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4hv.org :: Forums :: Projects
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Marko's DRSSTC v1.1

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Marko
Fri Jan 12 2007, 01:41AM Print View
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi everyone over here

I've done some work on a new DRSSTC these holydays. It's practically a whole new coil, secondary and control electronics are only from previous mockup.

I hammered a piece of brass in shape for driver board holder.
THe wide part will also act as an heatsink for bridge rectifier and as single ground point.




This is another piece of brass. It will be a spine for new H-bridge.




My heatsinks of choice. Cheap Spire CPU heatsinks, with threads engraved in their backs.



This is how I etched the board for H bridge. I found some old nail varnish my mom threw away. It was quick drying and soft when dry so it was perfect for engraving. I used sticky tape only for larger parts.



With my primitive etching techniques I couldn't get statisfactionary clearance between copper, so I forced the etching for 2 hours hoping acid will eat through 'edges'. But I ended with lots of small holes in board... luckily just cosmetic.
Board is double sided, and planes are used separately for DC supply to nullify parasitic inductances. I also tinned them, and put large blobs of cheap high-lead solder in places where I needed physical strength and smaller resistance.

Bridge outputs are used with both sides of the clad in paralell.



Some 30N60's soldered on. Resistors, diodes, TVS and stuff are from other side.



Brass is hammered and everything is bolted together making one pretty robust construction.




Front side populated. I'l use flat cables to connect gate drive and CT's to the board since they are pretty practical and low inductance.
I hoarded the board with decoupling caps. I put two sets of CT's on board in case I need them.




I made this casing in meanwhile. Board and bridge are shown in final arrangement. Secondary is shown in behind. I now need a nice primary form for 6mm copper pipe.

And yeah, bridge needs a proper high current capacitor... I even left exact space for vishay 76*146mm standard cap, but highest voltage I could get here was 100V 21000uF...

I'l also (ofcourse) add a nice acrylic dashboard, and then wire all things up.

I have to wait for toroid to dry it's polyester and most things will be done..





This is how I drilled holes for connectors... I taped a piece of perfboard ona desired place and followed the holes... But, it went very wrong first two tries, until I figured to use large piece of board with lots of tape to hold it in place.




update 13.01.07

toroid




For my top toroid connection, I used a small brass plate wich I can solder the wire to, and it seemed great.

I started thinking about doing the same to the bottom, but then I remembered those red-hot induction heater nuts!
Since this is going to be basically in middle of my primary, I made some cuts in it as shown on pics. I'm going to use weakly magnetic stainless steel screw for it.

I don't know how good idea is it, I can only hope coupling and RMS current will be low enough. Any toughts on it anyone?




23.1. ...

Some more construction pics. My tripod has died recently beyond fixing. Pics are much uglier now :(

I put two 1000uF 400V caps in paralell as bridge flters.
It's not much, 150 joules, but will be somewhere near lower limit of 20 bang energies.
They also don't look like they are rated forextreme pulse discharges.
I hope to get a real cap at once.

I use my old inty for this coil... it's the only thing that always worked perfectly no matter of anything!

The bent plexi dashboard has a michrophone connector for inty, plus two scope BNC's for tuning. (primary current and drive signal).

I have enough pipe for the primary... just need a good supports for it.














Hot wire plexi bender and cuter. (cutter is just a piece of wire suspended between two wooden sticks, works beautifully!)







These were pretty ugly after cutting, but then I managed to screw them together (through pre-drilled holes) and polish until perfection. I needed to use 3mm plexi as anyting thicker is tedious to bend.

Then I glued them together to get 2mm displacement. There are 5 of these 'displacements' so I needed to have holes like 10mm spread.



Pipe screwed in. It's nice to finally have a proper primary.
Second pic is mains connector and a fuse.




[Edit: Please don't mess with the formatting of the board]

11.2: so here is the coil, and ghetto MMC. Toroid is somewhere at limit of looking silly.. I hope it will do it's work at least. Just need to screw everything in place and fire it up!












13.3.07: First light, sort of. Ceramic caps are terribly undeperforming considering the power level, so back to the drawing board about them.




3.6.07. new CDE942C20P15K MMC:




New updates!

Zero current switching looks perfect.
The primary current on pic is 100A div, 120us. It grows, attempts to heterodyne 3 times and freewheels out after turned off.
Some small 20cm arcs from toroid for now.









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teravolt
Fri Jan 12 2007, 04:34AM
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1066
Firkragg I like your work can't wate to see the final product
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ragnar
Fri Jan 12 2007, 04:48AM
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1423
Marko, I love the heavy-duty brasswork and some very well designed copper plane. Can't wait to see it in action! =)
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Part Scavenger
Fri Jan 12 2007, 03:17PM
Registered Member #79
Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673
That thing is beautiful! Great work!
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Daniel Uhrenholt
Fri Jan 12 2007, 10:18PM
Registered Member #125
Joined: Fri Feb 10 2006, 01:52PM
Location: Aalborg, Denmark
Posts: 155
Nice Work!

I like the CPU heatsinks, time for me to go dumpster diving again

Good luck with it.

Cheers, Daniel
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Marko
Sat Jan 13 2007, 12:22AM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Thanks guys

I have the toroid finished, and I'l post pics of it tommorow here.. One more pic now.

Now, I have to find some 3mm acrylic...

And yeah, have to get my signal generator fixed, so I can test the new toroid and finally probe that beastie fulbridge.

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Steve Ward
Sat Jan 13 2007, 01:58AM
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1052
Nice clean work indeed.

One thing i haven't figured out is, where are your electrolytic storage caps for the H-bridge?
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Marko
Sat Jan 13 2007, 10:26AM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
where are your electrolytic storage caps for the H-bridge?


I don't have any screw terminal caps of that voltage, although I left space for 76*146mm vishay cap. (holes on left side of board).
I have some 100V 21000uF caps but I would have to stack 4 of these to make them work.

I used 1000uF 400V solder therminal caps before, and I can bolt two there if really needed, although I don't believe anymore they are rated for that high peak currents.

PS: update: toroid...

And, how do you guys generally fix your secondary base? while having a neat ground connection and easily movable secondary?
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Steve Conner
Sat Jan 13 2007, 08:59PM
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
This is how I fixed my secondary base. Conductive metals like copper and brass really don't induction heat much.

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Marko
Sat Jan 13 2007, 09:28PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Thanks a bunch Steve... I hope this brass plate will be good enough.

Next week I'm going for some 3mm acrylyc, finally a test for my new hot-wire bender.


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Marko
Tue Jan 23 2007, 03:57PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi... updated with lots of new pics. Added plexi bender and cutter.



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Avalanche
Thu Jan 25 2007, 10:10PM
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 829
It's coming on really nicely, good work!

I remember using one of those hot wire plexi benders at school, problem is the heating wire was way too far down - about 4" from the plexi, and I was never able to get good results. I might have to build one like yours and try it again!
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Marko
Thu Jan 25 2007, 10:28PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi avalanche

Wire is 3-4mm away from plexi on mine, andI actually toughtto bring t closer, but wasn't bothered to find longer screws (these were already becoming unstable).

Wire shouldn't be too hot but should almoust touch acrilyc for best results.

26.1.07: cut primary supports, and added a pic. They aren't looking too good...
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Marko
Sat Feb 03 2007, 01:02AM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi again.. Updated with some new pics.

One thing that bothers me... C. hooper pointed out steel screws I used on my primary supports.

They are chrome-nickel stainless steel and they don't seem to be noticeably magnetic.
Should I worry about these setting my coil on fire? (plexi wouldn't like to get hot at all.)

I used to have lots of ferrous things around my primary, sometimes even big plates or connection clips and didn't have any trouble...
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Dr. Spark
Sat Feb 03 2007, 01:41AM
Registered Member #290
Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673
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...
Sat Feb 03 2007, 02:42AM
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2431
Hmm, looks like that offset in your primary is creating a pretty decent hot spot in the flux... I wonder how that affects performance?


But in general, I wouldn't worry about the bolts.
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Dr. Spark
Sat Feb 03 2007, 03:56AM
Registered Member #290
Joined: Mon Mar 06 2006, 08:24PM
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Marko
Sat Feb 03 2007, 07:46PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Thanks chris.. I'l consider this thing lossy if I ever need to run it at 500W or so, I guess I won't have any problems.


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Marko
Sun Feb 11 2007, 12:47AM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
'evening.. Pics of almost finished coil finally! Just have to get some more wiring soldered and hooked up, and I hope for a first light tomorrow.

I also remembered I have an large amount of ceramic caps, in one of old MMC's, laying unused. They aren't best choice, but still much better than few polyester caps .

Each capacitor is rated 10nF 3kV, and I have 25 strings of 2 in series for 6kV 125nF, surge impedance ~10ohms. I didn't have enough bleeders for them all, so I just used two seris resistors over entire bank.. hope they won't care!

Since there's so many of them, each cap would suffer only 20 amps of peak current if I ran the coil at full 500amps.. with some luck I may get some bigger sparks with them!

Only thing I'm afraid for them is that they'l start to heat up due to losses, and detune the coil all the time due to their gross C/t dependence. Current and frequency are low so I may have some chance.


PS. 26.2. hope to continue this as soon as possible..
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Bennem
Sun Feb 11 2007, 08:55AM
Registered Member #154
Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 258
Nice looking coil
and well constructed!!
look forward to seeing pics of its first light!

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Marko
Sun Feb 11 2007, 08:24PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Ahh.. everythyng set ready, and I seem to have a bug on my bridge. I took great care and checked it few times, so no light today

School is going to additionally mess things up, but 'l find some time.

I added a shoot of mess I created...

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Marko
Tue Mar 13 2007, 07:25PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi, .. OK, it works.. sort of works.

I finally got myself motivated after a month or so.
Run was at 30V and I got up to some 3 inch sparks, but it tend s to lose feedback and do wierd things again.

Sparks look way more healthy than 15mm sparks my halfbridge coil gave for same input, now I just need to be careful not to do something stupid and blow the IGBT's.

Caps I used are also a bit poor, and they slightly increase temperature even with those short runs!

I surely won't be pumping more power before I get scope connectors and everything fixed in place.


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Marko
Fri Mar 16 2007, 03:22PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
at time, I get some 15cm sparks with 18% (60V) input voltage and pretty high ON time, over 250us. At more realistic 100us I seem to get only 10cm sparks.. point to point. There's only some little corona on breakout point and yet coil manages to drive my USB devices completely nuts. I'l have to continue with it in garage.

Part about tuning has become a bit erratic.. coil seems to work better when I tune lower than resonant even at these little powers. If undertuned, ceramic caps start getting hot and change capacitance heavily. And at some point, I got flashovers between primary and secondary, even though primary goes only for 4-5 centimeters over the secondary winding!


PS. just a quicky question about OCD: I see that faster comparators like LM311 are commonly used (wich I don't have any at moment), so can I use something like LM393 (1,3us)? Considering my period of about 10us it looks 'just fine', but should I perfer a faster comparator for some reason?

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Steve Ward
Fri Mar 16 2007, 08:30PM
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1052
I would think the slow comparator is OK, you can probably compensate by setting the limit a little lower than you would with a faster comparator.

It looks like those ceramic caps might be the source of all your problems... id ditch them if i were you.
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Marko
Sat Mar 17 2007, 12:07AM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I also hate the caps, but they still seem to work better from polyester I used before.. polypropylene are way more stable. I just wanted to see if they would work.

Expecting 400..500A as a final maximum for overdriven TO247 30n60's capacitors would suffer only 10..20 amps of peak curent each, but they simply aren't made for high frequency operation of any kind.






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Marko
Wed May 30 2007, 08:19PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi everyone

I bought a large amount of 942C20P15K caps and promptly ditched the ceramics.

The project was mothballed for a while (err, 2, or 3 months, or so) due to lack of motivation but I'm pretty sure it will get going now after school is over.

I also have enough caps to build a SGTC and possibly many other things...

These caps are really huge, more massive than I tought.
I don't think I will have easy time blowing those up.



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Part Scavenger
Thu May 31 2007, 03:13AM
Registered Member #79
Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673
About time you got to work on that thing!!!!

You do great work! I'm waiting with great expectations...
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teravolt
Thu May 31 2007, 04:27AM
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1066
hears what mine loo
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teravolt
Thu May 31 2007, 04:38AM
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1066
Firkragg nice design,can't wate to see it run. they were big for my project too and this this is how compact I got them. I haven't run them yet so and i dont know if they will flash yet.

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Dr. Spark
Sat Jun 02 2007, 04:00AM
Registered Member #290
Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673
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