system for an outstanding(not) duration of 2 hours.

Without the car alternator, your car battery will probably be dead before you can drive from Selangor to Melaka.

What are the parts inside a car alternator?

It’s got some bearings, some wiring here and there, some nuts and bolts…

Okay, stop. I don’t want to put you to sleep.

Let’s just focus on these four main part.

  • Rotor
  • Stator
  • Diode Assembly
  • Voltage Regulator

Part #1: Rotor

A rotor rotates. It doesn't get any simpler than this!
A rotor rotates. It doesn’t get any simpler than this!

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© Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons)

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Rotor, a.k.a Armature is found at the center of the alternator.

You can think of this as the heart of the alternator.

It is essentially an iron core, with copper wires coiled around it.

When the engine starts, the engine belt will cause the rotor to rotate. Hence, the name “Rotor”.

When electric current passes through it, it becomes an electromagnet. This is important for electromagnetic induction, which I’ll explain it in the coming section.

Part #2: Stator

This is a stator of an alternator. You can see the copper windings in the center.

This is a stator of an alternator. You can see the copper windings in the center.

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Image courtesy of Zureks (CC BY-SA 3.0).

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Not a surprise, the name “Stator” also implies that it is the stationary part of the alternator.

It houses copper wires, provides mechanical support and protection for the rotor.

You can think of this as the shell of the alternator.

Part #3: Diode Assembly

Diodes are tiny! They are only about half a centimetre long.
Diodes are tiny! They are only about half a centimetre long.

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Image courtesy of Morcheeba (CC BY-SA 2.5).

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Diode is a tiny electronic component that allows electric current to move only in one direction.

It’s like a valve, except for electric!

Typically, we use 4 diodes in a specific arrangement to convert alternating current into direct current.

Part #4: Voltage Regulator

Voltage regulators are usually integrated into the alternators, but some can be found next to it.
Voltage regulators are usually integrated into the alternators, but some can be found next to it.

Voltage regulator helps to monitor and regulate the electric current.

As the name suggests, it controls the voltage of the electric current in the circuit to make sure it’s not too high or too low.

  • If the current is too high, it’ll break the fuse and damage the component.
  • If the current is too low, our electrical parts can’t work properly. It’s like me when I don’t eat enough.

How does an alternator produces electricity?

It’s a symphony!

The four components have to work together hand in hand to generate electricity.

But first, I need to introduce you to some Physics 101 – Magnetic Induction by EdisonTechCentre.

Magnetic induction happens when you move a magnet close to a wire.

Both north and south pole have its own magnetic field.

These magnetic fields move the electrons in the wire which creates electric current.

Here’s how it works.

  • A magnet has a north pole and a south pole.
  • Let’s start with the north pole at the top and the south pole at the bottom.
  • As you rotate the magnet, the magnetic field passes through the wire.
  • This makes the electric current flow in a single direction.
  • After you rotate the magnet half a revolution, the north pole reaches the bottom while the south pole reaches the top.
  • This will also create a current, but now the electric current will flow in the opposite direction because the magnetic poles are in a different position.
  • Now if you rotate it very quickly, you get an alternating current(AC).

An alternating current looks something like this.

Alternating current alternates between positive, to zero, then to negative. For engineers out there, we call this a sine wave.
Alternating current alternates between positive, to zero, then to negative. For engineers out there, we call this a sine wave.

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Image courtesy of Omegatron (CC BY-SA 3.0)

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For an alternator, rotor is the spinning magnet, while the stator is the wires.

Here’s how it works on the car alternator.

When you start the engine, the petrol gets combusted and crankshaft starts to spin. This drives the engine belt.

Since engine belt is connected to the rotor of our car alternator, the rotor spins.

At the same time, small amount of current from the battery runs through the rotor’s copper wire and makes it an electromagnet.

So, rotor becomes this spinning magnet.

On the other hand, stator acts as the wire. It has copper coil loop windings all over it.

When the rotor spins, the magnetic field cuts through the stator’s copper wire which induces electric current.

Now, that is what we call electromagnetic induction, just like how it was explained in the video.

Great, we now have electricity!

We have produced an alternating current.

Alternating current alternates between positive, to zero, then to negative. For engineers out there, we call this a sine wave.

So now, we have this alternating current in the form of a sine wave in our circuit. 

Source

Image courtesy of Omegatron (CC BY-SA 3.0)

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But we have one tiny problem.

Our car can’t use alternating current, we need direct current.

This is where diodes comes into play.

Diode only allow current to pass through in one direction only.

It’s like a valve, but for electricity.

So with a smart arrangement of a few diodes, we can turn the negative current into positive current.

We call this “rectifying” the current.

Diode takes the negative current, and make them positive again. In fancier terms, we call this full-wave rectified.
Diode takes the negative current, and make them positive again. In fancier terms, we call this full-wave rectified.

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Image courtesy of Omegatron (CC BY-SA 3.0).

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Hmm… As you can see, the current is still jumping up and down, from positive to zero then back to positive again.

It fluctuates too much!

I don’t want my car headlights to be dim, then bright, and then dim again.

In this case, capacitors will help.

Capacitor stores electrical charges and releases them over time.

You can think of them like a tiny kidney. Once you drink enough water (or electricity), you have to release them.

This helps to smoothen the direct current into a steady flow.

Capacitor makes our rectified current into a smoothed ripple, so that we get a more consistent voltage.
Capacitor makes our rectified current into a smoothed ripple, so that we get a more consistent voltage.

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Image courtesy of SpinningShark (CC BY-SA 3.0).

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Now that we have the problems straighten out (puns!), our car alternator uses the electrical current to charge the car battery or power up our vehicle’s electrical system.

That my friend, is how alternator produces electricity.

Symptoms of a faulty alternator

Not a lot could go wrong with this thing.

Alternators are very robust and can usually last you a good 8 to 12 years.

Beyond that, your alternator may not be producing and providing consistent power supply.

This will cause ineffective functioning of components such as lights, radio and air conditioning etc.

You may start to notice any of these problems…

  • Car headlights is dim.
  • Dashboard light is dim.
  • Power window operating slowly.
  • Alternator making growling noise.
  • Dashboard warning light is turned on. Usually shown as a red battery icon. It may come on only when multiple electrical appliances are used.
  • Engine cranks very slowly.

All of the above are early signs of vehicle electrical system problems. If you notice any of them, you can take a few simple steps to isolate the root cause.

How can I diagnose a faulty alternator?

As you probably know by now, car battery and car alternator both provide electrical power to our car.

They are very closely related parts, so how do you tell if you have a bad battery, or a bad alternator?

Try this quick and easy way to test if your alternator is faulty.

Scenario #1: If your car can still start.

A digital multimeter is a handy tools to test electric current. It's easier to use and more accurate than traditional ones.
A digital multimeter is a handy tools to test electric current. It’s easier to use and more accurate than traditional ones.

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Image courtesy of Aka (CC BY-SA 2.5).

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  • Get a multimeter.
  • Turn the multimeter setting to 20 Volt DC.
  • Shut down your car completely.
  • Open the hood of the car.
  • Connect the red wire of the multimeter to the positive terminal of the battery.
  • Connect the black wire of the multimeter to the negative terminal of the battery.
  • Check the reading. Under normal condition, your battery should be giving you an average of 12 Volts.
  • Now, turn the vehicle ON.
  • Check the reading again. The voltage you want to see in multimeter at this time should be between 14.2 – 14.7 Volts.
  • Then, turn on all the electronics such as headlights, radio and others.
  • Check the reading again. If you get a similar reading (14.2 – 1.4.7 Volts), then the alternator is in good condition. But, if the reading goes way below and reach around 12.7V, it means that the alternator is not working properly.
  • When you are done, turn your car off.
  • Remove the black wire first, then the red wire.

Scenario #2: If your car don’t start.

You absolutely positively must have a pair of jumper cables in your car's trunk. It's a life saver!
You absolutely positively must have a pair of jumper cables in your car’s trunk. It’s a life saver!

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Image courtesy of Qurren (CC BY-SA 3.0).

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  • Double check if your car is really dead by cranking your engine for another 3 seconds.
  • If the car remains deadbeat, get yourself a jumper cable.
  • Jump start the car.
  • Let it run for 15 seconds.
  • Remove the jumper cables.
  • If the car dies shortly after, then it’s most likely the alternator’s problem.

So what went wrong?

When you have a faulty alternator, these are the likely culprit.

  • The engine belt has become loose.
  • The ball bearing in the alternators has worn out.
  • Connection terminals failed to connect properly.
  • Damaged or corroded wires.
  • Voltage regulator has lost its functionality.

But before you decide to replace your alternator altogether, you can check the engine belt tension and if the connection terminals are conducting properly.

It’s a common problem that may be mistaken as a faulty alternator.

It doesn’t take more than 5 minutes and it may save you hundreds of dollars!

But if the problem still persists, get a second opinion from an experienced car mechanic and you can consider looking for a new alternator.

How to replace an alternator?

This is a fantastic video by ChrisFix showing you how to replace an alternator in a car.

It shows you step by step on how to do it, much better than I could ever explain in words.

When using this video, please be reminded that not all car model are the same, but this videos should give you a general idea of what needs to be done.

Generally speaking, you need to…

  • Remove the engine belt
  • Detach the electrical wiring
  • Take out the faulty alternator
  • Replace it with the new alternator
  • Reattach the electrical wiring
  • Install the engine belt
  • Restore proper tension on the engine belt.

Now, the price.

I do have to tell you that price can vary a lot across different model.

Just like how you can’t compare a hawker store food to a fine-dining restaurant, you cannot compare a Proton alternator to a BMW alternator.

If you’re wondering how much they costs, here’s a very ROUGH estimate of car alternator.

A new original alternator will cost you around RM 2,000 ~ RM 3,000.

An aftermarket alternator can go anywhere from RM 250 to RM 500 on average, depending on the car model and year.

Workmanship can cost you anywhere from RM 50 ~ RM 200. Some model are ridiculously easy to install while some would be as take as much effort as going to the gym.

The Bottom Line

Alternator is a small generator can power our vehicle’s electrical system for close to a decade by using engine power.

That sums up everything you need to know about car alternator. I hope the article has been helpful.

You know, we would absolutely love to hear from you guys.Let us know what you think.

Have you ever changed your alternator before? How did you notice it, and how much did you change it for?

Leave a comment below and we’ll respond.

Until then, drive safe and drive smart!

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