Path: utzoo!attcan!uunet!decwrl!asylum!osc!jgk
From: jgk@osc.COM (Joe Keane)
Newsgroups: sci.electronics
Subject: Re: Electronic Car Brakes
Summary: Energy in a capacitor is proportional to volume.
Message-ID: <3831@osc.COM>
Date: 27 Sep 90 06:49:16 GMT
References: <8581@ncar.ucar.edu> <1414@atlas.tegra.COM> <1488@gold.GVG.TEK.COM>
Reply-To: jgk@osc.COM (Joe Keane)
Organization: Versant Object Technology, Menlo Park, CA
Lines: 17

In article <1488@gold.GVG.TEK.COM> grege@gold.GVG.TEK.COM (Greg Ebert) writes:
>The energy stored in a capacitor is proportional to
>the square of the voltage (1/2CV^2), but the volume (weight) of a
>capacitor is more linear with respect to voltage (and capacitance), so
>I would expect that using high-voltage capacitors might cut the mustard
>for fast-braking.

But if you increase the voltage rating the capacitance goes down.  The volume,
weight, cost, etc. of a big capacitor is proportional to the energy it can
store, pretty much independent of the voltage rating.  It does go up below say
20V because the thicknesses required get pretty small.

Theoretically, the energy stored in an electric field is `1/2*epsilon*E^2*V'
where where `epsilon' is the permittivity, `E' is the electric field density,
and `v' is the volume.  The first two are determined by the dielectric.  You
can chop up the volume in different ways to get different voltage ratings and
capacitances, but the energy stays the same.