March 2, 2011, 5:36 a.m.
posted by maxe
Upgrade Your Car's Alternator
It's possible to install so many electronic devices in your car that the battery continues to discharge even when the engine is running. Upgrading to a high-output alternator ensures that there's enough power to feed all the devices while keeping the battery charged.
An alternator is a device in modern automobiles that acts as the voltage generator for the engine (Figure). While the battery does the job of getting the engine started, once the car is running off fuel it technically doesn't need a battery anymore. You could even disconnect the battery while a car was running, and it would probably continue to run (this applies to older cars without a lot of electronics; newer cars would throw a fit because the battery keeps the voltage levels stable). If you've ever gotten a jump start and then driven around with a "dead" battery, you understand this feature.
An alternator in a car
Once the engine is started, it's actually the alternator's job to supply the electrical power for the whole car. As an electrical generator the alternator is very efficient, but its voltage tends to fluctuate. The car's battery acts to smooth out the voltage and keep it at around 1314V. In the process, the car's battery gets recharged.
A normal alternator might be designed to put out 100A. This might seem like a lot, but once you start adding high-power devices with hungry CPUs, you could easily exceed this level. Once that happens, the car will act as if the alternator has stopped workingthe battery will have to make up the difference between what the alternator is putting out and what the car's entertainment system is demanding. The battery can thus become completely discharged, and for conventional batteries, this essentially makes them "dead." If you don't realize that the real problem is that you've exceeded your alternator's capacity, you might think that your battery is dead and upgrade it to a new top-of-the line battery, only to kill that one, too.
The solution to this problem is to upgrade the alternator. You will probably want an auto shop to do the installation unless you are handy with a wrench and know how to set the right tension on a belt. Luckily, installing an alternator is almost always a simple (i.e., inexpensive) job. The alternator is usually right on top of the engine and easily accessible.
If you ever get "dying battery" or "dying alternator" symptoms such as dim headlights or difficulty starting, even though you know the battery and alternator are good, upgrading the alternator may be the solution. Also, if you've calculated your power requirements and they clearly exceed the 100A your alternator probably puts out (perhaps because you've installed your Alienware gaming machine in the trunk), you should definitely upgrade the alternator.
If you plan to upgrade your alternator, be sure you read "Add a Second Car Battery" [Hack #10] before you buy, because if you are planning on adding a second battery you may want to get a dual-output alternator that charges both batteries independently.