Author Topic: Project: FreakyDRSSTC MK1  (Read 1427 times)

Offline GrantV

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Project: FreakyDRSSTC MK1
« on: February 03, 2021, 11:50:53 AM »
Hi all,

Having previously successfully built a test bench SSTC, I am now building my first DRSSTC, so I am going to use this space to document my progress and ask questions :-)

To kick it off, I have posted my JavaTC output and ask you to please give it a quick sanity check and make any comments you feel may be helpful?

Note: My secondary is already done so any tweaks I would need to make will have to be in the primary circuit!

I will initially be using the CloudLeopard driver from Ali. I do have a Loneoceans UD2.7c board and will build this up and add a suitable interrupter as things progress.

For the bridge, I will be using my own version of the Loneoceans 80mm Fullbridge which uses 4x FGH60N60SMD IGBT's and will be running at around 200-250Apk

My MMC is a 4x4 stack of 0.15uF CD caps (942C20P15K-F)

« Last Edit: February 03, 2021, 01:36:29 PM by GrantV »

Offline GrantV

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Full Bridge PCB - v1
« Reply #1 on: February 05, 2021, 11:58:16 AM »
My pcb's have finally arrived after going on a bit of a world tour with Fedex ...

Anyway, just glad they are here now  :)

I have always wanted to learn how to use pcb software and get my own pcb's printed, so I figured this was a great opportunity ...

Having had great success using Loneoceans 80mm Full Bridge with my SSTC, I loaded up EasyEDA and got to work creating my own version of his board.

I know it's not perfect and has a couple of issues but it's mine and I am happy with my first attempt  8)



Offline Mads Barnkob

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Re: Project: FreakyDRSSTC MK1
« Reply #2 on: February 06, 2021, 10:01:32 PM »
Overall you seem to have a solid plan and all numbers are within a regular DRSSTC build. You did your home work and should have no significant problems from parts and dimensions chosen.

200-250Apk does however seem a little modest for a 40 cm long secondary coil, not that I would advise you to push it further, but the bridge might be a tad under-dimensioned to utilize the full potential of the secondary coil.

Looking forward to see the sparks :)
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Offline GrantV

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Re: Project: FreakyDRSSTC MK1
« Reply #3 on: February 07, 2021, 10:28:30 AM »
Overall you seem to have a solid plan and all numbers are within a regular DRSSTC build. You did your home work and should have no significant problems from parts and dimensions chosen.

200-250Apk does however seem a little modest for a 40 cm long secondary coil, not that I would advise you to push it further, but the bridge might be a tad under-dimensioned to utilize the full potential of the secondary coil.

Looking forward to see the sparks :)

Thank you Mads, I appreciate your response :-)

I am aware that I should be able to get considerably more performance out of my secondary. I prefer to build up (in power levels) in stages so that I learn as much as possible along the way :-)

Offline GrantV

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Bridge and Driver working
« Reply #4 on: February 11, 2021, 11:37:16 AM »
Hi there,

I completed the build on my bridge and am happy to report that it is tested and working ... (on the test bench) :-)



I have done some initial scoping and would appreciate your comments :-)

These scope shots are based on a very simple test configuration :-
Load : No load other than the 10K MMC Bleeder Resistor
Bus : 16V Lipo Battery
Gate drive : 24V
GDT cores are Epcos 26.6mm N30 with 12 turns cat 5 (dual primary/single secondaries)
Gate circuit : 15ohm gate drive resistor with reverse Schottky and a 26V G-E TVS
IGBT's are FGH60N60SMD
Driver is given a 130Khz signal to simulate feedback from the primary


excuse the duty cycle anomaly ... it had me scratching my head for a while lol




And now just making sure that the interrupter is working properly:

OK .... I give up .... How does a beat interval of 800uS = 10Hz/bps ???
« Last Edit: February 11, 2021, 01:08:51 PM by GrantV »

Online davekni

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Re: Project: FreakyDRSSTC MK1
« Reply #5 on: February 11, 2021, 08:13:01 PM »
The "10Hz" display should be the frequency of trigger events.  Perhaps the scope software gets confused by multiple closely-spaced triggers followed by longer 800us gaps.

Gate waveforms have enough overshoot to be clamped by the TVS diodes on every falling transition.  There appears to be much more parasitic inductance in gate drive than I would expect from your GDTs.  GDTs appear to be nicely wound.  What does the wiring from driver to GDT primary terminals look like?  Is it short and using twisted pairs?  It might be fine as-is.  The TVS diodes can likely handle the clamping power.  I'd try a high-duty-cycle run in this unloaded test setup to check that TVS diodes don't get too hot.
David Knierim

Offline GrantV

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Re: Project: FreakyDRSSTC MK1
« Reply #6 on: February 12, 2021, 09:17:08 AM »
The "10Hz" display should be the frequency of trigger events.  Perhaps the scope software gets confused by multiple closely-spaced triggers followed by longer 800us gaps.

Gate waveforms have enough overshoot to be clamped by the TVS diodes on every falling transition.  There appears to be much more parasitic inductance in gate drive than I would expect from your GDTs.  GDTs appear to be nicely wound.  What does the wiring from driver to GDT primary terminals look like?  Is it short and using twisted pairs?  It might be fine as-is.  The TVS diodes can likely handle the clamping power.  I'd try a high-duty-cycle run in this unloaded test setup to check that TVS diodes don't get too hot.

Hi Dave,

Thanks for your response.

The wiring from the driver to the GDT's is twisted but certainly not the best as this was just meant to be a quick lash-up for initial testing.

Please may I ask you to explain where and how you see the 'parasitic inductance' you are talking about in the waveforms? These are just my second ever GDT's so I am still trying to get used to what the waveform 'should' look like :-)

Pushing the on-time and/or the bps higher, I can hear the GDT's 'whining' ? and over 200uS 200bps the gate resistors do start to warm up but do not get overly hot. I have not noticed any heating of the TVS diodes but I will check that today.

EDIT: Unloaded, the TVS's gets up to around 60°C at 50% duty cycle and tops out at about 85°C at extreme duty cycles. The gate resistor does about the same.

Could the parasitic inductance be caused by the way I have run the leads from the GDT into the board?

« Last Edit: February 12, 2021, 03:07:59 PM by GrantV »

Online davekni

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Re: Project: FreakyDRSSTC MK1
« Reply #7 on: February 12, 2021, 07:49:27 PM »
Since the TVS diodes are not overheating even at extreme duty cycles, there is nothing to be concerned about.  For estimating inductance, I'm looking at the ~8% overshoot on rising Vge waveforms with your 15-ohm gate resistors.  Extrapolating down to low drain voltage, gate charge for FGH60N60SMD is about 150nC at 15V, or 10nF average capacitance.  Roughly 1.4uH in series with 15 ohms produces 8% overshoot with a square-wave input.  (Ran an LTSpice simulation to get this.  My quick estimate yesterday was off a bit.)  So, total gate drive inductance must be about 1.4uH.  An individual cat5 twisted pair is about 0.66uH/meter.  So 1.4uH implies just over 2m twisted pair length.  However, inductance on the GDT primaries counts double, since it is feeding two gates.  0.5m of twisted pair from driver to GDT could account for half of the 2m total.
David Knierim

Offline GrantV

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Re: Project: FreakyDRSSTC MK1
« Reply #8 on: February 14, 2021, 11:44:35 AM »
Since the TVS diodes are not overheating even at extreme duty cycles, there is nothing to be concerned about.  For estimating inductance, I'm looking at the ~8% overshoot on rising Vge waveforms with your 15-ohm gate resistors.  Extrapolating down to low drain voltage, gate charge for FGH60N60SMD is about 150nC at 15V, or 10nF average capacitance.  Roughly 1.4uH in series with 15 ohms produces 8% overshoot with a square-wave input.  (Ran an LTSpice simulation to get this.  My quick estimate yesterday was off a bit.)  So, total gate drive inductance must be about 1.4uH.  An individual cat5 twisted pair is about 0.66uH/meter.  So 1.4uH implies just over 2m twisted pair length.  However, inductance on the GDT primaries counts double, since it is feeding two gates.  0.5m of twisted pair from driver to GDT could account for half of the 2m total.

Hi Dave and thanks again for your response.

Thanks for your most detailed explanation, I think I understand what you were seeing in my waveform :-)

As I build, I'll keep an eye on that overshoot and make sure that I do not make it worse!

Offline GrantV

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DRSSTC themed 3D adult puzzle
« Reply #9 on: February 14, 2021, 11:49:44 AM »
Ok, well it took longer than expected and there were some problems with the setup of the laser cutter at the Maker Shop ... BUT .... my new DRSSTC themed 3D Puzzle is finally here  ;D


Offline GrantV

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Shielding?
« Reply #10 on: February 19, 2021, 11:48:30 AM »
Hi all,

I am using shielded 4 core DMX cable for my GDT and CT lines and was planning on grounding the shield/s, but, as there is going to be HF noise in the ground circuit, I am now second guessing myself as to wether this is a good idea or if I should just leave the shielding unconnected.

Your thoughts?


Offline Da_Stier

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Re: Project: FreakyDRSSTC MK1
« Reply #11 on: February 19, 2021, 04:08:15 PM »
Hi,

I don't really have any experience in the field of tesla coils, however I do have some expience with the topic itself.
If your GND potential has a lot of superimposed noise on it, it might not be the best idea to directly connect your shielding to it.
However leaving it completely floating might also be a bad idea since it can float at pretty high potential, if the field around it is strong enough.
A common approach that is used for example with ethernet cables is to couple the shielding to GND via a high value resistor and a small capacitance in parallel.
Common values are 100k and 1nF.

Another possiblility is to connect the shielding to any other static potential in your system which has less noise on it.
From an RF point of view it doesn't really matter if your shield is at GND or +5V or whatever, since powerplanes will always be connected to GND via decoupling caps.
This makes them basically shorted to GND anyway ... from an RF point of view of course.

I hope this might be useful,
Michael

Offline GrantV

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Re: Project: FreakyDRSSTC MK1
« Reply #12 on: February 19, 2021, 04:28:56 PM »
Hi,

I don't really have any experience in the field of tesla coils, however I do have some expience with the topic itself.
If your GND potential has a lot of superimposed noise on it, it might not be the best idea to directly connect your shielding to it.
However leaving it completely floating might also be a bad idea since it can float at pretty high potential, if the field around it is strong enough.
A common approach that is used for example with ethernet cables is to couple the shielding to GND via a high value resistor and a small capacitance in parallel.
Common values are 100k and 1nF.

Another possiblility is to connect the shielding to any other static potential in your system which has less noise on it.
From an RF point of view it doesn't really matter if your shield is at GND or +5V or whatever, since powerplanes will always be connected to GND via decoupling caps.
This makes them basically shorted to GND anyway ... from an RF point of view of course.

I hope this might be useful,
Michael

Hi Michael, thanks for your response and very useful info!

I agree that leaving it floating would probably be a bad idea so I think I'll go with your suggestion of connecting it through a decoupling circuit (cap/resistor) as you suggested  :)

Offline prabhatkumar

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Re: Project: FreakyDRSSTC MK1
« Reply #13 on: February 21, 2021, 05:36:49 PM »
Hey there,
I was browsing through the forum and found that your PCBs look great. I actually required the PCBs from loneoceans and also contacted him for the same and he did reply to me about the shipping prices and everything. I accepted it and told him I am ready to pay for the boards if he ships it. But his reply is awaited for more than a month now.
I actually required this board for a college research project( Its a phase shifted power supply). I had also built a simple SSTC with the help of the fellow members of this forum last year and would now Like to upgrade to a full bridge using this board.
Please tell me if you are willing to post the board files in the open domain :)or if its paid.
I am myself leaning PCB design and got familiar with the single sided designs but double sided and that also for power circuits will take some time and hence I am relying on other options.
Thank you

Offline GrantV

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Re: Project: FreakyDRSSTC MK1
« Reply #14 on: February 22, 2021, 11:01:07 AM »
Hey there,
I was browsing through the forum and found that your PCBs look great. I actually required the PCBs from loneoceans and also contacted him for the same and he did reply to me about the shipping prices and everything. I accepted it and told him I am ready to pay for the boards if he ships it. But his reply is awaited for more than a month now.
I actually required this board for a college research project( Its a phase shifted power supply). I had also built a simple SSTC with the help of the fellow members of this forum last year and would now Like to upgrade to a full bridge using this board.
Please tell me if you are willing to post the board files in the open domain :)or if its paid.
I am myself leaning PCB design and got familiar with the single sided designs but double sided and that also for power circuits will take some time and hence I am relying on other options.
Thank you

Hi there,

Thank you for your kind words :-)

I wouldn't have a problem with sharing these but am yet to get permission from Gao, so for the moment I would prefer not to.

Also, my board is far from optimal, so I think you would be better off with the bridge design from Dan (Profdc9) :-)

https://highvoltageforum.net/index.php?topic=353.0

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/full-bridge-transistor
« Last Edit: February 22, 2021, 05:22:03 PM by GrantV »

Offline prabhatkumar

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Re: Project: FreakyDRSSTC MK1
« Reply #15 on: February 22, 2021, 03:59:37 PM »
Thanks for the prompt reply !! I understand that you have mentioned that in the board, there is a lot to improve. I had also seen profdc9 boards which is also great. But for my requirement, I needed the gate drive transformer, the bulk capacitor, rectifier and the IGBTS/MOSFETS all in the same board which unfortunately is not there in profdc9's board( not a con, his boards are great given we usually have the gate drive section and logic section on the same board for the tesla coil).
And as far as permission from Gao, we all always acknowledge his immense contribution for teaching the theory of tesla coils and also how to build one. And your board is an inspiration from his work and given he has also made the schematics available to everyone I don't think it should be problem. I will also add the gate drive section( The FDD8424H on the same board and make it available if it turns out to be good:)
Still it would be nice if someone like Gao or Mads himself comment on this .
Thanks
« Last Edit: February 22, 2021, 04:02:36 PM by prabhatkumar »

Offline Mads Barnkob

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Re: Project: FreakyDRSSTC MK1
« Reply #16 on: February 22, 2021, 07:52:16 PM »
Still it would be nice if someone like Gao or Mads himself comment on this .

I am a bit unsure what you are asking me about? :)
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Offline prabhatkumar

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Re: Project: FreakyDRSSTC MK1
« Reply #17 on: February 23, 2021, 05:16:24 AM »
Hello Mads,
 I was asking about the release the of PCBS made by GrantV which are inspired by Gao's 80 mm full bridge plus. He is unsure whether he can release his version of PCBs over here as I required them urgently for a college research project. I will make sure his name and Gao's name are there in the final documentation.
Thanks

Offline Mads Barnkob

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Re: Project: FreakyDRSSTC MK1
« Reply #18 on: February 23, 2021, 08:13:55 AM »
Hello Mads,
 I was asking about the release the of PCBS made by GrantV which are inspired by Gao's 80 mm full bridge plus. He is unsure whether he can release his version of PCBs over here as I required them urgently for a college research project. I will make sure his name and Gao's name are there in the final documentation.
Thanks

I can not answer on behalf of Gao, contact him directly through his website/email at loneoceans.com if you want to publish his designs. If he wanted them public, he would properly have published them himself on his website. As he do sell some of his PCBs, both empty and populated, I would guess that it would be a no.

Modify profdc9's PCBs instead, would be much faster to just use something that is already public available instead of asking for complete solutions. If you require something urgently, you better just pay for the service or get working yourself. You are on the verge of breaking forum rules on asking directly for full instructions, designs etc.
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Offline prabhatkumar

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Re: Project: FreakyDRSSTC MK1
« Reply #19 on: February 23, 2021, 12:40:18 PM »
Thanks for the reply Mads. I wanted to redesign the board made by profdc9 but the thing is the design is in kicad and I am only familiar to eagle some what:(
Anyways thanks for the help. I think problems only shape the way to new solutions. I will sit and try to build the entire board on eagle itself when I have some free time.

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Re: Project: FreakyDRSSTC MK1
« Reply #19 on: February 23, 2021, 12:40:18 PM »

 


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post Re: Etching PCBs with a SLA 3d printer
[Printed Circuit Board]
TMaxElectronics
March 05, 2021, 11:26:36 PM

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