How Alternators Work

Virtually everyone knows there is a battery under the hood of most cars. As such, you may think that your car’s battery powers its electrical components. This is a common misconception, however. After your vehicle starts, it is the alternator that provides electrical power. If you have been asking yourself, “What is an alternator?” you should know a few things about this essential part.

What Does an Alternator Do?

It may be helpful to think of your vehicle’s alternator as a generator, because that is essentially what it is. In fact, some automobile manufacturers refer to alternators as generators. In simple terms, your car’s engine makes the it's wheels spin. The engine also spins the alternator through a drive belt, or serpentine belt, and pulley system. This causes the alternator to create electrical current.

How Do Alternators Work?

The alternator converts the rotational mechanical energy of the engine into the electrical energy your vehicle’s components need to function. It receives mechanical energy from the pulley, which is rotated by the engine belt, and uses magnetism to generate alternating current. Furthermore, it changes this alternating current into direct current that your vehicle can use.

Moving a magnet past a closed loop of wire makes an electric current flow in the wire. Alternators use this same basic principle.

What are the Parts of an Alternator?

Modern car alternators have a few essential components that allow them to do their job. If any one of these parts wears out or breaks, your alternator may fail. Here are some major parts of your vehicle’s alternator:

4 Crucial Components

1

Stator

The stator is a set of fixed or stationary wire windings. Several of these precisely spaced windings work with the rotor to generate an alternating current.

2

Rotor

The rotor is the part of the alternator that spins. It is supported on both ends with bearings and spins with the assistance of a pulley and drive belt. The rotor features an iron-core center that has a copper wire wrapped around it. Energizing the wire with an electrical current causes a magnetic field with north and south poles to develop.

3

Bridge Rectifier

The bridge rectifier converts the alternating current (AC) from the stator into direct current (DC) that your vehicle can use. To accomplish this task, the rectifier has several diodes. These diodes allow current to flow in one direction and prevent it from flowing backward. This changes the alternating current into direct current.

4

Voltage Regulator

The voltage regulator is the nerve center of the entire assembly. It is an electronic component and is responsible for maintaining the charging system voltage within a specified range.

These four components are not the only parts of your vehicle’s alternator, but they are components that generate usable electricity for your vehicle. You should realize, though, that your alternator also has other parts, including a housing, bearings, brushes, and bushings.

What are Common Problems with Alternators?

Most modern alternators are well-built components that can function for a long time. Still, they are not invincible. Eventually, your vehicle’s alternator may require repair or replacement. Typically, when alternators fail, the culprit is one of the following:

  • Bearing failures: The alternator’s rotor relies on bearings to keep it spinning freely and smoothly. Like the bearings in other parts of your vehicle, the alternator’s bearings can eventually wear out. If this happens, you are apt to hear a loud, grinding noise coming from under your car’s hood. These sounds should get louder as you listen near the alternator, if that is truly the problem. Furthermore, if the alternator’s bearings are well past their prime, the belt may whine, chirp or squeal.
  • Damaged regulator or rectifier: If your alternator has a damaged regulator or rectifier, you may face a variety of problems. These could include a dead battery, an illuminated battery warning or message on the instrument cluster, and dim lights when driving at night. Your vehicle may have an instrument readout that tells you how many volts the alternator is delivering. This should be between 12.3 and 14.4. If your car does not have a voltage gauge, you can use a voltage meter to test alternator output.
  • Bad belts: Your alternator needs the pulley and belt system to function optimally. Eventually, drive belts may fray or otherwise wear out. Regularly inspecting the drive belt for signs of wear is a good way to ensure your alternator’s rotor keeps spinning properly.
  • Worn Brushes: The brushes in the alternator are wear items and eventually they do wear out. This will cause the alternator to not charge properly and can also lead to a dead battery or illuminated warning light on the instrument cluster.
  • Over Heating: Heat is a major cause of failure in alternators. The alternator has vent holes that allow heat to escape and help to prevent overheating. When vent holes are plugged by 60% or more, failure is likely to occur. Also, if the battery does not hold a charge of 12.4 volts or more, the alternator will constantly try to recharge a depleted battery. This constant charging can cause an alternator to overheat.

Because the consequences can be significant, you do not want to ignore problems with your vehicle’s alternator. After all, if the alternator fails, you may find yourself stranded somewhere you would rather not be. You may also cause additional damage to your vehicle by putting off essential alternator repairs.

Alternator Maintenance

If your alternator fails, you probably need to replace it. You can, however, take certain steps to keep your vehicle’s alternator in tip-top shape.

First, keep a good battery under your car’s hood. Because car batteries and alternators go hand-in-hand, you should replace your old, damaged, weak, or ineffective battery. After all, a bad cell inside your battery can ruin your alternator. The opposite is also true. If you have a failing alternator but a good battery, your battery may disguise alternator performance issues. Eventually, though, both components are likely to require replacement.

If you think your vehicle’s alternator may be on the blink, you can ask a professional to test it. You can also remove the alternator from your vehicle and have it tested at the nearest AutoZone auto parts store.

Coming out on Top

Now that you have answered the question, “what does an alternator do,” you likely understand the importance of keeping your alternator in tip-top shape. If you want to come out on top, you cannot leave the health of your vehicle’s alternator to chance.

By watching for common problems, you know when to repair or replace your alternator. If something goes wrong, you need high-quality components and the right tools to achieve success. Take a look at your alternator today. If you find a problem and need any parts or tools, stop by your local AutoZone.

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