Re: Polyethylene and RF Chokes

To: tesla-at-pupman-dot-com
Subject: Re: Polyethylene and RF Chokes
From: "Scott Stephens" <Scott2-at-Mediaone-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 29 Mar 2000 06:53:01 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Tuesday, March 28, 2000 9:06 AM
Subject: Polyethylene and RF Chokes

>Original Poster: "Ryan Ries" <spud-at-wf-dot-net>
>
>Hey.  I've been trying desperately to make a working flat plate capacitor
>with polyethylene sheets and alluminum foil.

I just did that, what a mess :-(

>  When I get it done, it
>measures .03番, but it just shorts out as soon as I apply any voltage to
>it.

Mine did at one point, I took it apart and folded the foil back which fixed
it. I am not confident it will last long.

>  But I am sure that the poly is too thin, as well as extremely
>inferior.  If someone has some really thick polyethylene left over (or
>heck, some HV caps at that) that they can sell or send, I would be much
>obliged. :-)

My next trick will be to attempt a rolled cap, because I am not impressed
with the trouble it took to make the plate cap. I'm hoping planning the work
ahead, how I will roll, will save a lot of problems. I have a giant roll of
8 mil poly that is a foot thick and two feet high. I found it has slight
flaws (1mm streches, and is dusty), which I am afraid will result in
problems later. If you E-mail me in a week, I can tell you how the rolled
cap works, so you know if you want to mess with it. In searching the Tesla
ftp site, I remember someone described the process for a PVC roll cap, I
have to look that up now.

Anyways, maybe I can sell you enough for a cap. But I don't want to
dissapoint you if I can't make this poly stuff work. The things people are
saying about MMC is making me think real hard. My ideal I hope to test
sometime this year, is to evaluate how to use higher voltages (50 - 100 KV)
and lower capacitances (1nF) for lower-losses in spark gaps, primary
inductances, and smaller primary caps.

>Also, I have been thinking about making RF chokes. (I am using no safety
>circuit at all right now and haven't blown anything yet, but I still feel I
>should start protecting my investment. :))

You realy better, otherwise you may soon destroy your transformer and what
is connected to it in your home.

>  I saw the air-core chokes on
>the net that looked just like little secondaries.  If I build a couple of
>these, what values am I looking for, and what will do what?

You want a low-pass filter with a cutoff frequency well below your resonant
frequency, but reasonable too. I set mine for 30KHz, using a toroidal choke
and a .001uF 20KV ceramic cap. Definitely use a core to make the inductance
higher and kill the high-Q ringing that will occur. Some put resistors
across them too.

Scott