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

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Date: Tue, 09 Oct 2007 17:47:09 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: fFINAL REPORT Cu COIL vs Al COIL (fwd)


Hi Ed,

Neat! So basically we have a #10Al vs. #12Cu (which should be comparable).

I calc'd [17.47mohms, 9.558uH for Cu] and [11.73mohms, 9.546uH for Al]. 
I think the Aluminum you have has a slight higher resistivity than the 
common spec, but it's close. This may account for a small portion of the 
difference.

	Based on the measured resistance and my guess that the wire length is 12 feet in each case [measured that out originally but may have trimmed to resultant coils to whole turns, the resitivity of the copper is about 140 mWcm and that of the aluminum is 238 mWcm. That ratio is close to yours.  Of course the AC resistance should vary as the square root of the ratio.

In this case, we expect the two materials to act similarly. And it looks 
like they did! So, it's a good assumption that if the two materials were 
of the same gauge, there would certainly be a considerable difference 
and I think in this particular case, we would see slightly over the 
common 1.6 value. The slight change in L is due to the wire diameter. L 
would have been identical if using the same wire size. 

	The fact that the inductances are that close is because I adjusted the coil lengths to try to tune with the same Q meter capacitance at each frequency to make it easy to plot the results in Excel.  The winding is crude enough that it's not possible to make your comparison meaningful.

These measurements show what has been discussed and it acted out just as it 
should have. My comment about Q being 1.5 times higher even with the 
larger Al was obviously wrong. I must have looked at Cu and Al for this 
particular coil type and commented from that (which of course will never 
work for this size coil). But all in all, the material acted as should.

Thanks for making that measurement. As your comparing apples for apples 
with the Q meter, the calibration is unnecessary for the ratio which is 
what was most important.

Take care,
Bart"
	I agree that in principle the Q meter calibration shouldn't affect the comparison.  Problem was I did the whole frequency run for each coil at one time and it's difficult to reset the RF drive very accurately since it's way down the meter scale.  I thought the consistency was pretty good but not what one would like.  All in all this was a fun excercise and just tells me that if I decided to wind an aluminum primary I'd use bigger tubing than for copper.  I still suspect that, even with an NST, any primary that doesn't get "too hot to handle" doesn't have enough loss to have much effect on streamer length.  Could be wrong of course.  All in all a fun excercise.

Ed