Re: But how do they do it? (Was: Re: New Maxwell on ebay)

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

Original poster: DRIEBEN-at-midsouth.rr-dot-com 

Greg,

I think it has to do with the vacuuming down of the
dielectric/foil sandwiches and the clean dust free
environment in which commercially manufactured HV
caps are produced in. With the dielectric so vacummed
to the foil, there is very little space for air pockets
that lead to corona formation and ultimately, dielec-
tric failure. Also, they series multiple thin layers
of dielectric/foil instead of one thick layer. This
tends to allow for less corona formation and more E density.
The ratings that a commercial cap manufacturer as-
cribes to a capacitor is highly dependent on the applica-
tion for which it is designed, too (i.e. a filter grade
cap rated at say 50 kV -at- .1 uFD will be considerably
physically smaller than a 1000 pps pulse rated cap
with the same 50 kV -at- .1 uFD rating). The rugged pulse
rated cap will require more total dielectric thick-
ness for the same voltage rating than a more fragile
filtering (or low pulse rep, for that matter) cap.
And of course more dielectric thickness also requires
more dielectric surface area to maintain the same
capacitance rating. Finally, some of the most modern
capacitor designs appear to be able to combine rugged
high pulse rep rate with a relatively compact size (ultra-high
energy density) and the exact processes by which this is
accomplished may very well be regarded as trade secrets.


David Rieben

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
Date: Thursday, August 5, 2004 7:18 pm
Subject: But how do they do it? (Was: Re: New Maxwell on ebay)

 > Original poster: "Gregory Hunter" <ghunter31014-at-yahoo-dot-com>
 >
 > I've been following this thread, and I hafta know--if
 > any of you know--how do Maxwell and other commercial
 > cap builders do it? How do they get so much
 > high-voltage capacitance into such a small package? If
 > they are using polypropylene film, then why are
 > homebuilt caps of similar performance so much bulkier
 > than Maxwells? Are Maxwell, Plastic Capacitors Inc.,
 > et al, not bound by the capacitance formula like us
 > mortals? I'm aware that detailed info on this is
 > proprietary, but in general terms, how the heck do
 > they stuff so much multi-kv pulse cap into such a
 > small box???
 >
 > Just Curious,
 >
 > Greg
 >
 > > Scot, All,
 > >
 > > Actually the 37xxx units are rated to 1000 pps,
 > > plenty high for TC duty.
 > > The 31xxx series are the ones rated at 1 pps.  Most
 > > of the 37xxx are rated
 > > to 25 Arms as well, and the shot life specified
 > > (typically 10^8 or 10^9) is
 > > at 20% voltage reversal.  Unfortunately I have no
 > > knowledge of the 35xxx
 > > series . . .
 > >
 > > Sean Taylor
 > > Urbana, IL
 > >
 >
 >
 >