Hi Jeremiah,
Dielectric losses are only significant in the dielectric layer between your
cap plates. It has no measurable effect in the context of secondary
insulation, secondary form material, or coatings. I don't believe that
coating the secondary provides any benefit beyond keeping the windings from
shifting, protecting the windings from abrasion, and aesthetics. It won't
help with controlling racing sparks or pri/sec arcovers. I've always just
used whatever source of secondary wire presented itself - don't overthink
it.
PVC is an attractive, plentiful, and easy material to use. But know that
in and around spark gaps, in addition to not tolerating heat well, the
exposure to UV radiation will quickly turn the clean white to
brownish-orange. If you don't care too much about the color, then PVC is
fine as long as it's not structural in an RSG.
Regarding secondary size... Without exception, I have always found that as
far as performance, Bigger is Better. A bigger secondary warrants a bigger
top load, and there too, bigger is better.
Regards, Gary Lau
MA, USA
On Sat, Feb 9, 2019 at 11:59 PM Steve White <steve.white1@xxxxxxxxx> wrote:
> Hello Jeremiah,
>
> 1. Dielectric losses:
>
> It doesn't make much difference as long as you use some kind of plastic.
> Just make sure whatever you use isn't hygroscopic or that you seal it first
> to prevent moisture absorbtion. Most people use PVC even though it is
> lossier than some other plastics. My big coil uses PVC. Its best to apply a
> few coats of varnish before you start winding the secondary. This is to
> insure that the form doesn't absorb moisture. If you use colored PVC,
> insure that the coloring agent doesn't make it conductive.
>
> 2. Magnet wire:
>
> I would only use what is called "heavy-build" magnet wire. This has the
> thickest layer of insulation. It is not a matter of losses that you should
> be worried about, it is the voltage breakdown between turns. Some coils can
> develop 500 volts in voltage differential between turns so you want the
> best insulation you can get. I have seen magnet wire with green insulation,
> but it is single-build. I have seen some coils using it without apparent
> problems but I would stick with the heavy-build wire. All of the
> heavy-build wire that I have seen is the standard copper color. I am all
> for or an aesthetically pleasing coil but there some areas that you have to
> sacrifice aesthetics for performance.
>
> 3. Spark gap:
>
> I would not use any type of thermoplastic material (plastic which melts
> when heated) except in areas that you know will not get hot. That
> eliminates PVC and HDPE. Spark gaps get hot and you don't want your spark
> gap parts to be melting or getting soft while operating. This is especially
> true if you are building a rotary spark gap. I have seen these materials
> used for spark gaps but I wouldn't. You want to use some type of
> thermosetting plastic such as G10 (FR4) or bakelite (phenolic).
>
> 4. Secondary dimensions:
>
> Many dimensions can yield good results. Aspect ratios in the range of 4 to
> 5 generally work the best. I recommend that you use JAVATC to try out your
> preferred dimensions and other parameters. As a matter of fact, you should
> thoroughly design your coil with JAVATC before you commit to buying or
> building anything. This avoid wasting money and re-work.
>
> Steve White
> Cedar Rapids, Iowa
>
>
>
> ----- Original Message -----
> From: "Jeremiah Schmidt" <jeremiahschmidt1018@xxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Sent: Saturday, February 9, 2019 4:47:57 PM
> Subject: [TCML] Aesthetics vs. Performance
>
> So, I'm working my new coil in my mind right now and a few questions
> come to mind. Most of my questions revolve around my lack of understanding
> of the dissipation factor in dielectrics, and its overall effect on
> performance. It'll be an NST system. 12/60 or I saw a modded on the mail
> list to a 10.5/240. I guess that depends on my ability to mod one without
> breaking it. Anyway....
> Ill start with the magnet wire. So from what I've gathered thus far,
> Polyimides appear to be the optimal choice for coating. Due to the
> temperatures used in production, color choices are limited. But I'm trying
> to put max effort in the visual appeal of the coil also. So concerning
> performance, if I chose a sub-par coating to attain a certain color would I
> even be able to notice the losses? This also applies to my choice in
> material for the spark gap and secondary. HDPE seems to be an excellent
> choice, but I can get some pretty cool color schemes if I choose PC though.
> I've used PVC for everything so far so I really have no reference point to
> make comparisons.
>
> My next question, stepping away from the Df. Secondary size. I know
> several factors come into play when determining secondary size. But I
> personally prefer the looks of say a 6" od coil vs. a 4". And I'd prefer to
> make my coil with the former. Giving the proper setup, and same power
> supply for each, would there be any real losses/gains just from the coil
> form size?
>
>
> Alchemy(n): When scientific methods become more art than science.
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