[TCML] DIY Tank Capacitor - Plate configuration confusion
fsiyfr at okeechobee.com
Fri Sep 26 11:49:59 MDT 2008
That 942C is a clever approach to achieving certain specs. It analyzes down
to being two capacitors in series in one casing. The metalized film serves
as one plate for each capacitor, and it also serves as the connection that
places the two capacitors in series. There is no "floating" plate as far as
the operation of the capacitor. The "floater" serves simultaneously as a
plate for each of two capacitors and as the "strap" that connects the two
> -----Original Message-----
> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com]On
> Behalf Of Lau, Gary
> Sent: Thursday, September 25, 2008 9:17 AM
> To: Tesla Coil Mailing List
> Subject: RE: [TCML] DIY Tank Capacitor - Plate configuration confusion
> > -----Original Message-----
> > From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On
> > Behalf Of Dan Elyea
> > Sent: Wednesday, September 24, 2008 9:08 PM
> > To: Tesla Coil Mailing List
> > Subject: RE: [TCML] DIY Tank Capacitor - Plate configuration confusion
> > I probably missed some special case that is being considered, but a
> > statement was made that the layers of foil in the middle are not doing
> > anything. Not so. Each layer of foil in a capacitor is
> connected to one
> > terminal or the other, and takes a very active part in the
> operation of the
> > capacitor.
> I agree that plate/foil layers in the middle of a cap exist for a
> reason, but it is not true that all plates connect to terminals.
> Reference the Cornell Dubilier spec for our MMC caps at
http://www.cde.com/catalogs/942C.pdf. The construction diagram at the very
top illustrates two foil plates at the top. These are the two terminal
connections. Below the underlying layer of dielectric is a metallized film,
which acts as a "floating" plate, electrically between the two foil plates.
There is no terminal connection to this film layer. High current terminal
connections can be made to foil, but not to metallized film. The floating
plate exists so that the total terminal voltage rating is split between two
series-connected caps, so that neither one exceeds its corona inception
Regards, Gary Lau
> The capacitance is determined by the area of the conductor
> plates facing each other, the material of the dielectric, and the
> of the dielectric (the spacing between the plates). If all other factors
> remain the same and you increase the spacing between the conductors (foil
> whatever), you reduce the capacitance. Multiple plates (properly
> to the capacitor terminals) have the effect of increasing the total plate
> area, and thus the resulting capacitance. Look at the formula for
> capacitance and you'll see how the several factors affect capacitance.
> Increased plate area or higher dielectric constant increase capacitance;
> increased spacing between the plates decreases the capacitance.
> You probably know that already, and are likely posing some theoretical
> with floating plates. But, just-in-case, I decided to chip in. Sorry if
> totally missed the point being made. In a real capacitor, all the "foil"
> connected to one terminal or the other.
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