Re: Certain s.s. phenomena; to J.F. et al

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

Original poster: "Kennan C Herrick by way of Terry Fritz <twftesla-at-uswest-dot-net>" <kcha1-at-juno-dot-com>

 From Ken Herrick, interspersed:
 
On Tue, 13 Mar 2001 22:28:31 -0700 "Tesla list"
<<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com> writes:
> Original poster: "by way of Terry Fritz
<<mailto:twftesla-at-uswest-dot-net>twftesla-at-uswest-dot-net>" 
> <<mailto:FutureT-at-aol-dot-com>FutureT-at-aol-dot-com>
> 
> In a message dated 3/13/01 2:38:41 PM Eastern Standard Time, 
> <mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com 
> writes:
> 
> > 
>>...You are saying, I take it, that such a short coil, vs. the spark-length,
would not tolerate an attempt to establish a horizontal spark.  The spark would
just jump the coil to ground.
> 
> Ken, all,
> 
> It is true that the short coil may not tolerate a horizontal spark, 
> 
> but I was refering to the presence or absence of a breakout
> point.  I meant that if no point was used, and a toroid was
> used, the voltage would build up so high that the coil would 
> break down or arc-over, probably.
 
Right...we're together on this: rather than "horizontal spark" I should have
written "spark from the toroid"--it generally is horizontal, of course, but the
real significance being that the allowed top voltage would be higher & perhaps
too high for the coil to withstand it.

> >  
> >  > 
> >  > In any case, it would appear that tube coils of the typical 
> design,
> >  > have to have a breakout point for longest spark output.  This 
> seems
> >  > to be because of the double-tuned design, the resultant 
> frequency
> >  > splitting, the changes in Q and bandwidth with breakout, and 
> >  > probably related Z matching factors also.
> >  
> >  Well, perhaps...but a) spark-gap systems are also double-tuned, 
> b) I do
> >  not know what "frequency splitting" is, and 
> 
> frequency splitting is the split freq response that occurs in a 
> double-tuned
> over-coupled circuit.  
 
Got it!  The coilers' way of characterizing the double peak of an overcoupled
transformer.
 
I suspect that spark-gap systems have much
> less of a tendency to build up corona on the secondary and primary,
> despite the double-tuned design.  It may be because of the short
> amount of time that the energy is present compared to a CW coil.
> Also, tuning is not the problem in a spark gap TC, that it is in a
> CW coil.  In the spark gap TC, you tune the coil, the energy 
> transfers from primary to secondary, and all is well.  But in a 
> tube
> CW coil, with constant drive with changing impedances, and the
> peculularities of the system, seems to demand a point on the
> toroid for the longest spark:
> 
> If I tune my coil for breakout from a toroid, then I get short 
> sparks.
> If I tune for longest sparks from a point on top of the toroid, then 
> the 
> coil cannot break out without the point.  
 
...So clearly, the attainable voltage has been reduced.
 
The required difference 
> in
> tuning is surprisingly large.  The coil has to be severely 
> mis-tuned
> for operation with no breakout point, so this reduces the spark.
 
With no breakout point, you must be tuned at or near a resonant peak--or, at
least, nearer to one than for the case of using the breakout point, right? 
Because the voltage, to get breakout from the toroid alone, must be higher.  Is
that "mis-" or is it the other case that is "mis-"??
 
> Since the resonator is a tuned circuit, and the tank coil is a 
> tuned
> circuit, they both seem to fight for control of the oscillator to 
> some
> degree, and this makes the tuning situation complex.
 
I should say!  Mine is, I wlll say, more straightforward in that there's only
one resonance and I'm spot on it all the time.  But perhaps because of that I
sacrifice the capability for differing kinds of spark.  Have to look into that!

> 
> >  c) the secondary's Q should
> >  diminish essentially the same amount regardless of the manner in 
> which
> >  the spark is induced to initially break out.  I'd think that the
> >  differing relative impedances during the build-up and sparking 
> events
> >  (Z-matching, as you say) would likely constitute a major factor 
> in
> >  determining the differences in performance of tube, s.s. and 
> spark-gap
> >  coils.
> 
> Are you saying that the impedance changes a larger degree in a tube 
> 
> coil when it breaks out compared to a SSTC?  I hadn't thought about
> that.  I agree the Q's diminish the same amount in either type 
> coil,
> and this Q-drop is certain a big factor.
 
Not the secondary's circuit-impedance--I'd think its change would be the same
regardless.  I meant the relative impedances of primary & secondary circuits. 
I'd think the driving impedance of a tube-driven primary would be a whole lot
higher than that of the usual spark-gap primary.  My MOSFET-switched primary
would be somewhere in between.  Although, it's pretty low all during the
spark-time since it's being constantly driven during that time and consists
only of 3 untuned turns, MOSFET switches and electrolytic capacitors.

[snipped]
> 
> >  >I became intrigued & can now offer something
> >  >quantitative for a change:
> >  
> >  Spark rep-rate & duty cycle, power input: the same.  
> >  
> >  Emitting radius:                   3"      1.5"      a sharp awl-point
> >  E-field deflection on the scope:   8 cm    5 cm      4 cm
> >  
> >  Spark length, appearance:  Essentially unchanged: relatively fat,
> >  branched.
> >  
> >  Now that's interesting!!  The sharp point cuts the peak voltage 
> in half
> >  (surely reducing stress on the coil) but no more than that!  I'd 
> never
> >  have believed it.  At least as observed visually, no sparks reach 
> any
> >  conductor to ground during this test; they just end in air.  
> 
> Duane Bylund did say that his SSTC also saw the voltage cut in
> half with the point.  But the ball he used was only 1" dia, and his
> sparks were just 7" long.  His sparks were also the same length
> with or without the ball I seem to remember.  Your results are
> interesting because they show that it is only a tube coil that
> demands a breakout point for longest sparks, or a coil similar
> to a tube coil in its characteristics.  
 
Hmmm...don't know if I agree: I get much the same appearance/length of spark
from all 3 types of emitters.
 
>Your results are also
> interesting because they show that you don't need to build up
> such high voltages which perhaps stress your MOSFETS to 
> obtain a given spark length.  If you run with the breakout point,
> the impedance won't shift that much, and will shift at a lower
> power level.  This may permit better impedance matching, and
> better efficiency maybe.
 
I see it a little differently:  If I run with a breakout point, I could reduce
the quantity of secondary turns.  Still achieving breakout, I should then be
able to pump more current into the spark during the after-breakout period and
perhaps in that way reach a longer spark.  As soon as I can make up a new
secondary I'll check that out.  Although...I prefer to run such that I can
break out from the toroid if I use no breakout point.  But I have a feeling
that I can still reduce the secondary turns and continue breakout from the 6" x
24" toroid.
 
To pursue that thought, I just measured the reduced primary supply voltage that
is required to just break out from the toroid:  92V rather than the normal ~158
(to be multiplied by 4 and turned into ac in the 4-section 3-turn primary
coil).  That's a factor of 0.58.  So if I were to reduce the quantity of
secondary turns to, say, 2/3 of what I have now, I should still safely break
out--and perhaps with an even larger margin of safety since the secondary's Q
should go up.
 
(All of you 10 KV people take note of that 6" x 24" smooth-toroid breakout with
>>less than 370V<< applied to a 3-turn primary!  Hah!)
 
>Another interesting test would be to
> install a much smaller toroid, maybe just 1 foot in diameter or
> so, instead of the 26" toroid, (sort of a corona ring), and see if
> this has any effect on the spark length and fatness.  Maybe it
> would make the spark output longer.
 
Yes, but I prefer to keep the 6" x 24" in order safely to protect the secondary
from sparking.
> 
> Regarding the branching, maybe a coil that is always in tune
> produces such branched sparks?  My coil which sort of pulls
> into tune at least to some degree can produce straight sword-like 
> sparks.
 
Might well be.  I just tried exciting the system from an external signal
generator in order to check that out, as I have done many times in the past. 
Burned out a MOSFET so I think I'll lay off that for a while.
> 
> >  But perhaps
> >  it is the presence of nearby conductors, nevertheless, that 
> accounts for
> >  the only 2:1 difference in attained voltage between the toroid 
> and a
> >  sharp emitter. 
> 
> I seem to remember that Terry F also saw this same relationship
> in a spark gap TC (2:1 voltage difference after breakout).  It 
> seems
> the sparks are not a terrificly heavy load.
> 
> >  Marco DeNicolai had a relevant posting, on 1/31, on the subject.  
> 
> 
> I can't remember the posting.
 
He'd made a reply to a posting of Gary Johnson, on 1/31.  Also see Bert
Hickman's of 2/15.  They should be archived -at- pupman-dot-com but if you don't find
them I could fwd them to you.

> >  
> >  Very roughly, since I am unable precisely to measure my input 
> power, I
> >  measured around 1.5 mains KW going into 13/second sparks drawing 
> power 6%
> >  of the time.  Each spark, therefor, would contains 1.5/6% or 25 
> KW--over
> >  about 5 ms duration. That's what gets me 2.5-3 ft. sparks.  I'd 
> like to
> >  know how to "massage" that set of criteria so as to push that 
> spark out
> >  further!
> 
> The only thing I can think of to improve things is to somehow 
> improve
> the impedance matching of the system.  If you're willing to make 
> the
> sparks appear pulsed visually, then you can reduce the pulse rate
> even more, to reduce the input power.  The spark length will be 
> reduced some, but the power will probably be reduced even more.
 
It happens that the longest sparks are at the slowest spark rates since the
storage capacitors' voltages don't get sucked down so much.  At 40/second they
pull down quite a bit but then, I need to replace one section of 1000 uF with
1800 uF, and also beef up my switching inductors used for charging, so I can
draw the max. from my 115V line.

> Once this happens, then you can put more peak power into the
> coil, by using bigger MOSFETs if their available at a suitable 
> cost.
> Maybe using more primary turns, such as 5 or 8 will give better
> results.  I realize the effort involved in building such an 
> elaborate design.
 
Yes, more than 3 would give me a huge bundle; it's already almost 2" across.

> 
> It would be good if the impedance matching issue could be analyzed
> by computer to see what the best setup is.
> 
> My 36" spark tube coil drew about 7kW at 60PPS, so at 13 PPS,
> it would have drawn 1.5kW.  But the sparks would no longer have 
> been
> 36" at that pulse rate, they would have dropped to maybe 28"
> or so.   Do your sparks shorten if you reduce the pulse rate?
 
See above.

> 
> John Freau
> 
> >  
> >  Ken Herrick 
Ken Herrick