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Re: fFINAL REPORT Cu COIL vs Al COIL (fwd)
---------- Forwarded message ----------
Date: Mon, 08 Oct 2007 23:21:50 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
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.
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. 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
Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Mon, 08 Oct 2007 17:18:01 -0700
> From: Ed Phillips <evp@xxxxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Subject: fFINAL REPORT Cu COIL vs Al COIL
>
> Here is a final report on the experiment I ran to compare aluminum
> and copper conductors at RF. The coils were as close to the same as I
> could wind them without going to the trouble of putting them on a form.
> Just air core with masking tape to hold them in shape, hardly an optimum
> design but good enough for these measurements. Table looks OK here and
> hope it comes through. If not will resend IF anyone is interested. I've
> had my fun so the effort is not in vain.
>
> Al Cu
> _______________ ______________
> f Q C Leff Q C Leff Q
> (Cu/Al)
> 5000 565 103.5 9.78 655 102.2 9.91 1.16
> 4500 547 129 9.69 625 129 9.70 1.14
> 4000 515 164 9.65 600 163 9.71 1.17
> 3500 505 214 9.66 565 211 9.80 1.12
> 3000 479 293.5 9.59 535 291.5 9.66 1.12
> 2500 438 428 9.47 495 423.5 9.57 1.13
> 2400 425 463 9.50 490 460 9.56 1.16
> 0 0 0
>
> Frequencies in kHz, capacitance in uufd
>
> Data Al Cu
> WIRE 0.125" #12
> Rdc mW 12.3 17.3
>
> Bottom line is that the Q of the copper coil was close to 15% higher
> than that of the aluminum coil wound with a larger conductor. The
> inductance of the copper coil was about 1% higher so, assuming the AC
> resistance of the wire was independent of turn spacing, for the same
> inductance its Q would be 1% lower and the ratio of Q's would be about
> 14%.
>
> Here's some tortured reasoning saying this difference is reasonable
> and about what be expected. Per simple theory the ratio of the AC
> resistance of wires of the same size should vary inversely as the square
> root of the resistivities and should scale with wire size as the inverse
> of the diameter. Based on this I think it's safe to say that,
> independent of wire diameter, the ratio of AC resistance to DC resistance
> should scale inversely as the square root of the DC resistance. This is
> certainly comparable to the observed 14% and probably not coincidental.
>
> I should mention that these data were measured with a 50 year old [at
> least] Boonton 160A Q meter with "swap meet" calibration. All of the Q's
> were high enough that I had to use the X2.5 setting on the drive meter
> and it was mighty difficult to make sure the adjustment was the same each
> time.
>
> Ed
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