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Re: Caps.

Tesla List wrote:
> 
> Original Poster: "Charles Arruda" <carruda-at-channelseek-dot-com>
> 
> Has anyone tried to make a cap with a really nice powdered dielectric
> (High K) like Barium Titanate? BaTi has an K factor of about 1,200
> compared to other materials that are around 6-12. Would it load down the
> system or take to long to charge up with that much capacity?  

	Depends on what capacitance, of course. As far as "has anyone tried",
most of us have used HV filter capacitors with Barium Titanate
dielectric at one time or another.  They work pretty well for a short
time because of their very low series resistance, but heat up and change
capacitance after a few seconds or minutes, depending on the power
level.  I am using 3000 uufd capacitors of that sort here, three in
parallel with a 12 kV, 60 ma NST.  Most time I think I run safely is
about a minute;  have blown up (ceramic punctured and cracked) ones
which I ran for much longer.  So, solid dielectric ones will indeed
work.

What would
> be a clever way to make one with ordinary materials?
> 
> You could stack a few metal plates in a plastic container and fill the
> gap between them with the dielectric powder?  This would produce great
> storage capacity in a relatively small space - you could also remove/add
> dielectric and adjust the spacing between the plates (or remove plates)
> to produce a capacitor of just about any value and capable of very high
> potentials (with a good physical separation between the plates).

	Don't think this would work at all because of corona in the powder, not
so say straight voltage breakdown in the air within it.  The typical
unit I have destroyed (accidentally) and dissected (deliberately)
consists of a ceramic disk perhaps 2-1/2" diameter and ~ 1/2" thick. The
"plates" are silver applied to the flat sides and soldered to screw
studs.  Only two plates, one on each side of the disk, for a capacitance
of the order of 3000 to 4000 uufd at 20 kV.  The powder probably would
have a much lower effective dielectric constant because of the trapped
air, so you'd need more and bigger plates.  Also, since all of the
voltage drop would be across the internal air, you'd probably need a
pretty thick layer of powder between the plates.
> 

Sorry,

Ed