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Re: MMC question (SMT cap comment)



Hi Jim,

>Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
>That pretty much sums up the capacitor abreviations used (aside from
>SMD and special purposes caps, but who wants to use SMD caps on
>a TC ;ö))

Original Poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
>And why not use SMD caps.. very low series L, cheap... Put them all on
>a little board then pot it. At 500 V or 1 kV per cap, even the little
>1206 packages might work without breaking down. So you have 20 in
>a row to get 20 kV rating. It is still a pretty compact device. I
>confess I haven't seen polypropylene surface mount caps in a
>reasonable size, though.

Hmm, I have never seen SMD caps with a 500V or higher rating. The
biggest ones I have seen are rated at 100V and 220nF. These are
made from polyester and have a dv/dt of 35V/µsec. The test rating
(for 2s) is 350V/µsec. So, even if we neglect the polyester problem
(which we really can“t), we would still need a lot of rows to get a
useable amperage. Another problem might lie in the fact that they are
"S"MD. The distance between the layers and the end "plates" is
very small and the surface is "open" to grime and dust. This might
present a problem with corona and or voltage creepage along the
surface. If you pot it in something solid (like epoxy) you will never
be able to rebuild it. If you use an oil bath, then you have one of
the things I like to avoid around HV: oil ;o). And....... wouldn“t it
look kind of awkward having an 8" coil with a SMDMMC the size
of two cigarette packs? ;o)). It might be an interesting idea for
a µTC, tho. 2-4" sparks from a "cigarette pack and a 9V" {;./\)
Or how about feeding the output from this into an helium filled
bag floating above your head (sort of like a halo ;o)).

Coiler greets from germany,
Reinhard