Originally posted by APT CSVT:
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.
[b]
Do this one 80 amps of current at 1 ohm, according to your interpretation you need 80V for it to be possible(80=80*1) I think we all know most true 800-1000 watt class AB amps will draw this amount. Now figure 14V with 80 amps R=.175 Ohms. So you going to say that in order for an amp to draw 80 amps it has to be at .175 Ohm! I think there is a more advanced law that has efficiency figured in. I haven't looked for it yet, most likely will be in my calculator as well (HP 48G)
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).[/b]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
