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DRSSTC V

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dingo27

Wed Sept 15 2010, 10:56PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

This is my most advanced project to date, so i think its good to post it here. V stands for coil shape, nothing special :)

It all went somewhere 4 months ago, when i build mi H bridge. First with IRF530 and serial schottky SB560, which did not work quite well, but i needed it just to tune my logic circuits. I replaced it today with IRF740 and MUR860G fast diode. For filtering i'm now using 4x 400V 330uF, which fits nearly great - and i dont have any better/bigger.

That started with 74HC14 as sensing IC, also with 74HC132 which i needed if i wanted to interrupt my TC, because power supply is my main problem. As interrupt driver i used 3 inverters to made simple frequency generator. That worked... well it was not best thing in the world. I tried 555 interrupter from some Steve Ward's drsstc, which worked really great. Logic circuits was on proto board for some time, so it was time to make a it to a PCB and some box. First try was not such a success, it was on 5x8 cm universal board, but it didnt worked and i couldnt find mistake. So i replaced it with bigger, "2 floor" design which worked quite good, lots of room to work with, also some space for later add-ons. Because i cant get ucc27321/2 or similar driver (at a decent price) i use BD139/140-16 in h-bridge to drive GDT. Good, bad? You choose, i dont know.

TC has also its story, this is my second, not so greatly winded "testing" TC, with fres around 350-400KHz and 1100turns of 0.2mm wire dia. At first it had 6turns with center tapping, which later on i replaced with 24turns with taps at each 6 turns. It worked fine until it hit my biggest success (with this driver) - sparking from secondary to primary. It needed larger primary dia, but i didnt want to buy tube, so i made a "V" coil ( in english its probably cone type). That, even when it shorten spark length, was also a great success and a looker too :) . Topload is just bottom of 2 beer cans putted together.

Currently, i am only testing it with DC converter, as i am too chicken to put it straight to mains (but its rated for 400V). This design is more-or-less bulletproof, because i didnt blew any mosfet up to date, and i'm not even using zener or TVS on gates, just 1ohm resistor.

Yes, i am using iron powdered core (yellow one from PC SMPS), which i should not do, but i cant get suitable toroidal core at a right price.

Some pics:

Sparks you see are from 20V maybe 40W transformator and DC inverter, so its kinda - funny compared to all TC's here. I need to repair my PC SMPS to try with that.

Things to do -
1. complete "logic box", as i still dont have my front panel and PCB for it ready
2. get more power - actually, my goal is to achieve 5cm sparks from toroid to air,
3. make a TC and H bridge into one platform
4. Use proper modern mosfets, like STW20NM50 or similar, or IRG4PC50WPBF IGBT (which i need to test first). It was already designed to fit TO247 case as well.
5. Borrow or "get" a oscilloscope, i am making this whole thing "blind". Just tweaking things to see if it wil improve or not, it takes a lot time and nerves.

Finally, thanks guys at 4HV for help with some circuits, rayer.ic.cz for inspiration, stevesHV site for 555 interrupter and other sites as well

dmg

Thu Sept 16 2010, 04:48AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

This is a really neat coil, I just love how you designed the bridge, good job!

dingo27

Sun Sept 26 2010, 09:54PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

Thanks.

Today i put bridge into some wooden platform, it is nearly done, just some details to finish. When my GDT's will arrive, i will test with it.

In meantime, i tested it with PC SMPS, and got some nice sparks, which is hard to capture nicely with camera i have. Some photos of sparks (with new aeroplane topload :) )

Some days ago, i was playing with interrupters and advanced logic switching to combine them, it was pain in butt and didnt even worked like i was thinking it would be (fail), so i will desolder it and put just simple control circuit again.

TC position is not final, i think i will made independent platform for it. Now it is just laying on it without anything to hold it.

Whole album is here

dingo27

Wed Nov 10 2010, 06:26PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

Today i fixed wire plug and changed interrupter a little, and tested it, so here are some photos :)

and one video http://www.youtube.com/watch?v=1rya5aqbUzo
Sorry about quality, i cant get it better right now.

This is not on full power, because when i ran it, something started to smell, i think it is isolation on some magnetic wire, but everythig seems cool to touch. I must find out what it was before i move on.

Voltage was 40 -180V max, but changed a lot because it was low power test. More photos as always here

-------------------
14.11.2010 - the funny smell was from 20V on 16V capacitor, it didnt blew, so i think its working fine. I tried it with 160V but sparks was nearly same - around 7-8cm.

It seems for now that i will not develop it more, need to get variac or something to try it on 230V mains. bridge is rated for 400V max, so there is still a lot to do.

-------------------
8.12.2010 - before IGBT swap

As IGBT i will use IRG4PC50W, i already got them, just need to swap it which i'm not happy about.

dingo27

Thu Dec 09 2010, 05:47PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

Today i swapped all 1ohm IRF730 for IGBT IRG4PC50W (600V/55A, 220A pulsed). I was little dissapointed about performace, it wont spark lower than 60V, which with mosfets would.

IGBT's were expensive for my wallet, with 14E for stupid 4 transistors making most expensive transistors i ever bought. Thank god i had to buy only 4, not 10 or so.

Performance is little weaker, I think it is because of driver, which was not developed for this transistors (4x3700pF vs 4x600pF

). I think i raise voltage from 12 to 15V for it. I hope this is semi final step before making DRSSTC, only thing i'm missing is MMC (i already got 20nF, but i think that wont be enough)

Some pictures

---
I just calculated proper value for MMC (6nF, isnt it too small?) And i found very important detail - i was giving diameter values for radius values in Java TC! Fres is not 350-400kHz, but 850-1000kHz! That is changing a lot, thats why IGBTs are not as powerful as i thought, because it has huge drop of power with such high frequencies. It is a miracle that it can work in CW mode...

---
I managed to get it workingin DR mode, with 16.3nF mmc. It worked quite good, sparks hitting 14cm (double longer than without), so i pushed voltage tomax and now its sparking god knows where, i hope its not blown IGBTs
I tried it wothout mmc, but its also sparking somewhere.

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