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.
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?
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.
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.
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).
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?
