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 Duncan,

On 3 Apr 01, at 14:06, Tesla list wrote:

> 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?

Exactly my reasoning.
 
> 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

I wasn't the least bit concerned about a drop in unloaded Q of less 
than 1%. 

Regards,
malcolm