Explained: What Does the Alternator On a Car Do?

Lift the bonnet of your car and one of the first things you should see is the alternator – you just might not know it. This component, found in every internal combustion engine (ICE) car, is vital to your car’s performance, powering almost all of the vehicle’s electronic functions. In fact, while it can’t help get a car started, it even helps rejuvenate a car battery after you’ve got the engine running. Since it’s so important, you should know what it is, where it is and how to check if yours is working properly. All that and more is answered below.

What Is an Alternator In a Car?

The name “alternator” does little to suggest what its purpose might be, so let us break it down for you. Simply put, the alternator is an electrical generator that works when the car is running. The electrical system of any ICE vehicle is powered by these devices, which converts mechanical energy into electrical energy.

We won’t get into the science of it all here, but without an alternator, your car’s electric windows, power steering, windscreen wipers and dashboard lights would not work. Even small luxuries like heated seats and the radio would be dead, as would one of the most important safety features on any car: the headlights.

The alternator also plays its part in getting the car moving in the first place. Imagine a double-A battery; you use it until it dies then you discard it. Without an alternator, the same would happen with car batteries (unless you’re prepared to remove it from the car and charge it overnight every time, that is). This clever component uses the energy it creates to charge the car’s battery while the engine is running, whether the car is moving or simply idling at the side of the road or in traffic. Next time you turn your key in the car’s ignition, don’t just thank the battery – thank the alternator, too.

What Alternator Fits My Car?

Car alternators are suited to different cars based on several different types of measurement. The length, thickness, pulley diameter and mounting size of the part (in millimetres) must all be appropriate for your car. You should also make sure that you’re getting an alternator with the right amp specification, along with the correct connector type.

These days, it’s extremely easy to find out which alternator fits your car by checking online with retailers that sell them. Most online stores, particularly large chain businesses, have a function allowing you to enter your registration plate number to identify the vehicle. Upon doing so, they’ll present you with a list of all the alternators that they sell which will fit your car.

Alternatively, you can take a look at the alternator under the bonnet of your car and find the Original Manufacturer Number (abbreviated to ‘OEM number’) that’s printed on it. With this number noted down, it’s now a case of finding the same part from a retailer who should be able to search their own stock using the code. Be aware that the OEM “number” can actually include both numeric digits and letters.

If you’re still struggling to find the right alternator for your car, it should also be possible for the manufacturer (or one of their dealerships) to be able to identify the part for you via the car’s VIN. Entirely different from the OEM number, the Vehicle Identification Number is unique to every car, meaning that even two 2015 Vauxhall Corsas, for example, will have different VINs. With this information, the manufacturer should be able to tell you which alternator will fit.

Can You Jump Start a Car With a Bad Alternator?

Technically-speaking, the answer to this question is ‘yes’. You can indeed jump start a car with a bad alternator, but much like the scientists of Jurassic Park, you should ask yourself not whether you could but whether you should.

The answer to that question is ‘probably not’. If your battery is in good nick, then your car may be okay for a while, but it will inevitably run out of juice somewhere down the road. On the other hand, if your battery is getting on a bit and has seen better days, it’s likely that it may not last long at all. If you really must drive your car after jump starting it with a bad alternator, the first place you should be driving it to is the repair garage.

How to Test an Alternator In a Car

If you think your alternator might not be working as intended, but don’t want to pay out for a service just yet, there is a way to perform some DIY tests to assess its performance. Here’s how:

  1. Get Your Hands On a Multimeter – These can be purchased from most hardware or car accessory shops.
  2. Adjust the Settings – The DCV should be above 15.
  3. Connect the Multimeter (with the engine OFF) – Locate the positive & negative terminals on the battery and connect their respective cables.
  4. The Magic Number – The multimeter should now show a reading. The perfect figure is 12.6, but don’t worry if it’s not spot on.
  5. Start the Engine – When the engine starts up, the reading on the multimeter should increase to somewhere between 14.2 and 14.7.
  6. What It Means – A reading below 14.2 means the alternator is undercharging the battery, while a reading above 14.7 means it’s overcharging.
  7. Light It Up – Turn on the vehicle’s electronic devices – headlights, fog lights, radio, air conditioning – and make sure the multimeter reading does not drop below 13.
  8. Kill the Power – Shut everything down, including the engine, and check that the multimeter reading remains above 12.6

If anything on this list doesn’t go as planned, your alternator might be faulty. A professional mechanic will be able to confirm this and fix the problem.

Where Is the Alternator In a Car?

The alternator is always located under the bonnet of the car and is connected to the engine itself. You’ll most likely be able to identify it by first spotting the belt that is hooked onto it to generate the power that the device requires. The alternator is fairly large, with vents around the entire circumference of its circular body.

If your alternator has died on you, a replacement can be pricey, so you might be better off selling the car as scrap or salvage with Scrap Car Comparison and making profit from it that can be put towards something new. We can get you a selection of the best quotes in just 30 seconds and because we work with scrap dealers all across the UK, we can even arrange for your vehicle to be picked up at no extra charge. Use our online valuation calculator to find out how much money you could get by selling your car as scrap or salvage today.

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