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Re: [TCML] 6" Tesla coil plexiglass secondary - FOR SALE



Well, certainly not "advertising hype".

When I originally made the secondary, I followed the recommendations of TC guru Richard Quick, an early contributor to the mailing list (check the archives). A good summary of his recommendations in regards to secondary construction can be found here:

http://www.capturedlightning.org/hot-streamer/stk/tc/coilbld.htm

His main objection to PVC was its hygroscopic characteristic (it absorbs water). The moisture can cause inter-turn arcing in the coil. He (and others) recommend baking a PVC form and sealing it prior to winding. Also, PVC pipe often has surface unevenness that can make winding the coil tightly and evenly somewhat challenging.

To avoid these issues, I special-ordered the extruded 6" diameter, 1/8" wall plexiglass tubing from a wholesale supplier and followed Quick's exact recommendations, including the use of the bottom grounding plate. The secondary grounding strap is held against the secondary grounding plate with a thick rubber band (I cut mine from an old inner tube). The system works quite well on other coils I have built.

I also sealed the ends of the coil with 6" plexiglass cutouts and epoxy. I did not use solvent-based plexiglass cement or RTV to avoid detonating any trapped vapors inside. I drilled a very small hole in the center of the bottom end cap to equalize pressure inside the sealed tube.

The entire secondary was covered with a two-part epoxy, thinned with denatured alcohol. This coating causes no crazing of the plexiglass and has been perfectly stable over the years. It also provides excellent insulation, looks nice, and provides protection of the windings.

The plexiglass is not a "special low-loss version", just standard plexiglass.  I'm not sure such a thing as special low-loss plexiglass exists.

My experience constructing antennas as an amateur radio operator has shown that antenna insulators made of PVC will arc at voltage nodes, where plexiglass will not, especially in high-humidity.

Regards,

Don


--- On Tue, 1/15/13, Jon Danniken <danniken@xxxxx> wrote:

> From: Jon Danniken <danniken@xxxxx>
> Subject: Re: [TCML] 6" Tesla coil plexiglass secondary - FOR SALE
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Tuesday, January 15, 2013, 8:42 PM
> On 01/15/2013 11:53 AM, dfroula@xxxxxxxxxxxxx
> wrote:
> > 
> > Wound on low-loss plexiglass form. Far superior to
> lossy PVC coil form!
> 
> I don't think the difference in RF losses between a
> "low-loss plexiglass form" and a PVC form are even
> noticeable in a tesla coil.
> 
> Is this just advertising hype, or do have actual data from
> real-world operation showing "far superior" performance with
> a "low-loss plexiglass" form?
> 
> Also, is this a special "low-loss" version of plexiglass,
> because I have yet to come across any type of plexiglass
> that specifies lower RF losses in any of the plastics
> dealers I have come across.
> 
> Thanks,
> 
> Jon
> 
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
> 
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