Re: Steve's Q.C.W coil design
Dalus, Tue Mar 16 2010, 08:06AM

He controls the bus voltage in order to create optimal conditions for spark growth.

Re: Steve's Q.C.W coil design
raff, Tue Mar 16 2010, 09:30AM

so is it like half wave rectified mains(controlled) CW DR ? just guessing

Re: Steve's Q.C.W coil design
Coronafix, Tue Mar 16 2010, 09:51AM

What does the Q stand for? Maybe it stands for Q.

Re: Steve's Q.C.W coil design
Steve Conner, Tue Mar 16 2010, 10:09AM

Quasi.

As far as I know, it's a DRSSTC with the bus voltage controlled dynamically by a Class-D modulator.

I want one too

Re: Steve's Q.C.W coil design
brtaman, Tue Mar 16 2010, 10:11AM

I had very similar results to steves coil while testing my interupted sstc. No where near the output length though! That is a most impressive coil, I must say!

I codenamed the entire set-up "Prancing Sword", as the output was a single branching sword spark which at the right interrupter frequency gave off the illusion of dancing.

It was a PLL driver ala Mr. Conner, filtered half-bridge. I am sure that Mr. Wards system is much more complex than what I had set-up, mine seemed to mimic his coil to a great extent, too bad I never got around to adding a resonant capacitor. What I do remember is that a very specific coupling/primary geometry, phasing and PLL pot setting was required for the prancing sword, anything off the "ideal" just resulted in regular ISSTC output. Seeing this coil makes me want to revisit the project and add a resonant cap...

Re: Steve's Q.C.W coil design
Dr Hankenstein, Wed Mar 17 2010, 02:27AM

Yah, I took a close look at Steve's incredible coil at the Teslathon. Very ingenious and clever. I believe he's using a 4CX250B tetrode mounted on a liquid cooled heat exchanger for the modulator along with a really big SCR for the pulsed audio. Brilliant! Way to go, Steve!

Re: Steve's Q.C.W coil design
Steve Ward, Wed Mar 17 2010, 03:18AM

Dr Hankenstein nailed it on the head! Good job

Im not terribly eager to give out the details of the build, its really quite complex compared to any other project ive posted before. The thought of documenting it to the point of it being copy-able isnt really my idea of fun. Sorry guys, i just dont have the time for this stuff lately.

Conner explained it correctly, i modulate the bus voltage into a "high-impedance" DRSSTC operating at 350khz. The fact that i can operate with 16mS long ramp pulses (its arbitrary in fact) allows for 54" sparks from the 9" resonator.

Theres some more pictures of the system as it developed on my flickr page:



In a year from now, this will be the standard and we will all be waiting for the next cool tesla coil

Re: Steve's Q.C.W coil design
Arcstarter, Wed Mar 17 2010, 03:45AM

I have heard about this coil, but i have never seen it. My jaw dropped, and i got reallly pissed that i could not have come up with it.

That is amazing as hell!

Only a few questions, i promise. Unless you want to have the only one (i would have done it that way...).

Is this nearly the same driver and power/tank section of a drsstc?
Is the main difference the control of the buss voltage?

I have absolutely no idea how you did this, which pisses me off . But, it pisses me off in a 'good' way. I need to do random things like cramming bananas into the buss bars on IGBTs and stuff to see if i could come up with something.

Good luck.

!!!

Re: Steve's Q.C.W coil design
Dr Hankenstein, Wed Mar 17 2010, 03:51AM

The 4CX250B is in series with the Buss and is modulated with the 1600A SCR

Re: Steve's Q.C.W coil design
Arcstarter, Wed Mar 17 2010, 04:04AM

*gives Hankenstein an odd look*

I think i am starting to understand what Steve was doing. Just allowing the sparks to form before pushing a ton of power into it so that the conductive ionized path is created slowly to make the sparks grow in a certain way? And the reason for the really thick sparks just being because the on time is high, even though there is alot of time being spent to get the streamer to the max length?

Hmmm. If only i was smart enough to understand without an explanation . Also i have nothing to generate an arbitrary waveform, except my computer (which HAHA no.).

Re: Steve's Q.C.W coil design
Dr. Drone, Wed Mar 17 2010, 04:16AM

Re: Steve's Q.C.W coil design
BSVi, Wed Mar 17 2010, 08:59AM

Steve Ward, you are my engeneering idol ))

And the question (there are lots of them in this thread, i know)
What is the bus voltage profile vs "on" time in your QCW ? Is it just linear, or really needs to be arbitrary?

Re: Steve's Q.C.W coil design
Finn Hammer, Wed Mar 17 2010, 09:10AM



But Steve..

Most of your work was popularized with board kits from Eastern.
How is he going to make those boards, if you don't post details

Cheers, Finn Hammer
(With his tongue stuck firmly against his cheek)

Re: Steve's Q.C.W coil design
ragnar, Wed Mar 17 2010, 10:08AM

Tell me about it!

Re: Steve's Q.C.W coil design
vasil, Wed Mar 17 2010, 03:24PM

Steve, how would be the bus voltage? Something like that:



The tube modulates the voltage envelope, each ON burst re-ignite the streamer channel at higher voltage allowing it to grow?

If I would know how this is like, I will manage myself with other details.

Re: Steve's Q.C.W coil design
Steve Ward, Wed Mar 17 2010, 05:31PM

Vasil,

The bus voltage ramps up continuously over a period of 16mS maximum. During this time, the DRSSTC is operating "CW". It is very similar to how a VTTC operates on a level-shifter power supply.

On my flicker page you can see where i use a compound ramp to first grow a spark about 2-3 foot long, and then i ramp even faster at the end to make the channel split into a few branches.

What is the bus voltage profile vs "on" time in your QCW ? Is it just linear, or really needs to be arbitrary?

A straight ramp works quite good, though i've tweaked the shape slightly to get the longest sparks possible. The ability to generate a variety of shapes allows you to control the behavior of the spark. Slow ramping causes the spark to wander and curve, too fast causes the spark to split or sometimes become gnarly and kinked. You can change the ramp rate throughout the spark to give distinct features to it as it grows... the spark channel is itself the breakout point for future growth.

If only i were a PHD in plasma physics, i could probably get published if i wrote something :P.

Re: Steve's Q.C.W coil design
teravolt, Wed Mar 17 2010, 07:33PM

Steve do you think that sthe sword sparks are created by you buss modulation or the fact that your coil is 350k? I have been told by others that they think it is the 60hz wave component in a VTTC or some DRSSTC powered from recified AC that is the reponsible component of sword sparks and others that it is the secondary resonant frequency, what do you think? Just fom obsevation hear I think that is the buss modulation. Some how you building this gives me the impresion that you have been invesigating it and that is the a step to controling spark shape.

Re: Steve's Q.C.W coil design
Arcstarter, Wed Mar 17 2010, 09:15PM

Seriously, what is all this talk about a tube?

Did you use power transistors for the control of the buss? I'd have no idea how to do it even if i knew, just curious.

Re: Steve's Q.C.W coil design
cjk2, Wed Mar 17 2010, 10:41PM

I just want to express how amazing your coil length to spark length ratio is. Is this a record? You should really consider a patent so some company doesn't come along and create a "personal defense system" (weapon) or some other nonsense using this idea.

Re: Steve's Q.C.W coil design
Finn Hammer, Wed Mar 17 2010, 11:19PM

So if we could drive our tube coils off, say, 16Hz mains frequency, we could get in the ballpark of your design?

Cheers, Finn Hammer

Re: Steve's Q.C.W coil design
Dr. Drone, Thu Mar 18 2010, 12:53AM

Re: Steve's Q.C.W coil design
ScotchTapeLord, Thu Mar 18 2010, 02:17AM

:( The video is private...

Re: Steve's Q.C.W coil design
Dr. Drone, Thu Mar 18 2010, 02:24AM

Re: Steve's Q.C.W coil design
Arcstarter, Thu Mar 18 2010, 03:00AM

Holy crap! Eureka moment. Thanks alot, now i understand!

Also, incredible video! Good job Steve, thanks for the video Jeff, and thanks for uploading it Dr. Spark ;-D

Re: Steve's Q.C.W coil design
Dr Hankenstein, Thu Mar 18 2010, 06:11AM

Yah, those babies were at least four feet long...maybe closer to five! I've never seen anything like it..pretty bad ass! Must be the way he controls the 4CX250B buss modulator tube. Awesome. Steve..you da man!!

Re: Steve's Q.C.W coil design
Steve Conner, Thu Mar 18 2010, 09:31AM


This has been done. I remember Pete Bitar and the Tesla Rifle fiasco well.

Yes, it is a record, it beats my previous record of 5ft from a 4.5 x 13" resonator, though someone else may have beaten that in the meantime.

Great work Steve, I've ordered some 4CX250Bs, a big SCR and a water cooling bucket, and will try to repeat your results ;)

Re: Steve's Q.C.W coil design
Austin, Thu Mar 18 2010, 05:07PM

Great work Steve!

Re: Steve's Q.C.W coil design
BSVi, Thu Mar 18 2010, 05:15PM

I can't understand why are you talking about 4CX250B. What are they used for?

I think that Steve's design is fully solitstate.

Re: Steve's Q.C.W coil design
Goodchild, Thu Mar 18 2010, 06:10PM


lol it's a joke

Re: Steve's Q.C.W coil design
dex, Thu Mar 18 2010, 06:44PM

Well,you can measure secondary current waves and compare it with the spark effects observed.
That should provide some info in a start.

Re: Steve's Q.C.W coil design
Mates, Thu Mar 18 2010, 06:56PM

It might look like Dr. Spark spreaded misinformation (some might understand his posts in that way...). There are no tubes involved in this coil design. In case they are I eat my hat.


Cheers Mates

Re: Steve's Q.C.W coil design
Arcstarter, Fri Mar 19 2010, 02:26AM

I will tear a laptop screen apart and eat the plastic film inside!

Steve, we do not need you, we have put this among ourselves to figure it out!

Re: Steve's Q.C.W coil design
TeslaCoilBuilder, Fri Mar 19 2010, 12:14PM





Only 12 inch long, but I run it without modulated bus voltage and only 130Vdc on the bridge fres is also a bit lower (~325kHz)

Re: Steve's Q.C.W coil design
Mates, Fri Mar 19 2010, 08:56PM

I have a provocative question for Steve...
Is it the fact you have some commercial or let’s “publication” plans with the new coil setup, that you don’t want to reveal any details (that’s of course fully understandable) or is it because you actually don’t know what you are exactly doing that the streamers are so cool and “doing what you want" and you just empirically run into this phenomenon?

Mates

Btw: My guess about this setup is quite simple – valve (like a big IGBT or SRC) is in series with the bus and is driven by some kind of PW generator like tl494.

Re: Steve's Q.C.W coil design
Steve Ward, Fri Mar 19 2010, 10:17PM

Is it the fact you have some commercial or let’s “publication” plans with the new coil setup, that you don’t want to reveal any details (that’s of course fully understandable)

I might wish to write some paper for publication. But, im tired of people ripping off my stuff and putting very little effort into it themselves. Ive given away a fair amount of details and ideas, figure it out yourself if you think its easy.

or is it because you actually don’t know what you are exactly doing that the streamers are so cool and “doing what you want" and you just empirically run into this phenomenon?

The only part i dont fully understand is the physics of the plasma itself. Making the sparks straight was no accident, completely part of the design from the start, but it was based strongly on previous experience with quasi CW coils.

Btw: My guess about this setup is quite simple – valve (like a big IGBT or SRC) is in series with the bus and is driven by some kind of PW generator like tl494.

Its not a bad guess, and the design doesnt have to be as complex as what im doing, its just a question of the performance you expect. I happen to be quite comfortable with embedded micro-controllers and classic control theory applied to power electronics, both things make this project more advanced than your typical DRSSTC. To educate everyone who wants one of these gizmos to the level of understanding of the technology that i have is just not something i want to do (go to school and get your own EE degree, you'll be better off!). And yes, i do enjoy that my work has performed so well, but no im not trying to rub it in anyones face. If you notice, i wasnt the one to bring up the subject of my work in the first place.

I think anyone who is capable of reproducing my results already knows enough to design it their own way anyway, so im gonna leave it at that for now. Perhaps all they needed to know is *that* it could work so well, and now its just a matter of implementation.

I will soon record some various measurements of this system under different sparking conditions as i believe this would stimulate some great discussion.

Re: Steve's Q.C.W coil design
hvguy, Fri Mar 19 2010, 10:48PM

I built a coil very similar to Steve's about a year ago. It was a 4KW, power factor corrected, modulated SSTC with a ~7KHz band width that was designed to explore high power audio modulation. The results where good, I could get a 24" full audio flame but the audio quality was not quit as good as I had hoped for and the project was exceedingly expensive. There is still so much research waiting to be done with very high power (+10KW) CW systems, but, honestly, this stuff is far beyond the average coiler in terms of both budget and ability. The time it would take to document everything, publish it, and answer the inevitable slew of questions is just too much for anyone with a life outside of the project. I understand and agree with Steve's approach to his, very cool, system and I do feel that anyone capable of building something similar will likely use the knowledge gained from his videos, pictures, and this thread to move forward with a design of their own. I say good on Steve for putting as much as he has out there...

Re: Steve's Q.C.W coil design
cjk2, Fri Mar 19 2010, 10:50PM

I am quite interested in trying this with a buck converter as you used and a PLL based driver. Care to comment about the power requirements of this coil?

Re: Steve's Q.C.W coil design
Steve Ward, Sat Mar 20 2010, 01:14AM

The coil runs from 240V mains, Hankensteins amp meter said i was using about 15A typically. I havent done any serious power measurements for wall plug consumption other than that. I dont actually have power factor correction on this system since it was a prototype and i wasnt worried about getting the current draw way down. You can always operate it at like 1 pulse per second and just use a big filter cap bank and run it from a normal 120V 15A outlet. For my system the primary current is limited at 140A, this equates to about 100A peak from the synchronous buck converter, so keep the duty cycle low.

Re: Steve's Q.C.W coil design
hvguy, Sat Mar 20 2010, 02:32AM

I'm having site issues so the pictures associate with my post are no longer available as links, here they are for reference.

Re: Steve's Q.C.W coil design
raff, Sat Mar 20 2010, 03:04AM

OT

hey hvguy

your uploaded pictures seem to have virus? I get this RED SCREEN with a warning sign...

Re: Steve's Q.C.W coil design
cjk2, Sat Mar 20 2010, 04:09AM

Those results with a primary current of only 140A are very impressive. I am surprised you chose to use mini bricks for a current that low. Don't the to-247 devices handle 200A or so? Perhaps you have plans to build a bigger coil using this idea? I was also surprised by the fact that you used a synchronous buck converter, If i do attempt this type of coil, I will probably just use an ultrafast diode in place of the second switch.

Re: Steve's Q.C.W coil design
BSVi, Sat Mar 20 2010, 06:58AM

The physics is quite simple, I guess.

Firstly, you create plasma channel and heat it up. When plasma forms, it loads secondary and prevents excessive voltage rise - thats why streamer doesnt strikes into primary or strike ring.

Secondly, when air get ionized, you apply more power, and thus compenase for losses. The easiest way for current to get closed is to propangade throuh ionized air.

The streamer is held in vertical plane by toroid's field and, I think, you can get even longer sparks by increasing toroid's diameter.

And question again - what coupling do you use? I expect it to be near 0.4 or so. Quite impressive!

Re: Steve's Q.C.W coil design
dex, Sat Mar 20 2010, 10:39AM

Just on the contrary.The physics involved is quite complicated.
Many of the things ,especially regarding optimization of the driving mode for the longest possible spark:
a) given peak voltage
b) given peak power and frequency

are poorly understood...

Re: Steve's Q.C.W coil design
Steve Ward, Sat Mar 20 2010, 04:57PM

The streamer is held in vertical plane by toroid's field and, I think, you can get even longer sparks by increasing toroid's diameter.

I used to agree with that, but not anymore. The streamers are more than 6X the diameter of the toroid, certainly not "near field". The propagation is fairly independent of the toroid field i believe.

BTW, its not that i dont have any clue about the plasma stuff, im just not willing to claim that i understand it. So very basic observations are not likely to benefit *me*.

Those results with a primary current of only 140A are very impressive. I am surprised you chose to use mini bricks for a current that low. Don't the to-247 devices handle 200A or so? Perhaps you have plans to build a bigger coil using this idea? I was also surprised by the fact that you used a synchronous buck converter, If i do attempt this type of coil, I will probably just use an ultrafast diode in place of the second switch.

ONLY 140A?? I think you miss the implications of running long pulses, there is serious heating of the device. Though i did run similar conditions of about 80A peak using some TO-247 transistors and got to 45" sparks running them right at 600V bus, where they then failed (not unexpected).

BTW, i should mention that im over the whole idea of pushing parts way beyond their reasonable limits. It really doesnt get you anywhere in the long run.

Re: Steve's Q.C.W coil design
teravolt, Sat Mar 20 2010, 06:02PM

Hello Steve, it seems that the rather large primary has the added effect if increasing your coupling, do you think that that helps in power transfer to your spark since you use a system that is geared to a CW operation? It seems that your primary and secondary is more efficient than a regular setup. Because your tesla primary is a high impedance primary and you use less current do you have to increase the amount of voltage to make up the wattage or do think the coupling is good enough or both

Re: Steve's Q.C.W coil design
Arcstarter, Sun Mar 21 2010, 03:00AM

BTW, i should mention that im over the whole idea of pushing parts way beyond their reasonable limits. It really doesnt get you anywhere in the long run.

I am hereby revoking your coiler license!

My guess was that the plasma that forms when the buss voltage is low acts like a breakout point for the next increase in steamer size and so on. Whatever if i am wrong, i have it all worked out in my mind, how i think it would happen. I can just kinda visualize it working. I am weird like that.

Re: Steve's Q.C.W coil design
Dalus, Sun Mar 21 2010, 08:42AM

My guess would be that a ramped wave form of the bus voltage allows for a slower growth of a streamer. There is more energy put into a smaller distance of streamer then with a conventional DRSSTC. The more energy in a streamer the hotter it is and the longer it stays ionized. This is just a guess but it might be a nice project to research this with highspeed camera's whilst measuring different parameters of the coil and trying to figure out a relationship between them.

Re: Steve's Q.C.W coil design
brtaman, Sun Mar 21 2010, 11:11PM

Personally, I find it quite cool that you are not disclosing the exact way in which the QCW works. I think it may be grounds for a challange of sorts for all the coilers on the forum.

Basically we all start designing/experimenting on making a coil similar to Steve Wards and at a set point (3 months or so), we open a thread with pictures and disclose how we came to the result. I think it would be quite interesting to see how the different minds on this forum each had their own way of achieving the "Prancing Sword" style tesla coil?

What do you guys think about that? Personally I am already hunting for some mini-bricks or an extremely fast 32mm packaged brick, as to-247 and 264 just aren't going to cut it on the thermal front, as Steve mentioned.


Best Regards,
brtaman

Re: Steve's Q.C.W coil design
GeordieBoy, Mon Mar 22 2010, 05:11PM

A challange sounds like a good idea. I've already thrown out all my solid-state gubbins and started investing in those infamous 4CX250B's !

-Richie,

Re: Steve's Q.C.W coil design
cjk2, Tue Mar 23 2010, 03:58AM

Yes, I have been working on designing a full bridge, Driver, Class D amp, etc. Since I saw the pictures that Steve posted. I am going for to-247 based design to start, if I blow that up and don't get at least 40" or so, I will move up to minibricks :)

Re: Steve's Q.C.W coil design
Mates, Tue Mar 23 2010, 01:28PM


Actually I see it in exactly opposite way. Why classical CW SSTC does not produce long streamers? The answer might be in too much of energy in the beginning of the streamer. I think you don't need too much of energy to start the streamer but after it is started you need to pump more and more energy to keep it "alive" I see the bus modulation something like this:

Re: Steve's Q.C.W coil design
Turkey9, Tue Mar 23 2010, 02:19PM

With that wave form you would be ramping the power, not the voltage... makes sense because the total power is what needs to change, so just increasing voltage isn't the only way to do it. PWM the bus would be easier too in my mind.

Re: Steve's Q.C.W coil design
Dr. Drone, Tue Mar 23 2010, 04:02PM

Re: Steve's Q.C.W coil design
brtaman, Tue Mar 23 2010, 04:06PM



I will do you one better I am saving up for a couple 4CX1000As I will parallel all of them...you guys will have nothing on me...!

Re: Steve's Q.C.W coil design
ScotchTapeLord, Tue Mar 23 2010, 04:11PM


If too much energy in the beginning of the streamer caused poor sparks, then the SGTC would not be very impressive, considering its damped waveform... Though it seems to me that the DRSSTC has the opposite waveform from the SGTC, yet both produce similar effects.

Re: Steve's Q.C.W coil design
Steve Ward, Tue Mar 23 2010, 04:32PM

The streamer impedance is dynamic vs time and length (volume). IF you try to grow a long streamer in a short amount of time, you need a tremendous voltage to do it. If you allow the streamer to grow over a very long time, the voltage requirement can be much lower. Applying the right dv/dt to the spark as im doing in my system appears to yield extremely efficient spark propagation at fairly low voltages (less than 100kV i still claim).

If too much energy in the beginning of the streamer caused poor sparks, then the SGTC would not be very impressive, considering its damped waveform... Though it seems to me that the DRSSTC has the opposite waveform from the SGTC, yet both produce similar effects.

I claim the mechanism for spark growth is different from a "transient" coil like a SGTC or fast DRSSTC. In a DRSSTC, if you use a low enough tank impedance you can get similar secondary energy ring-up times as a SGTC. I do not see a "fast" DRSSTC as being much different than a SGTC. I think in terms of efficiently growing sparks *fast* the SGTC wins because it dumps the energy into the secondary faster than most DRSSTCs can withstand (the silicon is a limit). On my large experimental DRSSTC i used a 1.25uF tank cap and was able to get 12 foot sparks with just 5 RF cycles of drive. I think the secondary voltage rise time was on par with SGTCs.

Someone asked about coupling. Of course higher coupling is better in a steady-state energy transfer sense. It essentially means that you have less "reactive" energy stored in the primary. If i was to lower the coupling, id have to greatly increase the primary current to achieve the same results. If i thought i could get away with higher coupling, i probably would. I think the K is around .5 to .6 right now. I do get an occasional flash-over from the side of the secondary to the primary, but so far none of them have been very destructive. I think my over-current detector catches the condition pretty quickly before much energy can be put into the arc, which is also sort of a nice consequence of the higher coupling.

Re: Steve's Q.C.W coil design
dex, Tue Mar 23 2010, 08:54PM

If the frequency is below 500 khz,no matter what you do,and what driving mode you use,you will not get more than 5 foot long air sparks with less than 100 kV.That's not possible at normal altitude.That's what I claim

Re: Steve's Q.C.W coil design
Patrick, Tue Mar 23 2010, 08:57PM

Dam steve, once again you prove yourself to be an ace of the coiling. QCW is masterful in form and function. Yeah, i bet people stealing your work and not putting much of there own effort in, ticks you off.

-Patrick

Re: Steve's Q.C.W coil design
Coronafix, Tue Mar 23 2010, 09:05PM


40 years ago huh?....75 foot sparks!....mmm....
must have been for the Pine Gap secret UFO base that is accessed by submarines through the secret
tunnels under the Great Australian Bight.
Perhaps 75" sparks? Or perhaps it really is disinformation.

Re: Steve's Q.C.W coil design
Dr Hankenstein, Wed Mar 24 2010, 12:28AM

No, it's true. Back then I built a similar coil using a six-pack of 4CX250B's but due to only having a 60A electric service to the house, I was only able to obtain measly 68 footers..nowhere near as efficient or extreme as Chris's two-tuber. FCC shut me down, coil was desroyed in a hurricane and I haven't been able to acheive similar results since...rotten shame.

Cool thing about the 4CX250's is that the screen grid can be amplitude modulated for cool audio discharge. (Also known as "swamp modulation")

Re: Steve's Q.C.W coil design
tobias, Wed Mar 24 2010, 03:30AM

Holy crap!!
I'm 64 feet tall. A spark that long shall make a spectacular noise!!
What is the size of the coil to make sparks +68' ? Back then you guys were able to achieve what resonator/spark length ratio?

Re: Steve's Q.C.W coil design
teravolt, Wed Mar 24 2010, 04:52AM

Thanks for the reply on the coupling question, Richie mensioned that coupling and power are the two things that grow sparks in his website. Do you think that it is frequency or method of modulation ie. drsstc, vttc, sgtc ect. Dr. Spark and you have found that frequency is a factor for sword sparks and I have had others feal it is modulation that is responsible for sword sparks. Do you think that ramping the energy at a lower resonsnt freq like 100k might give simular results as your coil, if so perhaps a larger coil with larger igbt could be utilized.

Re: Steve's Q.C.W coil design
Mates, Wed Mar 24 2010, 07:40AM


I think the size of the resonator (resonant freq.) is pretty much the determining factor for sward-like sparks but not the only one. One of my fastest coil I have ever made was 220KHz and it never showed sward-like streamers

On the other hand, I also had a coil which resonant frequency was 380KHz, but because of slow transistors I had to drive it in 1/2 resonant freq – in that case it never showed sward like streamers , but the same coil once driven in full resonant freq. showed swards (unfortunately it was just a short run which destroyed the IGBT)

Re: Steve's Q.C.W coil design
teravolt, Wed Mar 24 2010, 01:42PM

thanks mates genraly all the coils that I have seen that have swod sparks have been small and therfore have higher frequency. The coils of this type that have streight sword sparks have some sort of AC modulation IE VTTC and others that have no filter caps and or are driven by half wave AC power sources. I am wondering if there is any corilation since Steve seems to be able to have some controle over the shape of his sparks.

Re: Steve's Q.C.W coil design
GeordieBoy, Wed Mar 24 2010, 02:13PM

In my experience it is the modulation envelope of the RF burst that mostly determines the spark appearance.

1. A very fast rate of rise of the RF envelope gives rise to multiple branches and a pretty typical lightening-like appearance to the sparks. Like in a conventional spark-gap TC. (Primary-side losses in spark-gap TC's dictate that the secondary voltage must always rise quickly over a small number of RF cycles. So they almost always display thin jagged sparks with multiple branches.)

2. A slow rate of rise of the RF envelope shape tends to produce fat sparks that grow in a straight line without branching. Nothing kills the straight sword-like sparks better than an abrupt increase in terminal voltage though, as this gives rise to branching instead of steady growth. As mentioned VTTC's and SSTCs running off half-wave rectified mains frequently display sword-like sparks due to the slow rate of rise of the AC half-cycles that define the RF envelope. However, if they are mistuned and suddently pull into tune with corona loading, the straight swordlike sparks will be replaced by gnarly sounding branched sparks.

3. Prolonged RF bursts seem to make the spark appearance more bushy and fuzzy as the conductive channel presumably moves around due to heating effects, air current and what have you. Just prolonging the application of a fixed level of RF doesn't seem to make the sparks grow any longer just get hotter and move around, so it doesn't seem worthwhile if you just want long sparks.

As for what is most efficient for growing the longest sparks possible regardless of shape I really haven't got a clue. Since Steve W is very relatively long 16ms bursts, and I would have thought there was quite a lot of energy in each of the bursts. So it's probably not really that efficient from a spark length vs bang energy input point of view, but the spark shape and brightness is very impressive.

The long bursts are quite hard on the power electronics because there is considerable power being dissipated over a significant amount of time. In DRSSTC's with short burst lengths you can run tremendous currents because the burst lengths are usually shorter than the thermal time constant of the semiconductor dies. One you start generating 16ms bursts, the dies are definitely going to heat up due to conduction and switching losses over that time!

It helps if you can keep the devices as cool as possible before the bursts so you have more headroom for heating during the transient overload during the burst. Maybe that is why Steve used water cooling!?!?

-Richie,

Re: Steve's Q.C.W coil design
teravolt, Wed Mar 24 2010, 07:46PM

Re: Steve's Q.C.W coil design
Steve Ward, Wed Mar 31 2010, 10:01PM

Dex wrote

If the frequency is below 500 khz,no matter what you do,and what driving mode you use,you will not get more than 5 foot long air sparks with less than 100 kV.That's not possible at normal altitude.That's what I claim

Its a curious thing. I suspect that you can set up proper conditions that allow the E-field to become high enough at the tip of the streamer only, which allows long distance propagation with fairly low voltages. This would rely on the existing streamer channel to be a very low voltage drop, and providing sufficient power to the spark channel to keep pushing charge out to the tip so you can establish the required E-field to further propagate breakdown. If there is any truth to what i say, i dont yet understand the time constants involved with these charges moving through the plasma channel. Identifying the time constants involved with tesla coil sparks, i believe, would unlock a huge potential for modeling and resolving a lot of questions about how to best make long sparks. Basically, spark impedance changes dynamically in time vs voltage and apparently the frequency of the source. In the case of the QCW coil, the spark impedance would appear to be much lower than in the case of "transient" coils that operate over just 10's of uS.

Re: Steve's Q.C.W coil design
teravolt, Thu Apr 01 2010, 02:51AM

Hi Steve, to bad you can't do a"time warp" with a stop action camera with simultaneous current monitoring of the secondary to see how the ramped rails and wave shape of the current in the secnondary affects the spark. It seems to me that since your coupling is around .5 you have a lot more control over the power being transferred to the spark than a transient type coil. If the coupling was any lower say .2 the spark shape would be more dependant on the energy stored in the reactance of the tesla and secondary ramp up. The QCW is more like a cross between a regular transformer because you have relatively high coupling witch allows for more direct energy transfer and a tesla wich uses Q for voltage amplification.

Is it harder to tune and keep tuned because the notches are sharper and farther apart with the extra cupling?

Re: Steve's Q.C.W coil design
dex, Thu Apr 01 2010, 07:53PM

The time constants and many other things that affect shape of high frequency sparks are poorly understood.What has been well researched and known is the phenomenon of gap breakdown for "leader free" HF sparks .100 kV or less means that you are dealing with leader free propagation of HF sparks.For such sparks tip radically differs from leader sparks and moving of the charges along the spark channel is pretty uniform while tip has the form of HF brush discharge of stremers.For 100 KV and 300-500 kHz ,max breakdown gap distance is about 5 feet (point to point).Which means that your experiments are already close to that limit.