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RE: [TCML] sealing a cardboard form

Dave -
I would venture an educated guess that very, VERY few Tesla coils have actually been built using the expensive Dolf''s varnish as a secondary overcoat. Based on closely monitoring this list for nearly ten years, attending a fair number of Teslathons, and coresponding with scores of TC builders over the years, I estimate that for operating amateur-built TC's of all sizes, the "real numbers" for secondary overcoatings may look something like this:
1. No secondary overcoating at all;
2. Clear varnishes of all types, including oil and water base types (most commonly polyurethane, but also good old fashoned marine spar varnish, etc);
3. Two-part epoxy materials;
4. Dolph's AC-43, "Glyptal", and other types of  commercially-sold "corona dope" insulating coatings.
I think that a very interesting experiment would be to wind at least 5 identical secondary coils, coat 4 of them with the most commonly used insulating material, and then subject them to ever-increasing electrical stress in a large bang-size coil, gradually increasing coupling until insulation failure (racing sparks, turn-turn arcing, etc.) occurs.
I'm strong proponent of evaluating new processes and materials in an attempt to improve the technology. Successful evaluation means pushing the stress levels to the threshold of failure, and beyond. If someone is willing to take the time to evaluate new "stuff", and understands that this unavoidably includes the risk of failure, then let's not dissuade them from trying.
If a small-to-medium size secondary fails this testing, what's the cost? At max, $20 or so of magnet wire, $10 worth of PVC pipe, and a few hours of labor, it's not terribly significant.
If DC Cox (or anyone else) has spent lots of time and money functionally evaluating multiple kinds of other secondary insulating materials before finally selecting Dolph's AC-43 as the very best, then I invite him to share this interesting and useful data with the TCML. 
Personally, I suspect that DC read some Dolph's advertising claiming that it was "good for high voltage applications", found that he could make a profit by re-packaging and re-selling this product at a markup, and thereby claims that it is "the best material" for insulating  TC secondary coils. 
If there really IS comparative test data, developed under controlled conditions, that shows the clear superiority of Dolph's for this specific application, then let's see it.
I happen to prefer two-part epoxy for coating secondary coils, and I have a number of very specific reasons for this preference (that I have shared with the TCML over the years through several detailed posts). However, I do not have side-by-side test data comparing epoxy with other materials, so I cannot prove it's superiority on all possible evaluation criteria. And no, I don't sell any epoxy coatings of any kind.
Herr Zapp

--- On Fri, 7/24/09, Dave Halliday <dh@xxxxxxxxxxxxxx> wrote:

From: Dave Halliday <dh@xxxxxxxxxxxxxx>
Subject: RE: [TCML] sealing a cardboard form
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Date: Friday, July 24, 2009, 11:19 PM

A couple of comments inline: 

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx 
> [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of PAUL THOMPSON
> Sent: Friday, July 24, 2009 3:36 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] sealing a cardboard form
> ----- Original Message ----- 
> From: "DC Cox" <resonance@xxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Friday, July 24, 2009 4:20 PM
> Subject: Re: [TCML] sealing a cardboard form
> >A Tesla coil secondary coilform is subjected to very high potential
> > stresses.  Why not just use a product especially developed 
> to seal high
> > voltage transformer windings?
> Because improvisation and learning is why I do this. If I 
> want a perfect 
> secondary, I can buy one. But why bother?

How many hours do you want to spend to find out that your 'great idea' was
an engineering rathole and that your time and materials have been wasted.
There are a lot of people offering advice here and the reason that people
keep coming back to specific things is that they have been tested by the
community and have been found to work the best.

MMC's, specific coatings, designs for spark gaps, etc...

> > Dolph's AC-43 is one such liquid especially designed with 
> high dielectric
> > resistance, and anti-tracking properties.
> Do you sell this stuff or what?

He probably does but I would doubt that he makes a lot of money off of it.
This is especially a factor considering just how many gallons of other
paints / varnishes / coatings / etc... he probably tried out before he found
that Dolph's worked the best.

I would hate to see the number of 5-gallon tubs of very expensive stuff he
has with just a couple pints taken out and a faint "Oh Snap!" still hanging
in the air.

> >
> > You certainly can take a chance with other products, but if 
> they don't do
> > the job then you have to completely replaced the coilform 
> and rewind the
> > coil.
> We learn by doing.

Or by watching other people doing the same thing and learning from their

Set RANT=off


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