RE: Water absorbtion of Gray PVC

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

Original poster: "David Trimmell" <humanb-at-chaoticuniverse-dot-com> 

Hi, I have to agree with Dan here. In all reality a <3Kw coil can easily
be wound on un-treated PVC with many years (many hours of total run
times) of use. I will add, though, that a quick rough up with a coarse
sand paper, and then hitting the coil with a heat gun to get it warm and
immediately spraying it with a acrylic sealant, doesn't hurt!

Regards,

David Trimmell

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, December 08, 2003 5:09 PM
To: tesla-at-pupman-dot-com
Subject: RE: Water absorbtion of Gray PVC

Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com>


Although your concerns and comments are valid, its really not necessary
(especially for the mere hobbyist)
to perform this long process of pre-treating a PVC or other hydroscopic
forms prior to winding.

Although your intent is good, i feel your comments may actually
discourage some beginners by making them believe
they need to go through this seemingly overwhelming pre-treatment
process.  This is especially true considering the
comments come from the two most experienced tesla coil firms, Resonance
Research Corporation and KVA Effects.  The beginner
may believe these firm's comments may hold more water so to speak than
the other people on the group.

The important points I think should be made are the following:

1.  Yes, hydroscopic secondary forms such as PVC will benefit from a
pretreatment process as described below especially
in higher power tesla coils (5kW + )

2.  For most small power coils, there is no need to pre-treat the PVC
secondary.  This is based on the experience of many of the members of
this list including myself.  I'm sure if you took a poll, the number of
people on this last that go through the elaborate process of
pre-treating a secondary prior to winding will be greatly outweighed by
the "just wind it" and go people of the list!

Many people on this list will claim sonotube or other cardboard forms
are the worst possible material for a secondary form
and should be avoided at all costs.  However, the best coils i've ever
seen were built with cardboard forms.

Dan



  > TCML,
  >
  > I have to back Dr. Rez on this one guys... We use PVC and
  > fiberglass forms.
  > We have accumulated hundreds of hours of run time on a dozen
  > or more PVC
  > coils all above 10kW. We have a really burnt PVC form we keep
  > in the shop as
  > a trophy...
  >
  > Sand, bake*, seal...
  >
  > Sanding breaks up the surface. HV arcs love to travel down
  > smooth surfaces.
  > We use coarse grit and leave the final finish rough. After
  > surface prep and
  > careful and gradual baking with tungsten strip heater, seal
  > the PVC with
  > commercial HV varnish. There's more to the process but those
  > are the basic
  > steps hobbyists should follow.
  >
  > Will you coil work the same if you don't follow these steps:
  > sure! Same
  > applies to O-rings and spray-on foam insulation.
  >
  > * don't over do this step. 20 degrees above ambient for two
  > hours is all
  > that is necessary IMO. If you use heat lamps, spread them
  > out, put them on a
  > variac and don't put them too close. "Hydroscopic" doesn't
  > mean it's full of
  > water and you have to dry it out.
  >
  > Jeff Parisse
  > kVA Effects
  > www.teslacoil-dot-com
  >
  >
  >
  > snip...
  >
  > All PVC is hygroscopic especially when used at high
  > frequencies. It's best
  > to sand interior and exterior, then paint with 3 separate of
  > Glyptal or
  > other HV insulation. Interior sanding is rapidly accomplished
  > by using a
  > sanding "flapper" on a dowel (or other extender) on an electric
drill.
  >
  >
  >