caps with porous plates ?

From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Saturday, April 18, 1998 10:31 AM
To:  Tesla List
Subject:  Re: caps with porous plates ?

Tesla List wrote:
> ----------
> From:  Boombast99 [SMTP:Boombast99-at-aol-dot-com]
> Sent:  Friday, April 17, 1998 6:47 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Re: caps and pvc?
> Great explaination of what causes one material to have a dielectric constant
> of 2.3 (like PE ) and another to have a value of 6,000 (like barium titanate).
> I have heard that some "super capacitors" have porous metallic plates to
> increase the surface area and thus the capacitance............any ideas on
> this Bert ?
>                   Dan


All electrolytic caps use the technique of using a thin anodized layer
for a dielectric and surface roughness or even porous electrodes to
dramatically increase surface area. Recently, this technique has been
extended to using carbon aerogels (and other materials) to dramatically
increase surface area and capacitance (Ultracaps or Supercaps). You can
get incredible surface areas vs volume with these material, and thus
incredible capacitance/volume. 

Very recently one of our favorite capacitor makers, Maxwell has
developed a new line of ultracapacitors. These have such a high
capacitance/volume that you can easily hold a several hundred Farad
capacitor in your hand - the technology can provide up to 40
Farads/cubic centimeter!. Some ads (by another vendor) have touted that
you could actually use these to start your car, and Mazda is
experimenting with an electric vehicle (called the "Bongo Friendee" :^))
that uses Ultracaps in a series/parallel bank having 1800 Farads at 92
Volts (peak energy = 7.6 MegaJoules)! Ultracaps can withstand very high
charging currents during regenerative braking that would "kill"

Like all electrolytic caps, they're polarized, and operate at low
voltages. Some supercaps use sulfuric acid as the electrolyte (much
nastier than mineral oil if they decide to explode). In short, they're
absolutely lousy for any kind of Tesla Coilin'...

-- Bert --