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Odin The All-Fragger: a large DRSSTC

Steve Conner, Mon Mar 20 2006, 12:37AM

Update Oct 2014: Odin had a successful weekend at the 2014 Cambridge Teslathon. The electronics ran fine with no issues and output was again limited by building size

5th test run was a success. Biggest spark is now 9ft

Latest (4th) test run was a success! I got an arc of 8ft (2.4m) which is a new personal best.

Output was limited by ceiling height again.

After the last blowout, I rebuilt the bridge using surplus SKM400GB123D bricks with 3.3 ohm gate resistors, and increased the current limit to 1kA. I carefully tuned the phase lead and deadtime while running at high current with the primary coil only. Then I kludged an extra turn onto the primary and made a second topload (8" x 36" approx) from aluminium ducting.

I then rolled it out for another test run with my evil henchman Jim, and Alan, one of the original pioneers of solid-state coiling. We started with the same configuration as the end of the previous run: single topload and 5 primary turns. Even though the primary current was increased, the spark length stayed much the same. Fiddling with the primary tapping point didn't seem to have much effect. I also wanted to try the lower pole frequency, but the PLL refused to lock to it reliably for some reason and fiddling with the primary tap didn't help at all.

Then we added the second topload and the new 6th primary turn. This made a dramatic difference to the output, I now got regular arcs to the floor and ceiling 8ft above. It also hit a strike target positioned 8ft away horizontally. We ended the tests due to worries about burning the floor or damaging stuff inside the suspended ceiling.

The output from the Rogowski coil was quite hard to analyse due to noise that was getting into it from somewhere. But it looked as if the PLL driver's control of soft switching was just "meh". Not so bad that it would blow something catastrophically, but not tight enough for really low switching losses. I think a phase lead driver could do better, so I won't recommend the PLL for ordinary DRSSTCs any more. For higher impedance, tighter coupled coils, and for QCWs and SSTCs where you want to modulate the phase shift, it works great.

Anyway, to the moon!

1406055696 30 FT4896 Odin Test Burntisland A1

1406055696 30 FT4896 Odin Test Burntisland1

1406055696 30 FT4896 Odin Test Burntisland2

Update July 2014: The third test run was somewhat of a disappointment. The sparks were very bright and loud at longer burst lengths, but not very long. We could not hit a target at 2m horizontal distance, and one of the SKM300GB12T4s failed after about 5 minutes runtime. :( I didn't get any photos or video footage myself, but several other people were filming. I will post pictures when I get any.

I set the system back up in the lab, as a half bridge with the remaining good IGBT. I broke the top off it so I could probe it at the die level, and I also added a small Rogowski coil around the emitter terminal. The following scope shots show the collector voltage (probed as close to the die as possible) and the Rogowski coil signal showing the emitter current of the same device. The PLL driver settings were as close as possible to the last fatal run, I just adjusted the frequency to account for the fact that it was running with no secondary coil. The DC bus voltage was reduced as I didn't really want a face full of IGBT goop if anything went wrong. :)

These results suggest that the PLL driver was set up with too much phase lead. The funny thing is that even with this large hard switched current, and turning off the IGBT as fast as possible with no gate resistors, and probing as close to the die as possible, the voltage waveform is very clean. I can't see any spikes that would endanger the breakdown voltage of the device. If I tune the phase lead for perfect ZCS according to the Rogowski coil signal, the spikes get somewhat worse, and if I tune it for leading current, the spikes get terrible.

My next move will be to set it up with SKM400GB123Ds, gate resistors, current limit increased to 1kA, and the PLL retuned for less hard switching. I will try to log the Rogowski coil waveforms while making sparks, and that should settle once and for all whether the PLL driver is good enough for the job.

1404900606 30 FT4896 10496059 10152608278251584 2505759111616666150 O

1404900606 30 FT4896 10454371 10152608278231584 3861835156770858505 O

Update May 2014(4): Second test run with smaller 0.3uF tank capacitor and SKM300GB12T4 bricks was a success!

We hit the HV lab ceiling with power to spare.

Test video!

Update May 2014(3) First test run ends in disaster! Not exactly sure why, see last post for discussion.

Update May 2014(2) Successful dummy load test at full bus voltage and >1000A peak. (the needle pegged at 1000

)

Update May 2014: Completed the primary

Update April 2014: Trial assembly of everything. It all seems to fit together OK

The overall height is an imposing 1.8m.

Update April 2014: Winding the secondary coil:
315mm dia X 1m height, 1175 turns of 0.75mm wire, coated with 2-part epoxy.
After overheating the cordless drill motor, we changed to an old Black & Decker mains powered drill connected to a variac, with a vacuum cleaner for cooling.

Update March 2014 (2): Constructing the front panel for the power electronics box. First in a series of timelapse movies

Update March 2014:
An enormous bank of GTO snubber capacitors was procured. 0.75uF total capacitance at eleventy billion volts.
The bridge has been tested to 750A peak with a dummy primary coil.
The bridge and driver have been bolted together and mounting rails added.
A 12" x 39" coilform made of grey PVC air duct has been procured, as well as 6kg of magnet wire and some low viscosity epoxy resin for coating.
A new interrupter has been constructed.

1395511425 30 FT4896 Win 20140316 125439

1395511425 30 FT4896 Win 20140321 195719

1395511425 30 FT4896 935523 10152031541521584 1934577150 N

1395511425 30 FT4896 1393820 10151999009056584 773641908 N

1395511425 30 FT4896 1459979 10152186540611584 1329840340 N

Update, July 2013-
The 600V test was a success. Output waveforms still looked great so I adjusted the interrupter duty cycle to draw the full 1kW output of my power supply, and soon the dummy load (a steel coffee can full of water) was hot enough to make tea!

The duty cycle ended up at 2% so the peak power must be around 50kW and the RF current about 100A peak. The coil is still untuned, so the current will be a triangle wave and the full 100A will be hard switched. Nevertheless, the heatsink was still cold when the tea was ready. No fan installed yet.

Update, July 2013-
This project has been going so long that I gave up on it several times, and lost or sold almost all of the original parts. Nevertheless it is back from the dead!

I was motivated by meeting a local artist who works in an old factory that would be ideal for firing giant Tesla coils. I ended up selling Mjollnir to him, so now I need another DRSSTC.

I've just completed the bridge and test fired it at 150V DC bus voltage into a dummy load composed of a steel can with wire wrapped round it. There is no resonant capacitor: I'm hard switching to get a feel for the bus inductance and voltage spikes. The waveforms look excellent and the water boils nicely.

The test details are:

Operating frequency 60kHz
Interrupter: 400Hz, 20% duty
DC bus: 150V, 2.6A

The three large black blocks are 50uF, 800V metallised film caps from Panasonic. They cost about Â£12 each. I think they are intended as high reliability DC bus caps for solar inverters and other kinds of SMPS.

I originally intended to use the SKM300GB123D IGBT modules from Semikron, but when I first tried to test the bridge, I discovered that I only had one good one, all the others I had kicking around were DOA! An anonymous benefactor donated some SKM200GB128Ds, a newer generation using "soft punch-through" technology. They seem about as fast as the 123 series but with lower voltage drop.

I also ordered some SKM400GB125Ds from a Hong Kong seller with good feedback. These are rated for resonant operation up to 100kHz in induction heaters. Once everything is proved out with the SKM200s, I'll swap them in.

The next step is to increase the DC bus voltage to 600V and try to brew tea in the dummy load.

Update, November 2007-

Unfortunately the sale fell through due to me not being able to get it built on time, not to mention worries about reliability. All I can say is that it will "Maybe" get finished "sometime" :|

Update, September 2007-

Well, I've had a fairly serious offer from a sponsor who wants to buy the drive electronics from Odin and make their own resonator to go with it. So, I've decided to get back to work! If it falls through, I'll try to bring it to Cambridge instead, and maybe hook it up to someone else's resonator.

I finished rewinding and wiring up all the drive transformers, and all four drivers appear to be good. I connected two of the drivers to a spare Semikron 300A halfbridge IGBT brick for testing.

The drivers hooked up. Yes those are Cat5 cables.

Gate waveforms, check. The top waveform is the trigger reference from the signal generator, the lower two are the gate voltages. We are driving the two 300A IGBTs CW at 25kHz, to +24 and -12V.

I hooked the halfbridge up to a ferrite transformer from an electronic NST, and fed it with 20V DC. It made a nice spark. This is possibly the most overkill flyback driver ever.

Oh noes! The transformer is on fire.

What's the matter, little transformer? 300A IGBT brick too much for ya?

This proves that the gate drivers work, at 20V DC bus voltage at least! The finished coil will operate at 600V DC bus, so I still have some way to go...

Update, June 2007-

I tried Hi-pot testing the new gate drive boards, and the results were dramatic. The isolation transformers were destroyed completely! :(

So I tried a new GDT design using Kynar wire on Teflon wrapped cores. It easily survived a zapping with a MOT! The scope trace shows the voltage across it taken with a 100x probe.

I bought some more Kynar wire and made eight of these new GDTs, but haven't got round to fitting them to the boards yet.

I also have some plans for a fibre optic link using Toslink parts, inspired by jrz126. I plan to use three fibres to transmit the interrupter signal, the DC link voltage control signal, and the PLL fine tuning signal. I was going to multiplex the signals using chips designed for digital audio, but it seems less hassle (and less chances for EMI to crash things!) if I just use three copies of jrz126's circuit.

1182026231 30 FT4896 Img 1900 Mot Destroy

1182026231 30 FT4896 Img 1902 500vperdiv

Update, March 11 2007-

After a long time off this project, I got back on it by building another two gate drivers. I now have a complete set together and working. I'll hi-pot test them tomorrow with a MOT or whatever.

Things I still need to do: Build the "hub" that connects all the Cat5 cables to the PLL driver, with the inverter in it that supplies power to the gate driver boards. Hook the SCRs in the voltage doubler up, and modify the SCR driver for more current. Hi-pot test the dodgy looking insulation in the H-bridge. Wire up all the power wiring and meters. Hook the IGBTs up and test the drive. Fix the secondary. Build a new primary. Sort out the tank capacitors. Get some kind of fibre optic system to control it all. Etc.

Update July 8 2006-

I built another brick driver and compared the outputs from both of them.

1152463181 30 FT1630 Imgp0814 Brickdriversx2

1152463181 30 FT1630 Imgp0815 Bdx2 Mindead

Outputs at 200kHz with deadtime control turned to minimum.

1152463181 30 FT1630 Imgp0816 Bdx2 Maxdead

Same with deadtime turned to max. The deadtime looks a little uneven, but that shouldn't be a problem at the lower frequencies I would use bricks with. I'm just using 200kHz because that's what the PLL unit from my other coil is set to, and I can't be bothered opening it to change it.

Update July 1 2006-

I got the H-bridge and meters bolted onto the old wooden frame from the OLTC 2.

I also replaced the OLTC 2 single turn primary with a rough 9 turn coil, but I don't have a picture of that. (It looks terrible.) I wound a couple more of the signal and power isolating transformers too.

Update on June 17 2006-

I finally managed to get one of the boards built and hooked up to a power supply and gate drive. It seems to work as planned, though I bought the wrong ribbon cable connectors to hook it to the IGBT properly. Also, I can't test the undervoltage lockout, because I forgot to get the right zener diodes for it.

The power isolating transformer's core gets a little hot, so it probably needs more turns.

other minor oops-ups:
-Got the cores mixed up in the Cat5, so the HF power is twisted together with the UVLO signal.
-Never noticed that the MOSFETs I bought aren't actually in D2pak footprints. They still sort of fit, anyway.

finished board

scope screenshot shows the gate of a 600A IGBT being driven with +24 and -12v at 200kHz. >_< The second trace shows the zero volts level.

board had to be kludged onto IGBT with two short pieces of wire.

Update on May 14 2006-

The boards are back from Gold Phoenix, omg omg! There will now be a short interlude while I build a set up, bolt them onto some IGBTs, and test them. Assuming they work, I plan to sell all the extra boards I don't need to you guys

Update on April 13 2006-

I finished the outboard driver PCB, got the safety clearances as big as I could, and generated the Gerber and drill files for it. I just need to revise the main PLL board to get rid of all the bugs that were in the last version. I should have the board order placed with Gold Phoenix by the end of today.

1145117820 30 FT1630 Img 1696 Driver Mockup

a paper mockup of the board to check component footprints

Now I've nearly got the outboard drivers done.

schematic. Note the optoisolators that act as undervoltage lockout, Richie Burnett persuaded me to put these in.

preliminary PCB layout (still got to check safety clearances)

The first step was to build the H-bridge.

I'm going to try attaching about a dozen pictures to this and see if it works.

four big inverter grade capacitors (3300uF @ 420V). The tops are wrapped with electrical tape to reduce the chance of the metal can coming into contact with the metal case I'm using to hold them.

two 300A 1200V half-bridge IGBT modules and one half-bridge SCR module for soft-start and DC voltage control

Don't ask what the insulation is made out of.

These funny shaped busbars connect the IGBTs to the capacitors with minimum stray inductance.

like so

The HF output terminals on the bricks aren't connected to anything yet.

woot!

This thread continues from

on the old board.

Re: Odin The All-Fragger: a large DRSSTC
ragnar, Mon Mar 20 2006, 04:09AM

I love it Steve!

How are you driving the bricks, and what model are they? I've got some semikron bricks that look like that... muahaha.

Re: Odin The All-Fragger: a large DRSSTC
Steve Ward, Mon Mar 20 2006, 05:50AM

Excellent. You always go out of your way for these ultra low inductance designs but... shouldnt it be soft switching anyway?

. Hey, where are your low inductance decoupling caps? Or ar those lytics so good that you dont need them? I expect at least 10 feet from a coil driven with that monster of an inverter! Good luck.

Re: Odin The All-Fragger: a large DRSSTC
Marko, Mon Mar 20 2006, 09:21AM

The last picture is the best...
Nice huge heatsink, you can build entire DRSSTC on it itself

Im troubling myself to find anything larger than small CPU cooler, maybe few rusty TO3 heatsinks. Not to talk about 40N60s, TVS supressors...

Good luck then

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Mar 20 2006, 12:54PM

Hi guys, thanks for the feedback! The "Nice large heatsink" was donated by Finn Hammer, its name is Finn's Fins.

blackplasma: The bricks are Semikron part# SKM300GB123D. I managed to get hold of the 400A version too, but I'm saving them till I've pop popped all the others

I don't know if anybody has used these in a DRSSTC before but I reckon they should work fine. If not, I tried to make sure the layout would fit the Powerex F and H series bricks too. I'm driving them with my PLL driver through a set of outboard gate drivers that I documented on my site.

steve: I was discussing this with Richie a while back. He said that commercial SMPS often just use the electrolytics on their own, and also I had trouble with resonances caused by the plastic film bypass caps on my last DRSSTC. So I'm going to try leaving them out this time. That's why I wanted the low inductance busbars, to get the electrolytics "closer" to the IGBTs so they would be effective. I think they have about 25nH ESL which is about average for inverter grade caps. I'll check the DC bus for spikes when I test it, and if necessary I'll add some caps in.

Re: Odin The All-Fragger: a large DRSSTC
vasil, Mon Mar 20 2006, 01:25PM

woot
If it will run OK, I will buy my own semkrons to build another drsstc.

Good luck Dr Conner!

Re: Odin The All-Fragger: a large DRSSTC
Hazmatt_(The Underdog), Tue Mar 21 2006, 11:51PM

You might want to switch out your cap stud screws from black phosphate SHCS for Stainless.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Mar 22 2006, 12:09AM

Why? Everyone should be too busy looking at the sparks to notice that my cap screws aren't shiny.

All kinds of steel are lousy conductors of high frequency current, so I arranged it that every joint has direct copper-to-copper contact (or copper to aluminium in the case of the capacitor teminal posts) and the screws are just for clamping force.

Non-magnetic stainless isn't too bad- they make radio antenna whips out of it after all- but it's still not as good as brass, copper, or aluminium.

Re: Odin The All-Fragger: a large DRSSTC
Hazmatt_(The Underdog), Wed Mar 22 2006, 06:11AM

*shruggs* I was just trying to consider how much current will go through the stud as opposed to the terminal face as opposed to current going through both. Not that I was worried about shiny, or cost, or corrosion or whatever.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Mar 22 2006, 10:12AM

I was kind of assuming that it would more or less all go through the terminal face since copper conducts so much better than steel. But I'll keep an eye on the screws and see if they do get hot, if so, I'll change them for some other material like non-magnetic stainless steel or brass. Not that I've ever seen a socket headed cap screw made of brass

Re: Odin The All-Fragger: a large DRSSTC
Sulaiman, Wed Mar 22 2006, 10:32AM

just wanted to add my admiration!
a very nice layout / construction.
I like the way you minimise inductance
I've had wires going through heatsinks to attempt the same, not very good

good luck (though you need it less than most of us!)
and keep us posted.

Re: Odin The All-Fragger: a large DRSSTC
Adam Horden, Wed Mar 22 2006, 02:15PM

Hi Steve,

Nice work looks very professional. Are those lytics in half a RS equipment enclosure? I have seen something simular shappped with the cut outs on the side in the RS cat.

At least some one is finally using some of the lytics I had and a big coil is been built!

How are you connecting the gate drive to the bricks?

Adam

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Mar 22 2006, 04:05PM

Hi Adam

Yes it's an old case from RS

I got it from a junk pile at the uni. It seems like a weird way to mount the caps, but it actually worked out easier than buying the big oversized capacitor clamps and cutting big holes in a piece of sheet metal.

I'm using outboard gate drivers, they will connect to the IGBTs via about 4" of ribbon cable with alternate cores connected to gate and emitter to give extra low inductance... I don't do the I word man

It turned out too much of a hassle to mount the drivers straight to the IGBTs, considering I want to use the same gate driver boards with CM600s in the future, and their gate terminals are in totally different places.

The drivers will connect back to the PLL unit using Cat5 network cables with the little 8-way modular jacks because they're cheap.

Re: Odin The All-Fragger: a large DRSSTC
Adam Horden, Wed Mar 22 2006, 08:10PM

Hi Steve,

**digs out notebook**

Its a nice idea and all your layouts look really low inductance. Do you apply the math to work out the actual inductance of the layout? I tried it on the one I will discuss below but I got really small numbers and decided that those could not be right!

I have all the parts to still build a big CM600 bridge. The modules would be built with smds and inside a can with BNC connectors to connect them to the driver and would bolt direct to a CM600.

The layout I decided on was simular to yours but imagine it been on its side with the bridge flat.

The bridge was a huge long length of heatsink like on your OLTC2 the same stuff. The bricks would have a laminated bus scheme but the caps on there side and bolted in mid air across the laminate. You end up with 6 electrolics across a low inductance laminate bus scheme. The DC in would bolt direct to a IRPACK SCR moudle the dual ones. Eveything lies flat with the caps horizonal to the bricks that are vertical.

The whole system would of been nice to build with lots of thick copper busbar. I also designed in a method of mounting polyester excel decoupling caps in there.

I still have 6 brand new cm600s and most of the design work done on the bridge. And I think I have a tray of caps left.

Adam

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Mar 27 2006, 10:31AM

Hi Adam

No I don't calculate the inductance. I just know that the less area enclosed by the loop that the current flows in (ie the closer together the conductors are) the better. It doesn't really take much more effort to make a low inductance layout than an ordinary one.

If you want to build a 600A bridge for "Team Odin" you would be more than welcome! We could fire it up at Cambridge sometime. I think they can bring in 400V three phase power for us without too much hassle.

Re: Odin The All-Fragger: a large DRSSTC
Part Scavenger, Wed Mar 29 2006, 03:46AM

OH YEAH! This is gonna be good. Doc Conner building another DRSSTC!

I look forward to this. You do great work man!

/*drooling over setup*

Re: Odin The All-Fragger: a large DRSSTC
Adam Horden, Wed Mar 29 2006, 11:17AM

Steve Conner wrote ...

Hi Adam

No I don't calculate the inductance. I just know that the less area enclosed by the loop that the current flows in (ie the closer together the conductors are) the better. It doesn't really take much more effort to make a low inductance layout than an ordinary one.

If you want to build a 600A bridge for "Team Odin" you would be more than welcome! We could fire it up at Cambridge sometime. I think they can bring in 400V three phase power for us without too much hassle.

Hi Steve,

I will build up a bridge with the parts I have.

Adam

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Apr 02 2006, 11:12PM

I've updated the first post with details of the new driver boards.

Re: Odin The All-Fragger: a large DRSSTC
robert, Mon Apr 03 2006, 05:23PM

Wow, looks nice.
Though i would do something about getting better isolation barriers, i always like to have at least 8mm for anything line-connected (well, might be because im currently doing PCB layouts for off-line SMPS things).
So id use optos with 10.6mm lead spacing (like PC817 or CNY81) or just bend your standard DIP to this larger spacing.
To save space, use 4-pinned ones, also reduces the chance of EMI pickup on the base lead (can be a large problem in noisy environments).

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Apr 16 2006, 11:51AM

Update: I finished the gate driver layout and also revised the main PLL board layout, and ordered a batch of each from Gold Phoenix. I expect to get 8 PLL boards and about 30 gate drivers.

Robert: I chose to use 6-pin optos because they bring the base lead out, so I could tie it to the emitter with a resistor in an attempt to make it less sensitive to EMI. :P And because 4N35s are pretty cheap I suppose.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun May 14 2006, 04:33PM

Update: Boards are back! Just got to stuff and test them. I updated the first post with a picture.

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sun May 14 2006, 04:40PM

Very nice! When will somebody make homemade board like theese..

Re: Odin The All-Fragger: a large DRSSTC
HV Enthusiast, Wed May 17 2006, 12:35AM

Its ashamed you are no longer interested in coils . . .

Re: Odin The All-Fragger: a large DRSSTC
Marko, Wed May 17 2006, 02:30PM

Steve, may I ask a question: What is additional 'UN10KN' mosfet used for?
Couuldn't you drive both of gate mosfets just simply from GDT?

(or im' most probably missing something) ?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed May 17 2006, 04:00PM

Dan: I quit doing the DRSSTC theory because it was making my head hurt and not going anywhere. I also decided to quit exhibiting at teslathons because of the money and hassle, and I decided not to try and beat Steve Ward's spark length record for the same reason. I guess I basically did all this stuff just to show off, and I can't be bothered any more.

However, I have a lot of IGBT bricks and capacitors stacked on top of my kitchen cupboards now, and I don't see any reason not to have some fun with them

Firkragg: If I drove both MOSFETs directly off the GDT, then they would both be "off" in between bursts. Then the IGBT gate could theoretically float to any voltage it liked. The VN10KM FET and its associated components are just an inverter that makes sure the bottom MOSFET stays "on" between bursts and clamps the IGBT gate to -12V. I tuned the component values so there would be no shoot-through between the two MOSFETs.

Re: Odin The All-Fragger: a large DRSSTC
Marko, Wed May 17 2006, 08:20PM

I'm an idiot.
What I tought was to connect Vcc rail to another leg of GDT to open the MOSFET by default, but I was faster in writing this than figuring out it will turn in chaos at end of burst. (inductve kick on secondary would mess up the thing).
Inverter is rather a better idea.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed May 31 2006, 08:43PM

Update on progress. I'm currently ordering parts to finish the new boards, both for myself, and a few other people. I sell a pack of all the parts you'll probably have trouble getting and won't know how to substitute.

The PLL boards are all sold now, unless someone cancels an order.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Jun 18 2006, 07:38PM

OMG update. Don't tell me the creepage distances are too small.

Re: Odin The All-Fragger: a large DRSSTC
ragnar, Mon Jun 19 2006, 07:40AM

Gorgeous, Steve!

Your boards are considerably more complex than my isodriver system, too ^^

Mine are crammed as closely together as non-surface-mount components permit. Even with a double-sided board, you couldn't get them closer =D It's a great feeling, and a topological nightmare, but I just love the spatial thinking involved.

...all I need now is pics... and not to hijack your thread.

What silicon are you using to drive the isolated power supply / ferrite?

I'm guessing for all the 'signal transformers' you're just using donut cores?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Jun 19 2006, 09:32AM

Hi BP

I never crammed my components that tightly. I planned to get it all on to a quarter Eurocard, but I had to lengthen it a bit. I had to leave room for the silkscreen, and even so, I had to put some of the component names under the components.

For the power supply I'm using two of the same STD12NF06 MOSFETs that I bought a pile of for the drivers.

The signal transformers are more ferrite sleeves really, they're a bit tall to be "donuts". I chose them because they were in the RS catalogue and looked about the right size. :P

Re: Odin The All-Fragger: a large DRSSTC
ragnar, Mon Jun 19 2006, 10:31AM

I've had really good experience with those "tall donuts" / ferrite sleeves... but then again even free common-mode chokes give better performance/waveforms than ferrite I pay good money for ^^

Silkscreen... pshh. I don't even print out my schematics or overlays when assembling my boards... which might explain why I blow so much stuff up

hehehe

Besides, it makes commercial obfuscation more straightforward... second to grinding chipnumbers and the black epoxy, that is.

I just loooove the bipolar* drive! Sexy waveforms! What kind of charge/capacitance are we talking here?

*I know it's deliberately 2/3----1/3

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Jun 24 2006, 09:47PM

It's a CM600HA-24H IGBT brick so the gate charge is about 5000nC, I think.

Today I took the single turn primary off the OLTC2 resonator and replaced it with 9 turns of 1/4" copper tubing. It could probably do with somewhat more, but 9 was all I could fit while still keeping good clearances.

I also managed to drop the resonator onto a concrete floor, breaking the secondary wire in about 3 places and shearing off half the nylon screws that hold the lid on.

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sat Jun 24 2006, 09:59PM

I also managed to drop the resonator onto a concrete floor

poor resonator..
I hate when this happens, I just recently burned a hole (from inside) in my DRSSTC secondary, just from pure carelessnes with toroid connection wire.
Now that part has bulged and is crispy to touch

So you are going to completely 're-use' OLTC 2 as a DRSSTC.
Sounds cool.

-me sees steve posting in 'attachments'
PS. OMG just saw it

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Jul 08 2006, 12:46PM

Yea, it's coming on slowly. I'm going to do more work on the frame tomorrow, and try to get the gate driver boards finished today. I'll try and post a pic of me wielding the finished coil a la Sam Barros for old time's sake

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sat Jul 08 2006, 01:00PM

looks pretty good to me.
Are you currently using conel or helical primary?

I also had problems with primary coils, and pipe I had was so degenerated that I had lots of places where turns touched mutually.
I had to use solid 2,7mm wire wich now makes trouble limmiting the primary current

It seems that only hope is to buy already wound pipe and just roll it 'as is' on there.

Primary from your MjÃ¶llnir looked pretty good, I like the style how is it 'pressed' between columns and inner pipe.

Re: Odin The All-Fragger: a large DRSSTC
Hazmatt_(The Underdog), Sat Jul 08 2006, 06:39PM

If you have space issues with 1/4" why not get 1/8" Copper tubeing or 3/16". It's an easy answer you know!

And don't come back with "well yea..but the current is going to heat it up really fast" So! you're going to all this trouble with everything, just put a circulator in the system with a small pump.

Re: Odin The All-Fragger: a large DRSSTC
GimpyJoe, Sat Jul 08 2006, 10:59PM

He's saying (I think) that the pipe he had was bent around and had been used for other things before he wound a primary with it so it had bumps and kinks in it. And I don't care how much current you have, it's still gonna be hard to heat up 1/8" copper pipe enough to need cooling

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sun Jul 09 2006, 12:20AM

Steve Conner wrote ...

omg updatez @ scopeboy.com

Hehe, always been my favourite site, keep it going

I'm pretty sure that copper pipe if it was 'used' cannot be wound nicely anymore, no matter how much you heat or punish it.

If it isn't already 'in roll' it's very hard to bend it into desired shape.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Jul 09 2006, 04:50PM

Omg updatez!

Hazmatt: I hope it won't come to needing water cooling. :-/ The spark output of this coil is probably going to be limited by how much power I can get at venues, so I want it to be efficient. If I can only get say 32A@240V, that's 6kVA or about 4kW, and I don't really want to waste one of those kilowatts making tea.

Firkragg: Yes I reused the copper tubing from my old Tesla-2 primary, and I wish I hadn't.

I had to scrap the "inner pipe" part of the Mjollnir primary, this new page explains

Re: Odin The All-Fragger: a large DRSSTC
Steve Ward, Mon Jul 10 2006, 12:03AM

Looking great Steve.

I dont know that 1/4" copper tube will handle the power... it will probably get piping hot at even 4kW. When i run my coil at 5kW for awhile, even the 2awg wiring gets quite warm. I recently replaced every connection that was made from steel hardware with brass... the steel was getting absurdly hot.

I also recently figured out why my coil blew up twice recently. I thought it was a voltage spike issue, but it really turned out to be that my old gate driver design floated the output HI when it lost power, and i happened to be running the control circuits on the same 240V feed. So after a few minutes of exceeding my 20A breaker, it would trip, then all the IGBT would blow up from shoot-through on the rails. My new gate driver doesnt have this problem and is also a far better driver.

What i did find in the end is that the little film decoupling caps dont really help much for voltage spikes, provided you keep the lytics connected to the IGBTs with a laminated bus structure. In the end i did end up using RCD snubbers across the IGBTs, which helped the voltage spiking, but i dont think the spikes harm the IGBTs anyway

.

Really looking forward to the end result Steve!

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Jul 10 2006, 09:02AM

Hi Steve

I found that my first attempt at a gate driver floated its output high in the same way. I think I documented that and the fix I used for it back over on the old board.

The more I think about it, the more I agree that 1/4" pipe is too wimpy. The pipe I have is slightly smaller than 1/4" in fact. I probably ought to start over with a bigger resonator too. But I'll probably go with it for testing, it should hold up for short runs.

It's good to know I was right in suspecting that I could leave the film decoupling caps out, too

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Jul 24 2006, 10:22AM

Update:

I'm real busy with work, and my band is in the middle of recording an EP, so Odin has got kind of neglected lately. I will finish it though!

I've wound all the isolating transformers and bought the Cat5 sockets. I decided to make a new primary from 3/8" copper pipe, cable ties, and the lid of an Ikea plastic laundry basket, so I need to go and do some shopping.

I also decided to order another batch of PLL boards, since I screwed up and couldn't supply them to everyone who wanted them.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri Aug 25 2006, 12:26PM

Ikea laundry basket sourced!

Nothing else to report except the record is getting mixed this weekend and then I can concentrate on the coil

I apologize to anyone that I said I would sell electronics to and then kept waiting. I've just ended up being way too busy with other stuff. I really want to get Odin finished and demonstrate that he works before I go selling the isolated gate drive system. I don't want to sell stuff unless I'm 100% sure that it's good. Well 95% maybe

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Mar 12 2007, 12:06AM

Update: I had to wander off and do a load of other stuff that pinched all my evenings and weekends, but I'm now back on this project! I spent ages designing it, and this year would be Tesla's 150th birthday, so it's got to be done.

Re: Odin The All-Fragger: a large DRSSTC
Download, Mon Mar 12 2007, 01:10AM

i have no idia what it does but i like it!

Re: Odin The All-Fragger: a large DRSSTC
Marko, Mon Mar 12 2007, 03:02PM

Hi steve

Well some good news.. there weren't DRSSTC's around for a while, I can't wait to see more progress!

Just regarding the HI-pot test, I would be a bit vary about those little transformers, if you plan hooking them up to a MOT!

Actually, I don't trust transformers wound with just enamelled wire even for low voltages, after I had some of them get their lacquer damaged and short out... You'l have 800 volts across your transformers!

Now I paranoidly use PVC insulated wires and I didn't regret that yet... CAT5, screened, various tiny coax and similar cables are also handy, but that's amtter of opinion I guess!

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Mar 12 2007, 03:22PM

You are right. If they're going to short out, I don't want to have the cap bank discharge through them and destroy the whole driver. So I need to test them to make sure they can stand the voltage plus a big safety margin. Hence, a MOT on a variac putting out, say, 1600V peak

If it does turn out to be a problem, I can rewind them with kynar wire-wrap wire or such like.

The primary and secondary windings are separated on opposite sides of the core, and I believe ferrite is an insulator (sort of)

Re: Odin The All-Fragger: a large DRSSTC
Marko, Mon Mar 12 2007, 03:43PM

Regarding ferrite, I managed to make it arc over at several hundred volts to kilovolt or so.
It probes as and insulator, but actually conducts HV pretty well once it ''breaks down'' at some point.

Real danger is, actually, not only blowing your driver but also blowing your IGBT gates, IIRC.

Good luck with Hi-pot test...

Re: Odin The All-Fragger: a large DRSSTC
Steve Ward, Mon Mar 12 2007, 05:32PM

I second that enamel wire sucks for GDT use, since its highly probable that the person winding it will end up scraping off some enamel when it rubs against the ferrite (which by the way, is an OK conductor, definately not an insulator!). Ive had my mag-wire GDTs fail in SSTC service with a plume of smoke and a shattered ferrite!

On my DRSSTC 2 im using cat-5 wire, which i tested with a 9kV NST for hours (its good stuff at 60hz). The NST failed before the twisted pair of cat 5 did!! Of course, this was a perfect, new piece of wire, no nicks in the insulation or any of that.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Mar 12 2007, 09:22PM

Oh well, you guys were right. All four driver boards failed the hi-pot test completely, the transformers sizzled and went up in smoke at about 500V. Back to the drawing board, I guess

Re: Odin The All-Fragger: a large DRSSTC
Marko, Mon Mar 12 2007, 09:59PM

Oh, it can't be that bad; just use some fat plastic insulated wire and I'm sure your transformers will be fine. You could also have used some of those plastic-enveloped cores if you really wanted to be paranoid, but plastic insulation itself is usually enough for many kilovolts.

Steve's DRSSTC 2 uses enamelled wire with just average insulation from core and some hot glue, obivously it worked fine to 800 volts or so.

BTW, any pics oburnt transformers?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Mar 12 2007, 10:38PM

The problem is that there isn't enough room on the core to wind the required number of turns with Cat5 or whatever. And the board is made to fit those cores, so it needs a major redesign.

I didn't let them smoke much, I turned the power off as soon as I saw they were breaking down

Re: Odin The All-Fragger: a large DRSSTC
Marko, Mon Mar 12 2007, 10:53PM

Yeah, transformers look sort of claustrophobic for thick wire... I guess you don't need more than 10 or so turns for signal transformer, for power, maybe you can increase frequency...

I hope you'l come up with some better ideas!

Re: Odin The All-Fragger: a large DRSSTC
Mike, Mon Mar 12 2007, 11:27PM

I actually took the wires from the cat5 out of the plastic tubing as it works much better that way and allows you to wind many more turns.
Dunno if you tried that yet.
Good Luck!

Re: Odin The All-Fragger: a large DRSSTC
Dr. Drone, Tue Mar 13 2007, 01:53AM

Re: Odin The All-Fragger: a large DRSSTC
Mike, Tue Mar 13 2007, 03:03AM

Whoa, those look pretty cool especially when dipped in epoxy. Good Idea!

On an off topic note, 14-16 foot sparks?? Awesome!

Re: Odin The All-Fragger: a large DRSSTC
Marko, Tue Mar 13 2007, 08:35AM

Surely, when talking about cat5 I meant just the wires not entire cable! There are also thinner wires like those from mouse cables and etc. but they have weaker insulation!

You could also dip the core in some resin and *then* wind on it to minimize chance of arcover to core.

I'm sure steve will get over it easily..

Re: Odin The All-Fragger: a large DRSSTC
Hazmatt_(The Underdog), Wed Mar 14 2007, 11:07PM

What I don't understand is why you guys use cat5 (300V insulated at best) pvc wire.

When I get into this I'm going straight to teflon wire and eliminate the arcing problem at the source.

Re: Odin The All-Fragger: a large DRSSTC
ragnar, Wed Mar 14 2007, 11:28PM

300V at best?

Try! Its breakdown voltage is MUCH higher than its breakdown rating.

Re: Odin The All-Fragger: a large DRSSTC
Steve Ward, Thu Mar 15 2007, 05:14AM

What I don't understand is why you guys use cat5 (300V insulated at best) pvc wire.

When I get into this I'm going straight to teflon wire and eliminate the arcing problem at the source.

Im sure the teflon wire is better, i just dont have any. This is why i tested the cat-5 with the NST. I was satisfied by the results.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Thu Mar 15 2007, 10:27AM

OK, well my plan is to reuse the same dinky ferrite cores, but wrap them in teflon plumbers' tape and then use that kynar insulated wire-wrap wire instead of magnet wire. It's about the same overall thickness as the magnet wire I used, but the insulation looks much better. I'll make a trial one and hi-pot test it again.

Re: Odin The All-Fragger: a large DRSSTC
thedatastream, Thu Mar 15 2007, 03:03PM

You need some proper triple insulated wire action of you are properly Hi-Pot testing your cores

Furakawa

Rubadue

It's the bees
James

Re: Odin The All-Fragger: a large DRSSTC
Dr. Drone, Thu Mar 15 2007, 04:25PM

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Thu Mar 15 2007, 05:40PM

Hmm, TEX-E wire looks pretty good. Richie recommended it to me too. I'm not trying to actually get any formal safety approvals though, so it would be overkill. If it can withstand 1600V peak at 50Hz for 5 minutes, I'll call it a success.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Jun 16 2007, 08:37PM

Update: I tried a new GDT design using Kynar wire on Teflon wrapped cores. It easily survived a zapping with a MOT at 1600V peak! I moved the pictures and write-up to the first post.

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sat Jun 16 2007, 08:45PM

Good luck steve!

Me and part scavenger had ugly problems with things going into arcover. I would really hate if you blow your IGBT's up after all!

Re: Odin The All-Fragger: a large DRSSTC
ragnar, Sun Jun 17 2007, 09:08AM

If you do get flashover or arcs, try not to breathe the fumes -- you probably already know Teflon has some pretty fantastic decomposition products at high temperatures.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Sept 08 2007, 10:11PM

The new gate drivers seem to be working :D

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sat Sept 08 2007, 10:14PM

The new gate drivers seem to be working :D

Oh, you are preparing odin for cambridge TT? :D

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Sept 08 2007, 10:28PM

Well, I think I've actually sold him, but if the deal falls through or gets delayed, he may well be appearing at Cambridge. See the first post for details.

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sat Sept 08 2007, 10:34PM

Meh, I understood it as you are just selling a set of PCB's.. don't you have more of those boards to pull out from somewhere? ;) Or everything but resonator is going too?

Re: Odin The All-Fragger: a large DRSSTC
ragnar, Sun Sept 09 2007, 01:33AM

"World's most overkill flyback driver"... yes.

The semiconductors are bigger than the flyback, Steve! Awesome stuff =-)

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Sept 17 2007, 12:57PM

Well, I now have a firm offer of money to complete this project, and a place for it to run when it's finished, so we are back on! I mostly stuffed another PLL driver board this weekend, and identified some suitable parts for a fibre optic link.

The plan is to fire it up at Cambridge, maybe using someone else's resonator and primary coil, to prove it works before handing over to the "customer". Of course, that's assuming that it *does* work! But I'll worry about that when the time comes.

Re: Odin The All-Fragger: a large DRSSTC
Marko, Mon Sept 17 2007, 02:01PM

You said you dropped and damaged the resonator.. but is it that bad that you can't run nor fix it?

Any pics of that?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Nov 12 2007, 04:35PM

Well, unfortunately I had to let down the guys who wanted to buy it, due to being too busy at work to finish it on time, and I had to miss Cambridge to get my wisdom teeth extracted! :( When I thought about it more, I really don't want to sell it anyway...

So the project is still no further on, except that I got a NST and tested the gate driver isolation barriers to 2kV peak for 5 minutes. All four of them passed. I also nearly finished stuffing another PLL driver board.

Marko, the resonator isn't too badly damaged and could easily be fixed, the problem just now is just a lack of time to work on it, and I don't really have a place to fire it up safely either. If it works, I expect it would spark at least 7ft, and if it doesn't, pieces could fly even further! Not really a good toy for a top floor apartment ;)

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sat Nov 17 2007, 08:56PM

Steve: I completely understand you - having ditched your car, I don't even know how would you transport it. And it's apparently not something you'd like to run in your apartment.

You don't have any kind of terrace on the top roof or like?

But your apparent loss of appetite for coiling... it's just too much work?

I can't really imagine how you feel... after all the years, OLTC's and everything - I may just be too-young-and-hot yet.

For example I'm supposed to be studying now, but can't because I'm supervising the coil winder and writing this. I have tons of unfinished projects dwelling all around...

I wonder if you could just have gone for some smaller scale coils (which can be very fun too).

I'd really like to se something from you since the forum is sort of dying out lately... just compare it to archives!

Regarding odin... do you guys happen to have some kind of lab, university or school or etc. you could keep him in and work? I don't know if that's an odd question.

Marko

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Nov 17 2007, 10:48PM

Hey Marko,

Thanks for asking! :P I did most of my coiling when I was a student and living at home with my parents. I had loads more spare time and energy because I didn't have to work for a living, and a big workshop in the basement and a garden to try things out that might catch fire...

I'm lucky to now have an engineering job where I make stuff for a living, but after a while I found that I couldn't be bothered trying to make even more stuff when I got home in the evenings. I still love engineering and I'm determined to make a career out of it, but I just can't do it every hour of the day!

The projects I've done at work are better than anything I've ever worked on here, but I can't talk about them since they're commercially sensitive.

I guess what I'm trying to say is, yes, I am probably getting too old for it, and it's up to people like you to carry on what we started! :P

Re: Odin The All-Fragger: a large DRSSTC
Dr. SSTC, Fri Aug 15 2008, 11:10AM

lol isnt that one of those satanist things that your doing with your hand

Anyways that coil is great too bad you cant finish it

Re: Odin The All-Fragger: a large DRSSTC
uzzors2k, Fri Aug 15 2008, 04:41PM

Lol, it's just a "this rocks" hand sign.

Any chance you'll be continuing with the coil Steve?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Aug 16 2008, 08:11PM

I don't really have any desire for a big DRSSTC now, or anywhere to run one safely if I did, so this project is shelved indefinitely :P The H-bridge looked a bit dicey anyway.

And yes, I was just trying to express how metal my H-bridge was

Re: Odin The All-Fragger: a large DRSSTC
uzzors2k, Sat Aug 16 2008, 10:14PM

That's a shame but I understand. I doubt the thrill of them is the same after building so many anyway.

Re: Odin The All-Fragger: a large DRSSTC
Dr. SSTC, Wed Aug 20 2008, 10:05AM

Dr. Quit The Dr. Thing! wrote ...

Hey Marko,

Thanks for asking! :P I did most of my coiling when I was a student and living at home with my parents. I had loads more spare time and energy because I didn't have to work for a living, and a big workshop in the basement and a garden to try things out that might catch fire...

I'm lucky to now have an engineering job where I make stuff for a living, but after a while I found that I couldn't be bothered trying to make even more stuff when I got home in the evenings. I still love engineering and I'm determined to make a career out of it, but I just can't do it every hour of the day!

The projects I've done at work are better than anything I've ever worked on here, but I can't talk about them since they're commercially sensitive.

I guess what I'm trying to say is, yes, I am probably getting too old for it, and it's up to people like you to carry on what we started! :P

maybe when you retire you will go back to coiling as new types of coil designes could be invented by that time

Re: Odin The All-Fragger: a large DRSSTC
Arcstarter, Thu Aug 21 2008, 04:48AM

Dr. Quit The Dr. Thing! wrote ...

I don't really have any desire for a big DRSSTC now, or anywhere to run one safely if I did, so this project is shelved indefinitely :P The H-bridge looked a bit dicey anyway.

And yes, I was just trying to express how metal my H-bridge was

I'll take the unused components!:P Just messin'...

Re: Odin The All-Fragger: a large DRSSTC
Marko, Sat Aug 23 2008, 01:07AM

Guys, living in a flat Steve just doesn't have a place he can run such a massive and loud monster. Still it's not an excuse not to build some smaller and quiet VTTC's or SSTC's! :D

Just looking back at this, if I was designing a 'commercial' DRSSTC driver that needs to work under specs, I would:

- use commercial DC-DC converters on each driver board;

- use either commercial GDT's or optocouplers for drive signal transmission. This gets rid of voltage standoff problems as I think.

The homemade transformers may just work, but we can't forget that wire isn't rated for more than like 300V or so actually.

Recently Reaching had some problems with EMI acting on toslink receivers, and they are really unnecessary since voltage isn't really too high. They are also pricey. If I had to use opto it would probably just be some faster optocouplers.

Marko

Re: Odin The All-Fragger: a large DRSSTC
Dalus, Sat Aug 23 2008, 10:14AM

It's not easy to build a DRSSTC in an appartment, but it isn't inpossible. I'm building my DRSSTC with a secondary hight of 1 meter in my bedroom

But I have the oppertunity to run and test it at the TU/e

Re: Odin The All-Fragger: a large DRSSTC
Reaching, Sat Aug 23 2008, 11:59AM

Yep marco youÂ´re right. ive had some problems with emi acting to the toslink receivers, but i solved the problem. for sure, you dont need to add a complete optical connection system like i did, and i said that a while ago. this is the first and last drsstc i build, using this really complex and expensive technique. i tried it and it works really good but youÂ´re right. it isnt really worth the effort and trouble. fast optocoupled devices or well build gdt drives are the way to go.

i used toslink cause i wanted to try it out, nothing more.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri Jul 19 2013, 07:22PM

And we're back!

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Fri Jul 19 2013, 08:56PM

That was quick

I'll have to have a proper read through the thread to catch up. Gate drive waveforms look fast, I'm guessing it's running reasonably cool even with hard switching?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Jul 20 2013, 10:48AM

The scope shot I just posted is of the H-bridge outputs, not the gate drive.

It's only hard switching about 10A, but I remember Finn or someone tried the Semikron bricks and got nasty ringing even with no load, so I'm pleasantly surprised.

The plastic film bus caps undoubtedly help damp ringing with their huge capacitance and relatively high ESR, and also I'm using about 1us of deadtime, though it's not visible with an inductive load. And I guess maybe the 128 series bricks switch softer and/or have lower inductance than the 123s.

My only worry is that at full power the harmonic current might be enough to burn out the bypass caps. They're rated about 13A RMS each.

Re: Odin The All-Fragger: a large DRSSTC
Finn Hammer, Sat Jul 20 2013, 06:46PM

Steve Conner wrote ...

but I remember Finn or someone tried the Semikron bricks and got nasty ringing even with no load, so I'm pleasantly surprised.

You should "seem to remember" because the ones I had bad experiences with were some ancient Toshiba types, real crap!

The white Semikrons come highly recommended overhere: Daniels Diablo Tonnere uses them, although the 400A version, and they have been running like thoroughbred racehorses ever since.

Cheers, Finn Hammer

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Jul 21 2013, 06:18PM

Induction tea brewing at 600V bus voltage, 2% duty cycle, 1kW average power (limited by power supply)

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Mon Jul 22 2013, 08:37AM

Nice kettle

I should have noticed the scope shot wasn't the gate drive, due to the lack of any artifacts whatsoever around the threshold. Are you going to use the 'OLTC II' power supply with that thyristor to control the bus voltage?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Jul 22 2013, 09:05AM

Yes, I plan to use the same voltage doubler circuit with two SCRs and an inductor for passive PFC. (In fact the actual SCR module and inductor salvaged from the OLTC2.

)

I have a more advanced controller for it though, that I used in my last two DRSSTCs. The firing angle is set by a 0-10V analog input so I can remote control it, and it has a soft start to avoid popping breakers if I forget to turn the control down to zero before powering up.

Re: Odin The All-Fragger: a large DRSSTC
brtaman, Mon Jul 22 2013, 09:18AM

Great to see Odin back on the workbench Steve. :) Cannot wait to see him generating some ozone.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Mar 22 2014, 06:03PM

Update March 2014:
An enormous bank of GTO snubber capacitors was procured. 0.75uF total capacitance at eleventy billion volts.
The bridge has been tested to 750A peak with a dummy primary coil.
The bridge and driver have been bolted together and mounting rails added.
A 12" x 39" coilform made of grey PVC air duct has been procured, as well as 6kg of magnet wire and some low viscosity epoxy resin for coating.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Sat Mar 22 2014, 06:58PM

Where did you get those capacitors... wish these kind of things were more avaliable for our use.. amazing work, keep it up!

Re: Odin The All-Fragger: a large DRSSTC
Mads Barnkob, Sun Mar 23 2014, 08:58AM

I like every bit of this update, good looking bridge and massive MMC!

Thomas W, ebay is always the answer, when I bought mine, it was however a Make offer auction and I got them somewhat cheaper:

I can see that Conner used a 6uF model of the same capacitor.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Sun Mar 23 2014, 09:20AM

Mads Barnkob wrote ...

I like every bit of this update, good looking bridge and massive MMC!

Thomas W, ebay is always the answer, when I bought mine, it was however a Make offer auction and I got them somewhat cheaper:

I can see that Conner used a 3uF model of the same capacitor.

Neat, i wonder if there are any UK sellers... if i buy them, i have no intention of paying over Â£300 in customs likely

Re: Odin The All-Fragger: a large DRSSTC
Paul Benham, Sun Mar 23 2014, 12:17PM

Hi Steve,

Nice to see the project is getting some further progress. My coiling has been on hold for the last few years due to moving house and being too busy at work.

It is looking great! Seriously impressive cap bank.

Cheers,

Paul

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Mar 26 2014, 10:01AM

I bought the capacitors (6uF, not 3) from a fellow 4hver in Finland. No customs issues as we're both in the European Economic Whatsitsname. They're overkill for the size of the bridge, but I can always add a second bridge later.

Just had a bit of a disaster with waterjet cutting of Tufnol primary supports that will set the project back a little while I source some more material and find an alternative way of making them. Not sure if Tufnol is ill-suited to waterjet cutting, or if the company I used just suck at it.

Secondary coil winding is scheduled for tomorrow evening.

Also this

Re: Odin The All-Fragger: a large DRSSTC
Goodchild, Fri Mar 28 2014, 03:48PM

Steve Conner wrote ...

I bought the capacitors (6uF, not 3) from a fellow 4hver in Finland. No customs issues as we're both in the European Economic Whatsitsname. They're overkill for the size of the bridge, but I can always add a second bridge later.

Also this

I have had very good luck with making the supports out of polycarb. I also know that polycarb cuts like butter on the water jet.

The only failure of polycarb primary supports I have ever had was when I melted the supports, however in all fairness to the polycarb the primary was at 375*C and the copper primary was starting to anneal...

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Mar 29 2014, 02:35PM

Yup. I'm using Tufnol because it doesn't melt, so I can run more power without getting into water cooling.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Sat Mar 29 2014, 03:24PM

Steve Conner wrote ...

Yup. I'm using Tufnol because it doesn't melt, so I can run more power without getting into water cooling.

I assume you would use oil and not water in such a situation, i have a feeling water could cause some problems with the current flowing though the water and pump side as well as the primary side...

Keep up the amazing work :)

Re: Odin The All-Fragger: a large DRSSTC
HV Enthusiast, Sun Mar 30 2014, 12:05AM

wrote ...

Just had a bit of a disaster with waterjet cutting of Tufnol primary supports that will set the project back a little while I source some more material and find an alternative way of making them. Not sure if Tufnol is ill-suited to waterjet cutting, or if the company I used just suck at it.

Hey Steve. I'd be happy to cut you some polycarbonate supports on my CNC for no charge. (Just pay for the material and shipping back to you)
I'd just need your drawing files.

Re: Odin The All-Fragger: a large DRSSTC
Goodchild, Sun Mar 30 2014, 05:32PM

Thomas W wrote ...

Steve Conner wrote ...

Yup. I'm using Tufnol because it doesn't melt, so I can run more power without getting into water cooling.

Actually, several people have run water cooled primaries including myself without issue.

Re: Odin The All-Fragger: a large DRSSTC
Hydron, Sun Mar 30 2014, 07:17PM

Adding to the above, the HV lab at the university I went to had a continuous flow water resistor which was regularly used at many kV. They just used long thin hoses to feed it from the tap and it all worked fine.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Mar 30 2014, 08:07PM

Thanks for the offer EVR, but a few people have offered to do it locally.

The only trouble with water cooling is that any DC voltage across the water system can cause electrolytic corrosion. AC voltage is no problem.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Sun Mar 30 2014, 08:25PM

Steve Conner wrote ...

Thanks for the offer EVR, but a few people have offered to do it locally.

The only trouble with water cooling is that any DC voltage across the water system can cause electrolytic corrosion. AC voltage is no problem.

Ah, okey then. My main thoughts were that if you have water flowing though a coil, it also provides a second circuit to allow current to flow... Has anyone tried measuring the current though the water pipes going around the pump and tank side of things?

I would really be interested if someone could do that, hooking their current probe around the pipe and seeing the current flow though the other direction compared to the one though the actual coil. :)

Re: Odin The All-Fragger: a large DRSSTC
Kizmo, Sun Mar 30 2014, 09:17PM

Goodchild wrote ...

Thomas W wrote ...

Steve Conner wrote ...

Yup. I'm using Tufnol because it doesn't melt, so I can run more power without getting into water cooling.

Actually, several people have run water cooled primaries including myself without issue.

I have taken i a step further: Water cooled igbt bridge and primary in same loop with mains powered water pump. Has been one of very few things that have never caused any trouble during my experiments :)

Re: Odin The All-Fragger: a large DRSSTC
Dr. Dark Current, Sun Mar 30 2014, 10:33PM

Hydron wrote ...

Adding to the above, the HV lab at the university I went to had a continuous flow water resistor which was regularly used at many kV. They just used long thin hoses to feed it from the tap and it all worked fine.

AFAIK this is also the method they use in high power tube transmitters with water cooled tubes.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Apr 07 2014, 10:21AM

Secondary is done

315mm dia X 1m height, 1175 turns of 0.75mm wire, coated with 2-part epoxy.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Mon Apr 07 2014, 10:55AM

Very nice! must say that it looked very bent at the end of the video!

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Apr 07 2014, 01:43PM

I blame the fisheye lens on the GoPro!

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Mon Apr 07 2014, 04:13PM

Steve Conner wrote ...

I blame the fisheye lens on the GoPro!

Oooooh, thats what it was

How long did that take you then?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Apr 07 2014, 10:21PM

The video is 25x actual speed, so the actual winding process took maybe about 20 minutes. However it took a half day of messing around to set up the jig, get it to work and clean up the mess afterwards.

Re: Odin The All-Fragger: a large DRSSTC
zilipoper, Wed Apr 09 2014, 05:10PM

Steve Conner wrote ...

The video is 25x actual speed, so the actual winding process took maybe about 20 minutes. However it took a half day of messing around to set up the jig, get it to work and clean up the mess afterwards.

omg another as Hell DRSSTÐ¡

we are waiting for streamers))))))

Re: Odin The All-Fragger: a large DRSSTC
Steve Ward, Fri Apr 18 2014, 04:45AM

Id suggest FR4 or G-10 for the primary supports. We have had it waterjet cut several times now with good results. even 1/8" thick FR4 is pretty tough stuff, id stick with less than 1/4" thick for waterjet "curf" (it leaves a non-square edge). Could also be cut out on a PCB mill if you know someone that has one.

Re: Odin The All-Fragger: a large DRSSTC
HV Enthusiast, Fri Apr 18 2014, 06:19PM

Well, that's what machining is all about. 99% set-up and jig making, and 1% actual machining! :)

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Apr 19 2014, 11:22AM

I decided on 1/2" Tufnol for the primary supports. 1/2" so I could drill and tap decent sized holes into the edge of it, and Tufnol because it was cheaper than G10. I don't even know where to get a G10 type material in that thickness, we lack a UK equivalent of McMaster Carr.

Waterjet cutting was a complete failure, but I managed to get someone else to make the parts on a CNC mill.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Apr 26 2014, 10:35AM

Update April 2014: Trial assembly of everything. It all seems to fit together OK

The overall height is an imposing 1.8m.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Sat Apr 26 2014, 12:34PM

Wow! that is quite somthing!

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Sat Apr 26 2014, 02:10PM

That is epic

I'm looking forward to seeing this fired up. It might motivate me to get on and finish building one too (although not quite that large!)

Re: Odin The All-Fragger: a large DRSSTC
Artlav, Sat Apr 26 2014, 04:07PM

Looks like a fragger all right:)

What are you going to power it with?
50KW full power sounds like a bit more than what a single 380V socket can provide.

On the other hand, you can run it for an hour on an electric car's battery. :)

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Apr 26 2014, 09:31PM

I plan to run it off single phase, 240V, 32A to start with. If that goes well, I have access to a few places with 63A 3-phase supply.

Re: Odin The All-Fragger: a large DRSSTC
Extreme Electronics, Sat Apr 26 2014, 09:49PM

De-Lurk...
Looking Good Steve, Will we get to see this at UK Thons sometime soon. Would love to see it working and (separately) up close.
Re-Lurk...

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Apr 26 2014, 09:56PM

Yeah! Too big for the living room so it has to go on tour

Re: Odin The All-Fragger: a large DRSSTC
RateReducer, Sun Apr 27 2014, 02:24AM

This coil looks awesome Steve! O___O

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Tue May 06 2014, 09:06AM

Update May 2014: Completed the primary

Re: Odin The All-Fragger: a large DRSSTC
teravolt, Tue May 06 2014, 07:37PM

whats the secondary frequency

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri May 09 2014, 09:26AM

Should be about 70kHz. Going to start tuning tonight.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun May 11 2014, 01:26PM

Dummy load test

The load consisted of the largest metal tray I could lay hands on. Even so it doesn't seem to load the tank circuit very well. The current limiter returns almost all of the energy to the DC bus and the coil draws hardly any current from the mains. This is good as it shows we have a nice low-loss primary circuit.

The current limiter is set for 750A, but the actual peak current seems to go to maybe 1100 or 1200A. This is because it only operates in increments of 1 cycle. If it trips on the first half-cycle, the second half-cycle will still be active and will ring it up even further. I expect this to calm down somewhat when loaded by the secondary. Nevertheless, the 200A IGBTs seem to handle it fine.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Sun May 11 2014, 02:25PM

Awesome, cant wait to see it when its done..! What happens if you put a magnet in the coil? i wonder how it would react, ahah.

Re: Odin The All-Fragger: a large DRSSTC
Hydron, Sun May 11 2014, 02:36PM

Looks good! I've used big cast iron pans as dummy loads in the past, though for a smaller coil than that. Even cooked a couple of eggs once (~2kW for >10 min, good thermal test of the primary circuit!).

Do you get much coupling into the aluminium box lid and frame? They seem fairly close to the primary given they're on-axis.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun May 11 2014, 02:44PM

Given that no sparks shot out of the corners of the box lid and it didn't catch fire, I think the coupling must be acceptable.

The field strength in this test was similar to what it will be when the coil runs at full power later.

I added the legs to the underside of the primary mainly to reduce coupling, after having problems with it in my previous DRSSTC. Eddy currents in the metal frame caused some impressive arcing and burning at the corners.

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Sun May 11 2014, 04:17PM

Is that running with those SKM200GB128 devices? Either way, looking mighty impressive so far

I was wondering if you were going to show a shot of the tray of boiling water towards the end

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun May 11 2014, 05:52PM

Yes it is the SKM200GB128s. Sadly there was no water in the tray as it was too shallow and badly warped to hold any. Must try again with a dustbin lid.

Re: Odin The All-Fragger: a large DRSSTC
Artlav, Sun May 18 2014, 06:25AM

About that IGBT brick driver of yours - do you have any write-up on it's design?

Specifically:
-Why +24, -12V? The gates are almost universally +-20V absolute maximum. Is that safe?
-Why GDT on the input, instead of optocoupled logic level signals and on-board driver for the FETs? I.e. HCPL3120 which is two of these in one.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun May 18 2014, 09:56AM

This thread contains details of the gate driver design. You can read some more about it here.

Overdriving the gate voltage isn't exactly "safe", but then neither is running the device at 3x its maximum pulsed current rating.

+24/-12 is safer than the +/-24 used by other DRSSTC builders.

The GDT approach is simpler, cheaper and faster than an optocoupler-based circuit. The total delay through my gate driver is less than 200ns. The only reason to use optocouplers for gate drive is if you need to pass a low frequency or DC component that a GDT couldn't handle.

Re: Odin The All-Fragger: a large DRSSTC
Artlav, Mon May 19 2014, 08:16PM

Steve Conner wrote ...
Overdriving the gate voltage isn't exactly "safe", but then neither is running the device at 3x its maximum pulsed current rating.

Hm, i thought running over the maximum pulse current was mostly a heat dissipation issue (within fusing reason), while overvoltage on the gates was a breakdown type of issue.
First is radiated away and you're good as new, second is eroding away and you breakdown and go BOOM.
No?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon May 19 2014, 09:15PM

Yes and no. The greater the junction temperature rise during the burst, the shorter the life of the device will be. There are fatigue mechanisms that set in far below the 200 degree delta-T that would be required to fuse it in a single shot. For example, in railway traction applications the bond wires often fall off the die.

Overdriving the gate will lower conduction losses and help the device to carry more current before desaturating, so in extreme cases it may reduce the temperature rise during the burst.

The effect is to lengthen the device's thermal fatigue life while shortening the life of the gate dielectric. The optimum gate voltage would be when both lifetimes were the same. I have absolutely no clue what it is, but everyone else seems to use at least 24V.

Re: Odin The All-Fragger: a large DRSSTC
Goodchild, Thu May 22 2014, 02:09PM

Hey steve, how are you getting +24/ -12 out of a GDT? Are you dong some fancy trickery with the GDT driver?

EDIT:

After looking at your link up top I see what you did. Very clever I may add.

In addition to the comments made above about gate drive voltages, I also like driving at the higher voltages (both on and off) I feel that the high voltage helps to force the IGBT into and out of saturation much faster than with lower voltages. This helps minimize the time spent in the linear portion of the switching cycle. Although this addition accounts for only maybe 10's of nS it does seem to help reduce losses.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Thu May 22 2014, 09:30PM

Oh dear... :(

Two issues, the first is why it popped at less than 1200A peak current. (The SKM200GB128D datasheet doesn't suggest a particularly good peak current capability, but other coilers claim to have used them.) The second is why the coil hardly produced any sparks at 1200A peak current.

Re: Odin The All-Fragger: a large DRSSTC
Kizmo, Thu May 22 2014, 10:01PM

Odin The All-Fragger was such a hardcore fragger it fragged itself.

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Thu May 22 2014, 10:39PM

I'm wondering where all the energy was going then if there was hardly any output?

Is the checker-plate below the primary getting hot from induced eddy currents?

Very clean exploded devices though

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Fri May 23 2014, 12:11AM

Hmmm, pity~ gonna scale up to some larger IGBTs then?

Where is that you are testing it at?

Re: Odin The All-Fragger: a large DRSSTC
Mads Barnkob, Fri May 23 2014, 06:09AM

What was the second issue? That all energy was just dissipated in the brick?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri May 23 2014, 07:19AM

The energy isn't really being dissipated anywhere. If the coil fails to break out, it gets returned to the DC bus. You can see that the mains current meter hardly moves until breakout begins (or until some current is needed to blow the silicon to smithereens :/ )

The impedance of the primary circuit is probably somewhat too low for the current limit. This is due to an unfortunate incident involving some large and sexy GTO snubber capacitors. One of the experiments I'll try later is to use a smaller tank capacitor and more primary turns: it's currently tapped at 3 out of 5. But today's test will involve installing some larger IGBTs (the SKM300GB12T4) and trying a few different primary tapping points. It blew up before I had a chance to start tuning.

The test location is the university high voltage lab.

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Fri May 23 2014, 09:38AM

Sorry to hear about the IGBTs demise. Return them for repairs

Any idea, why they survived the dummy load test and not the one with the secondary?

3 primary turns don't make much of a field. Could it be, that the PLL ramped up at the wrong pole, i.e. the lower one?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri May 23 2014, 09:54AM

I have no idea. The current limit was set the same in both cases, and the actual peak currents should have been lower with the secondary in place, due to energy transfer to the secondary. For all I know they might have been weakened during the dummy load test, or in the equipment they were salvaged from. Another possibility is that the fast rise time of my gate drivers produced some very high gate voltage transients at the dice. These bricks have quite high inductance internal gate wiring, and no internal gate resistors or TVS.

The ringup of the primary circuit is so quick that the concept of separate poles doesn't even seem to make sense. As far as I can tell, it is hitting the current limit within 1 cycle, before it even gets a chance to resolve itself into two separate pole frequencies and pick one of them. After hitting the current limit, the primary current decays away to zero and when the gate drive comes back on it is back where it started.

This makes it all very tempting to hit it with a bigger bridge that can supply say 3000A instead of 1000.

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Fri May 23 2014, 10:44AM

The scope shots seem to indicate a somewhat longer rampup. Might be due to the delayed response of the OCD. I wouldn't expect a secondary loading effect for the primary current on the first cycle. Even if perfectly tuned, energy transfer takes place on the time scale of the beats.

More primary inductance looks like a good idea.

Re: Odin The All-Fragger: a large DRSSTC
Artlav, Fri May 23 2014, 11:38AM

On a slightly off topic - did that module popped open on it's own, or have you dissolved the glue somehow?

I have a dead module of a similar construction that i'm curious to take a look inside, preferably without having to resort to a dremel.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri May 23 2014, 11:44AM

I "dissolved" the glue with a hammer and screwdriver. The Semikron bricks are quite a flimsy construction and the plastic top comes loose after a few good wallops. The older Mitsubishi/Powerex devices seem to be much more solid.

Re: Odin The All-Fragger: a large DRSSTC
Hydron, Fri May 23 2014, 12:51PM

Steve, is there any chance it's hard switching due to the PLL not having time to lock into ZCS before the current gets large?

Doesn't look like you have many cycles before hitting the limit with your low-Z primary, is it possible you're managing to get outside the switching SOA of the IGBTs on one of the early switching transitions? Even once could be enough to make it pop if it latches up or runs into second breakdown or something (I'm not sure exactly how they fail, but I do know that you need to be much more careful with the switching SOA than the general current limits).

It may be useful to run a frequency sweep of the primary when the secondary is in place to look at where it's in resonance, and check against what you get from the PLL at the start of the burst. I just ran a quick sweep on mine and got the graph below:

Edit: impressive pics of the dead IGBT, never seen the dies quite so uniformly black!

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri May 23 2014, 01:27PM

Neither of the datasheets I have even specifies the switching SOA. In other similar devices (CM300DU-24H etc) it is square up to the device's rated voltage and Icm.

The switching transitions look reasonably accurate in the first few cycles. However I think I spotted some weird behaviour when the gate drive comes back on after tripping the current limit. I'll add it to the list of things to check.

I swept the resonator with a signal generator at home before rolling it out for testing, and set the PLL up accordingly. I will have to test it again in situ, as the long wires connecting it to the power electronics probably added some inductance.

Re: Odin The All-Fragger: a large DRSSTC
Intra, Mon May 26 2014, 02:06PM

Steve Conner wrote ...

Another possibility is that the fast rise time of my gate drivers produced some very high gate voltage transients at the dice. These bricks have quite high inductance internal gate wiring, and no internal gate resistors or TVS.

Exactly.

If I saw the few your last videos right, you did control gate drive voltage manually, and if you won't use Zeners on the gates, your bricks will blow up even on 30Vbus. Zeners should defend your gates from spikes and overvoltage at the gate at all.

Re: Odin The All-Fragger: a large DRSSTC
Sigurthr, Tue May 27 2014, 01:26AM

I'm fond of high inductance primaries. Should you end up going that route I'd love to see lots of documentation on your progress and experiments.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed May 28 2014, 12:46PM

Intra wrote ...

If I saw the few your last videos right, you did control gate drive voltage manually, and if you won't use Zeners on the gates, your bricks will blow up even on 30Vbus. Zeners should defend your gates from spikes and overvoltage at the gate at all.

The problem is with the inductance of the gate wiring inside the brick. Even with a perfect clamp at the gate terminals, this inductance would cause overshoot at the dice.

The SKM300GB12T4 claims to have built-in gate resistors which should help. I also installed 24V TVS directly on the gate terminals this time (the TVS were mounted on the gate driver board before)

I don't understand what you mean by "control gate voltage manually".

For more info on primary inductance, see the thread I started on "What is a low impedance DRSSTC" where we develop some guidelines for choosing the primary impedance.

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Wed May 28 2014, 03:55PM

There's some info on SOA's for Semikron devices in the application manual (page 181 onwards) which you can get here -

Not sure if this is any use... there's nothing really device specific, but you can calculate some things from datasheet values.

For anyone intersted, that link is a brilliant application manual on power devices in general. I'm lucky to have a hard copy, I just need to read it

Re: Odin The All-Fragger: a large DRSSTC
Intra, Thu May 29 2014, 02:29PM

Steve Conner wrote ...

I don't understand what you mean by "control gate voltage manually".

oh, no, I thought you see your gate voltage before gate. you probably saw it from after the gate, from bridge directly. that's explains rise of meander.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Thu May 29 2014, 05:14PM

Yes, the square waveform on the scope is the output of one side of the H-bridge, using a x100 probe.

I built a new tank capacitor of 0.3uF, connected it up, and retuned the system with a signal generator. The new tuning point is about 4.4 turns. Ready for another high voltage test run tomorrow

Re: Odin The All-Fragger: a large DRSSTC
loneoceans, Thu May 29 2014, 06:25PM

Steve Conner wrote ...

Yes, the square waveform on the scope is the output of one side of the H-bridge, using a x100 probe.

I built a new tank capacitor of 0.3uF, connected it up, and retuned the system with a signal generator. The new tuning point is about 4.4 turns. Ready for another high voltage test run tomorrow

Looking forward to that! Are you using the same IGBTs or newer 400A ones?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Thu May 29 2014, 08:18PM

I'm using the SKM300GB12T4 this time. This is a newer, faster device with Icm of 900A.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri May 30 2014, 11:29AM

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Fri May 30 2014, 01:32PM

Congratulations!! Odin, the old tea stove, is finally making himself heard.

Re: Odin The All-Fragger: a large DRSSTC
Goodchild, Fri May 30 2014, 02:01PM

^^^^Priceless^^^^

Steve looks great! Glad it's finally kicking!

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Fri May 30 2014, 02:36PM

Brilliant

Looks like the roof is going to have to come off then.

So what's the official spark length? Or are you still optimising the tuning?

I'm probably not the only one waiting to see some video!

Re: Odin The All-Fragger: a large DRSSTC
Ash Small, Fri May 30 2014, 05:19PM

Eight years, two months, one week and three days, is this a record?

Can't wait til you take it on tour, Steve.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri May 30 2014, 08:54PM

Test video!

Re: Odin The All-Fragger: a large DRSSTC
Intra, Sat May 31 2014, 04:55PM

Nice.

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Sat May 31 2014, 10:12PM

Great stuff

Interesting to see the cycle-skipping current limit in action as well. I'm thinking the trigger source for that could come from a conventional desaturation detection circuit, with all 4 outputs OR'ed into the controller (instead of turning the IGBT off straight away). Maybe, maybe not, just thinking out loud as I've had too much whiskey!

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Jun 01 2014, 03:23PM

Your idea might well work as most IGBTs are short circuit rated for 10us, which isn't that far off one cycle. I could never be bothered implementing desaturation detection though. The main problem is that we use the devices at much higher frequencies than they were intended for, so the di/dt voltages across the package inductance get high enough to fool the usual desat circuits.

Also, the most likely cause of desaturation is that the opposite bridge leg has just failed short. When using half-bridge modules, you have to throw the whole module away at this point anyway, so it's not worth the bother stopping the failure from cascading. With large single devices like the CM600, it might be worthwhile.

The cycle skipping current limit is nice, but it's skipping somewhat more cycles than I'd have liked. :< Maybe the primary needs to be higher impedance still. Will be interesting to see what happens when the OCD is turned up after next Friday.

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Mon Jun 02 2014, 09:14AM

The cycle skipping current limit is nice, but it's skipping somewhat more cycles than I'd have liked. :< Maybe the primary needs to be higher impedance still. Will be interesting to see what happens when the OCD is turned up after next Friday.

I was thinking along the same line. Where is loaded Q at now? Did you observe any frequency jumps?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Jun 02 2014, 09:28AM

I think the loaded Q is around 6.

The PLL can't track an instantaneous jump, and I didn't notice any extreme hard switching, so I don't think there were any frequency jumps. As the loading increases, the frequency probably collapses from the upper pole to somewhere around the middle of the passband.

I wonder if performing a STFT of the primary current waveform would shed any light on this? Is there any way to "deconvolve" the frequency spectrum of the driving voltage from the current, to get the impulse response of the resonator at a given point in time?

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Mon Jun 02 2014, 11:21AM

As long as there is no hard switching, the input to the VFO should be a good indicator of zcs frequency. Running the coil at some lower Vbus to avoid pulse skipping might also help analysis. Dunno if a STFT would help. There's always a delay between primary current and the secondaries response to it.

Edit: You could do a STFT on both primary voltage and current and divide them, which gives Z in the frequency domain.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Mon Jun 02 2014, 09:23PM

Ooh, good idea, I think I will try that.

I measured the distance from the breakout point to the little burnt spots on the ceiling, 1.8m. So I haven't beaten the 2.1m output of the OLTC2 yet, but I don't think this will be too hard.

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Tue Jun 03 2014, 08:47AM

Been thinking about the frequency jumps, since they might be harmful to the electronics. I believe the jumps to happen only in the case, when, at the time Qsec drops below 1/k, primary fres is still below secondary fres. If secondary fres is then lower than primary fres, there will be no jumps. Where are the unloaded resonances?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Tue Jun 03 2014, 09:14PM

With the tuning used in the video, the unloaded resonances are roughly 69 and 88kHz. The secondary alone resonates at 78kHz.

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Wed Jun 04 2014, 09:33AM

My guess is then, that primary and secondary fres are quite close to each other. With arc capacitance secondary fres would drop below primary fres and you won't see any frequency jumps.
Lowering primary fres will probably reduce pulse skipping at the risk of getting frequency jumps.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Jun 04 2014, 10:22AM

Yes. I started out with the primary and secondary tuned the same, and have been lowering the primary fres for each test run. Each time I lowered it, the amount of pulse skipping at full power decreased, and the spark output got bigger. On the last run, the pulse skipping duty cycle was up to about 75%.

Interestingly the detuning decreased the spark output at very low power. When I ramped up the DC bus voltage slowly from zero, the earliest breakout seemed to occur with the two coils exactly in tune. Any detuning delayed it, but once breakout happened the spark growth was more impressive.

I will continue to detune with each run until I run out of primary turns or the performance starts to fall off. Once I run out of primary turns, I could add more tank capacitance, but I guess that might be counterproductive as it would lower the impedance of the tank circuit?

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Wed Jun 04 2014, 11:32AM

Interestingly the detuning decreased the spark output at very low power. When I ramped up the DC bus voltage slowly from zero, the earliest breakout seemed to occur with the two coils exactly in tune. Any detuning delayed it, but once breakout happened the spark growth was more impressive.

That's unexpected from theory. The ordering of frequencies at low power from low to high would be:
flow, fpri, fsec, fup,
for lower pole, primary fres, secondary fres and upper pole. Lowering fpri should move fup, i.e. the f you're running on, closer to fsec, which would decrease Qpri and so lead to earlier breakout. I should redo the math here.

At large arc capacitances fsec drops below fpri, but fup still reamains above fpri, which increases the fup to fsec difference and thus increases Qpri. Lowering fpri will allow fup to follow fsec closer and so keep Qpri lower.

Once I run out of primary turns, I could add more tank capacitance, but I guess that might be counterproductive as it would lower the impedance of the tank circuit?

Yes, I think so too, but you might get away with increasing the MMC. There are 2 effects countering each other, lowering fpri, which decreases Qpri and decreasing tank impedance, which increases Qpri.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Jun 04 2014, 01:09PM

Yes, it stuck out because it was the opposite of what I expected. I will have to investigate more, don't go tearing up all the theory in the meantime.

I also plan to try a larger topload, which will definitely need more primary capacitance.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Jun 15 2014, 07:00PM

Another update: One of my SKM300GB12T4s has blown out.

I'm going back to the lab to investigate the reasons for failure, here are the main possibilities I'm considering.

1) Hard switching- The PLL driver can't provide perfect soft switching at all times, because there is always a delay in tracking frequency changes due to the loop filter. I am pretty sure that any hard switching that might happen is well within the device's switching SOA, though.

2) Desaturation- The Semikron application notes suggest that the T4 chips start to run out of steam around 3x the nominal collector current rating. This is really not that much greater than the peak pulsed rating (Icrm) however they do specify it at 15V gate voltage, whereas I'm using 24.

3) General lack of beefiness- The T4 series are 2 generations newer than the good old Powerex H series bricks. They use about half the die area and run at twice the current density. Maybe there is just less headroom for abusing the maximum ratings.

4) Too fast switching. The T4 series are also about 3x faster than the H series. That means bigger voltage spikes from stray inductance and freewheel diode recovery. However I think this is low down the list as Semikron presumably redesigned the rest of the module to cope with the extra speed and tested that it could hard switch currents up to Icrm. It would take a huge phase error to push the hard switching current over Icrm and this would have been obvious on the scope during the earlier tests. Also my DC bus voltage is right at the low end of what 1200V devices are designed to handle, leaving plenty of headroom for spikes. And, the spikes would have appeared at the brick's AC output terminal, which I was monitoring with the scope.

Re: Odin The All-Fragger: a large DRSSTC
Ash Small, Sun Jun 15 2014, 11:23PM

Not sure if this is of any relevance, Steve. This is from an ON semi app. note:

"The transconductance also varies from device-to-device.
This parameter is defined as the change in collector current
for the change in gate voltage. It is by no means a constant
and a typical curve is normally shown in the data sheet."

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Tue Jun 17 2014, 11:14AM

Ash: Yes, it is sort of relevant.

Update: A box of surplus CM300DY-24H and SKM400GB123D just arrived in the mail. The sender also included a Steve Ward driver board, I wonder if this is some sort of hint?

Re: Odin The All-Fragger: a large DRSSTC
Avalanche, Tue Jun 17 2014, 11:58AM

I've sometimes wondered if it would be necessary to view the PLL phase error, and use a more complex loop filter built around an opamp integrator, with derivative added in the form of series capacitance (to speed up the response to sudden frequency jumps).

Characterisation of switching SOAs (for a given layout) is usually done with the 'double pulse test' from what I've observed, so that switching speed can be optimised (against everything else). This would allow you to know the maximum currrent that can be turned off with a given gate resistor value, or translate that to maximum phase error somehow (and shut down before the error gets that high). I suppose it could easily get overly complicated, you might have to implement some kind of soft turn-off when shutting down the IGBTs when there is a phase error and they would have to hard-switch

Just thinking out loud... probably mostly impractical in reality. Maybe bigger IGBTs are the way to go

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Tue Jun 17 2014, 01:16PM

No matter how complicated a loop filter you dream up, you can dream up some scenario that will defeat it.

The primary current of the Tesla coil can even contain more than one frequency, and no PLL can handle this as the VCO can only produce one frequency at a time.

Derivative gain will amplify ripple and lead to the duty cycle of the VCO output going uneven, which will cause hard switching.

You have to set off the disadvantage of the PLL (always some hard switching, but can quite probably be kept within the switching SOA) against the advantages (operation on upper pole frequency with primary tuned below secondary, very easy to implement pulse-skipping current limit, keeps running even for low values of loaded Q that might stop a feedback driver)

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Jul 09 2014, 10:10AM

Update July 2014: (Edit: removed comment about failed test run as I already covered it in a previous post)

I set the system back up in the lab, as a half bridge with the remaining good IGBT. I broke the top off it so I could probe it at the die level, and I also added a small Rogowski coil around the emitter terminal. The following scope shots show the collector voltage (probed as close to the die as possible) and the Rogowski coil signal showing the emitter current of the same device. The PLL driver settings were as close as possible to the last fatal run, I just adjusted the frequency to account for the fact that it was running with no secondary coil. The DC bus voltage was reduced as I didn't really want a face full of IGBT goop if anything went wrong. :)

These results suggest that the PLL driver was set up with too much phase lead. The funny thing is that even with this large hard switched current, and turning off the IGBT as fast as possible with no gate resistors, and probing as close to the die as possible, the voltage waveform is very clean. I can't see any spikes that would endanger the breakdown voltage of the device. If I tune the phase lead for perfect ZCS according to the Rogowski coil signal, the spikes get somewhat worse, and if I tune it for leading current, the spikes get terrible.

My next move will be to set it up with SKM400GB123Ds, gate resistors, current limit increased to 1kA, and the PLL retuned for less hard switching. I will try to log the Rogowski coil waveforms while making sparks, and that should settle once and for all whether the PLL driver is good enough for the job.

Re: Odin The All-Fragger: a large DRSSTC
Hydron, Wed Jul 09 2014, 12:46PM

I have also noticed that the spikes seem to be a little smaller when phase lead is set a bit too high. I didn't test with a rogowski coil so I'm at the mercy of any small phase error of my CT in judging the exact zero crossing, but I could see the diode start conducting in the voltage waveform when I'd adjusted for minimum voltage spikes. Can't say much more right now, in Asia on holiday so this is all from memory.

Re: Odin The All-Fragger: a large DRSSTC
Goodchild, Wed Jul 09 2014, 02:27PM

Steve, this is just my opinion. I have seen a lot of other systems run with the same IGBTs, and similar secondary and primary capacitor setups with little issue up at 1.2kA with the SKM200s. I personally have done this, without a single failure (as of yet). I donâ€™t think your trouble has been solely caused by the wrong secondary/primary configuration.

I think that you really need to take a hard look at your controller and gate drive setup. I strongly suspect that the reason you are detonating IGBTs is the fact that somehow the switches are hard switching or possibly partly operating in the linear area and not in the SOA.

If you have time, it may be worth your while to try a direct feedback driver with no PLL and/or direct GDT operation. I can send you one of my driver boards if you like, purely to see the different in operation. I know you swear by your PLL driver; however in the spirit of experimentation it may be worth it to weed it out as a potential problem causer. If it turns out operation is just as pore then you have simply eliminated it as the problem, no harm done.

The larger topload also sounds like a good addition.

Thatâ€™s my two bits at least.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Jul 09 2014, 03:05PM

I asked about this in a recent thread. The only person who posted any relevant results for the exact devices I destroyed was Kizmo who blew up a 128 series at about 1500A, a similar current to what caused my 128 series to fail. Most of the Semikron experience seems to be with the 123 and 124 series. The SKM300GB12T4 has no track record whatsoever, and only about 1/2 the die area of the devices normally used in Tesla coiling.

Also, from the previous post you can see that I am taking a hard look at my controller and gate drive setup, and it showed that there probably was excessive hard switching going on at the time of the failure.

This next run with the PLL driver will be its last chance. If it still causes excessive hard switching under real streamer load conditions, this will be obvious from the Rogowski coil signal. In this case I will replace the PLL driver with a feedback driver. An anonymous donor already sent me some of Steve Ward's phase lead driver boards as some kind of hint.

I would be interested to see the Rogowski coil signal from a big DRSSTC that is known to work reliably.

Re: Odin The All-Fragger: a large DRSSTC
teravolt, Wed Jul 09 2014, 04:51PM

other than the hard switching do you think that you might have any shoot through and would any dead time be good for your set up?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Jul 09 2014, 05:51PM

The PLL driver has adjustable dead time, I was using 500ns for the 12T4. I didn't see any signs of shoot-through on the Rogowski coil signal. I tried deliberately reducing the dead time, and some very obvious nasty spikes appeared, which shows that the Rogowski coil is capable of detecting shoot-through and that some dead time is needed.

I just ran the 12T4 up to 1500A at 600V bus voltage, while twiddling the fine tune knob back and forth to provoke a little hard switching, with no apparent ill effects. Now to repeat the experiment with the 128.

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Wed Jul 09 2014, 06:31PM

The funny thing is that even with this large hard switched current, and turning off the IGBT as fast as possible with no gate resistors, and probing as close to the die as possible, the voltage waveform is very clean. I can't see any spikes that would endanger the breakdown voltage of the device. If I tune the phase lead for perfect ZCS according to the Rogowski coil signal, the spikes get somewhat worse, and if I tune it for leading current, the spikes get terrible.

Isn't this as expected, i.e. no spikes with phase lead and increasing tendency as it gets low or turns into phase lag?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Jul 09 2014, 07:11PM

I think with phase lag, the current has already commutated to the diode in the bridge leg that is about to turn off. When the other leg turns on, it causes forced recovery of the diode and this generates a large and ugly spike. However the switches are guaranteed zero current turn-off.

With phase lead, the switch that is turning off hands the current over to the diode in the leg that is about to turn on. The switch doesn't get zero current turn-off, but it gets zero voltage and current turn-on and the diode gets soft recovery.

When I think about it, I guess phase lead gives the cleanest waveform because the IGBT turn-off is the slowest part of the whole process, slower than the turn-on or the diode recovery, so it generates less high frequency energy. This doesn't imply that clean waveforms equal efficient operation though, if anything the opposite.

Re: Odin The All-Fragger: a large DRSSTC
Ash Small, Wed Jul 09 2014, 07:54PM

Steve Conner wrote ...

I think with phase lag, the current has already commutated to the diode in the bridge leg that is about to turn off. When the other leg turns on, it causes forced recovery of the diode and this generates a large and ugly spike.

Can this spike not be controlled with a simple snubber capacitor across this diode, or would this lead to other problems?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Jul 09 2014, 08:36PM

Yes, the capacitor would just add to the diode's reverse recovery charge and make things worse.

Snubber capacitors can be used on an IGBT or MOSFET bridge, but not with phase lag. You need phase lead and deadtime. Instead of handing over to the diode, the device that is turning off hands the current over to the capacitor. The switching losses are reduced as the capacitor slows the rate of rise of voltage.

The arrangement is called quasi-resonant or sometimes Class-DE.

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Thu Jul 10 2014, 09:27AM

Yes, exactly. In the case of phase lead, the tank current takes over the recharging of parasitic capacitances, while in the case of lag, the turning on transistor will have to do it. The fast turn on times in the latter case leads to spikes, while for phase lead the transistor current during turn off might be reduced by the parasitics.

Re: Odin The All-Fragger: a large DRSSTC
Ash Small, Thu Jul 10 2014, 11:06AM

Ok. I certainly don't intend to go too far OT here, but would faster diodes be sufficient here?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Thu Jul 10 2014, 11:13AM

The diodes are built into the IGBT bricks, there is no option to change them.

They are already as fast and soft recovery as diode technology allows (at the time the old surplus IGBT brick was made)

Re: Odin The All-Fragger: a large DRSSTC
teravolt, Thu Jul 10 2014, 01:36PM

to bad a big series diode in the couldn't be added to each IGBT drain to block the reversal. do you think that it would help with hard switching

Re: Odin The All-Fragger: a large DRSSTC
Ash Small, Thu Jul 10 2014, 09:47PM

teravolt wrote ...

to bad a big series diode in the couldn't be added to each IGBT drain to block the reversal. do you think that it would help with hard switching

a big Schottky, maybe?

Instantaneous reverse recovery, and negligible forward voltage drop?

Re: Odin The All-Fragger: a large DRSSTC
Sigurthr, Thu Jul 10 2014, 11:52PM

Blocking the body diode with series and antiparallel schottkys is what I've been doing on my SSTC bridges. I've been wondering how it would perform in a DRSSTC environment. I haven't seen it used on DR coils yet.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri Jul 11 2014, 10:09AM

Unlike MOSFETs, IGBTs don't have parasitic body diodes. They have a parasitic zener-transistor-junction thing that breaks down at about 10V.

So when you see an IGBT with a diode built in, the diode is actually a proper fast and soft recovery diode on a separate chip, wire bonded in parallel with the IGBT die. There would be no point in "blocking" it unless you wanted to upgrade an old diode to a newer generation.

One thing *I* haven't seen is the Class-DE snubber capacitors used on a DRSSTC bridge. Well, Steve and Eric probably used them in phase shift controlled QCWs, but I wonder if they would help a lower frequency coil with IGBT bricks.

By a quick back-of-the-envelope calculation, a 50nF snubber capacitor would cut the switching losses of a 300 amp IGBT brick in half when it was operating in the phase lead mode and hard switching 300 amps of inductive current. This is just a rough figure, the actual value depends on the fall time of the specific IGBT.

However, if there wasn't enough commutation current to charge the capacitor, the switching losses would get worse than if there were no capacitor. Basically it moves the point of lowest switching losses from ZCS, to some finite current, which is certainly an advantage in a phase shifted QCW.

Re: Odin The All-Fragger: a large DRSSTC
Goodchild, Fri Jul 11 2014, 02:15PM

If I'm not mistaken I asked Steve about his setup, he tried them but never got them working properly, rather he took the simpler approach of just hard switching on turn off and ZCS on turn on, simple and effective. This was a while ago however, Iâ€™m not sure if he ever went back to that approach.

I managed to get full ZCS working a little while back. It's an incredibly effective method of switching and allows turn-off anywhere there is enough current to commentate the voltage in the parallel capacitor. In some cases you don't even need external snubbers, most of the time the parasitic capacitance of the switch is enough to commutate the voltage. Usually external capacitance is added when there is not enough rise or fall time for the switch to transition. Even then usually only a couple nF has to be added to extend the rise and fall time to 100nS or more.

The two reasons I like it is that it allows you to do phase-sift modulation of the bridge current and also completely eliminates spikes/nasty transients. You get a lovely linear rise/fall time with a dV/dt of your choosing.

The last benefit is that EMI and harmonics from bridge transitions are heavily reduced, due to the rise and fall times being much sallower. In contrast to ZCS where they must be as close to square as possible.

The disadvantage however is complexity. Such a setup is tedious to setup and tune and requires a very complicated controller. I used an FPGA, and Steve I think used a Soc.
I think that for a normal DR the advantages donâ€™t out way the added complexity. However in a QCW, this added control allows you to eliminate the class D modulator hardware, so the added complexity balances out in the end.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri Jul 11 2014, 03:18PM

Interesting info, thanks. I don't see how it adds much complexity to a normal DRSSTC, surely with a phase lead DRSSTC driver you can just add the snubber capacitors and turn the phase lead up a little more?

My PLL driver can be phase shift modulated by hooking a voltage in place of the target phase pot. I was wondering if this would be a good way of controlling a halfbridge Class-DE QCW.

With a halfbridge, you can't phase shift two bridge legs against each other, so phase shift modulation degenerates to either PWM or detuning. I'm proposing to do it by detuning upwards, so the current will be inductive and suitable for Class-DE commutation.

Re: Odin The All-Fragger: a large DRSSTC
Goodchild, Sat Jul 12 2014, 01:25AM

Steve Conner wrote ...

Interesting info, thanks. I don't see how it adds much complexity to a normal DRSSTC, surely with a phase lead DRSSTC driver you can just add the snubber capacitors and turn the phase lead up a little more?

My PLL driver can be phase shift modulated by hooking a voltage in place of the target phase pot. I was wondering if this would be a good way of controlling a halfbridge Class-DE QCW.

With a halfbridge, you can't phase shift two bridge legs against each other, so phase shift modulation degenerates to either PWM or detuning. I'm proposing to do it by detuning upwards, so the current will be inductive and suitable for Class-DE commutation.

I wish it was that easy, but phase lead is only the first part of the equation, you also need an extended dead-time between the high and low side switch transitions.

This dead time is = the rise + fall times. On most of the bridges I played with this amounted to about 250nS dead time, with a 400KHz Fres. For slower transistors (like bricks) this dead time will be even larger.

The problem is that this dead-time can't be introduces at the gates of the IGBTs because it would cause the IGBT to operate in the linear region for a large part of that dead time, it's also impractical to implement such a long RC when the gate C is so small.

So the only other option is to create it before the gate drive; for GDT drives this means 2 GDTs and added driver circuitry and delay circuit. Phase moderation adds even more circuitry on top of this setup.

I implemented every part except for the GDT drivers in an FPGA, this made all the parameters of the circuit, dead-time, phase lead, etc controllable and digitally tun-able.

I tried an analog version of this circuit before the FPGA, and although it works it was much more fussy and used a needless amount of analog cludgery.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Jul 12 2014, 04:44PM

Oh, I think I have all that analog cludgery already.

My PLL driver has a deadtime generator that inserts periods of 0V into the gate drive output, so it goes +12V, 0V, -12V, etc.

The 0V step seems to work OK when driving smaller devices directly, as it applies 0V to all of the gates. This doesn't turn them off as fast as a negative voltage would, though.

The outboard drivers translate both -12V and 0V into -12V, so the output from them is textbook stuff.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Sat Jul 12 2014, 05:17PM

Steve Conner wrote ...

Oh, I think I have all that analog cludgery already.

Oh? i thought it went +24, 0v -12v?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sat Jul 12 2014, 05:23PM

The PLL driver board's own output is bipolar for driving GDTs. If you want a waveform to pass through a transformer, it has to be symmetrical (to be pedantic, the positive and negative areas must be equal) so when using a GDT the positive and negative gate voltages must also be equal.

The outboard drivers use a small GDT followed by a MOSFET stage, so they don't have this limitation. The MOSFET stage turns +12V input into +24V output, and 0 and -12 go to -12V output.

Re: Odin The All-Fragger: a large DRSSTC
Goodchild, Tue Jul 15 2014, 01:30AM

Hmm well the you may be good to give it a try, particularly if you already drive the gates individually via high side gate drive. I would say give it a go.

I have found that tuning the ZVS in spice gives a good ball part before trying it on the real thing.

Re: Odin The All-Fragger: a large DRSSTC
Thomas W, Tue Jul 15 2014, 06:38AM

Steve Conner wrote ...

The PLL driver board's own output is bipolar for driving GDTs. If you want a waveform to pass through a transformer, it has to be symmetrical (to be pedantic, the positive and negative areas must be equal) so when using a GDT the positive and negative gate voltages must also be equal.

The outboard drivers use a small GDT followed by a MOSFET stage, so they don't have this limitation. The MOSFET stage turns +12V input into +24V output, and 0 and -12 go to -12V output.

Aaah okey. Im actually using a modified version of your driver for my x-ray transformer driver, it will also be able to be used for teslacoils.
the difference is im using a single transformer for the powersupply, 4 ouputs of -12v - 0v - +24v from a home built SMPS as a half-bridge from mains using a neat little IR chip.

If it works out well, would you mind me selling a few kits? ;)

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Tue Jul 22 2014, 07:01PM

Latest (4th) test run was a success! I got an arc of 8ft (2.4m) which is a new personal best.

Output was limited by ceiling height again.

Re: Odin The All-Fragger: a large DRSSTC
Mads Barnkob, Tue Jul 22 2014, 07:28PM

Finally!

Congratulations on landing it after only 8 years, 4 months and 2 days! I certainly hope I make it before that, I am already at 2Â½ years and assembly is not done yet :)

Are you going to do further pushing somewhere with more room for hot sparks?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Tue Jul 22 2014, 09:13PM

This thread has 1 page for each year.

Yes, we will take it back to the warehouse in Glasgow that was used for test run 3, but we might have to wait until the Games are over.

I will also have to get it playing the obligatory chiptunes, and maybe build a bigger bridge as I think the resonator is too big for the current one.

Re: Odin The All-Fragger: a large DRSSTC
Linas, Tue Jul 22 2014, 10:17PM

where did you get, and how does it cost to get aluminum toroid, i want one for my coil :(

Re: Odin The All-Fragger: a large DRSSTC
Sigurthr, Tue Jul 22 2014, 10:23PM

Awesome! Congrats! It's about time you get some sweet success after so much work has been put in.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Tue Jul 22 2014, 10:33PM

These toroids were a bulk buy by the Tesla Coil Builders of the UK many years ago. We paid Â£90 each and had them custom made by a metal spinning company. Unfortunately it is too small for the new coil :(

Re: Odin The All-Fragger: a large DRSSTC
Uspring, Wed Jul 23 2014, 10:47AM

Spectacular

You must have chnaged the frequencies quite a bit by adding the top load. Do you have any data on that? From the sound of the sparks it seems, that you are also using long bursts?

Wrt to the PLL driver: Too bad you couldn't make it work on the lower pole. It would have been interesting to get a side by side comparison of lower and upper pole operation. I'd expect to see the primary current peak to appear much more in lower pole mode. Your driver probably wouldn't be affected so much by it, since it would go into pulse skipping mode to get by it rather than by terminating the burst when it hits the OCD condition.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Wed Jul 23 2014, 11:48AM

The upper pole frequency was 89kHz with one topload and 74kHz with two.

Burst length was varied between 150 and 300us during the video.

I don't know why the lower pole wouldn't work.

Re: Odin The All-Fragger: a large DRSSTC
Linas, Thu Jul 31 2014, 08:45PM

Since i am reworking my coil MMC capacitor, you told in other thread that 0,7uF was too large .

What would you recommend for 50kHz coil running on CM600HA-24H bull bridge ?

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Thu Jul 31 2014, 09:53PM

0.75uF was too large for my coil running at the 89kHz upper pole frequency with 300 amp modules. For a 50kHz coil with CM600s, it would probably be fine.

The lower frequency means more primary inductance, and the primary impedance is sqrt(L/C). So lower frequency means higher impedance for a given value of C. Also the 600A bricks can handle twice the current, so they can drive half the impedance of my 300A ones.

In another thread I suggested the following relation for sizing tank capacitors:

sqrt(Lpri/Cpri) should be 10 to 20x (4/pi)(Vbus/Iocd). Values towards 10 give traditional DRSSTC operation, values towards 20 allow long bursts with lower current.

(You also know that 1/(2*pi*sqrt(Lpri*Cpri)) = about 0.9x (fres of secondary) so from these two equations you can calculate both Lpri and Cpri.)

From the picture I saw, your coil could do with a bigger topload.

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Fri Aug 29 2014, 12:15AM

Biggest spark is now 9ft

Re: Odin The All-Fragger: a large DRSSTC
Mads Barnkob, Sun Aug 31 2014, 03:00PM

That is some nice sparks and coil runs stable, you deserved this :)

I like the big secret shadow coil in the background!

Re: Odin The All-Fragger: a large DRSSTC
Steve Conner, Sun Nov 02 2014, 11:38AM

Odin had a successful weekend at the 2014 Cambridge Teslathon. The electronics ran fine with no issues and output was again limited by building size

Re: Odin The All-Fragger: a large DRSSTC
Extreme Electronics, Sun Nov 02 2014, 10:03PM

Thanks for bringing it Steve.

Most impressive..

More pictures at cambridge-teslathon-2014 near the bottom