Re: "These might interest MMC builders.." STK polypropylene capacitors

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

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


True, but if you elect to use the larger 0.15 at 3 kV DC the ratings jump up
to 216 Amps peak and 10.1 Amps RMS, certainly within the limits for a small
to medium NST powered coil.  10 caps in series would give you .015 uF with a
30 kV DC rating --- 4 times the Erms of a typical NST.

They are rated for high current, high freq, and high pulse applications with
high dV/dt.  Also seal healing characteristics.

Dr. Resonance

 >
 > At first glance, polypropylene capacitors for "$0.50 to $1.00 each" sounds
 > interesting, but once you get into the details of the specifications
things
 > don't look quite so good.
 >
 > First, STK does not offer a direct equivalent for the Cornell-Dubilier 942
 > series, which have become the defacto "standard" for MMC use.
 >
 > It looks like the best STK candidate would be the MP89 "high peak current"
 > series, but these are of double-metallized film construction, not the
 > metallized film/foil hybrid construction of the CDE 942 series. Compared
to
 > film/foil, the weakness of the double-metallized construction is at the
end
 > terminations of the roll, where the leads attach. These tend to fail (burn
 > away) in high peak current applications like a Tesla coil MMC.
 >
 > Comparing the specs shows how much more robust the CDE film/foil
 > construction is.
 >
 > The peak and RMS current ratings are as follows for a .015uF, 2,000VDC
 > capacitor:
 >
 > STK MP89, peak current 144A, RMS current 8.9A
 > CDE 942,    peak current 432A, RMS current 13.5A
 >
 > So, for a .15uF, 2kV capacitor the CDE 942 can handle THREE TIMES the peak
 > current of the STK capacitor. The cost differential is less than 3X, so
the
 > STK parts really are not cost effective compared to the CDE's.
 >
 > Regards,
 > Scott Hanson
 >
 >
 > ---
 > [This E-mail scanned for viruses by Surfside Internet]
 >
 >
 >