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NSTs and Cap Charging - A matter of "SGF" :-)

Malcolm, John, Ed, Richie, All,

	In an off list discussion, a new acronym occurred to me.  "SGF" = Spark
Gap Fibrillation.  The state of a spark gap where the firing becomes
uncontrolled or erratic such that efficiency is lost.

	As John Freau and R.E. Burnett mention today, with large cap values in an
NST systems, a static gap may not have the ability to add the needed
stability to the firing timing.  Thus, with a static gap, the firing may
drastically degrade into a chaotic state and efficiency my fall
drastically.  Just as the heart cannot pump blood efficiently when it's
timing is erratic, our TC's may not be able to pump power efficiently
without a sync gap acting as a sort of pace maker.  An analogy would be a
heart going into fibrillation.  Perhaps we could coin a new acronym for
this "Spark Gap Fibrillation (SGF) :-))  

	This may give sync rotary gaps a big advantage over static gaps especially
when these new larger cap values are used in NST systems.  Since they are a
bit under damped regarding gap timing, the rotary gap may be a required
component to keep these systems firing just as they should for best
performance.

	Of course,  all this has implications in big pig systems too...  I knew
all these fancy computer models would pay off some day ;-)


Making my place in acronym infamy... :-))

	Terry



At 02:25 PM 4/10/99 -0400, you (John Freau) wrote:

snip....
>
>Malcolm, all,
>
>It is possible that using a static gap, the NST has a harder time
>drawing excess power, vs. sync rotary.  Using a sync rotary, you could
>probably use the 565 Watt figure.  Since the losses are so high in
>the NST, it would need to draw maybe 920 watts to output 565 watts,
>I would think.  Also, many coilers (such as myself), often crank up 
>the input to 140 volts or so which will increase both the input and
>output power of the NST.  
>
>My recent tests showed 740 watts input to the 360 watt rated NST
>using resonant charging, at 120 volts input.  I think the power getting
>to the caps is considerably less than 740 watts due to NST losses.
>I'm using the lab type wattmeter to measure input to the NST.  I
>observed the input current waveform and it's not too distorted (not
>much harmonic energy), so the wattmeter should be reasonably
>accurate.
>
>> Case 2: larger capacitor
> 
>> Let Cp = 32nF and assume it charges to 17kV in a half cycle. 
>> Then Ec= 4.62J and throughput = 462W.
> 
>> In neither case is the VA rating of the transformer exceeded.
>> Comments? Flaws?
>
>With the larger cap, with static gap or sync rotary, I saw below rated
>power being drawn by the NST, unless I turned up the input voltage
>to over 120 volts input.  But I have to try fiddling a little more with
>the sync phase to see if I can get it to draw more power at 120 volts
>input.
>
>BTW, if any of my postings of yesterday seem to conflict, it is because
>some where written before my tests, some after.
>
>John Freau
>