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MMC size: (Was: Re: Success with PP Multi-Mini Cap)

Hello Ed,

Original Poster: Esondrmn-at-aol-dot-com
   -snip-
>Reinhard,
>How large is the finished cap?  How do you have it mounted?

The MMC cap, I am using now, is 49cm (19.3") wide, 7.5cm (2.9")
deep and 2.2cm (0,87") high. It has a capacitance of 30.8nF and
is rated for 12kVdc. I run it using a 7.5kV NST, which means the
peak voltage is around 10.6kV. As this cap is just a testbed, I didnīt
mount it in any fancy way. I just wired 12 caps in series and used
thick copper strapping to connect the 6 strings in parallel. No
equalizing resistors or safety gap.... yet. My final setup will be a
little different. All my TC components, except for the xformer box
and the control unit, are (or will be) mounted on a table. The
lower "shelf" contains the main spark gap, RF ground buss, etc.
The second shelf contains the MMC and on the third (top) shelf,
I will mount the primary, secondary and strike rail. My final
xformer setup will be 5.5kVA worth of modified neons and the
primary cap will be 120nF. I will use 15 caps in a row and 29
strings in parallel. I will be using 5Mohm equalizing/discharge
resistors across each cap (will be tried on my testbed setup,
first, to see if it makes a difference in TC spark length) and
heavy buss bars on the end connections. I havenīt decided yet
if I will cross link the parallel strings. The size of this 120nF cap
will be 65 x 65 cm (25.6 x 25.6"). However, it only will be 1.5
inches high. It is simply the second "shelf" of my TC table.
Mounting the caps is easy: I will turn the caps upside down,
so that the connectors face up. The shelf is surrounded by a
1.5" high frame (made of painted wood). The individual cap
strings will be mounted between strips of 1/2" wide x 1/4"
thick birch wood, which are nailed to the base board. The
friction hold is good enough to prevent them from falling out
(I tried this). This means I donīt need hot glue and it is easy
to "pull" a string for repairs. The other advantage: in between
the cap strings is a 1/2" wide air space. This should allow for
good cooling. The whole thing will be covered with a split
sheet of plexiglass. On top of the plexiglass, I will mount the
cap safety gap and a 90ohm 660W (actually, this is 3 220W
-at- 270 ohm resistors wired in parallel) limiting resistor in
series with the cap and the safety gap.

Using the 120nF cap will enable me to get ~6.75J. A similar
sized cap for a 15kV powered coil would be around 30nF.

Diagram:
(as always: use courier to view)

FFFFFFFFFFFFFFFFFFF
FsCCCCCCCCCCCCCCCsF
FswwwwwwwwwwwwwwwsF
FsCCCCCCCCCCCCCCCsF
FswwwwwwwwwwwwwwwsF
FsCCCCCCCCCCCCCCCsF
FswwwwwwwwwwwwwwwsF
FsCCCCCCCCCCCCCCCsF
FswwwwwwwwwwwwwwwsF
FsCCCCCCCCCCCCCCCsF
FswwwwwwwwwwwwwwwsF
FMc             McF
FFFFFFFFFFFFFFFFFFF

F: is the outer wood frame (painted blue)
C: are the caps (which are blue)
w: are the 1/2" wide and 1/4" thick birch wood strips (painted red)
FxF = 65 x 65 cm x 1.5" high frame

s: conecting (paralling) straps
Mc: Main (insulated) connectors that go to the TC tank circuit


Coiler greets from germany,
Reinhard