From: "Terrell W. Fritz"
Date: Sat, 11 May 2002 21:17:12 -0600
Subject: Re: [TSSP] Topload breakout potentials
Hi Paul,
All Tesla coils are tuned roughly 6% low ;-)
When big streamers are present, the streamers add capacitance to the top load
decreasing the resonant frequency. So to get the maximum power to the streamer
loaded coil, we start off with the primary tuned about 5-8% on the low side.
As the streamer grows to full size, the secondary resonant frequency drops to
match this lower tuning point of the primary.
For the streamer load formula that states a streamer is about 220k ohms in
series with 1pF per foot of streamer length, this roughly works out right.
I have never done it, but I wonder if a few bits of wire bent to the shape of a
streamer and stuck on a secondary toroid would drop the resonant frequency this
same amount. I suppose one might figure out how to put a 220k resistor in
there too.
I am working on getting a simple Faraday cage going so I can play again with my
measurement toys. I was not able to do much for quite some time since the
playroom was in another use. Now the room is free but computers and Ethernet
have spread in the house...
These reports are quite dated and the equipment now is far better but perhaps
of some interest:
http://hot-streamer.com/TeslaCoils/MyPapers/spark1/sparkgap.html
Not also the "raw data":
http://hot-streamer.com/TeslaCoils/MyPapers/spark1/1-42.txt
http://hot-streamer.com/TeslaCoils/MyPapers/spark1/1-8.jpg
http://hot-streamer.com/TeslaCoils/MyPapers/spark1/9-16.jpg
http://hot-streamer.com/TeslaCoils/MyPapers/spark1/17-24.jpg
http://hot-streamer.com/TeslaCoils/MyPapers/spark1/25-32.jpg
http://hot-streamer.com/TeslaCoils/MyPapers/spark1/33-40.jpg
http://hot-streamer.com/TeslaCoils/MyPapers/spark1/41-42.jpg
Be thinking of new information you may wish me to take for your efforts. I
have collected quite an arsenal of test equipment with vastly greater
capabilities since 1998 :-)))) Now it is time to get it working!!
Cheers,
Terry
At 11:25 PM 5/11/2002 +0100, you wrote:
>Marc wrote:
>
>> Topload toroid is a fairly smooth 6.5" aluminum ducting with
>> a total diameter of 30.5" so 6.5" x 30.5"
>> I tried measuring capacitance of it but i came up with 29.6pf,
>> wintesla says 33.01pf for it?
>
>Floating in free space, this toroid would have 32.462574 pF.
>Inside your room (with my guesses for walls, ceiling, etc) it
>comes out around 42.3pF, and in-situ above the coil it contributes
>36.2pF to the total shunt capacitance of the resonator.
>
>The toploaded secondary Fres comes out around 38.5 kHz, I assumed
>the toroid is mounted just clear of the top of the coil. The
>primary seems to be tuned a little lower - 36 kHz, so either
>the model is over 6% out on frequency, or you are doing the
>same as John - tuning the primary to the low side of the secondary.
>
>With a secondary Cee of 44.7 pF, your primary bang energy of
>0.5 * 52 nF * 34 kV^2 = 30J would give a peak topvolts of
>sqrt( 2 * 30J/44.7pF) = 1160 kV if tuned. This topload has a
>highest surface gradient of 0.031 V/cm per volt of topvolts.
>Therefore your toroid surface field will try to reach
>0.031 * 1160 = 36 kV/cm, which ought to give very early
>breakout with lots of short streamers.
>
>Incidentally, if tuned correctly, the average gradient along
>the secondary would be 1160kV/103cm = 11.3 kV/cm, and the
>stress factor for your h/d=4.6 winding is around 1.37, so
>giving a maximum gradient of 11.3 * 1.37 = 15.6 kV/cm, not
>including any 'corrugation' factor.
>
>The computer is currently working on the out of tune model using
>your tap settings and it should be done in a couple of
>hours, so it will be interesting to see what surface gradient
>that reaches.
>
>How can we determine whether Marc's and John's primaries are
>really tuned low, or whether the model is just not representing
>them properly?
>
>Tuning low seems to keep quite a lot of energy in the primary,
>thus reducing the peak topvolts but perhaps enabling the beat
>envelope to be sustained over more beats, thus generating
>fewer streamers but allowing them to grow longer. Is this a
>recommended way to deal with a too-small topload?
>
>--
>Paul Nicholson,
>--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.