What Happens When You Use Undersized Car Audio Power Wiring?

Having your local specialty car audio retailer install an amplifier in your car or truck is a great way to improve the performance of your audio system. The extra power will allow you to turn the volume up higher to extract more from your speakers. If you have a subwoofer installed, you’ll need to choose an amplifier that can produce lots of power. While there are some subwoofer, enclosure and amplifier options that represent excellent value, it’s pretty rare to find a deal on power wire. Delivering power to your amplifier is crucial to its performance and longevity. In this article, we will take a look at what happens when you skimp out on the power wire for your amplifier.

Why Is Power Wire Quality Important?

Unlike home audio and professional public-address audio systems, car stereos are asked to produce massive amounts of power from a relatively low voltage. For example, a 1,000-watt home theatre subwoofer amp might draw 10 to 11 amps of current from a wall outlet. A similarly powerful car audio amplifier will need to draw almost 100 amps from the charging system to deliver the same power to a subwoofer.

What does this have to do with power wire? In the 1880s, Nikola Tesla realized that transmitting power to homes at high voltages reduced losses due to the resistance of power cables. Power is calculated by multiplying the square of the current through a load by the resistance of that load. In the case of undersized wiring, the cable itself can become a significant load.

A good-quality four-AWG conductor should have a resistance of 0.268 milliohms per foot. Let’s look at an example where we have a run of 17 feet from the battery to an amp in the back of an SUV. Let’s also say the amplifier can produce about 1,000 watts of power, and as such, needs to draw 100 amps of current. Using good-quality, full AWG-spec four-AWG cable, there will be a drop of 0.456 volts across the power wire and 45.6 watts of heat generated. Since most vehicles have a chassis with a similar ground return path resistance, we lose another half-volt or so. Now, our amplifier is only seeing 12.4 volts instead of maybe 13.4 when the truck is idling. This voltage drop limits how much power it can produce without distorting and also makes the amp run hotter.

Car audio power wire is constructed from three common materials: pure virgin copper, recycled copper alloys and combinations of copper and aluminum. It’s nearly impossible to find out exactly what’s in the wires available from various brands. This is why the Consumer Technology Associated created the ANSI/CTA-2015 R2017 Mobile Electronics Cabling Standard. This set of guidelines describes not only the size of conductors (cross-sectional area) but the minimum number of strands, the minimum number of strand groups, the nominal resistance and the maximum allowable resistance per meter. Another important note is that the CTA-2015 standard allows for a maximum of 0.25 volt across the length of the cable.

Our Test Victim

Years ago, some of the staff here at BestCarAudio.com performed extensive testing on more than a dozen brands of entry-level car audio amplifier installation kits. Unfortunately, the worst kit of the bunch had wire with more than three times the resistance of the best in the group. That’s a scary proposition, considering all were called Four Gauge.

We asked around to find some inexpensive amplifier kits and one solution that came up a few times was the four-AWG kit sold by Princess Auto in Canada. Princess Auto is a chain of stores very similar to Harbor Freight in the U.S. We purchased their four-gauge amp kit for our test. The kit claims to include 17 feet of “4-Ga” clear matte power cable, 3 feet of ground cable and a nickel-plated ANL fuse holder with a 120-amp fuse. We measured the power wire, and it came in at 17 feet and 0.625 inch. The ground wire was 35.75 inches. Partially hidden under the fuse holder is a label stating “W/AWG Standard,” and the bottom of the packaging has “1600W” emblazoned across it. We assume that this label implies that a true four-AWG amp kit is suitable for use with an amp that can produce up to 1,600 watts of power.

We’ll use an ARC Audio ARC1000.2 amplifier rated to produce 1,200 watts of power into a 4-ohm load for our test. We’ll use our D’Amore Engineering AMM-1 to set the output of this very efficient amplifier to specific power levels to see how the wire behaves.

Wire Performance Test

If we analyze the chart below, we can see that the resistance of the wire increases as the current demands increase. However, the resistance remains relatively stable around 8.8 milliohms up to 40 amps of current flow. At this level, the amplifier is producing about 450 watts of power to our load resistor bank. If this was a product we were selling, that’s where we’d set the current limit.

As you can see, at current draw levels above 90 amps of current, the resistance started to skyrocket. At 110 amps, which was close to 1,175 watts of power to the dummy loads, the resistance increased to 9.7 milliohms, and the wire was at almost 50 degrees Celsius.

Part of our test included measuring the voltage across the power wire from where it was connected to our supply to where it connects to the amplifier. The voltage drop increased to more than 1 volt across the power wire at just over 105 amps of flow. Had we left the amp playing, the wire temperature and resistance would increase further, and the voltage drop would increase.

How Does the Princess Auto Amp Kit Stack Up?

If we were selling this amp kit and intended to follow the maximum allowable voltage drop of 0.25 volt, this kit would be capable of powering a roughly 350-watt amplifier. Unfortunately, that’s a pretty far stretch from the claimed 1,600 watts listed on the packaging.

If we wanted to be a little more generous, the wire started to heat up when flowing 90 amps of current. If you’re into playing marketing games, then perhaps this is good for an 800-watt amplifier? That said, we’d rather not waste 0.6 volt across the run of wire.

According to the ANSI/CTA-2015 standard, a 17-foot run of four-AWG cable should have a nominal resistance of 4.55 milliohms and maximum resistance of 4.818 milliohms. At 8.783 milliohms, this is almost twice the resistance of a good quality cable. Let’s revise our voltage drop chart and scale the resistance of this cable by 55% to see what happens.

In reality, the difference between the two conductors would be more considerable because the copper cable wouldn’t heat up as much, and the resistance would increase less.

Car Audio Power Wire Matters

It takes power to make power. If you can deliver more voltage to the amplifier in your car or truck, it can provide more power to your speakers and do so with less wasted energy and distortion. Skimping on power wire quality simply isn’t worth the small cost saving. Instead, talk to your local specialty mobile enhancement retailer about using high-quality, full American Wire Gauge (AWG) spec wiring when they install your amplifier. The investment will be worth every penny!

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.