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Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039
Well. Let me put things this way. On my scope, if i set it to about 20 cycles, it sounds like its really really low duty cycle. maybe 10% or so. I had it, at my 555 interrupters max. meaning, enough that my scope either showed a very SOLID green waveform (meaning HUNDREDS of cycles) or, when i was viewing a sample of 20 cycles, it actually showed a total of 3 levels.
Basically, im not going to count how many cycles that video was. its gotta be well over 100-200 cycles. VERY likely 50% duty, which i can tell because my variac hums quiet a bit with 20VAC in when i was doing non-burst mode. Oh well, lessons learned I guess.
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
ben123324 wrote ...
What exactly have the limits been? 300A by Kramnik, has anyone else blown a bridge and measured the conditions? The irg4pc50Ud might be a decent upgrade...
I killed my bridge running ~350A at up to 120uS on-time and continuous polyphonic operation for about a minute with ~14" white hot ground strikes (this was with a smaller coil than the 23" spark one).
I think that so long as you keep it from ground striking too much, provide adequate cooling, and avoid long runs with polyphony, it should be able to sustain that level of operation, although I personally prefer to turn down the pulsewidths and keep running it with polyphony. As far as I can tell, my failure was caused by overheating, not overcurrent - the transistors were burning hot!
It would definitely be worthwhile to try the irg4pc50Ud and see how far we can push it! At the moment, I think this coil can either work as a polyphonic musical DRSSTC demo with lower pulsewidths, higher coupling, and ~12 - 14" sparks, or just as a pure sparklength demo with higher pulsewidths, looser coupling, short run times, and 23" ground strikes.
Killa-X wrote ...
Most DRSSTC bridges have a snubber capacitor on them, is it not required on yours for some reason..?
The main motivation for not using a snubber is the laminated bus, and the fact that this allows us to keep the buscaps very close to the IGBTs. I tried deadbugging a 1uF 400V ASC snubber capacitor across the buscaps on the bottom of the board, but I didn't notice any difference when running with the primary/secondary with higher coupling and lower pulsewidth. It could definitely have helped though, since I only ran it up to 23" using the looser-coupled primary and secondary with the snubber in place. It's definitely worthwhile to try adding one in your case, I think. I'd also go lower on the resonant frequency, if possible.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
Killa-X wrote ...
Basically, im not going to count how many cycles that video was. its gotta be well over 100-200 cycles. VERY likely 50% duty, which i can tell because my variac hums quiet a bit with 20VAC in when i was doing non-burst mode. Oh well, lessons learned I guess.
You're running your bridge at only 20VAC? You should turn that way up and lower duty cycle. DRSSTC's want more voltage and less duty cycle to make long sparks. You'll have less loss and way more spark with more voltage.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Yeah I can't go lower frequency because I'm not going to buy more wire, have 3 coils for 200khz made of 34 awg so, putting them to use.
I said 20vac because any more and I'd break the breaker. That's what I was apparently running when I killed the bridge in burst mode at 120v. That video was full mains power, in burst mode, so doesn't draw near as much power as it would in a constant interruption tone.
Also I know coils like higher voltages. I run my 7' DRSSTC at 10 cycles (50khz) 390v for now...so..oh well, live and learn :). As cheap as these igbts are, was worth it.
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
Killa-X wrote ...
I said 20vac because any more and I'd break the breaker. That's what I was apparently running when I killed the bridge in burst mode at 120v. That video was full mains power, in burst mode, so doesn't draw near as much power as it would in a constant interruption tone.
Have you actually measured the current that it draws? It seems strange that you're pulling so much current at such a low voltage; I clamp-metered my coil drawing around 1.5 - 2A with 1' sparks (albeit with much lower pulsewidths than you're running!). Try checking the diodes, perhaps? The problem you're describing (high current draw, short sparks) seems like it could be attributed to a blown rectifier.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
when your running THAR many cycles its no surprise i was drawing a chunk :P way too much lol - my fault.
My coil: 178khz or ~5.6uS The ring-up time period until ring down: 170uS which is 5.88khz.
Can you do the math and figure this is 3.3% duty cycle..?
Now this is a LOOOOOOOOOT less cycles than i was doing when it blew. I recorded a video, testing different frequencys. I did not use an amp meter, because I knew i wouldnt pull much at all. But, I maxed my variac to the point it wouldnt go any higher. On my variac, this is 130VAC. So, if a perfect world, no voltage drop, you'd expect 367.64 Volts on the bridge. Amperage by then, only by a guess (for sure below 300A) was probably 280A.
I counted 32 positive spikes on the current waveform, so i can assume about 32 cycles to peak.
Still getting around that 20+ inch spark range, just thinner arcs obviously. My only question would be...How much higher could I safely go in on-time? I need to build a better primary, as this was just for testing. Once im in that 100V or more range, my waveform turns from a single climb, to two bumps. Which, I'm assuming means the sparks are drawing it prity damn close to resonance. Did have a nice ring to it at the higher voltages.
Would my sparks be longer / better going out the side? Also, short or long breakout? It seems on my big DRSSTC, a 4" breakout was better than a 14" breakout...
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
Hey there Dr. ISOTOP,
Just saw your project. Very nice design! Cool to see you using the CST current transformers. They are really great for the price and they are good up to about 1000A peak current. Good choice on IGBTs too. One of the co-ops working for me right now is presently working on the next iteration of our microBrute DRSSTC and that is one of the IGBTs that is being tested. You might also want to try some of the IXYS TO-247 based IGBTs of similar specs. They are similar in price.
Just one suggestion, since you are going to be selling these, i would make sure you sell them with fusing onboard (if you don't already have them) Line power is very dangerous and if something shorts out with fusing, it could make things very ugly fast. Also, if you are not already doing so, make sure the heatsinks are grounded to chassis (earth ground). So if you get punch thru on the devices, you don't have dangerous voltage exposed on your heatsink.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Killa-X asked me some questions about the interrupter, so I'll try to answer them to the best of my abilities (Kramnik designed it, so he can fill in the gaps for me)
Killa-X via PM wrote ...
Very cool. I updated my post with a video and coil details.
May I ask what chip your basing it around? Pondering if I have it around my room, as if its ATMEGA class, you cant put an ATMEGA16 code on a ATMEGA32..as when you get into timers and stuff (if you are) you can get into said variables that exist only to that chip...as every chip is different. ADC's for example..
Err...I don't remember; Kramnik will have to answer this one.
wrote ...
Will it have some sort of limiter to prevent going over X duty cycle / on time?
It has a note table of appropriate pulse lengths for the coil its being run with. The duty-cycle limiter idea seems like a good idea; if it doesn't already exist we'll be sure to add it.
wrote ...
How many voices can it play at once? And does it use an SD chip for .midi file, or some manual method of transcribing?
Two notes. The board has a MIDI jack on it for taking streams of MIDI notes from a host device; I believe there is also a computer-side application that can send arbitrary .midi files to the interrupter.
The interrupter also has selectable modes of operation, either MIDI or standard DRSSTC pulsed mode, and a programming jack for firmware upgrades.
EasternVoltageResearch wrote ...
Hey there Dr. ISOTOP,
Just saw your project. Very nice design! Cool to see you using the CST current transformers. They are really great for the price and they are good up to about 1000A peak current. Good choice on IGBTs too. One of the co-ops working for me right now is presently working on the next iteration of our microBrute DRSSTC and that is one of the IGBTs that is being tested. You might also want to try some of the IXYS TO-247 based IGBTs of similar specs. They are similar in price.
Just one suggestion, since you are going to be selling these, i would make sure you sell them with fusing onboard (if you don't already have them) Line power is very dangerous and if something shorts out with fusing, it could make things very ugly fast. Also, if you are not already doing so, make sure the heatsinks are grounded to chassis (earth ground). So if you get punch thru on the devices, you don't have dangerous voltage exposed on your heatsink.
Keep up the good work! Awesome stuff!
Thanks for the kind words Do you know of a good supplier for IXYS IGBT's? I've looked at them before, but they seem pretty hard to get a hold of.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Best place is probably through your local IXYS sales rep.
Another good resource is Just enter the part number and they will give you all the suppliers that have stock of a particular part as well as price.
IXYS is also VERY good at samples. So if you call your local IXYS rep and discuss your project with them, they are almost always willing to provide you with samples of everything you need.
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oneTesla - a small single-board DRSSTC
