I believe this is the article thatDan M C was talking about. I have the whole thing but can’t post the complete thing with pics. If any one wants a copy let me know and I will email you the file.
ALL ABOUT THE ELETRICAL SYSTEM
AND THE LOAD OF A SYSTEN
Got Juice
Making Sure Your Audio System Gets Plenty of Power
Story by: Steve Gibbs
Photography: Brian Maul
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 Load
If 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.
Now add a couple of coaxial speakers, an amp to power them, and a pair of auxiliary driving lights so your ride will look cool. While these devices don't require as much current as the subwoofer amplifier, they still add to the system's load. Let's say the amplifier driving the coax speakers adds another ten amperes of current draw. You've now added more than 30 amperes of load to a system designed to handle just 60. That's a substantial extra burden for a stock battery and alternator.
Knowing What's Watt
The biggest mistake made by many consumers (and some installers) is failing to beef up the charging system enough to handle the demands of additional audio and video equipment. Determining how much more electrical current you need depends on the equipment you install. Understanding the electrical system of your car will help you determine how much additional electrical current you need. It all starts with the turn of your car key.
Turning the key in the ignition begins the process of cranking the motor. Your car's battery supplies the electricity needed to get things going. Once started, the car's electrical burden shifts to the alternator. An alternator is a device that uses the engine's mechanical power (supplied by the alternator belt) to create alternating electrical current (AC). The alternating electrical current is rectified (changed) into direct current (DC) which is needed for all the devices in the vehicle that require electricity. The alternator also serves to recharge the car's battery after power is used during the cranking process.
Everything works perfectly so long as the power requirements of the vehicle don't exceed the alternator's power-producing capacity. If the power load is too much for the alternator, then power will be pulled from the battery. If the alternator and battery can't meet all the power needs, then the voltage available to power all the car's electrical devices is diminished. As we learned earlier, when voltage decreases, current flow increases, and current flow creates heat (due to resistance) in components. This is why a prolonged loud bass play sometimes will damage components if the charging system is inadequate.
"If the power reaching the amplifier drops to about 11 volts, it may cause some amplifiers to overheat and malfunction," explained Ray McKenzie, president of Xstatic Batcap, a maker of batteries and capacitors. "Some amps have circuits to prevent this type of thing, but the circuits may not always work properly and if they don't, damage can result."
One of the best car audio innovations in recent years is Class D amplifier technology. Class D amps, which are typically used for bass only, operate more efficiently than standard Class AB amps, meaning they require less current to achieve their rated power. For instance, a 1000-watt Class D amp can hit its rated power with about 80 amperes of current and operate comfortably on about 10-20 amperes of current. A 1000-watt Class AB amp would require perhaps 140 amperes to achieve 1000 watts of output power and about 20-50 amperes for normal play. The difference in the efficiency of your amp could determine whether or not you need a bigger alternator, a larger battery and/or a stiffening capacitor
Current Affairs
The first place to look to determine whether or not you car's charging system is cranking out enough power is the alternator. If you can see the alternator in your car -- not easy in some modern vehicles which are tightly packed under the hood -- the "hot" power rating may be listed somewhere on the unit. If you can't see it, go to an autoparts store or car dealership and ask them to look up the stock alternator on your vehicle. The hot power rating will tell you how many amperes it will produce when the motor has reached its operating temperature.
Once you know how many amperes the alternator produces, assume that the power is sufficient to power the vehicle's standard electrical devices with maybe ten amperes to spare. Now think about how much current draw your new system will add. If the number is greater than ten, then you should think about beefing up the charging system.
If you need only a small amount of additional current, the easiest way to enhance the charging system problem is to replace your existing battery with a larger one. This will allow the audio system to pull the power it needs on rare occasions when the alternator can't carry the entire load. But remember that this solution is only recommended if your charging system needs a slight boost, about 10 amperes. Pulling power from the battery too often will cause the battery to weaken more quickly than it should, and no one enjoys a dead battery.
Batteries are rated by the amount of cold-cranking amperes they produce. A small import car is likely to have a battery rated at 500 CCA. A large battery would have a CCA rating of 1,000. How big a battery should you install? Most experts say get one as the available space will allow. If your vehicle's charging system is significantly short on amperes, then adding a bigger battery will only create additional problems. Adding a second battery is an option, but is not recommended for a variety of reasons.
"I think multiple batteries are a bad idea for vehicles that are daily drivers," says Jeff Triplett, director of technical services for Memphis Car Audio. "A second battery has to be charged by the alternator just like the primary battery, so you're just creating more work for the alternator. If the motor is off and the system is running off battery power, the multiple batteries are OK. However, daily drivers simply have little to gain from multiple batteries."
Another strike against having multiple batteries is the safety issue. Batteries can be dangerous if improperly installed, so great care should be taken if you are thinking of putting in a battery in a non-stock location. Consult a qualified installer if you feel you must have a second or third extra battery.
Feed the Need
A capacitor is a good solution for the quick power response needed for bass-heavy sound systems. A capacitor, sometimes called a stiffening capacitor, is a device that stores electrical voltage and releases it as needed. This is extremely helpful when your electrical system is near its capacity and the music you are playing suddenly hits a thunderous, long bass note. A capacitor would release the needed power to meet the demand without stressing the system and then would recharge itself immediately, ready for the next big note. There also are batteries designed to function like capacitors. The Xstatic Battcap is an example. They contain a larger charge (measured in farads) than do most capacitors.
If your charging system is significantly short on current and you need more than a capacitor will easily handle, then the best option is to add a bigger alternator. Alternators are the fastest power source, meaning they can respond to power needs more quickly than the battery or even a capacitor. Of course, adding an alternator is usually a more expensive solution to your power needs; but it also may be the best solution. Again, though, if you decide to install a bigger alternator, then the question is, how big?
"Obviously, you have to have an alternator that physically fits the available space," explains Dennis Moore, who designs and builds ProPower Alternators for his company, The Mechanical Man in Southern California. "The next questions concerns how much of the alternator belt is in contact with the pulley. Small motors tend to have small pulleys. If there is not enough pulley in contact with the alternator belt, then the belt is likely to slip, squeak and burn up more quickly."
Moore noted that a good solution to the belt traction problem is to add a second pulley, called a "backside idler," to increase the amount of belt in contact with the main pulley. Of course, few people have the knowledge and skill required to add a second pulley to their alternator set up, so it's best to seek the advice of a professional installer when considering this option.
Think about your power requirements if you are considering a new alternator. If you are adding an entertainment system that will consistently create an additional 30 amperes or more of current draw, then you probably need an alternator that will provide at least that much additional power. Keep in mind that a big vehicle such as an SUV has a bigger stock alternator and can probably handle an additional 30 amperes of draw more easily than a Honda Civic. But as a general rule take a close look at your charging system if you add ten or more amperes of current draw.
Most car audio decisions usually come down to budget. Volume is often a matter of money, with loudness being determined by the thickness of your wallet. If you discover that you can't afford to install a charging system big enough to run the amps and speakers you want to buy, then it's a very good idea to get smaller amps and fewer speakers. You will be much more satisfied with slightly smaller components that sound great than with enormous equipment that is full of noise and likely to overheat and fail.
Topic Closed)
Members
Search
Register
Login
Dan M C
Printable version
