What Does a Car Alternator Do?

If you’ve ever wondered what a car alternator does, you’ve come to the right place. (Hint: it charges your battery.)
Written by R.E. Fulton
Reviewed by Melanie Reiff
Your car’s alternator charges the battery and converts the engine’s mechanical energy into electrical power which runs the vehicle’s electrical system
Most modern vehicles with internal combustion engines have an alternator, which works in tandem with the battery to keep your car running. While checking the alternator isn’t a regular part of most car maintenance schedules, it’s important to be on the lookout for signs of alternator trouble—without it, your car won’t run properly! 
Your guide to car parts like the alternator is
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What is an alternator, and how does it work?

Your car’s alternator has two jobs: 
  • Power the car’s electrical accessories (e.g. power windows, windshield wipers, heated seats)
  • Charge the battery while driving 
While you might imagine that the car battery is the power source that keeps your car’s electrical system, that’s actually only true when the engine is off. The battery’s primary role is to start the car, while the alternator is the generator that powers and charges while you’re driving. 

How it works 

The alternator consists of several key components that work together to accomplish these tasks. 
First, a drive belt (often the car’s serpentine belt) uses the power from the crankshaft to spin the rotor, a magnetic cylinder at the heart of your alternator. As the rotor spins, it creates a magnetic field that interacts with the copper windings of the stator to generate alternating current (AC). 
Converting the engine’s mechanical energy into electrical energy is the first step in the alternator’s functioning. A voltage regulator monitors that electrical input, and diode rectifiers convert the AC into direct current (DC), which is what your electrical accessories need to function. 
Finally, this whole process generates a lot of heat, so the alternator has a cooling fan to help dissipate some of that extra energy. 

What are the symptoms of a bad alternator?

When everything’s working properly, you shouldn’t have to think about your alternator. Most car alternators are built to last for seven to 10 years, so you can expect to get a lot of mileage out of this essential part. 
But everything wears out eventually, and the alternator is no exception. The most common signs of a
failing alternator
  • Dim or flickering lights: If you notice that your dashboard is dimmer than usual, or that your car’s display is flickering, a faulty alternator is the most likely cause. 
  • Faltering electrical components: Do your windows roll down really slowly? Can your heated seats not get past lukewarm? Your alternator might not be generating enough power. 
  • Whining or grinding noise: If there’s a mechanical problem inside your alternator, such as a bad bearing, you might hear noise from the engine compartment while driving. 
  • Foul or burning smell: A failing belt on the pulley that turns the rotor shaft can send the smell of burnt rubber wafting through your vehicle. 
  • Battery warning light: That little red battery light on your dashboard indicates a problem with your car’s charging system—not just the battery itself. It can be a solid indicator of alternator problems! 
One more sign of a bad alternator is a car that struggles to start—but how can you be sure it’s the alternator and not just a dead battery? There’s a simple test that can help you diagnose an alternator problem if your vehicle has trouble starting. Just
jumpstart the car
, then watch to see if it continues to run. If the car runs as normal after the jumpstart, then a drained battery is the most likely culprit—but if it fails again very quickly, it’s probably time for a new alternator. If you aren’t comfortable jumpstarting your car, take it to a mechanic for diagnostic testing.

How much can a car's alternator cost?

We won’t sugarcoat it for you: replacing a faulty alternator can be costly. But because your car won’t run without this essential component, there’s no real way around the expense, which averages between $350 and $500
Let’s break down those costs. A new alternator by itself costs between $130 and $320, depending on your vehicle’s make, model, and age. If you opt for a rebuilt alternator—that is, a used alternator that’s been refurbished by a mechanic—you might be able to cut costs, but you’ll be taking on added risks. On the other end of the scale, you’ll pay more to install an OEM alternator—unless your repairs are covered by an insurance claim that includes
OEM coverage
But the cost of parts is just the beginning. Depending on the circumstances, you might need to pay for a test of your charging system to narrow down the cause of the trouble, which usually costs between $30 and $50. If you need additional parts replaced—for instance, the
serpentine belt
is often replaced along with the alternator—that’s another cost added to your total. 
Finally, the cost of labor will factor into your total, unless you’ve got the automotive know-how to complete the replacement at home. In most cases, an alternator replacement should take between 1.5 and 2.5 hours, but the cost of labor varies from shop to shop and by regional market rates. You can help to keep your repair costs low with fair price estimates from real shops, generated by

Does insurance cover an alternator replacement? 

In most cases, the answer will be no. Because alternators overwhelmingly fail due to normal wear and tear, your car’s insurance policy generally won’t pay for these repairs. 
However, there are exceptions. If your car’s alternator is damaged in a crash, you may be able to file an insurance claim for the damages—if your policy includes
collision coverage
Not sure if you’ve got the right insurance to cover an alternator replacement? Download the
app to evaluate your current insurance coverage and shop for a lower rate from any of 55+ top insurance providers. 

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