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RE: PVC and oil, mmc enclosures



Original poster: "Oxandale, Terry by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Toxandale-at-spp-dot-org>

I built a neat "little" (that relative of coarse) MMC that consisted of 12
capacitors (those Hosfelt ones) per string (6 stings per board). Each string
was constructed by soldering the capacitors end-to-end, and then inserting
this string into a piece of 1" PVC pipe. The PVC end caps consisted of a
regular glue-on cap, but in the middle, I drilled and tapped (3/8" coarse
thread) a hole to accept a 3/8" aluminum rod that was threaded on one end
only. this rod then stuck out of the PVC cap about 1". Before screwing this
rod into the cap, I drilled a small 1/8" hole along it's axis completely
through the length of the rod, and then drilled and tapped (8-32) a
perpendicular hole to the long one, in close proximity to the base (the PVC
cap end), that was used to screw a set screw into. To assemble these PVC
caps, I glued the caps in place (fist slipping the capacitor string's end
leads through the 3/8" threaded hole. Next I inserted the capacitor lead
through the rods, and then screwed the rods into the PVC caps that are now
glued in place. Next I screwed the set screws into place, which secured the
cap leads inside the aluminum rods (not too tight or it shears the leads in
two). Now I have a complete string inside a PVC pipe with 3/8" aluminum
prongs sticking out either end. After building 6 of these assemblies, I then
needed a mounting board. I used a board made from 3/4" MDF, coated with
polyurethane. Then I took fuse blocks (amp or volt rating not available at
this writing, but they use the 3/8" diameter fuses), cut them in half, and
attached these halves to the board in such a way that the PVC strings can
now "snap" into these fuse block halves. Of course, it will take 6 fuse
blocks to attach the 6 PVC tubes. The back side of the board is used to
connect the group of six clips on each end (making a bus to connect all
clips together on each end) so that all 6 tubes will be wired in parallel to
each other. Wire the bus into the primary circuit, and now you can now
easily "tune" the capacitance in 8.3 nF increments by removing or inserting
these capacitor tubes into the clips (fuse block halves) this is not a small
compact arrangement, but if mounted flat, under the platform for the RSG
motor and all, it does become more convenient. My only concern before
undertaking this project was the heat buildup inside the tubes, but these
Hosfelt caps (on long runs of 10 minutes or longer) run cooler than the
Maxwell caps I have compared them with, and this may really sound weird, but
the performance is slightly better than the Maxell caps (the 35kv 30nF).
Currently I only run 4 caps, but with a larger toroid, I can put 1 or 2 more
tubes into the circuit. This technique has worked so well, that I went ahead
and built 2 additional boards (can stack the boards on top of each other,
and use forced air to cool them) for a total of 150nF of capacitance should
I get my 15" coil operational again. And should a tube go "bad", then I'll
just replace it quickly with a spare.

(un)Terry 



-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, November 12, 2001 12:47 PM
To: tesla-at-pupman-dot-com
Subject: PVC and oil, mmc enclosures


Original poster: "Jonathan Peakall by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jpeakall-at-mcn-dot-org>

Hi all,
 
I am building an MMC and, as always, have a few questions...
 
I have heard that filling PVC pipe with oil always leaks. Is this true? Is
it
the glue joints that tend to fail, and if so, could epoxy or polyester resin
be
used to glue end caps on to prevent this? What about a PVC enclosure flushed
with an inert gas? I would prefer oil for cooling purposes.
 
I have seen several breadboard style MMCs, and they look hard to replace an
individual cap. Any arrangement ideas out there that allow easy repair? 
 
Thanks!
 
Jonathan Peakall