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Re: rolled cap blowew out

Original poster: Chris Estes <estescc@xxxxxxxxxxxx>

Tesla list wrote:

>Original poster: Adriano.Mollica@xxxxxxxxxxx
>Hello list,
>after the last attempt to start the TC using lithuanian capacitors,
>that used to explod very quick and very often, i made a homemade
>rolled polyethylene cap.
>The dielectric thickness was 0.4 mm, since 1 mm should resist 60kv, i
>thought that 0.4mm should handle about 25kv.
>After the rolling up of the materials, i dip the roll into a tube
>filled with synthetic engine motor oil, and by a vacuum pump i
>removed all the air inside.
>unluckly, after few successful sparks, the capacitor stopped working
>and started to make a noise (probably an internal arc).
>i'm pretty disappointe 'cause i spend around 40 euros in materials,
>and many hours of work!
>how can i built a cheap, reliable, and FAST pulse discharge capacitor?
>i'm thinking about planar caps in air ( at least is the cheapest
>dielectric i know.!
>any suggestion?
>how much is the dielectric costant of the air, and its puncture voltage?
>37 nF cap wil probably be very large?

I've just finished an interesting design thats yeilded about 6.7 nf
with I'm guessing 50 Kv strength. Its a stacked plate cap that uses
corrugated cardboard and mineral oil for the dielectric. I place 2
pieces of cardboard between each plate to give about 250 mil (3/4 cm)
spacing. All the pieces of cardboard are oriented so that when looking
down on the stack you can see through the corrugation if that makes
sense. then i place the stack in a container and fill it with oil. The
orientation of the cardboard lets the air bubbles flow up and out quite
nicely. The most expensive component is all the oil and, I believe,
they will have a 'self healing' quality. If theres a puncture, all I
need to do is shake it around to jostle the oil a bit. The dimensions
are about 20cm by 35 cm by 35 cm for, as I said, about 6.7 nf. If you
wanted more farads in less space then you could probably just use one
layer of cardboard but I just needed about 7 nf for my NST resonant
condition and wanted to be sure about the dielectric strength. I
haven't tried this out yet as I'm still building the rest of my coil
but I can't see any serious flaw in my design so far. Good luck and
happy coiling.