One of the unsung heroes in your vehicle’s engine bay is the alternator. As you drive your vehicle, for performance or pleasure, the alternator quietly generates the electrical power required for vehicle operation. It works in conjunction with the battery to keep a continuous amount of electric current available both to recharge the battery while running and supply power for the electrical functions of your car including your ignition system, vehicle accessories, A/C, and heater.
Function of an Alternator
The function of the alternator is simply to generate electrical power by converting mechanical energy. In most cases, the mechanical input to the alternator is a belt driven pulley which is connected to the crankshaft pulley via the alternator belt. The alternator pulley is connected to a magnetized shaft that turns inside a stationary coil of wires. As the magnetized shaft turns inside the coil, an alternating current is generated. The alternating current is converted to direct current which your vehicle needs to run. There is a secondary electrical component called an electrical regulator that maintains the electrical voltage to prevent overcharging and undercharging of the battery. On older vehicles, the regulator was a separate part outside of the alternator, but on most new vehicles it is integrated into the alternator assembly for simplicity.
Common Symptoms of a Bad Alternator
So how do you know if you have a bad alternator? There are a number of common symptoms that indicate a bad alternator. Before trying to diagnose alternator issues, it’s important to check to make sure your alternator belt has the correct tension, as an under-tensioned belt can cause many of the same symptoms. The following symptoms can indicate that it’s time to replace your alternator:
Strange Noises – The alternator has two main bearings that allow the internal magnetic shaft to spin freely as it generates electricity. Over time these can corrode due to moisture, wear due to use, or fail due to an over-tensioned alternator belt that overloads the bearings. As they wear, the alternator bearings can emit a whining, whirring, or oscillating noise during vehicle operation because the worn bearings have additional friction between the shaft and bearing surface. The alternator may still produce power for a time, but eventually the bearings completely fail and the pulley can seize. A mechanic’s stethoscope can be handy in pinpointing the alternator as the origin of the noise, as sometimes it can be subtle.
Bad Smells – The alternator can emit a burning smell that typically indicates overheating. The regulator that controls and maintains the vehicle voltage can also overheat and emit a smell indicative that there is an issue with the alternator.
Dash Light – Most vehicles from the last 40 years have a battery light on the gauge cluster. When you initially turn the key to the on position, most vehicles show a battery or other symbol indicating a low voltage. When you start the vehicle, typically that light turns off once the alternator starts producing current. If the light remains on for more than a few seconds after starting your vehicle, it’s an indicator that the vehicle is not operating within the desired voltage range, which could mean that your alternator or voltage regulator have gone bad.
Dead Battery – A dead battery is a sneaky symptom of a bad alternator as the alternator isn’t always the first suspect when trying to identify the root cause. However, since the alternator produces the current that keeps the battery charged, a bad alternator can provide insufficient charge for the battery which can ultimately result in a dead battery. Beyond that, a bad regulator can add an electrical drain to the vehicle system and drain power from the battery while the vehicle is not in use. If your battery continues to die even after using jumper cables to jump start the vehicle, you may have a bad battery or a bad alternator.
Erratic Accessory Functions – Alternators typically have a running voltage of between 13.7 to 14.7 volts and the regulator attempts to keep the vehicle within that range. As accessories such as headlights, fog lights, heated seats, or a sound system demand more power from the electrical system, the alternator may not be able to keep up. If the alternator is not producing voltage at the full potential it may turn on the dash light to indicate a problem and prevent some of the systems from working correctly. In other words, the seat heaters may not get as hot as normal, the sound system may cause the headlights to dim, etc.
Replacing an Alternator
Once you have determined the alternator has either failed or is nearing that point, it’s time to replace it to make sure your vehicle continues to run without incident. Replacement of the alternator varies slightly based on the age and model of your vehicle, but replacement is pretty straightforward.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – Disconnect the battery cables (negative first) taking care to avoid electrical shock. As the battery leads are most often fastened using a nut, you will either need an adjustable wrench or a ratchet to get them off. You should use caution as there is risk of electric shock any time you work on your vehicle’s electrical system. Ensure that your tools and your hands don’t complete a circuit by accident or you could be shocked.
Step 2 – Disconnect the electrical leads on the alternator. This could be a connector attached into a plug receptacle on the alternator housing or it could be a nut holding the cable connection on a stud. Depending on the connector type, you sometimes need the help of a small screwdriver but these can often be removed without tools as well.
Step 3 – Release the tension on the belt and remove the drive belt. If you have an older vehicle with a V-groove belt, releasing the tension could be as simple as loosening the fasteners holding the alternator to its bracket. There could also be a fastener that you loosen to take pressure off a tensioning pulley. If you have a serpentine belt (a wide flat shaped belt running everything together), you may just need to use a large socket and breaker bar to release the tension on the belt to remove it. Some vehicles also require a special belt tensioning tool for this task.
Step 4 – Once the belt it removed from the alternator pulley, remove the alternator from its bracket. This will typically require removal of a small number of fasteners and can include spacers.
Step 5 – Once you have removed the alternator completely, replace it by following these steps in reverse order. Be sure to inspect the belt as there is no better time to replace it since it’s already off the car.
Best Car Alternator Brands
When it comes to selecting a replacement alternator for your car, there are tons of brands out there and the decision can be tough. Some options may be extremely inexpensive, but they won’t serve you well if the part only lasts a few months due to poor quality. On the other hand, some may be expensive so how do you know whether they have the quality to match? To help narrow your search, we have provided a short list of our favorite alternator brands below as we have found them to be a good balance of quality and value over the years.
AC Delco is a global supplier and one of General Motors’ premier suppliers for original equipment replacement parts. They offer 37 different product lines around the globe and provide parts for all major vehicle systems, as well as off-road, marine, and industrial equipment. They have been in the alternator business for quite some time, as well as have been players in the broader vehicle ignition market (such as spark plugs, distributors, ignition coils, etc). They make high quality alternators that are affordable and readily available.
Denso is one of the leading global suppliers for replacement and OEM level parts for automotive manufacturers. Denso was founded in late 1949 and has a long history of high level technology advancement throughout the years. They make alternators that are OEM equipment on many vehicles, and do so at a price that doesn’t break the bank. If you have ever bought spark plugs, you’ve probably at least heard Denso’s name. In addition to being a major player in the spark plug world, they also make a great, cost effective alternator.
Bosch is another replacement part and OEM level supplier that offers high quality and durable parts. Bosch is the OEM manufacturer for many alternators, most notably for many of the German auto manufacturers. Bosch parts also find their way into many other non-German vehicle makes and models as well. Bosch makes everything from spark plugs to throttle position sensors to alternators. Bosch is well known for making a myriad of excellent yet affordable electronic components and their alternators are no exception.