Author Topic: RDRSSTC - Project Build  (Read 17941 times)

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
RDRSSTC - Project Build
« on: October 01, 2023, 11:01:03 PM »
Hello,

While I am still wrapping up my RSSTC I'd like to start planning my next build. For that I want to step up to DRSSTC territory. I want this to be a ramped coil as well that will hopefully help prepare me for a QCWDRSSTC in the future.



High level plan:

My aim is a compact design with the best secondary to arc length ratio.



Driver Questions:
  • Considering the UD1.3b, how crucial is phase lead? I've noticed it in later UD versions. Should I integrate it into UD1.3? https://kaizerpowerelectronics.dk/files/stevehv.4hv.org_files/universal_driver_1.3b/DRSSTC_pndriver1_3b.pdf
  • For a more compact RDRSSTC, would driving the IGBTs at around 18-20v vs. the UCC27423's 15v max make a significant difference, considering the improvement in current capabilities?
  • Can I bypass the push/pull MOSFET output stage and simply use two UCC27423s, given that a single UCC27425 was adequate for my half bridge RSSTC?
  • Are there notable differences between regular and ramped DRSSTCs in terms of component stress and operation, aside from the arc appearance?



Thank you!
 
« Last Edit: October 03, 2023, 02:09:20 AM by ZakW »

Offline Lucasww

  • High Voltage Experimenter
  • **
  • Posts: 52
  • Karma: +4/-0
    • View Profile
Re: RDRSSTC - Project Build
« Reply #1 on: October 03, 2023, 08:21:23 AM »
Phase lead will be very helpful if you are planning to run long on-times, which you will be doing with a ramped coil.

With 15v input on your GDT, assuming 1:1 turns ratio, you will realistically be able to get 13-14v consistently on your igbt gates. The FGH75T65SHD datasheet shows that they should be fine at that voltage. However, what concerns me more is the possibility of ringing on your gates causing the voltage to drop potentially below 10v, which could easily cause desaturation. This isn't as much of an issue with the typical 18-24v gate drive most use. I'm using FGH75T65SHD in my QCWDRSSTC and have had no issues driving them at 19v.

Whether or not you can bypass the output mosfets is really up to what gate drive voltage you want. If you want the voltage to be above 15v, you will either need the mosfets, or a higher voltage gate drive chip. Most higher voltage chips with suitable rise times and propagation delays are SMD and quite small, so you may have trouble keeping them cool. I would recommend just using the mosfets.

As far as operation and component stress, You will generally want higher coupling, and a higher impedance primary circuit. The stress on your components ultimately depends on tuning, current and on-time. Properly tuned phase lead will greatly reduce switching stress, especially with long on-time.

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #2 on: October 03, 2023, 07:36:37 PM »
Hello Lucasww, I appreciate the insight!

Quote
Phase lead will be very helpful if you are planning to run long on-times, which you will be doing with a ramped coil.
Thank you for confirming that. I will see about adding it. I assume I can copy the phase lead portion from the UD2.7 into the UD1.3?

I would like to build the UD1.3 from scratch, is that typically not advised? It would be a good chunk of work but give me a lot of experience using PCB software, I have an okay foundation. Ideally, I would have the whole DRSSTC on one PCB or at most two. Similar to Loneoceans full bridge SSTC build on a single PCB.

Quote
With 15v input on your GDT, assuming 1:1 turns ratio, you will realistically be able to get 13-14v consistently on your igbt gates. The FGH75T65SHD datasheet shows that they should be fine at that voltage. However, what concerns me more is the possibility of ringing on your gates causing the voltage to drop potentially below 10v, which could easily cause desaturation. This isn't as much of an issue with the typical 18-24v gate drive most use. I'm using FGH75T65SHD in my QCWDRSSTC and have had no issues driving them at 19v.
Looking back on some scope captures of my gate drive signal from my SSTC using a UCC27425 at 15V Vcc I was getting 15.6-16V on the gate. I used a commercial 1:1 GDT.  Not quite as low as you mentioned but it sounds like a good idea to include the push/pull stage to achieve a higher gate drive voltage. I will aim for 18v or so.

Quote
As far as operation and component stress, You will generally want higher coupling, and a higher impedance primary circuit. The stress on your components ultimately depends on tuning, current and on-time. Properly tuned phase lead will greatly reduce switching stress, especially with long on-time.
I have read that higher coupling and impedance is beneficial. Is a higher impedance achieved by more primary turns and a smaller resonant capacitor?

Good to hear that phase lead is so effective!


Thanks again!



Offline Lucasww

  • High Voltage Experimenter
  • **
  • Posts: 52
  • Karma: +4/-0
    • View Profile
Re: RDRSSTC - Project Build
« Reply #3 on: October 07, 2023, 08:51:39 AM »
Quote
I would like to build the UD1.3 from scratch, is that typically not advised? It would be a good chunk of work but give me a lot of experience using PCB software, I have an okay foundation. Ideally, I would have the whole DRSSTC on one PCB or at most two. Similar to Loneoceans full bridge SSTC build on a single PCB.
Building a board from scratch is fine, although it is quite a bit more work, as you mentioned. make sure you use large ground planes to help avoid interference, which is an issue when driving tesla coils.

Quote
Looking back on some scope captures of my gate drive signal from my SSTC using a UCC27425 at 15V Vcc I was getting 15.6-16V on the gate. I used a commercial 1:1 GDT.  Not quite as low as you mentioned but it sounds like a good idea to include the push/pull stage to achieve a higher gate drive voltage. I will aim for 18v or so.
Interesting that you got higher voltages on the gate than you have on the input. Still, the mosfet push/pull buffer is a good idea. 18v should be perfectly fine.

Quote
I have read that higher coupling and impedance is beneficial. Is a higher impedance achieved by more primary turns and a smaller resonant capacitor?
Yes. For QCW coils with >20ms on-time people usually use 7-15nF capacitance, and whatever inductance gives the right frequency. For a mains-ramped coil, your ontime will be probably under 5ms, so slightly more capacitance may be good to get a bit more current. Maybe somewhere around 20-30nF. Typical DRSSTCs use much higher capacitances like 100-500nF

Offline Mads Barnkob

  • Administrator
  • Executive Board Member
  • *****
  • Posts: 2344
  • Karma: +77/-0
  • Denmark
    • View Profile
    • Kaizer Power Electronics
Re: RDRSSTC - Project Build
« Reply #4 on: October 11, 2023, 07:38:51 PM »
Quote
Looking back on some scope captures of my gate drive signal from my SSTC using a UCC27425 at 15V Vcc I was getting 15.6-16V on the gate. I used a commercial 1:1 GDT.  Not quite as low as you mentioned but it sounds like a good idea to include the push/pull stage to achieve a higher gate drive voltage. I will aim for 18v or so.
Interesting that you got higher voltages on the gate than you have on the input. Still, the mosfet push/pull buffer is a good idea. 18v should be perfectly fine.

A high voltage could indicate that you have ringing being rectified or your measurements are not fast enough to capture the ringing.

Why not drive the gates even harder, if you are worried about switching losses? Usually 24VDC is used in the UD1.x/UD2.x drivers. Limiting gate voltage in commercial applications is a way to limit the C-E maximum current, we are beyond trying to nurse our IGBTs like that.
https://kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics
https://www.youtube.com/KaizerPowerElectronicsDk60/join - Please consider supporting the forum, websites and youtube channel!

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #5 on: October 11, 2023, 09:14:42 PM »
Quote
Building a board from scratch is fine, although it is quite a bit more work, as you mentioned. make sure you use large ground planes to help avoid interference, which is an issue when driving tesla coils.
I already started, much more complicated than my last SSTC. Going to be a lot of work.

Quote
Yes. For QCW coils with >20ms on-time people usually use 7-15nF capacitance, and whatever inductance gives the right frequency. For a mains-ramped coil, your ontime will be probably under 5ms, so slightly more capacitance may be good to get a bit more current. Maybe somewhere around 20-30nF. Typical DRSSTCs use much higher capacitances like 100-500nF
Good to know, I will keep this in mind!

Quote
A high voltage could indicate that you have ringing being rectified or your measurements are not fast enough to capture the ringing.
Quote
Interesting that you got higher voltages on the gate than you have on the input. Still, the mosfet push/pull buffer is a good idea. 18v should be perfectly fine.
Regarding the higher gate voltage. I attached a picture of my SSTC gate waveform. It is at 15.6V so probably a little bit of ringing, other than that I think it looks great.



Quote
Why not drive the gates even harder, if you are worried about switching losses? Usually 24VDC is used in the UD1.x/UD2.x drivers. Limiting gate voltage in commercial applications is a way to limit the C-E maximum current, we are beyond trying to nurse our IGBTs like that.
Haha great point, Mads! I was planning on driving them at a higher voltage but just never landed on a value. I agree though, no real point in going easy on them given how they are being used.




Offline Lucasww

  • High Voltage Experimenter
  • **
  • Posts: 52
  • Karma: +4/-0
    • View Profile
Re: RDRSSTC - Project Build
« Reply #6 on: October 11, 2023, 10:25:23 PM »
Waveforms look great. You might be able to get away with slightly less gate resistance for faster transitions, but it's probably perfectly good as is, especially if you decide to raise the voltage

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #7 on: October 12, 2023, 12:43:59 AM »
Quote
Waveforms look great. You might be able to get away with slightly less gate resistance for faster transitions, but it's probably perfectly good as is, especially if you decide to raise the voltage

Thank you. Just to clarify that scope capture was the gate drive from my Ramped SSTC that I was referencing when looking at potentially excluding the push/pull buffer stage from the UD1.3.

For a coil like this, providing a higher gate drive voltage seems to be the best way to go. I will be sure to include the push/pull buffer so I can increase the voltage.


Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #8 on: December 23, 2023, 10:49:07 PM »
Hello,

Picked this project back up and have a few questions before I start working on the PCB.

1. Half wave vs full wave rectification for the bridge - I used a single diode in my RSSTC for halfwave rectification for the bridge. It was a SMD 600v 10A 100A peak standard diode, never had any failures with it. Since this is a Ramped DRSSTC currents should be much higher. My assumption is that a full bridge part/package would be better suited to handle the power and heat dissipation, could I also get away with using a beefier single diode instead? Although, I never did have a heating issue with using a single diode in my RSSTC. I am not sure which solution is better.
       - If I use a full bridge but my ZCD is only half wave rectification via a single 1N4148, would there be an issue with the bridge being powered from both cycles instead of just the half cycles like with a single diode? The ZCD wont trigger and power the
               bridge on for all cycles since it is only outputting a signal on the positive half cycle, which is fine. I only run the interrupter at low BPS, I don't care much for higher BPS.

2. I am aiming for as little bridge inductance as possible but I would still like to include TVS diodes across CE. Are two 1.5kW 220V in series better or can I get away with a single diode 1.5kW 400v type for each?
       - 220v https://www.mouser.com/ProductDetail/652-1.5SMC220CA
       - 400v https://www.mouser.com/ProductDetail/576-1.5SMC400CA

3.Since I am trying to simplify the design a bit I really just added the phase adjust to the UD 1.3b. However, the push/pull transistor stage parts after the UCC27423 are outdated. I have seen other use IRF530/IRF9530, 100v 17A parts but I don't think I need such highly rated MOSFETs. Plus they have much high Qg compared to lower voltage parts. While I have found other parts with better characteristics https://www.mouser.com/ProductDetail/Diodes-Incorporated/DMN6068LK3-13?qs=4YT44p7w2bsq47X783VrzA%3D%3D it is hard to find if they have a PNP counterpart, like the IRF530 vs the IRF9530. Does anyone know of a way to identify a close alternative for a complimentary NPN/PNP stage?
       - Most PNP parts I have found differ slightly, is this expected and still usable or should Vdss and Id match a close as possible?
       - Example of something that might match the PNP DMN6068LK3 above -  https://www.mouser.com/ProductDetail/Diodes-Incorporated/ZXMP6A16KTC?qs=7EMYER6HMn3fGPb2RALoHA%3D%3D

4.Finally, for my last few builds I have cascaded the logic power section instead of tying each linear regulator to DC input (~22v). I guess it comes down to causing more heating in the main 20v regulator and less in the 9v and 5v. With this method I haven't noticed excessive heating in the first regulator. I also have small SMD heatsinks I can also stick on if I need to help dissipate heat. Is there a 'right' way to do it?

Thanks,
Zak


« Last Edit: January 07, 2024, 09:47:08 AM by ZakW »

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #9 on: December 28, 2023, 08:34:05 PM »
Quote
1. Half wave vs full wave rectification for the bridge - I used a single diode in my RSSTC for halfwave rectification for the bridge. It was a SMD 600v 10A 200A peak standard diode, never had any failures with it. Since this is a Ramped DRSSTC currents should be much higher. My assumption is that a full bridge part/package would be better suited to handle the power and heat dissipation, could I also get away with using a beefier single diode instead? Although, I never did have a heating issue with using a single diode in my RSSTC. I am not sure which solution is better.
       - If I use a full bridge but my ZCD is only half wave rectification via a single 1N4148, would their be an issue with the bridge being powered from both cycles instead of just the half cycles like with a single diode? The ZCD wont trigger and power the
               bridge on for all cycles since it is only outputting a signal on the positive half cycle, which is fine. I only run the interrupter at low BPS, I don't care much for higher BPS.
Going to just use the same single diode and I will see how it goes.

Quote
2. I am aiming for as little bridge inductance as possible but I would still like to include TVS diodes across CE. Are two 1.5kW 220V in series better or can I get away with a single diode 1.5kW 400v type for each?
       - 220v https://www.mouser.com/ProductDetail/652-1.5SMC220CA
       - 400v https://www.mouser.com/ProductDetail/576-1.5SMC400CA
Looks like others have used a single 400v TVS. I will do the same.

Quote
3.Since I am trying to simplify the design a bit I really just added the phase adjust to the UD 1.3b. However, the push/pull transistor stage parts after the UCC27423 are outdated. I have seen other use IRF530/IRF9530, 100v 17A parts but I don't think I need such highly rated MOSFETs. Plus they have much high Qg compared to lower voltage parts. While I have found other parts with better characteristics https://www.mouser.com/ProductDetail/Diodes-Incorporated/DMN6068LK3-13?qs=4YT44p7w2bsq47X783VrzA%3D%3D it is hard to find if they have a PNP counterpart, like the IRF530 vs the IRF9530. Does anyone know of a way to identify a close alternative for a complimentary NPN/PNP stage?
       - Most PNP parts I have found differ slightly, is this expected and still usable or should Vdss and Id match a close as possible?
       - Example of something that might match the PNP DMN6068LK3 above -  https://www.mouser.com/ProductDetail/Diodes-Incorporated/ZXMP6A16KTC?qs=7EMYER6HMn3fGPb2RALoHA%3D%3D
Sounds like the IRF530 vs the IRF9530 pair work well. I might try and find complimentary parts with similar but better characteristics if possible.

Quote
4.Finally, for my last few builds I have cascaded the logic power section instead of tying each linear regulator to DC input (~22v). I guess it comes down to causing more heating in the main 20v regulator and less in the 9v and 5v. With this method I haven't noticed excessive heating in the first regulator. I also have small SMD heatsinks I can also stick on if I need to help dissipate heat. Is their a 'right' way to do it?
I am just going to cascade the regulators and add a small SMD heatsink to the 20v regulator if needed.



Finished my first pass on the UD 1.3b with added phase lead. I incorporated the staccato interrupter onto the same PCB. Finally, I redesigned the full bridge layout to be similar to Loneoceans easy bridge setup. IGBTs will lay flat and mount to the top of the heatsink.

Here are my designs so far. Feedback would be appreciated. I still need to go through my schematic a few extra times to ensure I did not make a mistake.



















-Zak




Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #10 on: December 28, 2023, 09:16:47 PM »
Generally looks good.  You may want to add tape where IGBT leads cross other planes.  Solder mask by itself may be good enough, but not reliable at high voltages.

If you want to use higher current bridge rectifier, use it as a single diode.  Two bridge diodes can be paralleled to double current.  Wire bridge's two AC terminals together.  Use that and either + or - output (but not both) as the two diode leads.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #11 on: December 28, 2023, 09:33:53 PM »
Quote
Generally looks good.  You may want to add tape where IGBT leads cross other planes.  Solder mask by itself may be good enough, but not reliable at high voltages.
Thanks, Dave. The IGBTs will be mounted either above or below the PCB (limitation of the 3d model) so the leads will be curved to allow some clearance from the PCB. 

Quote
If you want to use higher current bridge rectifier, use it as a single diode.  Two bridge diodes can be paralleled to double current.  Wire bridge's two AC terminals together.  Use that and either + or - output (but not both) as the two diode leads.
There isn't really enough room for a full bridge, worse case I could also stack two single diodes on one another to increase current capabilities. I did also find higher current diodes in the same package so I am not too worried.
« Last Edit: January 07, 2024, 09:45:50 AM by ZakW »

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #12 on: January 07, 2024, 02:50:26 AM »
Alright, modified UD 1.3b is assembled and so is the new bridge. I have been working like a mad man the last couple of days on this.









Nailed the 3D printed clamp first try. Printed with 100% infill and seems plenty rigid, doesn't flex as far as I can tell. Had to redo the heatsink and ended up making the IGBT leads/spacing a little bit too long but I already have a couple things I want to change anyway.



Testing and first issue:

Powered up the driver with the GDT connected to the full bridge. Signal generator connected to + pin of the CT feedback, running at 400kHz. At 25v it draws around 0.11A, nothing gets hot. Onboard interrupter is working. The damn OCD LED is stuck on though...I have tried adjusting the variable 10k pot but I cant seem to get it to turn off.

Any ideas as to why it would be on as soon as it is powered up? I am not supplying any power to the full bridge yet. Retracing the 1.3b driver so far, I have matched the sections exactly in my schematic. I will continue probing around to see if I can figure anything out in the mean time. I am just not very familiar with this driver at all.

EDIT: Fixed the issue. Turns out I was missing a ground connection for the OCD feedback input section. Soldered a small jumper and the light is off now! I will start testing other parts of the driver now that everything isn't disabled.


Thanks!



Alright, not out of the woods yet. I think I made a mistake in my PCB. Here are the schematics I referenced, 1.3b and 2.1c



Links to both:
1.3b - https://kaizerpowerelectronics.dk/files/stevehv.4hv.org_files/universal_driver_1.3b/DRSSTC_pndriver1_3b.pdf
2.1b - https://kaizerpowerelectronics.dk/files/stevehv.4hv.org_files/universal_driver_2.1b/UD2_1revbschem.pdf

When I was looking at how I was going to add phase lead into the 1.3b schematic I excluded the 74hc14 inverting stage, circled in red in the 1.3b schematic. Looking at the 2.1b there is an extra inverting stage, also circled in red. I added all of the highlighted section in 2.1b nothing else. Scoping the output of my driver it looks like it is constantly running and stops only when the interrupter pulses, which is the opposite of what it should be doing. Seems like the missing inverting stage is the cause.

Here is my schematic for reference:



I would really appreciate if someone would be willing to take a look and confirm my error.

If I did miss a stage I might be able to cut some traces and use jumper wires to at least correct the issue and test the board. I can then work on fixing the issues and eventually ordering another one.


« Last Edit: January 07, 2024, 09:45:27 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #13 on: January 07, 2024, 04:20:51 AM »
Quote
Nailed the 3D printed clamp first try. Printed with 100% infill and seems plenty rigid, doesn't flex as far as I can tell. Had to redo the heatsink and ended up making the IGBT leads/spacing a little bit too long but I already have a couple things I want to change anyway.
Clamps look great!
Yes, lead spacing is long and likely to cause problems.  I'd mount IGBT bodies up against ECB edges to get leads as short as possible.  Given ECB layout, leads can't be as short as would be ideal (ie. with pads at ECB edges).

Quote
Fixed the issue. Turns out I was missing a ground connection for the OCD feedback input section. Soldered a small jumper and the light is off now! I will start testing other parts of the driver now that everything isn't disabled.
Ground should be as close to a solid copper plane as possible.  If a section is floating, I'd connect it with several wires at different locations to be a closer approximation to a ground plane.

Overall looks like great progress.
David Knierim

Offline AstRii

  • High Voltage Engineer
  • ****
  • Posts: 278
  • Karma: +9/-0
  • Czech Technical University in Prague
    • View Profile
    • UHVlab - Tesla Coils | High Voltage | Education
Re: RDRSSTC - Project Build
« Reply #14 on: January 07, 2024, 04:21:41 AM »
What is the purpose of the 3D printed clamp? You could mount the transistors directly to the heatsink. That extra metal pad between IGBT and thermal pad also seems unnecessary. It's all adding high thermal resistance and so the cooling will be worse.
I also believe a thermal pad on its own is not good enough, it should be used in combination with thermal paste (maybe I'm wrong on this?)
Bc. Marek Novotny
Czech Republic, Czech Technical University in Prague
www.uhvlab.org

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #15 on: January 07, 2024, 04:30:01 AM »
Thanks, Dave! Looks like I missed your response while I was editing my last post with another issue.

Quote
Yes, lead spacing is long and likely to cause problems.  I'd mount IGBT bodies up against ECB edges to get leads as short as possible.  Given ECB layout, leads can't be as short as would be ideal (ie. with pads at ECB edges).
Quote
Ground should be as close to a solid copper plane as possible.  If a section is floating, I'd connect it with several wires at different locations to be a closer approximation to a ground plane.
Noted, I will make these changes to the next version.

Quote
What is the purpose of the 3D printed clamp? You could mount the transistors directly to the heatsink. That extra metal pad between IGBT and thermal pad also seems unnecessary. It's all adding high thermal resistance and so the cooling will be worse.
I also believe a thermal pad on its own is not good enough, it should be used in combination with thermal paste (maybe I'm wrong on this?)
The clamps are better for distributing the force of the mounting screw to the body of the IGBT or MOSFET for increased thermal transfer. The screw, if too tight, can cause the IGBT to even lift a bit too. The small aluminum pieces are there for thermal mass to absorb rapid spikes in temperature due to the ramped nature of the coil, the heat is then more slowly distributed to the larger heatsink. I do have thermal paste on the IGBT to the aluminum pieces.
« Last Edit: January 07, 2024, 09:47:27 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #16 on: January 07, 2024, 04:51:55 AM »
Quote
The small aluminum pieces are their for thermal mass to absorb rapid spikes in temperature due to the ramped nature of the coil, the heat is then more slowly distributed to the larger heatsink. I do have thermal paste on the IGBT to the aluminum pieces.
Thought about suggesting this on my previous reply:  The "small" aluminum pieces would be better if larger, and even better yet if copper.  If necessary to shorten leads, they could be thicker.  Thickness is a trade-off.  Increases thermal mass and reduces thermal spreading resistance, but does also increase vertical thermal resistance a bit.  Overall I'd guess somewhat thicker would be net benefit for thermals besides allowing shorter leads.  Larger area would make the most improvement.
Are your thermal pads compliant?  If rigid such as mica or ceramic, then thermal paste is needed on each side of pads too.

Quote
Looking at the 2.1b their is an extra inverting stage, also circled in red. I added all of the highlighted section in 2.1b nothing else. Scoping the output of my driver it looks like it is constantly running and stops only when the interrupter pulses, which is the opposite of what it should be doing. Seems like the missing inverting stage is the cause.
That "also circled in red" inverter appears to be a limit on maximum on-time and duty cycle.  Would cause trouble for a coil running 5ms on-time.  Sounds like you have another inversion mistake somewhere, perhaps a FF Q instead of QN output or such.  I have a hard time following schematics drawn without normal FF and gate symbols, so not sure where your inversion error is.  (BTW, I moved to KiCad from DesignSpark largely because KiCad has better symbols available.)
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #17 on: January 07, 2024, 05:13:51 AM »
Quote
Thought about suggesting this on my previous reply:  The "small" aluminum pieces would be better if larger, and even better yet if copper.  If necessary to shorten leads, they could be thicker.  Thickness is a trade-off.  Increases thermal mass and reduces thermal spreading resistance, but does also increase vertical thermal resistance a bit.  Overall I'd guess somewhat thicker would be net benefit for thermals besides allowing shorter leads.  Larger area would make the most improvement.
Tried using what I had on hand. If it gets too hot I can always add thicker aluminum.

Quote
Are your thermal pads compliant?  If rigid such as mica or ceramic, then thermal paste is needed on each side of pads too.
I am using soft silicone pad material.

Quote
That "also circled in red" inverter appears to be a limit on maximum on-time and duty cycle.  Would cause trouble for a coil running 5ms on-time.  Sounds like you have another inversion mistake somewhere, perhaps a FF Q instead of QN output or such.  I have a hard time following schematics drawn without normal FF and gate symbols, so not sure where your inversion error is.  (BTW, I moved to KiCad from DesignSpark largely because KiCad has better symbols available.)
I use KiCad as well. I have a plug in that I use to download footprints and 3D models directly from Mouser, it is really useful and streamlined. Download the file and it auto adds it to the library.

I will look through my schematic some more tomorrow. Been working on this for about 9 hours straight today.

Update:

Using my function generator I input a 200kHz signal into the CT input and measured the interrupter output as well as the driver output. Confirmed that the coil is running until the interrupter signal starts which is backwards.

Yellow = GDT output
Purple = Interrupter output







« Last Edit: January 07, 2024, 07:27:17 AM by ZakW »

Offline flyingperson23

  • High Voltage Technician
  • ***
  • Posts: 189
  • Karma: +5/-4
  • noob :)
    • View Profile
Re: RDRSSTC - Project Build
« Reply #18 on: January 07, 2024, 03:59:49 PM »
The small aluminum pieces look very close to the heatsink and are electrically connected to the igbt. Maybe make the thermal pad a little bigger than the aluminum on all sides so it doesn't arc over like in https://highvoltageforum.net/index.php?topic=2643.0

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #19 on: January 08, 2024, 01:34:00 AM »
Quote
The small aluminum pieces look very close to the heatsink and are electrically connected to the igbt. Maybe make the thermal pad a little bigger than the aluminum on all sides so it doesn't arc over like in https://highvoltageforum.net/index.php?topic=2643.0
Good call, thanks for pointing that out. Better safe than sorry. The pack of sheets I have come in varying thicknesses I will get a thicker sheet with more clearance.

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #20 on: January 08, 2024, 02:25:29 AM »
Fixed the output, the driver appears to be switching correctly now. Got a crash course on the logic used and followed it to the driver IC. I used an non invert/invert instead of a dual inverting driver IC. Must have mixed up that parts along the way and installed the wrong IC.

Looking at the bridge now!

Update:using my signal generator I was able to get a small breakout at 400kHz using my variac. The coil seems to be running CW and is not being interrupted. Still looking into it.

Quote
That "also circled in red" inverter appears to be a limit on maximum on-time and duty cycle.  Would cause trouble for a coil running 5ms on-time.
Can you explain a bit more about this? I don't see the equivalent in the 1.3 driver.
« Last Edit: January 08, 2024, 03:33:01 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #21 on: January 08, 2024, 04:22:12 AM »
Quote
Can you explain a bit more about this? I don't see the equivalent in the 1.3 driver.
The R/C network on the inverter input is a delay that monitors enable signal.  If on too long, the inverter input goes high, output low, which removes enable.  After a longer off-time delay, inverter output goes back high, allowing enable to pass through the AND gate again.  This helps prevent coil burn-out if enable is accidentally stuck on or set to too-high a duty cycle.  That feature appears to have been added after UD1.3.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #22 on: January 08, 2024, 05:03:07 AM »
Quote
The R/C network on the inverter input is a delay that monitors enable signal.  If on too long, the inverter input goes high, output low, which removes enable.  After a longer off-time delay, inverter output goes back high, allowing enable to pass through the AND gate again.  This helps prevent coil burn-out if enable is accidentally stuck on or set to too-high a duty cycle.  That feature appears to have been added after UD1.3.
Thanks for the clarification.

So after scouring post after post it sounded like the typical fiber connector inverts the interrupter signal. I cut the trace from pin 2 of the 74hc14 and wired it directly to pin 3 of the 74hc74 and it is working!!! The driver only runs during the interrupter pulse, current consumption is way lower (of course). Now I just cant get it to work off of CT feedback.

I can get it to work using my signal generator but that is it. Using a 400kHz signal I am getting about 3in arcs. I tried flipping the phase but scoping the bridge and driver I am not seeing the coil trying to oscillate.

First core (white wire) has 1 turn through both blue and green wire cores. 32 turns on all cores.



Update: Right now I am just trying to get the primary to oscillate so I removed the secondary. I have a chunk of metal inside the primary to absorb some energy.

Primary: 7 turns or 18awg wire, 6.8nF cap. JavaTC says it should oscillate around 877kHz. That is about twice as high as I want so I will try increasing the capacitance to 20nF, that should get me to 511kHz. Still though, I should be seeing the primary oscillate even if it is around 880kHz, right?

I also tested at what voltage is too low for using the signal generator as feedback. Anything under 2v and the output of the driver becomes unstable, cutting out completely at around 1.3v. I rewound a new CT using 2 N87 cores with 22T on each for ~500:1. Flipped phasing around, still cannot get it to oscillate on its own.


Update #2: Referencing Dave's suggestion here - https://highvoltageforum.net/index.php?topic=1373.msg10197#msg10197
Quote
My favorite way to fix startup issues is to make the driver self-oscillating near the coil's resonant frequency.  That can be done to UD2.7 by adding a ~50k resistor from positive comparitor output (IC8 pin 7) to its inverting input (IC8 pin 3), removing R7, and adjusting the value of C33 to get a reasonable frequency.  This works only when jumper SV1 is inserted.  Adding the 50k resistor may be easier soldering by using the open pad for R7 as a connection to IC8-7 and and one end of D1, D2, or R2 for a connection to IC8-3.

50k did not work for me though. I added a 100k pot and tried different values. I still need to measure the resistance but at a certain point I can get the driver to oscillate and subsequently the primary does as well. This is with CT feedback. I added the secondary in there to see if I could get any output. The variac was thumping hard, I tried removing the ferrite rod from my DIY inductor and the thumping was less loud, however when I removed the jumper (no phase lead) the coil came alive! I referenced Loneoceans suggested inductor size but I likely need to fine tune it.

So it seems to be working with self-oscillation as well as no phase lead.

Update #3: Correction, it is working intermittently with phase lead. The self oscillation seems unstable and very finicky. I also switched to a larger secondary I had on hand. I was using one of my mini 2in coils but the larger coil is easier to test on. Managed to get ~10in arcs at around 75v but they were not very straight.

New coil Fres (unloaded) is 500kHz.

JavaTC says 5 turns @ 20nF should put me around 457kHz with 0.324 coupling.
 
« Last Edit: January 09, 2024, 05:31:42 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #23 on: January 09, 2024, 05:38:07 AM »
Quote
I cut the trace from pin 2 of the 74hc14 and wired it directly to pin 3 of the 74hc74 and it is working!!!
I'm not quite following this mod, but if you are bypassing an HC14 stage, you may be missing out on HC14 hysteresis.  Slow rise and/or fall times from optical receiver may trigger subsequent logic at different voltages and therefore different times if not cleaned up by HC14 hysteresis.  Generally best to add an extra stage of HC14 inversion rather than removing one.  Though I'm not certain exactly whether your mod has this issue or not.  Obviously working for now.  Just a risk of possible issues in the future.

Quote
50k did not work for me though. I added a 100k pot and tried different values. I still need to measure the resistance but at a certain point I can get the driver to oscillate and subsequently the primary does as well. This is with CT feedback. I added the secondary in there to see if I could get any output. The variac was thumping hard, I tried removing the ferrite rod from my DIY inductor and the thumping was less loud, however when I removed the jumper (no phase lead) the coil came alive! I referenced Loneoceans suggested inductor size but I likely need to fine tune it.
You may need to decrease size of C6 to get your relatively high frequency with a reasonable self-oscillation feedback resistor value.
BTW, QCW and ramped coils are particularly prone to startup problems, since bus voltage is low when oscillation needs to start.  QCW coils often use FPGAs or other logic to force some number of startup cycles, or use a PLL to have oscillation running prior to feedback being sufficient.  My self-oscillation modification is an alternative, one I use in my QCW coil.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #24 on: January 10, 2024, 06:16:43 AM »
Quote
I'm not quite following this mod, but if you are bypassing an HC14 stage, you may be missing out on HC14 hysteresis.  Slow rise and/or fall times from optical receiver may trigger subsequent logic at different voltages and therefore different times if not cleaned up by HC14 hysteresis.  Generally best to add an extra stage of HC14 inversion rather than removing one.  Though I'm not certain exactly whether your mod has this issue or not.  Obviously working for now.  Just a risk of possible issues in the future.
I skipped IC1F pins 5 & 6 and wired my interrupter directly to pin 1 of IC2A (74HC08). My signal was being inverted one too many times, that seemed to have fixed the issue. Might not be the best solution but at least it got it working for now.



Quote
You may need to decrease size of C6 to get your relatively high frequency with a reasonable self-oscillation feedback resistor value.
BTW, QCW and ramped coils are particularly prone to startup problems, since bus voltage is low when oscillation needs to start.  QCW coils often use FPGAs or other logic to force some number of startup cycles, or use a PLL to have oscillation running prior to feedback being sufficient.  My self-oscillation modification is an alternative, one I use in my QCW coil.
I tried adjusting this but I cant seem to get consistent results. Tuning this does impact the look and sound of the arcs, sort of like my previous coil. Once adjusted correctly the popping and snapping is minimal.

Speaking of which, I cant seem to get good sword arcs with a topload attached. I took a short video and some scope captures. My secondary Fres is 500kHz unloaded so my primary is still out of tune at around 550kHz. I know the topload is lowering the Fres even more but is that why the arc sounds snappy and loud? In the pictures below you can see the blue trace (bridge output) how the sword arcs make a really uniform smooth output but when the arcs are snapping it is more trumpet shape.


Blue = Bridge output
Yellow = TL3116 output (pin 7)
purple = CT feedback (SV1 jumper)

No topload



Blue = Vge


Notice how this waveform is uniform compared to when a topload is used.


Blue= bridge output



Topload on






Do the 'no topload' waveforms look alright? I haven't tried tuning phase lead yet.

« Last Edit: January 10, 2024, 07:47:37 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #25 on: January 11, 2024, 05:05:06 AM »
Quote
I skipped IC1F pins 5 & 6 and wired my interrupter directly to pin 1 of IC2A (74HC08). My signal was being inverted one too many times, that seemed to have fixed the issue. Might not be the best solution but at least it got it working for now.
Yes, not the best solution.  Missing hysteresis of HC14.  Would be better to patch in the spare HC14 instead.  Might stay working fine as is.  I haven't analyzed in detail what issues could be caused by this specific circuit missing hysteresis.

Quote
purple = CT feedback (SV1 jumper)
Triangle-wave shape looks like running in SSTC mode rather than DRSSTC.  Would expect closer to a sine wave.  Even SSTCs with reasonable coupling factor look more sine wave like than your captures, which are all triangle-wave shaped.  Is MMC way too large or perhaps failed shorted?

Quote
Speaking of which, I cant seem to get good sword arcs with a topload attached. I took a short video and some scope captures.
I think the issue is too short a breakout on top of the top load.  Top load shields breakout tip, reducing electric field at tip.  Takes higher secondary voltage before breakout starts.  Breakout is already well up line quarter-cycle ramp.  Once breakout occurs, voltage is high enough to make arc grow too fast for sword sparks, fast like normal DRSSTC arcs.

Quote
My secondary Fres is 500kHz unloaded so my primary is still out of tune at around 550kHz. I know the topload is lowering the Fres even more but is that why the arc sounds snappy and loud?
Even farther out of tune may contribute to arc behavior.  However, QCW coils (and I presume RDRSSTC coils too) work best operating at upper pole.  Two ways to get upper-pole operation.  One is to keep primary frequency a bit above secondary (unlike normal DRSSTC tuning).  Other is to have pre-startup oscillation at a higher frequency (upper pole frequency).  Latter approach works only if coupling is high enough and secondary frequency is not too far above primary frequency.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #26 on: January 11, 2024, 06:02:41 PM »
Quote
Yes, not the best solution.  Missing hysteresis of HC14.  Would be better to patch in the spare HC14 instead.  Might stay working fine as is.  I haven't analyzed in detail what issues could be caused by this specific circuit missing hysteresis.
I will make an update to my schematic and PCB file to include an extra stage.

Quote
Triangle-wave shape looks like running in SSTC mode rather than DRSSTC.  Would expect closer to a sine wave.  Even SSTCs with reasonable coupling factor look more sine wave like than your captures, which are all triangle-wave shaped.  Is MMC way too large or perhaps failed shorted?
I am having issues getting the coil to run at different frequencies. It seems to always oscillate much higher than what javaTC predicts, I know it is just an estimation but I cannot seem to change the frequency much regardless of MMC value or primary. It tends to always be around 500kHz even though I aim for 400kHz or a little lower.

I did notice that after increasing coupling, changing the MMC amount and turn count the feedback signal (purple) was a lot more sinusoidal.

Quote
I think the issue is too short a breakout on top of the top load.  Top load shields breakout tip, reducing electric field at tip.  Takes higher secondary voltage before breakout starts.  Breakout is already well up line quarter-cycle ramp.  Once breakout occurs, voltage is high enough to make arc grow too fast for sword sparks, fast like normal DRSSTC arcs.
You were right, I increased the length and the snapping went away!  ;D

Quote
Even farther out of tune may contribute to arc behavior.  However, QCW coils (and I presume RDRSSTC coils too) work best operating at upper pole.  Two ways to get upper-pole operation.  One is to keep primary frequency a bit above secondary (unlike normal DRSSTC tuning).  Other is to have pre-startup oscillation at a higher frequency (upper pole frequency).  Latter approach works only if coupling is high enough and secondary frequency is not too far above primary frequency.
Sounds good, I have been reading as much as I can about tuning.

Question regarding checking secondary and primary tuning with a signal generator. I found this video https://www.youtube.com/watch?v=GLyW1zRZymk and they show this diagram for how everything is all connected:



Is that correct? I always see the MMC in series with the primary unlike the diagram. I followed the diagram and was able to find the resonant frequency of my current MMC & primary as well as the secondary with a 20in wire to simulate loading. Secondary with topload and wire was 360kHz and the primary was 310kHz  but again when I ran the coil it was quite a bit higher than what was measured. I am at a loss for this.

Edit: I see your post here https://highvoltageforum.net/index.php?topic=783.msg5109#msg5109
Quote
What values do you have for L1, C32, and C33?  Also, what IGBTs are being used?
I am using the standard values per the schematic, 150nF 150pF for C32 and 220pF for C33. What impact does adjusting C32 have?
Quote
2) C33 should be a bit lower for your relatively-high frequency operation of 280kHz.  I'd suggest 470pF, or 680pF at most.
Per Loneoceans notes, I think 220pF for C33 is correct. Ideally I want to operate somewhere in the range of 350-450kHz, depending on the secondary used. I am using a place holder until I get everything running correctly.

Update: Seems like it is the phase adjustment portion of the driver that is causing the issues, copied from the 2.1b and added to 1.3b. When the SV1 jumper is in place the primary fres is around 555kHz, hardly changes with added capacitance. If I remove the jumper fres drops to ~320kHz and responds when MMC is adjusted.
« Last Edit: January 12, 2024, 05:53:15 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #27 on: January 12, 2024, 05:05:30 AM »
Quote
I did notice that after increasing coupling, changing the MMC amount and turn count the feedback signal (purple) was a lot more sinusoidal.
Good, sounds like progress.

Quote
Is that correct? I always see the MMC in series with the primary unlike the diagram. I followed the diagram and was able to find the resonant frequency of my current MMC & primary as well as the secondary with a 20in wire to simulate loading. Secondary with topload and wire was 360kHz and the primary was 310kHz  but again when I ran the coil it was quite a bit higher than what was measured. I am at a loss for this.
That video is measuring frequency of a parallel-resonant circuit, seeing where impedance peaks (maximum impedance frequency).  If measuring series resonant, drive impedance will be minimum at resonance.  Either works for primary.  However, was secondary removed for primary measurement?  Presence of secondary changes primary frequency due to coupling.  For secondary, series resonant mode is the only reasonable way to check.  Any connection to top will change capacitance.  For measuring secondary, it can be in place, but primary coil must be open-circuit to not affect secondary.
Any pair of coupled resonant circuits has two resonant frequencies, neither of which are same as individual frequencies.  Upper pole and lower pole frequencies.  Most QCW and ramped DRSSTC coils run at upper pole frequency.  You can measure those two frequencies by measuring with both coils in place, secondary bottom grounded, and MMC connected.

Quote
I am using the standard values per the schematic, 150nF for C32 and 220pF for C33. What impact does adjusting C32 have?
C32 is a small cap just to filter out any high-frequency noise (such as coupled from bridge output switching events) that might cause unintended comparitor switching.  Presuming we are looking at the same schematic, C32 is the capacitor across CT secondary.  Value is usually 150pF.  If you are using 150nF that could explain problems!  C33 value of 220pF should be good for your frequencies.

Quote
When the SV1 jumper is in place the primary fres is around 555kHz, hardly changes with added capacitance. If I remove the jumper fres drops to ~320kHz and responds when MMC is adjusted.
Operating with SV1 removed is likely to damage circuitry with excess CT output voltage.  I'd check R2 to see if it is still 1k.  Although if you really have 150nF for C32, that would avoid the damage, providing sufficient load to CT output.
« Last Edit: January 12, 2024, 05:07:01 AM by davekni »
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #28 on: January 12, 2024, 06:36:33 AM »
Quote
Good, sounds like progress.
Maybe a little, but tuning it today was frustrating.

Quote
That video is measuring frequency of a parallel-resonant circuit, seeing where impedance peaks (maximum impedance frequency).  If measuring series resonant, drive impedance will be minimum at resonance.  Either works for primary.
Thanks for the clarification. If I understand you correctly, I can have the MMC series or parallel? Are there any benefits or drawback to either configuration? When I google DRSSTC schematics I only see MMC in series with the primary.

Quote
However, was secondary removed for primary measurement?  Presence of secondary changes primary frequency due to coupling.  For secondary, series resonant mode is the only reasonable way to check.  Any connection to top will change capacitance.  For measuring secondary, it can be in place, but primary coil must be open-circuit to not affect secondary.
I took several measurements today and noted all of the values. I also measured under different configurations: with and without primary in place, different toploads, finally a 20in wire to simulate arc.

For the secondary testing I just connect my signal gen to the base and hang a probe near by. Tested various size toploads and noted the Fres.

For the primary I set it up like the schematic suggested so I guess I was measuring parallel-resonance instead. I took measurements with and without the primary around the secondary. Another thing I noticed was the impact of grounding the secondary. I wasn't sure which was correct so I noted those values as well. Grounding the secondary made the Fres quite a bit lower.

Quote
primary coil must be open-circuit
As in not being connected to the MMC?

Quote
Any pair of coupled resonant circuits has two resonant frequencies, neither of which are same as individual frequencies.  Upper pole and lower pole frequencies.  Most QCW and ramped DRSSTC coils run at upper pole frequency.  You can measure those two frequencies by measuring with both coils in place, secondary bottom grounded, and MMC connected.
So if I know the Fres of the secondary is say 500kHz but when the primary is in place and the MMC is connected (secondary is grounded) I can remeasure and determine the upper pole and lower pole? Will the Fres peak higher than 500kHz for upper and the same for a Fres below 500kHz for lower? I was reading Loneoceans DRSSTC and QCW pages but he never explained how he took these measurements.

Quote
C32 is a small cap just to filter out any high-frequency noise (such as coupled from bridge output switching events) that might cause unintended comparitor switching.  Presuming we are looking at the same schematic, C32 is the capacitor across CT secondary.  Value is usually 150pF.  If you are using 150nF that could explain problems!  C33 value of 220pF should be good for your frequencies.
That was a typo  :( I updated my post to correct it. I did install a 150pF cap like the schematic suggests.

Quote
Operating with SV1 removed is likely to damage circuitry with excess CT output voltage.  I'd check R2 to see if it is still 1k.  Although if you really have 150nF for C32, that would avoid the damage, providing sufficient load to CT output.
I did notice without SV1 that feedback voltage was high, I think around 6.4V at times. I only removed it out of frustration. I will check R2 to verify its value and run it with the jumper installed going forward.

Final note on testing: I am using a multi turn primary with 8 turns. I have several caps soldered in place to be able to easily add and remove them. I use two 10nF caps as well as several small 6.8nF for smaller increments. I measured the primary Fres which came out to 310kHz but when the coil was running , bridge output and feedback both showed it running over 500kHz... what could cause this? The secondary Fres without a topload was 530kHz, with a topload and 20in wire, it dropped to 360kHz. So the primary seems to be running far off from resonance.

Sometimes I get what looks like a good primary tap & MMC but then OCD trips at or near120v. So I make a slight adjustment but then OCD trips at a much lower voltage. If it doesn't trip then the arcs are loud, snappy and branched.  >:( 

How might I assume a safe primary current for my IGBTs? I know Loneoceans has a section on how OCD CT voltage correlates to current and how to adjust that voltage via R10 but I am wondering how you can assume this part can run a 250A or 500A? I can double check the datasheet if the answer is there but I assumed since the IGBTs are being driven harder we assume they can handle higher peak currents.

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #29 on: January 13, 2024, 07:38:18 PM »
Quote
Thanks for the clarification. If I understand you correctly, I can have the MMC series or parallel? Are there any benefits or drawback to either configuration? When I google DRSSTC schematics I only see MMC in series with the primary.
Any given inductor and capacitor together can form a resonant circuit.  Frequency is the same whether driven in series or parallel.  Most DRSSTC primaries are driven in parallel.  (Only exception I'm aware of is ZVS driven coils.)  Measuring primary frequency can be done in parallel or series configuration.  Doesn't matter.  Frequency is the same.

Quote
As in not being connected to the MMC?
OK to have one primary lead connected to MMC as long as other lead is open or other side of MMC is open.  Just avoid any closed circuit on primary.  Break that closed circuit at any one point, where ever is convenient.

Quote
So if I know the Fres of the secondary is say 500kHz but when the primary is in place and the MMC is connected (secondary is grounded) I can remeasure and determine the upper pole and lower pole? Will the Fres peak higher than 500kHz for upper and the same for a Fres below 500kHz for lower? I was reading Loneoceans DRSSTC and QCW pages but he never explained how he took these measurements.
Yes for the two pole frequencies.  Probably easiest to measure the assembled system through the primary.  Have secondary in place, bottom grounded and top to top load (and arc simulation wire if you want loaded frequencies).  Then measure frequencies the same way you measured the single isolated primary frequency.

Quote
I did notice without SV1 that feedback voltage was high, I think around 6.4V at times. I only removed it out of frustration. I will check R2 to verify its value and run it with the jumper installed going forward.
SV1 can be installed in either position (with or without phase lead), just not left open.  UD2.7 CT (SV1) voltages are intended to be high, often peak at 50 to 100V.  Without SV1 installed, voltage can go even higher, so fry resistors.  However, in your case, perhaps CT secondary current is too low for reliable US2.7 feedback.  Perhaps CT ratio is too high for a relatively low primary current coil.

Quote
Final note on testing: I am using a multi turn primary with 8 turns. I have several caps soldered in place to be able to easily add and remove them. I use two 10nF caps as well as several small 6.8nF for smaller increments. I measured the primary Fres which came out to 310kHz but when the coil was running , bridge output and feedback both showed it running over 500kHz... what could cause this? The secondary Fres without a topload was 530kHz, with a topload and 20in wire, it dropped to 360kHz. So the primary seems to be running far off from resonance.
Once you measure upper pole frequency, see if that is close.  For initial experiments I'd include top load but no arc-simulation wire.  If operating frequency doesn't match upper pole, then perhaps self-oscillation component values are such that it oscillates at too high a frequency.  Might help to post your schematic as it is now including any self-oscillation modifications.

Quote
Sometimes I get what looks like a good primary tap & MMC but then OCD trips at or near120v. So I make a slight adjustment but then OCD trips at a much lower voltage. If it doesn't trip then the arcs are loud, snappy and branched.  >:( 
Scope current during these conditions to see what actual values are, along with frequency and shape.  Scoping across 51 ohm CT burden resistor is a good option (doesn't require another CT just for scoping).  If SV1 is set for phase lead, scope across just 51 ohms, not including phase-lead inductor.

Quote
How might I assume a safe primary current for my IGBTs? I know Loneoceans has a section on how OCD CT voltage correlates to current and how to adjust that voltage via R10 but I am wondering how you can assume this part can run a 250A or 500A?
Ramped coils have long on-times (quarter or half line cycle).  Rated peak currents are generally for 1ms, 225A I think for your part.  I wouldn't go above 250A for a ramped coil.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #30 on: January 14, 2024, 02:27:58 AM »
Quote
Yes for the two pole frequencies.  Probably easiest to measure the assembled system through the primary.  Have secondary in place, bottom grounded and top to top load (and arc simulation wire if you want loaded frequencies).  Then measure frequencies the same way you measured the single isolated primary frequency.
I'll give that a shot.

Quote
SV1 can be installed in either position (with or without phase lead), just not left open.  UD2.7 CT (SV1) voltages are intended to be high, often peak at 50 to 100V.  Without SV1 installed, voltage can go even higher, so fry resistors.  However, in your case, perhaps CT secondary current is too low for reliable US2.7 feedback.  Perhaps CT ratio is too high for a relatively low primary current coil.
Being completely unfamiliar with the UD, I only installed a 2 pin header instead of a 3 pin. I see now why it is a 3 pin header. My only option is to run SV1 closed unless I remove the inductor and short the connection.

I still need to check the 1K resistor (R6) to make sure it is not fried.

For the inductor I took apart a misc part that I had on hand and added a couple layers and measured with LC meter until I was around "9 - 15uH; works well with TO247 IGBTs" - loneoceans. I can move the slug up or down to vary the inductance. I think that should be fine.



Quote
Scope current during these conditions to see what actual values are, along with frequency and shape.  Scoping across 51 ohm CT burden resistor is a good option (doesn't require another CT just for scoping).  If SV1 is set for phase lead, scope across just 51 ohms, not including phase-lead inductor.
ground lead would be connected to TP1, but are you saying to then scope at TP2 or 3?



Updated schematic using logic symbols instead of IC's. Added notes about things I need to update but this schematic is accurate for the modifications I have made so far.



Quote
However, in your case, perhaps CT secondary current is too low for reliable US2.7 feedback.  Perhaps CT ratio is too high for a relatively low primary current coil.
Quote
Ramped coils have long on-times (quarter or half line cycle).  Rated peak currents are generally for 1ms, 225A I think for your part.  I wouldn't go above 250A for a ramped coil.
My CT is 33:1:25, so 825:1

I'll have to check loneoceans notes on calculating the output voltage given my turns ratio in order to figure out how to set the OCD to the correct value. So far nothing as died so I am grateful for that. Wish my last SSTC had OCD, would have save so much $$$!

Thanks for the all the information!

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #31 on: January 14, 2024, 03:38:08 AM »
Quote
ground lead would be connected to TP1, but are you saying to then scope at TP2 or 3?
Yes, ground to TP1 and probe to TP2.  That is scoping directly across 51 ohm resistor.  Represents current that way.  (TP3 includes phase lead, so would be leading actual current phase and a bit higher amplitude too.)

Quote
Updated schematic using logic symbols instead of IC's. Added notes about things I need to update but this schematic is accurate for the modifications I have made so far.
Thank you.  Makes discussion much clearer.  BTW, self oscillation may work better if R6 is increased from 1k to ~5k as mentioned near the end of this post:
    https://highvoltageforum.net/index.php?topic=1914.msg14854#msg14854
Above post recommends changing R2, the label from common UD2.7 schematics.  This is R6 for your schematic.  Increasing R6 value should help make self-oscillation frequency more stable and easier to adjust.

Without self-oscillation, using 4148 diodes increases CT feedback voltage necessary to start oscillation, relative to UD2.7 schematic that uses schottky diodes.  (Some UD2.7 versions use 1N4148 instead.)  However, 1N4148 or equivalent is good for a self-oscillating version as you now have.

Quote
My CT is 33:1:25, so 825:1
Thus for feedback CT input, +-250A primary becomes 250/825=0.303A, which is +-15.45V across 51 ohms.  Should be fine.

Quote
I'll have to check loneoceans notes on calculating the output voltage given my turns ratio in order to figure out how to set the OCD to the correct value.
Hope I'm not encouraging you to become too lazy by calculating for you.  Fairly simple.  0.303V becomes 3.03V across 10 ohm OCD burden resistor.  Because shutdown takes a cycle (where current can continue to increase slightly), set trip point slightly under 3.03V.

Quote
For the inductor I took apart a misc part that I had on hand and added a couple layers and measured with LC meter until I was around "9 - 15uH; works well with TO247 IGBTs" - loneoceans. I can move the slug up or down to vary the inductance. I think that should be fine.
For a crude approximation, 9uH/51ohms=176ns.  15uH/51ohms=294ns.  This approximation only works when frequency is low enough where 294ns is a small fraction of 90 degrees (of 1/4 cycle).  In your high frequency use, time lead will be less than this simple calculation.  So you may need more inductance depending on both IGBT speed and delay through driver.  Driver delay can be reduced a little by using AC08 instead of HC08.  But AC08 requires good ground plane and supply bypassing due to fast switching.  Use only if ECB layout is good and AC08 is not in a socket.

Quote
Thanks for the all the information!
You're welcome.  Glad it's been useful.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #32 on: January 14, 2024, 04:21:43 AM »
Quote
Thank you.  Makes discussion much clearer.  BTW, self oscillation may work better if R6 is increased from 1k to ~5k as mentioned near the end of this post:
I missed that recommendation. I will give that a try.

Quote
Without self-oscillation, using 4148 diodes increases CT feedback voltage necessary to start oscillation
Not quite sure I follow. Regardless of the self-oscillation mod are you suggesting to swap out D1 & D2 with 4148 type diodes?



Quote
Hope I'm not encouraging you to become too lazy by calculating for you.  Fairly simple.  0.303V becomes 3.03V across 10 ohm OCD burden resistor.  Because shutdown takes a cycle (where current can continue to increase slightly), set trip point slightly under 3.03V.
Not at all. On the contrary, I was trying not to be a burden by asking you for step by step instructions but I appreciate you doing it. I am adding as much as I can to my notes so I can reference these calculations in the future. Growing up I always copied schematics and never invested time into learning theory. So now I am trying to increase my understanding via projects but it can be tough.

Quote
For a crude approximation, 9uH/51ohms=176ns.  15uH/51ohms=294ns.  This approximation only works when frequency is low enough where 294ns is a small fraction of 90 degrees (of 1/4 cycle).  In your high frequency use, time lead will be less than this simple calculation.  So you may need more inductance depending on both IGBT speed and delay through driver.  Driver delay can be reduced a little by using AC08 instead of HC08.  But AC08 requires good ground plane and supply bypassing due to fast switching.  Use only if ECB layout is good and AC08 is not in a socket.
That makes sense, I guess I can make that determination after I scope across the CT resistor. I am comparing the CT feedback to the primary output, right? A lot of DRSSTC scope shots I see dont always label the traces.







« Last Edit: January 14, 2024, 04:38:47 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #33 on: January 14, 2024, 04:52:35 AM »
Quote
Not quite sure I follow. If I wasn't using the self-oscillation mod are you suggesting to swap out D1 & D2 with 4148 type diodes or add diodes like the OCD CT input?
The schematic you show in above post shows MBR0530, a schottky diode as used in most UD2.7 schematics.  This is best for standard UD2.7 without self-oscillating mods.  This post explains normal (not self-oscillating) startup a bit, though for an SSTC circuit with HC14 feedback:
    https://highvoltageforum.net/index.php?topic=840.msg5667#msg5667
UD2.7 input startup is similar.  CT feedback voltage required from first half-cycle is the forward voltage drop of D1 with ~14uA of current flowing through it (quiescent current through 100k R27).  Schottky diodes have much lower Vf, especially at low current, making startup easier.  (D1 is from above post, which is D6 in your schematic.  R27 is R3 in your schematic.)
However, for self-oscillation, schottky diodes clamp the self-oscillation feedback voltage to a low value, reducing frequency stability.  1N4148 diodes allow more voltage there for cleaner self-oscillation.  Because voltage is already oscillating at close to operating frequency, little additional CT feedback voltage is needed to lock to coil frequency.  The higher Vf doesn't increase required startup CT feedback voltage in self-oscillating configuration.

Quote
Not at all. On the contrary, I was trying not to be a burden by asking you for step by step instructions but I appreciate you doing it. I am adding as much as I can to my notes so I can reference these calculations in the future. Growing up I always copied schematics and never invested time into learning theory. So now I am trying to increase my understanding via projects but it can be tough.
An excellent way to increase understanding is with analog simulation.  Many free options available.  My favorite is LTSpice.  Analyzing self oscillation of just the comparitor circuit would be a good place to start.  Doesn't require simulating entire coil.

Quote
I am comparing the CT feedback to the primary output, right?
Yes,  CT feedback current across 51 ohm resistor only (TP2 to TP1 from previous post).  Or some people use a third CT with separate burden resistor for scoping.

Quote
A lot of DRSSTC scope shots I see dont always label the traces.
Yes, that is a common problem that I sometimes complain about.  Hard to respond appropriately to unlabeled scope traces.
« Last Edit: January 14, 2024, 04:54:09 AM by davekni »
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #34 on: January 14, 2024, 05:04:58 AM »
Quote
The schematic you show in above post shows MBR0530, a schottky diode as used in most UD2.7 schematics.  This is best for standard UD2.7 without self-oscillating mods.  This post explains normal (not self-oscillating) startup a bit, though for an SSTC circuit with HC14 feedback:
    https://highvoltageforum.net/index.php?topic=840.msg5667#msg5667
UD2.7 input startup is similar.  CT feedback voltage required from first half-cycle is the forward voltage drop of D1 with ~14uA of current flowing through it (quiescent current through 100k R27).  Schottky diodes have much lower Vf, especially at low current, making startup easier.  (D1 is from above post, which is D6 in your schematic.  R27 is R3 in your schematic.)
However, for self-oscillation, schottky diodes clamp the self-oscillation feedback voltage to a low value, reducing frequency stability.  1N4148 diodes allow more voltage there for cleaner self-oscillation.  Because voltage is already oscillating at close to operating frequency, little additional CT feedback voltage is needed to lock to coil frequency.  The higher Vf doesn't increase required startup CT feedback voltage in self-oscillating configuration.
Thanks for that, I will take a look at that post. I copied the 2.1b schematic which uses MCL4148 diodes instead of the MBR0530. I have some regular 1N4148W diodes I can try in their place.

Quote
An excellent way to increase understanding is with analog simulation.  Many free options available.  My favorite is LTSpice.  Analyzing self oscillation of just the comparitor circuit would be a good place to start.  Doesn't require simulating entire coil.
I have been meaning to get more into simulation. It is on my list to start practicing.


Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #35 on: January 14, 2024, 05:15:53 AM »
Quote
Thanks for that, I will take a look at that post. I copied the 2.1b schematic which uses MCL4148 diodes instead of the MBR0530. I have some regular 1N4148W diodes I can try in their place.
I expect any diode with "4148" in part number has similar characteristics to the original 1N4148.  No reason to change parts.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #36 on: January 14, 2024, 05:22:38 AM »
I decreased R6 (normally a 1K (R2 in 2,1b)) to 560ohms and now I am getting a much better closer to operating frequency output range. Before I swapped out the 1K resistor with a 5K and the TL3116 was oscillating at most several mHz anything lower than 1mHz was not stable. I am using a 50k POT for adjustment.

I will take the other measurements and share my findings, probably tomorrow.


Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #37 on: January 14, 2024, 05:31:22 AM »
Quote
I decreased R6 (normally a 1K (R2 in 2,1b)) to 560ohms and now I am getting a much better closer to operating frequency output range. Before I swapped out the 1K resistor with a 5K and the TL3116 was oscillating at most several mHz anything lower than 1mHz was not stable. I am using a 50k POT for adjustment.
Just looked back at your updated schematic from a few posts ago.  C15 will need to be larger than 220pF, ~1nF, to go along with 5K for R6.  I'd recommend changing C15 rather than going so low for R6 value.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #38 on: January 14, 2024, 06:15:53 AM »
Here are scope captures showing phase lag/lead.

Purple = probe across 51 ohm resistor
Blue = bridge output
Yellow = TL3116 output (I don't think it applies, just had the input on during captures)

This is with the ferrite slug fully seated





Switching looks good to me, not a lot of spikes.



This is with the slug removed





Switching looks worse, is that too much lead?

Edit: Looking at the first picture I am trying to calculate the primary current.

Isecondary=Vburden/Rburden

4.56V/51ohms = 0.089A

Iprimary = Isecondary * Turns ratio

0.089A * 825 turns = 73.43A flowing through the primary?
« Last Edit: January 14, 2024, 06:30:05 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #39 on: January 14, 2024, 07:53:58 PM »
Quote
This is with the ferrite slug fully seated
Quote
Switching looks good to me, not a lot of spikes.
Looks reasonable, but would be better with slightly more phase lead.  You'll need a bit higher inductance to get enough.

Quote
Switching looks worse, is that too much lead?
No, this is far too little phase lead.  Slug removed is minimum inductance so minimum phase lead.

Quote
0.089A * 825 turns = 73.43A flowing through the primary?
Yes.

BTW, for a bit of detail, look at the little bumps in bridge out just prior to switching in your first two slug-in scope captures.  In the second of those first two (at 50ns/div), the bump lasts roughly from division 3 to 4, with the main switching starting at division 4.6.  The beginning of that bump at division 3 is when one set of IGBTs turns off.  The end of the bump at division 4 is when current reverses, pulling bridge output back to it's previous value.  Then opposite set of IGBTs turns on starting at division 4.6.  (Current sense trace appears to be ~70ns delayed from reality.  Not sure exactly why, but seems somewhat common.  Perhaps due to parasitics of CT.)  With ideal phase lead, that bump becomes the real output transition and opposite IGBTs turn on just as current is passing through zero, around 100ns more phase lead than you have now.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #40 on: January 14, 2024, 09:38:24 PM »
Quote
Looks reasonable, but would be better with slightly more phase lead.  You'll need a bit higher inductance to get enough.
More phase lead. Inductor values: With slug 34.1uH, without 7.1uH.

Currently, I have it about halfway seated. If the goal was to reduce that dip as much as possible I think where I have it set now is it.







Quote
No, this is far too little phase lead.  Slug removed is minimum inductance so minimum phase lead.
Oops, I was looking at that backwards.

Quote
BTW, for a bit of detail, look at the little bumps in bridge out just prior to switching in your first two slug-in scope captures.  In the second of those first two (at 50ns/div), the bump lasts roughly from division 3 to 4, with the main switching starting at division 4.6.  The beginning of that bump at division 3 is when one set of IGBTs turns off.  The end of the bump at division 4 is when current reverses, pulling bridge output back to it's previous value.  Then opposite set of IGBTs turns on starting at division 4.6.  (Current sense trace appears to be ~70ns delayed from reality.  Not sure exactly why, but seems somewhat common.  Perhaps due to parasitics of CT.)  With ideal phase lead, that bump becomes the real output transition and opposite IGBTs turn on just as current is passing through zero, around 100ns more phase lead than you have now.
I appreciate the breakdown, thanks!



The arcs seem to all be splitting, usually into two from the breakout. I have yet to get a single straight arc. In an effort to get straighter arcs I am going to try and increase primary impedance by winding a new primary. Currently I am using high MMC value with few turns. I am going to try and reverse that to see if I can slow arc growth down a bit to reduce branching.

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #41 on: January 15, 2024, 02:50:56 AM »
Quote
Currently, I have it about halfway seated. If the goal was to reduce that dip as much as possible I think where I have it set now is it.
Looks good, though I'd consider setting it for slightly more phase lead still (slug farther in).

Quote
The arcs seem to all be splitting, usually into two from the breakout. I have yet to get a single straight arc. In an effort to get straighter arcs I am going to try and increase primary impedance by winding a new primary. Currently I am using high MMC value with few turns. I am going to try and reverse that to see if I can slow arc growth down a bit to reduce branching.
Sounds like a good plan.  I'm certainly no expert on making single straight arcs, but slower ramp rate fits my limited experience.
Edit:  Another change to try is increasing breakout point length.  Found with my QCW coil that if breakout was too short more voltage was required to start arc (as expected).  That higher voltage caused immediate branching as arc grew rapidly initially.
« Last Edit: January 15, 2024, 03:33:08 AM by davekni »
David Knierim

Offline yourboi

  • High Voltage Enthusiast
  • *
  • Posts: 34
  • Karma: +1/-0
    • View Profile
Re: RDRSSTC - Project Build
« Reply #42 on: January 18, 2024, 10:40:47 PM »
Hi I'm just lurking around this thread. Do you have a copy of the 3d print file for the igbt clips? They look pretty solid. Thank you for your time.

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #43 on: January 19, 2024, 03:31:23 AM »
Quote
Hi I'm just lurking around this thread. Do you have a copy of the 3d print file for the igbt clips? They look pretty solid. Thank you for your time.
Sure happy too!

I just tired uploading the .OBJ file and .stil but I am not allowed to on this site. I will try saving them to a google drive and linking them.

Edit: Sent you a pm
« Last Edit: January 19, 2024, 04:06:50 AM by ZakW »

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #44 on: January 19, 2024, 10:06:31 PM »
Bit of an update, in my quest for straighter arcs that split and branch less I am starting to run into an issue. I have tested MANY configurations and so far haven't found a solution yet but I am now noticing some odd behavior from the driver.

I am not sure if it is due to the self-oscillation mod but the driver wont lock onto the primary feedback and oscillate at that frequency. Regardless of what I have the self-oscillation signal set at at, above or below the primary Fres it doesn't seem to kick it out of that mode. It typically oscillates around 250kHz. This occurs the closer I get to matching the primary Fres with the secondary. If it was the oscillation mod I would expect to see the feedback frequency change as I adjust the POT but it doesn't.

Here is an example of what is happening. The coil is running at around 270kHz in the beginning and then switches to running at 397kHz, which happens to be what I measured the secondary Fres at with the current topload and primary in place (open circuit). If I change the primary Fres by added or reducing capacitance I can get the coil to run on feedback again but of course the output suffers. I know that ideally the primary is detuned slightly to compensate for arc loading but I just wanted to share this behavior.

Blue= bridge output
purple= primary feedback across CT resistor

Phase lead isn't ideal either, I was just doing some quick tests.






This shows where the transition occurs.


Any ideas what could cause this? Sometimes the whole on-time of the coil will be with it running around 250-270kHz, primary current (purple) just stays flat around 2 volts depending. When it is operating on primary feedback the current usually spikes towards peak voltage.

Update: So I was messing with it some more and noticed when I turned the self oscillation frequency too high the arcs were curving downward and striking the MMC. I am running it without a topload since arcs seem to be a bit more straight. The low side resulted in louder arcs and more branching.

I was curious to see if the higher self oscitation freq was causing the arcs to curve due to being above the sweet spot (350-450ishKHz).

Purple = CT feedback
Blue = bridge output
yellow = tl3116 pin 7 output.

Overall ramp profile

Zooming in on the beginning we can see it is running at off of the self oscillation frequency +600kHz before it switches to the actual primary frequency. 




I can get straighter arcs by setting the mod closer to the primary Fres but they are still splitting. The only time I managed to get short straight arcs was when I used around 20turns on a primary and low capacitance. Output was poor but they were straight. Any other ideas for how I might get them to stop splitting initially?

« Last Edit: January 20, 2024, 02:24:47 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #45 on: January 20, 2024, 06:02:14 AM »
Quote
This shows where the transition occurs.
H-bridge output voltage is varying, probably due to a parasitic resonance of local bridge snubber cap(s) and bulk cap(s).  Such resonances are common and usually not a problem.  However, occasionally they are problematic, such as when at 2x coil operating frequency.  Not sure if this is contributing to any of your issues or not.  You can try adding snubber capacitance or reducing interconnect inductance to bulk caps to see if either helps.
Edit:  Forgot, no bulk caps on an ramped coil.  Perhaps some other resonance between snubber caps or ...

Quote
Here is an example of what is happening. The coil is running at around 270kHz in the beginning and then switches to running at 397kHz, which happens to be what I measured the secondary Fres at with the current topload and primary in place (open circuit).
Looks like switching from lower pole frequency to upper pole frequency.  Much more common problem is reverse of that.  Perhaps upper pole frequency with a bit of arc loading happens to match your measured secondary frequency.

What self-resonant values are you using now?  Did you make any changes per my reply #37?

Feedback amplitude is on the low side of typical.  1000:1 CT may be too high a ratio for your relatively-low-current coil.  I'd consider reducing CT ratio for more reliable feedback.  However, that may make no difference.  Even your low feedback amplitude appears to be sufficient.

Quote
The only time I managed to get short straight arcs was when I used around 20turns on a primary and low capacitance. Output was poor but they were straight. Any other ideas for how I might get them to stop splitting initially?
Yes, slow ramps make for straight arcs.  The hard part is getting ramp fast enough for long arcs while starting smoothly enough to avoid branching.  Being limited to ramp shape of line quarter-cycle is an extra constraint compared to QCW.  However, I see successful line ramped coils here.  Perhaps someone with a good result can offer ideas.
« Last Edit: January 20, 2024, 06:06:23 PM by davekni »
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #46 on: January 21, 2024, 10:18:40 PM »
Quote
H-bridge output voltage is varying, probably due to a parasitic resonance of local bridge snubber cap(s) and bulk cap(s).  Such resonances are common and usually not a problem.  However, occasionally they are problematic, such as when at 2x coil operating frequency.  Not sure if this is contributing to any of your issues or not.  You can try adding snubber capacitance or reducing interconnect inductance to bulk caps to see if either helps.
Edit:  Forgot, no bulk caps on an ramped coil.  Perhaps some other resonance between snubber caps or ...
I will try adding some snubber capacitors. My leads from the full bridge PCB to the MMC and coil primary are longer than I want but make testing easier, I know that is not ideal.

Using the formula from Mads site https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/snubber-capacitor/:

Assumptions:
Ls = 200nH
Ipeak = 200A
Vtransient = 500V
Vbus = 200V

= 88.9nF, just wanted to get a rough estimate.

Quote
Looks like switching from lower pole frequency to upper pole frequency.  Much more common problem is reverse of that.  Perhaps upper pole frequency with a bit of arc loading happens to match your measured secondary frequency.

What self-resonant values are you using now?
5 turns on my primary and 20-30nF for my resonant cap. The issue doesn't seem to show up when I am above the resonant frequency of the secondary. I check my primary output and CT feedback frequency if it is to high I add a small amount (2.2nF) and remeasure, I see the primary frequency drop accordingly but as soon as I get close to resonance (coil with topload = 462kHz) the primary switches to a much lower frequency (around 350Khz), much lower than what adding a single 2.2nF cap would cause.

Quote
  Did you make any changes per my reply #37?
I am missing where the post number is, can you link it for me?

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #47 on: January 21, 2024, 10:30:44 PM »
Quote
5 turns on my primary and 20-30nF for my resonant cap. The issue doesn't seem to show up when I am above the resonant frequency of the secondary. I check my primary output and CT feedback frequency if it is to high I add a small amount (2.2nF) and remeasure, I see the primary frequency drop accordingly but as soon as I get close to resonance (coil with topload = 462kHz) the primary switches to a much lower frequency (around 350Khz), much lower than what adding a single 2.2nF cap would cause.
This is normal behavior for standard drivers without self-oscillation.  If primary frequency is slightly above secondary, oscillation is at upper pole.  If primary is slightly below secondary, jumps to lower pole.  Self-oscillation can help force upper pole operation, but only if primary frequency isn't too far below secondary.

Quote
I am missing where the post number is, can you link it for me?
Look at the top of each post to any thread.  There's a line such as this one from your last post:
     Â« Reply #46 on: Today at 10:18:40 PM »
I'm referring to reply 37 of this thread, 9 posts before your above one.  It's in page 2 of this thread.  In case that isn't clear enough:
    https://highvoltageforum.net/index.php?topic=2651.msg20288#msg20288
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #48 on: January 22, 2024, 01:00:02 AM »
Quote
Look at the top of each post to any thread.  There's a line such as this one from your last post:
     Â« Reply #46 on: Today at 10:18:40 PM »
I'm referring to reply 37 of this thread, 9 posts before your above one.  It's in page 2 of this thread.  In case that isn't clear enough:
    https://highvoltageforum.net/index.php?topic=2651.msg20288#msg20288
Got it, I see the post number now. Missed that earlier.

Quote
Just looked back at your updated schematic from a few posts ago.  C15 will need to be larger than 220pF, ~1nF, to go along with 5K for R6.  I'd recommend changing C15 rather than going so low for R6 value.
I did update the values and it helped to reduce the upper limit frequency. Making adjustments easier.

Quote
This is normal behavior for standard drivers without self-oscillation.
I am confused because I am using self oscillation.

Like you mentioned I probably want to aim for upper pole operation. For my current Secondary I measured the resonant frequency with the primary in place but open circuit. It was around 462kHz with a topload, no wire for streamer loading. So upper pole is going to be a bit above that? That is what I want to tune my primary for, slightly above 462kHz? If that is the case then I also want to run the oscillation mod at or around that frequency as well, right?

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #49 on: January 22, 2024, 05:30:27 AM »
Quote
I am confused because I am using self oscillation.
Just mentioning that your experience was matching normal w/o self oscillation.  Appears for some reason self oscillation isn't helping force upper pole frequency.

Quote
So upper pole is going to be a bit above that?
Yes.  How far above depends on coupling (and on primary frequency).  High coupling (generally good for QCW and ramped coils) makes upper pole frequency higher and lower pole frequency lower.

Quote
That is what I want to tune my primary for, slightly above 462kHz?
If self oscillation doesn't work to allow lower primary frequency, then yes.

Quote
If that is the case then I also want to run the oscillation mod at or around that frequency as well, right?
If using self oscillation only to start oscillation and not to force upper pole operation, then yes.

Self oscillation can cause upper pole operation even with primary frequency lower than secondary frequency.  That's what my QCW coil does.  However, I think that works best when primary-to-secondary coupling is high.  My QCW coupling is higher than most at 0.7.  I think one or two other forum members have had success with self oscillation forcing upper pole with coupling around 0.4 or 0.45.  Not sure if anyone has tried with lower coupling than that.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #50 on: February 14, 2024, 01:58:17 AM »
Started tinkering again after a short break. Seems like I was able to fix a couple issues, but splitting arcs is my main problem now.

Significantly shortening primary connections and increasing coupling seems to have fixed the pole switching issue as well as the primary not changing its frequency when the tank cap is adjusted. Wrapping the primary directly to the secondary outer former I was able to get a coupling of 0.57k, per JavaTC.

Arc splitting:
  • I have tried everything I can think of to get the arcs to be straighter. So far, the best I can get is without a topload, the arcs are long but they split at the breakout point to form a V but it is very consistent. Both arcs are about ~21in long. With a topload I get several main arcs that then split along their length as well.
  • I have tried increasing primary turns to around 13 all the way down to 2. Higher turns at lower voltage produces much shorter but straighter arcs, at higher input voltage they begin to split all the same. Lower turns significantly increase arc current but can lead to more splitting. 5-6T seems to be the sweet spot.
  • I tested short stubby coils as well as long tall coils, geometry doesn't seem to make a major difference. Best results so far with the shorter coil.
  • Running the coil at higher Fres doesn't seem to reduce splitting either
Looking back on my RSSTC build, I could adjust the primary height to fix arc splitting. Lower primary made for shorter straighter arcs, while raising it caused the arcs to get longer it also made them split at a certain point. Adjusting the primary height with this build doesn't seem to have the same effect if any really.

Could a full bridge DRSSTC simply be supplying too much power to the coil for such a short ramp time with arc splitting being largely unavoidable?

Any ideas or advice would be appreciated.

-Zak

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #51 on: February 14, 2024, 05:32:30 AM »
Quote
Could a full bridge DRSSTC simply be supplying too much power to the coil for such a short ramp time with arc splitting being largely unavoidable?
Certainly one possibility.  Ramped coil doesn't allow changing ramp rate as a QCW coil does.  Another possibility is that feedback doesn't take over from self-oscillation at low enough voltage.  Scope primary current during ramp.  If it jumps up suddenly too far into the ramp (at too high line voltage), that sudden start may be causing branching.  Sudden jump in current may happen when feedback takes over, making frequency match (presumably upper) pole frequency.  If that is the issue, adjust self-oscillation frequency to more closely match upper pole frequency.  (Match frequency just before current jump to frequency after.)
« Last Edit: February 14, 2024, 06:07:17 AM by davekni »
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #52 on: February 14, 2024, 06:25:45 PM »
Quote
Another possibility is that feedback doesn't take over from self-oscillation at low enough voltage.  Scope primary current during ramp.  If it jumps up suddenly too far into the ramp (at too high line voltage), that sudden start may be causing branching.  Sudden jump in current may happen when feedback takes over, making frequency match (presumably upper) pole frequency.  If that is the issue, adjust self-oscillation frequency to more closely match upper pole frequency.  (Match frequency just before current jump to frequency after.)
*I will edit this post and attach the scope capture later.*

I forgot to mention a couple other changes I made. I reduced gate resistance for each IGBT from 15ohms to 10ohms and shortened the GDT output connections.

To your point when I was testing the other day, I probed the self oscillation output, CT output and primary. With the changes I made the self oscillation appeared to switch as soon as the ramp starts. I did not zoom in super close but the current ramped up smoothly as expected (like what I would see with my SSTC). I will post the capture for this later.

The oscillation mod is acting differently too (in a good way), it is more sensitive and usually has to be set quite high. Before it would work below or above resonance. I think Rafft had a similar experience with his QCW coil. It typically runs somewhere around 650kHz, going far above that causes no oscillation and running at a lower frequency causes primary to secondary arcing. Again, a similar issue I had with my RSSTC.



EDIT: Scope captures.

Yellow=Self oscillation output
Purple=primary current via CT
Blue=Primary output

Self oscillation is running around 781kHz before the coil turns on. Looks like that drops to 625kHz on startup and then all the way down to 490kHz at the halfway point.









« Last Edit: February 15, 2024, 05:57:24 AM by ZakW »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #53 on: February 15, 2024, 07:11:20 PM »
Quote
EDIT: Scope captures.

Yellow=Self oscillation output
Purple=primary current via CT
Blue=Primary output

Self oscillation is running around 781kHz before the coil turns on. Looks like that drops to 625kHz on startup and then all the way down to 490kHz at the halfway point.
Scope captures all look good.  Thank you for posting.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #54 on: February 16, 2024, 03:50:58 AM »
Had my first bridge failure. Not bad considered I killed around ~15 or more IGBTs & MOSFETs with my RSSTC.

OCD did not seem to trigger when it failed. I might have it adjusted too high.

I did have moderate success with some initial testing to reduce arc branching. I added a small wire wound inductor on the primary output in an effort to limit the initial current to the primary. I was only able to mess with the coil and look at the scope for a bit before it failed. But it managed to reduce branching quite a bit! Primary current was much lower for ~1.5ms or so before ramping up as usual, I think this is what helped to reduce branching. The coil failed after reducing the tank cap. I will have to take a look at it more this weekend and see what I can find out and do some more testing.

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #55 on: February 17, 2024, 08:56:42 PM »
Quote
Primary current was much lower for ~1.5ms or so before ramping up as usual, I think this is what helped to reduce branching.
Agree, that sounds likely.  Slower start helps reduce branching.  However, whatever is causing that change 1.5ms into ramp might be a cause of failure.  Only guess that comes to mind is that feedback isn't taking over from self-oscillation for initial 1.5ms under conditions of this test.
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #56 on: February 17, 2024, 10:20:39 PM »
Quote
However, whatever is causing that change 1.5ms into ramp might be a cause of failure.  Only guess that comes to mind is that feedback isn't taking over from self-oscillation for initial 1.5ms under conditions of this test.
That is what I was thinking too but I did not get the chance to do enough testing. Since I haven't had a failure until recently these are the original IGBTs and I think I have stressed them A LOT. I noticed some uneven heating in two of the IGBTs before they failed so I think they were already compromised.

I will do some more testing and post my results.

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #57 on: May 18, 2024, 01:55:42 AM »
Hello again,

After a nice 3 month break I want to pick up where I left off. I'd like to start with lessons learned so far in my initial full bridge design and how I plan to overcome them in later iterations. I made several design mistakes that ultimately led to the bridge failing repeatedly. I would also like to take a moment to highlight that making mistakes is how you learn, and you can only help yourself by learning the most you can from them. That is why I am sharing my mistakes so as to help others avoid the same pitfalls.

Mistake #1 - PCB Mounting Hole Clearance
I used two mounting screws and a 3D printed spacer to secure the full bridge PCB to the large heatsink base. As you can see from the pictures either the silkscreen failed or the screw (when tightened) scratched through the silkscreen enough to cause it to short out. This issue coupled with my second mistake led to several more failures as I continued to troubleshoot. For high power/voltage connections do not rely on the silkscreen for adequate insulation!




Proposed solution: I plan on either using much more clearance around the mounting hole or mounting the PCB in another way.

Mistake #2 - IGBT Heatsink Isolation
As you can see from the pictures the plan was to use small blocks of aluminum to help rapidly pull heat away from the part so it could then more slowly dissipate through the silicone thermal pad into the larger heatsink. My mistake was not adding enough clearance for the through hole drilled in the aluminum block. This essentially rendered the thermal insulation pad useless and led to intermittent shorts between the other IGBTs via the main larger heatsink.





Proposed solution: I have redesigned some 3D printed clips for the IGBTs. The clip itself will mount to the heatsink and then press the body of the IGBT into the heatsink. This will maintain the benefit of ‘pressing’ the part for better heat transfer while also removing the issue surrounding shorting the collectors together.




Mistake #3 - Bridge Power Input Design
The UD1.3 driver I am using has a built in ZCD that receives a small AC signal from a mini signal transformer on the full bridge. That needs to be powered on (connected to mains) for the controller to work. The way I had the PCB traces routed would not allow me to insert a power switch without also disconnecting power for the AC signal transformer. To get around this I used the fuse mounting points for a switch and inline fuse instead.



Solution: Adjust the layout so a switch can be added to control bridge power while keeping the signal transformer powered.

Mistake #4 - PCB Layout & IGBT Lead Length
As you can see from the pictures the lead length for each part is much longer than anticipated. In order to have enough clearance for the underside of the PCB I had to raise it up to the point where the leads had to be long in order to connect.




Proposed solution: I am redesigning the bridge to ensure better clearance and shorter lead lengths. Additionally, I will be switching from a full bridge design to a half bridge as I continue to test my designs.

Once I redesign the bridge and receive the new boards I will continue testing ways to reduce arc branching. A promising lead I discovered before the bridge failed was adding a small air core inductor in series with the primary. I was unable to get any scope captures but I was able to visibly see a smoother ramp in the initial current as well as the arcs being noticeably straighter and often only a single arc would form. Which is very promising!

Here is a quick video of the performance I was able to get from the coil. The first video you can see the output is decent but has many branches, the second video was after I adjusted coupling, primary turns, tank cap, shortened leads, and reduced the top load size. That resulted in two arcs usually which was the best that I could get with the current configuration.


I suspect that the output branches so much because I cannot adjust the ramp input (like a typical QCW) combined with the increased power of a dual resonant full bridge. Because of that the branching may be inherent with the design, however, after seeing the improvement the inductor made to the output I am hopeful that I will be able to get even better performance yet. The half bridge may also function to reduce overall output power and thus help with branching.

Every project, mistakes are made and lessons are learned  ;D I plan on doing something with all of these parts someday, maybe pouring epoxy over them to make some coasters or something... These are all the parts I have accumulated over the last couple of years.


I haven't started on the redesign for the half bridge yet so it will take some time.

Stay tuned!

-Zak
« Last Edit: May 18, 2024, 09:54:33 AM by ZakW »

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #58 on: June 02, 2024, 12:41:50 AM »
Update on my progress so far, I decided not to create a new PCB for the bridge quiet yet and instead opted to create a low inductance half bridge from copper foil tape. So far so good.

My main goals: arc appearance (straight as possible), arc length, arc length to secondary size.

Here is a video of what all of my tinkering has led to, solid 19in arcs @120v input with little branching.

https://www.youtube.com/shorts/_QRPqyiH22c

/>
Currently, I am still thinking that due to the short ramp time of ~8ms that mains ramped coils have to operate in, there is only so much that can be done to boost arc length at the cost of increased branching. Both ramped SSTC and DRSSTC do not have any issues hitting 12-15in sword arcs, it is when you try and get every last bit of power from the coil where tuning becomes so critical.

IGBTs are mounted on a small heatsink and do not heat up whatsoever.

Setup:
  • Primary = 2T 14awg wire
  • 4.1uH air core inductor in series with the primary (more on this later)
  • Half bridge (more on this later), with reduced DC split rail caps 0.33uF instead of normal 1uF.
  • Very small topload (more on this later)
  • Resonant MMC = ~94nF
  • Secondary feedback instead of primary (more on this later)

Primary turns - anything more than 2 turns and the arc length tanks, 3-4T gives a max of like 10in arcs :(

Series inductor - the goal here was to add some inductance to slow the inrush of current into the primary. So far I think it is working as intended but I still plan to test the coil without it. Another thought is that I am getting the advantage of only having 2T on the primary so there is more voltage present on the secondary while the additional resistance from the inductor is being mitigated by the resonant capacitor, might not be correct…

Half bridge - after the full bridge died I built a half bridge to continue testing, and reduce part usage in case something else failed. I noticed the bridge output was very square, and not sinusoidal-ish like my previous RSSTC. Being that both coils used around 2T on the primary I reduced the DC split rail caps from 1uF to 0.33uF, this improved output by a couple inches. Smaller DC split rail caps respond more quickly to changes in current, providing a more stable current output to the primary.

Topload - Smaller toploads seem to work much better. Even a large washer is sufficient. I am not sure if this is because I am using tiny coils with high res frequency wound with thin wire but the output is branched and short with most toploads I have tried regardless of tuning. More on this later.

MMC - this is so large due to the added inductance. I need to buy some larger caps so I am not dealing with so many. All are ~2000v DC caps that I HAVE NOT soldered any in series to increase voltage rating, so far none have heated or failed. My assumption is that the voltage doesn’t have time to ring up to such high levels compared to a traditional DRSSTC?

Feedback - From all my testing I think it safe to say that for a mains ramped coil, secondary feedback works best. I could not get anywhere close to the level of optimization when using primary feedback nor could I get reliable operation. When using primary feedback minor adjustments caused large swings in behavior and output.

OCD - I am still using the OCD CT so hopefully that will shut the driver down in the event of over current. OCD has not tripped with the half bridge. I even turned down the threshold from max 3.03v to around 2.5v if I recall.

Current measurement - using the primary current CT with a 51 ohm burden resistor to monitor current ramp.

Scope captures & findings: Blue = Bridge output (differential probe) Purple = primary CT with 51 ohm burden resistor

Ideal current ramp - Example from the video above

  • Ideal tuning of C, L, and primary height
  • Arcs sound much more like QCW arcs instead of normal ramped arcs
  • Little to no branching
  • Arcs do not start getting long until ~100v input

Too much current too soon

  • Current is ramping too much before half wave peak
  • MMC to high
  • Primary could be set to high also
  • Coil detuning to resonance too early
  • arcs begin to split and branch

Normal current

  • Short but straight arcs
  • Sounds like RSSTC
  • Not optimized, needs tuning
  • Works on lower voltage input


My understanding & theory:
Once sufficient voltage is applied to the bridge (~100v) the coil initially starts oscillating way too high and far away from resonance for the given primary tank capacitance and inductance. Therefore resonant energy transfer is low. As the arc starts and begins to grow it begins detuning the coil pulling it lower. This is exacerbated by not having a topload to stabilize frequency, which I think in this application is an added benefit. This cycle continues as the arc grows causing more and more energy to build steadily rather than sharply. This leads to straighter arc formation and less branching.

Tl:dr - as arc length increases, frequency decreases, resonant energy transfer increases.

Please poke holes in my theory. That is what I have concluded so far and would love to hear some feedback from others.

-Zak
« Last Edit: June 02, 2024, 12:56:05 AM by ZakW »

Offline Benjamin Lockhart

  • High Voltage Technician
  • ***
  • Posts: 136
  • Karma: +15/-0
    • View Profile
Re: RDRSSTC - Project Build
« Reply #59 on: June 02, 2024, 08:36:07 AM »
This is interesting!

An off-axis series inductor will lower the effective coupling, so that's something to bear in mind. It may not actually give you more secondary voltage, I'm not sure.

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #60 on: June 02, 2024, 08:49:11 AM »
Quote
An off-axis series inductor will lower the effective coupling, so that's something to bear in mind. It may not actually give you more secondary voltage, I'm not sure.
Do you mind elaborating a bit? Is proximity an issue or are you saying because it is simply in series with the primary?

Here is a quick picture of the inductor soldered to the tank cap and primary. It is about 6in away from the coil


Here is a picture of the half bridge since I haven't shared one yet.


-Zak

Offline Michelle_

  • High Voltage Technician
  • ***
  • Posts: 180
  • Karma: +2/-0
    • View Profile
Re: RDRSSTC - Project Build
« Reply #61 on: June 02, 2024, 04:44:30 PM »
Mistake #1 - PCB Mounting Hole Clearance
Proposed solution: I plan on either using much more clearance around the mounting hole or mounting the PCB in another way.



Bad choice of fastener for a few reasons IMO. I would recommend a machine screw (that will have finer and less sharp threads) combined with a nonmetallic washer, or even a nonmetallic machine screw depending on the case. For stuff like this it's good to have a few taps and drills around, for example an M3 or M4 bottoming tap would make really nice mounting holes on that block. Another problem with using Philips head screws like that is the grip with the tool, they are prone to slipping, stripping, and you often have to push down hard which can lead to issues possibly like what you have where the fastener is gouging into the surface because you're driving it down. A machine screw with an allen key driving it, and especially with a washer underneath, is a lot more gentle and precise not to mention being able to produce more torque.

Another possibility is to eliminate the fastener by making posts for the PCB mounting holes instead to locate it, and then rely on clips or brackets of some kind, or even just the IGBTs to hold it down.

Not being critical, just offering suggestions to make the design more serviceable.

« Last Edit: June 02, 2024, 04:48:35 PM by Michelle_ »

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #62 on: June 02, 2024, 10:29:02 PM »
Quote
Here is a video of what all of my tinkering has led to, solid 19in arcs @120v input with little branching.
Look great to me!  Though I don't have any directly comparable experience.

Quote
Currently, I am still thinking that due to the short ramp time of ~8ms that mains ramped coils have to operate in, there is only so much that can be done to boost arc length at the cost of increased branching.
Yes, I'd agree.  In particular, ramp time is generally only 4ms or even a bit less.  Only 1/4th cycle of line voltage is increasing.  And even the last bit of that is rather flat.

Quote
Ideal current ramp - Example from the video above
You have managed to stretch the ramp time to ~5ms!  Not sure just what combination of circuit parameters and arc loading effects causes this.  But it likely explains why your tuning is so specific and doesn't fit well to typical wisdom about ramped coils (such as being best with as high coupling as possible).

Quote
Smaller toploads seem to work much better. Even a large washer is sufficient.
Small top load combined with low coupling is unusual for a ramped coil.  Perhaps part of your achieving longer ramp time.
Larger top loads often require a longer and/or sharper breakout in order to start arc early enough during ramp.

Quote
Scope captures & findings: Blue = Bridge output (differential probe) Purple = primary CT with 51 ohm burden resistor
I'm guessing your CT is still 825:1.  Had to search back through thread to find that number.  Would be convenient to mention volts-to-amps conversion on scope traces of current.

Quote
Quote
    An off-axis series inductor will lower the effective coupling, so that's something to bear in mind. It may not actually give you more secondary voltage, I'm not sure.
Do you mind elaborating a bit? Is proximity an issue or are you saying because it is simply in series with the primary?
Using random simple example numbers: a 1uH inductor in series with a 1uH primary is the same as a 2uH primary with sqrt(1/2) as much coupling.  You could achieve same result with a higher inductance lower coupling primary, such as a larger diameter 2-turn coil.
Higher coupling is generally better for ramped coils.  However, your specific case of stretching ramp to ~5ms will likely not hold if parameters are optimized in a conventional way.

Quote
Here is a picture of the half bridge since I haven't shared one yet.
Looks good.

Quote
I reduced the DC split rail caps from 1uF to 0.33uF, this improved output by a couple inches. Smaller DC split rail caps respond more quickly to changes in current, providing a more stable current output to the primary.
Split capacitors are in series with 94nF MMC.  Most significant effect of reducing them is to reduce effective MMC capacitance.  That tuning happens to work better for your coil.
Other perhaps-significant effect is to reduce total Vbus capacitance (1uF plus two split caps in series).  Vbus capacitance is charged to peak of line voltage (170V) at ramp start (unless discharged by a bleed resistor).  Don't see any initial spike at ramp start in your scope captures, however.

Quote
My assumption is that the voltage doesn’t have time to ring up to such high levels compared to a traditional DRSSTC?
You have primary current measurement.  MMC voltage can be calculated based on current and frequency.

Quote
OCD has not tripped with the half bridge.
Presuming 825:1 CT, 5.1V across 51ohms on current trace translates to 82.5A.

Quote
Proposed solution: I plan on either using much more clearance around the mounting hole or mounting the PCB in another way.
For line voltage to ground, your existing screw with an insulating washer should be fine.  Presume mounting structure is grounded.
To minimize any unintended extra line-to-ground voltage at TC frequency, a small cap from line to Vbus- will bypass such higher frequency current.  ~5nF is typical, usually called a "Y cap" in power supply designs.
« Last Edit: June 02, 2024, 10:35:47 PM by davekni »
David Knierim

Offline ZakW

  • High Voltage Engineer
  • ****
  • Posts: 227
  • Karma: +7/-0
  • YouTube @QZW_Labs
    • View Profile
Re: RDRSSTC - Project Build
« Reply #63 on: June 03, 2024, 01:08:47 AM »
Quote
Look great to me!  Though I don't have any directly comparable experience.
Thanks! I am just happy that the output is at least consistently straight and not branching. It has been very frustrating trying to get straighter arcs. 21in is the record for me to beat, that is what I was able to get with my RSSTC. I think I am going to make another temporary full bridge with copper tape and try that now that I have things working again.

Quote
You have managed to stretch the ramp time to ~5ms!  Not sure just what combination of circuit parameters and arc loading effects causes this.  But it likely explains why your tuning is so specific and doesn't fit well to typical wisdom about ramped coils (such as being best with as high coupling as possible).
So I have the primary almost directly wrapped to the secondary form. There is still a gap since I have epoxy inside and an outer form but it is as close as it can get. Are you saying that the added inductor is effectively lowering the coupling by being included regardless of how close the primary is to the secondary?

Quote
Small top load combined with low coupling is unusual for a ramped coil.  Perhaps part of your achieving longer ramp time. Larger top loads often require a longer and/or sharper breakout in order to start arc early enough during ramp.
When I use a topload even though the frequency drops a bit the output is just terrible. The arcs are very 'squiggly' and branched even though the coil is operating close to what it was before with a smaller topload. Current also goes way up. Could this be related to the fact that my coils are wound with very thin wire (44-41awg) and have different parameters than traditional coils with lower resistance thicker awg wire?

I also think that by not having a large topload the coil is more easily detuned as the arc grows further assisting it getting to resonance in such a short window.

Quote
I'm guessing your CT is still 825:1.  Had to search back through thread to find that number.  Would be convenient to mention volts-to-amps conversion on scope traces of current.
Thanks for checking, you're correct. I just fired up the scope to see what the peak voltage was with this smaller coil I am testing. At peak it is at 10v, so that is ~162A.

Quote
Using random simple example numbers: a 1uH inductor in series with a 1uH primary is the same as a 2uH primary with sqrt(1/2) as much coupling.  You could achieve same result with a higher inductance lower coupling primary, such as a larger diameter 2-turn coil. Higher coupling is generally better for ramped coils.  However, your specific case of stretching ramp to ~5ms will likely not hold if parameters are optimized in a conventional way.
I can try removing the inductor and decreasing the coupling of the primary to see if I can achieve the same output. I do think that having the inductor allows me to more easily tune it since I can tap the coil or add and remove turns, while keeping the primary fixed. Seems to have been easier to manage vs rewinding the primary a thousand times like I have before.

Quote
Split capacitors are in series with 94nF MMC.  Most significant effect of reducing them is to reduce effective MMC capacitance.  That tuning happens to work better for your coil.
Other perhaps-significant effect is to reduce total Vbus capacitance (1uF plus two split caps in series).  Vbus capacitance is charged to peak of line voltage (170V) at ramp start (unless discharged by a bleed resistor).  Don't see any initial spike at ramp start in your scope captures, however.
So this is roughly what the bridge output looks like with the smaller 0.33uF caps. You can see it is more sinusoidal. With the 1uF caps the waveform was much more square, regardless of the MMC tuning. This was something that I noticed in my RSSTC. When I reduced the DC caps from 1uf to 0.3uF I had a large increase in output. However, the SSTC coil was running closer to primary resonance and was leading to the IGBTs failing due to too much current.
Blue = bridge output purple = current CT


Quote
You have primary current measurement.  MMC voltage can be calculated based on current and frequency.
I will look into calculating this.

Thanks for the feedback so far everyone :)

Offline davekni

  • Executive Board Member
  • *******
  • Posts: 2971
  • Karma: +140/-2
  • Physicist, engineer (electronic), and hobbiest
    • View Profile
Re: RDRSSTC - Project Build
« Reply #64 on: June 03, 2024, 05:02:19 AM »
Quote
There is still a gap since I have epoxy inside and an outer form but it is as close as it can get. Are you saying that the added inductor is effectively lowering the coupling by being included regardless of how close the primary is to the secondary?
Many factors affect coupling.  Close diameter increases coupling.  So does raising height of primary.  So does spreading out the primary turns vertically (even for the same center height).  Whatever your coupling may be before adding external inductor, that coupling will be reduced by adding the inductor.

Quote
I also think that by not having a large topload the coil is more easily detuned as the arc grows further assisting it getting to resonance in such a short window.
That may be a key way you stretch ramp time - by hitting optimum tuning near end when line voltage is starting to drop.

Quote
I do think that having the inductor allows me to more easily tune it since I can tap the coil or add and remove turns, while keeping the primary fixed. Seems to have been easier to manage vs rewinding the primary a thousand times like I have before.
Yes, adjustability is an advantage to added inductor.  Even just stretching its length suffices to adjust it (lower inductance).  You may need the resulting lower coupling in order to get the optimum ramp extension past 4ms.

Quote
So this is roughly what the bridge output looks like with the smaller 0.33uF caps. You can see it is more sinusoidal. With the 1uF caps the waveform was much more square, regardless of the MMC tuning. This was something that I noticed in my RSSTC. When I reduced the DC caps from 1uf to 0.3uF I had a large increase in output.
Yes, that's because bridge output now effectively includes part of MMC.  The half-bridge is still generating close to a square wave.  The other side has ~0.58uF (0.33uF in parallel with series of other 0.33uF in series with 1uF Vbus cap).  The sine wave contribution is from that passive side of bridge.  Sine wave current generating sine wave voltage across 0.58uF.

David Knierim

High Voltage Forum

Re: RDRSSTC - Project Build
« Reply #64 on: June 03, 2024, 05:02:19 AM »

 


* Recent Topics and Posts

post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
November 05, 2024, 10:03:21 PM
post Re: New UD2.9 smd DRSSTC drivers
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
November 05, 2024, 09:54:43 PM
post Re: First DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
November 05, 2024, 09:52:05 PM
post Re: First DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
November 05, 2024, 07:45:57 PM
post First DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Aranox
November 05, 2024, 07:02:18 PM
post Re: High Voltage High Current Supply Ideas
[General Chat]
JoeBusic
November 05, 2024, 05:35:53 PM
post Re: The evolution of a solid state Tesla coil
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Anders Mikkelsen
November 05, 2024, 02:39:18 PM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Anders Mikkelsen
November 05, 2024, 02:26:49 PM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
November 05, 2024, 08:15:12 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 05, 2024, 05:32:32 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
November 04, 2024, 11:39:19 PM
post Re: New UD2.9 smd DRSSTC drivers
[Dual Resonant Solid State Tesla coils (DRSSTC)]
TXtesla
November 04, 2024, 04:00:50 PM
post Re: High Voltage High Current Supply Ideas
[General Chat]
rikkitikkitavi
November 04, 2024, 12:48:31 PM
post Re: New UD2.9 smd DRSSTC drivers
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Late
November 03, 2024, 09:44:10 PM
post Non sparking Tesla coil, how to?
[General Chat]
JoeBusic
November 03, 2024, 09:43:36 PM
post Re: Welcome new members, come say hello and tell a little about yourself :)
[General Chat]
JoeBusic
November 03, 2024, 09:36:04 PM
post Re: Welcome new members, come say hello and tell a little about yourself :)
[General Chat]
adamcord
November 03, 2024, 10:23:58 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 03, 2024, 06:03:58 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
November 03, 2024, 05:25:35 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 03, 2024, 05:16:10 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
November 03, 2024, 04:56:37 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 03, 2024, 03:51:55 AM
post Re: DRSSTC with litz-wire primary and 40 x TO247 IGBT H-Bridge
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 03, 2024, 03:17:00 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 03, 2024, 02:59:46 AM
post Re: DRSSTC with litz-wire primary and 40 x TO247 IGBT H-Bridge
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
November 03, 2024, 02:00:35 AM
post Re: DRSSTC with litz-wire primary and 40 x TO247 IGBT H-Bridge
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 03, 2024, 01:40:36 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
November 03, 2024, 12:22:24 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 02, 2024, 11:03:44 PM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
November 02, 2024, 10:42:13 PM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
November 02, 2024, 10:05:29 PM
post Re: is this blocking cap nessary
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
November 02, 2024, 02:25:54 AM
post is this blocking cap nessary
[Dual Resonant Solid State Tesla coils (DRSSTC)]
thedoc298
November 02, 2024, 02:14:33 AM
post Re: High Voltage High Current Supply Ideas
[General Chat]
klugesmith
November 01, 2024, 09:38:08 PM
post Re: My SSTC's IGBT's blow up when toroid is added
[Solid State Tesla Coils (SSTC)]
Frantisek
November 01, 2024, 02:37:57 PM
post Re: High Voltage High Current Supply Ideas
[General Chat]
huntergroundmind
November 01, 2024, 02:00:15 PM
post Re: DIY X-RAY generator made of eBay parts
[X-ray]
inanium
November 01, 2024, 07:58:44 AM
post Re: Proper capacitance size
[Spark Gap Tesla Coils (SGTC)]
MRMILSTAR
November 01, 2024, 04:16:16 AM
post Re: Proper capacitance size
[Spark Gap Tesla Coils (SGTC)]
Benjamin Lockhart
October 31, 2024, 09:54:55 PM
post Re: Proper capacitance size
[Spark Gap Tesla Coils (SGTC)]
Hysteresis
October 31, 2024, 09:34:24 PM
post Proper capacitance size
[Spark Gap Tesla Coils (SGTC)]
BibberCoils
October 31, 2024, 06:46:32 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic Circuits]
betalab99
October 31, 2024, 02:06:00 PM
post Re: [WTS] Yard Sale (IGBT's/Wires/Cooling/wire/induction/BusCaps/Coils/Magnetrons)
[Sell / Buy / Trade]
Late
October 31, 2024, 07:32:50 AM
post Re: [WTS] Yard Sale (IGBT's/Wires/Cooling/wire/induction/BusCaps/Coils/Magnetrons)
[Sell / Buy / Trade]
dbach
October 30, 2024, 08:12:44 PM
post Re: [WTS] Yard Sale (IGBT's/Wires/Cooling/wire/induction/BusCaps/Coils/Magnetrons)
[Sell / Buy / Trade]
dbach
October 30, 2024, 08:05:46 PM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 30, 2024, 07:19:07 PM
post Re: Induction heater safety
[Electronic Circuits]
petespaco
October 30, 2024, 03:16:41 PM
post Varying Frequency of A slayer exciter
[Solid State Tesla Coils (SSTC)]
vvs2000
October 30, 2024, 02:43:01 PM
post Re: Induction heater safety
[Electronic Circuits]
rikkitikkitavi
October 30, 2024, 12:45:19 PM
post Re: High Voltage High Current Supply Ideas
[General Chat]
rikkitikkitavi
October 30, 2024, 08:17:10 AM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
nzoomed
October 30, 2024, 07:47:59 AM
post Re: MidiStick V2.0: Next gen tesla coil interrupter
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
damion
October 30, 2024, 12:50:31 AM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 29, 2024, 11:18:56 PM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
nzoomed
October 29, 2024, 10:34:44 PM
post Re: 160mm DRSSTC II project | Questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Late
October 29, 2024, 06:40:34 PM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 29, 2024, 06:15:51 PM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
nzoomed
October 29, 2024, 10:07:32 AM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 29, 2024, 01:57:49 AM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
nzoomed
October 28, 2024, 10:27:13 PM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 28, 2024, 07:17:39 PM
post Re: 160mm DRSSTC II project | Questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
futurist
October 28, 2024, 10:04:46 AM
post Re: [WTS] Yard Sale (IGBT's/Wires/Cooling/wire/induction/BusCaps/Coils/Magnetrons)
[Sell / Buy / Trade]
Late
October 28, 2024, 06:48:45 AM
post Re: Induction heater safety
[Electronic Circuits]
davekni
October 28, 2024, 04:18:04 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
October 28, 2024, 04:12:35 AM
post Re: Induction heater safety
[Electronic Circuits]
thaumatichthys
October 28, 2024, 12:16:47 AM
post Re: Enamel on secondary breaking down?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
nzoomed
October 27, 2024, 10:36:34 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic Circuits]
petespaco
October 27, 2024, 06:33:55 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic Circuits]
betalab99
October 27, 2024, 06:05:04 PM
post Re: My SSTC's mosfets blow up when toroid is added
[Solid State Tesla Coils (SSTC)]
Mads Barnkob
October 27, 2024, 05:32:16 PM
post Re: 160mm DRSSTC II project | Questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Late
October 27, 2024, 02:07:38 PM
post Re: 160mm DRSSTC II project | Questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Late
October 27, 2024, 12:51:21 PM
post IGBT Gate Drive Transformer (GDT) Design, Construction and Test
[Electronic Circuits]
Mads Barnkob
October 27, 2024, 11:38:24 AM
post Re: My first QCW
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 27, 2024, 06:24:25 AM
post My SSTC's IGBT's blow up when toroid is added
[Solid State Tesla Coils (SSTC)]
Frantisek
October 26, 2024, 08:49:05 PM
post Re: My first QCW
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mathieu thm
October 26, 2024, 07:49:37 PM
post Re: [WTS] Yard Sale (IGBT's/Wires/Cooling/wire/induction/BusCaps/Coils/Magnetrons)
[Sell / Buy / Trade]
dbach
October 26, 2024, 03:51:05 PM
post Re: [WTS] Yard Sale (IGBT's/Wires/Cooling/wire/induction/BusCaps/Coils/Magnetrons)
[Sell / Buy / Trade]
noahsarc
October 26, 2024, 03:46:13 PM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 25, 2024, 11:18:22 PM
post Re: DRSSTC Main Capacitors Topology
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 25, 2024, 11:13:29 PM
post Re: DRSSTC Main Capacitors Topology
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
October 25, 2024, 10:52:23 PM
post Re: Triodes in the 5 to 10 kW range?
[Vacuum Tube Tesla Coils (VTTC)]
Avenger
October 25, 2024, 09:05:37 PM
post Re: My first QCW
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mathieu thm
October 25, 2024, 07:46:41 PM
post Re: Induction heater safety
[Electronic Circuits]
rikkitikkitavi
October 25, 2024, 11:07:20 AM
post SSTC USB interrupter based on Raspberry Pi Pico
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
AdamRozdrazewski
October 25, 2024, 10:28:43 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
October 25, 2024, 06:26:52 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
October 25, 2024, 05:53:02 AM
post Re: Induction heater safety
[Electronic Circuits]
davekni
October 25, 2024, 05:23:14 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
October 25, 2024, 05:17:02 AM
post Re: Induction heater safety
[Electronic Circuits]
petespaco
October 25, 2024, 04:40:47 AM
post Re: Triodes in the 5 to 10 kW range?
[Vacuum Tube Tesla Coils (VTTC)]
unrealcrafter2
October 25, 2024, 01:23:27 AM
post Re: [WTS] Yard Sale (IGBT's/Wires/Cooling/wire/induction/BusCaps/Coils/Magnetrons)
[Sell / Buy / Trade]
dbach
October 25, 2024, 01:17:18 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
October 25, 2024, 01:14:28 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
October 25, 2024, 12:32:31 AM
post Re: Benjamin's DRSSTC 2 in progress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
October 24, 2024, 08:21:32 PM
post Re: Steve's schematic can apply the TC4422 chip
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Glad_Yard
October 24, 2024, 08:05:34 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
October 24, 2024, 04:56:50 AM
post Re: QCWDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
October 24, 2024, 04:48:31 AM
post Re: DIY X-RAY generator made of eBay parts
[X-ray]
zgoode
October 24, 2024, 12:44:43 AM
post Re: Flyback speaker - Help adjusting scope waves and gate voltage
[Transformer (Ferrite Core)]
klugesmith
October 23, 2024, 08:44:01 PM
post Re: 160mm DRSSTC II project | Questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
futurist
October 23, 2024, 05:57:48 PM
post How to send waveform generator output to high voltage?
[General Chat]
kenw232
October 23, 2024, 05:02:59 PM

Sitemap 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 
SimplePortal 2.3.6 © 2008-2014, SimplePortal