Re: "best" former material?

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

Original poster: "Ray von Postel by way of Terry Fritz <twftesla-at-uswest-dot-net>" <vonpostel-at-prodigy-dot-net>

John:
Thank you.  The information is helpful.

> > John:
> >  What is it about the materials you mentioned that make them suitable for
> > coil
> >  secondary
> >  formers?  Is it their dielectric constant, lack of water absorption, or
> what?
>
> Ray,
>
> I mentioned Polystyrene, polypropylene and polyethylene for their
> low dielectric loss at TC frequencies.

Isn't this the same as saying that from the standpoint of dielectric loss
at the operating frequency, we could just as well go back to cardboard covered
with shellac?  After all, it has low dielectric loss at the low operating
frequencies
of Tesla coils.

>

> Yet their cost is reasonable.

> But in general, there is often too much concern about losses in
> a secondary form.  One of the things that makes polypropylene
> and polyethylene good is they don't carbon track anywhere as
> much as PVC.

Or certainly not as readily as shellac covered cardboard!

> In any case, the losses in these forms won't
> noticeably affect your electric bill either way.   I wouldn't bother
> with the Pyrex, it's lossy, heavy, brittle, etc.  If I had to chose
> from a bunch of selections like that, I'd chose polypropelene
> or polythylene for their low low losses, and resistance to carbon
> tracking and burning up.  Styrene is low loss, but carbon
> tracks.  The advantage of styrene is it may be a little more
> rigid.  I would probably give more weight to rigidity than electrical
> loss, because the electrical loss is so low anyway.
>
> You could use the 3 or 4 bars of polystyrene to hold the winding,
> but it won't make the sparks longer, and it won't save on your
> electric bill.  Why do you think that the losses are significant,
> and worth taking such measures?

The significance of the losses is that they exist.  Since they exist
they should be taken into account in just the same way as you take
into account any other coil perimeter.  You have to evaluate looses
before you know if you can live with them.  Apparently your experience
tells you that you can live with it.  So be it.

The reason for using the bar method of construction for a secondary is
to minimize the amount of dielectric in the field. It is probably not
significant,
but minimal dielectric also means minimum tracking. You can't burn
what isn't there.

> been used by a number of coilers, usually when a large form was
> not available or was too costly or heavy.
>
> John Freau
>
> >

I would summarize by saying, "Use any electrical insulation for a secondary
form
that doesn't burn easily,
readily available, affordable, and mechanically workable.  You won't see the
difference in the operation
of the coil."

Again, thank you.

Ray