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Adam Munich

Wed Sept 28 2011, 10:05PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

So seeing as my x-ray machine requires only one 100ohm pot to be completed, I need another project. Now I was thinking about a 1'*4' DRSSTC to play my bass guitar through, and at first I was like: damn that's clunky...

BUT THEN, I came across steve ward's QCW coil.

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Wow, that is quite amazing. That coil is about what, 1' tall and shoots out those huge lichenburg sparks?! I jelly, and in order to remedy this I must build one of those coils.

Does anyone happen to have any useful info those QCW coils?

[gren hopes this project won't take as long as his x-ray machine did]

Dr. ISOTOP

Wed Sept 28 2011, 10:53PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Ward's coil uses a modulated synchronous buck converter with 300A bricks as the power supply for a full bridge of minibricks (at least it did at one point, not sure what it uses now). Turns out if you feed a DRSSTC with a long triangular ramp, you can control the spark growth and get those long, straight sparks.
The design is pretty new, so there's not much info out there.
The hard part is the buck controller; regulating the pulse is not easy.

magnet18

Thu Sept 29 2011, 01:41AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
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Posts: 624

Dawmn, That's impressive.
Has he posted a schematic anywhere?
I can't find one on google

Weston

Thu Sept 29 2011, 04:10AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

Magnet18, Steve has not posted that much info about his QCW coil, and no schematic. From what I understand, this was to prevent the (often unaccredited) copying of his work.

Think of it as a challenge to design your own version. The concept is not that hard to understand. Sparks propagate differently depending on the rate of the rise in power. Steve has found a sweet spot where the sparks can propagate directly up and he can get large sparks from a small resonator without a fear of primary strikes.

Like bwang said, Steve uses a synchronous buck converter to directly modulate the buss voltage of a DRSSTC. He uses a primary with a relatively high impedance for a lower rise of current and to enable longer bursts. I believe his original coil had around a 300Khz secondary.

There is a thread which Steve started about his QCW coil that you should be able to find with the forum search. I also know Eric Goodchild was or is working on a QCW coil.

Dr. Dark Current

Thu Sept 29 2011, 09:25AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

An idea for a "QCW-like" coil using standard parts, non-DR version:
-Build a standard SSTC with the 4046 as the oscillator and run the bridge from smoothed dc supply.
-Modulate the VCO on the upper slope of the resonance curve (above resonant frequency).
-Certain waveform inputs to the VCO should produce a QCW-like effect, as the VCO frequency is indirectly regulating output power. Try falling ramp waveforms in the several ms to a few tens of ms range, with variable slope.

I wanted to try this idea but it seems like it's never gonna happen, so I post it here for you to experiment. If you succeed it would be nice to hear about your results.

Adam Munich

Thu Sept 29 2011, 10:55AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

"Magnet18, Steve has not posted that much info about his QCW coil, and no schematic. From what I understand, this was to prevent the (often unaccredited) copying of his work."

It's a bad idea to not share your discoveries, for if you don't --they disappear with you.

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Drivers aside, it seems like the most logical way to start would be to make that short secondary. From the looks of it in the video, it seems to be 1 foot * 5 inches.

Here is some useful info I found on some other thread:

So, the coil is 9" tall, runs at 350khz and uses a 4CX250B in series with the bus to modulate it? It seems like the most logical option now would be to build a 350khz coil of similar dimensions...

Goodchild

Thu Sept 29 2011, 03:50PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

If you are interested my web site has a couple schematics for QCW modulators I have tried including the one that I finally got working perfectly. A link to my site is at the bottom of my post. The schematics on my site are not direct copyable, you do have to do some research for them to make sense and be buildable.

The QCW needs 3 things to make it work properly:
1: A resonant frequency of 350KHz or more! This is important as the lower you go in frequency the more your sparks are going to branch.

2: A method of modulating the output power so to "ramp" the power into the spark, this is what is used to control the spark growth. the dp/dt determines also how the spark branching will be effected. A larger dp/dt with result in more branching were a smaller dp/dt will result in less branching. This figure has to be adjusted also for the length of sparks you are producing. a longer spark needs a smaller dp/dt.

3: You need a high impedance tank circuit say >20ohm this is also to help control current rise times with the extremely long on time.

This type of coil run in basically the same mode as a VTTC only the tube is replaced with a bridge of IGBTs and the mot/cap is replaced with a class D amp. The advantage to having a controllable modulator is that unlike a VTTC you are not limited to the length of the mains AC for your ramp time. As I said before this length of time is critical when making sparks and at 33 or so inches VTTCs max out because they have no more ramp to work with.

I did spend a great deal of time and silicon to get this to work right, it's not a project for beginners or even moderate coil builders. You should have a good knowledge of SMPS control theory and power electronics if you want to attempt this project.

ScotchTapeLord

Thu Sept 29 2011, 04:12PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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Posts: 635

Grenadier wrote ...

It's a bad idea to not share your discoveries, for if you don't --they disappear with you.

It's not so much a discovery as a creation. Material creations can succeed their creators regardless of whether or not people know about them.

One of the big issues here is the power supply and its controller, where shielding and protective circuits are crucial to the design's success. I had the pleasure of working with Steve a couple weeks ago, and his power circuitry is far beyond hobbyist grade, with regard to the components, layout, and mechanical structures (heatsinks and enclosure). Even with all that, it still suffered a pretty severe meltdown.

Grenadier wrote ...

So, the coil is 9" tall, runs at 350khz and uses a 4CX250B in series with the bus to modulate it? It seems like the most logical option now would be to build a 350khz coil of similar dimensions...

There is no tube. Linear regulation of the supply is out of the question for any appreciable amount of power. You need a synchronous buck for best results. It works the same way as a class D audio amplifier, essentially.

Adam Munich

Thu Sept 29 2011, 05:14PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Limited to the AC cycle time in a VTTC...

So if I'm understanding correctly, this is a solid state DC coil which operates in the mode of a VTTC. Wouldn't it be possible to rectify and smooth a VTTC to achieve the same effect? With a big enough bus cap, you should have enough stored energy in there to power the long resonations...

"It works the same way as a class D audio amplifier, essentially."

Not necessarily. Have we forgotten about the magnetic amplifier?

Dr. Drone

Thu Sept 29 2011, 05:49PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
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