Author Topic: DRSSTC design guide - progress report  (Read 2185 times)

Offline Mads Barnkob

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DRSSTC design guide - progress report
« on: March 21, 2017, 10:43:04 AM »
Hello all

This is my attempt to write a long guide about practical DRSSTC design. I try to cover the most critical design issues in a way that most electronics interested should be able to understand. I have tried to hand pick the necessary theory and calculations to our specific purposes of building a DRSSTC.

It is a work in progress and I would like to invite you all to help me make it better, correct and add more topics.

Topics of the DRSSTC design guide
01. Rectifiers (done)
02. Busbar and primary circuit (done)
03. IGBTs (done)
04. DC bus capacitor (done)
05. PFC (20% done)
06. Snubber capacitor (done)
07. MMC / tank capacitors (95% done)
08. GDT / driver (5% done)
09. Secondary coil (done)
10. Topload (done)
11. Grounding and EMI (done)
12. Tuning and testing (25% done)
13. Featured Tesla coils (40% done)
14. DRSSTC FAQ
15. Online design tools

I hope this guide can help others to understand why and how components are chosen for a DRSSTC.

This thread will serve as a status for the complete guide, when I add new data it will be posted here.
« Last Edit: December 12, 2018, 01:05:33 PM by Mads Barnkob »
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Offline Tardief

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Re: DRSSTC design guide - progress report
« Reply #1 on: June 22, 2017, 11:44:59 PM »
Hi,
We are planning to build a Tesla Coil with 4x CM600HA-24H. I saw in your list that it failed at 56kHz. Could you explain me what thas it mean? Unfortunately i cant find it at 4hv forum and i cant post there.
Should we make the secondary for a lower frequency?
Thanks

Offline Mads Barnkob

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Re: DRSSTC design guide - progress report
« Reply #2 on: June 23, 2017, 10:01:04 AM »
Hi,
We are planning to build a Tesla Coil with 4x CM600HA-24H. I saw in your list that it failed at 56kHz. Could you explain me what thas it mean? Unfortunately i cant find it at 4hv forum and i cant post there.
Should we make the secondary for a lower frequency?
Thanks

You should naturally get a much lower resonant frequency than 56 kHz with such a large brigde, simply because you need some height for the 5+ meter long sparks, so you will properly end up around 35 kHz. Failure at 3500 Ampere peak is also extremely high, you can run yours at 2000 Ampere and still have solid sparks :)

I am looking forward to see a build thread on this huge Tesla coil  :o
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Offline Tardief

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Re: DRSSTC design guide - progress report
« Reply #3 on: June 23, 2017, 06:26:04 PM »
Thanks!
Will do.   :)

Offline Mads Barnkob

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Re: DRSSTC design guide - progress report
« Reply #4 on: April 08, 2018, 10:36:36 PM »
I have finally finished the chapter 11 on Grounding and EMI, you can read it here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/grounding-circuit-protection-and-emi/

Please do ask questions and come with feedback on how to improve the chapter or if there is any errors :)
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Offline profdc9

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Re: DRSSTC design guide - progress report
« Reply #5 on: April 08, 2018, 10:57:30 PM »
Mads,

One question I have is this, and it may be related to EMI/grounding issues.  Yesterday I was working on getting my through-hole UD2.7C board to work with my tesla coil.  I set up the Tesla coil to tune the lead inductor by placing three soup cans inside the primary coil where the secondary coil should be.  I plugged in the gate transformer to the UD2.7C, as well as the two current transformers for feedback and overcurrent.

I have my primary bus on a variac and set to a low voltage (around 30 VAC with the line voltage being 120 VAC) and placed a 100X probe to monitor one leg of the full bridge with the ground clip on the earthing ground and the other clipped onto the bus lead on the full bridge.  I am using a voltage doubler.  The other I had clipped to the ground of the UD2.7C board and a test point so I can monitor the bus current.

Things were going ok.  The bus voltage looks very noisy and ringing, but the bus current seems to grow and then recede after the interrupter turns off.  So far so good.  Then suddenly my UD2.7C board stops working.   I have checked the solder connections, and can't anything wrong.  The 74HC08 chip goes bad.  I replace it, and then the 74HC74 chip goes bad, and I replace the 74HC14 chip because I figured something happened.  Then for some reason the 74HC08 chip goes bad again!  And I have to replace that...

Should I put common-mode chokes on the gate driver as well as the feedback and overcurrent transformers?  I think I will try that anyways, but I am wondering if there are voltage spikes making their way into the board from the full bridge.  I tried to stick to the UD2.7C as closely as I could when laying out the circuit, however, I did have to change the undervoltage lockout circuit because there was no through-hole available part.

I also soldered a 5.1V zener diode on the 5V supply to try to absorb any transients as well.  Any suggestions?

Thanks,

Dan

Offline Mads Barnkob

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Re: DRSSTC design guide - progress report
« Reply #6 on: April 09, 2018, 09:06:08 PM »
Mads,

One question I have is this, and it may be related to EMI/grounding issues.  Yesterday I was working on getting my through-hole UD2.7C board to work with my tesla coil.  I set up the Tesla coil to tune the lead inductor by placing three soup cans inside the primary coil where the secondary coil should be.  I plugged in the gate transformer to the UD2.7C, as well as the two current transformers for feedback and overcurrent.

I have my primary bus on a variac and set to a low voltage (around 30 VAC with the line voltage being 120 VAC) and placed a 100X probe to monitor one leg of the full bridge with the ground clip on the earthing ground and the other clipped onto the bus lead on the full bridge.  I am using a voltage doubler.  The other I had clipped to the ground of the UD2.7C board and a test point so I can monitor the bus current.

Things were going ok.  The bus voltage looks very noisy and ringing, but the bus current seems to grow and then recede after the interrupter turns off.  So far so good.  Then suddenly my UD2.7C board stops working.   I have checked the solder connections, and can't anything wrong.  The 74HC08 chip goes bad.  I replace it, and then the 74HC74 chip goes bad, and I replace the 74HC14 chip because I figured something happened.  Then for some reason the 74HC08 chip goes bad again!  And I have to replace that...

Should I put common-mode chokes on the gate driver as well as the feedback and overcurrent transformers?  I think I will try that anyways, but I am wondering if there are voltage spikes making their way into the board from the full bridge.  I tried to stick to the UD2.7C as closely as I could when laying out the circuit, however, I did have to change the undervoltage lockout circuit because there was no through-hole available part.

I also soldered a 5.1V zener diode on the 5V supply to try to absorb any transients as well.  Any suggestions?

Thanks,

Dan

The switching spikes is first and foremost from low voltage testing, I put some information about that in another thread with links to read more about that: https://highvoltageforum.net/index.php?topic=259.msg1685#msg1685

Is your oscilloscope grounded through the mains plug? Else you might just be shunting noise through the common ground in the oscilloscope between the inverter and driver ground.

Do you have any unused input pins on the 74xx ICs that is ungrounded? That can make them act up very weird from crosstalk.
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Offline Laci

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Re: DRSSTC design guide - progress report
« Reply #7 on: April 09, 2018, 11:24:48 PM »
Around a week ago,while I was running my SSTC at low currents(so short arcs)the nearby laptop got crazy.The wirless mouse stopped working and no longer could I use it.It's interesting that my ~160kHz coil destroyed a 2.4GHz device.Maybe bad grounding or unstable tuning can cause really high frequency harmonics,or just the too large magnetic field internally blown up the mouse.
Another thing is the FM range.I wonder how many of my neighbours are able to listen to the radio while my coil is running :P.
« Last Edit: April 09, 2018, 11:28:35 PM by Laci »

Offline profdc9

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Re: DRSSTC design guide - progress report
« Reply #8 on: April 10, 2018, 02:43:19 AM »
The switching spikes is first and foremost from low voltage testing, I put some information about that in another thread with links to read more about that: https://highvoltageforum.net/index.php?topic=259.msg1685#msg1685

Is your oscilloscope grounded through the mains plug? Else you might just be shunting noise through the common ground in the oscilloscope between the inverter and driver ground.

Do you have any unused input pins on the 74xx ICs that is ungrounded? That can make them act up very weird from crosstalk.

My oscilloscope is grounded through the mains.  I double-checked it with a continuity checker, no problem there.

The UD2.7C board doesn't have any ungrounded pins in the layout, I made sure of that.  So I don't think that's the case.

Yesterday I ran the board and so far it seems to be holding up.  Maybe I was careless about ESD handling?  At any rate, I ordered some more replacement chips from Digikey in case something else goes wrong.  I also put common-mode chokes on the transformers as well (three turns around a small ferrite toroid).

I actually have some traces from yesterday in this thread ( https://highvoltageforum.net/index.php?topic=302.msg1909;topicseen#new ).  I have some weird ringing that I am working on troubleshooting.  I have a full bridge of FGH60N60SMD IGBT's so it's nothing too difficult to drive I think; I only have 2 kW available from my home circuits to work with.  I am not sure yet if the ringing is an artifact of the way I'm probing the bridge or if its actually there.  Certainly the overshoot seems to change as I increase the voltage.  I have been able to get it to operate for a few half cycles without OCD trip at 300 A at full voltage with soup can load. 

I reread the thread you pointed to and I am not really having a problem with slow rise time, mostly just these weird ringing artifacts.  I'll keep looking.  I have read that the primary coil itself can have self-resonance that can cause oscillations on the bus signal.

Dan

Offline sparkydownunder

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Re: DRSSTC design guide - progress report
« Reply #9 on: April 10, 2018, 02:14:54 PM »
Hi Mads

Your post on grounding and EMI dosent seem to have a conclusive suggestion for proper grounding. Im going to be using my coil at home and on the road a bit.

If i use a line filter on my earth connection I should still avoid using my existing house earth correct (even if running in the garden)? What do you use for your testing? what size spike/plate?

thanks in advance and thanks for your amazing guide! Im so close and wouldnt be where i am without it :)

Offline profdc9

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Re: DRSSTC design guide - progress report
« Reply #10 on: April 12, 2018, 08:04:24 PM »
I wouldn't use your mains earth ground to ground your Tesla coil.  You can use a counterpoise to ground the secondary coil, which is basically a large metal sheet you spread on the floor under the Tesla coil.  It can be as simple as taped together aluminium foil, chicken coop wire, metal window screen material, or my preferred material, aluminium roof flashing, because it is not crinkly, and if you round of the corners you will get less arcing there.  The wire to the counterpoise should not be too long or else the inductance of the wire will be too large and the counterpoise is not effective.  Also, ground the bottom of the secondary coil to the strike ring as well.  Make sure the wire to the counterpoise is not routed near anything else, or the secondary might arc to those other objects.

Dan

Offline Mads Barnkob

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Re: DRSSTC design guide - progress report
« Reply #11 on: April 15, 2018, 09:54:45 PM »
Hi Mads

Your post on grounding and EMI dosent seem to have a conclusive suggestion for proper grounding. Im going to be using my coil at home and on the road a bit.

If i use a line filter on my earth connection I should still avoid using my existing house earth correct (even if running in the garden)? What do you use for your testing? what size spike/plate?

thanks in advance and thanks for your amazing guide! Im so close and wouldnt be where i am without it :)

Because there is no conclusive suggestion, it is very dependable on the specific situation. It is hard to point out one good solution when there is very little data to back it up with, but on the other hand there is a great deal of information on what not to do.

I have used single rod grounding systems, from smallest to my largest drsstc, but we also have a good moist and highly conductive soil in Denmark.
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Offline Nijin

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Re: DRSSTC design guide - progress report
« Reply #12 on: July 28, 2018, 02:19:15 PM »
Yesterday I run my big drsstc for the first time indoor. I use a long aliminium rod for ground. It was vertically attached to a chair. When the arc touched the rod, the braker oppened. I suppose that the arc short circuited the secondary and then the current in the bus where to big for the braker.

Also when I want to stoped the coil, I stoped the Bus supply and I tried to run the coil without supply to discharge the BUS. There was a huge flash on the Bus but the coil is fine (thanks god !).

I don't know what happened, How can I stop the coil and discharge the Bus cap safely ?

And a last question, Franzoli told me to connect the gnd of the driver to the case which is connected to the Coil ground. There is no risk to connected the gnd to the coil ground ?
Everything is a fuse if you pass enough current

Offline FilipŠebík

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Re: DRSSTC design guide - progress report
« Reply #13 on: July 29, 2018, 07:16:58 PM »
Yesterday I run my big drsstc for the first time indoor. I use a long aliminium rod for ground. It was vertically attached to a chair. When the arc touched the rod, the braker oppened. I suppose that the arc short circuited the secondary and then the current in the bus where to big for the braker.

Also when I want to stoped the coil, I stoped the Bus supply and I tried to run the coil without supply to discharge the BUS. There was a huge flash on the Bus but the coil is fine (thanks god !).

I don't know what happened, How can I stop the coil and discharge the Bus cap safely ?

And a last question, Franzoli told me to connect the gnd of the driver to the case which is connected to the Coil ground. There is no risk to connected the gnd to the coil ground ?

Your breaker popped because there was too much current draw in the primary (I guess)
And use resistors to discharge the bus caps. Probably something like 100k? Maybe more maybe less
And yes connect the ground to the driver case because it can save your circuit when the primary strikes the driver case.

And you are better of using a aluminium sheet plane on the ground under the coil that is like 4 times or so bigger than your topload but you just have to try to see what is better

Offline Mads Barnkob

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Re: DRSSTC design guide - progress report
« Reply #14 on: July 29, 2018, 11:12:55 PM »
Your secondary was not short circuited in the way you would pop a breaker from circuiting your mains supply from it. A ground strike is a very low impedance load to secondary coil and suddenly it will present itself as a heavy load to the primary circuit and inverter, so its simply pumping all the energy possible into the inverter and that happens to be enough to trip your breaker, this is normal for heavy ground strikes, but use a bigger supply or turn down your OCD setting.

If you want a guide on how to calculate your DC bus capacitor bleeder resistors, see here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/dc-bus-capacitor/

There is no danger in grounding all metal parts together and also secondary transformer side supplies to the same ground, as long as you have it connected to a ground rod or artificial ground plane / counterpoise made out of some either aluminium sheets as suggested above, could also be chicken wire fence or aluminium food foil.
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Offline Mads Barnkob

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Re: DRSSTC design guide - progress report
« Reply #15 on: December 12, 2018, 01:00:34 PM »
It has been a very long time under way with the next chapter to go in review and it is the widely sought for: MMC design and calculations

You can read the article at: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/mmc-tank-capacitor/  and to see it, the password is "test".

The reason for the password is to avoid google indexing and random visitors reading it before it has been reviewed by people with experience in the field.

This is where I need your help, there is most likely some spelling errors, bad sentences, does-not-make-any-sense chapters or calculations errors. Please reply to this thread about such findings for a discussion about it.
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Offline Uspring

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Re: DRSSTC design guide - progress report
« Reply #16 on: December 13, 2018, 12:23:30 PM »
Thank you for the update :)
I've stumbled over the equation you used to calculate the power dissipation in the cap. I've tried to reverse engineer it and it looks, like it applies to the case of a single charge up of the cap. It, e.g., does not incorporate the burst length. Inside a burst the caps are charged and discharged a number of times.
I'd use

P = Irms^2 * ESR

where Irms is taken from Conners equation. In your example that would be for a single cap (13A)^2 * 0.005Ohms or about 0.8W. The according temperature rise of 9 degrees would barely fit into the "good" range of tolerable temperatures. That also matches the Irms spec of the caps.

The calculation for the number of half cycles to obtain a given primary current disregards loading of the primary tank by the secondary and arc loads. The rationale is this: Each time the voltage across the primary tank jumps by a certain value (as caused by the bridge), then this value is added to the MMC peak voltage after a half cycle. The primary current calculated from this is always an upper limit. Ideally secondary and arc loading should limit primary current so that OCD shut downs (to prevent transistor and MMC overload) won't happen.

Offline Mads Barnkob

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Re: DRSSTC design guide - progress report
« Reply #17 on: December 14, 2018, 08:38:52 PM »
Thank you for the update :)
I've stumbled over the equation you used to calculate the power dissipation in the cap. I've tried to reverse engineer it and it looks, like it applies to the case of a single charge up of the cap. It, e.g., does not incorporate the burst length. Inside a burst the caps are charged and discharged a number of times.
I'd use

P = Irms^2 * ESR

where Irms is taken from Conners equation. In your example that would be for a single cap (13A)^2 * 0.005Ohms or about 0.8W. The according temperature rise of 9 degrees would barely fit into the "good" range of tolerable temperatures. That also matches the Irms spec of the caps.

When I looked into my MMC calculator code, I did notice that there was something wrong as there was no accounting for on-time, but was mere single pulse * BPS, I tried to understand how I came to that formula and my only explanation is a old excel sheet for SGTC, which also lacks accounting for on-time. I need to get both calculator and article corrected.

I follow your argument with the Irms and the rating of the capacitor, that makes sense that it will quite quickly get to operate at its maximum permissible hot spot temperature of 105 degrees Celsius, but that still seems a bit far from reality of what I have seen with that coil used in the example.

I also had some old WIMA white paper on dissipation losses that I tried to give a go, but its an even worse result. Maybe I am getting something wrong with the RMS voltage?
Xc = 5.05 Ohm
ESR = 0.005 Ohm
Tan rho = ESR/Xc
Watt = ((Vrms^2)*2*pi*70000hz*0.45uF*tan rho
C/W -> W/K = 1/11 = 0,0909
Temp rise =(((2000/1.41)^2)*2*PI()*70000*(0.45/1000000)*(0.005/5.05))/(1/11) = 4000~ degree Celsius



The calculation for the number of half cycles to obtain a given primary current disregards loading of the primary tank by the secondary and arc loads. The rationale is this: Each time the voltage across the primary tank jumps by a certain value (as caused by the bridge), then this value is added to the MMC peak voltage after a half cycle. The primary current calculated from this is always an upper limit. Ideally secondary and arc loading should limit primary current so that OCD shut downs (to prevent transistor and MMC overload) won't happen.

I will make that a primary explanation and selling point for that method, that it is a worst case scenario. That method is also in my view one that should give the most over-engineered MMC.
« Last Edit: December 14, 2018, 08:48:23 PM by Mads Barnkob »
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Re: DRSSTC design guide - progress report
« Reply #17 on: December 14, 2018, 08:38:52 PM »

 


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post Re: My X-Ray Machine
[X-ray]
Mads Barnkob
November 28, 2018, 07:14:52 PM
post My X-Ray Machine
[X-ray]
neukyhm
November 28, 2018, 04:42:32 PM
post Re: How sensitive are Tesla coils to Arduino boards?
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Mads Barnkob
November 28, 2018, 09:55:58 AM
post How sensitive are Tesla coils to Arduino boards?
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Laci
November 27, 2018, 08:50:54 PM
post Re: My First SSTC
[Solid state Tesla coils]
sjsimmo
November 27, 2018, 09:56:16 AM
post Re: My First SSTC
[Solid state Tesla coils]
Mads Barnkob
November 27, 2018, 08:53:35 AM
post Re: My First SSTC
[Solid state Tesla coils]
sjsimmo
November 26, 2018, 02:28:22 AM
post Re: My First SSTC
[Solid state Tesla coils]
pentode
November 23, 2018, 11:18:58 AM
post Re: My First DRSSTC
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
November 23, 2018, 06:39:47 AM
post Re: My First DRSSTC
[Dual Resonant Solid State Tesla coils]
sjsimmo
November 23, 2018, 03:48:47 AM
post Re: Nokia Siemens Flexi BTS base station teardown: Power amplifier (part 1 and 2)
[Radio frequency]
Mads Barnkob
November 22, 2018, 10:03:48 PM
post Re: Usable vacuum tube?
[Vacuum tube Tesla coils]
Mads Barnkob
November 22, 2018, 11:36:49 AM
post Re: Usable vacuum tube?
[Vacuum tube Tesla coils]
sjsimmo
November 22, 2018, 01:17:32 AM
post My First SSTC
[Solid state Tesla coils]
sjsimmo
November 21, 2018, 11:43:46 PM
post Re: My First DRSSTC
[Dual Resonant Solid State Tesla coils]
sjsimmo
November 20, 2018, 11:12:10 PM

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