Re: Essex magnet wire

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Gary,

I have noted that if one uses Sonotube (cardboard) for the primary form and
you slightly wet it, the Q drops like a rock.  You may try a damp paper
towel inside the secondary of a plastic form to see the dramatic affect
water has on a coil's Q.  Interestling that you have found that the coating
on the wire is also "hydroscopic", I think is the term.  Such things could
make one heck of a humidity meter...

Cheers,

	Terry


At 02:51 PM 4/1/2001 -0500, you wrote:
>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.
>
>Lots of gotchas in this business!
>
>Gary Johnson
>