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Goodchild

Thu Sept 29 2011, 11:41PM

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

Ummm... I would start with a plain DRSSTC first before you go attempting a QCW. The QCW is about 10 magnitudes harder to build than a regular DRSSTC.

If I were you these are the steps I would take to get to a QCW:
1: Build and perfect a regular DRSSTC using Steve Ward's UD1.3b or 2.1b learn the ins and outs of a DRSSTC how to tune one tweak ect..

2: Build the class D / sync buck, get it working with static resistive loads at first and make sure you can make clean ripple free ramps.

3:Build a high impedance DRSSTC and bridge to go with the QCW and mate it with the sync buck.

4: Play with the sparks!

There's a big difference to knowing how something is going to work and making it work! In my experience with electronics and solid state tesla coils, you can't rush learning. You have to take small steps to achieve your overall goal.

So start with a plain DRSSTC first learn the lay of the land with this type of coil before attempting something like a QCW. By doing so you will save yourself a lot of headaches, money, and time.

Adam Munich

Thu Sept 29 2011, 11:54PM

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

/me tends to do things the hard way.

Maybe an SSVC is the way to go. I want something that likely will not explode if I screw up, because when things explode I tend to abandon the project for months and it takes a long time to get anything done. Sure an SSVC would probably be a bit tougher, but in the end more reliable.

So, basically that is a DC VTTC with the bus voltage adjusted? Even then, how does one even make a 5-20kV ramp?

Adam Munich

Fri Sept 30 2011, 01:21AM

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

Alright, it is now decided: this will be an SSVC coil. Why? Can't explode & glowy tubes are awesome.

So this video

seems to be the only source of information on these coils.

What I gathered from the video is:
* The tesla coil is a standard VTCC, run on DC.
* He uses a pair of CM200 IGBTs to drive a transformer wound on two of those big TSC cores. I happen to have one, and it should be enough (2 seems overkill).
* The bus caps are 450V, so he is likely supplying the CM200s with 220 - 300V.
* There is a big capacitor in series with the transformer's primary to cancel inductance or something
* The transformer is doubled by MOCs and a big stack of to-220 diodes
* It makes a ramp
* The CM200s are driven by an arduino, simple enough
* The ramp peaks at 20kV and runs for about 15ms

All and all it doesn't look all that complicated. The question though is, how do I get a ramp out of a transformer like that? It was suggested that I lay a wooden plank atop a pole pig, but I have my doubts as to whether that is a good method...

How I will audio modulate this remains unknown. Maybe if I set the pulse length short enough I can just send pulses to the coil to directly make the sound. Frequency will of course be limited to the low end, but that's aright since I'd be using this for bass anyway.

Dr. ISOTOP

Fri Sept 30 2011, 02:43AM

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

The "SSVC" is just as bad...you still have to deal with a pulsed, regulated, modulated DC-DC converter which drives an ill-behaved load (the coil itself). Plus you'll have to deal with winding a stable, high-power 10KV transformer

I'll reiterate - the hard part of this coil is the modulator, not the coil. A small DRSSTC is not terribly hard...lots of people have done it before, and there are people in the community who can help you. The pulsed class-D amp, however, is an odd beast. Try to build one, and you're venturing into fairly new territory. It is not clear what the best way to regulate the ramp is, or whether the class-D amp is even necessary at all (there are several people out there who are trying to integrate the ramp into the coil driver logic via techniques like pulse-skipping [see the "PSQCW coil" thread in the Projects subforum]).

Adam Munich

Fri Sept 30 2011, 03:20AM

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

Yeah... but tubes glow

Winding transformers isn't hard, the fryback is still alive and kicking so it can be done without oil. Plus this TSC core needs a job, and @ 20V/turn I'll need only 1000 turns to make 20kV (10kV == 500T).

Phillip Slawinski

Fri Sept 30 2011, 03:43AM

Registered Member #1732 Joined: Thu Oct 02 2008, 02:34PM
Location: Huntsville, AL
Posts: 112

Grenadier wrote ...

Alright, it is now decided: this will be an SSVC coil. Why? Can't explode & glowy tubes are awesome.

WRONG!!!! Can explode ...........

Grenadier wrote ...

All and all it doesn't look all that complicated.

Not that complicated? Yeah sure! It was easy... the thing practically built itself!

(if only)

Grenadier wrote ...

* He uses a pair of CM200 IGBTs to drive a transformer wound on two of those big TSC cores. I happen to have one, and it should be enough (2 seems overkill).

Maybe one U core would be enough. You have to wind more primary turns (to avoid saturating the cores), and this means more secondary turns for the same voltage output. More secondary turns means smaller wire. The wire I have now is #24, and that's a bit small for even 600W output. The windings get quite warm. So if you go with one core, you're going to want to up the frequency so you can use fewer turns. This will limit the peak power output of the system, but if you're only planning to run something like an 833C then, no big deal. The 833C really starts to complain over 600W of power input.

I didn't use the TSC cores you speak of. I got them from another source, they may be similar to the TSC cores though?

Grenadier wrote ...

* The bus caps are 450V, so he is likely supplying the CM200s with 220 - 300V.

The 450V rating is for one cap. I have two, and they're wired in series. I've run up to 800V on this power supply. Normally I run ~400V, since that's about all I need to max out the 833C. This supply was designed to run a bigger coil. I recently acquired a 3CX2500H3, but I haven't had the time to put that into a new coil yet.

Grenadier wrote ...

* There is a big capacitor in series with the transformer's primary to cancel inductance or something

The capacitor is in series with the primary it resonates with the leakage inductance of the primary, and also serves as a DC blocking cap.

Grenadier wrote ...

* The transformer is doubled by MOCs and a big stack of to-220 diodes

Yep, MOCs and TO-220 diodes, I don't remember the exact model. I got some that were rated for 1200V @ ~30A. The diodes see pretty high peak current off the transformer.

Grenadier wrote ...

* It makes a ramp

Yep, it sure does. Very observant...

Grenadier wrote ...

* The CM200s are driven by an arduino, simple enough

Sorta ... Maybe you can do it with the Arduino framework; I didn't use the Arduino framework. I wrote the controller in ASM. I only used that Mega because it was the only spare ÂµC I had at the time.

Grenadier wrote ...

* The ramp peaks at 20kV and runs for about 15ms

20kV is the peak that the ANODE (on the tube) sees. I've taken the supply up to 12KV before, but at that point I feared for my Tube's life, so I backed down. You'll note if you look at the 833C datasheet that 20kV is WAAAAAY over spec. The tube I have installed is the only one I've seen that's able to handle that kind of abuse. (I've tried a few others)

The bottom line: SSVC isn't *easy*, I wouldn't recommend it as a beginner project.

I must give Credit where credit is due: I got some help from Steve Ward during the concept stage of the SSVC, so I can't take full credit for the SSVC. Steve gave me the idea to use a modulated SLR supply.

I haven't even finished this project, so I don't have any schematics or something like that to give away ( Not that I'd give it away anyway). I do have a few boards left, but I'm reluctant to sell them, the price would have to be right....

Adam Munich

Fri Sept 30 2011, 03:53AM

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

I'm just wondering *how* you got the ramp waveform out of the transformer, since I really haven't a clue!

As for the cores, it's a big one that can handle on average 35V/T before saturating. 20V gives me a decent safety margin.

I don't really plan on running it over 600W. Just enough to give me a decent bass amp. As for the "not recommend as a beginner project" part, I certainly don't recommend you make your first x-ray machine play nice with micro controllers and powered off of LiPos

But I'm not one to turn down a challenge, and this is a challenge indeed.

Dr. ISOTOP

Fri Sept 30 2011, 06:07AM

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

Phillip Slawinski wrote ...

I must give Credit where credit is due: I got some help from Steve Ward during the concept stage of the SSVC, so I can't take full credit for the SSVC. Steve gave me the idea to use a modulated SLR supply.

I haven't even finished this project, so I don't have any schematics or something like that to give away ( Not that I'd give it away anyway). I do have a few boards left, but I'm reluctant to sell them, the price would have to be right....

I've always wondered, how are you modulating the SLR? AFAIK PWM would throw off the resonance condition (the duty cycle would be limited to fo, 1/2fo, 1/3fo, etc to maintain ZCS).

Phillip Slawinski

Fri Sept 30 2011, 12:58PM

Registered Member #1732 Joined: Thu Oct 02 2008, 02:34PM
Location: Huntsville, AL
Posts: 112

Grenadier wrote ...

Winding transformers isn't hard, the fryback is still alive and kicking so it can be done without oil. Plus this TSC core needs a job, and @ 20V/turn I'll need only 1000 turns to make 20kV (10kV == 500T).

Winding transformers isn't difficult, but be sure you have a good design. The design of the transformer will determine the performance you can get from the system. The transformer I have in my supply now leaves something to be desired, which is why I redesigned it, and had custom bobbins made. You probably won't need to go to that length.

You want the coupling on the transformer as tight as possible. This means it's important to have the windings coaxial. The lower the leakage inductance is, the larger resonant cap you can use. Also you can get away with running a higher frequency for a given power output, this means you can use fewer primary turns, and thus fewer secondary turns for a given output voltage. Another added benefit of the higher modulation frequency is tighter regulation.

1000 turns, wow. What kind of wire size would you plan to use for this? I use #24, in a single layer that spans a little less than the length of the winding window. When I'm running around 300-400W input into the SLR the windings seem to stabilize at around 160ÂºF - 190ÂºF or so, which is quite warm.

Did you account for using a doubler when you made your turns calculations above? The doubler isn't there to just give more voltage, it also serves the crucial functions of rectifying and filtering the output. I should note that the doubler was one of the most expensive parts, if not the most expensive part of the project. This is because the diodes not only need to be high voltage but high current as well. They see pretty high peak currents. From the simulation I recall the peak currents being 30 amps or so. The good news is that the diodes don't see much current at turn off thanks to the whole ZCS thing. You may be able to get away with smaller diodes, and bring the cost down. I designed this supply to run a much larger coil than it's presently running, so it's quite overbuilt for running an 833C coil.

Grenadier wrote ...

As for the cores, it's a big one that can handle on average 35V/T before saturating. 20V gives me a decent safety margin.

35V / Turn at what frequency?

I'm running about 100V / turn on my transformer. My switching frequency is around 60kHz The primary is four or five turns (can't remember).

Grenadier wrote ...

I don't really plan on running it over 600W. Just enough to give me a decent bass amp.

If you plan to play music that changes things. Music is generally more power hungry than just making long sword sparks at a few PPS. That 600W figure I threw out is what I use to make 60" sword sparks at about 1PPS. Audio of any kind is going to use more power if you want decent volume out of the coil. If you want CW audio modulation, then I wouldn't recommend a single phase SLR. The bandwidth is pretty low unless you add more phases, or use a pretty high switching frequency.

Originally I implemented this with a transformer isolated buck supply. I wasn't able to get the performance I wanted with that, but then I didn't pursue it very long before switching to modulated SLR. I think the SLR is a much nicer topology anyways because it is *automagically* protected from shorts on the output. A fixed amount of energy is allowed to pass through the system on each cycle, no matter what the load is. This has come in handy more than once. Originally this 833C coil was a traditional VTTC with MOTs.

When I hooked this to the modulator I forgot to remove the doubler diode (which was rated at 10kV). At some point I exceeded 10kV on the B+, and the diode went out with a bang. This left a short from B+ to ground, when this happened the power consumption of the modulator went down rather than going up, and nothing was broken in the modulator.

bwang wrote ...

I've always wondered, how are you modulating the SLR? AFAIK PWM would throw off the resonance condition (the duty cycle would be limited to fo, 1/2fo, 1/3fo, etc to maintain ZCS).

The SLR operates with 1/2 wave pulses, just like any other SLR supply. An unmodulated SLR has a duty cycle of 50%. (A output on 1/2 cycle, Off 1/2 Cycle, B on 1/2 cycle) The modulation is achieved by varying the length of the off time. This modulates the duty cycle, but does not change the on time for each pulse.

Adam Munich

Fri Sept 30 2011, 01:16PM

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

I didn't account for the doubler..., so yes I'd need only 500T (but likely less, being conservative here). I figured the doubler provides a some sort of special function aside from doubling...

The SLR supply: I take it that each pulse you get out of the system == 1 SLR cycle to the transformer? That doesn't sound right, because you'd need huge peak currents to get anything out of it.

If that is not the case and the transformer is powered continuously, then how do you manage to get a ramp out of that CW?

Bandwidth isn't much of an issue. A 5ms pulse == a max pulse freq of 200Hz, which is fine for bass guitar. Power might be a problem; though that's what bigger parts are for once you get something working.

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