RE: More primary AC resistance measurements

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

Hi Barry:

I have a couple more measurements to make and then I think I'll hang up the
meter leads for a while.  I just wound a two-layer #14 solid coil with no
unused turns, same total inductance as all the others.  It will be
interesting to see if the two-layer construction is responsible for the
elevated resistance and inductance change at higher frequencies, or whether
the unused turns were responsible for this on the two-layer tubing coil.  I
also want to re-measure the #10 stranded coil.  I think there may have been
a measurement error due to the use of some alligator clips on that coil,
but even so, I doubt the error was more than 100 milliOhms or so.  I would
like to polish up the .03" thick ribbon and re-measure that one, but I
can't promise that I'll get to that anytime soon :(.

The graph was created very manually.  I found a web site with .PDF blank
graphs, http://www.engj.ulst.ac.uk/sidk/graph/graph.htm, opened the one I
was interested in with Acrobat, did a screen capture (Alt-PrintScreen), and
pasted that into MS Paint.  Then the fun began, adding hash lines, labeling
axes, and plotting lines, all from Paint.  After all the pixel-level
editing, I converted it to a GIF file in Photoshop.  I'm sure that MathCAD
could have done this in a snap, but you use what you have...

Regards, Gary Lau
MA, USA


Original poster: "B2 by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<bensonbd-at-boo-dot-net>

Hi Gary,
Great measurements.  Thanks for posting them.  

It is interesting that, in going from DC to 800 KHz, the copper tubing
(1 layer) changed in resistance by a factor of 16.23, whereas the number 14
(tight wound) changed in resistance by a factor of 11.58.  The thick copper
ribbon (0.030) increased in resistance by a factor of 53.16.  The thinner
(0.008) copper ribbon increased in resistance by only a factor of 6.51.
The number 7 litz wire increased in resistance, more than the others, by a
factor of 84.33.

    Looking at the data from yet another point of view, w.r.t. the copper
tubing (1 layer) at a median TC frequency of 200 KHz, the percentage of
resistance variation is: 0.030 copper ribbon-14 percent increase, number 7
Litz wire 25 percent increase, number 14 (close wound) solid copper-60
percent increase, 0.008 copper ribbon-40 percent increase.  Copper tubing
appears to be the better primary conductor.  The copper ribbon seems to get
better as it gets thicker.  0.05 inch thick (oxygen free) copper ribbon
might be even better than tubing??

    It would be interesting to see what a number 14 solid copper close
wound (same inside diameter as before) with 30 turns would measure.

    Your log graph looks really great.  How did you do it?
    
Cheers,
Barry