Re: Acrylic Caps vs. Glass Caps!! (fwd)

---------- Forwarded message ----------
Date: Thu, 15 Jan 1998 22:03:50 -0800
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Acrylic Caps vs. Glass Caps!! (fwd)

Tesla List wrote:
> ---------- Forwarded message ----------
> Date: Thu, 15 Jan 1998 12:45:29 -0600
> From: Zuma <mwise-at-ns.sosis-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Acrylic Caps vs. Glass Caps!!
> I recently was told not to use Acrylic because it was very lossy.
> But the one thing that I didn't understand is Glass, so I have been told
> is probably the worst capacitor to use, which I agree with. But what I
> don't understand is that Polyethylene has around a 2.2 k factor, right.
> Acrylic has around a 2.8 k factor. Glass has around a 5 or 6 k factor.
> On this I am assuming that the lower the k factor is, the lower the loss
> factor is. Is this right?? If so Acrylic is not a very bad dielectric
> to be used. In Fact compared to Glass my opinion would be that Acrylic
> would be a better dielectric than Glass by a long shot. Assume this
> polyethylene is a 1 on a 1-10 scale, glass is a 10 on a 1-10 scale.
> Based on that what would you rate Acrylic(plexiglass) between 1-10.
> Any input into this would be greatly appreiciated. Because if I am
> correct about acrylic being many many times better than glass I am
> going to construct a cap using acrylic sheets and it is going to be
> thoroughly saturated with oil&kraft paper between every plate.
> Tanks Chrisj


There's really no direct relationship between the dielectric constant
and dielectric loss. 

Rather than rate LDPE, acrylic and glass on an arbitrary 1-10 scale, a
better way may be to compare the degree of "lossiness" between the
three. If we use LDPE as a standard of comparison (dissipation factor of
about 0.10 x 10^-3), then acrylic (PMMA) is between 220 and 500 times
lossier, and glass is between 225 and 1900 times as lossy as LDPE. So,
while you COULD say that acrylic is marginally better than glass, in
reality they are both comparatively lossy as dielectrics for Tesla Coil
caps. If you're going to put the time, effort, and $ into making your
own cap, wouldn't you want to get gthe best performance... especially if
the material cost was the same or less??

Safe cappin' to you, Chris!

-- Bert --