Re: MMC advice

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Peter Lawrence <Peter.Lawrence-at-Sun.COM> 

Guys,
      if you want to be really conservative put 600 VAC per capacitor in your
MMC. 600 VAC is about where edge corona starts, pretty much independent of
construction materials. Forget about DC rating entirely for MMCs.

Personally I've been making my MMCs with 750 VAC per capacitor and not had
a problem.

-Pete Lawrence.

 >
 >Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
 >
 >
 >If you have a 30 kV DC rating divide by 2.5 to get the equiv. AC rating.
 >
 >Example,   30 kV DC / 2.5 = 12 kV Erms rating for the string
 >
 >BTW, these are not my rules --- Beau Meskin, Pres. of PCI, developed this
 >rating method with considerable work in his cap lab which is well-equipped
 >to measure corona formation, etc, etc.  He said in all commercial work both
 >his company, Maxwell, CSI, and most other cap mfgrs use 3 x DC pulse rating
 >for the equiv. AC rms rating.
 >
 >The main problem is corona formation at the edge of the foil.  If you exceed
 >these ratings you will definitely be getting corona formation (no
 >exceptions) and eventually the cap will fail.  It's only a question of time,
 >and in the case of MMC's, which one in the string fails.
 >
 >Yes, as Dan pointed out, you can push them, but if they fail right when you
 >need the machine to work properly (Teslathon, haunted house, etc.) then you
 >end up with egg on your face  -- you become the "bumbling engineer" not the
 >shining knight.
 >
 >We usually use the 2.5 times rule and so far have had no failures or
 >intermittant problems.  As a former TV technician (in the 60's) I can tell
 >you the intermittant type failures are the worst --- they drive you
 >partially crazy trying to ascertain the exact problem not to mention the
 >tremendous waste of your time.
 >
 >At only $3 per cap why take chances?
 >
 >
 >Dr. Resonance
 >
 >Resonance Research Corporation
 >E11870 Shadylane Rd.
 >Baraboo   WI   53913
 > >
 > > So what are you really saying?  Take your transformers AC voltage and
 > > calculate peak.  Multiply this by 2-2.5 and then divide by the
 > > individual cap DC rating to give number of caps per string?
 > >
 > > Cheers, Chris (NZ)
 >
 >