Re: Essex magnet wire

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

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi Gary, Malcolm, All!

<snip>


>> It is my guess that the
>> wire coatings on these spools soak up water from the atmosphere,

<snip>

>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.


Could it be that any adsorbed water simply acts as a parallel leakage
path to earth, i.e. shunt resistance?

The insulation used on wires contains polar groups - in the case of
polyurethanes and the like there's plenty of C=O groups which carry a
permanent electric dipole.  Water molecules being themselves polarised
would tend to stick to any polar layers on the insulation, simply
being adsorbed onto the surface, and a surface layer of water
molecules will provide a conductive leakage path for any charge "up
top".

If true, I would predict that coating the coil with a thin layer of
something non-polar, like polythene, should reduce this problem.
Unfortunately, applying such a coating is not going to be simple.  If
you had high temperature insulation on the wire, you might be able to
get the whole coil powder coated somewhere, but this involves cooking
the whole thing to a couple of hundred C so you do need high grade
insulation to start with, plus there will be a risk that during
heating, turns will come loose en masse as the wire expands.
Alternatively, you might get away with painting on a solution of
polystyrene dissolved in a suitably volatile solvent, but this is
going to be messy.  Likewise with molten paraffin wax.  Bit of a pain
whichever way you go.  I have coated a couple of small coils with
beeswax.  This was a bit messy, but as it melts at lowish temperatures
it's really quite nice to do from a technical viewpoint - no loose
turns of wire and no burned fingers.  Also, it smells good ;-)

Just my 0,2 nanometres' worth.

Dunckx