Re: Solid State Disruptive Coil Spark Gaps
Bjørn, Thu May 04 2006, 06:21AM

Even if it should blow up at the first live test it is a significant development. The modules are simple enough that almost anyone can do their own tests.

Re: Solid State Disruptive Coil Spark Gaps
Steve Ward, Thu May 04 2006, 08:24PM

Neat idea Terry. The only issue i see is that it cant quench... im not sure how much of a drawback that is really going to be. Are you planning on firing it up with a Tesla coil soon?

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Thu May 04 2006, 10:11PM

Hi Steve,

The latest report with all the circuit details is here:



It seems to be working perfectly!!

I was originally going to make a little Off-Line style coil that would be easy and simple but the SIDACs were too low of current (we really don't know "how much" current it takes to blow them )) So I got to thinking about and IGBT assist and here I am...

I hope to get a little coil going soon (waiting on #40 wire )

It cost about $16.30 per 900V section so it is kind of expensive for a hobby 15kV NST that might need 23 sections at $375!!! But that cost is trivial for say a museum or commercial coil system... LOTs of uses in spark gap replacemtn really. It can easily be adjusted to run those big IGBT bricks >:)))

But I am really thinking of OLTC, flyback, ignition coil, MOT, etc. systems that run at lower voltage but higher current. I seem to be going for smaller super simple coils these days that anyone can whip up and play with ) No, transformers or iron, no "real" brainy electronics... Just small simple and fun stuff :o)))

I forgot to mention it is all Public Domain... I don't do the patent mess )) So party hardy...

I have no idea about the quench... However, I have a 30V power isolated supply on the gate circuit and a TO-92 transistor could drop that gate voltage like a rock, perhaps with just a little 555 timer added... A "quench circuit" would have to start up within say a microsecond and rip the voltage down after a certain time. The 100 ohm gate resistor allows the power supply to stay up through all that if it can setup really quick... Probably a simple circuit addition, but I have not thought about it at all...

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Fri May 05 2006, 02:55AM

Hi,

I compared my new SIDAC / IGBT circuit to a bare SIDAC to see how the losses compared.

At low currents the SIDAC was not super lossy. However at high currents, the SIDAC was very lossy and probably would not work for a spark gap in a Tesla coil at all. I wrote up a little blurb here:



The bare SIDACs worked fine for my DF-SRSSTC trigger circuit and it seems to work ok in some low powered stuff. However, if you need to push over say 50 amps, you had better throwin in the IGBT thing

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
teravolt, Fri May 05 2006, 03:33AM

like your circuit Terry. do you think this circuit could be usefull for clamping over voltages on mosfets? If the sidacs are replaced with transorbs do you think it could be used as a clamp

Re: Solid State Disruptive Coil Spark Gaps
Part Scavenger, Fri May 05 2006, 04:09AM

Man what a sweet idea! That's almost as efficient as Steve W's DRSSTCs! SSDCSGTC, that's a finger full. SSSGTC maybe?

Cool, cool, cool. Thanks for sharing Terry!

Re: Solid State Disruptive Coil Spark Gaps
Desmogod, Fri May 05 2006, 04:34AM

Didn't TDU experiment with something similiar? His SSSSSTC I believe.

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Fri May 05 2006, 06:03AM

Hi,

like your circuit Terry. do you think this circuit could be usefull for clamping over voltages on mosfets? If the sidacs are replaced with transorbs do you think it could be used as a clamp

I don't know why not. It is fast and could clamp one heck of a lot of current. But you have to use SIDACs. Transorbs and such would turnoff too soon. You need the SIDACs to stay shorted for a long time even if the voltage drops.

Didn't TDU experiment with something similiar? His SSSSSTC I believe.

Yes. His stuff is here:



He said he was having problems with quenching, but that may also have been due to the SIDAC's poor high repetitive current losses. I am not sure about the quenching yet.

I am trying to figure out how to make a coil with it now out of all the stuff I have laying around. I had realy not planned any of this... Now I have to make yet another coil

That's almost as efficient as Steve W's DRSSTCs!

It is actually more efficient than just shorting the gap with a wire too!!



Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Bert, Fri May 05 2006, 01:02PM

Great work Terry!

I suspect the circuit can easily be made to quench by using a triggerable IGBT stage at the base of the stack. By removing the triggering signal at the first or second notch, energy transfer back to the primary cap should be virtually inhibited (except for small transformer action back through the free-wheeling diodes).

BTW, you may also need to add voltage equilizing resistors across the IGBT's when cascading them.

Re: Solid State Disruptive Coil Spark Gaps
Steve Conner, Fri May 05 2006, 03:20PM

Ohh, now that is clever!

I wouldn't worry about it being incapable of quenching. If the coil is properly designed, the sparks should eat up the energy quick enough that it doesn't really matter. Just as long as it turns off quick enough that it doesn't latch on permanently and short the charging supply.

Can anyone think of a way to make it triggered? (ie simulating a rotary gap instead of a static) I'd be inclined to start by just clobbering the top of the stack with a positive HV pulse to try and turn a few of the SIDACs on.

I don't think Bert's method would work either for triggering or quenching. Turning on one stage only makes about 1000V of difference to the breakdown voltage, and turning a single stage off would cause uneven voltage distribution.

Re: Solid State Disruptive Coil Spark Gaps
Bert, Fri May 05 2006, 04:26PM

Hi Steve,

I agree that triggering and quenching in this manner will become increasingly difficult as the number of stages is increased, but it should easily work for MOT powered coils. A more clever approach may be necessary for higher voltages.

I disagree that there will be little impact on performance with no quenching - poor quenching on disruptive coils shows a very marked performance impact. Once the bottom switch is "softly" turned off (say at the first or 2nd notch), it merely needs to stand off the induced primary voltage from transformer action from the resonating secondary. Assuming that similar (i.e., low) coupling coefficients are used as for other "disruptive" coils, a single 1200 - 1700 volt IGBT may do the trick (assuming it also has a free wheeling diode). The fact that there is now an uneven voltage distribution across the entire switch shouldn't matter as long as we can turn it off at the right time. Since it also becomes increasingly easier to quench during subsequent notches, perhaps one could aim for 2nd notch quenching instead of first.

For synchronous triggering, how about connecting a small HV pulse transformer secondary in the main current path and hitting it with a triggering pulse. You could do this on the bottom of the IGBT chain (using a negative-going spike) to keep the insulation needs of the transformer reasonable. You could even put the triggering transformer in the ground return of the charging path in order to keep it out of the high current TC primary path.

Bert

*mod edit fixed double post*

Hi Steve,

Hmmm.... after thinking about it a bit more, you may be right re: quenching not being as great a factor, since this is a more efficient "spark gap" it wouldn't dissipate as much energy as regular spark gaps, thereby allowing more energy to cycle back into the secondary on each transfer.

Looks like the real proof is in the testing....

Bert

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Fri May 05 2006, 09:47PM

Hi,

I posted another paper at:



Mostly dynamic power and resistance measurements just to double check things. The server is real busy these days so you might have to try a little to get in.

I was contacted by a person that has a big async DC MOT coil (60 inch arcs) and he can make PC boards. He is an engineering manager type so he knows stuff and is willing to spend some money so the project is underway!!!

I am not planning on doing anything with quenching or triggering at the moment. Too much to do just to get the first one going!

Cheers,

Terry

*mod edit fixed double post*

Hi,

Yet another paper...



High current tests...

The IGBT I used sort of conks out at 380 amps and falls out of saturation even with "40V" on the gate! But it does not blow up and works well to 350 amps peak. Any IGBT could be used, so I may look for another...

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Tesladownunder, Sat May 06 2006, 05:53AM

The reason I worry about the quenching is that with my SIDAC string in place of a spark gap, sparks were only 2 inches with 5kV input. However, add a series spark gap and sparks increased to 6 inches. This does not sound like a high current problem causing the SIDAC to become inefficient, but more like a quenching issue.
If one had to arrange the IGBT's to turn off then the simple system gets more complicated.

Great idea though and look forward to testing with a coil.

If it works I will try to find out when I said something like "just wait until you get SIDAC bricks and see what they do for TC's"

Peter

Re: Solid State Disruptive Coil Spark Gaps
robert, Sat May 06 2006, 11:15AM

Just out of interest, it would perhaps work with a (fast) SCR too if a antiparalell diode would be used.
It just takes a little different gate circiut.
Now i dont really know if suitably fast SCRs are avialible at the necessary currents and if the price would be acceptable but chances are that it is.

Re: Solid State Disruptive Coil Spark Gaps
Steve Conner, Sat May 06 2006, 05:21PM

Just to remind folks that 4hv has a rule against double posting. Please don't double post unless 48 hours or more have elapsed _and_ you have new information to add. Otherwise, please just edit your post using the edit button, which looks like this

We do this because we don't want people posting just to bump their thread and get it marked new.

I combined Terry's and Bert's double posts into single posts.

robert: SCRs don't have high enough di/dt capability to be useful in a Tesla coil. If they did, we would use them in preference because they give more bang for the buck than IGBTs. The guys on TCML went through all that when we were planning the OLTC a couple of years back. I once calculated that once the frequency of your coil drops below 25kHz, inverter grade GTO SCRs start to give more value for money in both OLTCs and DRSSTCs. (GTOs switch faster than regular SCRs even when you circuit commutate them rather than using the GTO mode.)

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Fri May 12 2006, 02:03AM

Hi,

I has been 48++ hours and new test results are in )))

I still am a bit naughty for posting from another list... >:))



But the whole world of tesla coiling "changed" today(!!!!)... I have "been around" ""long enough" to "know" too ;))))))))))))))

But all should enjoy )))

Sell those "old" spark gaps on E-bay while you still can :o))))

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Fri May 12 2006, 03:05AM

Looks good Terry and i have to admit, you got me.
Anyways, i just started drafting a prototype spark gap circuit to run with my 4kV/38mA coil. I just ordered some Sidacs and i already have some IGBTs I can use. I'll cut a board tomorrow and hopefully by early next week have this thing running and get some data from it. I'll probably being running about (6) IGBTs in series. Should be interesting!

Re: Solid State Disruptive Coil Spark Gaps
Desmogod, Fri May 12 2006, 03:15AM

Curious considering my "Future of Tesla Coiling" thread was posted about 24 hours prior to this.
Do you have any pictures of operation, ideas on efficiency etc?

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Fri May 12 2006, 10:36AM


Check the two papers Terry has already posted as well as his latest post. He has lots of data there.

Re: Solid State Disruptive Coil Spark Gaps
Steve Ward, Sun May 14 2006, 05:42AM

Hey Conner McSteve,

a thought just popped into my head... how does your OLTC perform if you let it ring out for many notches? Is there a major hit in performance? Terry's "spark gap" is basically a simplified OLTC that doesnt have the ability to quench, so it would be easy to set one of your OLTCs like this and compare performance.

Terry,

We can see that your switch works just fine as a switch, but until you test it to make sparks, we will never know for sure how it works in a TC. Your test cant make assumptions about streamer formation, since we dont completely understand that part yet, so someone will just have to test your switch and see how it "really" performs.

I still prefer the "complex" DRSSTCs, much better use of the silicon i think.

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Sun May 14 2006, 12:41PM

In regards to quenching, it may not be necessary with a high efficiency solid state switch. Remember, that in a conventional Tesla coil, quenching is necessary as energy transfers back and forth between primary and secondary and a considerable amount of the energy will be lost as heat due to losses within the spark gap. In a spark gap coil, we would like the spark gap to quench (usually within a few notches) to reduce these spark gap losses and keep most of the energy on the secondary side. However, since there is no spark gap or source for high losses with a solid state spark gap, quenching may not be necessary.

Of course, if the solid state spark gap turns off too soon or at a point where energy is at a maximum on the primary side, that could reduce performance.

But as was mentioned, lots of experimentation still needs to be performed to see exactly how this new circuit works, what effects no quenching has, and so far . . .

Re: Solid State Disruptive Coil Spark Gaps
Steve Conner, Sun May 14 2006, 01:15PM

Hi Ward McSteve,

The OLTC really worked much the same if I let it ring out. The spark output was no different as far as I could tell. The primary circuit did get a bit hotter though due to more losses, and the charging voltage tried to kick up higher due to boost converter action, what with the switch being on longer.

Better use of the silicon is all very well, but "pretty is what works" It seems to me that there's still an entry barrier to DRSSTCs due to them being hard to understand, although Steve Ward has done a lot to lower that with the simple feedback driver and ready-made PCBs. Terry's new thingy is "Just like a spark gap but solid state", and it comes with the trusted Fritz brand name so folks will be comfortable with it.

I think it's kind of like the Chevy vs. riced-out Honda debate. The DRSSTC is the "Hot import" of Tesla coiling. You can make that Honda go faster than a Corvette, but it takes a lot of work with strange new technologies that can go wrong spectacularly. There may not be a clean answer, and there will always be plenty of champions on both sides.

I believe a DRSSTC can give about 4ft of streamers from four TO-247 IGBTs. I personally got 36", and trashed the IGBTs in the process, but I think others have done better since. I was running 600V devices on 400V DC, and I don't think anyone has ever tried TO-247s on a 600V DC bus, which would be the fair comparison since Terry's stack uses the 900V devices.

If you can't get 4ft from four TO-247s, there's always the OLTC record, 6'9" with 4.2kW :P If you can beat that (either directly, or scaled, by achieving bigger Freau and Watts numbers) we'll know the higher voltage tank circuit is more efficient than my 1kV system was. Break out the MOTs Terry!

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Sun May 14 2006, 02:41PM


Other than some of the finer points and details regarding the DRSSTC, i don't believe the DRSSTC concept is hard to understand at all. The concept is quite simple and really not at all more difficult to understand than the conventional spark gap coil, although the implementation using electronic devices makes them a bit more complex.


Correct. I have run my DRSSTC II system using 600V TO-247's as a drop in replacement for the 40N60's and have achieved output arcs exceeding 7 feet with these. There really is no difference between the TO-247s and ISOPAKs other than thermal properties (assuming identical dies). If you can cool a TO-247 properly, it should perform no better or worse than the same die in a SOT-227 package. I don't know why everyone believes these SOT-227 devices have some sort of magical property to work more profoundly than a TO-247. Its just thermal impedance, nothing more . . . If you're smart enough to develop a system to provide adequate cooling, that the TO-247 will work just as well.

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Mon May 15 2006, 04:39AM

Hi,

There is a new paper here where I try to "tell all" in one single document:



Copy and past the link I guess... Or go here...
Going to take me a few years to figure this "forum" stuff out

This server does not have nuclear terrorist defenses so it should be easier to get through to.

It sounds like Dan might get the first "real" system going! I wired up a quickie with the two modules I had. It is not optimal at all but it did make sparks! I made a little 20 meg movie:



I need to get boards on order. and a few other parts... 20 IGBTs will be here Tuesday. I am still working on heatsinking.

how does your OLTC perform if you let it ring out for many notches? Is there a major hit in performance?

Remember that the OLTC is a fairly high loss system. Low voltage and high current. The SISG thing is high voltage at lower current so the losses are far less like in a conventional coil. The primay "Q" is proportional to Lpri so this system can support far higher primary inductances for far higher "Q". However, I did run it into like 650nH/600nF here for high current testing which is similar to the OLTC case and the resistance is about 0.050 ohms:



Dan explains that now the gap losses are "gone" so running a coil with many notches should not be a problem. Do note that if you run the primary without the secondary (or out of tune), the caps might explode now since the firey spark gap can no longer be counted on to burn up the power!! Also, many notches drives up the primary RMS current a bit. System losses are sort of "all different" now.

I believe a DRSSTC can give about 4ft of streamers from four TO-247 IGBTs

One should check out this fire breathing IGBT in the SUPER TO-247 package!



Junction to case is 0.20 C/W. 1200V, 120/240 amps and 595W!! I have run them to 800 amps and they seem to "like" that!!

Rell.com has like 7000 leaded versions and is trying to sell them for like $8 each!! But a part broker might have already grabed them... They normall go for about $15. Mounting them to a heat sink is a challenge though. At 600W that would be water cooled copper! Fortunately in the SISG case, just a little heat sink is fine.

I still prefer the "complex" DRSSTCs, much better use of the silicon i think.

There is one big advantage the SISG might have. It should be very hard to break. It is "made" out of over voltage devices and everything is very well protected. I think the circuit can take a full streamer hit without damage. That alone might be its claim to fame in the commercial coiling world.

Of course, it might pave the way for future stuff too. Looke what Jimmy and all did with the OLTC!!

All the small testing is done now. Mark, Dan and me are ordering parts and boards for a full system, so we'll see how it goes!

Cheers,
Terry

Late news...

I have updated the master "tell all" document at:

http://drsstc.com/~sisg/SISG.pdf

I will try to keep it "updated" as time allows... A little slow now while I wait for parts...

I now have all the parts on order for a ~250W dual MOT coil. Should be going by next weekend... Mark or Dan will probably have their's going sooner Pretty good for "idea - to final working coils" in three weeks!!

Peter mentioned "The reason I worry about the quenching is that with my SIDAC string in place of a spark gap, sparks were only 2 inches with 5kV input."

My 14.6 watt test at 1.8kV got to 5 inches with a 150nF primary cap

I think the SIDACs can take about 100 amps peak for "one" cycle and then they seem to conk out or go highly resistive. That was the problem with your test. Many nights I stared at your site wondering "why" it did not "work"... I think I know know... SIDACS just can't pass the primary current for any length of time... But they can "trigger"

If this all works out, as it now appears it will, it will be real cool But what is even cooler is all the extensions and new stuff this could introduce!! People already "got plans" for sync triggering and quenching... Even talk of a "PIC" that could detect "situations" and act "appropiately"!! We can only hope that a giant thing may come of it like the DRSSTC did for solid state coils!!! Plans of even a Wysock model 13 class SISG gap

Some think that with all this modern stuff, that Tesla coils have gotten boring. But really is is just a 100 year old technoly "catching up" to the modern world!! It sure is hard!!! But it is coming very fast now

I look forward to arcing the next coil to all the SISG circuits to see if I "can" blow it up There is a chance a negative streamer could mess up the gate voltage in the negative direction delaying or turning off the IGBT at a bad time... Probably should use "uni-directional" TVSs ) If it gets to the point where one "can't" blow it up, that is a real big step in this sport!!

Cheers again,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Dr. Drone, Tue May 16 2006, 09:52PM

Re: Solid State Disruptive Coil Spark Gaps
coaster_chris, Wed May 17 2006, 08:56AM

That's a job very nicely done Terry!!
The scope readings show good effecient results, and now seeing the movie of it al working...
SWEET! !

Chris

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Mon May 22 2006, 06:36AM

Hi,

Today I finally got everything working!!!

Firing at 3600V 150nF 120BPS 117W

It could arc to ground 23 inches!! 23 inches at 117W puts the Freau number at 2.13!! I ran out of time today to do any other tests but everything seems perfect!! It could probably arc further if I tried to tune the coil in and everythig

The IGBT sections seem to be working perfectly!! I wrote up the latest details in the ongoing PDF file here:



Mostly pictures of all the stuff. Here is a big picture of the final gap:



Here is an arc (15 inches):



There is a newer movie here done a few days ago (14 MB):



The MOT charging system was messed up so I was working on that the last two days.

I hope to get it going at the full 5400 volts tomorrow. Maybe I can get 35 inches out of it at 262 watts

Cheers,
Terry

Re: Solid State Disruptive Coil Spark Gaps
ragnar, Mon May 22 2006, 11:22AM

Terry! That's just... bloody brilliant!

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Mon May 22 2006, 11:29AM

Awesome Terry. I haven't got around to getting my set-up running yet as i've been busy finishing up a few other things, but will get to it soon.

Dan

Re: Solid State Disruptive Coil Spark Gaps
GimpyJoe, Mon May 22 2006, 02:37PM

Nice! Do you think it could work reasonably well with just one IGBT section and run on mains with a voltage doubler or tripler? That would be great, a small lightweight coil with the simplicity of a SGTC and the portability of an SSTC.

Re: Solid State Disruptive Coil Spark Gaps
williamn, Mon May 22 2006, 02:41PM

Very cool Terry! You have my attention, I started work on one of these coils this weekend.

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Mon May 22 2006, 03:08PM


Isn't that what an OLTC is???

Re: Solid State Disruptive Coil Spark Gaps
Dr. Dark Current, Mon May 22 2006, 05:14PM


..but much simpler without any timers...?! Maybe another contribution to my "Super Simple Tesla Coil" ?

J.M.

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Mon May 22 2006, 06:21PM

Nice! Do you think it could work reasonably well with just one IGBT section and run on mains with a voltage doubler or tripler? That would be great, a small lightweight coil with the simplicity of a SGTC and the portability of an SSTC.

That is actully how all this got started. I was trying to make a simple small coil with SIDACS (like my DF-DRSSTC trigger circuit) but they did not have the current drive ability. So I started looking for a way to get an IGBT to help them... The rest is history I guess I can start thinking about that project again now that this is pretty much done

Unlike the OLTC, there are no timers, controls, or other brains... It really is just like a "spark gap" (but DC). One can fiddle with the SIDAC voltages to get it to fire at any voltage. One section could probably do say 1000, 1100, 1199.99 volts :o) Of course there are bigger higher voltage IGBTs too. Nothing is very critical and there are many things that could be adapeted or changed around. So far, an SISG system has never failed I think over heating the IGBTs is the only obvious way and that is a bit hard to do.

Here is the latest news as of an hour ago. This pretty much finishes the project up here, be sure and see the nice movie!! I guess I forgot to "talk"

--------------------

Hi All,

It's been 24 days now and it is pretty much all finished )

Without messing with coupling, tuning (probably real close), or any thing like that, I can fairly easily hit 24 inches at 117W - and 30 inches at 183W. The Freau number there is 2.22 in both cases. That number seems very "constant".

I was only able to go to 5 sections instead of six due to the limited safety area in my basement. With six sections, it should get to 263 watts for 36 inches. The whole mess could probably be more optimal, but my goal here was just to get "one" working )

I made a movie here, with a good camera this time, of it doing 30 inch hits (25 MB MPG movie file)



Got to the lower right and click "free". It makes you wait about 30 seconds to read the ads and click off the popups. Then type in the funny letters and download. I have been using a lot so buy everything in the ads and donate to them ) It certainly solves the big file distribution problem!! It is a plain MPG file that even a modern DVD player should play if you burn it to disk...

The little heat sinks get to about body temperature for short runs which is just right according to the calculations. Bigger heat sinks and/or a fan would be good for extended operation.

The full data on everything is here (might take a while to DL since it is 'busy" ):



I still need to finish this up, but it is up to date as of last night. Let me know, off list, if there are any errors or something I should add or polish up. It was written in parts, very fast But it is the best way to document stuff like this. A far cry from the OLTC :o)))

Nothing has blown up yet and everything seems perfectly happy. The only bug was the DC MOT charging which I had to whip up a high voltage blocking inductor for. But that was a mundane typical MOT coil issue.

You have to be careful to turn up the variac until is just starts to run smoothly (120 BPS) and no more. If you turn up the voltage too high, the BPS rate can go up dramatically and overheat the IGBTs. Higher BPS does not seem to increase spark length other than making them sound funny. Sort of "screetchy".

Thanks for everyone's help, input, and encouragement!!! Looks like we all have a new toy )))

BTW - The dual MOT system has an extremely dangerous primary system!! Be very careful when working on them especially now that there are electronic circuits and stuff in there to fiddle with. Be ultra sure that the power is off before working on them. Be very careful of the output arcs since it is possible for a primary to secondary break over to present lethal currents on the secondary. Note too that the primary circuit can be almost at full power, but totally silent!

--------------------------

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Mon May 22 2006, 07:07PM

Looks good Terry. I think the next test is to make a true comparison between a spark gap coil and SISG coil ensuring identical break-rates.

Re: Solid State Disruptive Coil Spark Gaps
Reaching, Mon May 22 2006, 08:45PM

hehe, exactly what i tried to build long ago with an scr and you did it with simple parts. incredible.
mhh, okay, i have many 600volt high pulsed current igbts, capacitors, a mot, coils etc, . have to make one

mhh, i searched but i didnt found anything called sidac in germany. a sidac is called diac in germany but no one sells them. now thats the question, can i use triacs as a sidac replacement? or can i use a transient voltage surpressor instead of the sidacs, something like this?

Re: Solid State Disruptive Coil Spark Gaps
Self Defenestrate, Mon May 22 2006, 09:25PM

Finally a simple solid state option for my 1kv coil. No more "shrinking gap" effect with this. Cool.

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Mon May 22 2006, 10:22PM

mhh, i searched but i didnt found anything called sidac in germany. a sidac is called diac in germany but no one sells them. now thats the question, can i use triacs as a sidac replacement? or can i use a transient voltage surpressor instead of the sidacs, something like this?

A TVS will not work since the SIDAC has to "stay on" "longer"... The "SIDAC" (no one knows, or will admit, to what SIDAC "really" stands for) has a data sheet here.



One may be able to wire up things like a DIAC to do the same function... I don't know...

Teccor makes them:



Here is probably far far more than anyone wnats to know about them (94 pages!) )



A wiki -



Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Mon May 22 2006, 10:58PM


Thats an easy one. SIDAC simply stands for Silicon Diode for Alternating Current. Its a pretty old term.

Dan

Re: Solid State Disruptive Coil Spark Gaps
Steve Conner, Tue May 23 2006, 01:24PM

ON Semiconductor make SIDACs, you may be able to get samples. They really aren't quite the same as diacs: a diac is a small signal device for triggering, a SIDAC is much beefier.

If you don't have access to the big electronics distributors (maybe your mom won't let you use her credit card ) I heard that SCRs can be used as ghetto SIDACs. If you leave the gate terminal disconnected, they will self trigger when you exceed their rated voltage. You might need to connect the gate to the cathode through a largish resistor to get it working stably. Also, you'll still need the TVS to stop the IGBT gate from getting fried.

Now I think about it: if we used SCRs instead of SIDACs, wouldn't that allow us to make a triggered gap? It would just be a case of pinging a few of the SCR gates at the earthy end of the stack, and the rest would trigger by themselves.

SCR gates are easy to drive, so you could conceivably even trigger them all. I've seen a commercial gadget for this, that consists of a ferrite toroid transformer for each SCR, with a single heavily insulated cable passed through the middle of all the toroids. You dump current through the cable and it triggers all the SCRs at once. This would never work to drive IGBTs, but using the SCRs as helpers, it's a different story.

That would get rid of the objection that SCRs aren't supposed to be used in this self-triggering mode (although I once read a Philips datasheet where it said that it doesn't hurt them) and also get you a nice triggered gap with a very wide operating voltage range.

Terry is a genius

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Tue May 23 2006, 01:58PM


Yep. I've built a high rep rate high voltage switch (35kV) using SCRs in just this fashion for a client two years ago. Works great. Although the SCRs do self-trigger, we used TVRs in parallel with all devices so they would break-down before the SCR. Our particular switch was used to discharge a 0.1uF @ 35kV at rates up to 100Hz.


We used individual drive transformers with separate primaries, but i've also seen them drive with a single primary.


Sure it would. I've already built a circuit like this. In fact, you don't even need transformers at all. One single gate signal turns on the entire stack
of IGBTs. I posted this circuit awhile back, but can repost again if interested. Works extremely well and I was planning on using it to create a MOT based SSTC, but at the time, the DRSSTC hit the scene, and I abandoned the work on that particular project. It would work well as a spark gap though ,but would require an external voltage to run and trigger, as opposed to Terry's which is just drop in and go.

Dan

Re: Solid State Disruptive Coil Spark Gaps
Steve Conner, Tue May 23 2006, 03:05PM

I'm talking about a switch that uses SCRs to trigger IGBTs, in the same way that Terry's switch uses SIDACs to trigger IGBTs. Are you saying that you built that already?

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Tue May 23 2006, 03:29PM

Yes, i have. This was used in a crowbar switch. But you don't need the IGBTs. The SCRs alone can handle the current. With SIDACs, you need the IGBTs because SIDACS cannot handle the current.

I've actually done two designs, the first one being with IGBTs alone and using a single drive signal to turn on the the entire stack. The second design used SCRs alone in place of the IGBTs. This is more in regards to your comment about the "triggered" design, not the self-triggered design like Terrys.

As far as self-triggering, i don't see any reason why you could not replace the IGBT stack i was using with a single SIDAC with a voltage divider and a similar discrete firing circuit to initiate the IGBT stack.

Re: Solid State Disruptive Coil Spark Gaps
Reaching, Tue May 23 2006, 05:35PM

mhh, i got something to work with an scr ,some zeners and a few resistors but i dont know if it would work in tc duty.
if i understand it correctly, the sidacs have a minimum on state current, they will stay on until the minimum hold current drops, exactly like a scr, i wonder that they really turn off. my test setup uses a 300volt zener ,a 100k resistor and a 600volt scr. if i turn up the voltage to say 302volt, the scr turns on and stays on, maybe thats the way to go for those who cant get sidacs. but i dont know if this setup will turn off as a spark gap replacement.

hehe, okay, Update

you dont even need sidacs, it works with scrs, i build a single module which should switch at 360volt hooked it up to my 400volt dc transformer , made a small primary,secondary,mmc really far out of tune, lol, but i got 5mm arcs with a nice "humm" now i know, it works with scrs instead of sidacs with a small circuit change. now i can order some parts and build my scrsgtc (or sisg without sidacs,)

heres the modified shematic without sidacs but with an scr

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Tue May 23 2006, 08:48PM

Sweet

This is probably smaller and cheaper than the SIDACs! It is fun to see the new ideas people come up with for this!! I bet someone is going to put a microprocessor on it soon ))

SISG could also stand for Silicon Spark Gap (SiSG) too. Then "SiSG" could sort of cover all the solid state spark gap replacements... But we'll just have to see where the future goes )

I gotta get my old "spark" gaps on E-bay soon!!! Sell them before they are worthless... Might be too late

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Marko, Tue May 23 2006, 09:06PM

I think you should add a resistor, some few hundred ohms in series with SCR to prevent blowage from masisve current going trough the gap, you want the IGBT to switch it (not the SCR )?

For some more serious coils maybe.

PS.
I don't know if this is needed for Sidac's but I had SCR's burn up easily in similar conditions.
I think it's going to share too much current with IGBT and (maybe) blow up if overstressed.

Re: Solid State Disruptive Coil Spark Gaps
Steve Conner, Wed May 24 2006, 11:34AM

That's pretty cool Reaching! Try removing the three zeners and see if it still works with the SCR self-triggering.

Re: Solid State Disruptive Coil Spark Gaps
Reaching, Wed May 24 2006, 12:14PM

mhh, i tried it yesterday too and i blew up an scr trying to self trigger it. but i dont know if it will work when you put say 6 boards in series. cause the scr needs a few mA to switch on in my case 8mA, so thats 3,6watts at 450volts so use heavy 2 watt zeners or so. i tried R1 as 100k and the scr switches on, but i dont know what happens if you put 6 boards in series. i dont have the right equipment to measure whats going on in this circuit. in a few days i can finish a nice test setup with 6 boards, a mot ,74nF 4kV mmc and a 7,5x20cm secondary with a nice sphere toroid, that should work fine for the beginning and for further tests.

Re: Solid State Disruptive Coil Spark Gaps
colin heath, Thu May 25 2006, 06:17PM

Reaching said

if i understand it correctly, the sidacs have a minimum on state current, they will stay on until the minimum hold current drops, exactly like a scr, i wonder that they really turn off. my test setup uses a 300volt zener ,a 100k resistor and a 600volt scr. if i turn up the voltage to say 302volt, the scr turns on and stays on, maybe thats the way to go for those who cant get sidacs. but i dont know if this setup will turn off as a spark gap replacement.

SCR's or Thyristors as us Brits know them Will turn on without a gate current if rate of rise of voltage or current exceeds the rating of the device (thats why they use snubbers). However they will not turn off until the voltage or current reverses. Great on an AC system but difficult on DC.

Cheers

Colin

Re: Solid State Disruptive Coil Spark Gaps
Reaching, Fri May 26 2006, 12:46PM

okay, i got it to work on 600volts with my new tvs, scrs etc. it works fine and i get ca 5cm streamers from my test setup(with a 600volt igbt!) . but now i have a problem i cant fix. i cant put two boards in series with the modified shematic,. maybe someone can help me to find the bug, .

the next problem is, that i cant use the scrs to switch at its maximum voltage without gate connected, maybe some internal protection or so, so i need to trigger them at a certain voltage.

maybe it´ll work like this

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Fri May 26 2006, 11:39PM

Hi,

I never thought that the SIDACs might be hard for folks to get

I have about 45 of the 300V ones ( PN# 3000F1-ND) I could drop in an envelope(s) and send over there... Let me now if anyone needs some. We''ll just say small quantites are free

First come, first serve... If I run out... Well..., I'll have to think of something...

Write me a private message thing on this forum if you need some. It takes about a week or two to get over there (like an eternity...). Include the "exact" mailing adress just like it needs to be on the mailing lable for your country. Make a picture if it is like in chinese or somthing Let me know how many you "need". I'll just write it all off to R&D

I thought the IGBTs might be a problem... But we could bulk buy SIDACS on this side of the water and send them over if needed?? DigiKey has like 700 left...

The SISG.pdf file has like 700 downloads for this!!!! I can see SIDACs being in short supply

I know practically nothing about SCRs, so I can't help much there...

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Steve Conner, Sat May 27 2006, 02:43PM

Terry,

Just about any component is hard to get when you don't have a credit card, and your dad can't be bothered ordering stuff from DigiKey for you. :P Whenever I've done projects for 4hv, I always try and use the most popular components I can, but still I get e-mails asking if they can replace the UCC37322 driver chip with two 2N3055s and a piece of wet string. Wet string because it's so hard to find resistors here in xyz country.

There's no getting round the fact that sometimes you need exotic components to do exciting things. I wouldn't worry about the component availability: if people are genuinely fired up to build the SISG, they should be able to manage little setbacks like not being able to find any SIDACs.

We have done 4hv.org worldwide bulk buys before, and if the SISG takes off, I guess we could end up doing a bulk buy of SIDACs and 1200V IGBTs?

Re: Solid State Disruptive Coil Spark Gaps
HV Enthusiast, Sat May 27 2006, 05:12PM


Little setbacks, like not being able to find any SIDACs, usually lead to new innovations. That wet string might be the next craze in solid state Tesla coiling . . .

Re: Solid State Disruptive Coil Spark Gaps
Steve Conner, Sat May 27 2006, 06:17PM

I thought you tried wet string for "Passive Current Limiting" in DRSSTCs a while back, but it never caught on. Don't hit me, I just ordered your new book from Amazon.

On the self-triggering of SCRs: I went and looked up the datasheet for some Philips T0-220 SCRs I have here.

http://www.semiconductors.philips.com/acrobat/datasheets/BT152_SERIES_1.pdf

It says that the device can withstand 200A/us di/dt when it's triggered properly using the gate, but only 15A/us when it's self-triggered by overvolting from anode to cathode. And that self-triggering is "Not recommended". It only seems to work for the 400V and 600V models too, I guess the 800V one just asplodes.

Re: Solid State Disruptive Coil Spark Gaps
Marko, Sat May 27 2006, 11:50PM

Could they be triggered by some kind of simple resistive divider on gate (if we are so glad to leave the zeners out) ?

Re: Solid State Disruptive Coil Spark Gaps
Desmogod, Thu Jun 08 2006, 02:47AM

terry,
Is there any chance you can post the pcbexpress files for your pcb's ;)

Re: Solid State Disruptive Coil Spark Gaps
Self Defenestrate, Thu Jun 08 2006, 03:08AM

Started breadboarding for a try, still looking for a good SCR though. I'll post results as they come along.

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Thu Jun 08 2006, 08:23PM

Could they be triggered by some kind of simple resistive divider on gate (if we are so glad to leave the zeners out) ?

Maybe. You sort of need a "trigger" to charge the gate up and all. Perhaps just one SIDAC could be used and the others in the string replaced by resistors. Probably lots of ways of doing it.

Is there any chance you can post the pcbexpress files for your pcb's ;)

They are here under the main document:

Started breadboarding for a try, still looking for a good SCR though. I'll post results as they come along.

You can breadboard them fine. Just use heavy wire for the high current stuff.

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Marko, Sun Jun 11 2006, 08:52PM

I got an idea: could the triggering be done trough a current transformer, so sidac's/SCR need to conduct only a little of current while rapidly turning IGBT on?

Or that may lead to delay and overvoltage again...?

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Mon Jun 12 2006, 06:59AM

Hi,

Tonight I used the SISG for the lightning ball experiment in the other forum here. I did not think much about using it first since there was no time and it had to go!!

It fired twice:

1. 1800V 60e-6F into probably ~15ohms (97.2J). The timing on the SISG was set for 400uS and it turned off with about 800 volts still on the cap. The SISG survived this.

2. 5400V 60e-6F into probably ~15 ohms (875J). All the IGBTs shorted to zero ohms.

So ether the IGBTs over heated for the raw energy or the short timing opened them and and heating once again got to them. The IGBTs showed not physical damage at all (SUPER -TO247 package).

I have not had anytime to think more on it but I wanted to write it all down before I forgot.

More -- After some calculation, the instant thermal heating on the die in the first case was well below its rating. Breaking open the circuit at 400uS was also fairly easy.

However, in the second case the die critically over heat in about 50uS. The higher current (into about 8.22 ohms) dissipated 10X the power and the IGBTs never had a chance. Then they get hit with another 28 joules to finish them off for sure.

So easily explained and no problem at all for Tesla coil stuff. But the 8.22 ohms is probably good for a conventional spark gap now in the case of the plasma ball experiment. The 800V at 400uS gives great knowledge there A very complex dynamic high current ohmmeter...

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
vasil, Mon Jun 12 2006, 01:22PM

Just one question:
SISG topology can work with MOSFETs also instead IGBTs?
I have some small secondaries (higher frequnecies) around....

Re: Solid State Disruptive Coil Spark Gaps
Marko, Mon Jun 12 2006, 04:26PM

Yep, but mosfets will blow themselves up when you put 100's of amps trough their high ohmic resistances (power waste is I^2*R). You need IGBT with constant voltage drop to handle that current.

I think you don't need some seriously fast GBT's while there is only one hard transistent per bang..

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Mon Jun 12 2006, 04:30PM

SISG topology can work with MOSFETs also instead IGBTs?

Sure! Mosfets will not be able to take the super currents of IGBTs, but for smaller lower current stuff that is not a problem. The speed is not an issue since it is a simple "once per bang" switch. You will need an anti-parallel diode to allow high currents to pass in the opposite direction. I am not sure the FET body diode will like that in many cases. You may be able to use a pretty plain big diode for that since again speed is not an issue.

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Sun Sept 17 2006, 05:25AM

Hi All,

The SISG is the only coil I use now )

I only run at 4800V "still" due to space limits. It could go to 6800V if I take out the jumpers >:-))

In preparation for high speed pictures follwing TDU's work, I have a number of "big" streamer pictures online now:















The schematic is here:



A scarry coil in that it is "silent" till it "goes off"!!! And it packs more than leathal power!!! But a neat and easy performer so far ) Scares me and Gerry ))

A warning not to go playing with the streamers!! There is very little between you and "electric chair" currents there!!!

But the SISG continues to run flawlessly, happily, and impressivly... The Cp cap is underated as I have it, but a proper new cap will be ordered when this one blows. )

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Mark Dinsmore, Thu Sept 21 2006, 04:56AM

Hi,

Has anyone ever thought about using a laser capacitor charging type power supply to run a SISG? They are essentially high power constant current power sources, capable of kilovolts of output and at least hundreds of watts of power. The constant current (which I think is adjustable) would give you a nice, stable, and adjustable break rate, and eliminate the dissipation from the charging resistors. It would be essentially a very high power relaxation oscillator. They would be bulletproof in this application, as they are designed to charge caps that are suddenly discharged when the laser fires. They show up on ebay from time to time, or there might be some way to convert a tig welder into a similar source.

Mark

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Thu Sept 21 2006, 05:19AM

Hi,

As far as I know, a real dedicated HV cap charging supply should work fine. I use a MOT, diodes, and resistors just because anyone can easily reproduce those.

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
Tesladownunder, Tue Oct 24 2006, 04:47PM

If this is to be regarded as a stable sytem usable for long running museum demos then primary strikes need to be considered. I am still concerned about a primary strike letting smoke out even though the IGBT's are on at that stage.
Have you actually tested primary strikes or do you rely on dragons to keep them at bay?

Peter

Re: Solid State Disruptive Coil Spark Gaps
teravolt, Wed Oct 25 2006, 03:00AM

I like Reaching's modified SCR scematic to. why not get rid of the mosfet portion all together and replace the SCR with a hocky puck of about 1200v and use sidacs, or zeners, or a comparitor to trigger it. An inductive circuit would have to be in series to make enough inductive kikback to turn off the SCR. what does any body think. N.

Re: Solid State Disruptive Coil Spark Gaps
J. Aaron Holmes, Wed Oct 25 2006, 04:55AM


Those big "puks" look real neat at first, but then you look at the numbers. The turn-on times are awful. The turn-OFF times even worse. Add to that a very substantial voltage drop and they're pretty much unusable for this purpose. They'd eat a crazy amount of power during turn-on, I think (if your SIDACs didn't catch on fire first ).

Lately Dynex and a few other power semiconductor makers have started making what they call "pulse power" thyristors. Those may show more promise, but are undoubtedly very expensive. They are specifically meant to replace conventional thyratrons, and come in voltages all the way up to 12kV! I suspect the price tags are in the several-$k range, not unlike the bigger 6.5kV IGBT bricks.

Regards,
Aaron, N7OE

Re: Solid State Disruptive Coil Spark Gaps
Terry Fritz, Mon Oct 30 2006, 08:36PM

Have you actually tested primary strikes or do you rely on dragons to keep them at bay?

It is very difficult for a streamer to hit the primary in the new design. But I have been too chicken to actually try it A lot would depend on system power too.

Big SCRs will "punch through" and break if the dV/dt is too fast. In the case of the SISG, that is about 10++ times faster than they are rated. Maybe a low dV/dt coil coil be designed though. SCRs would be cool if they could be made to work.

Cheers,

Terry

Re: Solid State Disruptive Coil Spark Gaps
teravolt, Tue Oct 31 2006, 04:13AM

when DI/DT was brought up and punch through I agree. some time when I get more time I will investigate it

Re: Solid State Disruptive Coil Spark Gaps
J. Aaron Holmes, Tue Oct 31 2006, 05:01PM

No investigation of SCRs would be complete without taking a look at the "pulse power" thyristors now being offered by Dynex (and perhaps others) as I mentioned above. Perhaps these would be better? Not being much of an EE guy myself, I'm probably not the best person to take up such an investigation, however

For example:
(Dynex "pulse power" thyristors)

Note that the on/off times for these are WAYYYYY better than the average "puk" SCRs. No idea how much they cost (and, not surprisingly, nobody seems to stock them), however "a lot" is a fair guess!

Regards,
Aaron, N7OE