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

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

Original poster: "John" <fireba8104-at-yahoo-dot-com> 

Why dose everyone pick on me? :-/
I didn't start this tread, I only posted information from the website and 
uploaded the picture so others could see. No good deed goes unpunished.. 
AHHHHH   :)

Hi Scott,
I'm not sure the current is of as big of a problem as one might conceive. 
You might have to use more in parallel to meet the ratings but they also 
have a higher voltage 3kv compared to the 2kv of CDE's caps. This might not 
entirely make up for the current problem but with price it has a fight 
chance. I also remember others using GE caps of the same construction with 
only a few problems- I'd have to check with Terry to totally verify. Still 
they just might not be worth it.

Cheers,
John



Tesla list <tesla-at-pupman-dot-com> wrote:
Original poster: "Scott Hanson"

John -

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 spec! s 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