Re: RQ Schematics

Subject:  Re: RQ Schematics
  Date:   Tue, 22 Apr 1997 20:25:25 +0500
  From:   "Alfred A. Skrocki" <alfred.skrocki-at-cybernetworking-dot-com>
    To:   Tesla List <tesla-at-pupman-dot-com>

On Mon, 21 Apr 1997 21:55:15 -0400 Thomas McGahee
<tom_mcgahee-at-sigmais-dot-com> wrote;

> Precisely, Alfred! I am in total agreement with about 95% of what you say.
> And you don't think that people sometimes open up their main gaps too far?

As I say to my kids when they hit their thumb instead of the nail 
with a hammer, Boy that really dumbs don't it! Cause it sure ain't 
smart! <G> I can understand though that in the excitement on could 
get carried away...

> Your objection about the safety gaps seems to assume that the safety gap
> and the main gap are in parallel. 'Taint necessarily so. Many people use RF
> chokes between the neon and the main gap. Believe me, the voltage that
> develops across such a choke can be enormous. Like very heavy, white angry
> sparks about an inch long! Got chokes? try putting a little temporary
> "spark gap" across one of the beasts using some #21 bare wire, and watch
> the sparks fly! Watch the metal melt! Stand in awe at the savagery of the
> nasty white sparks! (We are assumimg the Tesla coil is operating and
> hurling huge discharges into the ceiling of your garage).
> The logical conclusion of your paragraph above is that in the arrangement
> where the main spark gap is across the transformer, there is no need for a
> separate safety gap. OK, let's look at that conclusion as if it were
> correct. You are objecting because with this arrangement we get to
> *eliminate* a part? Save time and money? Use the parts for some other
> purpose? You consider this a negative? (Scratch, scratch....) Hmmmm. That
> looks like a positive point to me. :)

Actually what I was saying is that there would be no protection 
against HV kick-back, surges ect. What I'm visualizing here is yes 
the gap across the neon transformer's secondary will protect the 
secondary windings BUT it still leaves the capacitor with it's full 
charge to assault the secondary again on the very next cycle. With the 
safety gap across the capacitor AND the neon transformer, as it would 
be with the capacitor across the neon transformer, not only is the 
neon transformer's secondary protected but the capacitor is 
discharged as well, putting an end to the cause of the safety gap 
firing in the first place. To me this would seem to give added 

> But enough with the jesting!! The main special reason why the capacitor
> should *not* be across the transformer has to do with resonant rise. This
> is a condition where low frequency resonance between the neon transformer
> and the tank capacitor causes the voltage across the transformer to rise
> SIGNIFICANTLY above its rated voltage. I think many of us forget that, or
> are ignorant of that fact. Hey, coilers, the resonant frequecy of the tank
> circuit is not the *ONLY* resonance in effect in your Tesla coil! Or why
> else do you think you can pull that main spark gap back REALLLLY far and
> sometimes sustain some pretty long main spark gap arc??? Or why is it that
> you can sometimes get your Tesla coil to operate with only 30 volts coming
> out of the variac??? Resonant rise. Number one killer of neons. Initiating
> cause of arcover and burnt windings and fried neons.

This is why one SHOULD put a safety gap across the capacitor that is 
across the neon transformer, that way the 'resonant rise' would be 
by-passed to ground. Of course this would also prevent one from 
benefiting from the resonant rise and the extra output it should 
bring. This is where the trade off would seem to be.
> Hey, try a simple experiment if you have a meter that can measure 40KV AC.
> Connect your neon alone up to the meter and measure the voltage. Then
> connect JUST your tank capacitor in parallel with the neon and measure the
> voltage now. Aw, what the heck, guys, I don't want any of you to blow your
> neon up or totally trash your beloved capacitor just to prove that there is
> a really good reason not to have too much resonant rise in your circuit, so
> use a variac and only put in about 60 VAC for each of the above trials.
> Now, on some Tesla coils things will look fairly normal, but on other Tesla
> coils, the voltage will appear about DOUBLE. Maybe Barry Benson or some of
> the other coilers that have experienced the effects of resonant rise will
> come forward and put in their two cents worth here. There *IS* a difference
> in what voltage the transformer "sees" when you wire the capacitor up
> differently. Placing the capacitor directly across the transformer *CAN*
> set up a resonant rise that quite easily exceeds the breakdown voltage of
> the neon. Pole pigs are oil immersed and take the abuse without blinking.

Actually this is a very good example of why one should put a choke on 
each leg of the neon transformer's secondary, the choke will block 
the RF from getting back to the neon's secondary windings. 

> By the way, remember all that talk about "matching your transformer to the
> capacitor"??? Well, if you have done that, then you have most likely set up
> a 60HZ resonance between the transformer and the capacitor. Now, such
> resonance can be VERY useful... but it can also put voltages across your
> neons that are MUCH higher than you dreamed! Ah, the wonders of the
> resonant circuit!!!

This is why it is soo difficult to produce a program that will 
accurately predict the output of a TC, the ratio of transformation may 
be easy to calculate from the ratio of primary to secondary 
capacitance but determining the actual voltage in the primary is no 
easy feat!

> The resonant rise can be bad or good, depending on how you look at it.
> Alfred, the resonant rise can actually be beneficial in circuits using
> things like 5KV neons. Assuming that the 5KV neon can take fairly
> continuous 10KV RMS voltage, that is. I have been doing a lot of research
> on the question of neon demise, and resonant rise is often the unsuspected
> culprit.

I've been playing with microwave oven transformers to drive small to 
medium TC's and the resonant rise could be of decided benefit with 
them too, especially considering their low output voltages.

> > In the arrangement with the capacitor across the transformer and a 
> > safety gap across the transformer with the operating gap in series we 
> > have full protection from high voltage surges and kick-back to the 
> > transformer for this would fire the safety gap! 
> OK, I admit that a REALLY GOOD safety gap helps much to remove the danger
> associated with the capacitor across the transformer. But, tell me... is
> your safety gap as robust as your main spark gap? If not, then you may be
> in for a nasty surprise somewhere down the road. Not EVERY spark gap can
> absorb the full current stored in the tank capacitor. I wonder what happens
> then??? To the transformer that is in parallel with the safety gap, that
> is. Poof.

VERY GOOD argument for building substantial safety gaps!
> There are multiple ways of looking at most things. In the arrangement where
> the main spark gap is across the transformer, the transformer will actually
> still see the capacitor across itself. Check it out for yourself. When the
> spark gap is not firing, the capacitor is connected across the transformer
> via the very LOW 60HZ resistance of the Tesla primary. Ah, so you ask, then
> EVEN in this arrangement the capacitor is across the transformer. The
> answer is YES!!! But the difference is that there is also this very MACHO
> Spark Gap designed to take huge surgees of obscene current levels without
> vaporizing (too much or too long...) :)  This SAME Macho Spark Gap shunts
> the nasty super-currents through itself, thus saving the frail and feeble
> neon for yet another surge of sixty cycle current. (or 50 Hz current for
> the European coilers out there). I hope that the picture is becoming
> clearer.
> > The only condition 
> > the gap would not protect against is a total short of the capacitor 
> > but the neon transformer is designed to take a dead short for a 
> > limited period of time besides that condition would cause excess 
> > current flow in the primary which would trip the protective breaker 
> > that should be in the primary circuit.
> The current limiting in the neon is built in, and actually does *not* cause
> excessive primary current. Increased current, yes, but not excessive
> current. In normal use driving a neon gas tube, the neon transformer is
> actually running in current limited mode all the time. The output voltage
> of a 12KV neon when actually driving a neon tube is disgustingly low.
> Something like one or two KV MAX. 

I don't think neon transformers are being operated in the current 
limited mode in a Tesla coil. 

> Neons have their problems, and always will. Or, as Ed Wingate would put it:
> Enough with the stinking neons and the H&R transformers... be a man, buy a
> pole pig, and abuse it all you want. You can hardly kill the beasts. Ed
> sounds like a pretty up front macho guy to me, and I have begun searching
> for a pole pig or potential transformer. When I find one that has a low
> enough price tag I'm going to buy that sucker, throw a couple of $45
> Variacs and arc welders and a clothes dryer in series with the input side,
> and build a three-phase Twin Tesla coil connected up to a 100 KiloJoule
> 50KV 200 mfd military surplus infinite duty cycle pulse capacitor (charged
> by a model T Ford spark coil left over from my high school science fair
> project 30 years ago, and a string of 10,000 1N914 diodes that I got real
> cheap at a ham fest in Hohokus, NJ) that will blast holes in my fluorescent
> light fixtures at a distance of several feet! Of course I will post
> pictures for everyone else to salivate over. Pictures of me with a light
> bulb in my mouth standing next to my four foot diameter 15,000 RPM Salient
> Pole bi-synchronized variable speed counter-rotating air cooled 2 HP 5 inch
> thick teflon coated G10 compressed air operated optimally quenched rotary
> spark gap with brass fitted non-thoriated pure tungsten inserts
> aerodynamically shaped to produce maximum air turbulence, arranged in a
> semi-elliptical pattern of fibonacci related prime number segments with
> multiple vacuum quenched modified Richard Quick static series gaps using
> water-filled solid copper electrodes a la Bert, in a search for pure
> synergy. The design was lifted verbatim from a tape soon to be released by
> TCBOR, and is based on work by John, Ringo, Malcolm, Ed, Fred, Jim,
> Michael, Richard, Richard, Billy, Bob, Bert, Bert, Bert, and Ernie. If I
> left anyone out I am sorry. :)

I had a 14KV pole pig about 20 years ago, now I'm VERY SORRY that I 
sold it!!! Once you've crossed the six feet point on discharges there 
is really no other way to go but to a pole pig.

> A final note. I mentioned tongue-in-cheek that a discussion of Tesla
> circuitry would most likely lead to some heated discussions. I hope,
> Alfred, that you and any other coilers that prefer the
> capacitor-across-the-neon circuit do not take any offense at my remarks
> above.

I certainly don't! I'm always open to others observations, it 
accelerates the learning curve. <G> Besides - No man is an island 
unto himself... (I don't know who deserves the credit for that line 
but it is definitely true)

> I do not want such discussions to generate heat, but rather light.

I think science has always benefited from intelligent debate of 
differing views.

> You made some excellent and insightful remarks in your post. One can,
> indeed, run a decent Tesla coil with the capacitor across the transformer.
> I have done it many times myself. I have a few coils in which I do it that
> way *on purpose*, to make advantageous USE of the resonant rise. But there
> are new coilers out there that may be totally unaware of the potential (pun
> intended) resonant rise and how it can cause a poor neon transformer to arc
> over internally. If such a discussion helps them to see the issue a bit
> more clearly, then our mutual jousting and jesting may be of some use after
> all! Enjoy!

Tom, I have personally enjoyed our comparison of views and this whole 
conversation has caused me to rethink my approach to utilizing 
microwave transformers to drive Tesla coils, so it has already been 
of immense use!


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                           Alfred A. Skrocki
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