Re: fFINAL REPORT Cu COIL vs Al COIL (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 10 Oct 2007 20:24:46 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: fFINAL REPORT Cu COIL vs Al COIL (fwd)

Hi Adam,

The difference between Al and Cu as far as resistivity is about a 2 awg 
sizes. The Al is larger relatively to 2 awg sizes larger on Ed's setup. 
Both coils are basically 3" in length, 12 turns each, with a diameter of 
3.5". The difference is material and wire size (which we expect both to 
be similar at that point). The diameter will change the inductance 
slightly and inductance is really of no concern in this test.

The AC resistance is very high in both cases as compared to the DC 
resistance (approximately 1000 ohms AC vs. 17 ohms DC at the 5MHz run). 
That's just a rough translation in my head, but it will be somewhere 
near that. About 1/2 that ACR at the 2.5Mhz run. Those numbers are for 
Copper. The aluminum was even higher!

Ed mentioned in one of the posts today that aluminum should be fine if a 
larger diameter is used and he's absolutely correct. If you increase the 
diameter of aluminum accordingly, you have an equivalent copper 
conductor. In the primary coil, this is doable, but on the secondary, 
the geometry and turns would be effected far more and may not be the 
best thing to do (irregardless of losses). Both mechanical and 
electrical to deal with in the secondary. You can of course ignore the 
mechanical and just wind the same size with Al. The problem then is ACR 
and DCR increases. Maybe a couple inch difference in spark length, but 
even that is not a big deal (IMHO).

The main point in all of this testing is that "material directly affects 
the coil by it's permeability". There is a difference between aluminum, 
copper, or any other material used. Radio frequencies affect losses, but 
it can be dealt with when using non-ferromagnetic materials and 
certainly becomes a problem if using ferromagnetic materials.

To say that aluminum is bad for RF is not an intelligent statement. It 
depends on the application (frequency, conductor size, shape, and current).

Take care,
Bart





Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Tue, 09 Oct 2007 15:17:43 -0700
> From: Ed Phillips <evp@xxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: fFINAL REPORT Cu COIL vs Al COIL (fwd)
>
> I forgot, (and am too lazy to go searching through the
> hundreds of posts on this subject) are the two coils
> wound with the same diameter, wire gauge, and turns?
> When you say "the coils are as close to the same as I
> could wind them" are you referring to physical or DC
> electrically?
>
> thanks
> Adam"
>
> 	Same physically.  Same ID and outside length but with different wire sizes of course.  The Al wire was pretty hard and I had enough trouble trying to wrap it around a form which would relax to ~ 3" ID that I wouldn't want anyone to see it - pretty ugly but still did the job.
>
> 	Note that the Al wire size was 0.125" OD, probably nearer #8 than #10.  I was way too cheap to buy #8 copper and make a direct comparison and couldn't find any #12 so did with what I had.
>
> Ed
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