DRSSTC

Things at the limits.

DRSSTC

Postby Tyler Christensen » Sat May 14, 2011 12:38 am

Just an update on what I've been doing lately, as I haven't been active in the fusion side of things (since I'm at MIT and my fusor is in Washington). Just finished the third major revision of my tesla coil controller, which will be the final design for the electronics. Fired it up and got a good 5-6 feet of ground strike arc and 7-8 feet of corona. Now to make a better primary and larger top-load for more arc length. This coil is midi controllable and is optically coupled to a control computer via a SPDIF fiber cable. Controller is using a series inductor across the feedback current-detect inductor to get a phase-lead current signal (prediktor input design) so that the timings can be adjusted for zero ringing in the bridge.

Power supply is a fairly simple boost converter taking 3-phase input, with an adjustable output up to 800V. I've run the coil up to 750V on the bus so far at 8kW.

Been a great project, learned a lot about high power semiconductors (and how much of a pain they are to turn on at 60khz), precision timing of logic, all sorts of things. And learned lots of things not to do in revision 1 and 2. Hard to believe just two years ago I was barely able to get a bridge of IRFP450's going at 500 watts to power my fusor.
Attachments
IMG_0057.JPG
The boost converter
logic.jpg
Logic driver
gate driver.jpg
Isolated gate drivers
ring.JPG
Phase adjusted for no ringing by switching before the reverse recovery diode goes into conduction
IMG_0043.JPG
Full-bridge of CM600 bricks, has local DC bus snubbers as well as RCD snubbers on both outputs just incase the phase offset ringing correction fails for some reason
fire.JPG
coil outside.JPG
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Re: DRSSTC

Postby Doug Coulter » Sat May 14, 2011 10:27 am

Good to hear from you, and good work! Most people don't realize (but I bet that doesn't include you) how hard it can be to just get the "conceptually trivial" things working right.
I'm still amazed sometimes how hard things are that should be "easy". I'd put 8kw well outside the "easy" category though. Are you just driving the coil CW? I bet that'd be fun to modulate and make a singing spark!

Our recent acquisition of a bunch of spark gap tubes has made me think of coiling again, or making a big marx generator just for fun.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: DRSSTC

Postby Tyler Christensen » Sat May 14, 2011 12:38 pm

It is definitely not CW, ran about 0.5-1% duty cycle last night, with peak currents in the bridge tripping my current limit set at 3kA. It is audio modulated and can play MIDI files, or any realtime midi instrument. Some people took video which I'll post if I ever get the footage from.

Should have lots of fun projects to report on as summer comes up (finals next week then I'm free to play with high voltage for three months)
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Re: DRSSTC

Postby Jerry » Sat May 14, 2011 10:44 pm

I have been wanting to build one of these as well. I have a 8" secondary wound and ready and a bunch of big ole IGBTs just waiting...
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Re: DRSSTC

Postby Tyler Christensen » Sun May 15, 2011 3:45 am

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