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My first drsstc.

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LAN_403

Arcstarter

Fri Oct 23 2009, 07:50PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I finally made up my mind on what i was going to do.

It will run with a CM400 halfbridge brick. I will use the same driver i have been using.

To drive the CM400, seeing that at this frequency it will take plenty to drive it, i made a dual totem pole driver, from irf510/irf9520 mosfets. Each totem pole driver will have their own ucc for gate drive, one inverting, one non inverting. It is a simple schematic. I took the idea of capacitive gate drive from Steve Ward's driver that is directly connected to the gate of his bricks. I will use a large ferrite toroid, and make a 1:1:1 GDT. Using 24v on the dual totem pole driver, i should have 24v on the gates. That is plenty, because i will probably run no more current than 700 amps, which is 100 amps under the CM400's pulse current.

Because i will be using a brick IGBT, i need lower operating frequency. 160KHz would simply not work

. I wound a new secondary. I used 32 gauge. It is still 4.5" by 24.4" of winding, which after my 40 something pf of topload, would be around 66KHz. I hope this is low enough, otherwise i will use more topload. There is not a single flaw in the windings, that i could see. No gaps or bumps, or overlaps. I thank TheBoozer for that, i could not have done it without the gear motor and foot pedal.

If you want the schematic for the speed control i used for my winder, just ask me. It uses a 555, and the frequency excursion is no more than 300hz with a normal operating frequency of 2KHz.

I will use some arrangement of CDE capacitors for the tank capacitor. I have not yet calculated that.

Once more progress is made i will probably better organize this thread. As things happen i will update.

Here is a crappy video of the coil being wound.

Now, for some pictures. Pictures will explain the progress much better than i can with words

The CM400 mounted to it's heatsink. I just put the IGBT on the heatsink and marked the holes with a sharpie. I drilled a 7/32 inch hole, and tapped it with a quarter inch 20 thread pattern tap.

Very simple gate driver without heatsinks. I have not yet found the 10uf decoupling capacitors, i need to find around 10-20uf of quality film capacitors for the DC blocking, and i need to find a good high-ish current connector for input and output. I will likely use some wire from an RCA cable for the gate drive input.

Gate driver with the heatsinks. No sil pads yet, and a very dark picture.

The back of the gate driver. It looks pretty nasty. No real traces needed, i used solder :D. But, the solder is only about 4 holes long.

The secondary, right after winding. It does not look perfect, thanks to wire discoloration.

That was a bad picture.

The secondary after 20 coats, and after its first course grit sanding.

Same.

Coronafix

Sat Oct 24 2009, 01:30AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Looks good, it's amazing how much easier a pedal controlled motor makes winding a secondary. huh?
I unfortunateley burnt out the motor on mine, but I managed to wind a dozen or so coils on it first.

Arcstarter

Sat Oct 24 2009, 02:30AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Thanks.

Absolutely. Last coil i wound had no pedal, no speed control. I had to plug it in when i wanted it to start, which really sucked! With so many turns it was nice, but it is thin, with a few times less tensil strength than the 24 gauge i wound with before. It would have been easy to break without some speed control.

I have not burnt any motors out, luckily. This one sure gets warm. I leave it running as much as 12 hours or more, and the temperature is the same as after an hour or so. Just a little bit hotter than what i can touch without it being uncomfortable. I have, however, broken the threaded rod that connected the main rod on the winder to the motor. That was right after a coating of poly, so all the polyurethane just ran to the bottom :/.

Time to try to fix the pictures...

Proud Mary

Sat Oct 24 2009, 09:25AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Well done, Arcs!

Arcstarter

Sun Oct 25 2009, 02:44AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Thanks for the kind words, Harry

After the first course 220 grit sanding, i did two coats of poly. I figured it was still too uneven, so i did another 220 grit sanding, and now, after the two more coats i put on today, it is finally pretty much even, with few bumps. Next is 500 grit then more coats of poly, then the 1000 grit, probably with some water. That is how i always did it with glass beads when i used to make them with the mapp gas torch.

The buss caps will be some 101C CDE caps i have on the way. I did some calculations with some help from TheBoozer, and i figured out what i will likely do for the tank circuit.

The secondary is about 130mh, and 45pf after the topload, so about 65.8KHz.

The primary will be ~9.5uh, which is 7 turns.

The tank cap will be .68uf with probably 3 parallel strings of 3 series .68uf CDE caps. Those two figures give me a primary freq of 62.5KHz. 3.7 ohms primary impedance. Assuming i want 700 amps on the primary, that would be 2616 volts peak across the primary.

And, theoretically, it would take 2590 volts to get 700 amps to pass across 3.7 ohms. Don't you love it when things add up?

Arcstarter

Mon Oct 26 2009, 09:24PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Made a tiny bit of progress in the past two days.

I made a little ugly board that will connect the gates of the CM400 brick to the GDT. It has 8 Zeners for gate protection (you can say 4 zeners, a couple 18v zeners in series making up each one), it has 4 10 ohm resistors, 2 in parallel for 5 ohms for each gate, and it has a paralleled schottky diode for quick fall time... It used a fairly high current connector (that i ripped off of some old board) to connect it to the GDT, via some shielded RCA cables. There are not actual RCA jacks, but i do not know what to call the wire itself. I guess coaxial? It is ugly, but for a drsstc that will cost nothing other than the secondary wire (which i got someone else to buy for me

), it's fine.

I made the GDT, which i really don't need to get into any specifics. It is a run-of-the-mill GDT, with a large ferrite toroid. I used CAT-5 wire, this time all the conductors for the first time. There are 8 conductors. I will parallel 4 for the primary, and 2 for the secondaries. Cable ties are used for a ghetto way of securing the wires to the core.

I have done a tiny bit of work on the secondary. I think since last time i made an update to this thread, i have only put a coat. There are now 25 coats in all. I am going for 30 coats, for the sake of being an even number (yes, i am really that obsessive). I still need to do the 500 grit sanding, and the final 1000 grit sanding. For now, here is a picture. It is already pretty shiny.

BTW sorry for the crappy pictures. They always turn out really dark, even after using Photobucket's auto-correct (which really helps alot). That is what you get with a $100 camera...

uzzors2k

Mon Oct 26 2009, 10:18PM

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

Wow, that secondary looks good already! What kind of varnish are you using?

brtaman

Mon Oct 26 2009, 10:23PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Yeah, great looking secondary arcs! The green wire is looking very good.

raff

Mon Oct 26 2009, 10:58PM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

for a minute there I thought it was a beam from a green laser pointer

Arcstarter

Mon Oct 26 2009, 11:51PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Hah, thanks a lot guys!

I am using Minwax quick drying polyurethane. I think that might be what Dr. Spark is using, though I'm not sure about that. I have used half a quart of it on this secondary

. It does not feel like i brushed that much...

Now that this coat has dried for about 7-8 hours, i will probably sand it tonight. If not, maybe tomorrow. Ya never know, with me

. I'm not sure that it will look too good when i am done, i think i can still see a little bit of the scratches from the sanding. I'm not sure, it is too dark. Maybe the polyurethane did not penetrate well. I will see when i am done :).

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