Re: Capacitors


I checked out your diagrams and I'm not clear on how you'd get them to work!
(A) appears to have no connections for either side of the cap (B) appears to
only have one set of plates and (C) is similar to (A). You want in ssuch a
design to arrange for one plate to overhang the dielectric on one side, the
next on the opposite side and so on, and all the plates on either side should
be connected together with a nice bus-bar, either side forming either terminal.
Allow substantial borders without foil to prevent flahover on the edges - ie a
good 1-2" dependant on voltage. You need more spacing on the edges where the
plates come out of the cap. Voltage rating is dependent on total dielectric
thickness. You probably need about 0.1" thickness at least for 10kV, you might
need to do two in series using 0.06" LDPE.

However, you may want to save a *lot* of effort (believe me cutting and
stacking one of these is BORING!) by going for the MMC design. This uses
series/parallel arrays of lots of small polypropylene capacitors that you can
find in many common component catalogs. I got mine from RS - they were EVOX -
Rifa PHE428 types, rated 0.047uF at 2500V. I used strings of  7 of these in
series, and 10 of these strings in parallel, for a total of 0.067uF at
17,500kVDC. Terry has had some success using far fewer than this - also look at
Gary Lau's and Finn Hammer's pages for more examples.

Alex Crow

Tesla List wrote:

> Original Poster: "Tabraze Malik" <tab-at-malik13.freeserve.co.uk>
> Hi all, it Tabraze,
> As you all know I'm new to Tesla coils. I first began researching coils 4
> weeks ago, and I feel I am ready to build one.
> There is still some confusion over the construction of capacitors.
> I have decided to build a vertically stacked plate capacitor, but I am a
> bit confused as to how to orientate the plates and dielectric with respect
> to each other. I have included a bitmap of what I think capacitors like
> these should look like. Please could anyone tell which one is correct?
> Also I will be using the following formula to calculate capacitance:
> C=(((8085*10^ -12)*DC*A)/D)*(N-1), but how can I find out how much voltage
> the capacitor can take? When I use the specs of the transformers secondary
> to find its impedance then using that value to find the capacitance I need
> will the output voltage of the transformer be the voltage that the
> capacitor can take? If this is true will I have to make a 2nd capacitor,
> connect it in series with the 1st to increase voltage, then make another
> two connected in series which will be connected in parallel with the 1st
> series to bring the entire bank to the required capacitance. will this make
> a safe capacitor? or do you suggest using more series/parallel combinations?
> I intend to connect the plates together using aluminium ducting cut into
> strips. Is this ok? I am thinking of soldering the aluminium strips to the
> plate. Is this a good idea? will I have to use special solder?
> I intend to seal the capacitors so is it a good idea to use a pressure
> release system in the capacitors?
> I have included the design of the pressure release system in the 1st
> bitmap. could anyone suggest improvement methods? will this system be
> adequate? Has this been used before?
> http://users.better-dot-org/tfritz/Capacitor2.bmp
> <<< I posted the bitmap file at the above site.  Since the Tesla list has
> so many members and many of the server links are over modem, file
> attachments are not allowed on the list.  A single 300K file multiplied by
> 500 members means Chip's computer would have to send out 150 megabytes of
> E-mail over his modem!  We ask that you post such files on the web or offer
> to send it to those that are interested directly.  I can post them too but
> I only have so much time in a day... - Terry >>>