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Re: MMC cap bank



Original poster: "Crow Leader by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

Tesla list writes:
>Original poster: "Dr. Resonance by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>
>My info comes direct from Beau Meskin, Pres. of PCI in Chicago, who has
>visited my lab and commented on the MMC project.  He said they would work
>for a while but would ultimately fail due to excessive corona at the caps
>edge plate surface.  He said the only way to prevent this from occuring is
>to immerse them in oil, usually silicon oil, which is the way all of their
>commercial caps are mfg.
>His standard .01 and .02 MFD units are rated at 20 kV Erms and 60 kV DC peak
>which represents a 3:1 ratio.  I know this ratio is not necessary for
>average experimenters work but I was just pointing out a potential problem
>with the experimenter running 14. 4 kV Erms on a 9 kV Erms bank.
>Beau has been experimenting with RF caps since we were all knee high to a
>grasshopper (or less) and is a very respected professional in this area.
>PCI, CSI, and Maxwell all use silicone oil in their caps.  Short cuts

I don't believe Maxwell uses silicone like everybody else. They somehow 
even pull off using paper in high rep pulse caps, where everybody else just 
uses polypropylene and a compatible oil. My General Atomics caps is full of 
isopropyl biphenyl, and my PCI caps are silicone oil, all of which are AC 
and RF duty rated.
>would
>only prove problamatic at a later date.  I know we can run the MMC hard but
>we always use at least a 2:1 or 2.5 ratio of DC to AC to prevent problems.

3:1 was also the approximate DC/AC ratio I got from Mr. Meskan for RF duty 
AC capacitors made with polypropylene and silicone oil. This won't apply to 
different types of caps, where Plastic Capacitors even states in product 
sheets that their filter style caps of paper and mylar, no matter what the 
voltage rating (upto 5kV per section) will show corona at 1kV or so. Corona 
is a big deal in AC capacitors, and has little to do with DC voltage ratings.
>And, it seems the problems usually occur right when you want to impress
>someone --- Murphy's Law of course.
>MMC's and Terry's work with them is terrific.  I only meant to point out
>that failure would be a probable mode when operated as the poster posted on
>the Tesla List.  Running at DC ratings in a non-oil cap just won't work for
>extended periods of time.
>I have seen the research but it can't be shared publically --- a sort of
>"mfgr's secret".  And the big boys guard these well.
>Dr. Resonance
>Resonance Research Corporation
>E11870 Shadylane Rd.
>Baraboo   WI   53913
> > When the MMC Cap "thing" started a couple of years ago, nobody (not even
> > the manufacturers) knew enough about their caps to have a clue as to how

I can look at a cap spec sheet and read the AC voltage rating at 60Hz and 
take a good guess that at above that, you're going to hit the corona 
inception voltage, and it's going to be lower at higher frequencies.
> > they could be rated to Tesla Coiling stresses. This problem was resolved
> > in
> > a collective effort right here on the list, with the majority of work
> > done by the moderator himself.
> > It was experimentally proven, that the producers voltage rating of the
> > caps was
> > very conservative, and that their DC rating could be used as the AC

No. Outside tesla coiling, people expect parts to last more than a few 
hours, usually in the thousands. Nobody is overbuilding parts because it's 
lots of fun.
KEN
> > rating
> > in Tesla coil service.