An alternator is a crucial part of a vehicle’s electrical system, responsible for powering accessories and keeping the battery charged. Without a functioning alternator, the car’s battery would quickly run out of juice and die in its tracks, leaving the driver and occupants stranded. Knowing when an alternator is going bad, when it’s time to replace it, and how to do it can prevent unexpected breakdowns and ensure smooth vehicle operation.
This guide will dive into everything there is to know about an alternator, including how it works, signs of wear and tear, how to test it, and more. Having experienced two alternator failures in the last six years where I was left stranded on a highway on cross-country road trips, I know just how important a reliable alternator is. So let’s dive in.
Understanding the Alternator and How it Works
In short, an alternator generates electricity by converting the engine’s rotational energy into electrical energy via electromagnetic induction. Coming from my perspective as an engineer, alternators are one of the most interesting parts of a car, generating electricity to keep everything running right. They may look simple, but a lot is going on inside.
The alternator consists of several major components that work together to make this happen, including the pulley, rotor, stator, voltage regulator, bearings, and housing. As the engine runs, it drives the alternator pulley via a belt connected to the crankshaft. This pulley then spins an internal electromagnetic core called the rotor, which generates a magnetic field as it turns. This magnetic field sweeps past the wire coils that make up the stator, and an electrical current is induced, which then gets directed to the vehicle’s electrical and charging systems.
In addition to the parts that actually generate the electricity, a built-in voltage regulator ensures that the voltage output remains within the optimal range to prevent overcharging or undercharging the battery. There are also bearings within the alternator that allow the rotor to spin smoothly, and the housing and cap protect these internal components from the elements to extend the alternator’s life as much as possible.
Over time, the various parts of the alternator can wear out due to heat, moisture, and the demand from any additional electrical accessories. Recognizing signs of wear and tear and addressing alternator issues before complete failure can help the vehicle run reliably.
Causes of Alternator Wear and Tear
Mechanical wear and tear is the most common cause of alternator failure, with the bearings being the biggest culprit. Designed to allow the rotor to spin freely, the bearings can eventually degrade due to friction and heat. Once the bearings begin to fail, the rotor won’t spin as freely and the alternator will not produce electricity as efficiently, causing it to overwork itself and wear out even faster, leading to complete failure.
Another common issue with alternators is the demand from various accessories and other parts of the electrical system. Things like aftermarket stereo systems, GPS units, radar detectors, dash cameras, and other extra accessories can cause the alternator to work more than it needs to. This is also why alternators tend to wear out faster when systems like air conditioning and defrosters are used more often since these are electrical-heavy features that force the alternator to work harder.
Lastly, even though alternators have protective housings and caps, they aren’t completely shielded from the elements. Humidity and moisture can get in there over time and start corroding internal parts, leading to failure. No matter what’s causing the alternator to start going bad, there isn’t really much preventative maintenance that can be done. That’s why it’s important to know what to look for when an alternator begins to fail.
Symptoms of a Failing Alternator
Identifying the symptoms of a failing alternator early can prevent unexpected breakdowns and costly repairs. One of the most common signs is dimming or flickering headlights. As the alternator begins to fail, it may not provide sufficient power to the vehicle’s electrical system, causing the lights to lose brightness. Another indicator is the appearance of warning lights on the dashboard, such as the battery light, which often signifies an issue with the charging system.
A tell-tale sign of a failing (or failed) alternator is a dead battery, as the alternator is no longer able to charge it properly. If a vehicle has difficulty starting, especially after being parked for a short period, it may be due to an alternator that isn’t recharging the battery. If the bearings completely fail and everything locks up, there might even be smoke and a burning smell coming from under the hood as the belt spins on an alternator that isn’t spinning along with it.
Once an alternator fails, the battery can still power the car for a short period of time before functions start failing and the vehicle eventually dies. After going through this multiple times myself, I know the importance of using this limited amount of time to either find a shop nearby or at least get off the main road or highway. Typically dash lights will start to flicker or go out, power windows will strain to operate, and the radio will cut out. After this starts, there’s usually around 30 to 60 minutes before the car dies, as long as the battery is in good shape.
Knowing When to Replace an Alternator
Since it’s always better to replace an alternator before it completely fails in the middle of nowhere, it’s a good idea to regularly test it, and the easiest way to do so is with a multimeter. A relatively cheap and effective tool, a multimeter measures things like voltage, current, and resistance.
An easy way to test an alternator is to check the battery’s voltage with the engine off, which should typically measure 12.6 to 12.8 volts. From there, fire up the engine and test the voltage again. With the engine running and the alternator working right, the battery should produce around 13.5 to 14.8 volts. If the voltage does not go up with the engine running, it’s a good indication that the alternator isn’t doing anything. If it’s going higher than this, the alternator is not regulating itself correctly and is overcharging the system.
Another way to test an alternator is to perform a load test, which can also be done at home with a multimeter, though most auto parts stores perform this service free of charge. In short, the alternator’s output is checked under various load conditions, such as when the engine is revved or the air conditioning, headlights, radio, and other accessories are turned off and on. A properly functioning alternator should keep the battery voltage within the specified range under all of these conditions. Anything else and there’s a good chance the alternator is failing.
How to Replace an Alternator
The process of replacing an alternator varies between vehicle makes and models, but the general steps are the same in most cases. It usually requires common tools such as a socket set and wrenches, not to mention the aforementioned multimeter. DIYers with intermediate experience working on cars can usually handle an alternator replacement, though some cars are notoriously difficult to work on. On average, replacing an alternator can take between two to four hours, depending on the vehicle and experience level.
First, ensure the vehicle is parked on a level surface and the engine is cool. As with any electrical repair, always disconnect the negative battery cable to prevent any shorts or shocks. Locate the alternator, which is usually mounted near the front of the engine and driven by the serpentine belt, and remove any components or covers obstructing access to the alternator.
Next, release the tension on the serpentine belt by rotating the tensioner pulley and slipping the belt off the alternator pulley. Disconnect the electrical connectors from the alternator, including the main power cable and any smaller control wires; sometimes the starter is also wired directly to it. Remove the mounting bolts securing the alternator to the engine, and it should come right out if nothing else is in the way.
To install the new alternator, perform the same steps in reverse order. Finagle the new alternator into place and secure it with the mounting bolts. Reconnect the electrical connectors, ensuring they are firmly attached, and then reinstall the serpentine belt. I always recommend throwing on a new serpentine belt during this repair, since there’s no additional labor involved and there’s a good chance the old one was ready to go. Finally, reconnect the negative battery cable and start the engine to test the new alternator as described above.
It seems like a daunting task for DIYers without much experience, but many alternators are relatively easy to reach from the top and can be swapped pretty quickly. Some makes and models require pulling a wheel or front hub assembly off or even lowering part of the subframe. In these cases, it’s recommended to go through a shop for anyone who isn’t experienced.
Find Everything Needed to Replace an Alternator at CARiD
Once an alternator starts failing, it’s time to swap it out for a new one before getting stranded, and CARiD has everything needed for the job. Finding the alternator itself is easy since CARiD’s website allows you to search for parts by year, make and model. This ensures you always get the right part, because nothing is worse than going through the process of getting the old alternator out, only to realize the new one doesn’t match.
Beyond the alternator, CARiD and its sister site TOOLSiD have all the tools needed to do the repair, including socket sets, wrenches, and multimeters, not to mention that new serpentine belt to ensure a complete fix. Plus, CARiD’s 24/7 chat feature connects customers with experts who are always ready to assist, ensuring you get the right parts and tools to get the job done.
