Uzzors' First SSTC
uzzors2k, Thu Nov 22 2007, 08:31PMI finally did it. After being on the forum for over 2.5 years it's pretty embarrassing not to have made one yet, but better late than never.
Fres: 525 kHz
Winding dimensions: 11cm diameter, 20.5 cm tall
PLL courtesy of Steve Conner. Jugding by the output waveform when driving a resistive load the poor driver does ok. 10 ohms looked pretty square, so I assume the driver is good enough for the task. The internal diodes of the IRFP450s are not disabled as of yet. I know IRFP450s have terribly slow internal diodes, so I'll disable them soon. The coil is still in the lash-up phase and in need of tuning. So far I've achieved 15cm ground arcs, so 3/4 of the secondary length. I haven't been able to take it to full power yet as the fets heat too much.
There is much work to do on it still, but for now I'm focusing on tuning. Is there any point in reducing the coupling? It's at max right now.
Re: Uzzors' First SSTC
Dr. Dark Current, Thu Nov 22 2007, 09:14PM
Nice work
Dr. Dark Current, Thu Nov 22 2007, 09:14PM
Nice work
Uzzors wrote ...
Is there any point in reducing the coupling? It's at max right now.
I think you actually have too low coupling.. spread the turns a bit, you'll notice you can then add more turns to maintain the same output power. Here the higher coupling the better, make it as high as possible without flash over.Is there any point in reducing the coupling? It's at max right now.
Re: Uzzors' First SSTC
Marko, Fri Nov 23 2007, 12:19PM
Awesome to see someone finally build a driver with discrete parts. I tried building a driver out of IRFZ44-based halfbridge completely discrete but I didn't get but to light a flourescent lamp near the secondary.
I don't know whether you should use external diodes or not. They are expensive and may not be needed at all.
I admit IRFP450's are difficult to drive, but you should be able to do with very high speed using larger signal transistors like 2N2222+2N2907 and higher drive voltage, at speed comparable to UCC's.
BD's are very slow in comparison. You could try to use class AB instead of class B in order to prevent transistors from going into cutoff - that might give you somewhat faster transitions.
With smaller transistors I didn't see much improvement from class AB, though.
Regarding coupling, I second that you should increase it as much as possible - flashover is what usually limits it.
Marko
Marko, Fri Nov 23 2007, 12:19PM
Awesome to see someone finally build a driver with discrete parts. I tried building a driver out of IRFZ44-based halfbridge completely discrete but I didn't get but to light a flourescent lamp near the secondary.
I don't know whether you should use external diodes or not. They are expensive and may not be needed at all.
I admit IRFP450's are difficult to drive, but you should be able to do with very high speed using larger signal transistors like 2N2222+2N2907 and higher drive voltage, at speed comparable to UCC's.
BD's are very slow in comparison. You could try to use class AB instead of class B in order to prevent transistors from going into cutoff - that might give you somewhat faster transitions.
With smaller transistors I didn't see much improvement from class AB, though.
Regarding coupling, I second that you should increase it as much as possible - flashover is what usually limits it.
Marko
Re: Uzzors' First SSTC
uzzors2k, Wed Nov 28 2007, 04:56PM
I think I have it tuned now, the sparks are bigger and it can run from the full 230V at least. I forgot to mention I was using a SS variac, which is why the sparks were more branch like before. Without it I get the normal sword-streamers. I'm satisfied with the output, nice 20 cm streamers, but IMO the fets heat too much. What is normal for an offline halfwave SSTC? My fets have an 8 cm fan keeping them cool, but after just 1 minute the heatsink is 60-70 degrees? I'm no good at estimating temp, but they're hot enough to only be held for a few seconds at a time before becoming uncomfortable. How cool do yours stay?
I measured the primary current with a 33 turn CT combined with 33 load resistor. This gives a 1A = 1V ratio, so with the scope set to 10A div in the scopeshot. Looks like 18A to me, which explains the IRFP450s sweating like they are. 65W of dissipation per device, so 130W on the puny heatsink! I've tried a few different primary inductances, but all they did was lower the primary current to 10A, while halving the streamer length. Better coupling needed as well maybe? Probably, but I can't get plastic pipe wide enough and long enough, so it'll have to stay as is.
I think I'll just put up with the massive heating current and enjoy longer streamers for shorter lengths of time
The GDT and gate drivers get warm too anyway. (btw, I gave up and switched to UCC's, the BD1XX'es are just too slow at these frequencies.)
]1196268907_95_FT34743_halfwave_230v_sstc2.zip[/ file]
Next up is to box everything up!
uzzors2k, Wed Nov 28 2007, 04:56PM
I think I have it tuned now, the sparks are bigger and it can run from the full 230V at least. I forgot to mention I was using a SS variac, which is why the sparks were more branch like before. Without it I get the normal sword-streamers. I'm satisfied with the output, nice 20 cm streamers, but IMO the fets heat too much. What is normal for an offline halfwave SSTC? My fets have an 8 cm fan keeping them cool, but after just 1 minute the heatsink is 60-70 degrees? I'm no good at estimating temp, but they're hot enough to only be held for a few seconds at a time before becoming uncomfortable. How cool do yours stay?
I measured the primary current with a 33 turn CT combined with 33 load resistor. This gives a 1A = 1V ratio, so with the scope set to 10A div in the scopeshot. Looks like 18A to me, which explains the IRFP450s sweating like they are. 65W of dissipation per device, so 130W on the puny heatsink! I've tried a few different primary inductances, but all they did was lower the primary current to 10A, while halving the streamer length. Better coupling needed as well maybe? Probably, but I can't get plastic pipe wide enough and long enough, so it'll have to stay as is.
I think I'll just put up with the massive heating current and enjoy longer streamers for shorter lengths of time
The GDT and gate drivers get warm too anyway. (btw, I gave up and switched to UCC's, the BD1XX'es are just too slow at these frequencies.)
]1196268907_95_FT34743_halfwave_230v_sstc2.zip[/ file]
Next up is to box everything up!
Re: Uzzors' First SSTC
Dr. Dark Current, Wed Nov 28 2007, 05:03PM
Hey uzzors- nice sparks!!
From your pictures it seems to me you still have poor coupling.. Add some turns and wind the primary closer to the resonator and make it longer (vertically), I recommend doing this until you start getting flash overs- then back up a little
I don't know why your fets heat up, I used little IRF740's and they got a bit hot after a minute, but on small heatsinks and without a fan. Though they were making just ~17cm arcs.
I was using the "Mini SSTC" driver, maybe you could give it a try.
Dr. Dark Current, Wed Nov 28 2007, 05:03PM
Hey uzzors- nice sparks!!
From your pictures it seems to me you still have poor coupling.. Add some turns and wind the primary closer to the resonator and make it longer (vertically), I recommend doing this until you start getting flash overs- then back up a little
I don't know why your fets heat up, I used little IRF740's and they got a bit hot after a minute, but on small heatsinks and without a fan. Though they were making just ~17cm arcs.
I was using the "Mini SSTC" driver, maybe you could give it a try.
Re: Uzzors' First SSTC
uzzors2k, Wed Nov 28 2007, 05:58PM
Thanks. It's probably a coupling matter like you say. More turns and winding the primary higher up would probably help. The problem is the secondary is wound on 110mm diameter secondary, which is the largest pipe size available. I found some sort of converter piece which I'm using now, but the length is limited. So changing the coupling is impossible atm. Before I was just using some plastic sheets, but they arced over rather easily. How much primary current are you running through your SSTC, jmartis?
uzzors2k, Wed Nov 28 2007, 05:58PM
Thanks. It's probably a coupling matter like you say. More turns and winding the primary higher up would probably help. The problem is the secondary is wound on 110mm diameter secondary, which is the largest pipe size available. I found some sort of converter piece which I'm using now, but the length is limited. So changing the coupling is impossible atm. Before I was just using some plastic sheets, but they arced over rather easily. How much primary current are you running through your SSTC, jmartis?
Re: Uzzors' First SSTC
Marko, Wed Nov 28 2007, 06:20PM
I guess you now notice the problem!
I wonder how are 14amp mosfets living t all with that kind of current
You should definitely increase coupling, as much as possible. At some point it's going to flash over though :(. You can try moving the primary somewhat up, but it's a gamble.
Making a wider primary former could help somewhat, and best of all would be an inverse conical primary (although at much larger angle) like those used with SGTC's.
You could hardly get better, unless if you used a ferrite transformer and base feed to the coil. That's an intristic limitation for the SSTC's.
Ata point you might really want beefier switches, fullbridge and so on. 20cm spark after all isn't too bad for two IRFP450's.
Marko, Wed Nov 28 2007, 06:20PM
I measured the primary current with a 33 turn CT combined with 33 load resistor. This gives a 1A = 1V ratio, so with the scope set to 10A div in the scopeshot. Looks like 18A to me, which explains the IRFP450s sweating like they are. 65W of dissipation per device, so 130W on the puny heatsink! I've tried a few different primary inductances, but all they did was lower the primary current to 10A, while halving the streamer length. Better coupling needed as well maybe? Probably, but I can't get plastic pipe wide enough and long enough, so it'll have to stay as is.
I guess you now notice the problem!
I wonder how are 14amp mosfets living t all with that kind of current
You should definitely increase coupling, as much as possible. At some point it's going to flash over though :(. You can try moving the primary somewhat up, but it's a gamble.
Making a wider primary former could help somewhat, and best of all would be an inverse conical primary (although at much larger angle) like those used with SGTC's.
You could hardly get better, unless if you used a ferrite transformer and base feed to the coil. That's an intristic limitation for the SSTC's.
Ata point you might really want beefier switches, fullbridge and so on. 20cm spark after all isn't too bad for two IRFP450's.
Re: Uzzors' First SSTC
uzzors2k, Wed Nov 28 2007, 07:47PM
The RMS current is only 12.7A so they're playing within the survivable range.
I've put a CT on it and after some fiddling I've gotten the same output as with antenna feedback. The resonance point seems less defined with a CT. Also I had to reverse the phasing. Both worked, but one had a lower fres, with a little less output, while the opposite phasing had the same output as the antenna feedback and higher fres. The higher fres was higher than the antenna fres. Seems odd to me, but CTs use current feedback while antennas use voltage, so it must be caused by the current/voltage phase shift.
Pulling ground arcs works fine, the benefit of PLL I guess. Beefier switches are what I really want as lower on resistance could double run times, to the point where the UCC's and GDT are the limiting factor. However this coil will be mostly used as an HV supply for my x-ray setup so the run times won't be long at all.
uzzors2k, Wed Nov 28 2007, 07:47PM
The RMS current is only 12.7A so they're playing within the survivable range.
I've put a CT on it and after some fiddling I've gotten the same output as with antenna feedback. The resonance point seems less defined with a CT. Also I had to reverse the phasing. Both worked, but one had a lower fres, with a little less output, while the opposite phasing had the same output as the antenna feedback and higher fres. The higher fres was higher than the antenna fres. Seems odd to me, but CTs use current feedback while antennas use voltage, so it must be caused by the current/voltage phase shift.
Pulling ground arcs works fine, the benefit of PLL I guess. Beefier switches are what I really want as lower on resistance could double run times, to the point where the UCC's and GDT are the limiting factor. However this coil will be mostly used as an HV supply for my x-ray setup so the run times won't be long at all.
Re: Uzzors' First SSTC
Coronafix, Thu Nov 29 2007, 11:56AM
I looked at this when you first posted, but I had to come back to it and say well done!!!
I really like the PLL driver, it's just so elegant. Really nice sparks Uzzors, they're as long as the
coil, right!?! And the fact that you didn't use Mosfet drivers is an extra nice touch.
Good job!
Coronafix, Thu Nov 29 2007, 11:56AM
I looked at this when you first posted, but I had to come back to it and say well done!!!
I really like the PLL driver, it's just so elegant. Really nice sparks Uzzors, they're as long as the
coil, right!?! And the fact that you didn't use Mosfet drivers is an extra nice touch.
Good job!
Re: Uzzors' First SSTC
Tom540, Thu Nov 29 2007, 04:02PM
He did use them, in the end.
Tom540, Thu Nov 29 2007, 04:02PM
GDT and gate drivers get warm too anyway. (btw, I gave up and switched to UCC's, the BD1XX'es are just too slow at these frequencies.)
He did use them, in the end.
Re: Uzzors' First SSTC
uzzors2k, Thu Nov 29 2007, 05:12PM
BD1XXes are just no good for more than 150 kHz, but other common signal transistors will work at high frequencies. I've ordered some better signal transistors so I'll see how they work. My next SSTC will be gatedriver-chip-free, guaranteed. (I hope I don't have to eat my words later.
)
I like PLL too, it has so many benifets, I don't know if I'll every use anything else.
uzzors2k, Thu Nov 29 2007, 05:12PM
BD1XXes are just no good for more than 150 kHz, but other common signal transistors will work at high frequencies. I've ordered some better signal transistors so I'll see how they work. My next SSTC will be gatedriver-chip-free, guaranteed. (I hope I don't have to eat my words later.
)I like PLL too, it has so many benifets, I don't know if I'll every use anything else.
Re: Uzzors' First SSTC
Reaching, Thu Nov 29 2007, 06:12PM
i used a bdxx and irf9530/530 stage in 2 of my sstcs and it works just fine even up to 2,1mhz in case of my hf driver. so i dont know how you wired them but for me those bd types worked well.. at 2mhz the bd stage put out a nice squarewave with load resistor, so i dont know.
i already own some (without driver chip) sstcs. its not that difficult at all
Reaching, Thu Nov 29 2007, 06:12PM
i used a bdxx and irf9530/530 stage in 2 of my sstcs and it works just fine even up to 2,1mhz in case of my hf driver. so i dont know how you wired them but for me those bd types worked well.. at 2mhz the bd stage put out a nice squarewave with load resistor, so i dont know.
i already own some (without driver chip) sstcs. its not that difficult at all
Re: Uzzors' First SSTC
uzzors2k, Thu Nov 29 2007, 07:16PM
The BD1XXs have no problem running gates directly, but through a GDT they really slow down. I actually used something similar to your discrete driver to begin with, but I would get massive amounts of ringing on the output with an IRF9530/630 stage. The switching speed was good, but the ringing ruined everything. Even with coax cable the waveform was poor. I was under the impression that the output capacitance of the fets ruined the waveform on me. And using just BD1XXs alone with 4nF of gate capacitance total doesn't work too well. Is this the circuit you use?
And you've tested it with a half-bridge of IRFP450 equivalents at 2 MHz and gotten good waveforms? There must have been something wrong with my core then, even with UCC's the waveform isn't as good as I had expected.
uzzors2k, Thu Nov 29 2007, 07:16PM
The BD1XXs have no problem running gates directly, but through a GDT they really slow down. I actually used something similar to your discrete driver to begin with, but I would get massive amounts of ringing on the output with an IRF9530/630 stage. The switching speed was good, but the ringing ruined everything. Even with coax cable the waveform was poor. I was under the impression that the output capacitance of the fets ruined the waveform on me. And using just BD1XXs alone with 4nF of gate capacitance total doesn't work too well. Is this the circuit you use?
And you've tested it with a half-bridge of IRFP450 equivalents at 2 MHz and gotten good waveforms? There must have been something wrong with my core then, even with UCC's the waveform isn't as good as I had expected.
Re: Uzzors' First SSTC
Firnagzen, Fri Nov 30 2007, 02:43AM
Nice sparks!
Is there any reason there's a lower limit on the frequency of this? I mean, an upper limit seems perfectly fine... But a lower limit?
And another thing. No audio modulation? Steve's PLL has that option too, you know. Audio modulation seems all the rage these days.
EDIT:
Was about to close this topic when I realized something. You haven't reported any MOSFET deaths yet. Is that due to not mentioning them, or your first set of MOSFETs are still alive? If they're still alive, I am amazed! And then I'm going to scrap my current circuit board and replicate yours.
Firnagzen, Fri Nov 30 2007, 02:43AM
Nice sparks!
Is there any reason there's a lower limit on the frequency of this? I mean, an upper limit seems perfectly fine... But a lower limit?
And another thing. No audio modulation? Steve's PLL has that option too, you know. Audio modulation seems all the rage these days.
EDIT:
Was about to close this topic when I realized something. You haven't reported any MOSFET deaths yet. Is that due to not mentioning them, or your first set of MOSFETs are still alive? If they're still alive, I am amazed! And then I'm going to scrap my current circuit board and replicate yours.
Re: Uzzors' First SSTC
Steve Ward, Fri Nov 30 2007, 07:12AM
That scope shot looks like you might be switching a little too early... have you tweaked the phase control much? Getting the switching down better should help the mosfet heating a good deal. I usually like to scope both primary current and gate driver output at the same time so i can verify the phase relationship between the switching and the primary current.
Steve Ward, Fri Nov 30 2007, 07:12AM
That scope shot looks like you might be switching a little too early... have you tweaked the phase control much? Getting the switching down better should help the mosfet heating a good deal. I usually like to scope both primary current and gate driver output at the same time so i can verify the phase relationship between the switching and the primary current.
Re: Uzzors' First SSTC
uzzors2k, Fri Nov 30 2007, 12:00PM
I play with the phase control all the time, but it seems to alter the switching frequency. Turning the pot from one direction will give no output, then suddenly noisy sparks, then perfect streamers, and then steadly decreasing streamer size. This is when turning counter-clockwise. I recently noticed that the coil seems to detune when objects are brought near, a sign of running fixed frequency. Or that I've set the frequency range to tight, one 15k and 16k don't give much roaming range... Will the fres rise or lower when objects are brought near? I haven't scoped the GDT output and primary current at the same time yet. I've just turned the pot until the streamer length peaks. I'll scope everything and check whether it's running properly or just fixed frequency.
Firnagzen, there's no lower limit, but the BD1XX's are too slow to switch heavy loads properly at high frequencies. Audio modulation would be a piece of cake to implement, if I could run the SSTC from filtered mains. I've killed about 3 pairs of mosfets so far, IIRC.
uzzors2k, Fri Nov 30 2007, 12:00PM
I play with the phase control all the time, but it seems to alter the switching frequency. Turning the pot from one direction will give no output, then suddenly noisy sparks, then perfect streamers, and then steadly decreasing streamer size. This is when turning counter-clockwise. I recently noticed that the coil seems to detune when objects are brought near, a sign of running fixed frequency. Or that I've set the frequency range to tight, one 15k and 16k don't give much roaming range... Will the fres rise or lower when objects are brought near? I haven't scoped the GDT output and primary current at the same time yet. I've just turned the pot until the streamer length peaks. I'll scope everything and check whether it's running properly or just fixed frequency.
Firnagzen, there's no lower limit, but the BD1XX's are too slow to switch heavy loads properly at high frequencies. Audio modulation would be a piece of cake to implement, if I could run the SSTC from filtered mains. I've killed about 3 pairs of mosfets so far, IIRC.
Re: Uzzors' First SSTC
Marko, Fri Nov 30 2007, 02:30PM
One thing I missed out, absolutely do use a small value (500nf..1uF) DC blocking cap in series with your halfbridge output. That should save lots of mosfet lives if anything goes cardinally wrong (but not from overcurrent in operation).
Marko, Fri Nov 30 2007, 02:30PM
One thing I missed out, absolutely do use a small value (500nf..1uF) DC blocking cap in series with your halfbridge output. That should save lots of mosfet lives if anything goes cardinally wrong (but not from overcurrent in operation).
Re: Uzzors' First SSTC
uzzors2k, Fri Nov 30 2007, 03:01PM
I put one in a few days ago, but its good you noticed Marko. Will it be needed once the coil is working properly?
I scoped the outputs without becoming any wiser. At 50Hz half-wave it's hard to make anything out, and at 50V DC the waveforms were still fairly fuzzy. But I did see something. Turning the pot does changes the phasing difference between the primary current and GDT output as expected, but it also seems to alter the frequency. Is this normal? I couldn't hit resonance exactly at 50V because it would suddenly drop out of resonance, and I would have to turn the pot back until a pop came, and then back to get close to fres again. Bringing anything near the topload would bring the phasing closer to perfect switching, before the popping thing occurs and I have to reset the system. Very strange. I haven't had that problem from half-wave rectified, but that might be because the power is applied in bursts, allowing the system to reset.
Is the gate drive good enough? I really expected better from UCC's. I'm using a 470nF blocking cap and 5 ohm resistor on the primary side.
uzzors2k, Fri Nov 30 2007, 03:01PM
I put one in a few days ago, but its good you noticed Marko. Will it be needed once the coil is working properly?
I scoped the outputs without becoming any wiser. At 50Hz half-wave it's hard to make anything out, and at 50V DC the waveforms were still fairly fuzzy. But I did see something. Turning the pot does changes the phasing difference between the primary current and GDT output as expected, but it also seems to alter the frequency. Is this normal? I couldn't hit resonance exactly at 50V because it would suddenly drop out of resonance, and I would have to turn the pot back until a pop came, and then back to get close to fres again. Bringing anything near the topload would bring the phasing closer to perfect switching, before the popping thing occurs and I have to reset the system. Very strange. I haven't had that problem from half-wave rectified, but that might be because the power is applied in bursts, allowing the system to reset.
Is the gate drive good enough? I really expected better from UCC's. I'm using a 470nF blocking cap and 5 ohm resistor on the primary side.
Re: Uzzors' First SSTC
Bauerb2, Fri Nov 30 2007, 09:12PM
5 ohm on the pirmary side?? i thought they are supposed to go on the secondary side in series with the mosfet gate....
anyway, i believe the resonant frequency of the coil increases as you bring things closer to the topload. the close objects decrease the secondary side capacitive value and increase Fres.
Try removing the 5ohm resistor from the primary side of your gdt, and keep those 1.2ohm resistors on the mosfet gates. i think the extra resistance in your circuit causes some rise/fall delays, especially at +500kHz. i had fet gate resitors of 10ohm and dropped them down to 2ohm and it helped out a great deal.
-Andrew
Bauerb2, Fri Nov 30 2007, 09:12PM
5 ohm on the pirmary side?? i thought they are supposed to go on the secondary side in series with the mosfet gate....
anyway, i believe the resonant frequency of the coil increases as you bring things closer to the topload. the close objects decrease the secondary side capacitive value and increase Fres.
Try removing the 5ohm resistor from the primary side of your gdt, and keep those 1.2ohm resistors on the mosfet gates. i think the extra resistance in your circuit causes some rise/fall delays, especially at +500kHz. i had fet gate resitors of 10ohm and dropped them down to 2ohm and it helped out a great deal.
-Andrew
Re: Uzzors' First SSTC
..., Sat Dec 01 2007, 12:43AM
I had that popping effect on my pll coil as well, the problem was due to the r1 and r2 (ie, pins 11/12 iirc) not being correct. One of them sets the center frequency, the other the amount of tuning range possible with the pll. Then just twiddle them until it starts working
That scope shot looks great for the gate drive (especially at the frequency you are operating at). The fets heating could be from the coil not running perfectly in tune, but it more likley that you just need more primary turns.
..., Sat Dec 01 2007, 12:43AM
I had that popping effect on my pll coil as well, the problem was due to the r1 and r2 (ie, pins 11/12 iirc) not being correct. One of them sets the center frequency, the other the amount of tuning range possible with the pll. Then just twiddle them until it starts working
That scope shot looks great for the gate drive (especially at the frequency you are operating at). The fets heating could be from the coil not running perfectly in tune, but it more likley that you just need more primary turns.
Re: Uzzors' First SSTC
Marko, Mon Dec 03 2007, 09:11PM
Always use the DC block cap, you can't count on anything else to provide the safety it does.
How did you kill your mosfets firstly? I bet you could save at least some of them if you used the DC block.
Try using the resistors on gates, and use diodes in reverse in order to get fast turnoff and some deadtime. You might also want to try using some smaller resistors - 5 ohm on primary side limits your peak current to 3 amps at most while UCC's can source 9.
Marko, Mon Dec 03 2007, 09:11PM
I put one in a few days ago, but its good you noticed Marko. Will it be needed once the coil is working properly?
Always use the DC block cap, you can't count on anything else to provide the safety it does.
How did you kill your mosfets firstly? I bet you could save at least some of them if you used the DC block.
Is the gate drive good enough? I really expected better from UCC's. I'm using a 470nF blocking cap and 5 ohm resistor on the primary side.
Try using the resistors on gates, and use diodes in reverse in order to get fast turnoff and some deadtime. You might also want to try using some smaller resistors - 5 ohm on primary side limits your peak current to 3 amps at most while UCC's can source 9.
Re: Uzzors' First SSTC
Tonic, Thu Dec 06 2007, 09:40PM
Congratulations, your sparks looks great for first SSTC :)
But I won't forgive betraying for those UCC's! I will keep your promise to make next driver without those chips
What BD's replacements have you ordered?
Tonic, Thu Dec 06 2007, 09:40PM
Congratulations, your sparks looks great for first SSTC :)
But I won't forgive betraying for those UCC's! I will keep your promise to make next driver without those chips
What BD's replacements have you ordered?
Re: Uzzors' First SSTC
Dago, Fri Dec 07 2007, 01:02PM
If you want bigger sparks and you have more power available I suggest using a toroid. Using a toroid made the sparks ALOT bigger and hotter on my coil.
Dago, Fri Dec 07 2007, 01:02PM
If you want bigger sparks and you have more power available I suggest using a toroid. Using a toroid made the sparks ALOT bigger and hotter on my coil.
Re: Uzzors' First SSTC
Wolfram, Fri Dec 07 2007, 01:56PM
I had the exact same experience. For cheap and simple toroids, check out biltema for flexible aluminium ducting, it worked well for me.
Anders M.
Wolfram, Fri Dec 07 2007, 01:56PM
I had the exact same experience. For cheap and simple toroids, check out biltema for flexible aluminium ducting, it worked well for me.
Anders M.
Re: Uzzors' First SSTC
Zum Beispiel, Fri Dec 07 2007, 02:33PM
I love that place. Good quality tools for cheap prices.
But seriously, throwing a (small) topload there will help you get more power. Not sure how much more your resonator can take though. Might catch fire or something
Zum Beispiel, Fri Dec 07 2007, 02:33PM
Anders M. wrote ...
For cheap and simple toroids, check out biltema for flexible aluminium ducting, it worked well for me.
Ah, Biltema. The best thing ever to come from Sweden For cheap and simple toroids, check out biltema for flexible aluminium ducting, it worked well for me.
I love that place. Good quality tools for cheap prices.But seriously, throwing a (small) topload there will help you get more power. Not sure how much more your resonator can take though. Might catch fire or something
Re: Uzzors' First SSTC
uzzors2k, Sat Dec 08 2007, 09:25PM
Biltema? I should have known.
I can't work on one project for too long before becoming restless, so I've wrapped this one up. I spent the last week optimizing a small flyback smps for the regulated 12V, and today was spent mounting everything on a board. The sparks have become longer and more spindly after assembling the SSTC, and the fets don't heat as much anymore either. I think it might have something to do with the flyback's voltage regualtion, but it's nothing I'll bother fixing. I like the coil as is, but mostly I can't wait to start on something new. Thanks for all the input on this, maybe someday I'll revisit it and tweak it some more.
uzzors2k, Sat Dec 08 2007, 09:25PM
Biltema? I should have known.
I can't work on one project for too long before becoming restless, so I've wrapped this one up. I spent the last week optimizing a small flyback smps for the regulated 12V, and today was spent mounting everything on a board. The sparks have become longer and more spindly after assembling the SSTC, and the fets don't heat as much anymore either. I think it might have something to do with the flyback's voltage regualtion, but it's nothing I'll bother fixing. I like the coil as is, but mostly I can't wait to start on something new. Thanks for all the input on this, maybe someday I'll revisit it and tweak it some more.
Re: Uzzors' First SSTC
flannelhead, Sat May 03 2008, 11:19AM
Back on the discrete GDT driver, did you ever try with different signal transistors, for example 2N2222+2N2907?
flannelhead, Sat May 03 2008, 11:19AM
Back on the discrete GDT driver, did you ever try with different signal transistors, for example 2N2222+2N2907?
Re: Uzzors' First SSTC
lpfthings, Sat May 03 2008, 11:51AM
wow that looks nice, love the arcs too. I wish i had something like tht on my desk, would be pretty cool to watch. Any details on the secondary?
lpfthings, Sat May 03 2008, 11:51AM
wow that looks nice, love the arcs too. I wish i had something like tht on my desk, would be pretty cool to watch. Any details on the secondary?
Re: Uzzors' First SSTC
uzzors2k, Sat May 03 2008, 01:22PM
I never did anymore experimentation, but in hindsight I see that the GDT was probably the real limiting factor. For one thing the core was too small and of a random material from a noise suppressing choke, and to top things off I barely had enough turns on it. The extra magnetizing current + crappy core took a lot of power out of the gate driver, which is proven by the fact that the UCCs preformed just as poorly as my discrete driver. In my class E coil I used a BD139/40 totempole without problems at 1,4MHz, so they can switch the gate fast enough as long as the impedance between them and the gate is low. Aka use a good GDT.
Thanks lpfthings, the secondary winding is 11cm in diameter and 20.5cm tall. I used 0.3mm wire IIRC, so around 650 turns.
uzzors2k, Sat May 03 2008, 01:22PM
I never did anymore experimentation, but in hindsight I see that the GDT was probably the real limiting factor. For one thing the core was too small and of a random material from a noise suppressing choke, and to top things off I barely had enough turns on it. The extra magnetizing current + crappy core took a lot of power out of the gate driver, which is proven by the fact that the UCCs preformed just as poorly as my discrete driver. In my class E coil I used a BD139/40 totempole without problems at 1,4MHz, so they can switch the gate fast enough as long as the impedance between them and the gate is low. Aka use a good GDT.
Thanks lpfthings, the secondary winding is 11cm in diameter and 20.5cm tall. I used 0.3mm wire IIRC, so around 650 turns.
Re: Uzzors' First SSTC
Marko, Sun May 04 2008, 01:34PM
Yes, the GDT is indeed a biggest limiting factor - to the point where, as you could see, the fast gate drivers won't make much difference from just transistor totem poles.
The biggest problem in GDT design is leakage, not magnetising inductance. Using ''just enough'' turns is actually best thing to do, because it reduces leakage inductance - which is effectively in series with the windings, slowing down rise and fall times, while magnetizing inductance just adds some comparatively negligible magnetizing current burden.
You only have a problem if you saturate the transformer badly enough for the secondary voltage to drop into linear region for mosfet's (in most cases you will be able to see the waveform 'sloping down' towards the end of half-cycle).
A great help in GDT design for high frequencies is shielded cable - RG 147 coax or multi-cored coax cables make great GDT's with their shields used as primaries and cores as secondaries.
But, as you could find out, even with these 'crappy looking' gate waveforms you still pushed mosfets to the end of their rating and produced sparks.
So there's probably no point overkilling anything without need.
Faster gate drive might increase efficiency a bit, but I'm not sure how much just comparatively to DC losses.
Looking back at this Steve Conner's basic PLL circuit, I don't think it's a good circuit, and I wouldn't recommend it to anyone anymore. It has several pitfalls, most of which can be solved easily by using phase comparator 2, as in Steve Ward's PLL circuit:
I myself have gone with direct feedback and current transformer approach. I don't consider antenna feedback reliable anymore because of unpredictable phase shifts it creates just depending on it's position towards the secondary.
After circuit's reliability is proven I'll post it up, but it got almost as complex as PLL and may be no advantage. I designed it primarily because of my poor understanding of PLL and lack of similar designs published on internet.
Marko
Marko, Sun May 04 2008, 01:34PM
Yes, the GDT is indeed a biggest limiting factor - to the point where, as you could see, the fast gate drivers won't make much difference from just transistor totem poles.
The biggest problem in GDT design is leakage, not magnetising inductance. Using ''just enough'' turns is actually best thing to do, because it reduces leakage inductance - which is effectively in series with the windings, slowing down rise and fall times, while magnetizing inductance just adds some comparatively negligible magnetizing current burden.
You only have a problem if you saturate the transformer badly enough for the secondary voltage to drop into linear region for mosfet's (in most cases you will be able to see the waveform 'sloping down' towards the end of half-cycle).
A great help in GDT design for high frequencies is shielded cable - RG 147 coax or multi-cored coax cables make great GDT's with their shields used as primaries and cores as secondaries.
But, as you could find out, even with these 'crappy looking' gate waveforms you still pushed mosfets to the end of their rating and produced sparks.
So there's probably no point overkilling anything without need.
Faster gate drive might increase efficiency a bit, but I'm not sure how much just comparatively to DC losses.
Looking back at this Steve Conner's basic PLL circuit, I don't think it's a good circuit, and I wouldn't recommend it to anyone anymore. It has several pitfalls, most of which can be solved easily by using phase comparator 2, as in Steve Ward's PLL circuit:
I myself have gone with direct feedback and current transformer approach. I don't consider antenna feedback reliable anymore because of unpredictable phase shifts it creates just depending on it's position towards the secondary.
After circuit's reliability is proven I'll post it up, but it got almost as complex as PLL and may be no advantage. I designed it primarily because of my poor understanding of PLL and lack of similar designs published on internet.
Marko
Re: Uzzors' First SSTC
uzzors2k, Mon Oct 20 2008, 06:48PM
Well, it was time for an upgrade. I started working on this coil again a few months ago. Adding a topload, readjusting the VCO range, upgrading to a fullbridge, making a new GDT, testing, building a box, etc. Long story short, the new coil worked long enough to get about 5 streamer pictures throughout the building phase. NOT because I can't put a SSTC together without blowing mosfets (a GDT wire did come loose, but only cost half of the full bridge) but because of flashovers. Apparently from primary to secondary, high current arcs do noticeable damage on thin magnet wire...
That coil was hand-wound and the only I have of it's size.....
As a note of warning to others, use varnish!!!! I didn't, and as though this isn't punishment enough, I had to rewind half the coil before I started the upgrade due to the former changing size and wires criss-crossing. Words can probably describe how I feel, but none I can think of.
uzzors2k, Mon Oct 20 2008, 06:48PM
Well, it was time for an upgrade. I started working on this coil again a few months ago. Adding a topload, readjusting the VCO range, upgrading to a fullbridge, making a new GDT, testing, building a box, etc. Long story short, the new coil worked long enough to get about 5 streamer pictures throughout the building phase. NOT because I can't put a SSTC together without blowing mosfets (a GDT wire did come loose, but only cost half of the full bridge) but because of flashovers. Apparently from primary to secondary, high current arcs do noticeable damage on thin magnet wire...
That coil was hand-wound and the only I have of it's size.....
As a note of warning to others, use varnish!!!! I didn't, and as though this isn't punishment enough, I had to rewind half the coil before I started the upgrade due to the former changing size and wires criss-crossing. Words can probably describe how I feel, but none I can think of.
Re: Uzzors' First SSTC
..., Mon Oct 20 2008, 08:45PM
Yeah, I have burned up a few secondaries about the size due to flashovers. Varnish doesn't help, but putting a flat piece of plexiglass with a hole in the middle for the secondary on top of the primary is supposed to help (although it seems like that would only help for strikes from the top of the coil, i believe that it is supposed to change the electric field for the better).
Other than that just raise the primary or use a wider diameter primary (and probably add turns to keep the same load in your bridge).
Glad to see that you got it working so far! That coil is turning out really nicely.
Also, for testing that secondary is 100% workable, just unwind the charred turns, solder the remaining wire together, and wrap the bottom of the coil in electrical tape. It looks ugly, but works great
..., Mon Oct 20 2008, 08:45PM
Yeah, I have burned up a few secondaries about the size due to flashovers. Varnish doesn't help, but putting a flat piece of plexiglass with a hole in the middle for the secondary on top of the primary is supposed to help (although it seems like that would only help for strikes from the top of the coil, i believe that it is supposed to change the electric field for the better).
Other than that just raise the primary or use a wider diameter primary (and probably add turns to keep the same load in your bridge).
Glad to see that you got it working so far! That coil is turning out really nicely.
Also, for testing that secondary is 100% workable, just unwind the charred turns, solder the remaining wire together, and wrap the bottom of the coil in electrical tape. It looks ugly, but works great
Re: Uzzors' First SSTC
uzzors2k, Fri Nov 07 2008, 11:54AM
Thanks Peter.
I've completed the coil! I tried 5 different primary configs before I found that just lumping all of the turns at the bottom works best. The secondary doesn't need to be lifted at all, and no arc-overs have occurred yet. I'm not sure if it's pushing as much power as I've had it at while maxed, but it runs without problems now.
Youtube video: Take that half-wave rectified without a topload!
uzzors2k, Fri Nov 07 2008, 11:54AM
Thanks Peter.
I've completed the coil! I tried 5 different primary configs before I found that just lumping all of the turns at the bottom works best. The secondary doesn't need to be lifted at all, and no arc-overs have occurred yet. I'm not sure if it's pushing as much power as I've had it at while maxed, but it runs without problems now.
Youtube video:
Take that half-wave rectified without a topload!Print this page