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First DRSSTC 40n60 minibrick topology

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Mike

Thu Jul 10 2008, 09:18AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Update: It has been a while since i posted. I have been working hard. Everything was finished, i built the MMC, assembled the secondary on to the base and hooked up everything. After a slight bit of torubleshooting i found a short one the board and finally had first light. Short video at

Sparks about 1ft- 1 and a half. this is around 50% input on the variac so about 50v. I havn't really tuned it yet or anything..so hopefully i can get something better. Anyways pic to come later :P

Marko

Thu Jul 10 2008, 01:41PM

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

Nice work mike!

Your sparks look CW though, you really should decrease your ON time, especially if your surge impedance is low as it appeared.

Also, are you doubling the input voltage? If not those are great sparks for 50V but to make use of your IGBT's you really want to give them higher voltage. Rectified 240V should be just right.

Marko

Mike

Thu Jul 10 2008, 04:41PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

yeah your right the on time is pretty high, i will lower that, also yeah its only 120v right now, i will use a doubler later once i get everything working correctly :D

Mike

Sat Jul 12 2008, 08:27PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Update: Pictures of the finished coil. I added screening at the bottom to keep out interference, i also put up a topload, and I added shielded RCA cable for the interrupter transmission.
Full Coil

The Primary

The RF screening

inside view of the pcb, fullbridge, current transformers and MMC

And of course a youtube video of the arcs. At 100% input on 140vac, i get about 3.5 to 3.75ft arcs. :D

teslacoolguy

Sun Jul 13 2008, 12:54AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

Nice work MIKE. Just a note, if you decrease the legnth of wire that connects all those ferrite transformers yhe performance might be a little better because there is alot of leakage inductance there.

uzzors2k

Sun Jul 13 2008, 03:39PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Good looking sparks you're getting. I was about to mention something about your secondary, but I assume you've already heard.

Mike

Sun Jul 20 2008, 07:23AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Sorry about the long time after posting. I had some failures :'(

Two of the 40n60's failed :'( This happened most likely because of my stupidity. I just threw a second topload on the coil and cranked up the voltage. at about 70% the failure happened. I am guessing it was out of tune tso much that it killed them.

After that happened, I ordered new TVS's for the igbt gate and emitter collector since i was using series components that was adding to stray inductance. I also took my gdt and shortened the wires on it to reduce extra inductance. Got it working tonight and got some awesome arcs,

Unfortunately I am going to have to make a new GDT completely because i noticed a black burn on a group of windings, i know it happened before tonight but im not sure why =\

Anyways, here is the video. 3 ft arcs to ground . Enjoy

Reaching

Sun Jul 20 2008, 08:31AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

Nice, but the sound is horrible.

what do you use as your interrupter? the break rate is way too high and i think the on time is way to high too.
you will kill more igbts if you leave it like this. im pretty sure about that.

what i wonder, why is you inerrupter getting mad when you hit your ground target. ? That sounds like some sort of overcurrent is kicking in?? if so, then it sounds weird. i never had a drsstc where i could "hear" the overcurrent tripping.

normal on times should be in the range of 100 to 300ÂµS. and since i build large and small drsstcs and some commercial ones, i found the off time limit to be 1mS. that means 1000Pulses per second or 1khz. if you go higher, then the current draw and the stress on the components is getting higher and higher, not the linear way!

Mike

Sun Jul 20 2008, 09:12AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

haha exponential? scary.. but yeah i think my interrupter is messed up.. I will have to build a new one and shield it etc.

Marko

Sun Jul 20 2008, 12:20PM

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

Mike, your igbt's are failing because you are using too high on time or too low characteristic impedance of your primary tank.
on time looks really long to me too, sparks still look CW and PRF is still really high as Reaching noticed.

In case interrupter was not properly set you need over current detection to finish the cycle instead of it.

Characteristic impedance of primary circuit and coupling determine rate of rise of primary current, so there's no universal vague estimation of ON time you need, someone may attain 500A of current in 50us while someone else will need 200us for same.

Do you scope the output of your interrupter before you run it? You absolutely need to.

From what I know from your caculations, you also badly need higher primary characteristic impedance, if you are indeed using 7uH primary and 450nF cap, you are way too low and you'll continue blowing IGBT's if you don't do something about that.

My first (and only current attempt)also had very low (about 4 ohms) surge impedance and I would hit 600A after only like 70us, at 100khz, efficiency was poor and not enough energy was transferred to spark per cycle.

You need a lot more primary turns and smaller tank cap, or keep the primary as is but reduce size of your secondary and tank cap.

10-15ohms would be a better figure of characteristic impedance for start.

You also need to scope your primary current with a current transformer to get some figures, watch it and slowly increase ON time. It is important to know what current are you hitting. With those IGBT's you might get great sparks probably without even exceeding their rating for much.

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