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From: wmb@sun.uucp (Mitch Bradley)
Newsgroups: net.analog
Subject: Re: Big Capacitors
Message-ID: <1812@sun.uucp>
Date: Mon, 26-Nov-84 18:33:18 EST
Article-I.D.: sun.1812
Posted: Mon Nov 26 18:33:18 1984
Date-Received: Wed, 28-Nov-84 03:14:55 EST
References: <178@ihnet.UUCP>
Organization: Sun Microsystems, Inc.
Lines: 33

> I heard a rummer which I am not quite ready to believe.
> Someone said a company somewhere makes a 1 farad capacitor.
> It fits in the hand and costs $10.
> I took electrical engineering once, 
> and micro farad capacitors were substantial.
> How can this be??!!
> Is it just a myth?  If not, how does the damn thing work??
> If it is just a rummer, what capacitance values (a few volts) are available
> in industry.
> How does cost increase with capacitance.
> Is the trend to increase surface area, or to use better dielectrics?

It is true.  I saw a data sheet for it about 2 years ago.
As I recall, it was made by Panasonic, and it looked sort of like
a battery.

My memory isn't very good, but I recall that it was low voltage
(less than 10 volts, I believe).  I think it was some kind of
electrolytic technology with a very thin dielectric film.
The dielectric in electrolytic capacitors is a chemical film
which is formed on the metal surface of one of the plates.

For a given technology, physical size of capacitors tends to increase
(roughly) as the product of voltage * capacitance.  Cost tends to
be a fixed cost plus a variable cost that is roughly linear with physical
size.  Of course, it depends strongly on the technology (electrolytic,
tantalum, mica, ceramic, etc) and even more on the manufacturing volume.

This 1 farad cap was intended for applications like keeping circuits
running during power outages.  I doubt that its high-frequency characteristics
are very good.

Mitch Bradley