Re: Advice on secondary

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

On 30 Jan 2005, at 11:51, Tesla list wrote:

> Original poster: FIFTYGUY@xxxxxxx
>
> In a message dated 1/29/05 11:23:47 PM Eastern Standard Time,
> tesla@xxxxxxxxxx writes:
> P.V.C has a very high dissipation factor, they actually use radio
> frequency to weld P.V.C. (albeit at a very high frequency) I do not
> recall the exact figures but polyethylene and styrene both have rather
> low dissipation factors.  (anyone have a C.R.C. handbook handy?)
>
>      Could not find dissipation factors in my 83rd ed. of the CRC
>      "Handbook
> of Chemistry and Physics."
>      My 2nd ed. of the "Polymer Handbook" lists the following
>      dissipation
> factors (at 60 Hz!):
>
>      Poly(methyl-1-pentene)                              .00007
>      Poly(styrene), general purpose                   .0001-.0006
>      Poly(styrene), high impact                          .0004-.002
>      Poly(styrene), high heat                              .0005-.003
>      Poly(ethylene), {low, med, and hi-density]   <.0005
>      Poly(propylene)                                   <.0005
>    Poly(carbonate)                                   <.0009
>      Epoxy cast resins                                   .002-.010
>      Poly(vinyl chloride)                                   .007-.020
>      Poly(vinyl chloride), chlorinated                    .021-.019
>      Poly(vinylidene  chloride)                             .03-.045
>
>      Also lists "Arc Resistance, ASTM-D-495[s]", with Cellulose
>      Acetate,
> Poly(ethylene) med density, and Poly(imide) at the top,
> Poly(propylene) high, Nylon 66 and Poly(styrene) middle, Polycarbonate
> and Epoxies lower, and Poly(vinyl chloride) at the bottom.
>      From the 1st ed. of the McGraw-Hill "Electronics Engineers'
>      Handbook",
> a table from "Standard Handbook for Electrical Engineers", 10th ed.",
> properties of insulating films. Include dissipation factors at various
> frequencies:
>
>      Material:                             dissipation factor @ 10^3/
>      @ 10^6 Hz
>
>      TFE tetrafluoroethylene                  .0002/.0002
>      Polyethylene                                 .0003/.0003
>      Polyimide                                   .0003/.0010
>      Polypropylene                                .0003/.0003
>      Polyurethane elastomer                      .06/---
>      Cellulose acetate                               .10/.10
>      Polyamide                                   .010/.016
>      Vinylidene chloride                          .045/.075
>      Polyvinyl chloride                              .16/.14
>
>      So it would appear that polystyrene is low dissipation, and PVC
>      sucks.
> However, my gut feeling is that this is purely academic, since I've
> read that after breakout the Q plummets to a whopping 6 or so. I'm
> guessing a typical secondary coil form won't dissipate more than a
> percent or two of the total energy of a typical TC. I would also guess
> drying to remove water content would more help prevent losses through
> breakdown than from dissipation.
>      I bet the secondary wire has more losses than the coilform,
>      although
> again due to low post-breakout Q it can't be that important. If the
> standard model shows a series 220K Ohm resistance in the streamer, I'd
> work to make the air more conductive to cut losses!
>      I think the only folks who would have to worry about coilform
> dissipation factors are those running in high-power CW.
>
>  > Ideally no core at all would be best, Styrofoam is about as close
>  as > your going to get to no core at all.
>
>      Or a form-less coil. But I think it would be fragile compared to
>      a
> coil that retains its former. One of these days I'll get around to
> making one - I bought the electrical epoxy to do it, and made up the
> former. At the moment, I'm happy with the scrap SDR sewer pipe I've
> been scrounging for free.
>
> -Phil LaBudde

I have a spacewound secondary wound on some thickwall sewer pipe
(no previous sealing or other treatment) which has a Q in excess of
300 at 165kHz. With Q's that high, differences in dielectric
dissipation are a non-issue. The only secondary I wound which came a
cropper was wound on some sonotube-type stuff with the tar paper
removed. It was largish, spacewound and its Q barely clocked in
around 40 with powered results to match. It was varnished but I
didn't bother to dry the stuff prior to coating. My fault of course.

Malcolm