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Re: Beating Solved
Tesla List wrote:
>
> > > Subject: Beating Solved
> > Subject: Re: Beating Solved
> > > Subject: Beating Solved
>
> >From bturner-at-apc-dot-netWed Sep 4 22:26:52 1996
> Date: Wed, 04 Sep 1996 11:35:21 -0700
> From: open_minded <bturner-at-apc-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Re: Beating Solved
>
> Tesla List wrote:
> >
> > > Subject: Beating Solved
> >
> > >From hullr-at-whitlock-dot-comThu Aug 29 22:33:00 1996
> > Date: Thu, 29 Aug 1996 11:02:39 -0700
> > From: Richard Hull <hullr-at-whitlock-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Beating Solved
> >
> > Tesla List wrote:
> > >
> > > >From tesla-at-america-dot-comTue Aug 27 22:57:57 1996
> > > Date: Tue, 27 Aug 96 20:00 EDT
> > > From: Bob Schumann <tesla-at-america-dot-com>
> > > To: tesla-at-pupman-dot-com
> > > Subject: Beating Solved
> > >
> >
> > Big Snip
> >
>
> Richard:
>
> Just quick point of contention here on mylar caps -
>
> Granted, mylar isn't the *greatest* dielectric in the world, but it's
> a damn sight better than say, oil-paper power-factor correction caps.
> I built a small table-top coil many years ago (In fact, it's pictured
> on my homepage) which used (2) 0.005uF, 45KVdc 'wrap&fill' (built by
> Custom Capacitors, found in surplus) mylars in parallel, driven by a
> 9KV neon. Coil produced spectacular 14" discharges from the 4"
> secondary(!) and the caps barely got warm, even after several minutes
> of 'on' time.
>
> Mylars *can* work. What I *DO* agree on is the *case style*. You are
> indeed correct about the oil-filled, cylindrical caps. I too had one
> go ballistic on me.
>
> - Brent
Brent,
I have to yet disagree on one point you mentioned. The dielectric loss
at Tesla Coil frequencies with kraft paper and foil in oil is full order
of magnitude BETTER than capacitor grade mylar end foil construction. I
would go for the paper jobs over mylar any day. These paper caps were
the original pulse power caps. They are still very good for that purpose
and beat mylar by a factor of 10! I have purchased Capacitor grade mylar
some years ago and have personally constructed mica, glass, paper, mylar,
teflon, styrene, polyethylene and polypropylene caps! The lowest heating
(disappation factor according to the data sheets was indeed reflected in
my experiments. I chose 200 KHZ as the test frequency and 800 watts as
the input power. In order of heat (dissapation losses), we found the
follow results in order most lossey to least lossey. Most lossey-mylar
then mica, glass, paper, polyethylene, polypropylene, styrene, Teflon.
Radio guys love mica, but it is terribly lossey stuff!!! Why do they use
it??!! It will run comfortably and survive well for years at continuous
use temperatures of 700 degrees farenheit!! Mica only fails when the
structure of crystalization is lost around 900 degrees. (turns to dust)
Transmitter systems need this kind of durability. Also, Mica has one of
the highest K factors 5-8 of any dielectric and so a smaller, higher
value cap can be made with mica. Also, their value is incredibly stable
over enormous temp extremes. (important in final tanks) Mica has a very
high standoff voltage. Everything recommends mica for high voltage hot
duty continous service, except its terrible lossey nature at RF
frequencies. This makes them terrible for Tesla coil work, if losses are
a concern. In transmitters they will pay for the losses (power companies
will sell them all the power that want) in a trade for robust service.
Mylar is really bad too its has a disappation factor of .001% at DC but
rises above 1-5KHZ to about 5% in the low RF spectrum! (similar to mica.)
It is not normally ever used above 60HZ in circuits where energy
transfer is critical. Main use DC filters and low power coupling in AF
circuits.
Glass (potash based) is actually pretty good! Amateurs make theirs out
of lime glass (window glass) and the caps are no good. Tesla used potash
glass bottles only! (specified by him in a letter to Scherff May 1899.
Also mentioned in the Colorado Springs Notes.)
Paper-foil is superb for low end pulse work. It was used extensively in
the early atomic pulsed energy systems prior to world war II where the
values of the caps exceeded micas cost/availability factor. Paper will
take a lot of heat, like mica, and under oil will hold off a good amount
of voltage. Good choice from DC to 100Khz. They get real lossey above 1
MHZ
The four best plastics are teflon, styrene, polypropylene, and
polyethylene. in that decending order. There is so little dissapation in
all of these that they are virtually identical in dissapation factor!
(.001% into the GHZ range) The deciding factor is usually one of voltage
stand off with Teflon and Polypropylene being the best. Heat is also a
factor and Teflon is best with polypropylene second. Teflon has micro
holes in it like swiss cheese and is just not found in the cap industry.
So polyprop makes the best pulse caps. The most stable of these
materials value wise is modified-cross linked styrene.
ANY CAPACITOR ON THE PLANET WILL PERFORM IN TESLA SERVICE. How long, at
what cost, and with what form of output is quite another matter.
The color of the spark always tells me a lot about a persons capacitor.
purple or purple-violet tells me the fellow is a novice and his caps are
at the very bottom of their performance curve. Brilliant pretty blue
sparks are better but indicate high loss in the tank capacitor is still
taking place. Rich blue-white sparks indicate only satisfactory
operation. Snow white arc channels only fringed in brilliant blue
indicate top performance operation and snyergistic tank operation and
energy transfer. With enough power input, to over come losses, Mylar
and mica can give quite impressive sparks. Both will heat rapidly and
only the Micas stand much chance of survival if long runs are the norm.
properly constructed poly caps, especially "volumetrically inefficient"
ones just do not heat at all, under any conditions! They will perform
efficiently, flawlessly and forever in Tesla coil service when operated
within their voltage specification range.
Richad Hull, TCBOR