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Another MMC cap story.
Hi,
Just wanted to add to the pile of MMC success stories.
A few weeks back I built myself one. The caps are rolled construction
PP (film & foil), 14mm dia x 33mm long, with axial leads. Nothing
special to look at - they all have a serrated edge of the yellow
wrapping sticking out a couple of mm, not stuck down. Anyway, they're
.047uF 1500V dc (450V ac) 2000V/uS PF = 0.0005 -at- 1kHz.
I used 120 in total, in 6 parallelled strings, each of 20 in series, for
a nominal rating of 14.1nF 30kV dc or 9kV ac. It turned out to be bang
on 12nF on my (dubious) meter, and voltage - who knows ? It all fits
snugly in an ABS box 80 x 180 x 120 mm. The caps were $1.17 (Aust)
each, I think.
I have only tested it for a few short runs, a few times, on very
'temporary' coils. Mostly on a 4.5" coil with a primary of 6 turns of 6
sq mm stranded insulated earth wire (7 x 1mm dia Cu), wound on 6.5" od
pvc pipe, then slipped off & taped up to be a self-supporting helix,
'tuned' just roughly enough to throw some sparks for testing things.
Most of this has been at 7.5kV / 30mA, but some at 12kV/30.
So far the cap has performed faultlessly, and the sparks I get out of
these setups is not that far short of how those secondaries performed in
their 'proper' setups, with my PE plate cap in oil, and at 15kV.
Admittedly it hasn't had a hard life yet (but it will), but it seems to
me to be a good thing, & far less mess & hassle than the PE & oil one.
Next one will use strings of probably 30 for good measure (& 40 if the
budget would stretch), but if this one survives a while, maybe 20 is
enough. People seem to be getting good results so far with fewer, e.g.
16. Keeping on the lookout for a surplus, or cheap source; and trying
to get Philips 375s or 376s at a decent price..........
There are so many good reasons to like these, from my point of view.
All have been discussed already, so I won't go on.
Cheers,
PhilC.