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Re: Interesting Effects


>> Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
>> 
>> Hello All,
>> 
>> 
>> Playing around with my 8" coil I have noticed something interesting
>> (probably been seen before and commented on) and would like to hear some
>> comments on it. My main gap is set so that I do not need the full power
>> setting on my variac. The spark gap will start to fire somewhere around the
>> 80%  (Variac is a 0-250V model) setting. After the gap begins to conduct I
>> can reduce input voltage (to about 60% on the variac). This doesn't
>> come as a surprise to me, but I have noticed the following:
>> 
>> a.) Reducing the input voltage until the gap is on the ragged edge of
>> conduction, will get me less streamers, but they are a lot longer and very
>> lazy.
>> 
>> b.) Going higher than the 60-65% (to about 80% meaning ~220V) setting gets
>> me shorter streamers, but more of them. Their speed doesn't change
>> much, tho.
>> 
>> c.) "Overvolting" the NSTs (they are designed for 220V, and I am "giving"
>> them 255V. They do NOT saturate at this voltage, I have checked this)
>> doesn't get me any more streamers and does not change their length.
>> However, they start swirling around the toroid like crazy (about once
>> around every second or two).
>> 
>> Now, this is a surprise to me. I figure that at the 60% setting I must have
>> the lowest BPS rate, while at the other end of the scale (255V) I must have
>> the highest BPS rate. The noise that the spark gap makes would support this
>> theory. (More power in = faster recharge rate). >From what I have heard
>> (haven't built my RSG yet) going up in BPS rate will get you longer
>> sparks (otherwise why would coilers do this?).
>> 
>> Before I forget: I am using a 7.5kV NST with 75mA and a 25.5nF cap. The
>> 25nf cap is about 80% of the capacitance necessary for resonant charging.
>> The results (a thru c), however, will work with any cap value I have used
>> so far (9,10,12,15,20nf). I did retune the priamary for every cap used. Of
>> course, the more capacitance used, the longer the sparks get, but the
>> effects are the same.
>> 
>> WHY?!?!?
>> 
>> Coiler greets from germany,
>> Reinhard
>> 


I Reinhard,

	I am familiar with the resonant effect you are seeing.  You can turn the
variac up to a certain value to get the gap started and then you can turn
it down significantly and the gap will continue to fire.  This is caused by
a rather complex resonant interaction between the neon, primary cap, and
the gap.

	In this situation, the maximum firing voltage is not occuring at the peak
of the AC waveform.  There is a point, after the peak, were the firing
voltage is greater.  If the gap were to fire sooner (at the peak) then the
voltage would be reduced due to the resonant effects.  I know that is not
clear but it is hard to explain.  Models and waveforms show the effect well.  

	On page 10 of my last paper "Modeled and Actual Voltage and Current
Waveforms within a Tesla Coil", you can see where my system fires long
after the peak in the AC waveform.  If the firing time moves to the left,
closer to the peak, the overall voltage drops and the actual firing voltage
decreases.

	I was planning on writing a paper on this sometime.  The intital voltage
needs to be high to get the system started.  Then there is are resonant
rise effects that actually make the AC waveform voltage higher than without
the gap firing.  The gap finds it's own maximum voltage "sweet spot" and
goes on from there. 

	Terry
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