Re: Essex magnet wire

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Gary,

On 1 Apr 01, at 14:56, Tesla list wrote:

> Original poster: "Gary Johnson by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <gjohnson-at-ksu.edu>
> 
> As I report to this list aperiodically, I am working on a solid state
> driver to drive a Tesla coil secondary directly at the base (no
> primary).  A knowledge of the input impedance is very important in
> this application, and I have been side tracked for some months trying
> to make sense out of my measurements.  I reported a couple of months
> ago that humidity was a factor, and I now have some more information
> to share about humidity.
> 
> I bought a spool of 14 gauge Heavy Soderon magnet wire from Essex in
> 1994. I recently wound a coil from this spool on a section of 8 inch
> PVC pipe, close wound.  I put the coil in an oversize styrofoam box
> with an electric skillet filled with water, and measured the input
> impedance as the relative humidity rose from 30 percent to 100
> percent.  The impedance rose by 17 percent, but the dc resistance rose
> 13 percent because the temperature increased.  A 4 percent difference
> is close to my measurement uncertainty, so I cannot be positive that
> humidity has even a small effect on this coil.  There was condensate
> on the winding when I took the panel off.
> 
> When I was getting into this impedance measuring activity, I bought
> three more spools of Heavy Soderon magnet wire from Essex, in 1997,
> (16, 18, and 20 ga).  Doing the same test with coils from these spools
> resulted in changes in input impedance from 200 to 300 percent, as
> humidity rose from 30 percent to condensing.  It is my guess that the
> wire coatings on these spools soak up water from the atmosphere, and
> that water in the coating contributes a significant fraction of the
> total impedance (maybe 20 - 30 percent) even at ambient relative
> humidities below 50 percent.  It is also my guess that Essex made some
> minor change in manufacturing process between 1994 and 1997 that
> caused this vast change in hydroscopic or hydrophillic character in
> the Heavy Soderon coating. 
> 
> It is also my belief that input impedance is an important parameter in
> disruptive Tesla coil operation.  I see reports on this list of some
> coils that just do not work as well as it seems like they should, and
> I would not be surprised if some of these were built with water
> absorbing magnet wire. I don't know of any way to tell if this is a
> problem by just looking at the wire.  One would need to measure the
> input impedance or the Q in non-disruptive mode for two different
> humidities.

I once did exactly that in conditions of good isolation. The 
resonator in question had a Q which measured 320 on a day when 
humidity would have been about 10% and 300 on the following day when 
humidity would have been around 80%+. Since R is inversely 
proportional to Q that is an ESR change of less than 1%. I have found 
that streamers from this coil do not propagate as far in higher 
humidity and I attribute that to ionization phenomena.
       I once thought base impedance mattered in a disruptive coil 
but after long consideration came to the conclusion that it didn't.
Reason - it is a simple transfer of a block of energy. Zbase would 
have an important impact on a CW drive system.

Regards,
malcolm