DRSSTC frustration
Marko, Sun Sept 23 2007, 08:48PMFinally car was out of garage and air chilled enough to work in the garage; I brought the DRSSTC in by first chance.
I was eager to test my solid state variac with it and full of optimism.
I hooked up a snubber choke in series with dimmer, set up all the wiring, shifted the RF ground from mains to water pipe and got ready.
Started carefully dimming up, coil buzzed.
Then dimmer started to violently shift the power level, depending on how far my hand was from it. And even so I couldn't dim to less than 60V because it would turn off. It gives hardly any power at low voltages, and just isn't a good solution for this.
Now what - I carefully ramped the voltage up all to 150V what my choke allowed, and got PUNY 15..20cm arcs and streamers barely visible even in dark. The coil worked perfectly fine for all tests before, OCD worked and ON time was trimmed to about 200us.
I didn't bother to try anything, unplugged the power and sealed the garage. I'm completely frustrated. Where will I get 6 foot arcs? Where is my mind?
Why I came to idea to use those solder-terminal electrolytic caps?
I may tweak it to give 40cm arcs before blowing the IGBT's everybody will stare and say 'wow', then I'l look at sites with coils of same size doing 2 meters and get depressed.
I could just have built a short-stupid normal SSTC for same effect for like 1/10 of work and cost.
In two years I wasted so much (parent's) money into development of these things, and still came nowhere. Other kids get cell phones, PC's and cameras for their birthdays, I got CAPS which never found any use at all. 1:0 for 'other kids'.
The saddest part is how much money I burned into MISTAKES. I was actually buyng handfuls of metalized polyester and ceramic caps to build MMC! Where was my dumb mind?
Why did I order solder terminal litycs when I knew they won't work?
Why did I do all the useless philosophies with gate drive, before figuring out it's ''just easier'' to use UCC's?
I just needed to be impatient.
Sins from the past always have their vengeance.
If I saved all the money I could have it all done now.
Now I bought right caps, but that didin't make the problem gods any happier.
I'm completely frustrated with all I've done on this project. I don't want to put any more work into it when I know I can't help it.
I can get four 100V 21000uF litycs from school if I ask nicely, but I can't risk redesigning the entire internals of the coil. I'l never get a 4700uF 400V cap I designed the bridge for.
I don't have money for a variac, and dimmers I built were complete waste of time and $$.
I don't want to bring the BORROWED scope to garage, I don't want to move it at all since I'l break it sooner or later.
I don't know if the coil is in tune at all. I'm on last primary turn because I had no more copper pipe. Can't add additional string of caps because tank impedance is alarmingly low.
Can I mock up some wire to get additional turn or two? I don't even have any trashed thick wire I can cut up.
Can I get more desperate than this???
Unless god is going to sell me an oscilloscope, variac, large lityc, PCB's, heatsinks, a handful of IGBT's, 10m spool of copper pipe and SHIPPING for $50 I don't know what to do next with this thing. :(
*cries*
Re: DRSSTC frustration
Shaun, Sun Sept 23 2007, 08:52PM
wow.
Shaun, Sun Sept 23 2007, 08:52PM
wow.
Re: DRSSTC frustration
vasil, Sun Sept 23 2007, 09:48PM
Calm down, you are probably out of tune.
Sometime the big results are not present at first time, you have to tinker a bit (it's the best part in coiling, IMHO). And why do you want 6 feet sparks? 40 cm are not enough? :)
vasil, Sun Sept 23 2007, 09:48PM
Calm down, you are probably out of tune.
Sometime the big results are not present at first time, you have to tinker a bit (it's the best part in coiling, IMHO). And why do you want 6 feet sparks? 40 cm are not enough? :)
Re: DRSSTC frustration
Steve Conner, Sun Sept 23 2007, 09:55PM
Could be worse, at least you didn't spend it all on drink :P
Steve Conner, Sun Sept 23 2007, 09:55PM
Could be worse, at least you didn't spend it all on drink :P
Re: DRSSTC frustration
Reaching, Sun Sept 23 2007, 10:08PM
yeah, thats the difference between theory and practice. dont bother with formulas and calculations. try it out! play a bit
im a bit confused about your money problems. why building dimmers and other solid state "waste" when a variac form ebay is to get for a few bucks. even a 4700µF lytic is worth maybe 5$ on ebay, can i sell you some :P shipping costs would be twice the costs of the cap,lol.
everyone here who build drsstc had problems somewhere. everyone here blew up hundrets of $ for its hobby like me, you and all the others. i really dont want to think about what huge amount of money i spent over the years into my projects.
Reaching, Sun Sept 23 2007, 10:08PM
yeah, thats the difference between theory and practice. dont bother with formulas and calculations. try it out! play a bit
im a bit confused about your money problems. why building dimmers and other solid state "waste" when a variac form ebay is to get for a few bucks. even a 4700µF lytic is worth maybe 5$ on ebay, can i sell you some :P shipping costs would be twice the costs of the cap,lol.
everyone here who build drsstc had problems somewhere. everyone here blew up hundrets of $ for its hobby like me, you and all the others. i really dont want to think about what huge amount of money i spent over the years into my projects.
Re: DRSSTC frustration
Hazmatt_(The Underdog), Sun Sept 23 2007, 10:19PM
Take a break, then come back to it with a clear mind.
Not everything is going to be a success on the first go-around, its part of learning.
Hazmatt_(The Underdog), Sun Sept 23 2007, 10:19PM
Take a break, then come back to it with a clear mind.
Not everything is going to be a success on the first go-around, its part of learning.
Re: DRSSTC frustration
Steve Ward, Sun Sept 23 2007, 11:25PM
Hey, i use those stupid solder terminal caps on my smallest DRSSTC, and they work ok. You should be able to get some promising results with what you have. I think you are probably just not tuned up properly. Can you possibly set up a CT with your scope and take a pic of the primary current waveform? Then maybe i can suggest some tuning based on the shape of the waveform.
Anyway, cool off a bit. This stuff can be very frustrating if you allow it to get to you so much. Just think of how many experience points you will have gained by struggling through this project.
As to buying the "wrong parts". Ive done that a number of times... but you would be amazed at how often i actually go back and use those parts that i thought were useless. For example, i accidentally ordered some 74HC147s (not 14s) and threw them in a drawer (since when would i need a 10 to 4 priority encoder?). Well... a few years later i ran into a problem where that was in fact exactly the part i needed. Ive also mistakenly bought many SOIC parts, but now they are completely useable with my new PCB fab methods. So keep with the hobby long enough, and those ceramic and polyster caps will show some use somewhere (ceramics are pretty good for low inductance snubbering, polyesters are good for any AC application that isnt too high of current).
BTW, seeing coils that outperform my own doesnt depress me, it inspires me to do better... i hope you can keep the same mind set.
Steve Ward, Sun Sept 23 2007, 11:25PM
Hey, i use those stupid solder terminal caps on my smallest DRSSTC, and they work ok. You should be able to get some promising results with what you have. I think you are probably just not tuned up properly. Can you possibly set up a CT with your scope and take a pic of the primary current waveform? Then maybe i can suggest some tuning based on the shape of the waveform.
Anyway, cool off a bit. This stuff can be very frustrating if you allow it to get to you so much. Just think of how many experience points you will have gained by struggling through this project.
As to buying the "wrong parts". Ive done that a number of times... but you would be amazed at how often i actually go back and use those parts that i thought were useless. For example, i accidentally ordered some 74HC147s (not 14s) and threw them in a drawer (since when would i need a 10 to 4 priority encoder?). Well... a few years later i ran into a problem where that was in fact exactly the part i needed. Ive also mistakenly bought many SOIC parts, but now they are completely useable with my new PCB fab methods. So keep with the hobby long enough, and those ceramic and polyster caps will show some use somewhere (ceramics are pretty good for low inductance snubbering, polyesters are good for any AC application that isnt too high of current).
BTW, seeing coils that outperform my own doesnt depress me, it inspires me to do better... i hope you can keep the same mind set.
Re: DRSSTC frustration
Sulaiman, Mon Sept 24 2007, 12:25AM
Marko, I have a good idea how you feel
for a long time I renamed my DR-SSTC as SD-SSTC ... Semiconductor-Destroying (or Soul-Destroying) SSTC
I had to stop for a while to save my sanity and whatever little spare cash I had (negligible).
I got lucky - Avalanche gave me a working 'scope and things got better from there on, (Thanks again Avalanche)
lots of scavenging later things are looking better.
Looks to me like you've got a basically good setup
relax for a while,
borrow the 'scope and use it (for a while) ONLY for low power testing
(pri - sec resonance, low-level signals etc.)
You WILL get there eventually.
Good Luck - stay cool and keep on coilin'
Sulaiman, Mon Sept 24 2007, 12:25AM
Marko, I have a good idea how you feel
for a long time I renamed my DR-SSTC as SD-SSTC ... Semiconductor-Destroying (or Soul-Destroying) SSTC
I had to stop for a while to save my sanity and whatever little spare cash I had (negligible).
I got lucky - Avalanche gave me a working 'scope and things got better from there on, (Thanks again Avalanche)
lots of scavenging later things are looking better.
Looks to me like you've got a basically good setup
relax for a while,
borrow the 'scope and use it (for a while) ONLY for low power testing
(pri - sec resonance, low-level signals etc.)
You WILL get there eventually.
Good Luck - stay cool and keep on coilin'
Re: DRSSTC frustration
Dr. Drone, Mon Sept 24 2007, 12:37AM
Dr. Drone, Mon Sept 24 2007, 12:37AM
Re: DRSSTC frustration
Bennem, Mon Sept 24 2007, 07:28AM
Hi Marko,
I understand your frustrations especially when one happens to seem to go two
steps forward then four steps back.
I would advise that you listen to the replies that folks have given,
and take some time off this project and come back to it with a fresh approach.
I have used four 470uf soldered type caps in parrallel for my second DRSSTC, taken from
TV sets, and they work fine, so perhaps play around with tuning a bit more?
I think we've all had 'splatterd' loads of silicon at some point in our projects!
It took me just over a year to get my first DRSSTC parts, and still turned to drink!....lol
so...cheer up!...you'll get there!!
Mel
Bennem, Mon Sept 24 2007, 07:28AM
Hi Marko,
I understand your frustrations especially when one happens to seem to go two
steps forward then four steps back.
I would advise that you listen to the replies that folks have given,
and take some time off this project and come back to it with a fresh approach.
I have used four 470uf soldered type caps in parrallel for my second DRSSTC, taken from
TV sets, and they work fine, so perhaps play around with tuning a bit more?
I think we've all had 'splatterd' loads of silicon at some point in our projects!
It took me just over a year to get my first DRSSTC parts, and still turned to drink!....lol
so...cheer up!...you'll get there!!
Mel
Re: DRSSTC frustration
Zum Beispiel, Mon Sept 24 2007, 11:22AM
This has been said already, but what the heck:
Don't worry. These things take time. Believe me, I know how frustrating it is when something doesn't work (Especially when you know it should work, but doesn't).
The same thing about blown parts: When you build something that you have no previous experience from, you are bound to destroy some silicon. I've saved every one of those anti-static bags that the parts are packed in. And when I compare the amount of those bags to the amount of working stuff I've build, I wan't to cry. With the money I've spent on parts that I blew up, I could have probably gotten myself that Tektronix TDS2014B that I've been wanting, or something else fun.
My bigger SSTC blew up 5 times before I got it working reliably. And as you know a DRSSTC is about 100 times more complex than a "stupid normal SSTC".
Don't give up. You're a smart guy, you'll get it working eventually.
Zum Beispiel, Mon Sept 24 2007, 11:22AM
This has been said already, but what the heck:
Don't worry. These things take time. Believe me, I know how frustrating it is when something doesn't work (Especially when you know it should work, but doesn't).
The same thing about blown parts: When you build something that you have no previous experience from, you are bound to destroy some silicon. I've saved every one of those anti-static bags that the parts are packed in. And when I compare the amount of those bags to the amount of working stuff I've build, I wan't to cry. With the money I've spent on parts that I blew up, I could have probably gotten myself that Tektronix TDS2014B that I've been wanting, or something else fun.
My bigger SSTC blew up 5 times before I got it working reliably. And as you know a DRSSTC is about 100 times more complex than a "stupid normal SSTC".
Don't give up. You're a smart guy, you'll get it working eventually.
Re: DRSSTC frustration
uzzors2k, Mon Sept 24 2007, 02:28PM
You have the wrong perspective on it Marko, it's not wasted time or money if you've gained experience. Which you have. All the "solid state junk" is good learning and teaches electrical principals, hell, I learnt a lot just following your threads. Every hour and semiconductor "wasted" is the price of experience and learning. Eventually you'll become so 1337 that you stop having failures, and only then do you stop learning.
uzzors2k, Mon Sept 24 2007, 02:28PM
You have the wrong perspective on it Marko, it's not wasted time or money if you've gained experience. Which you have. All the "solid state junk" is good learning and teaches electrical principals, hell, I learnt a lot just following your threads. Every hour and semiconductor "wasted" is the price of experience and learning. Eventually you'll become so 1337 that you stop having failures, and only then do you stop learning.
Re: DRSSTC frustration
101111, Mon Sept 24 2007, 03:23PM
Now i am feeling lucky, i found my 20mhz oscope and got it calibrated for free.
I have done so much testing and failing 98% of every thing i build don't work.
101111, Mon Sept 24 2007, 03:23PM
Now i am feeling lucky, i found my 20mhz oscope and got it calibrated for free.
I have done so much testing and failing 98% of every thing i build don't work.
Re: DRSSTC frustration
colin heath, Mon Sept 24 2007, 07:00PM
Hey you haven't seen a frustrated bloke till you seen me at a teslathon trying to run a ssstc drsstc or anything else with silicone. Not one has worked until i get it home,cool down and take a fresh look.
Cheers
Colin
colin heath, Mon Sept 24 2007, 07:00PM
Hey you haven't seen a frustrated bloke till you seen me at a teslathon trying to run a ssstc drsstc or anything else with silicone. Not one has worked until i get it home,cool down and take a fresh look.
Cheers
Colin
Re: DRSSTC frustration
Marko, Fri Sept 28 2007, 06:46PM
Guys, thanks a lot. First post is apparently pointless, but I just felt so much easier after confessing my sins.
I focussed back on work.
The dimmer has died, went completely short.
I added another 3 primary turns, and scoped it while tuning. Tuning up or down for like 2 turns makes very little difference.
Using a 50V supply I get around 200amps of current, if my current transformer is fine what I don't know, although OCD tripping is consistent with that. Tuning much lower current stays about the same, but output diminishes.
I don't get much of current or output rise after 100us so I limited it there.
Now, spark output is still completely poor no matter what I do. With 200A I get like 3-4cm streamers. I feel that for any significant spark length I'm have to hit enormous currents like 800amps which is far beyond capabilities of my IGBT's and caps.
Everyone shouted ''use low characteristic impedance'', and I'm afraid I got it too low now.
My coupling may also be too low, I don't know.
If caps are good, I don't know what else could be going wrong.
I'm using water pipe for ground, and since then, it seems that arcing on my bridge has stopped. Interestingly it makes no difference when I connect it to mains ground, so I'l leave it on pipe for now.
I'l get around posting some pics.
Marko
Marko, Fri Sept 28 2007, 06:46PM
Guys, thanks a lot. First post is apparently pointless, but I just felt so much easier after confessing my sins.
I focussed back on work.
The dimmer has died, went completely short.
I added another 3 primary turns, and scoped it while tuning. Tuning up or down for like 2 turns makes very little difference.
Using a 50V supply I get around 200amps of current, if my current transformer is fine what I don't know, although OCD tripping is consistent with that. Tuning much lower current stays about the same, but output diminishes.
I don't get much of current or output rise after 100us so I limited it there.
Now, spark output is still completely poor no matter what I do. With 200A I get like 3-4cm streamers. I feel that for any significant spark length I'm have to hit enormous currents like 800amps which is far beyond capabilities of my IGBT's and caps.
Everyone shouted ''use low characteristic impedance'', and I'm afraid I got it too low now.
My coupling may also be too low, I don't know.
If caps are good, I don't know what else could be going wrong.
I'm using water pipe for ground, and since then, it seems that arcing on my bridge has stopped. Interestingly it makes no difference when I connect it to mains ground, so I'l leave it on pipe for now.
I'l get around posting some pics.
Marko
Re: DRSSTC frustration
vasil, Fri Sept 28 2007, 07:16PM
Is it your GDT/ driver output/ primary phased corectly together? I mean you get oscillations even it is not correct phased but the streamers dont grow. Did you try to reverse the primary connections? I observed that in drsstc work the winding direction of the secondary regarding the winding direction in the primary coil is important.
vasil, Fri Sept 28 2007, 07:16PM
Is it your GDT/ driver output/ primary phased corectly together? I mean you get oscillations even it is not correct phased but the streamers dont grow. Did you try to reverse the primary connections? I observed that in drsstc work the winding direction of the secondary regarding the winding direction in the primary coil is important.
Re: DRSSTC frustration
Danielle, Fri Sept 28 2007, 08:10PM
I have had the same problem you have right now so I am constructing a new driver that will hopfully work under all conditions and faults and report what they are. I am also building a new much more rugged brige because 72" wasnt enough. If you find what is wrong I think it will help me too. Just to tell you what I found so you might not have to truble shoot in the dark is all the diodes and UCCs were good and the signal from the inturupter was being fed to the CT but no osscilation was occuring because it appered that only 1 IGBT was switching. If you have these same sighnes please tell me what you see as the gate signal. All my components are good and I caint find the faluar.
also I did see that the whay you connect the signal from the UCC output to the brige matters too not only the phasing from bridge to bridge.
Danielle, Fri Sept 28 2007, 08:10PM
I have had the same problem you have right now so I am constructing a new driver that will hopfully work under all conditions and faults and report what they are. I am also building a new much more rugged brige because 72" wasnt enough. If you find what is wrong I think it will help me too. Just to tell you what I found so you might not have to truble shoot in the dark is all the diodes and UCCs were good and the signal from the inturupter was being fed to the CT but no osscilation was occuring because it appered that only 1 IGBT was switching. If you have these same sighnes please tell me what you see as the gate signal. All my components are good and I caint find the faluar.
also I did see that the whay you connect the signal from the UCC output to the brige matters too not only the phasing from bridge to bridge.
Re: DRSSTC frustration
Marko, Fri Sept 28 2007, 08:26PM
OK, what was I doing entire last year if I couldn't find the phasing?
I'l take pics tomorrow so you see what I'm at.
BTW, for those who don't know, project thread is here
Marko, Fri Sept 28 2007, 08:26PM
OK, what was I doing entire last year if I couldn't find the phasing?
I'l take pics tomorrow so you see what I'm at.
BTW, for those who don't know, project thread is here
Re: DRSSTC frustration
Tom540, Fri Sept 28 2007, 08:49PM
Hmm to me it sounds like it could be a few things. My coils don't have OCD so I run into trouble when I do certain things but I think they can apply to any DRSSTC which are:
1. my MMC has too much capacitance. 2. the coupling is too low. or 3. My topload is too large and bogging down the bridge. In those cases I get too much current draw. not enough sparkage and blown IGBT's and of course frustration. Oh yeah and the phasing thing. I don't know if this helps you but it seems like everytime i had the same problems you you did this is why. Also, I'm a snap cap user myself.
Tom540, Fri Sept 28 2007, 08:49PM
Hmm to me it sounds like it could be a few things. My coils don't have OCD so I run into trouble when I do certain things but I think they can apply to any DRSSTC which are:
1. my MMC has too much capacitance. 2. the coupling is too low. or 3. My topload is too large and bogging down the bridge. In those cases I get too much current draw. not enough sparkage and blown IGBT's and of course frustration. Oh yeah and the phasing thing. I don't know if this helps you but it seems like everytime i had the same problems you you did this is why. Also, I'm a snap cap user myself.
Re: DRSSTC frustration
Marko, Sat Sept 29 2007, 07:15PM
I tapped the primary a turn lower, and coil pumped. I was running at 50V from a small 80VA transformer, and it gave a nice 10cm streamer and 25cm sparks. And with only about 150us of on time! That was by far best 50V performance ever.
Bad news is, my dimmer is deceased and I can't be bothered to fix it.
This is a situation where it's most frustrating not to have a variac.
I'll have to find a way to regulate the input voltage into coil. I don't know, should I bother to remake some kind of dimmer, or just find a bunch of light bulbs and paralell them by required power? Or something similar?
I can't risk to give full 325V to coil and blow it up. If I slowly increase the voltage I'l at least have some chance to photograph the coil before it dies and show me to someone as a proof that I have a decently working coil.
I used a Mercury lamp ballast choke to charge to about 100V and did some single-bangs. Nice one-foot streamers, but didn't measure spark length. It should be somewhere around 30-40cm. Best ever performance for this iteration of coil.
OCD tripped during these shots so coil could have done even more.
Now it's all about if it does or does not blow up.
First pic is a tune running slightly lower than resonant frequency, current rises almost linearily and settles softly down after turned off. Poor spark output. Current is 500A div.
This is at best tune. Current inevitably heterodynes, but still doesn't go over 200A and sparks look good for 50V in!
This is ZCS measure. Shown is gate voltage so add IGBT delays, but otherwise looks good.
This is the produced spark:
I tried to photograph a short burst (charged bus cap to 100V) but couldn't do much with 320 iso. How do you guys photograph bursts and single bangs?
The largest visible streamer there is about 30cm.
Marko, Sat Sept 29 2007, 07:15PM
I tapped the primary a turn lower, and coil pumped. I was running at 50V from a small 80VA transformer, and it gave a nice 10cm streamer and 25cm sparks. And with only about 150us of on time! That was by far best 50V performance ever.
Bad news is, my dimmer is deceased and I can't be bothered to fix it.
This is a situation where it's most frustrating not to have a variac.
I'll have to find a way to regulate the input voltage into coil. I don't know, should I bother to remake some kind of dimmer, or just find a bunch of light bulbs and paralell them by required power? Or something similar?
I can't risk to give full 325V to coil and blow it up. If I slowly increase the voltage I'l at least have some chance to photograph the coil before it dies and show me to someone as a proof that I have a decently working coil.
I used a Mercury lamp ballast choke to charge to about 100V and did some single-bangs. Nice one-foot streamers, but didn't measure spark length. It should be somewhere around 30-40cm. Best ever performance for this iteration of coil.
OCD tripped during these shots so coil could have done even more.
Now it's all about if it does or does not blow up.
First pic is a tune running slightly lower than resonant frequency, current rises almost linearily and settles softly down after turned off. Poor spark output. Current is 500A div.
This is at best tune. Current inevitably heterodynes, but still doesn't go over 200A and sparks look good for 50V in!
This is ZCS measure. Shown is gate voltage so add IGBT delays, but otherwise looks good.
This is the produced spark:
I tried to photograph a short burst (charged bus cap to 100V) but couldn't do much with 320 iso. How do you guys photograph bursts and single bangs?
The largest visible streamer there is about 30cm.
Re: DRSSTC frustration
Steve Conner, Sat Sept 29 2007, 07:44PM
Hey Marko, glad you got it working. To photograph single bangs I've used a fancy digital SLR that can be cranked up to 3200 ISO, and then post-processed with Photoshop or IrfanView's gamma adjustment.
Steve Conner, Sat Sept 29 2007, 07:44PM
Hey Marko, glad you got it working. To photograph single bangs I've used a fancy digital SLR that can be cranked up to 3200 ISO, and then post-processed with Photoshop or IrfanView's gamma adjustment.
Re: DRSSTC frustration
Marko, Sat Sept 29 2007, 08:13PM
Hi steve
OK, sort of working.. I'm still very afraid about what would happen if I cranked it up?
I can't judge anything by waveforms I see. I'm already close to IGBT SOA, how can I know where will they blow up once I'm far above it?
I also can't see to what is my OCD set to, I didn't pull out any outputs I can hook a voltmeter to.
Now I'm unsure should I build a new dimmer or not. I would definitely go for a larger ST circuit because it's unbeatably rugged, and stand higher power dissipation. Without any fine circuitry it should be free of high-impedance nodes and bomb/tesla coil proof.
I need to get heatsinks for the SCR and resistors which I'm out off.. and would need to build some kind of box for it.
Marko
Marko, Sat Sept 29 2007, 08:13PM
Hi steve
OK, sort of working.. I'm still very afraid about what would happen if I cranked it up?
I can't judge anything by waveforms I see. I'm already close to IGBT SOA, how can I know where will they blow up once I'm far above it?
I also can't see to what is my OCD set to, I didn't pull out any outputs I can hook a voltmeter to.
Now I'm unsure should I build a new dimmer or not. I would definitely go for a larger ST circuit because it's unbeatably rugged, and stand higher power dissipation. Without any fine circuitry it should be free of high-impedance nodes and bomb/tesla coil proof.
I need to get heatsinks for the SCR and resistors which I'm out off.. and would need to build some kind of box for it.
Marko
Re: DRSSTC frustration
Danielle, Sun Sept 30 2007, 05:13AM
For the IGBTs I was using the same 30N60s and pumping over 900A, 1200A is where it failed but that was because an arc came around from the top avoided the strike ring and hit the bridge directly! I would say you can safely run them if you have really good cooling up to 800A. run it at 140VAC in so 400VDC and you can get some 70+ inch sparks.
Danielle, Sun Sept 30 2007, 05:13AM
For the IGBTs I was using the same 30N60s and pumping over 900A, 1200A is where it failed but that was because an arc came around from the top avoided the strike ring and hit the bridge directly! I would say you can safely run them if you have really good cooling up to 800A. run it at 140VAC in so 400VDC and you can get some 70+ inch sparks.
Re: DRSSTC frustration
Steve Conner, Sun Sept 30 2007, 12:34PM
The only way to know for sure is to destroy hundreds of IGBTs with overcurrent and do statistical analysis on the results, in conjunction with a computer model of the IGBT's guts. That was probably how the manufacturer did it, and it would need done all over again with a lower target lifetime to give you the answer you want with any degree of confidence.
No hobbyist that I know of has blown up enough devices under properly controlled conditions to give an answer that I would take seriously. The closest we have to an answer on IGBT overdriving probably comes from people like Greg Leyh at Stanford, who really did do some of the things I explained above and published papers on them. But his conclusions only hold for the same IGBTs that he investigated, and don't necessarily apply to other makes and models.
Hence I have always said that if you need guaranteed reliability, you shouldn't go outside the datasheet ratings. You just don't know what will happen when you exceed them: it could last 20 years or fail tomorrow.
Steve Conner, Sun Sept 30 2007, 12:34PM
marko wrote ...
how can I know where will they blow up once I'm far above it?
how can I know where will they blow up once I'm far above it?
The only way to know for sure is to destroy hundreds of IGBTs with overcurrent and do statistical analysis on the results, in conjunction with a computer model of the IGBT's guts. That was probably how the manufacturer did it, and it would need done all over again with a lower target lifetime to give you the answer you want with any degree of confidence.
No hobbyist that I know of has blown up enough devices under properly controlled conditions to give an answer that I would take seriously. The closest we have to an answer on IGBT overdriving probably comes from people like Greg Leyh at Stanford, who really did do some of the things I explained above and published papers on them. But his conclusions only hold for the same IGBTs that he investigated, and don't necessarily apply to other makes and models.
Hence I have always said that if you need guaranteed reliability, you shouldn't go outside the datasheet ratings. You just don't know what will happen when you exceed them: it could last 20 years or fail tomorrow.
Re: DRSSTC frustration
Marko, Sun Sept 30 2007, 04:59PM
OK, OK, level of scariness is now exponentially increasing.
After messing with the coil for a while I felt it is time to hook it up to full mains voltage.
I lowered the on time to <100us, and carefully increased the OCD setting a bit. (A bit because I don't know what is it really set to.
The streamer was absolutely intimidating, like 60..70cm long, flailing and incredibly loud. It did not although hit the 1 meter target.
OCD was actually limiting the on time to just few cycles, current would hit like 500A before being turned off. When I wanted to photograph the scope camera's battery died, and coil was overwhelmed in massive flashovers some of which started more like racing arcs, from half of the secondary and then hit the primary.
I have never seen this kind of flashover before, and I don't know how to protect from it.
It would probably do it even if I had a conical primary. I raised the scondary for like 1,5cm, it helped a bit, but not enough.
What can I do to stop the flashovers?
Another bad thing I noticed only on the pic, is the arcing on the bridge again. It seemed to stop after I separated the secondary base ground, but now it's back.
I'l post more pics as soon as my camera charges.
And I need some consolation before continuing this...
Marko, Sun Sept 30 2007, 04:59PM
OK, OK, level of scariness is now exponentially increasing.
After messing with the coil for a while I felt it is time to hook it up to full mains voltage.
I lowered the on time to <100us, and carefully increased the OCD setting a bit. (A bit because I don't know what is it really set to.
The streamer was absolutely intimidating, like 60..70cm long, flailing and incredibly loud. It did not although hit the 1 meter target.
OCD was actually limiting the on time to just few cycles, current would hit like 500A before being turned off. When I wanted to photograph the scope camera's battery died, and coil was overwhelmed in massive flashovers some of which started more like racing arcs, from half of the secondary and then hit the primary.
I have never seen this kind of flashover before, and I don't know how to protect from it.
It would probably do it even if I had a conical primary. I raised the scondary for like 1,5cm, it helped a bit, but not enough.
What can I do to stop the flashovers?
Another bad thing I noticed only on the pic, is the arcing on the bridge again. It seemed to stop after I separated the secondary base ground, but now it's back.
I'l post more pics as soon as my camera charges.
And I need some consolation before continuing this...
Re: DRSSTC frustration
Reaching, Sun Sept 30 2007, 06:16PM
mhh, where do you get the flahovers on the bridge? that would make me nervous. is it from a wire to your heatsink or inbetween traces?
You really have to solve it befor trying to crank up the whole thing. although looks great, nice work!
For racing sparks i would just try to raise the secondary another 1,5cm or more until they stop
Reaching, Sun Sept 30 2007, 06:16PM
mhh, where do you get the flahovers on the bridge? that would make me nervous. is it from a wire to your heatsink or inbetween traces?
You really have to solve it befor trying to crank up the whole thing. although looks great, nice work!
For racing sparks i would just try to raise the secondary another 1,5cm or more until they stop
Re: DRSSTC frustration
Marko, Sun Sept 30 2007, 06:45PM
Now I thought worst part of my frustration is over, but then comes even worse.
I tried to run the coil again and something blew up as I turned it off. One UCC went short.
I have no clue what could it be yet, everything happened too fast. Some IGBT's may be gone although bridge is not short and caps hold the voltage, I can't tell until I disassemble the bridge COMPLETELY.
Failure happened as I turned the interrupter off, and it could be linked with bridge arcs or secondary flashovers. Current was mere 500A at that point.
Arcing between the bridge taces is a very old story.
It's all due to completely idiotic bridge design I'm so ashamed off. Although I have reduced RF impedance between those traces to near zero they still arc, I don't have clue why.
They arced much more while I used mains ground for my secondary base ground.
The worst thing is that I can't do ANYTHING on that part. Arcs between nodes connected with so low impedance (I've put mid-point grounded 0,68uf caps in between) between them.
Why these happen is a big mystery to this time, I would be very grateful if anyone could give explanation.
Arcs specifically happen between current transformer ground trace adn positive +325V plane.
I can't by any practical way fix or insulate the traces.
I would simply have to change the entire bridge layout and throw this one to bin.
By changing the layout I also assume putting new, proper electrolytic caps inside, and this requires completely changing all the coil's internals, driver board, faceplates, everything.
It is a ''bad plan that cannot be altered''.
My primary is whole other story. I have absolutely no clue why am I suffering such bad flashovers. They come from like half of the secondary, How can I help to stop these?
I would have to raise the secondary for like 10cm for that.
Stupidest thing is that I'm using only 2 turns of my original primary and rest serves to attract flashovers.
I need to build a new primary too if I really want to do anything.
So, what I need to do is practically throw this coil into trash and build new one. Save the driver board, secondary and toroid.
Where does this torture end? All I want now is to have this coil burst into flames and finally be gone forever.
Now this makes me want to cry
Marko
Marko, Sun Sept 30 2007, 06:45PM
Now I thought worst part of my frustration is over, but then comes even worse.
I tried to run the coil again and something blew up as I turned it off. One UCC went short.
I have no clue what could it be yet, everything happened too fast. Some IGBT's may be gone although bridge is not short and caps hold the voltage, I can't tell until I disassemble the bridge COMPLETELY.
Failure happened as I turned the interrupter off, and it could be linked with bridge arcs or secondary flashovers. Current was mere 500A at that point.
Arcing between the bridge taces is a very old story.
It's all due to completely idiotic bridge design I'm so ashamed off. Although I have reduced RF impedance between those traces to near zero they still arc, I don't have clue why.
They arced much more while I used mains ground for my secondary base ground.
The worst thing is that I can't do ANYTHING on that part. Arcs between nodes connected with so low impedance (I've put mid-point grounded 0,68uf caps in between) between them.
Why these happen is a big mystery to this time, I would be very grateful if anyone could give explanation.
Arcs specifically happen between current transformer ground trace adn positive +325V plane.
I can't by any practical way fix or insulate the traces.
I would simply have to change the entire bridge layout and throw this one to bin.
By changing the layout I also assume putting new, proper electrolytic caps inside, and this requires completely changing all the coil's internals, driver board, faceplates, everything.
It is a ''bad plan that cannot be altered''.
My primary is whole other story. I have absolutely no clue why am I suffering such bad flashovers. They come from like half of the secondary, How can I help to stop these?
I would have to raise the secondary for like 10cm for that.
Stupidest thing is that I'm using only 2 turns of my original primary and rest serves to attract flashovers.
I need to build a new primary too if I really want to do anything.
So, what I need to do is practically throw this coil into trash and build new one. Save the driver board, secondary and toroid.
Where does this torture end? All I want now is to have this coil burst into flames and finally be gone forever.
Now this makes me want to cry
Marko
Re: DRSSTC frustration
Finn Hammer, Mon Oct 01 2007, 06:25AM
Marco,
I have 6 similar sized DRSSTC`s, all equipped with Steve Conners PLL driver.
_One_ of them repeatedly produced similar flashovers from the bottom 100-150 mm of the secondary, to the top of the conical primary. These flashovers are then 100 -150 mm long.
I might have a clue to the situation that produces them.
I tuned the primary to the low pole of the combined system.
Now, if the driver locked on to the low pole, it would arc.
If it locked on to the high pole, it would stop arching.
I have not read the full thread, so I don`t know how you have tuned your primary circuit, and I have no clue to how you can force a feedback system to operate at a desired pole, but at least here is something you can investigate.
Cheers, Finn Hammer
Finn Hammer, Mon Oct 01 2007, 06:25AM
Marko wrote ...
I have never seen this kind of flashover before, and I don't know how to protect from it.
It would probably do it even if I had a conical primary. I raised the scondary for like 1,5cm, it helped a bit, but not enough.
What can I do to stop the flashovers?
I have never seen this kind of flashover before, and I don't know how to protect from it.
It would probably do it even if I had a conical primary. I raised the scondary for like 1,5cm, it helped a bit, but not enough.
What can I do to stop the flashovers?
Marco,
I have 6 similar sized DRSSTC`s, all equipped with Steve Conners PLL driver.
_One_ of them repeatedly produced similar flashovers from the bottom 100-150 mm of the secondary, to the top of the conical primary. These flashovers are then 100 -150 mm long.
I might have a clue to the situation that produces them.
I tuned the primary to the low pole of the combined system.
Now, if the driver locked on to the low pole, it would arc.
If it locked on to the high pole, it would stop arching.
I have not read the full thread, so I don`t know how you have tuned your primary circuit, and I have no clue to how you can force a feedback system to operate at a desired pole, but at least here is something you can investigate.
Cheers, Finn Hammer
Re: DRSSTC frustration
Steve Conner, Mon Oct 01 2007, 11:02AM
Marko, why so sad? You built a DRSSTC and it works, that is something to be proud of. The flashovers and exploding components are all part of the fun
About the mysterious arcs on your H-bridge, can you draw the schematic of your power board, draw a lightning bolt on it or something to indicate the two nodes that it's arcing between, and post it here?
Finn: Mjolnir does the same thing too, and I never quite figured out why one pole/mode made it flash over but the other didn't. My best guess is that the two resonant modes actually have different voltage profiles on the secondary.
In the upper mode, the induced voltage in the secondary due to the primary current is 180' out of phase with the voltage due to the secondary's own current in its self-inductance. This makes the voltage gradient shallower at the bottom of the secondary, where the primary's magnetic field is strongest.
In the lower mode, the induced voltage is in phase, so the voltage gradient is steeper at the bottom.
Don't even ask how the induced voltage can transfer power when it's 180' out of phase with the current. I don't know, but the math says it works, the experiments say that it works, and I have experimental evidence that the primary and secondary magnetic fields are out of phase on the upper pole.
The ability to choose one pole or the other is something that only my PLL driver can do, AFAIK. A self-oscillating driver will snap to whichever one oscillates most readily.
The poles/modes thing is really mostly of concern at startup when you're trying to build up voltage to ignite your streamers. Once a good streamer load has developed, the loading flattens everything out and the exact drive frequency doesn't seem to matter so much.
Steve Conner, Mon Oct 01 2007, 11:02AM
Marko, why so sad? You built a DRSSTC and it works, that is something to be proud of. The flashovers and exploding components are all part of the fun
About the mysterious arcs on your H-bridge, can you draw the schematic of your power board, draw a lightning bolt on it or something to indicate the two nodes that it's arcing between, and post it here?
Finn: Mjolnir does the same thing too, and I never quite figured out why one pole/mode made it flash over but the other didn't. My best guess is that the two resonant modes actually have different voltage profiles on the secondary.
In the upper mode, the induced voltage in the secondary due to the primary current is 180' out of phase with the voltage due to the secondary's own current in its self-inductance. This makes the voltage gradient shallower at the bottom of the secondary, where the primary's magnetic field is strongest.
In the lower mode, the induced voltage is in phase, so the voltage gradient is steeper at the bottom.
Don't even ask how the induced voltage can transfer power when it's 180' out of phase with the current. I don't know, but the math says it works, the experiments say that it works, and I have experimental evidence that the primary and secondary magnetic fields are out of phase on the upper pole.
The ability to choose one pole or the other is something that only my PLL driver can do, AFAIK. A self-oscillating driver will snap to whichever one oscillates most readily.
The poles/modes thing is really mostly of concern at startup when you're trying to build up voltage to ignite your streamers. Once a good streamer load has developed, the loading flattens everything out and the exact drive frequency doesn't seem to matter so much.
Re: DRSSTC frustration
Tom540, Mon Oct 01 2007, 02:59PM
Marko,
Whenever I tried raising my secondaries to get rid of flash over all it seemed to do was raise current and have bad coupling. I just started using a wider primary instead. I always make my primaries 2 inches wider than the secondary. Might be worth a try.
-Tom
Tom540, Mon Oct 01 2007, 02:59PM
Marko,
Whenever I tried raising my secondaries to get rid of flash over all it seemed to do was raise current and have bad coupling. I just started using a wider primary instead. I always make my primaries 2 inches wider than the secondary. Might be worth a try.
-Tom
Re: DRSSTC frustration
Marko, Mon Oct 01 2007, 08:38PM
Arcs happen between feedback-sensing CT stack hot output (yep, the one that goes into zener clamps and 74HC14 ) and + pole of the bus cap. Arcs are surprisingly small, and it was actually odd that it took so long for something to blow.
Why in world did I put low voltage traces onto the HV board like this??
I could have easily swapped the CT sets, I have no idea why haven't I done at least that. Then it would arc to OCD CT which has only 5 ohms to ground anyway.
The litycs are shunted with center-grounded set of caps to pass any HF to ground. GND of control board is grounded too. That's all that is odd, rest is nearly exact copy of steve's coil.
I can draw a schematic if really needed...
I haven't had time to investigate today, but it seems that failure took out random components on +15V rail. OCD NE555 and one UCC are found failed for now.
I believe this arc is what killed them. The failure happened as I turned off the interrupter; I heard a small pop and flash. (didn't notice where, but I suspect it was on bridge).
I curse this design now. I have so much better ideas to design this thing now. I don't know why I anchored everything to the bottom of the case, and not building the bridge and control into drawer-like construction I could easily pull out for repairs. The nice piece of wood ended perforated with holes and coil so hard to work on.
All I can do is tune the primary up or down respectively.
My primary current is already very high for the spark size I'm producing. The pic shown is the primary current before failure, hitting about 600 amps at least. It's running mere 7-8 cycles and although interrupter was <100us, OCD limited it to about 70. I had to see such monstrous dI/dt on a DRSSTC yet.
The surge impedance of primary is just around 4,8 ohms
My current is already very high considering poor sparks I'm producing. Other coils do like 5 feet with 600+ amps where I struggle for 3.
If I tune the primary higher, the current will get even worse. Remember that those IGBT's are rated for like 240amps of peak current in DS.
It is feasible for me tu build a conical primary with more turns, but I need to be absolutely sure that it's not a waste of time since masses of coils use it happily, along with as low Z as I have.
Marko, Mon Oct 01 2007, 08:38PM
About the mysterious arcs on your H-bridge, can you draw the schematic of your power board, draw a lightning bolt on it or something to indicate the two nodes that it's arcing between, and post it here?
Arcs happen between feedback-sensing CT stack hot output (yep, the one that goes into zener clamps and 74HC14 ) and + pole of the bus cap. Arcs are surprisingly small, and it was actually odd that it took so long for something to blow.
Why in world did I put low voltage traces onto the HV board like this??
I could have easily swapped the CT sets, I have no idea why haven't I done at least that. Then it would arc to OCD CT which has only 5 ohms to ground anyway.
The litycs are shunted with center-grounded set of caps to pass any HF to ground. GND of control board is grounded too. That's all that is odd, rest is nearly exact copy of steve's coil.
I can draw a schematic if really needed...
I haven't had time to investigate today, but it seems that failure took out random components on +15V rail. OCD NE555 and one UCC are found failed for now.
I believe this arc is what killed them. The failure happened as I turned off the interrupter; I heard a small pop and flash. (didn't notice where, but I suspect it was on bridge).
I curse this design now. I have so much better ideas to design this thing now. I don't know why I anchored everything to the bottom of the case, and not building the bridge and control into drawer-like construction I could easily pull out for repairs. The nice piece of wood ended perforated with holes and coil so hard to work on.
Steve wrote ...
In the upper mode, the induced voltage in the secondary due to the primary current is 180' out of phase with the voltage due to the secondary's own current in its self-inductance. This makes the voltage gradient shallower at the bottom of the secondary, where the primary's magnetic field is strongest.
In the upper mode, the induced voltage in the secondary due to the primary current is 180' out of phase with the voltage due to the secondary's own current in its self-inductance. This makes the voltage gradient shallower at the bottom of the secondary, where the primary's magnetic field is strongest.
Finn wrote ...
I tuned the primary to the low pole of the combined system.
Now, if the driver locked on to the low pole, it would arc.
If it locked on to the high pole, it would stop arching.
I tuned the primary to the low pole of the combined system.
Now, if the driver locked on to the low pole, it would arc.
If it locked on to the high pole, it would stop arching.
All I can do is tune the primary up or down respectively.
My primary current is already very high for the spark size I'm producing. The pic shown is the primary current before failure, hitting about 600 amps at least. It's running mere 7-8 cycles and although interrupter was <100us, OCD limited it to about 70. I had to see such monstrous dI/dt on a DRSSTC yet.
The surge impedance of primary is just around 4,8 ohms
My current is already very high considering poor sparks I'm producing. Other coils do like 5 feet with 600+ amps where I struggle for 3.
If I tune the primary higher, the current will get even worse. Remember that those IGBT's are rated for like 240amps of peak current in DS.
It is feasible for me tu build a conical primary with more turns, but I need to be absolutely sure that it's not a waste of time since masses of coils use it happily, along with as low Z as I have.
Re: DRSSTC frustration
Steve Ward, Mon Oct 01 2007, 09:48PM
Marko,
Your suspicions of using too little surge impedance is very true as far as i can tell. At one point i had rebuilt my original DRSSTC using a .6uF tank cap. The primary current was very high (1100A) and i could only manage about 5 foot of spark from the machine. After increasing the tank Z (.45uF cap now), it runs around 700A for 6+ foot of spark. I still think that the impedance might be a bit on the low side, but its performance is pleasing enough for me.
The whole impedance thing is messy to analyze because the apparent impedance depends not just on primary components, but the secondary side (mainly the sparks) and the coupling coefficient. But in general, id say you shouldnt go with less than 6 ohms for Zsurge, and try to keep coupling as high as practically possible (usually its flash-over limited). This is of course really only applicable to my style of DRSSTCs. I think Conner's PLL stuff mucks things up and makes them even harder to analyze... almost as if the PLL adds another order or 2 to the system (its certainly not as easy to model as a proportional feedback control with a delay!).
The other purely experimental conclusion Ive come to is that a lower surge impedance only pays off if your IGBTs can support it. Thats to say that i think a lower Z only allows a longer max spark, but you need higher currents to achieve spark lengths possible with a higher Z at a lower current. Many of my coils have an extremely non-linear response of spark length vs Vin, Ipk. Typically Ipk will rise fast vs Vin (and only increase marginally after about 50% of Vin's max), but spark length takes an extreme jump near about 65% of Vin's max. Before that jump, the primary current is very high, and the output is very weak. Its possible that you are at this point, in which case your IGBTs are not capable of more power so you need to increase Zsurge to lower the peak current to get past the knee in the curve.
Steve Ward, Mon Oct 01 2007, 09:48PM
Marko,
Your suspicions of using too little surge impedance is very true as far as i can tell. At one point i had rebuilt my original DRSSTC using a .6uF tank cap. The primary current was very high (1100A) and i could only manage about 5 foot of spark from the machine. After increasing the tank Z (.45uF cap now), it runs around 700A for 6+ foot of spark. I still think that the impedance might be a bit on the low side, but its performance is pleasing enough for me.
The whole impedance thing is messy to analyze because the apparent impedance depends not just on primary components, but the secondary side (mainly the sparks) and the coupling coefficient. But in general, id say you shouldnt go with less than 6 ohms for Zsurge, and try to keep coupling as high as practically possible (usually its flash-over limited). This is of course really only applicable to my style of DRSSTCs. I think Conner's PLL stuff mucks things up and makes them even harder to analyze... almost as if the PLL adds another order or 2 to the system (its certainly not as easy to model as a proportional feedback control with a delay!).
The other purely experimental conclusion Ive come to is that a lower surge impedance only pays off if your IGBTs can support it. Thats to say that i think a lower Z only allows a longer max spark, but you need higher currents to achieve spark lengths possible with a higher Z at a lower current. Many of my coils have an extremely non-linear response of spark length vs Vin, Ipk. Typically Ipk will rise fast vs Vin (and only increase marginally after about 50% of Vin's max), but spark length takes an extreme jump near about 65% of Vin's max. Before that jump, the primary current is very high, and the output is very weak. Its possible that you are at this point, in which case your IGBTs are not capable of more power so you need to increase Zsurge to lower the peak current to get past the knee in the curve.
Re: DRSSTC frustration
Marko, Mon Oct 01 2007, 11:27PM
Hi Steve
Yes, I have got way too mean about the low impedance thing and now I suffer the consequences.
I don't actually see what's wrong with using quite high impedance within reasonable limits, it's better for IGBT's. Steve C. used 50nF cap along with a bigger primary, and produced great sparks while not punishing his IGBT's for much at all. I don't remember now, but I think he didn't even drive them out of datasheet rating in normal runs and used 15V gate voltage.
200nF cap would give me about 7 ohms of tank impedance, still a bit low, I would actually target 100nF and 14ohms. This requires complete primary rebuild, though.
Cap will need to be rearranged to stand like 10kV at that point
Good things I've learned from all this, the small TO247 IGBT's are as capable as ISOTOP's when heatsinked well. 5 foot sparks should at least be feasible.
At this time flashovers are biggest concern, especially those at bridge. Could these odd racing flashovers be linked to too fast rate of primary current?
I don't believe even conical primary is going to fix them and something must be done.
I noticed many people use tighter coupling than me, helical primaries, throw sparks 4x secondary length and are fine about flashovers.
Marko, Mon Oct 01 2007, 11:27PM
Hi Steve
Yes, I have got way too mean about the low impedance thing and now I suffer the consequences.
I don't actually see what's wrong with using quite high impedance within reasonable limits, it's better for IGBT's. Steve C. used 50nF cap along with a bigger primary, and produced great sparks while not punishing his IGBT's for much at all. I don't remember now, but I think he didn't even drive them out of datasheet rating in normal runs and used 15V gate voltage.
200nF cap would give me about 7 ohms of tank impedance, still a bit low, I would actually target 100nF and 14ohms. This requires complete primary rebuild, though.
Cap will need to be rearranged to stand like 10kV at that point
Good things I've learned from all this, the small TO247 IGBT's are as capable as ISOTOP's when heatsinked well. 5 foot sparks should at least be feasible.
At this time flashovers are biggest concern, especially those at bridge. Could these odd racing flashovers be linked to too fast rate of primary current?
I don't believe even conical primary is going to fix them and something must be done.
I noticed many people use tighter coupling than me, helical primaries, throw sparks 4x secondary length and are fine about flashovers.
Re: DRSSTC frustration
vasil, Tue Oct 02 2007, 05:13AM
I have flashes on secondary myself when using cilindrical primaries until I turned to flater primaries forms, like this:
primary. It is easier to adjust just raising or lowering the primary.
It is possible that the flashes risk depends by the raport radius of primary/ radius of secondary. I observed that many drsstc that perform very well have some large secondaries it is possible that larger secondaries process power much better and have longer sparks.
The low voltage and the power stage have to be completely separated and the stages have to be powered one after another. I usually turn on the interrupter ON, then the driver, then I apply the power on the bridge. When closing, I crank down the variac, turn OFF the bridge, turn off the driver and the interrupter at last. When turning OFF the interrupter is possible to have some juice in the DC capacitors across the UCCs in the driver, turning the driver in CW mode and burning the UCCs.
vasil, Tue Oct 02 2007, 05:13AM
I have flashes on secondary myself when using cilindrical primaries until I turned to flater primaries forms, like this:
primary. It is easier to adjust just raising or lowering the primary.
It is possible that the flashes risk depends by the raport radius of primary/ radius of secondary. I observed that many drsstc that perform very well have some large secondaries it is possible that larger secondaries process power much better and have longer sparks.
The low voltage and the power stage have to be completely separated and the stages have to be powered one after another. I usually turn on the interrupter ON, then the driver, then I apply the power on the bridge. When closing, I crank down the variac, turn OFF the bridge, turn off the driver and the interrupter at last. When turning OFF the interrupter is possible to have some juice in the DC capacitors across the UCCs in the driver, turning the driver in CW mode and burning the UCCs.
Re: DRSSTC frustration
Steve Conner, Tue Oct 02 2007, 10:55AM
Hi guys,
I am up to 100nF now and the output seems a little better. I still have the OCD set to the datasheet rating of 400A.
The PLL certainly makes the analysis different, but I don't think it's harder. Since I always know which of the two resonant modes it will be driving, I just analyse it as a CW system operating at that frequency.
This is why I talk in terms of real power flows, surge impedances and loaded Q's, because I see the whole thing as one big matching network between an inverter that delivers real power and a streamer that consumes it.
So, I start with a desired peak power, which I work out from the desired spark length using the Freau formulas and what not from classic coiling.
Then, the impedance of the streamer load is roughly the breakout voltage of the bare toroid squared, divided by the peak power I intend to deliver. This is a consequence of the non-linear nature of the streamer load, which adjusts itself to try to clamp the toroid voltage somewhat like a zener diode.
Adding a breakout point makes surprisingly little difference to the impedance, because the streamer growth is driven by the electric field in the entire space that it grows through, and the breakout point is just a small local disturbance at one end.
Now, the output impedance of the inverter is just the same formula but with 4/Pi times the DC bus voltage.
So, I design the primary circuit to have a surge impedance about 10 times the output impedance of the inverter, and the resonator to have a surge impedance about one-tenth of the streamer load impedance. I get the coupling as tight as possible, tune the primary to a slightly lower frequency than the secondary, and that's all there is to my design method. None of these values appears to be critical.
I know that the system is not CW, that the real power flow is not constant throughout the burst, and that you can't avoid exciting the other mode to the one you're trying to drive, to some extent. But I just ignore these things to make the analysis simpler, and I still seem to land in the ballpark :P
Marko, maybe your feedback CT is generating a high voltage because it doesn't have a proper burden? :|
Steve Conner, Tue Oct 02 2007, 10:55AM
Hi guys,
I am up to 100nF now and the output seems a little better. I still have the OCD set to the datasheet rating of 400A.
The PLL certainly makes the analysis different, but I don't think it's harder. Since I always know which of the two resonant modes it will be driving, I just analyse it as a CW system operating at that frequency.
This is why I talk in terms of real power flows, surge impedances and loaded Q's, because I see the whole thing as one big matching network between an inverter that delivers real power and a streamer that consumes it.
So, I start with a desired peak power, which I work out from the desired spark length using the Freau formulas and what not from classic coiling.
Then, the impedance of the streamer load is roughly the breakout voltage of the bare toroid squared, divided by the peak power I intend to deliver. This is a consequence of the non-linear nature of the streamer load, which adjusts itself to try to clamp the toroid voltage somewhat like a zener diode.
Adding a breakout point makes surprisingly little difference to the impedance, because the streamer growth is driven by the electric field in the entire space that it grows through, and the breakout point is just a small local disturbance at one end.
Now, the output impedance of the inverter is just the same formula but with 4/Pi times the DC bus voltage.
So, I design the primary circuit to have a surge impedance about 10 times the output impedance of the inverter, and the resonator to have a surge impedance about one-tenth of the streamer load impedance. I get the coupling as tight as possible, tune the primary to a slightly lower frequency than the secondary, and that's all there is to my design method. None of these values appears to be critical.
I know that the system is not CW, that the real power flow is not constant throughout the burst, and that you can't avoid exciting the other mode to the one you're trying to drive, to some extent. But I just ignore these things to make the analysis simpler, and I still seem to land in the ballpark :P
Marko, maybe your feedback CT is generating a high voltage because it doesn't have a proper burden? :|
Re: DRSSTC frustration
Marko, Tue Oct 02 2007, 12:48PM
OK, 5 foot spark with just 400A of primary current? I'm beginning to realize how this has nothing with size of IGBT's, frequency pole or characteristic impedance. It's all about altering the reality by bending your perception of it.
I got completely lost trying to understand steve's post, I need to do a lot of googling before I just begin so.
All I can naively ask, what exactly I need to do to lower my primary current/spark size ratio and stop the damned flashovers?
You can consider increasing the tank impedance done.
This is contradictory with information you guys just gave about tuning the primary higher.
So how should I tune, higher or lower than secondary Fres?
That would be odd since diodes are fine, and voltage should be clamped to 5V at most.
I need to disassemble the coil for this, and I fear I won't be doing that until weekend.
I can only appreciate all the theoretical information you guys can give me ^ ^
Marko
Marko, Tue Oct 02 2007, 12:48PM
I am up to 100nF now and the output seems a little better. I still have the OCD set to the datasheet rating of 400A.
OK, 5 foot spark with just 400A of primary current? I'm beginning to realize how this has nothing with size of IGBT's, frequency pole or characteristic impedance. It's all about altering the reality by bending your perception of it.
I got completely lost trying to understand steve's post, I need to do a lot of googling before I just begin so.
All I can naively ask, what exactly I need to do to lower my primary current/spark size ratio and stop the damned flashovers?
You can consider increasing the tank impedance done.
tune the primary to a slightly lower frequency than the secondary, and that's all there is to my design method. None of these values appears to be critical.
This is contradictory with information you guys just gave about tuning the primary higher.
So how should I tune, higher or lower than secondary Fres?
Marko, maybe your feedback CT is generating a high voltage because it doesn't have a proper burden? :|
That would be odd since diodes are fine, and voltage should be clamped to 5V at most.
I need to disassemble the coil for this, and I fear I won't be doing that until weekend.
I can only appreciate all the theoretical information you guys can give me ^ ^
Marko
Re: DRSSTC frustration
Steve Conner, Tue Oct 02 2007, 04:13PM
Hey Marko,
I guess it was unfair of me and Finn to bring up the PLL driver thing. The PLL driver has an extra degree of freedom. You can operate on either resonant mode, no matter what you tune your primary to.
Since you are using the self-resonant driver, you should probably tune your primary a bit lower than your secondary, because that's what most other users of this driver seem to do. Once you have raised the tank impedance, just play with the primary tapping point till you get the best sparks that your current limiter allows, and if they still aren't good enough, try a different size of toroid or something.
I don't really understand how the self-resonant one works. All I know is that if you tune the primary lower than the secondary, it will operate on the lower resonant mode, and vice versa.
According to my notes, the 5ft arc needed 450A peak, 300uS burst length and 200Hz rep rate, and over 3kW. :|
Steve Conner, Tue Oct 02 2007, 04:13PM
Hey Marko,
I guess it was unfair of me and Finn to bring up the PLL driver thing. The PLL driver has an extra degree of freedom. You can operate on either resonant mode, no matter what you tune your primary to.
Since you are using the self-resonant driver, you should probably tune your primary a bit lower than your secondary, because that's what most other users of this driver seem to do. Once you have raised the tank impedance, just play with the primary tapping point till you get the best sparks that your current limiter allows, and if they still aren't good enough, try a different size of toroid or something.
I don't really understand how the self-resonant one works. All I know is that if you tune the primary lower than the secondary, it will operate on the lower resonant mode, and vice versa.
According to my notes, the 5ft arc needed 450A peak, 300uS burst length and 200Hz rep rate, and over 3kW. :|
Re: DRSSTC frustration
Tom540, Tue Oct 02 2007, 05:14PM
It's a good think you're getting all this help. I learned this the hard way. I hacked up my primary at leat 12 times trying to get this part right.
Definitely raise that tank impedance. It sure saved me some IGBT's, of course after I had replaced dozens of them.
My coils couldn't run on a MMC capacitance greater than 35nF. My latest one uses 27nF and gets 24 inch sparks maybe more if I actually had taps on the primary. The FGA40n60's I was using can only handle 160 amps pulsed so adding more turns and lowering that MMC value was crucial.
Tom540, Tue Oct 02 2007, 05:14PM
It's a good think you're getting all this help. I learned this the hard way. I hacked up my primary at leat 12 times trying to get this part right.
Definitely raise that tank impedance. It sure saved me some IGBT's, of course after I had replaced dozens of them.
My coils couldn't run on a MMC capacitance greater than 35nF. My latest one uses 27nF and gets 24 inch sparks maybe more if I actually had taps on the primary. The FGA40n60's I was using can only handle 160 amps pulsed so adding more turns and lowering that MMC value was crucial.
Re: DRSSTC frustration
Marko, Tue Oct 02 2007, 10:12PM
Steve, you do keep confusing me:
This is contradictory again. You advise me to tune to lower pole, but you also say that it will give steep voltage gradient and flashovers. I hope you didn't get me serious when I said I want the coil to self destruct.
I myself am completely unsure what happens with flashovers at higher or lower tuning at full power, I blew the coil before I could have done anything about that.
What I know is that when tuned slightly lower current rises almost linearily and spark output is not too good in overall.
At best tune the current heterodynes but peak value doesn't get much higher in same time period.
If I go significantly higher than resonant the current ramps up and output is poor.
That's a small tank cap, even for a smallish coil. What frequency/tank impedance were you running at that point?
Now how high is it feasible to go? If I used really high impedance I could pump lots of energy into the coil without actually exceeding IGBT SOA. Spark length/power input efficiency may be worse, but who cares about that as long as sparks are long.
Marko, Tue Oct 02 2007, 10:12PM
Steve, you do keep confusing me:
In the upper mode, the induced voltage in the secondary due to the primary current is 180' out of phase with the voltage due to the secondary's own current in its self-inductance. This makes the voltage gradient shallower at the bottom of the secondary, where the primary's magnetic field is strongest.
In the lower mode, the induced voltage is in phase, so the voltage gradient is steeper at the bottom.
Since you are using the self-resonant driver, you should probably tune your primary a bit lower than your secondary, because that's what most other users of this driver seem to do. Once you have raised the tank impedance, just play with the primary tapping point till you get the best sparks that your current limiter allows, and if they still aren't good enough, try a different size of toroid or something.
This is contradictory again. You advise me to tune to lower pole, but you also say that it will give steep voltage gradient and flashovers. I hope you didn't get me serious when I said I want the coil to self destruct.
I myself am completely unsure what happens with flashovers at higher or lower tuning at full power, I blew the coil before I could have done anything about that.
What I know is that when tuned slightly lower current rises almost linearily and spark output is not too good in overall.
At best tune the current heterodynes but peak value doesn't get much higher in same time period.
If I go significantly higher than resonant the current ramps up and output is poor.
My coils couldn't run on a tank capacitance greater than 35nF. My latest one uses 27nF and gets 24 inch sparks maybe more if I actually had taps on the primary. The FGA40n60's I was using can only handle 160 amps pulsed so adding more turns and lowering that tank cap was crucial.
That's a small tank cap, even for a smallish coil. What frequency/tank impedance were you running at that point?
Now how high is it feasible to go? If I used really high impedance I could pump lots of energy into the coil without actually exceeding IGBT SOA. Spark length/power input efficiency may be worse, but who cares about that as long as sparks are long.
Re: DRSSTC frustration
Steve Ward, Wed Oct 03 2007, 04:39AM
The spark length will plateau earlier with higher tank impedance because you simply cant achieve the higher peak powers. Take the extreme example of the typical SSTC... my big one took about 7kVA to make 3 foot sparks but only had about 50A of primary current (at 400VDC). Of course, as you found the other extreme isnt so great either, and results in a poor impedance match to the output spark.
The tuning for the heterodyning of the primary current is the tuning i always go for. It implies a proper energy transfer to the secondary, and gives a nice point for shut down (since driving beyond that point doesnt seem to help much anyway). This tuning might be tricky to obtain with higher tank Z, but perhaps with proper detuning it could work (otherwise you will get a lot of beating).
Of course the best way to learn this stuff is to try it out and see what happens.
Steve Ward, Wed Oct 03 2007, 04:39AM
The spark length will plateau earlier with higher tank impedance because you simply cant achieve the higher peak powers. Take the extreme example of the typical SSTC... my big one took about 7kVA to make 3 foot sparks but only had about 50A of primary current (at 400VDC). Of course, as you found the other extreme isnt so great either, and results in a poor impedance match to the output spark.
The tuning for the heterodyning of the primary current is the tuning i always go for. It implies a proper energy transfer to the secondary, and gives a nice point for shut down (since driving beyond that point doesnt seem to help much anyway). This tuning might be tricky to obtain with higher tank Z, but perhaps with proper detuning it could work (otherwise you will get a lot of beating).
Of course the best way to learn this stuff is to try it out and see what happens.
Re: DRSSTC frustration
Finn Hammer, Wed Oct 03 2007, 05:59AM
Excuse my ignorance, but this heterodyning....
Is it a more precise (single word) description of what can also be described as a waveform with notches? 2 frequences beating?
Cheers, Finn Hammer
Finn Hammer, Wed Oct 03 2007, 05:59AM
Steve Ward wrote ...
The tuning for the heterodyning of the primary current is the tuning i always go for.
The tuning for the heterodyning of the primary current is the tuning i always go for.
Excuse my ignorance, but this heterodyning....
Is it a more precise (single word) description of what can also be described as a waveform with notches? 2 frequences beating?
Cheers, Finn Hammer
Re: DRSSTC frustration
Bennem, Wed Oct 03 2007, 06:18AM
On my feedback type DRSSTC i have noticed two major tuning points.
1: In tune, which produces spark output lineaily as you increase buss voltage,
but you dont seem to get the longest sparks this way.
2: Add more primary inductance (i add another 0.5 - one turn)
I then notice that it takes more buss voltage to produce an output
spark, infact i hardly get much spark perfomance until i reach approx
70% on my variac, then 'whooosh' it snaps out with longer sparks.
The primary current rises quickly whilst under the 70% of variac,
after the 70% the current hardly rises at all
but you have to be carefull not to detune too much as to ring up
too much current that will blow your IGBT's......in my experiance with DRSSTC's
Bennem, Wed Oct 03 2007, 06:18AM
On my feedback type DRSSTC i have noticed two major tuning points.
1: In tune, which produces spark output lineaily as you increase buss voltage,
but you dont seem to get the longest sparks this way.
2: Add more primary inductance (i add another 0.5 - one turn)
I then notice that it takes more buss voltage to produce an output
spark, infact i hardly get much spark perfomance until i reach approx
70% on my variac, then 'whooosh' it snaps out with longer sparks.
The primary current rises quickly whilst under the 70% of variac,
after the 70% the current hardly rises at all
but you have to be carefull not to detune too much as to ring up
too much current that will blow your IGBT's......in my experiance with DRSSTC's
Re: DRSSTC frustration
Steve Conner, Wed Oct 03 2007, 09:42AM
Hi Marko,
The relationship that Finn and I have observed between operating on the lower resonant mode, and flashovers, only holds true for the PLL driver. There is no evidence that it happens with the self-resonant driver.
The "heterodyning" effect would imply that you have primary and secondary tuned to exactly the same frequency. I think the self-resonant driver can actually generate an output with two frequency components under that condition, exciting both modes equally, whereas the PLL has to choose one or the other.
Steve Conner, Wed Oct 03 2007, 09:42AM
Hi Marko,
The relationship that Finn and I have observed between operating on the lower resonant mode, and flashovers, only holds true for the PLL driver. There is no evidence that it happens with the self-resonant driver.
The "heterodyning" effect would imply that you have primary and secondary tuned to exactly the same frequency. I think the self-resonant driver can actually generate an output with two frequency components under that condition, exciting both modes equally, whereas the PLL has to choose one or the other.
Re: DRSSTC frustration
Marko, Wed Oct 03 2007, 02:05PM
Guys, thanks a bunch. I have nothing more to do than try this out.
Can this be just the dynamic tuning thing? If that's important for DRSSTC at all...
Marko, Wed Oct 03 2007, 02:05PM
Guys, thanks a bunch. I have nothing more to do than try this out.
70% on my variac, then 'whooosh' it snaps out with longer sparks.
The primary current rises quickly whilst under the 70% of variac,
after the 70% the current hardly rises at all
but you have to be carefull not to detune too much as to ring up
too much current that will blow your IGBT's......in my experiance with DRSSTC's
Can this be just the dynamic tuning thing? If that's important for DRSSTC at all...
Re: DRSSTC frustration
Marko, Tue Oct 09 2007, 02:27PM
Well, this weekend I wasn't able to do much work.
After a day of pondering I still can't find what's wrong with the control board. I found a lot of dead components and replaced nearly all actives from the board (except UCC's and few diodes which test good).
Output is just dead 0. So I'm back on the beginning, and need to revert everything from the garage back into my room which is a terrible mess as of now. So cleaning first.
So the current state of things is, this DRSSTC is dead, and will be enormous pain to repair.
I know it will blow up again on full power so I can't use this bridge design.
New coil needs to be built in order to do any progress, and I don't have money for that.
I'l see if I can at least fix this to give it some 50 or 100V runs and try out higher surge impedance.
How much wasted effort was this
Marko, Tue Oct 09 2007, 02:27PM
Well, this weekend I wasn't able to do much work.
After a day of pondering I still can't find what's wrong with the control board. I found a lot of dead components and replaced nearly all actives from the board (except UCC's and few diodes which test good).
Output is just dead 0. So I'm back on the beginning, and need to revert everything from the garage back into my room which is a terrible mess as of now. So cleaning first.
So the current state of things is, this DRSSTC is dead, and will be enormous pain to repair.
I know it will blow up again on full power so I can't use this bridge design.
New coil needs to be built in order to do any progress, and I don't have money for that.
I'l see if I can at least fix this to give it some 50 or 100V runs and try out higher surge impedance.
How much wasted effort was this
Re: DRSSTC frustration
Tom540, Tue Oct 09 2007, 03:20PM
The frequency was around 330KHz. I didn't really pay much attention to impedance but it's around 17 Ohms with a 27nF tank cap and ~8-10uH primary inductance. Tuned slightly lower. I had to do it this way anything over 33nF would blow the IGBT's. In fact 33nF wouldn't work either.
Not wasted at all. Once you get it working to your satisfaction you'll just want to tweek it more and more and eventually you'll destroy it again. It's all part of the design/learning process. By the way I think your bridge is most likely fixable. You could peel off copper and grounding from the board and maybe add a ton of the thick white RTV to prevent that arcing.
Tom540, Tue Oct 09 2007, 03:20PM
That's a small tank cap, even for a smallish coil. What frequency/tank impedance were you running at that point?
Now how high is it feasible to go? If I used really high impedance I could pump lots of energy into the coil without actually exceeding IGBT SOA. Spark length/power input efficiency may be worse, but who cares about that as long as sparks are long.
The frequency was around 330KHz. I didn't really pay much attention to impedance but it's around 17 Ohms with a 27nF tank cap and ~8-10uH primary inductance. Tuned slightly lower. I had to do it this way anything over 33nF would blow the IGBT's. In fact 33nF wouldn't work either.
How much wasted effort was this
Not wasted at all. Once you get it working to your satisfaction you'll just want to tweek it more and more and eventually you'll destroy it again. It's all part of the design/learning process. By the way I think your bridge is most likely fixable. You could peel off copper and grounding from the board and maybe add a ton of the thick white RTV to prevent that arcing.
Re: DRSSTC frustration
Marko, Tue Oct 09 2007, 09:49PM
I guess I'l have to remove the CT connections completely and somehow solder the cables to CT outputs in air. As it is the thing would be very hard to insulate with silicone, and I guess it's my best try for this bridge.
Yet still it may arc to another CT set and blow through wire insulation. Heck, it may blow my GDT too now.
I'm never safe with these things...
Marko, Tue Oct 09 2007, 09:49PM
I guess I'l have to remove the CT connections completely and somehow solder the cables to CT outputs in air. As it is the thing would be very hard to insulate with silicone, and I guess it's my best try for this bridge.
Yet still it may arc to another CT set and blow through wire insulation. Heck, it may blow my GDT too now.
I'm never safe with these things...
Re: DRSSTC frustration
Sulaiman, Tue Oct 09 2007, 11:24PM
Marko,
to arc from the secondary base wire to the CT implies high voltage on your "earth" wire.
If you have a long earth wire or a poor earth this could happen.
I use my TC in the shed or garden with a nearby earth rod,
if you can't get a good earth try several meters of aluminium cooking foil layed on the concrete/ground/floor,
makes a good earth/counterpoise. (with your existing earth for 'safety')
Sulaiman, Tue Oct 09 2007, 11:24PM
Marko,
to arc from the secondary base wire to the CT implies high voltage on your "earth" wire.
If you have a long earth wire or a poor earth this could happen.
I use my TC in the shed or garden with a nearby earth rod,
if you can't get a good earth try several meters of aluminium cooking foil layed on the concrete/ground/floor,
makes a good earth/counterpoise. (with your existing earth for 'safety')
Re: DRSSTC frustration
Marko, Wed Oct 10 2007, 12:32PM
Sulaiman, my secondary base ground is completely separate from the coil and mains ground, with specific reason to prevent these flashovers.
They happen specifically between positive pole of my bus cap and feedback CT input.
Interestingly they were small never blew anything even though I grounded the - of my low voltage section
Until now, when control board got completely fried.
Marko, Wed Oct 10 2007, 12:32PM
Sulaiman, my secondary base ground is completely separate from the coil and mains ground, with specific reason to prevent these flashovers.
They happen specifically between positive pole of my bus cap and feedback CT input.
Interestingly they were small never blew anything even though I grounded the - of my low voltage section
Until now, when control board got completely fried.
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