Your vehicle needs a lot of electricity to feed a variety of electronic devices and systems. When your engine is not running, that is the job of your battery, but once you start the motor, another device, known as an alternator, comes into play. It is a major component of your vehicle’s charging system that performs several important functions at the same time. The alternator supplies power to each and every electronic device found in your vehicle as well as charges your battery, so it can provide enough power to start the engine next time you turn the ignition key or push the start button.

To generate current, your alternator relies on electromagnetic induction, which occurs when a conductor moves through a magnetic field. The alternator features a big electromagnet, called a rotor, and a set of wires, known as a stator, which work in tandem to develop current. The outer end of the rotor has a pulley driven by your drive belt. When the engine is running, the rotor spins inside the stator, causing the latter to generate alternating current (A/C), which is then conducted to the rotor field winding with the help of brushes and slip rings. 

As you might notice, your alternator generates A/C, while all devices found in your vehicle need direct current (D/C) to operate. To resolve this issue, your alternator is equipped with a diode rectifier bridge that converts A/C into D/C by not allowing alternating current to flow both ways. This direct current flows to your voltage regulator, which does exactly what its name suggests, and is then supplied to the rest of the vehicle, powering your onboard computer, headlights, stereo, etc. If your alternator does not have a voltage regulator, this means your engine control module provides voltage control itself.

Despite the fact that your vehicle is driven by the combustion process, you’ll not be able to drive without a properly functioning alternator. If it fails or malfunctions, you’ll face a variety of problems, including dimmed headlights, taillights and dashboard lights, engine stalling, inability to start the engine due to a dead battery, abnormal noises and many others. 

While your alternator is a reliable device designed to survive the test of time, it can fail over time just like any other part found in your vehicle. This may happen in one of the following ways.

Your alternator doesn’t generate enough current (undercharging)

A failing alternator cannot charge the battery and supply the rest of the vehicle with the proper amount of electricity. As a result, you can experience problematic engine starts and eventual stalls. You will also notice dimmed or blinked dashboard lights as well as onboard electronics problems and failures. In many cases, the check engine light will also come on.

An alternator that overcharges

This is usually caused by incorrect voltage regulator operation. An overcharging alternator may shorten the life of your vehicle’s bulbs and onboard electronics, and cause the check engine light to illuminate.

Abnormal noises coming from the alternator

This is the main symptom of worn-out alternator bearings. The sound should be more noticeable at higher RPM. At the same time, the alternator can function properly, so no electronics related problems will appear.

Alternator troubleshooting

There are two main parameters that need to be checked when it comes to an alternator. They are charging voltage and amperage. The first one is easy to check with a simple digital multimeter. All you need is to connect a multimeter to your battery’s terminals. At idle, the voltage provided by the alternator should be from 13.8 to 14.2 volts with lights off. As for the amperage, it can be checked with an inductive probe around the battery wire. An alternator diagnosis can be even easier if a special system tester is used. Such charging/starting testers can be found in just about any repair facility. They allow for testing all aspects of alternator operation with just a push on the button.

Sometimes, undercharging can be caused by a loose or slipping drive belt. On the other hand, overcharging can be a result of an internally shorted battery or an improper operating voltage regulator. That’s why it is always a good idea to check your drive belt and battery before disassembling or replacing the alternator. If the alternator is the source of the problem, it can be rebuilt or replaced with a new unit in less than no time. Most repair facilities will recommend you to replace a bad alternator because of its relatively low cost.