zoomer

iTrader: (3)

resisttivity is the reciprocal of conductivity and is the bulk property of the conductor.. yes copper has definitely less resistivity and more conductivity that aluminum. About 30% less or conducts about 50% more...
Resistance per length of wire depends on resistivity and the cross section.. look it up for you beenie cap guys..
http://en.wikipedia.org/wiki/Resistivity

what that means is that for equal resistance in a cable the aluminum one has to have 50% greater cross section . and would be cost effective if aluminum where 33% cheaper than copper (this is high school math guys)

I cannot find any standard tables for resistance per foot for CCA and it would also depend on how much aluminum vs copper there is.

there you have it way too much work for sunday morning

and your statement that copper conducts more current just does not make any sence.. the amount of current that flows depends on ohms law I=V/R where R is the combined resistance of the car battery and charging system, the wire, and the load the amp is presenting at any time depending on power draw (or how loud you want it and the music waveform)

JohnVroom

My point is to be careful, I probably overstated the concept, but identical cables of 4 gauge copper vs aluminum that both read an identical .1 ohms are not identical as far as their current carrying capacity, so ohms law while applicable is a little misleading (in fact simple DMM use will be misleading, the resistivity would need to be measured under load). resistivity of the valence electrons and all that... is the crux of ohms law

to oversimplify a 16 gauge and a 2 gauge copper wire can measure the same resistivity...


probably worth posting the relative conductivity of metals: Conductive Materials or Metal Conductivity - TIBTECH innovations -

edit: deleted link as the link as I couldn't tolerate reading it, interesting to theorists only

zoomer

iTrader: (3)

John... Just for the record, I am an electrical engineer and spent the last 25 years with a major electronics test equipment company. I would be happy to take this discusssion private.. leave me a private message and I will even be happy to call you... my dime.

But.. first off. you cannot accurately measure such low resistance with standard DMMs. the accuracy and precision is just not good enought. so no wonder you measure both the same.
Ohms law holds perfectly here. Valance electrons what?
Yes I did post a conductivity table from wiki.. this is not rocket science... and unless there is appreciable temperature rise.. which I doubt. but I would be happy to entertain data regarding this... the current the conductor carries wold not affect the resistance

Haunz

iTrader: (3)

^ like he said. Your DMM may measure the same resistance putting a couple of milliamps through the conductors.. now try and pass 100amps of current and measure the reistance..

This is probably the #1 reason why aluminum wire is coated with copper.

zoomer

iTrader: (3)

it is probably coated to make it look like copper.. Aluminum wire is used exclusively by your power utility cause of cost and weight.. No corrosion issues..

JohnVroom

Valence electrons: it is the resistance of the electrons attaching and detaching from the metal atom that determines conductivity (the electrons in copper move around easier than aluminum and much more so than steel)
this is the fundamental root of ohms law (I still believe in electron flow)

p=R A/l
p=static resistivity R= resistance due to material A= cross sectional area l=length of conductor
the resistivity of a length of wire is a combination of length, area, and resistivity of the metal

In the world of power lines with miles of cable this is a significant issue to design a system around. But in car audio again my point is using a DMM you will not see the difference between copper or Aluminum in an automotive application (I probably should have said in ohms (or voltage) unloaded). If you measure amperage during a full power run THEN you will see the difference which when you talk about runs of 0 gauge wire and 10s of thousands of watts turns this into a significant issue. If I was running a modest 1000 watt system I would be wondering why I was reading this far into this thread.

The bottom line is always cost and aluminum has a significant price advantages so CCA is a needed product, full copper lines are still available for a price. But the buyer should be aware of the consequences of CCA and you will not detect it at the store, you will discover the limitation in practice. Now ask me again why I recommend 4 gauge for small systems and 0 gauge for medium systems.

Haunz

iTrader: (3)

Who cares what it looks like ? The layer of aluminum oxide that will form on aluminum is an issue, and as I say is probably the # 1 reason to coat the wire... ever try to solder aluminum wire?

Haunz

iTrader: (3)

I run nothing but 2/0 or larger COPPER wire for any of my installs, for the record..

Robin W.

It's pretty well known that Aluminum isn't as good a conductor as Copper, but what about all the Brass fuse holders/distribution blocks/battery terminals/ring terminals not to mention the total number of connections between the battery and the amp and back to the battery.
Electrical Conductivity of Materials
The above page uses copper as a base line or 100% with the other materials compared to it. Brass is ~28% as conductive as copper and Aluminum is ~61%.
Where do you normally see failures in an electrical connection? In the middle of the wire? Or at the battery/ring terminal/fuse/distribution block/amp???

I'm not saying the wire isn't important, but every connection you make is just as important as the wire you use. Look at the system as a whole when trying to reduce the total resistance of your power/ground wiring, not just go big on the power wire and think it's perfect.

Just my $0.02

Dukk

...but....they're GOLD plated!!!!!