Re: pure water capacitor?
In theory it sounds easy -- in practice it's a nightmare. It is very
difficult to keep ions from migrating from the electrodes in the water and
producing slight contamination. They breakdowns begin to occur. Special
electrode materials such as plattinum are required and the whole process
becomes a great learning experience with little true results.
Stick to rolled PE --- a lot easier.
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Wednesday, February 16, 2000 12:50 PM
Subject: pure water capacitor?
>Original Poster: "Mark Broker" <broker-at-uwplatt.edu>
>I'm a very new member to the TC community. I've been interested in
>building one, or two for quite some time, but have never had the
>opportunity ($$$, tools, ect) until recently.
>I'm a senior majoring in Engineering Phyisics (don't ask....) and am
>involved with the SPS (Society of Physics Students). The SPS occasionally
>gives physics demos to local schools. We have a POS 250kV 1/2 wave TC that
>must be 20 years old. I thought that a nice medium-sized 1/4 TC might make
>an excellent "gift" to the SPS as a going-away gift.
>I've been trying to do some research regarding design issues, when I came
>across a list of dielectrics for some materials for use in capacitors. The
>dielectric constant for pure water is around 85 with an infinite breakdown
>voltage! This means that two 12" x 12" plates spaced 1/8" apart will give
>a capacitance of .020uF! I thought it would be a pretty sweet idea: a pure
>water cap in a plexiglass (or lexan (?)) box. But, I have NEVER seen this
>mentioned anywhere I've looked. The only problem I can see is
>contamination: everything has to be 110% clean before adding water. This
>Are there any reasons why I shouldn't try to use this?
>For the record, I'm looking at a 15kV/120mA+ NST.