I was sitting here thinking about how people's car electrical systems affect amplifier output. And then I thought of a neat test. Being that I'm 15,000km away from my car right now, I'm wondering if someone on this forum could give this a try and report their results.

1.) Meter resistance (in ohms) between the positive post of your battery terminal, and the positive input terminal on your biggest amp.

2.) Turn the system on at a low level, and measure the resistance again.

3.) Gradually increase the volume level taking measurements along the way.

4.) Finally, at full volume measure the resistance.

This should illustrate how your electrical cabling, contact points, and fusing affect current draw as demand increases.

Merry Christmas

Adam

 

umm, it's pretty much impossible to measure the resistance on a cable that is carrying current, though you could measure the conductance and take the inverse, which would give you the resistance.

a better test would be to have 2 volt meters, one on the battery, and one at the amplifier, accurate to 2 decimal places would be enough.

 

Basically, I'm looking to show how a conductors capacity to carry electrons is deminished as current increases. While I have no proof, I'm thinking that oversized wiring can help decrease voltage fluctuations caused by resistance at high current levels.

 

What Paul said. It isn't the increased amount of current that's the problem. It's smaller gauge wire that heats up that's the problem. Heat causes increased resistance.

As far as voltage drop goes...if the cable you use is rated to handle the current you are drawing then it doesn't take much to see a .5 or so voltage drop. Say you're using #8 wire. The resistance for #8 is like 0.0007 ohms per foot, and you are expecting to draw...I don't know...say 45 amps.

The formula is IxR(per foot)x Length. so I is 45 R per foot is .0007 and length is probably 20 feet. Right there is a .63 voltage drop.doesn't sound like alot, but in the 12v world that's 5%.

Why am I discussing electrical theory on the first of 10 days holidays? I need a beer...

 

hmm i always thought it was resistance that caused the heat...

 

resistance causes heat which inturn causes more resistance and so on and so on and so on and so on

you need resistance to cause heat in the first place

 

Well...

While there is a simple way to account for wire losses, we still have connectors and fuses. That is what the test is targeted at, the combined response of that leg of the circuit.

 

Speaking from a purely electrical, and industrial standpoint, connectors, when properly applied, and properly designed, should have ZERO loss.

unfortunately, car audio companies seem to think that a 1/4" set screw is sufficient for 1/0 cable, this is why I use industrial connectors, where the set screw is at least as big as the hole for the wire.

Fuses would be the only real concern to me, but much of their effect can be countered by running multiple fuses in parallel, so, say you needed a 200A fuse... run 1 150 amp fuse, and 3 more 50 amp fuses in parallel... that way each fuse sees a maximum of 50 amps, all the time and if the others blow, the 150 MAY still keep you running. This gives less load on each fuse, and more paths for the electrons to follow. Again, this is quite common in nidustrial applications. Usually, a 1200 amp fused disconnect will have either 2 600 amp fuses, or 3 400 amp fuses in parallel.

Say each fuse had a 0.1 ohm reading across it...4 fuses in parallel would have a 0.025 total resistance... big improvement.

 

I do more commercial than industrial, but aren't the parallel fuses used only because you're running parallel runs of cable? For a 1000A feeder @600v I generally see parallel runs of a smaller mcm cable (6 cables instead of 3). Or are you saying that in the actual disconnect there can be 6 fuses for the 3 phase feed? I don't think I've ever seen it. I'm not doubting you or anything...like I said, I haven't spent a whole lot of time in Industrial...but I have spent alot of time in the 600v commercial world.

Anyhow...I have one of those fuseblocks with the DVM on it, and when I was running two amps...1x1100 wrms and 2x185 wrms, to their limits the DVM never read below 14.4v. Unless I ran the stereo without the engine running.

I don't know how acurate those things are, but I never saw any voltage drop. So I just measured the resistance across a 30 and a 60A fuse. The 30 reads 1.4 ohms and the 60 is 1.7. Seems kinda high to me...someone else wanna test their fuses and see if you get the same ridiculous numbers?