What Is an Alternator and Why Is it Important?

The alternator is the component that provides electrical power for a car, and also charges its battery. It is attached to the engine. The alternator is driven by the engine's serpentine belt (or V belt.) Alternators have a cylindrical shape, and are usually about 6" across by 6" deep.

How Does an Alternator Work?

When the engine is off, the alternator is not turning and the battery powers the electrical system. The battery will eventually drain if the engine isn't started for a long time. The alternator keeps the battery charged, but only while the engine is running.

Basically, the alternator converts mechanical energy into electrical energy. It’s comprised of four major components:

  1. Stator: a set of copper wires that surround the rotor.
  2. Rotor: a magnetic part that is spun by the alternator pulley.
  3. Diode: a semiconductor that converts the electricity from Alternating Current ( AC) to Direct Current (DC). (Autos use DC current.)
  4. Voltage regulator: a part that stops the power from flowing to the car battery if the voltage goes too high.

The process works like this:

  • The engine powers the alternator via a drive belt which turns the pulley attached to the alternator.
  • The rotor inside the alternator is attached to the pulley, and spins when the engine is running.
  • The spinning rotor produces an electromagnetic field that creates AC electricity in the stator.
  • The diode converts the electric current from AC to DC.
  • The DC current is then passed through the voltage regulator to the car battery, which proceeds to power the electrical system.

What Happens When the Alternator Fails?

Alternator dodge

When an alternator begins to fail, the battery doesn’t get as much power as it should. This results in reduced electrical power. Some symptoms include dimmer lights or slow power windows. Eventually the alternator will fail completely. The battery will quickly drain as it isn't being charged. Soon, you won’t be able to start your car. To keep the battery from dying as a result of a bad alternator, it’s a good idea to monitor your alternator. You can then replace it as soon as begins to fail.

How to Monitor an Alternator?

New alternators produce a charging voltage of 14.1 or 14.2 volts right after the engine starts. Usually the voltage drops to 13.9 or 14 volts after a minute or so. An alternator that is beginning to fail will produce less voltage. It might only produce 13.9 volts right after startup, and 13.6 or 13.7 volts after a few minutes. The easiest way to monitor this voltage is to buy a USB charger with a voltage meter that plugs into a 12v outlet in your car. These only cost $10-$15.

How is an Alternator Replaced?

Replace alternator

Image Credit: AutoRex

When you have an alternator that needs to be replaced, you have two options:

  1. Bring your car to a shop and have them replace it for you
  2. Replace it yourself at home

Replacing the alternator yourself is actually a pretty easy DIY project if you have the right tools. You just need to do a search on your car to find the right part number and then order an OEM alternator. It's always best to order from a reputable OEM parts seller like MoparPartsOnSale.com.

The replacement process varies between makes and models, but the general idea is to:

  • Disconnect the battery
  • Disconnect the main power cable from the alternator
  • Remove or loosen the alternator belt (and inspect it for damage)
  • Remove the old alternator and then install the new one