Speed & Sound: Plugged In – Power Distribution
Text by Dave MacKinnon (www.osmlabs.com) Photos by the Manufacturers
By now, all of you have seen car audio installations that incorporate what seems like large-diameter power wires. These cables can be nearly a half-inch in diameter for systems under 1,000W and nearly an inch in diameter for systems rated more than that. This may seem like overkill, but in fact, it’s just adequate for most systems.
The size of the wire you use to power up your amplifiers and other high-current devices (lights, winches, etc) is called its gauge. If you are using good-quality wire, you will see a size printed on the jacket such as 8 AWG or 4 AWG. AWG stands for American Wire Gauge and it is a universal standard for determining the size of a conductor. We’ll talk more about this at the end of the article.
Unfortunately, our cars run on a 12V electrical system. Optimistically, we might see 13.6V to just under 14V at the battery when the car is running. The problem is that we need to draw massive amounts of current from this low-voltage electrical system to produce large amounts of power. Why? Because the laws of physics state that power is the product of voltage times current. If we want to power a 100W light bulb from a 13.6V electrical system, that light bulb will draw 7.36 Amps of current.
When we start to talk about car audio systems and large amounts of power, we also need to take into account the efficiency of the amplifiers. Most Class AB amplifiers operate between 60 and 75 percent efficiency at full power, and at less than half that at lower power levels. Class D amplifiers increase this up to around 90 percent for some of the best designs. So, let’s say you want to install a 1,500-watt amplifier, and the amp in question is 80 percent efficient, you need to supply the amp with 1,875 watts of power. At 13.6V, that’s an awe-inspiring 137.9 amps of current. That’s way more than a piece of 4 AWG cable is rated for – they max out their effectiveness at about 100A.
What happens when a conductor isn’t large enough? Its resistance causes the voltage at the end of the wire to be too low to allow the load device to operate properly. For most car audio amplifiers, this means that the amp won’t make as much power as rated. For example, the CEA-2006 amplifier specification states that amplifiers tested to this standard are to be supplied with 14.4V; unfortunately, that is a number rarely achieved in a car, but at least the standard makes amplifier ratings comparable.
Another issue with respect to power distribution is that people forget that current must travel in a loop – from one terminal of the battery and back to the other. I see countless audio system installations where a large 4 AWG or even 0 AWG power wire has been run from the battery to the amplifier, but the negative terminal of the battery remains a tiny piece of 8 AWG cable. It’s no wonder these systems often suffer from headlight and dash lights that dim with the beat of the music.
Speaking of dimming lights, there are some great solutions to this very common problem. The first is to ensure you have adequately large power wire for the size of system you have installed. You cannot have oversized wire, so get as much as you can afford. The second step is to complete what is known in the industry as the ‘big three’ connections. This refers to the connection of the positive terminal of the amplifier to the positive terminal of the battery through an appropriately sized and located protection device (fuse or circuit breaker). The other two connections are to ensure there is an additional, equivalent-sized ground wire running from the negative terminal to the chassis. The removal of all paint and primer at the chassis connection is critical. Finally, you need to do the same for the negative terminal of the amplifier. The same size wire should be run from the negative of the amp to the chassis, with all paint and primer removed.
The next step in upgrading your audio system would be to include an upgraded battery or a stiffening capacitor. Both of these devices store electrical energy. A battery stores a significant amount of energy, but the rate at which it is released is limited. A cap can store a small amount of energy, and release it very quickly. Caps can help stabilize the voltage of a car’s electrical system when you are playing very dynamic music at high listening levels. A cap, however, does nothing to increase overall system volume (output) or its available playing time. If you want more power or longer play time, a larger battery or a secondary battery are your only solutions.
It is absolutely critical that proper fusing is used any time you connect a wire to a power source such as a battery. Fusing not only protects the device you have connected (such as an amplifier), but protects you as well. Imagine the scenario where you have installed a large 0AWG conductor in your car and it runs from the front to the back to feed a large amplifier. If your car were to get into an accident such that this large wire was pinched and shorted out, without proper fusing, the battery could easily explode, and at the very least, you could prevent a fire.
I mentioned earlier about wire sizing. This is a case where you can’t judge a book by its cover. Although the American Wire Gauge standard is the most common way of describing wire size, it appears that many wire manufacturers have taken liberties with the naming, and sell undersized wire in an oversized package. It’s like a small hot dog in a big bun, and unfortunately, it just doesn’t have the current carrying capacity of real cable. The other thing to look for is the material that the power wire is made of. Pure copper is ideal, as it conducts well. However, a lot of inexpensive cables use copper-clad aluminum. Aluminum is less expensive, but it unfortunately has about 30 percent more resistance than copper. This means, for the same size wire, less power is actually getting to your amplifier. I recommend going up at least one size in cabling when using CCA cables. So if you needed an 8AWG conductor, use a 6AWG. If you needed 4AWG, then use 2AWG… or just use good copper conductors.
Finally, if you are running multiple amplifiers in a system, there are nearly an endless combination of power distribution blocks available, many with fuse holders built in. You can select the size of the cable going into the block, and the size and quantity of cables exiting. Companies put significant effort into the design of these blocks, and some are very cool looking.
Don’t overlook proper size wiring, no matter what you are hooking up. As I mentioned, anything that draws current – auxiliary lights, power inverters, air conditioners in campers, winches and so forth – can present a significant load on your factory electrical system. Feeding them all properly will help ensure they operate reliably and to their maximum capacity.
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