Re: Capacitor construction

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

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

> Glass will work, but it's lossy, and must be placed in oil for
> best results.  The dielectric constant is high at about 6, but
> the Q depends on the dissipation factor which is rather poor
> for glass.  You'll probably lose about 15% in spark output
> length using a glass plate cap vs. a low loss cap.  The
> primary tank in a Tesla coil runs in a low Q mode anyway,
> but glass caps increase the overall losses.  If you want to
> insist on building your own caps, an alternative would be
> to used rolled polyethylene, or flat layers of polyethylene.
> Such construction gives good results and low losses,
> and can be built very cheaply if you can obtain the parts
> for free, or almost so.  Such caps are bulky however.
> Glass caps, despite their shortcomings do work, and that's
> what Tesla himself used.  He used glass bottles which used
> to fail on a regular basis.
>
> John Freau
>
>
>