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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