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My First SMALL DRSSTC (Now with 4X Secondary Length Performance)

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StevenCaton

Wed Apr 15 2009, 02:17AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

Coil looks great Phillip

Is that brass weatherstrip on your primary? It makes for a nice tight primary coil, and looks pretty good too.

However, in a drsstc I think you should go with Cu to cut down the primary resistance.

You did say it was only for testing purposes though.

Phillip Slawinski

Wed Apr 15 2009, 02:22AM

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

It's .7" copper strip. It was old stock, so it's a little tarnished. I'll clean it up for the final product. I have to redo the secondary, as that didn't come out as planned either.

Dr. Drone

Wed Apr 15 2009, 02:57AM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Phillip Slawinski

Wed Apr 15 2009, 03:45AM

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

Dr. Spark wrote ...

I must add a little comment here, as offered to leave the coil with me at the Thon and would get it working and mail back. Comment back was â€˜Nice offer but would not learn that wayâ€â€¦.. wow, I was impressed!

This is what it is all about, building the coil and finding bugs and improving, always thinking of next coil and what was learned from previous design will be used as a basis in the next design; however, improved.

A flat primary will work; however, concerned about flash over and coupling. Remember that a DRSSTC is a pulse machine, so power transfer from primary can make or break spark length.

Rgs,
Ch

Hi Chris,

I'm glad I did decide to tackle this myself, as I have learned a whole lot from this project. The offer certainly was nice though!

Regarding the primary:

I am a little concerned about flashover, but this is just an experimental setup, so I'll see how it goes. I've got a rail of IGBTs so no worries

My coupling is sitting around .13 right now, which is just about right. I should also address the lack of strike rail. I have put one on since I took this photo, so no worries there.

I've still got a month or two of debugging and polishing left on this coil, but that's okay. I'm getting a lot of mileage on this project. By the way, I decided to give Acrylic a try. I have a 2'x2' sheet of black acrylic I'm going to use for the final base. I'm also looking into moving to a full bridge of MiniBrick IGBTs so I'll have better thermal handling. I want to be able to run this thing hard at high break rates. Hopefully I'll have a real showpiece to bring to the 2010 W.W.T.

By the way, I figured out why my last secondary was smoking, and it is so simple I'm surprised I didn't see it before.

D'oh! Gotta hate those shorted turns.

Angstrom

Wed Apr 15 2009, 03:48AM

Registered Member #1900 Joined: Fri Jan 02 2009, 06:44PM
Location: Texas
Posts: 29

Hmm that is rather spectacular...

Phillip Slawinski

Wed Apr 15 2009, 04:20AM

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

Here's the current bridge design I'm using. I think this is about as good as it's going to get for the TO-247's that I'm using. It turns out that the tab is not isolated, but in fact connected to the collector. I didn't know this before, and this explains why chunks of the board were blown off in previous failures. I also moved the bus caps much closer to the board, which drops stray inductance.

This isn't the final board I'll be using. I overexposed the board a somewhat and I had to use a sharpie to touch up some of those areas. Unfortunately the touch-up was not perfect. Also, I will tin plate the next bridge

**Note** This is an older version of the bridge, spacing is much improved on the new version, see above. Also the mounting of the caps has been improved. The caps are still in the same physical location.

Phillip Slawinski

Wed May 13 2009, 01:38AM

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

I got the coil working. Need to to some tuning, but all of the major issues are fixed.

A few things have changed since I took the image above. I changed out the LEDs (who cares, but I thought I'd mention it). I also got rid of that stupid coaxial interrupter connection. I made my own optical link and it works beautifully :) Now I can run the coil farther away from me and not get bitten every time I try to adjust pulse width, or frequency. I'm now able to fit everything in the box quite easily. I ended up pulling the MMC featured in my first post back into service. I removed the sides of the box for better cooling (that's a lie, they fell off

)

As it turns out the coil could have been working for the past week or so, I just didn't realize it was out of tune. I've been so caught up fixing other gremlins with the driver board and bridge that I didn't believe it could be something so simple as tuning.

twist2b

Wed May 13 2009, 08:00PM

Registered Member #2086 Joined: Tue Apr 21 2009, 02:33AM
Location:
Posts: 117

I LOVE the prettyness :P

The winding always looks gorgeous... how long did it take?

Phillip Slawinski

Wed May 13 2009, 08:23PM

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

Thanks for the kind words.

The secondary didn't take that long to make, maybe three hours of work. I messed up when I was coating it, I let the epoxy sit for too long before applying it and it wasn't fluid enough to get the bubbles out or leave a smooth finish.. The box is sort of a prototype box that I put together to make sure I could fit everything.

I am going to rewind a new secondary with red enamel coated wire. I am going to rebuild the box out of black acrylic. This should give it a nice appearance :)

I ran the coil again today and I was able to get 18" sparks, and then the bridge died. I think I'm going to have to move to ISOTOP IGBTs.

Phillip Slawinski

Sun May 24 2009, 05:47PM

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

I've been hard at work redesigning the bridge for my DRSSTC. I just finished building the bridge yesterday. I decided to go with IXGN60N60C2D1 IGBTs, which should allow me to run 500A quite easily. The IGBTs I was using would struggle to do 310A. The new bridge I've constructed is smaller than the old one despite the increased power handling. I also decided to get rid of the voltage doubler, as I believe it was unable to keep up with the current demands of the coil. I increased the size of the RF bypass cap to 10uF, this is double the size of the previous cap. Aesthetically the new bridge looks much better than the previous one, or so I think.

I haven't tested the new bridge yet, as I'm waiting on my new scope to arrive. (TDS-2024B

)

For a size reference the heatsink is 3.75"x2.75".

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