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PVC, Re. Bert's response on Pyrex
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From: Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent: Thursday, March 05, 1998 12:50 AM
To: Tesla List
Subject: Re: PVC, Re. Bert's response on Pyrex
Tesla List wrote:
>
> ----------
> From: Alfred A. Skrocki [SMTP:alfred.skrocki-at-cybernetworking-dot-com]
> Sent: Tuesday, March 03, 1998 3:14 PM
> To: Tesla List
> Subject: Re: PVC, Re. Bert's response on Pyrex
>
> On Wednesday, January 14, 1998 6:10 PM Eleanor Flood
> [SMTP:eflood-at-bellsouth-dot-net] wrote;
>
> > Tesla List wrote:
> >
> > Heck even well
> > > > baked out cardboard tubing that is saturated with polyurethane and allowed
> > > > to dry under heat is superior to glass!
> > > >
> > > <SNIP>
> > >
> > > Alfred,
> > >
> > > Got to disagree with you a bit here, Alfred. The difference in
> > > dielectric loss between PVC and glass is really not all that great...
> > > and Pyrex (at about 30) is actually about 1/4 as lossy as PVC. Even soda
> > > lime glass is only 1-2X as lossy as PVC. While using glass, or PVC for
> > > that matter, as a dielectric in a Tesla Coil tank cap would be quite
> > > lossy, use of this material in a coilform is a significantly different
> > > application. PVC, although quite lossy, makes an excellent coilform due
> > > to it's excellent insulating properties after proper pre-treatment. Its
> > > dielectric loss properties have relatively little practical impact on
> > > secondary Q when compared to other losses in an operating system
> > > (streamers in particular...).
> > >
> > > Jim, your Pyrex coilform will work just fine.. and may actually have a
> > > higher Q than if you wound it on PVC.
> > >
> > > At no loss for words in Illinois... :^)
> > >
> > > -- Bert --
>
> I have to disagree with Bert! First he is compairing PVC to Pyrex which IS
> NOT what I was talking about! I have built secondaries out of; open wood
> frames, cardboard, PVC, polyethylene, plexiglass, vicor glass, and Pyrex
> glass. I found that IF you bake out the cardboard and then saturate it with
> polyurethane it has less losses than ANY glass or even plexiglass and is
> second to Polyethylene! The key factor is the cardboard MUST be totaly
> dried out befor being sealed in with the polyurethane.
>
> > We are now using afore mentioned coated cardboard tubing for secondary
> > coil. Planning a PVC one shortly. Note a reference to proper
> > pre-treatment. Please, how?
>
> Coat the PVC with polyurethane inside and out before winding the secondary
> the coat again when done.
>
> > Plan to make coil as open air as possible by cutting slots lengthwise in
> > PVC about 1/4' apart, this is just a thought, would it be worth the
> > trouble?
>
> NO! If I understand you correctly you are talking about laying the wire in
> precut groves in the PVC, this will increase the distributed capacitance
> and thus lower the secondary output.
>
Alfred,
My original reply was regarding an earlier post to answer a question
about Pyrex from Jim Heagy. Although my response was requoted in the
last post, it lost some of its context since the earlier posts were not
also requoted. It was the earlier posting that directly compared Pyrex,
PVC, and cardboard coilforms.
However, I still stand by that post. There's a BIG difference between
using glass, Pyrex, or PVC as a dielectric in a tank capacitor and using
it as a coilform. PVC and Pyrex make excellent coilforms based more on
their dielectric strength and low leakage current than their dielectric
loss characteristics. Dielectric losses in a coilform are simply more of
a secondary (npi :^)) concern.
However, the simple fact is that Pyrex, with a loss tangent of 36-40 x
10^-4, has less than 1/20 the dielectric loss of PVC, at 800-1200 x
10^-4. Heck, Pyrex was even used as a coilform by Breit, Tuve, and Dahl
for their oil-immersed 5 MV, 100 kHz coil ("High Voltage Laboratory
Technique", page 109, Meek and Craggs). While they probably would have
used PVC had it been available back then, I doubt that cardboard would
have worked as well as Pyrex.
I also contend that, although you might be able to measure differences
in instrumented Q between identically wound coils on these materials,
there will be virtually NO performance difference when the sparks are a
flyin', since other factors (streamer losses in particular) will easily
drop the effective secondary Q by an order of magnitude.
However, if you've got a leaky coilform, that's a different story. I'm
not disputing that you can make wooden or cardboard coilforms that will
work well after proper pretreatment. And for larger coils there may be
no other readily available, affordable alternative. Heck, Ed Wingate
gets great performance from large cardboard resonators with no
pretreatment! However, I also suspect that cardboard's voltage-standoff
and leakage current characteristics are not as good as some of the other