RE: design for new capacitor

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

Many years ago I built a pair of 450pF caps for an R-C NST protection
network, using some double-sided .09" thick copper-clad G10.  The
dielectric thickness was more than adequate (especially since each cap
saw only half of the tank voltage), but near-heroic measures were needed
to keep arcing from occurring at the edges of the plates.  Any insulator
will surface-track much, much further than its normal stand-off
distance.  I ended up needing at least a 1.25" clearance zone on both
sides around each plate, which took quite a bit of the available plate
area.  Stacking the several needed plate assemblies was difficult and
complicated by needing to be encased in oil or Vaseline jelly to prevent
corona at the plate edges, despite the clearance zone.

If you're a glutton for punishment, have fun, but if you just want a cap
to work the first time and keep working, build an MMC, using proven
polypropylene pulse-grade caps.  If you must choose the lowest cost
option, use salt water/glass bottle caps.

Regards, Gary Lau
MA, USA


> Original poster: "Dr. Adriano Mollica" <adriano.mollica@xxxxxxxxxxx>
>
> Hello list,
>
> i just bought on ebay a certain quantity of douple faces copper fiber
glass
> plate for very cheap.
>
> i will like to use them to make a capacitor, and i believe that it is
> possible.
>
> But i'm worring about the design. infact, every single plate is
already  a
> little capacitor "as is",  and if  i'm right , the thickness of the
> fiberglass will be 1.6 mm, that is very big (this will lead to a high
> punture voltage resistance , but low capacity).
> So , how should i connect the plates one to another in parallel
> cinfiguration trying to avoid any "corona" , and external spark? and
so on,
> considering that the plates will be in a number of 20-40 and i cannot
> overlap them due the double face!!!
>
> Any ideas?
>
> bye bye
>
>
> ----- Original Message -----
> From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Wednesday, March 01, 2006 5:53 AM
> Subject: 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?
>  >  >thanks!
>  >  >
>  >  >
>  >
>  > 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.
>  >
>  >
>