Contour Enthusiasts Group Archives Forums Modifications Audio what gauge wire do i need?

R = R. If you are measuring the voltage across the wire, then that is the resistance you should be checking the voltage across. Wire should have very little resistance, almost zero. We really don't care what the resisance of the wire is when computing current draw. What we want to know is the resistance of the load, or speakers in our case. We use the nominal 2 or 4 ohms for exaplme, but really should be measured for acuricy.


Your calculations are not quite right.

80A into a 1 ohm load = 80V, 6400w ((80^2)/1)

I seriously doubt you are actually drawing that much current with a 1000w amp. 1000w into 1ohm (1 ohm is most current draw) is only 31.62A.

Here's where I think the confusion lies. The voltage I am using is not the DC voltage out of the batter or alternator. It is the AC voltage measured at the load (woofer) after the amplifier. No where does the 12.5V or 14.4V come into play, except that the amp can provide the voltage gain from battery to the load.

BTW, I have the same calculator (at home).

Actually the resistence in the wire is one of the reasons why you want bigger cable. How else do you account for voltage loss between the battery and at the amplifier. There will be a loss, it of coarse depends on the current as well. But the cable itself has to have some resistence, how can it not?




At 100 percent efficiency maybe yes, but what amp is 100% efficient. A class AB is at most 35%, the rest is turned into heat. To even that equation out (my math is rusty, sorry) 100/35=2.857 31.62*2.857= 90.28. Maybe thats not the way to arrive at this solution, like I said its been awhile but no way does a 1000 watt true power amp draw 31 amps. Fuse ratings for PPI A600 is 60amps, a Hifonics Zues (old school seies 6) was 80amps and it would blow those fuses all day. I have an inductive amp probe (meter that clamps around the power wire), on a class D rated at 1000 watts the amp drew a peak of 123amps at clip. I know for sure it was not putting out 6400 watts.



I see what you are saying about the AC voltage coming from the amps output. That is not relivent, (maybe relivent is a bad word to use, maybe not required instead) but the DC voltage from the car is. The power supply is demanding from that and amplifier power supplies run off DC current from the car. The amplifiers demands are the amperes that are traveling through the power wire. That is what should be calculated.

Dnew any thoughts from you?

Seriously doubt it?

Okay, here is the first example I came
across in some back issue mags.

This particular amp is a Clarion. Model
APX1000.2. It's rated at 270Wx2 at 4 ohms,
525Wx2 into 2 ohms.

The test was performed with a supply voltage of 13.8, and 2.35 volts of signal input. The results were:217.56 watts per channel in 4 ohm srereo, and 761.70 into 4 ohm mono. I know, so what?

At full power in two channel mode the APX1000.2 proved 56% efficient, normal for amps of this type [class AB]. It posted a much better 67% at full output in bridged mode. Both numbers are pretty respectable for a class AB amp, where typical efficiency measures about 50% at full power. At it's lowest measured voltage [12.6] the amp consumed 89.5 amperes. Although Clarion doesn't list an idle current measurement, we measured it drawing an acceptable 2.1 amperes with no signal input.

Auto Sound & security 4-01

Yes, the wires do have resistence. This is exactly why you have different gauge wire requirements for different lengths. But it is usually not taken into account for calculating current draw because it's relative resistance is so minor compared to a 4ohm load, for example. A one ohm load would get a lower percentage of the power compared to a system with a 4ohm load, if the total current were the same.



31A that I calculated / 35% efficiency = 88.6A current draw. That's my confusion, then.

123A draw at 35% efficiency = 43A into 1ohm for example is 1853w actual output.



True, and see next post.

Wonder where Dave is...

I think I'm on KnuKonceptz side of this argument. The effeciency of the amp would play a big part in the amperage draw that a amplifier requires.

Apt, I understand where you are coming from, but I think you are looking at the wrong end of the amp to get the results you need. What you are measuring is the amperage at the output of the amplifier, but you should be measuring how much juice it takes to create that output. Your math is correct, but you are just looking at it the wrong way.

Damn, that was tough to stick up for Knu!!

That's where my biggest error lies. Efficiency. I realize nothing's perfect, but did not realize that it was that low (~35%), wow! I would have guessed in the 85% range.

Just be glad that there are no Class A amps in cars! There would not be a need for heaters.

Hey I have one! It is a Soundstream Picasso. Gets hot as hell!

The Picasso is a class A amplifier??? wow, i had no idea anyone made one.

That is what the box says. It is a very nice amp.....compliments my HU nicely.