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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
In the end the best I got was 81" from a 30" tall resonator, and it needed over 4kW of power input to do that. The OLTC is quite limited in its bang energy, and delivers it in one short wallop. The DRSSTC can achieve a much bigger energy, and delivers it more slowly, so it can grow long sparks from a short coil without flashing it over. My OLTC 2was flashing over the whole length of the resonator towards the end, although the sparks weren't that long.
To explain: An OLTC or conventional coil dumps all the energy into the secondary as fast as possible to minimize primary circuit losses. The streamers then form and suck it out. A properly tuned DRSSTC seems to deliver the power just as fast as the streamers can eat it and no more, so there's no harsh spike of voltage that would aggravate flashovers or racing sparks. In practice, we can slow the energy transfer in a conventional coil by loosening the coupling, but an OLTC can't tolerate the low coupling because of its high primary losses, so it ends up with this wham-bam energy transfer.
I think that giant 2500V IGBT has got to do something spectacular, though You should get twice the spark length of my OLTC 2 (which had a 1200A 1200V switch)
When I think about it, I get kind of depressed that I lost the "Battle Of The Giant SSTCs". I guess if it weren't for me, we wouldn't know that OLTCs sucked, so it wasn't all wasted effort :-/
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
When I think about it, I get kind of depressed that I lost the "Battle Of The Giant SSTCs". I guess if it weren't for me, we wouldn't know that OLTCs sucked, so it wasn't all wasted effort :-/
Yeah, but I don't think you should 'quit' TC's and everything because of 'frustrations' , funds etc. You don't need to beat any of world records but for me such claims and putting 'wtf d00d' page over there seems boring.
For jrz126, I think he should try to make secondary as small as posible with tiny wire (winding 110mm or bigger tube with 0.1mm etc. wire could be an interesting battle) and then find ways to move breakout avay from it to avoid flashovers.
Maybe to leave some empty space between toroid and top secondary winding, or, who says that toroid needs to be at top of secondary anyway? (small corona ring is now needed to remove danger of top-turn breakout)
Maybe with few more ideas you could make a pretty good coil in the end. Conner and Terry Fritz will probably help you the most in this area.
Registered Member #242
Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210
Thanks a bunch Terry, finally someone with some info :)
I’m going to read up on those SISG’s…I think I might already have all of the parts I need to build one. How would I set it up to fire off of 120Vac and 220Vac? Using a voltage doubler...I could probably figure it out on my own, but I figure I might as well ask.
That IGBT is rated for 2500V, and as of right now I am limited to a 220V outlet. I’m also going to use some snubber caps (1000VDC 0.56uf KPF type). I’ve got a total of 24 to use.
I "think" voltage doublers will charge in 1/60th of a second so the BPS would "always" be 60 BPS max? So we end up with either 300V at 120 BPS or 600V at 60BPS.... I am thinking the 600V would be better. Maybe there is a simple way to switch between them? I really think you want to use the 220VAC but you could use the 120VAC too for testing like me. Make the input power stuff real "flexible". At 300V we might be able to run at 240 BPS too which seems to have odd advantages... Wysock and Parisse love 240 BPS and their coils spark super good!! My new test coil will look into that, but it is a few weeks out.... We are now learning MUCH about streamer and how to make them long
I used resonate charging but that was sort of a complex thing requiering a pretty finicy inductor. I would avoid that even though it "could" do wonderful things.
I "think" a voltage doubled 220VAC thing would give the best bang for the buck. Maybe others would know better? If you have a 220V variac that could go to 256.7 VAC that would be perfect? Do you have a variac and if so what kind?
I think OLTCs are hurt a little by secondary losses so we need to be careful of that. I think Bart's program does Rac of the secondary prediction but I have always used MandK since that matches measurements for me. Paul has a ton of great data about Rac and how to keep it low. Coupling is also an area where I really had no choice on my OLTC. But maybe ScanTesla can show us a better approach. It can itterate though all the variables looking for the "best" configuration. It works fine for OLTCs too
We should study Steve's coil too that he says sucks to see if there are any areas that could be improved.
I have not played with the OLTC other than my original one. The goal then was just get it to work "at all".... But we know so much more now...
SISG firing voltage is controlled by the number and value of the SIDACs used. You can set it for anything...
SISG don't quench on like the first notch "yet"... So tht is a bit of an issue but my OLTC did not perform that much better anyway with first notch quenching and I think Steve found that too... I really see "no" reason not to make it an SISG... The firing system I had needed current taps off the line and all for sync... That all seems usless now with the SISG...
The OLTC may not be the best performing coil on earth, but it is the "simplest" in many ways. The SISG combined with the OLTC might make it the simplest "period"...
Registered Member #242
Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210
Terry Fritz wrote ...
Hi Jeff,
I just realized it was "you"
Yeah, it's "me"...kinda sounds like you recognize me from somewhere?
I "think" voltage doublers will charge in 1/60th of a second so the BPS would "always" be 60 BPS max? So we end up with either 300V at 120 BPS or 600V at 60BPS.... I am thinking the 600V would be better. Maybe there is a simple way to switch between them? I really think you want to use the 220VAC but you could use the 120VAC too for testing like me.
Could I set the SISG up so that I can control the breakdown voltage by using a jumper? Lemme see if I can get a schematic...the girlfriend only has dial up, so its quite slow...well I made a quick sketch...
I used resonate charging but that was sort of a complex thing requiering a pretty finicy inductor. I would avoid that even though it "could" do wonderful things.
well that can always be an upgrade I suppose...
I "think" a voltage doubled 220VAC thing would give the best bang for the buck. Maybe others would know better? If you have a 220V variac that could go to 256.7 VAC that would be perfect? Do you have a variac and if so what kind?
I have only have a 10 amp 120V variac :(
Well I better get going, the girlfriend is giving me the evil eye right now, and saying something about a "joining a 'my boyfriend is an electrical engineer' support group".
Oh yeah, I noticed steve used some flexable cable to connect his primary to the bricks. What should I look for in this cable?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The cable I used is coaxial speaker cable for PA systems. It has about 12AWG worth of wire crammed into it.
To drive that brick off 220v you probably want a voltage tripler or quadrupler to get you up to 1kV DC bus voltage
Firkragg, I just changed the wtf d00d page to something a bit less "dum". I was ill and real depressed when I wrote it
In response to the original question about gate charge, I found that my new gate driver design with discrete MOSFETs rated 12A@60V can drive a 600A brick fine. What affects the turn-on and turn-off times the most seems to be the stray inductance of the wiring between driver board and brick: not the choice of MOSFETs or whatever.
Most big bricks seem to have gate resistors built into them that limit how fast you can turn the thing on. I believe the popular CM600HA-24H has 0.8 ohm worth of resistance in there, so if a gate driver for these bricks goes to 20V, there's no point in designing it to deliver more than 25A.
Registered Member #242
Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210
Well I just put in an order to Digikey...so it will hopefully be here Monday or Tuesday. That will give me some time to get the brick ready to go.
A voltage Tripler?...I didnt know they existed. I should probably figure out what voltage I am going to run at...My Cap bank is going to be somewhat difficult to connect up. They have the tabs, not the axial leads. here's the datasheet. (1000VDC working volts and 0.56uF.) So I'd prefer to not have to reconfigure it too much to run at a higher voltage.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yup, you get voltage triplers, check out I believe they draw a DC component from the line however, which can be a real pain in some circumstances.
I would connect the cap bank for 2000V right from the word go. The extra voltage will give your coil a real kick in the back side, I wouldn't be surprised if it turned out the best performing OLTC ever.
Registered Member #242
Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210
Whats the benefit of using the coax cable? Is the coax cable just being used for the shielding conductor? Old Monitor cables had a steel braided sheilding over the cable, would that also work? I've got plenty of both lying around, but the braiding from the monitor cable would be much more flexible.
Also, how should I go about heatsinking this monster?
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OLTC project
You should get twice the spark length of my OLTC 2 (which had a 1200A 1200V switch)
