drsstc primary strike protection
Ben Solon, Fri Mar 30 2012, 09:19PMhey, i noticed here
that steve uses the .1 caps to protect the power electronics from primary strikes. the caps however are limited by their voltage rating and may punch through if the stike is bad enough though. i just had a thought: would something like a gas discharge tube with a breakdown just over the maximum voltages seen in normal operation? this way it would both suppress overvoltage due to bad conditions on the bridge(just like the tvs diodes and snubbers) and the primary strikes that would kill the protective features(tvs diodes and snubbers).Re: drsstc primary strike protection
dude_500, Fri Mar 30 2012, 11:08PM
Well, overvoltage shouldn't really burn out a TVS. That's the whole point of them. They breakdown and ensure that the voltage never exceeds their designed breakdown voltage. You can't put "too much voltage" across a TVS, because the device will prevent the voltage from going that high. All you can do is put too much power through them to physically burn them up. I don't think a typical ground arc could ever do that though.
That being said, I'm not exactly sure where you would put a TVS diode. Across the 0.1uF protection cap?
dude_500, Fri Mar 30 2012, 11:08PM
Well, overvoltage shouldn't really burn out a TVS. That's the whole point of them. They breakdown and ensure that the voltage never exceeds their designed breakdown voltage. You can't put "too much voltage" across a TVS, because the device will prevent the voltage from going that high. All you can do is put too much power through them to physically burn them up. I don't think a typical ground arc could ever do that though.
That being said, I'm not exactly sure where you would put a TVS diode. Across the 0.1uF protection cap?
Re: drsstc primary strike protection
Ben Solon, Sat Mar 31 2012, 01:23AM
yes, that makes sense, but with a really powerful or long strike, you *may* possibly burn them out. the 1.5KE220CA which may people use can only dissipate 7W on an infinite heatsink. 1500W pulsed but still. with a tube, you can dump a lot more power into them. if you have a tvs rated for 1.5kW and breakdown of 600v, you can only pulse 2.5A. a tvs diode is really nothing more than a spark gap anyways.
But then why don't people do this? i have never seen a coil with a tvs protection for this purpose. strike rails are all fine and good, but unless you have the primary in a cage, there is still a small possibility that you can get a strike.
and where to put them? because the dc bus is at an ac neutral "ground", and the arcs are looking for rf ground, you could put a tvs or tube from the igbt emitter-collector connection(both for a full bridge) to rf ground. this way, the resonant ring up on the primary circuit has 1200v before it shorts the tank and primary. but it only has 600v before an arc grounds itself.
and argue with me
i want to learn!
Ben Solon, Sat Mar 31 2012, 01:23AM
yes, that makes sense, but with a really powerful or long strike, you *may* possibly burn them out. the 1.5KE220CA which may people use can only dissipate 7W on an infinite heatsink. 1500W pulsed but still. with a tube, you can dump a lot more power into them. if you have a tvs rated for 1.5kW and breakdown of 600v, you can only pulse 2.5A. a tvs diode is really nothing more than a spark gap anyways.
But then why don't people do this? i have never seen a coil with a tvs protection for this purpose. strike rails are all fine and good, but unless you have the primary in a cage, there is still a small possibility that you can get a strike.
and where to put them? because the dc bus is at an ac neutral "ground", and the arcs are looking for rf ground, you could put a tvs or tube from the igbt emitter-collector connection(both for a full bridge) to rf ground. this way, the resonant ring up on the primary circuit has 1200v before it shorts the tank and primary. but it only has 600v before an arc grounds itself.
and argue with me
i want to learn!Re: drsstc primary strike protection
dude_500, Sat Mar 31 2012, 06:01AM
Keep in mind a 10kw coil being dumped into a TVS through an arc will dissipate very little actual power into the TVS because of the voltage divider between the TVS diode and the arc itself. The arc has many times the voltage of the TVS rating, so the arc will dissipate the vast majority of the energy. It can be thought of exactly like a resistor divider if you know the actual topload voltage.
dude_500, Sat Mar 31 2012, 06:01AM
Keep in mind a 10kw coil being dumped into a TVS through an arc will dissipate very little actual power into the TVS because of the voltage divider between the TVS diode and the arc itself. The arc has many times the voltage of the TVS rating, so the arc will dissipate the vast majority of the energy. It can be thought of exactly like a resistor divider if you know the actual topload voltage.
Re: drsstc primary strike protection
Ben Solon, Sat Mar 31 2012, 03:09PM
ok, now that i think about it the arc does eat up a lot of energy with heat/light/etc.
so to use this design where would you put the tvs diodes? same place i pointed out , or where steve was his caps?
Ben Solon, Sat Mar 31 2012, 03:09PM
ok, now that i think about it the arc does eat up a lot of energy with heat/light/etc.
so to use this design where would you put the tvs diodes? same place i pointed out , or where steve was his caps?
Re: drsstc primary strike protection
Steve Conner, Sat Mar 31 2012, 06:22PM
I must admit that I don't see the point of using TVS in this way.
What would blow your IGBTs would be the differential mode overvoltage. This is clamped by the IGBTs' antiparallel diodes and the DC bus capacitors, so there is no point in putting TVS across the IGBTs, except as band-aids for an excessively high inductance bridge layout. And even then. you may find that modern IGBTs have a bigger avalanche rating than the TVS that are supposed to be protecting them.
The common-mode overvoltage appears between primary and secondary of your GDT, causing it to arc over. The 0.1uF cap shown in Steve's design seems to do a perfectly good job of keeping it down. It's what I've always used in my DRSSTCs. (one of them also has the ferrite clamp on the GDT wires, but I built another without it, and it didn't seem to make much difference)
Technically speaking that capacitor is a Class Y unit and shouldn't be more than 4700pF for safety reasons, but I ignore that. It's hardly the biggest electrical safety violation around Tesla coils.
If you used a gas discharge tube instead of a capacitor, things could get messy, because they are a short circuit once they arc over. From the negative rail of your DC bus, that would be a short between the mains and ground through the bridge rectifier. Things would go boom.
If you used a TVS, it probably doesn't have the right safety approvals for Class Y service, being made of silicon and not at all self-healing.
Steve Conner, Sat Mar 31 2012, 06:22PM
I must admit that I don't see the point of using TVS in this way.
What would blow your IGBTs would be the differential mode overvoltage. This is clamped by the IGBTs' antiparallel diodes and the DC bus capacitors, so there is no point in putting TVS across the IGBTs, except as band-aids for an excessively high inductance bridge layout. And even then. you may find that modern IGBTs have a bigger avalanche rating than the TVS that are supposed to be protecting them.
The common-mode overvoltage appears between primary and secondary of your GDT, causing it to arc over. The 0.1uF cap shown in Steve's design seems to do a perfectly good job of keeping it down. It's what I've always used in my DRSSTCs. (one of them also has the ferrite clamp on the GDT wires, but I built another without it, and it didn't seem to make much difference)
Technically speaking that capacitor is a Class Y unit and shouldn't be more than 4700pF for safety reasons, but I ignore that. It's hardly the biggest electrical safety violation around Tesla coils.
If you used a gas discharge tube instead of a capacitor, things could get messy, because they are a short circuit once they arc over. From the negative rail of your DC bus, that would be a short between the mains and ground through the bridge rectifier. Things would go boom.
If you used a TVS, it probably doesn't have the right safety approvals for Class Y service, being made of silicon and not at all self-healing.
Re: drsstc primary strike protection
Steve Ward, Sat Apr 07 2012, 05:22AM
Ive actually gone a step further and build full EMI filters on my DC bus for power electronic protection. There is a "Y-cap" from each side of the bus to ground, then a common mode choke where the DC power enters the tesla coil housing. At the same time, i do have very good strike rail and shielding placement around the electronics of the tesla coil, so i dont test this safety system too much.
Steve Ward, Sat Apr 07 2012, 05:22AM
Ive actually gone a step further and build full EMI filters on my DC bus for power electronic protection. There is a "Y-cap" from each side of the bus to ground, then a common mode choke where the DC power enters the tesla coil housing. At the same time, i do have very good strike rail and shielding placement around the electronics of the tesla coil, so i dont test this safety system too much.
Re: drsstc primary strike protection
Terry Fritz, Sat Apr 07 2012, 10:28PM
I buy about $1000 worth of TVSs a year so maybe I know something. Ok, Mine are like 24V 5000W...
But a little TVS is not going to take a giant power hit despite the fact that they are really tough. You would be better off with big MOVs in general that have a lot of thermal mass to absorb real power.
But the advantage of TVSs is that they are super fast!! Like pico second reaction times! In my world of super power LiPO batteries and Neodymium magnet motors, the folks really can hit some super (~5nS) spikes that would go right past a slow old MOV and cut up the FET die.
So my suggestion would be to use big MOVs to take the power of the hit, but also parallel bit higher voltage TVSs that can clamp very high speed spikes. The TVS takes the fast spike and then the MOVs take over for the power dissipation.
Just a thought there...
Terry
BTW - This long forgotten paper might be helpful too. That really did work.
Terry Fritz, Sat Apr 07 2012, 10:28PM
I buy about $1000 worth of TVSs a year so maybe I know something. Ok, Mine are like 24V 5000W...
But a little TVS is not going to take a giant power hit despite the fact that they are really tough. You would be better off with big MOVs in general that have a lot of thermal mass to absorb real power.
But the advantage of TVSs is that they are super fast!! Like pico second reaction times! In my world of super power LiPO batteries and Neodymium magnet motors, the folks really can hit some super (~5nS) spikes that would go right past a slow old MOV and cut up the FET die.
So my suggestion would be to use big MOVs to take the power of the hit, but also parallel bit higher voltage TVSs that can clamp very high speed spikes. The TVS takes the fast spike and then the MOVs take over for the power dissipation.
Just a thought there...
Terry
BTW - This long forgotten paper might be helpful too. That really did work.
Re: drsstc primary strike protection
Steve Conner, Sun Apr 08 2012, 07:26AM
Wow, Terry Fritz.
I don't see why the DRSSTC protection thing wouldn't work, but the odds of a dead short across the inverter output are pretty slim. Except in some of the more adventurous builds that use multiple inverters with the outputs combined, where failure of one inverter would short out the others. Steve Ward and a few others have used ballasting inductors to mitigate this.
Just for the record, is there an official site with all of your papers on it? We regularly get questions about the Terry Filter here, and it would be nice to be able to point people to the original experiments.
Steve Conner, Sun Apr 08 2012, 07:26AM
Wow, Terry Fritz.
I don't see why the DRSSTC protection thing wouldn't work, but the odds of a dead short across the inverter output are pretty slim. Except in some of the more adventurous builds that use multiple inverters with the outputs combined, where failure of one inverter would short out the others. Steve Ward and a few others have used ballasting inductors to mitigate this.
Just for the record, is there an official site with all of your papers on it? We regularly get questions about the Terry Filter here, and it would be nice to be able to point people to the original experiments.
Re: drsstc primary strike protection
Terry Fritz, Mon Apr 09 2012, 11:44PM
Steve said,
That is what was blowing my DRSSTC up when the streamers hit primary. The primary strike currents were turning the opposing FETs on when they were not supposed to be on and cross conducted very dramatically. I still have the videos too... But mine was a little odd. Remember the sudden speeds at which a strike can dump dramatic currents...
Even I just go here:
The Internet seldom forgets*.
drsstc.com Did catch some later stuff like the paper of interest.
I you want a copy of everything you cam PM me... I forget the size but I finally bought a DVD burner just to distribute that many years back. I have not logged into DRSSTC.COM in 5+ years... But the Cobalt SUN server still sits here on my desk so we still talk I still have a NOS one too in storage, but the SUN things never die!!!! 
I usually let others answer the Terry Filter things since the kids probably know more than Daddy there now
Terry
*I may have been among the first to actually loose some good Internet site stuff too
Terry Fritz, Mon Apr 09 2012, 11:44PM
Steve said,
I don't see why the DRSSTC protection thing wouldn't work, but the odds of a dead short across the inverter output are pretty slim
That is what was blowing my DRSSTC up when the streamers hit primary. The primary strike currents were turning the opposing FETs on when they were not supposed to be on and cross conducted very dramatically. I still have the videos too... But mine was a little odd.
Remember the sudden speeds at which a strike can dump dramatic currents...Just for the record, is there an official site with all of your papers on it?
Even I just go here:
The Internet seldom forgets*.
drsstc.com Did catch some later stuff like the paper of interest.
I you want a copy of everything you cam PM me... I forget the size but I finally bought a DVD burner just to distribute that many years back. I have not logged into DRSSTC.COM in 5+ years... But the Cobalt SUN server still sits here on my desk so we still talk
I still have a NOS one too in storage, but the SUN things never die!!!! I usually let others answer the Terry Filter things since the kids probably know more than Daddy there now
Terry
*I may have been among the first to actually loose some good Internet site stuff too
Re: drsstc primary strike protection
Gregory, Tue Apr 10 2012, 03:07AM
Ward, are you using the same ground of secondary or a separated ground? Here I made the same and I'm using separated grounds like you told me in a email. I'm using EMI filter in the driver before de rectifier with the Y caps to the same ground.
Gregory, Tue Apr 10 2012, 03:07AM
Ward, are you using the same ground of secondary or a separated ground? Here I made the same and I'm using separated grounds like you told me in a email. I'm using EMI filter in the driver before de rectifier with the Y caps to the same ground.
Re: drsstc primary strike protection
Steve Ward, Mon Apr 16 2012, 07:06PM
I do hook up mains ground to my tesla coil base along the secondary ground and my EMI filtering ground. I fear that if i do not tie mains ground to RF ground, there could be a very high RF voltage there when the tesla coil arcs to RF ground, dumping large charges back and forth at high frequency. Since my power cable is shielded for strike protection, its shield gets tied to the RF ground too. Its very likely that my power cables are a source of radiated EMI, id like to see if i can reduce that with big ferrite beads on the cable.
I also use a couple of EMI filters. There is one on my DC bus as i mentioned, i think this is mainly for protection of the power circuit from high voltage transients during strikes, but probably cant control the EMI going out over my power cable. I use a DC power supply that is remote from the tesla coil, so the DC has an EMI filter at both the tesla coil, and the power supply output. I use another EMI filter on our 3 phase AC power feed, which also has some filtering of the ground wire, to hopefully stop sending common mode noise down the AC power, which would make the whole building's power potentially noisy with common mode RF.
As a side story, Ive had one of my DC PFC power supplies literally explode because of RF ground noise not being coupled with the power electronics bus. The voltage was enough to break down the isolation between the heatsink (at wild RF ground potentials) and mains voltage (which was not coupled in any way, as an EMI filter would have provided with Y-caps from line to ground). So the IGBT insulation failed causing the input rectifiers to explode and catch fire, with 3 phase 100A available to feed the arc. After adding my DC bus "EMI" filters, this problem is no more, because if the RF ground bounces, the power electronics bus will have to bounce too, so its all common mode and doesnt matter hopefully.
Steve Ward, Mon Apr 16 2012, 07:06PM
Ward, are you using the same ground of secondary or a separated ground? Here I made the same and I'm using separated grounds like you told me in a email. I'm using EMI filter in the driver before de rectifier with the Y caps to the same ground.
I do hook up mains ground to my tesla coil base along the secondary ground and my EMI filtering ground. I fear that if i do not tie mains ground to RF ground, there could be a very high RF voltage there when the tesla coil arcs to RF ground, dumping large charges back and forth at high frequency. Since my power cable is shielded for strike protection, its shield gets tied to the RF ground too. Its very likely that my power cables are a source of radiated EMI, id like to see if i can reduce that with big ferrite beads on the cable.
I also use a couple of EMI filters. There is one on my DC bus as i mentioned, i think this is mainly for protection of the power circuit from high voltage transients during strikes, but probably cant control the EMI going out over my power cable. I use a DC power supply that is remote from the tesla coil, so the DC has an EMI filter at both the tesla coil, and the power supply output. I use another EMI filter on our 3 phase AC power feed, which also has some filtering of the ground wire, to hopefully stop sending common mode noise down the AC power, which would make the whole building's power potentially noisy with common mode RF.
As a side story, Ive had one of my DC PFC power supplies literally explode because of RF ground noise not being coupled with the power electronics bus. The voltage was enough to break down the isolation between the heatsink (at wild RF ground potentials) and mains voltage (which was not coupled in any way, as an EMI filter would have provided with Y-caps from line to ground). So the IGBT insulation failed causing the input rectifiers to explode and catch fire, with 3 phase 100A available to feed the arc. After adding my DC bus "EMI" filters, this problem is no more, because if the RF ground bounces, the power electronics bus will have to bounce too, so its all common mode and doesnt matter hopefully.
Re: drsstc primary strike protection
ScotchTapeLord, Mon Apr 16 2012, 07:27PM
I hope you have something equally spectacular planned for the next NY Maker Faire!
ScotchTapeLord, Mon Apr 16 2012, 07:27PM
Steve Ward wrote ...
As a side story, Ive had one of my DC PFC power supplies literally explode because of RF ground noise not being coupled with the power electronics bus. The voltage was enough to break down the isolation between the heatsink (at wild RF ground potentials) and mains voltage (which was not coupled in any way, as an EMI filter would have provided with Y-caps from line to ground). So the IGBT insulation failed causing the input rectifiers to explode and catch fire, with 3 phase 100A available to feed the arc. After adding my DC bus "EMI" filters, this problem is no more, because if the RF ground bounces, the power electronics bus will have to bounce too, so its all common mode and doesnt matter hopefully.
As a side story, Ive had one of my DC PFC power supplies literally explode because of RF ground noise not being coupled with the power electronics bus. The voltage was enough to break down the isolation between the heatsink (at wild RF ground potentials) and mains voltage (which was not coupled in any way, as an EMI filter would have provided with Y-caps from line to ground). So the IGBT insulation failed causing the input rectifiers to explode and catch fire, with 3 phase 100A available to feed the arc. After adding my DC bus "EMI" filters, this problem is no more, because if the RF ground bounces, the power electronics bus will have to bounce too, so its all common mode and doesnt matter hopefully.
I hope you have something equally spectacular planned for the next NY Maker Faire!
Re: drsstc primary strike protection
Gregory, Thu Apr 19 2012, 04:42AM
I have one EMI filter at my tesla coil DC input that is grounded with a separated gorund. The secondary have a rf ground and the filter another. I have anoter EMI filter at the driver AC input to the same filter ground. I'm using one remote DC supply too, I will put one filter at its output. I will try to use the same ground for all the filters and the secondary but I'm afraid that with the same ground the EMI filter will no help to prevent igbt destruction over primary strike condition. Or it's will help even more than now?
Gregory, Thu Apr 19 2012, 04:42AM
I have one EMI filter at my tesla coil DC input that is grounded with a separated gorund. The secondary have a rf ground and the filter another. I have anoter EMI filter at the driver AC input to the same filter ground. I'm using one remote DC supply too, I will put one filter at its output. I will try to use the same ground for all the filters and the secondary but I'm afraid that with the same ground the EMI filter will no help to prevent igbt destruction over primary strike condition. Or it's will help even more than now?
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