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Marko's DRSSTC v1.1

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Marko

Sun Jun 03 2007, 04:21PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Teravolt that is one insane MMC... I'm going to use only 8 caps in mine, and I think it's still more than enough...

We've been building air conditioner into my room these days, but I'l be sparking on as soon as I clean the mess over here!

Ps. added a pic of the MMC so you can flame it.

Marko

Thu Jun 07 2007, 11:03PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi..

I did some experimental runs with 30V bus voltage. I set up everything including new MMC, new connections, and OCD. I don't want to make any more noise at past midnight.
I also fixed my coax cables so I don't need to drag probes around anymore.

Current peaks just under 100A with 30V in. it looks like a tad too much, but this tunage made biggest sparks.
With new caps I get 10+cm arcs at this voltage, so they really were worth!

I'l make sure to post a lot of pics tomorrow.

One thing I'm just wondering about, could anybody give me an image of maximum current and spark length I could get with a fullbridge of TO247 30N60's?
.. where should I set my current limiter to make sure not to blow them (the datasheet rating is 240A peak, so I guess not much..)

Steve Ward

Fri Jun 08 2007, 05:20PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I think Jimmy H made a smaller DRSSTC that used similar IGBTs and ran them at about 500-600A pk, but at a higher frequency. It was a half-bridge and made about 2 foot sparks last i remember.

Anyway, your current will not necessarily grow linearly vs voltage input, since streamer loading is usually non-linear from what ive seen. So it will likely clamp the current to some lower than expected value.

I would expect those IGBTs to handle >350Apk under the right conditions. Of course, they may very well do 2X that.

Marko

Fri Jun 08 2007, 10:27PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hey Steve, thanks for this.

U put some more pics at the end of main post.
I did some more runs from isolation transformer (wich liits the power to some 70W) and got some 15..20cm arcs (I keept that really short because of noise, huh!)

I scoped for ZCS and it looks almost perfect as it is now.

THe bad thing has recently happened, and makes me really unhappy with my paranoid low-inductance layout.

At one point, all sudden, I noticed small arcs jumping between PCB traces on my bridge as I turned the coil on!

Arcs were jumping between DC bus and current transformer traces, seemingly to mains ground.

What seems to be happening is that DC bus, being isolated, capacitively couples to coil's output and builds up high enouhg voltage to start arcing over.

When I disconnected the scope cables the arcs stopped. When circuit board is floating it doesn't seem ot provoke arcs.
They were really small and apparently not energetic enough to do any harm, but they are still really worying me.

They could have blown my GDT or silicone insulators - I haven't even grounded the heatsinks yet!

I think a good solution for this will be two DC-blocking caps of few hundred nf in value from both DC bus rails to system ground.

They may not be needed when running from mains but still I don't want to risk any chances.

EDIT: I have put caps from my DC busses to ground, and grounded the circuit board 'GND'.

At first it looked that arcing stopped, but started showing up again as I drew arcs from the topload! (60V input)

Although impedance between two points is practically nil, I still get kilovolts between them!

I'm really sad and frustrated with this board design.
I tought, I have small clearances between IGBT legs anyway, this should be fine for 300V; etc.. now I guess not.

But even after that I'm in risk of blowing my GDT or something else.

Arcs are very mall and harmless for now, like static, but it makes the thing look like it can do nothing but blow up at somewhat higher input voltage.

Arcstarter

Tue Nov 24 2009, 06:03AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

This is old and outdated, but i am just curious, what ever happened to this?

Mates

Thu Nov 26 2009, 04:13PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Yeah, I even did not see any post from Marco for a while - everything is ok buddy?

Regarding your PCB problem with spark overs:
I have question and also a small advice.

How good is your grounding? It could be the problem...

You can make easily wider isolation paths using small drill with a diamond ball on the tip (every hobby shop sells such drills). After that you could apply some isolation polish.

Steve Conner

Thu Nov 26 2009, 06:21PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I heard from Marko recently, he just entered 1st year at university (engineering, believe it or not!) and seems to be really busy with work.

Dalus

Thu Nov 26 2009, 08:27PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

Hehe indeed the first year is quite though, very high studyload. He'll be back when he has some time to spend.

Marko

Fri Nov 27 2009, 04:13PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hello guys, thank you. This is such a pleasant surprise to see.
I must admit I stopped posting here a while before I even started the university. I'm not sure why, I think I just got too depressed.
Now my life changed so much that I can't believe it, and at least because I just have to study a lot. I wish I encountered people like this before.

Regarding this coil, I must admit it's mostly in dead-book now. The heatsinks have been taken to make another CW coil which is now at Tesla museum in Smiljan, the control circuit died and was never fixed and there's not much more to be had from the remains. I saved the secondary coil though, and I hope to revive it in big fashion one day, with help of steve. I strongly disbelieve that will happen these holidays, despite I'll take efforts at organizing time I never did in my life, so next summer is most realistic prediction, as I have one near finished project to work on these short holidays.

Marko

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