SO YOU WANT a killer car audio system. You might think all you have to do is go out and buy some big amps and big speakers, plug them in and start cranking out massive sound. If that's your plan, you may be disappointed. Adding a bunch of car audio components to your car without first considering the vehicle's electrical system may leave you with a lot of annoying distortion, damaged components and a dying battery. Not what you had in mind, of course.
The fact is, big bass-oriented audio systems require more electrical power than what most stock electrical systems are designed to produce. If you want 500 or perhaps 1,000 watts of power, your car must be able to produce enough "juice" to drive the components. If your electrical system is inadequate, your sound system will never deliver its rated performance. You also may end up damaging your equipment. That's an incredible bummer if you just spent several hundred dollars on amps and speakers.
"If you keep constant electrical stress on the charging system, the amount of voltage decreases. As voltage decreases, current increases and that creates heat in your components," explains Tom Eliopoulos of Ohio Generators, explaining a principle of Ohms Law. "Heat is the enemy of all components. It's bad for voice coils, amplifiers - everything."
Unfortunately, many car audio fanatics tend to overlook, or perhaps avoid, the subject of charging systems when they consider installing a new sound system. One reason the subject is so unpopular is that electricity is so darn complicated. Even technicians may have trouble explaining all of the issues involved with vehicle charging systems. It's easy to get confused when you start thinking about watts and volts, amperes and amplifiers, current, farads, capacitors, resistance and so forth. Can anybody offer a simple explanation? Probably not, but we'll try.
A Heavy LoadIf you're like most drivers under 30, you probably enjoy listening to rap, hip-hop, or alternative music, which are often heavy on bass. Therefore, the car audio system of your dreams is likely to include a subwoofer, which is a good place to begin a discussion of charging systems.
Big, loud bass music requires a big subwoofer. Let's say you purchase a sub that handles 300 watts RMS. If you want the sub to perform to its potential, you'll need a well-designed subwoofer enclosure and an amplifier with a similar RMS output power rating. If your amp doesn't provide enough power to the sub, then the subwoofer will not perform to its potential. It is very likely that the amplifier will be overdriven and create distortion through the subwoofer.
Now let's say you install a 300-watt mono amplifier to power the subwoofer. Your vehicle's charging system must produce enough electrical current to run the amp. How do you know how much current is needed? Here's a simple formula: divide the RMS power rating of the amplifier (in this case, 300 watts) by the amount of voltage your car's electrical system will produce. Most cars have a standard 12-volt system that actually cranks out about 13.8 volts with the motor running. So, 300 watts divided by 13.8 volts equals 21.7 amperes of current. Your car's electrical system will need to produce an additional 21 amperes (the term for measuring electrical current) of electrical current to power the amplifier and subwoofer at a reasonable performance level.
It's important to note here that most cars come from the factory with an electrical charging system (an alternator and battery) that is adequate for the car's stock equipment, normally a radio and CD or cassette player, lights, horn, rear window defogger, heater, air conditioner, cigarette lighter, and so forth. Most small- to medium-sized cars are equipped with an alternator that generates about 60 amperes of current. If you add a subwoofer and amp that require at least 21 additional amperes, that means you have added a third more "load" to the electrical system.