Re: low vs high frequency tesla coils?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi again, Joseph!

Date: 18 January 2001 15:27
Subject: Re: low vs high frequency tesla coils?


>Original poster: "joseph gallo by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <juzeppy-at-hotmail-dot-com>
>
>Hi Ralph, Dunckx
>I got the idea to put the two 3kv 20mil amp transformers in
series from the
>poptronics july article where they use four 4kv 30mA
transformers to get 8kv
>at 60mA.for a tesla coil.
>I am using open core France transformers with a plastic
nameplate that
>snapps off and has a date stamped on it.  I tried them in
series with
>alligator clips. there was no corona that I could see on
the windings.
>Fortunately I have not seen a transformer fail. What do I
have to look out
>for. I don't want to fry my trannys but it is tempting to
get the higer
>voltage.   Could I place them in mineral oil to better
insulate the
>windings?
>joseph


Well, it looks like I may need to repent on this one.
Someone else (your forgiveness, I forget who) said these
trannies could be single ended, i.e. without a grounded
centre tap, and from the fact you've tested them OK in
series I think I'm at fault.  If you've seen the same thing
done in an article with the same kind of transformer then I
am likely quite wrong all round.  If you've actually tried
them out and there's no trouble then it looks good :-)
Certainly 6kV will be a lot more fun than 3kV as you say.

I also doubt you really need to indulge in oil insulation
with 2x 60VA.  If it makes you feel better, and if you have
nothing else to fall back on, a bit of engineering overkill
won't hurt, it'll simply increase the mess, time and effort
before you're operational. A good filter is a better
investment of your resources IMHO.  Around 12k ohms in each
HT leg should do - made out of say three or four lower value
resistors in series each about 3W rating and for a cheap
solution, a _small_ bottle cap (~500pF) before the resistors
to ground each side, I think maybe a 4 fluid ounce bottle -
someone closer to home in the US would be a better source of
info on that as I don't know what local products might come
in that size bottle. Plus a simple safety gap at the tranny
outputs and - you're in business.

Terry has posted somewhere* the details you need regarding
capacitor size to enable you to get the best out of your
trannies - I'd hazard a guess (but Terry's calculations will
be better) that you'll want around 66nF which will give you
a whole joule's worth of bang at 120bps, which should amount
to a very impressive spark, with any luck 2 feet :-)

To return to your original query, low frequency is going to
be better than high anyhow.  Several folks have posted
details of TC design software you can get on the web and you
can do worse than trying them. 150kc/s or lower might be a
fair aim with 66nF in the primary.

Do keep us informed on progress.  Best of luck!

Dunckx

*The data I have is bellow. - Terry

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm