If your battery was the star of a show, the alternator would be considered the best supporting actor (though the Academy Award would probably be awarded to the engine, for best performance).
Batteries get a lot of credit, but their job is short-lived. Your battery’s role is important in getting your car to start, but your alternator is the one doing the work, as you drive, to keep your vehicle powered. The alternator keeps the battery charged while the vehicle is running by converting mechanical energy from a rotating pulley into an electrical current. Your vehicle depends heavily on the alternator to power the electrical system.
How Alternators Work
Alternators used to be referred to as generators because that’s essentially what they are. They generate AC power through electromagnetism. The alternator is powered by a belt that is mechanized by the rotation of the vehicle’s engine.
The alternator is made up of a series of components including the stator and rotor, diodes, voltage regulator, and a cooling fan. Here’s how each component contributes to the alternator’s function:
- Stator and Rotor – Work in unison to convert energy into electricity. Magnets inside of the unit spin and create an “alternating current.”
- Diodes – Transform alternating current into direct current to charge the battery as well as ensure the current travels in only one direction, from the alternator to the battery.
- Voltage Regulator – Similar to a surge protector, it ensures the voltage in the charging system stays in a suitable range.
- Cooling fan – Creating energy also creates a significant amount of heat. The fan inside or outside the alternator protects the system by helping to dispel the heat.
Alternators do not require much maintenance and often have a life span between 7 to 10 years. However, when the alternator is beginning to fail, you may notice some unusual behavior from the vehicle. You may even wonder “why are my headlights flickering?” While that’s just one of a few symptoms, here’s how to tell if the alternator in your car is faulty or is beginning to fail:
- Electrical Failures – Dimming headlights and dashboard lights, as well as electronic accessories that lag, including windshield wipers, power windows and seats may operate more slowly than normal.
- Battery Light On – As part of your OBD (On-Board Diagnostics) your dash lights communicate any troubles your vehicle is experiencing, including the electrical system. When the alternator’s power is beginning to wane, the light that is shaped like a battery, or the letters ALT or GEN will illuminate on the dash.
- Weak Battery – Batteries do not last long, especially here in Arizona. While your alternator’s primary task is to continue replenishing the car’s battery, it can only do so much. If the battery is extremely weak or has already died, the alternator cannot revive it. You can test to see which component is at fault by jump-starting your car and immediately removing jumper cables. If the alternator is having difficulty charging the system, the car will likely die again. However, if the car continues to run, the battery is most likely at fault.
- Burnt Rubber Smell – The alternator works with pulleys and a series of belts. If belts aren’t turning freely, the increased friction causes the belt to heat up and produce a burning rubber odor. Likewise, if you recognize a smell comparable to an electrical fire, it could be caused by a belt slipping on the alternator’s pulley. Tightening the belt up should resolve the issue. However, if it doesn’t, your alternator bearings could be in failure, and it should be tested by a qualified technician.
- Whining Sound – To produce the electrical current needed to generate power, small components are spinning inside the alternator. If any of these tiny components fail, such as worn bearings, you may hear a grinding or whining sound.
How to Diagnose a Faulty Alternator
If you suspect your alternator is in failure without a warning light, open the hood and visually inspect the belt on the alternator. If it appears glassy or burnt, this could indicate it is slipping. When the belt is loose, it slips on the pulleys instead of traveling smoothly. This causes friction from the metal on rubber contact, heating up the rubber and accelerating the belt’s wear. Tightening the tensioner should resolve the issue. Take care not to make the tension too tight, however, to avoid damaging the alternator’s internal components.
Replacing the Alternator: OEM vs. Rebuilt
Replacing an alternator can be quite costly, though necessary. When replacing your alternator, you have the option to purchase Original Equipment Manufacturer (OEM) or a rebuilt alternator. Original parts are more costly but are often more reliable. A rebuilt alternator involves removing the original alternator from the vehicle and sending it to a specialty shop for rebuilding or a previously rebuilt alternator will be installed. Keep in mind that purchasing a rebuilt alternator can be risky, as you are installing a previously failed alternator. While the major components inside have been replaced, there’s no guarantee it will work like new.
Whether you purchase new or rebuilt, when replacing the alternator, it’s a good idea to have your technician replace the serpentine belt as well. Since the serpentine belt must be removed to replace the alternator, you can save on the cost of the labor by doing both at the same time.