I've spent the last 8 months doing a variety of audio related research and design. I've researched and modified a number of Class D home amplifiers, I've designed complex crossover networks for hi-fi home theater use, and I've designed proper sub and speaker boxes using tools many of you don't even know exist, modeling frequency response, cabin gain, cone excursion, impedance, and a variety of other factors. WinISD basic edition is a child'* toy compared to the stuff I've been using.

I came back here and saw a few things I didn't agree with, so here'* a writeup that will help some of you design a car audio system properly.

This writeup will be focused on power and how much power your car can handle.

Alternators

Most GM cars come with a small variety of 105 amp rated alternators, most commonly the CS130D I haven't been able to find the ratio of the crank pulley to the alternator pulley, but lets assume that in a typical scenario, we're getting 90amps while cruising.

Wiring

Most GMs come with factory 4 gauge copper wiring. This is all well and good for the stock system, but problems can arise when you put greater load on them. More on that later.

Crutchfield actually has a pretty good way to determine if your electric system is capable.

In order to calculate your needed wattage, first determine the RMS power rating of the amplifier you are using. Lets use the JL 1000.1 because its very popular and well rated. This amplifier is rated for 1000W RMS.

Next, double that rating. Why? Because amplifiers (even automotive Class D) are typically 50% efficient. This means that in order to provide 1W of power, it needs to draw 2W of power from the electrical signal. The extra 1W of power is dissipated as heat, which is why amps get hot when run at high volumes. In our case, the JL 1000.1 is at best 50% efficient, so lets use that. According to calculations, we need 2000W total. Now, since wiring is rated by amperage, we divide 2000W by 13.8V to get the amperage. In this scenario, we are left with 145 amps if we are to use to its maximum potential.

The following chart provided by crutchfield.com outlines the size **copper** wire you will need:

.

I say copper because copper clad aluminum does not have the same capacity, and you will typically need to increase wire diameter by 1-2 sizes to compensate.

According to that chart, we would need a minimum of 4 gauge in our engine bay (brand new, not corroded), and 2 gauge running to the trunk.

Now back to the alternator problem. As we remember from earlier, we need 145 amps. However, our alternator only produces ~90 amps at idle at 13.8V. Lets say in a magical scenario we do produce 100 amps at 13.8V. This would allow us to output ~700W from our 1000W amp.

What happens when we try to produce more power than our electrical system is capable of? Our voltage drops, our lights dim, and heat starts to rise in our alternator and our wiring.

So what is a factory system capable of producing? Safely, around 500W. You have to consider that your sound system is not the only component in your car that draws electricity.

Good write up

Good writeup as said above...this needs to be stick'd

Great information. This is also the reason that Digital amps such as the JL HD series and the Alpine PDX series are usually what I recommend since they are closer to 90% efficient.

Great post, easy to understand, clear reasoning, and telling us what happens in the real world.
As I understand it the ignition draws 4-6 amps, a/c & heater around 10, lights around 12-14, rear defogger another 12, wipers up to 15, other sevices (ecm etc) another 5 or so.
A drive on a cold wet night leaves only around 30 amps for your stereo assuming the alternator is ok so more than 350 watts and you are approaching full load for the charging system, bad wiring will make matters worse.
I guess the moral of the story is if you want a concrete shattering stereo upgrade your alternator and make sure your wiring can handle the load.
Roger.

Wow X, great effort here but you kind of missed the boat. You said that you spent 8 months doing audio related research and design and then gave some examples but none of which were directly related to car audio, did any of that research and design deal specifically with car audio applications and products? There are a few half truths and opinions passed off as facts so i'm gonna pick up where you left off to try and clarify a few things.

If I were to believe your write up, my class D amp that'* rated at 50% efficiency is only going to put out 50% of it'* rated power, so my 1000 watt amp is now a 500 watt amp, unless I feed it 145 amps of current, even though it'* only got 105 amps worth of fusing on it. That makes absolutely no sense! I'm not sure where you got your info from but that'* not how it works. Also, to say Class D amps are typically 50% efficient would only be true if you added "when wired down to 1 ohm" to the end of that statement. However, you happened to pick a great example by using the JL 1000.1 because it is not a very efficient amp so it may very well be only 50% efficient at best. But that'* not the case with most good Class D amps. Mine for example, the Sundown SAZ-1500D is 86% efficient at 4 ohms. But the thing manufacturers don't tell you is that as the ohm load goes down, so does the efficiency. That'* a very important reason I don't pay too much attention to efficiency when getting a sub amp. The SAZ-1500D is rated as follows:

1 ohm mono 1500W x 1CH
2 ohm mono 800W x 1CH
4 ohm mono 400W x 1CH

I don't know of many people who are gonna buy an amp that does 1500rms only to run it at roughly 25% of it'* abilities. The amp makers never advertise the efficiency at 2 or 1 ohm cause it'* not as impressive of a number as the 4 ohm rating. It'* called marketing. Much the same as advertising an amps max watt output. But continuing on with your example, you're saying that you need to feed the JL 1000.1 with 145a of current in order for it to put out 1000rms....you do realize that amp only has 3 35a fuses, totaling 105a, right? So you think you can feed 145a of current into that amp without blowing it'* fuses? That right there should have been a dead giveaway of the fault in your logic.

But back to efficiency, contrary to popular belief this rating DOES NOT determine how much power the amp will be able to put out. If that were the case, my Sundown SAZ-1500D would not be able to put out over 1900rms @ 1.23ohms on 12.85 volts as it did in this clamp test. Keep in mind that this amp is only 86% efficient at 4 ohms, in the test it was wired to 1.23 ohms so the efficiency was considerably lower than what it'* rated at. So the moral of the story is that efficiency should be considered but not a deal breaker. Case in point, the JL 1000.1

As for the old Copper vs. CCA argument, yes copper is a better conductor of electricity than aluminum but it also costs quite a bit more as well. Aluminum conducts roughly half the capacity of copper, so does that mean if you run CCA wire from your battery (with a voltage of 14.4) to your amp that you're only going to get 7 volts of power to it? LMAO. No, that'* not what that means. As you all know, electricity takes the path of least resistance, and since the aluminum wire is clad with copper, the electricity will flow along the copper just fine, losing out only the difference in what the core can carry. The real world result of that is measured in tenths and/or hundreths of a volt. So you've got to decide if it'* worth it to pay $1.50 a foot for CCA wire or $3.50 a foot for copper, is that one or 2 tenths worth it? For those of us not competing or running very high powered setups (3k and up), the difference will be negligible. But if it helps you sleep better at night, knock yourself out I've been running over 2k watts in my car for the past 3 years and have CCA wire and it'* not oxidized and the case isn't hardened due to heat, my amps don't get hot and my lights only dim when i'm clipping, seems to work perfectly fine!

Here'* the clamp test results in it'* entirety:

SAZ-1500D:


POWER : 1970 Watts
AMP VOLTAGE (measured) : 49.25 V
AMP CURRENT (calculated) : 40 A
ACTUAL IMPEDANCE (calculated) : 1.23 ohms
SUPPLY VOLTAGE : 12.85 V

Power clamp video
http://www.sundownaudio.com/misc/_AM...D/CIMG2493.MOV

Voltage Measurement video
http://www.sundownaudio.com/misc/_AM...D/CIMG2494.MOV

Some amps are indeed much more efficient. I simply used the JL 1000.1 to point out how easy it is to be mislead into thinking that your car can support gobs of power. The post was made to raise awareness.

Ugh...

I used the 1000.1 as an example. Obviously if someone knows their amplifier has a different efficiency, it is irrelevant. Your particular amp is one of the best amps on the market and does in no way represent the vast majority of amps that people will be buying. The concepts I pointed out still apply. Also, fuse ratings are not by any means a limit of the amp'* current draw as they are only there for short circuit protection. What I said still holds true. If you know your amp'* efficiency, do the math and you'll figure out what it will draw under full load.

As far as CCA, I cannot tell you how many headaches it gave me in my car. I literally wasted 4 hours of my time and $100 of money I could barely afford replacing a starter only to find out that the CCA I had wired to my block ground had SEVERED from corrosion an inch away from the terminal. Yes, there was 2" of 1/0 gauge CCA clamped in the terminal, and I riped it off like a sheet of paper when I wiggled the wire. It is absolutely horrible to use in an engine bay where it will be exposed to heat fluctuations and moisture. You might have a different opinion, but the simple fact is that its pure garbage in that environment. It corrodes very easily and loses voltage significantly faster than copper. In fact, 1/0 gauge CCA is slightly worse than 2 gauge copper from the research I've done, only copper doesn't corrode as quickly.

Trunk is a different story of course, but my personal preference is to stay away from it.

Ask John, there'* a reason this wire starts electrical fire in houses and consequential lawsuits. Not in my car. Its not just about the power handling man.

I have no problem with your example at all, my problem is with your misinformation. I promise you that little JL 1000 watt amp won't pull anywhere close to 145a....my Sundown does nearly twice the rated power of that JL yet in the clamp test I provided it only pulled 40a. The Sundown is rated at 86% effeciency but that'* at 4 ohms, in the test it was wired to a little over 1 ohm so the efficiency was far closer to 50% than 86% for sure. Not only that, but 145a is pretty much the max current capacity of 4ga. wire and i'm sure that JL wouldn't use such a small guage power/ground connection if it was necessary to max it out in order to get rated power out of the product. Not only that but 4ga. wire, on an amp that puts out 1000 watts and needs 145a of current to do it....not the best wire for the job considering most people have power wire run of 15ft or better.

i cant open your vid but generally the rule of thumb for electronics engineers is calculate normal operating current and double it for fuse protection, so if you have 50a normal operating current then there would be 100a fuses.

you cant really compare dc input current to ac output current theres too many different variables. i do know im running 1200w on my stock batt, alt, and wiring, and once i got everything tuned and cleaned up it doesnt even dim the lights unless your stopped for a little while