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Re: Success with PP Multi-Mini Cap
At 11:47 3/04/99 -0700, Adam <psycho-at-tradewind-dot-net> wrote:
>I might be a little out of line here, but it seems very possible, given the
>success stories and ease of construction/use/resuseabilty/etc that
>polypropylene MMC caps could become the new standard in TC caps, replacing
>the oh-so-fun motor oil drenched LDPE nightmares of days gone by.
>
>So, in the grand tradition of TC standards, wouldn't it be nice if someone
>wrote a general construction file? You know, like instructions for basic
>design, availability of components, possible pitfalls, expected costs,
>design issues, areas for improvement, etc.
I think construction is actually the easy bit. The major factor needing to
be defined is how far we can stretch the voltage envelop of the cap
ratings, and how long these will subsequently survive.
The last posted design used strings 16 x 1.6kV = 25.6 kVDC
This is clearly below the DC rating figure we (royal we = "the list") would
recommend. For 15 kVAC a rating of > 40 would be considered minimum, and
50kVAC a standard to aim for.
The problem then becomes, for the same C value, to go to 50 kVDC would be
another 16 caps SQUARED, or 256 caps.
Down in Australia these are about $2 each, and we are now talking the same
money as a Maxwell pulse cap !!
For cost-effective use the million dollar question is how far "over-rated"
commercial DC caps are and how far we can push this for AC Tesla use.
I don't think these issues are answered yet and we will have to wait to see
how long these units survive before reasonable advice can be given. If we
can in fact use 30 kVDC then these do become cost efficient, moreover they
should be much easier to repair in the event of failure cf. a Maxwell or
similar unit. Theoretically only one string should fail ..... initially
cap by cap, then as the stress rises it may be quite dramatic, like the old
strings of fire-works ;-)
Watching this thread with considerable interest !
If I were to build one, I guess the advice I would give Adam is to make the
unit easily extendable, both in string length and number. These may well
have to be adjusted in the future ;-)
cheers
Mark
http://www.cobweb-dot-com.au/~dkfinnis