How Alternators Work

By: Josh Briggs  | 

Alternator Replacement

You may not have to replace your alternator entirely if you're handy in the garage.
You may not have to replace your alternator entirely if you're handy in the garage. Noll

For the most part, alternators are less expensive than say, a power steering pump or air conditioner compressor. Nevertheless, you have alternatives to forking out a lot of cash for a replacement alternator. Many automotive stores sell remanufactured or rebuilt alternators at a discounted price. For instance, a Beck/Arnley alternator for a 2002 Honda Accord with a 3-liter V6 engine can cost $229 new, versus $163 for the same part, only remanufactured [source: PartsAmerica].

While alternators are relatively inexpensive in comparison to some of the other components on your engine, some can be expensive depending on the car make. If you owned a 2005 Porsche 911 Carrera GT for instance and wanted to replace the original Bosch alternator, you could expect to pay well over $300, and that's for a remanufactured component [source: Autoparts Warehouse].


Sometimes alternators are easily accessible and simple to replace for the amateur mechanic. With a modest amount of automotive experience and the proper tools, replacing an alternator in your garage can be done. But more and more cars don't have room under the hood, and the alternators can be difficult to reach without first removing several other components. In this case, it's best to take your car to an experienced technician who can do the job quickly.

If you happen to own an alternator that has a repair kit available for sale, you can really save some money. Alternator repair kits run between $12 and $30, depending on which components you need to fix. Again, you need the proper tools and a little know-how, but if you're able to find the right kit and know what you're doing, you can rebuild an alternator for a fraction of the cost of even a remanufactured unit.

One thing is certain: A bad alternator will ruin a good battery if you don't address it quickly. Batteries can only be recharged so many times before they'll lose their ability to hold a charge. For the most part, if the battery isn't relatively old, it should survive. But an older battery that is constantly drained and charged, drained and charged will have a shorter life span than a battery operated under normal conditions. The average life span of a battery is usually around 48 months [source: Battery Stuff].

High-output alternators have become popular with custom car shops and in high-performance cars. They produce higher voltage at idle and make more power for vehicles that draw an excessive amount of electricity. For example, custom cars with lavish audio and video systems draw more electricity than the stock alternators can handle. As a result, companies such as HO Alternators make alternators for several makes and models. Some custom shops are even installing dual-alternator systems to handle the additional electrical loads seen in custom vehicles.

For more information on vehicle electrical systems and related HowStuffWorks articles, please check out the lots more information section below.

Vehicle Alternator FAQ

What does an alternator do for a car?
The alternator works with the battery to generate power for the electrical components of a vehicle, like the interior and exterior lights, and the instrument panel.
Does an alternator need power to work?
An alternator actually generates power for your vehicle. Alternators produce AC power through electromagnetism formed through the stator and rotor. The electricity is channeled into the battery, providing voltage to run the various electrical systems.
How many amps should a car alternator put out?
It depends on the amp rating of your car's specific alternator. You can check your owner's manual to learn the maximum amps your alternator should put out.
Do alternators produce AC or DC?
Alternators create AC power.
How much does it cost to replace an alternator?
A new alternator can cost anywhere from $500 to $1,000.

Originally Published: Jun 9, 2008

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More Great Links

  • How to install a car battery


  • (May 31, 2008)
  • AutoPartsWarehouse (June 8, 2008)
  • "Battery Tutorial." (June 2, 2008)
  • Encyclopedia Britannica. "Electric Generator." 2008. (May 28, 2008)
  • Engineers Edge. "AC Alternators About." (May 27, 2008)
  • (May 31, 2008)
  • PBS Online. "Tesla-Master of Lighting: War of the Currents." (May 30, 2008)
  • Sullivan, Kevin. "Alternator Fundamentals." Auto Shop 101. (May 27, 2008)
  • Tesla Memorial Society of New York. "Tesla AC Electricity." (May 29, 2008)