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RE: Capacitor construction



Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>

The family of Panasonic caps you mention is excellent for MMC use, but the
specific one you chose is .01 uF.  While one can easily construct an MMC
array with a suitable number of these (I made one from .015 uF caps), there
is economy in choosing a higher uF value per cap.  Typically the higher the
unit uF, the less expensive it is in terms of $/uF.  So if you chose to use
.056uF units, you would need 5.6 times fewer caps, and since .056 caps are
less than 5.6 times the cost of .01 caps, you would end up paying less.

I don't know how far this economy can be stretched.  The Geeks are selling
.15uF/2000V caps for $2.50.  From a $/uF perspective, this is excellent.
But the down side of such a large uF/unit cap is that a single string of 12
would yield a .012uF/24kV cap.  How well a single string can handle the
entire primary tank current is unclear to me.  Were multiple strings of
smaller caps used, the current per cap would be spread out over the number
of strings, and the ESR of the strings would be divided by the number of
strings.

Gary Lau
MA, USA


>Original poster: "Daniel Barrett by way of Terry Fritz
<twftesla-at-qwest-dot-net>" ><dbarrett-at-clearcube-dot-com>
>
>    Thanks, everyone for the thoughts on the glass plate caps! So, as I
>understand this, glass will work but it's a bit lossy at these frequencies
>and can tend to 'crater' after a while. I guess I'm now sold on the MMC
idea
>:)
>    So my next question is what are the optimal (Okay, the best bang/buck
>coefficient) caps to choose?
>I'm looking at my trusty DigiKey catalog, and have come up with these
>Panasonic metalized polypropylene film caps. These are rated for 1600 VDC
>(500AC) with a dissipation factor of .2 above 10kHz and are recommended for
>pulse applications. One hundred of these can be had from Digikey for $.97
>each (P10507-ND).
>Would these be a good choice to build the MMC from?
>
>Thanks for the help!!!
>db