When you put batteries in your TV remote control, they eventually die and you toss them out and replace them. Your cell phone, however, has a rechargeable battery that you plug in to charge. Since most of us do not plug our cars in (yet) and we don’t toss out our car battery on a regular basis, how does the battery charge?
The answer is—the alternator.
In order to start you car, the battery needs to power up the engine. But once the car is running, the engine powers the alternator, which is what charges the battery. While your car is running, the alternator creates electricity (13.6-14.3 volts) and recharges the battery to its original state of charge (like plugging in your cell phone).
The alternator is always working … always! In fact, I think it’s one of the hardest working electrical parts in your car. When your car is running, the alternator is constantly creating electricity to provide the engine and car accessories with power.
Some Things to Consider
When jump starting your battery, your alternator could seriously overload, which can kill it. If this happens, replace or recharge the battery before replacing the alternator. This will prevent the second alternator from dying.
To generate power, most cars use a ribbed belt connected to the alternator to rotate the armature inside the alternator. If the belt breaks, you’re stuck since your charging system won’t be able to run at all.
The tension placed on the belt is really important. The belt should be taut. If it isn't, it could be one of two things. If the belt tensioner is loose, it will need to be replaced. If the belt tensioner is too loose or too tight, an incorrect belt may have been installed. In either of these situations, your car could stall. Your belt needs to be like the three bears—just right.
Over- or Under-Charging?
If your alternator is undercharging (less than 13.6 volts), you can expect trouble on the road. If your alternator is overcharging (over 14.5), this can be troublesome, too. Symptoms of overcharging can be a swollen battery or a seeping, leaking battery, or if both headlights fail at the same time, along with other electrical components. To check your alternator, use a volt meter on both positive and negative terminals while the engine is at idle.