Kaizer DRSSTC I

Introduction

Building a Dual Resonant Solid State Tesla Coil have been the ultimate goal since I started experimenting with high voltage apparatuses 3 years ago.

A DRSSTC is the modern day topology of driving a Tesla coils taking advantage of IGBT technology, pulse rated capacitors and a very low inductance primary circuit layout.

Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

Read this document about safety! http://www.pupman.com/safety.htm

Considerations

Due to IGBT technology the resonant frequency have to be lower than what is normally acceptable in a regular solid state Tesla coil. The higher frequency the more demanding is the current delivering ability of the gate driving circuit and switching losses will stress the bridge more than good is.

 

Specifications

Bridge 4x IXGN60N60C2D1 IGBTs in a full bridge configuration
Bridge supply 0 – 260VAC through a variac, 2x 35A rectifier bridges in parallel and 2x BHC 3300uF 450V filtering capacitors in parallel. (each: ESR 39mOhm@100Hz, Z 27mOhm@10kHz and 53A Iripple@70KHz@50 Degrees celcius)
Primary coil 320 mm diameter, 10 mm diameter copper tubing ~ 28,27 mm², 9 windings. Tapped at 5,4 turns.
MMC 6 strings in parallel of 2 in series Cornell Dubilier (CDE) 942C20P15K-F capacitors for 0.45uF at 4000VDC rating and 81 A Irms.
Secondary coil 160 mm diameter, 605 mm long, 2200 windings, 0.25 mm enamelled copper wire.
Resonant frequency Around 65 – 70 kHz.
Topload 127 x 620 mm aluminum flex tube with aluminium tape toroid.
Input power 130BPS, 9 cycles, 500A limiter: 2500W at 250VAC at 10A.
Spark length Up to 1500 mm long sparks.

Schematic

Bridge section

Driver section

Same as Steve Wards universal driver version 1.3. Just made on single sided PCB without SMD components.

 

Construction

20th March 2009

Bought 30x IXGN60N60C2D1 from Digikey USA, import taxes etc. almost killed me.

7th April 2009

Bought 60x 942C20P15K-F capacitors through Dr.spark, again hello import taxes.

15th May 2009

Bought heat sinks cheap from Germany.

19th May 2009

Started converting Wards latest DRSSTC driver to single sided board.

23rd July 2009

Started 3D designing the full bridge.

It is bulky, on 2 heat sinks with capacitors between them, its too big and needs to be overhauled.

23rd August 2009

Redesigned the full bridge

The two IGBTs in the middle are turned 180 degrees to have the supply at one side of the heat sink and output on the other, it got compact, neat and only one overlap with bus-bar, I am very happy with this design.

24th August 2009

Made a spreadsheet to ease experimenting with different DRSSTC settings, this was also a try to collect some of the different theory and put it side by side, it might not all make sense.

27th August 2009

Bought 50 meter of 10 mm copper tubing, two drain pipes 160 mm diameter x 1000 mm and 1,5 mm copper sheet.

Here is the collection of parts for the DRSSTC.

8th September 2009

Finished converting Wards latest drsstc driver to single sided board

12nd September 2009

Finished assembling the single side board ward DRSSTC driver

16th September 2009

Etched, assembled, tested and housed interrupter with burst mode.


19th September 2009

Cut out bus-bar from copper sheet and assembled IGBTs, heat sink, capacitors with bus-bar, home made 8mm brass spacers are used. Leads to the primary are 16mm^2 stranded 90 Degree Celsius machine tool wire.

25th September 2009

Found a aluminium box and transformer for the driver, wound a GDT and started preparing decoupling capacitors, TVS and Zener diodes for the bridge.

With all the wonderful theory about GDTs in the wiki, it would be a shame not to check it out instead of just going for a high permeability core with 10 turns on CAT5 cable. So here goes

Its a Epcos ring core, material: N30, good up to 5MHz, Aemm^2: 95,89, AL: 5750nH

Inductance with 10 turns: L = AL * N^2 = 5750 * 10^2 = 575 uH

Peak current: Ipeak = (Vin * t * D) / Lmag = (24 * (70000/1000000) * 0,5) / (575 * 10^-6) = 1460 mA

Irms = Ipeak * 0,577 = 842 mA

Minimum number of turns needed to avoid saturation

t, 50% duty cycle = (1 / 70000) / 2 = 7,3*10^-6

Nmin = ( V x t ) / ( B x Ae ) = (12 * (7,3*10^-6)) / (0,2 * (95,89*10^-6)) = 4,6 turns

Current needed to drive a single 60N60 IGBT gate

I = Qc / t = (146*10^-9) / (1/70000) = 10,22 mA, including magnetising current, double this figure.

So it all seems to have overhead enough to drive a full bridge.

3rd October 2009

Started on construction of the MMC.

10th October 2009

Made the round platform plates for the coil to be built on, they were cut out from 19 mm MDF wood plates with a modified router, also shown in the picture, very neat for making circular cuts.

11th October 2009

Finished MMC construction, features a 80 mm fan that delivers 30 cubicmeters/hour of air.

5th November 2009

Debugged PCB design of the driver Forum thread link

Tested driver and interrupter on a small DRSSTC I put together just for testing purpose, blew the half bridge when I ran it in CW without feedback, I guess there is no way I could have treated that poor little coil any worse…

12th December 2009

Made primary form and winded the primary coil onto it, with a strike rail and mounted on the upper platform, took me 1½ hours just to wind the coil through the holes and also spend quite some WD40.

The coil is a true helical coil with 4 mm steps between the supports.

27th March 2010

It is far from satisfying to wind half a secondary to learn that you have used a ruler with 2 scales and you started with a 100 mm offset in the wrong direction…

The second try on the secondary was winded in 2 hours using my new coil winder rig, its 2200 turns of 0,25 mm enamelled wire on a 160 mm diameter pipe, winding length is 605 mm, its currently hardening its second layer of varnish till I get time to visit my parents again as its staying at their garage while getting varnished.

Top end termination is a banana plug in a home made brass nut, fixed to the plexi top with nylon screws so no metal is inside the secondary coil. The bottom termination is made from a home made brass nut soldered to a strip of 1 mm copper where the secondary wire is also soldered to.

2nd August 2010

I made a fitting piece for holding the CTs as the cable shoes were too wide to go through the CTs

7th August 2010

Today I assembled some of the parts on the platform, its beginning to look like a DRSSTC! Also I painted it black some weeks ago!

9th September 2010

The top-load is done, measuring 130 x 620 mm, made from aluminium ducting on a wooden form, smoothed with filler for metal and covered in aluminium tape.

17th October 2010

Final testing of driver features, got a 555 acting as a feedback at 70KHz while my signal generator is used to simulate over current input signal.

FIRST LIGHT! YIPPEE!  See further down for demonstration video.

22nd October 2010

The layout of the electronics have reached their final state

3rd November 2010

I made a new interrupter with selectable BPS, either from 3 to 15 or 130 to 500. On time from 1 to 20 cycles and burst mode.

5th November 2010

First test run, the coil is still slightly out of tune. Achieving sparks around 120 centimetres.

After a few adjustments of no more than 5 centimetres on the primary coil at a time, what seems to be the sweet spot have been found. Sparks will now fly out at 145 centimetres.

A run was made with the breakout point going straight up, beautiful sparks and some very heavy sparks directly between top-load and earth rail.

A final adjustment of the primary tap would be the end of the days testing, the variacs 10A fuse blew after the coil had been running for 5 minutes.

150 centimetre long sparks! Running from 250VAC in at 10A, 9 cycles ~200-225uS on-time, 500A limiter.

Conclusion

A years work have come to an end with a result I am very satisfied with and still I did not make a spark longer than my own height, which was one of my goals.

The metal filler used for the top-load to smooth the surface is way too hard to sand down without damaging the aluminium tubing underneath. I will use ordinary wall filler if I use this method for top-load construction again.

A full bridge of IXGN60N60C2D1 SOT-227 package IGBTs is slightly too small for a Tesla coil this size, I will upgrade with some heavier silicon, preferably a Powerex CM300-24H brick.

Demonstration

17th October 2010: First light

5th November 2010: Stress test

5th November 2010: High BPS ground strikes

86 Responses to Kaizer DRSSTC I

  1. Pingback: Kaizer DRSSTC I is alive! | Kaizer Power Electronics

  2. Jimmy says:

    G’day mate, nice site ya got here.
    I notice you’ve not posted the schematics for this coil. Any particular reason or, like myself, do you just get sidetracked easilly lol.

    Could you post them or perhaps give me a look at them? I’d really like to replicate this.
    In the meantime, Thanks for posting all the other info… picked up a couple of tricks that maybe will help with the exploding mosfet syndrome that my plasma speaker suffers from atm.

    Thanks in advance mate.
    Jim

  3. Mads Barnkob says:

    Hello Jim

    I never got around to update the schematics with all the prototype corrections, thats why and I got sidetracked 🙂

    I will take a look at them tomorrow and get them online

    Kind regards
    Mads

  4. Mads Barnkob says:

    I found out why I never uploaded them, it’s all just on paper in the stack of papers to go through…

  5. Rob says:

    Hello, I’m trying to make the same board with through hole components. Could you share the part number you used for the N and P channel Fet’s for the gate drive circuit?
    Thanks, ~Rob.

  6. Mads Barnkob says:

    Hey Rob

    Its IRF540 and IRF9540

    Kind regards
    Mads

  7. Alex says:

    Nice! Is that you in one of the photos, the guy to the left?

  8. Mads Barnkob says:

    Hey Alex

    Thanks and yes, that is me working on the topload 🙂

    Kind regards
    Mads

  9. Hei says:

    Nice coil!
    I see you have put two 440V TVS in series, wouldn’t the peak kill the IGBT(600V) before it clamp by the TVS (880V) ?

  10. Mads Barnkob says:

    Hey Hei

    I am sorry that I do not have the time to give you a complete answer, but modern IGBTs are build with some over head and built in protection, the TVS are there to protect it from the further stress that it sees in a DRSSTC when it is driven a good portion beyond its recommended limits.

    Kind regards
    Mads

  11. Tobias says:

    Hey,
    gratulations to this neat coil. I am, just like some of the posters before me, trying to build a DRSSTC based on Steve Ward’s universal driver. Could you rethink publishing your board layout? It would just save so much time (to bugfix all the other parts of the system 😉 ).
    Thanks, Tobias
    P.S. : Your SSTC Macro pictures are really nice. Interesting spark-look.

  12. black-sama says:

    so beautiful DRSSTC
    which is you used to driver?

  13. Mads Barnkob says:

    Hey black-sama

    Thanks for the kind words and I use a slightly modified version of Steve Wards universal driver, some day when I find the time, I will post the schematic.

    Kind regards
    Mads

  14. Ivan says:

    Hi Mads, give me please one slide PCB. I cant made himself.
    P.S Sorry if I write something wrong, I’m from Russia, and English is not my strong

  15. Martin says:

    Hi, do you still have one sided Steve Wards universal driver pcb (in eagle)? Thx very much…

  16. Chris says:

    Hey Mads, sorry i was messaging you on your sstc, i was just wondering, i got some 8″ conduit aluminum pipe for my toriod and im wondering what would be the best to put in the center? I was thinking of using aluminum sheet laying arround that i can cut in a circle? Or do you have any better idea?

  17. Mads Barnkob says:

    Hey Chris

    If you look at http://kaizerpowerelectronics.dk/wp-content/gallery/2009_08_27_-_kaizer_drsstc_i/IMG_1096.jpg

    I made two round pieces of wood with curved edges made with a router, to find the curve of the pipe. The two circles of wood are held together with some spacers also made from wood. The pipe will now fit nicely around the two circles and is being held in place with a elastic string.

    Kind regards
    Mads

  18. Chris says:

    Hey mads just wondering if i can send you pics of my bridge? Just want to know ypur opinion

  19. Mads Barnkob says:

    Hey Chris

    Please use a image upload service, lots of them free, and put a link here to the images 🙂

    Kind regards
    Mads

  20. Chris says:

    Hey mads! I have my tesla coil is finnaly finished! Soo i turn on my interupter and cranked up my power supply it start buzzing louder as i bring the power but there is no break out!! Soo i decided to grab a hammer with a rubber handle and when i went close to the toroid i got 2″ of and major electric shock through the handle! So why isint it showing major sparks! Please let me know what it could be! I have a talent show in two days.

  21. Mads Barnkob says:

    Hey Chris

    What was the input voltage at? Some coils need over 100-150VDC on the bus before you see proper break out. The buzzing can be quite loud for someone not used to it.

    Remember you are dealing with over 100kV here, it will jump through and around everything, your best isolation is distance!

    You could also try to reverse polarity of your feedback current transformer.

    Kind regards
    Mads

  22. Chris says:

    I took my toriod off and i got about 3 feet of arc off the metal rod, but as soon as i put my toriod back on i get nothing but il get 3″ of arc if i tune the primary to the maximum turns which is 10 turns. My input voltage is 120 ac.

  23. Mads Barnkob says:

    Use a web tool like javatc to calculate the tap point on the primary with toroid on. This only sounds like your coil is out of tune, by a lot! You should properly down around 4-5 turns with toroid on.

  24. Chris says:

    Hey Mads, I have already tried many tunning place with my toriod and when i went down to 4 to 5 turns, the coil will start arcing to the primary, i cant use javatc causr my laptop quit working of course. But i tried alot of different taps on the coil, is there only like one specific spot that will work?

  25. Mads Barnkob says:

    Hey Chris

    You really need to use a calculator as JAVATC. The sweet spot of the tune is within 10 mm and can be very hard to hit without some help from a calculations or previous experience.

    Try to tune the primary at a frequency a little lower than the secondary circuit, as the streamers will load the secondary and reduce its resonant frequency at maximum spark length.

    Arcing between primary and secondary can be caused by too tight coupling, try to raise the secondary up higher.

    Kind regards
    Mads

  26. Chris says:

    Thanks mads 🙂

  27. Chris says:

    Hey again!! 🙂
    I used the javatc calculator and i got some info, if my coil with toroid is in my garage the secondary resonance is 30khert and tune it to 7.5 turns, then when its outside its at 35 kherts at 6.387 turns. Does this make any sence??

  28. Chris says:

    I just tried out what it said on the javatc and i still get 0 arcs but i still her the buzzing noise. Why does it work but very porely when increase the turns? But when i take the toroid off i get nothing until i bring down the primary turns?

  29. Chris says:

    My tap connecter that goes in my prymary gets really hot would this have anything to with it?

  30. Chris says:

    Sorry i keep messaging you alot, but now if i have it taped at 7.5, i get very very small arc out of the break out point. Im not exacly sure how to set the current limit on but its steves 1.3 desing and the red light turns off as soon as tge interrupter is turned on. Im not sure if my problem is from the current limiter, because as soon as i pull the toriod off, i get massive arcs.

  31. Mads Barnkob says:

    Hey Chris

    Resonant frequency changes with surroundings, objects close to the coil will affect it.

    If the primary tap gets hotter than the wiring or coil, its contact surface is too small or it is a too small gauge .

    I think you are calculating something wrong, since it is only a tuning and coupling issue when you have gotten so long sparks. Could you post med all the details for javatc and all about your build here? So I could take a look on the numbers 🙂

    Kind regards
    Mads

  32. Chris says:

    Of course! I think your right. Mmc bank is at .375 uf Primary is close to 10 turns at 20.5″ oustidi diameter, inside dia is 10.25 with .375″ copper tubbing and it height is at 1.25. The stand is exacly 12″ high. Secondary tube is 51″ long with 48″ of 26 awg 2987 turns. So theres 1.5″ gap on each end. The toroid, minor is 8″ and major is 40″ wide. The thinkness of the two peace in between the aluminum flex pipe is about 6″ my cables are 4 awg going to primary.

  33. Chris says:

    Oh yes and the diamiter of the secondary is 10″

    Thank you!!

  34. Chris says:

    Oh and the shop cealing is about 144″ high and wall is 60″ away

  35. Chris says:

    Yeah i think im making mistakes on javatc, my primary is flat. And i have trouble entering the info on that an with secondary hope you can help me out i really appreceat it. Got a talent show at school coming soon.

  36. Chris says:

    I think im might have to buy 24 awg wire :/ because it would bring my resonance frequence up but then having my my toroid on would bring me to 43 khertz to 45 which bring my primary winding down.

  37. Mads Barnkob says:

    Hey Chris

    Your secondary is fine and it is a lot of work to make a new one. I have calculated your resonant frequency to around 31 kHz and with your MMC at 0.375 uF you should tap the primary coil at 11.5 turns.

    You have the following choices:

    1) Make the primary coil bigger, 6″ inner diameter and then make it with maybe 14 turns, tap it at around 12.

    2) Increase the capacitance of your MMC to atleast 0.5 uF, if not 0.6 uF so you will be able to use your current primary coil at around 9-10 turns tapped.

    Any way I think you should have a larger inner radius on your primary coil as it is somewhat close to the secondary and give the secondary about 1″ more height in regard to primary coil to get lower the coupling factor.

    Kind regards
    Mads

  38. Chris says:

    Alright thanks Mads 🙂

    If i was to change the secondary to 24 awg i know its alot of work but would i increase the output power? Or would it be the same with 26awg when i tune the primary?

  39. Mads Barnkob says:

    Hey Chris

    Output would be the same and with 24AWG your secondary will also be able to withstand longer run times before heating up. I think you should try to alter your primary to 14 turns and bigger diameters as I described, this would be the cheapest solution.

    Kind regards
    Mads

  40. Chris says:

    Hey again! I was just wondering, if im using two cm300 12nf with my bus at 6800uf 500v whats the max ac volts i can put in the bridge without stressing it out to much?

  41. Mads Barnkob says:

    Hey Chris

    For IGBTs only go to about 2/3 of their voltage rating, filtering capacitors you should see no danger, in amateur use, to go to about 90%+ of the voltage rating. But be sure to monitor heat dissipation in all components, we do drive them harder than intended! Around 320VAC would give 450VDC, which I would consider maximum for your filtering capacitors.

    Kind regards
    Mads

  42. Chris says:

    Hey mads,
    Finaly got some arcs!! Im using a piano as an interupter and now when i push any key, you can hear the sound of the piano but the sound is very distorded and the arcs keep making a poping sound, what would cause that?

  43. Mads Barnkob says:

    Hey Chris

    Are you using a midi keyboard through a midi controller or are you using the normal output from the speaker of a keyboard?

    If you are using the latter it is no wonder, you are trying to on/off modulate with a AM signal, that will not work very well as you have discovered. Another issue could be interference from the electromagnetic field around the Tesla coil.

    Kind regards
    Mads

  44. Chris says:

    Im using the 1.0 midi interfacer thats hooked to my piano, so if i put it outside would it makea big difference?

  45. Mads Barnkob says:

    I think you need distance and shielding, lots of shielding on all your driver parts. The popping sound is very likely from interference.

  46. Chris says:

    Yeah i had a sheilding problem, id like to put 220 ac in it but do i need a step up transformer from 120 to 220 or can i connect direct from ac with two live wires going to the bridge?

  47. Pingback: Kaizer DRSSTC 1 – high BPS video | Kaizer Power Electronics

  48. Arc says:

    Hey Mads,
    What do you think about driver “Predicter” from Hammertone?

  49. Mads Barnkob says:

    Hi Arc

    Finn Hammer did all the foot work when he designed the phase lead adjustable driver with a inductor in the feedback circuit. A design that quickly spread and most use it today in Steve Wards universal driver 2.1b, myself included.

    Finn developed and documented his experiments here: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?68820.0

    Steve Wards universal driver schematics: http://www.stevehv.4hv.org/leadcomp/

    Kind regards
    Mads

  50. Harsh Dwivedi says:

    I am new to solid state Tesla coils please I need some help please can you help me with making the pancake primary and the connections in a drsstc I mean the connections between the interruption driver bridge and coil please contact me on my email id please help me.Thanks

  51. Mads Barnkob says:

    Hi Harsh

    I am not sure what you are asking for? Take a look at the pictures from my different Tesla coils for inspiration on how to make different connections in the primary circuit.

    Kind regards
    Mads

  52. Harsh Dwivedi says:

    Hi Mads
    First my story,I wanted to make a Tesla Coil first I went with the slayer exciter and 9v TIP31C coils on YouTube but I wanted something bigger I want to make three coils one with NST other with flyback transformer and the third a DRSSTC . Ive been on Steve wards site and on loneoceans.com studying about coils but failed to understand anything clearly this is because of my less experience with cicuiting I just wanted your help for the construction of the spiral base primary and the entire circuiting connections in a DRSSTC that are between the Interruptor, the Driver and the halfbridge also I’ve seen all your coils and that frying pan toroid is nice also I’ve completed that Steve wards universal driver construction version 2.7.
    Thanks
    Regards
    Harsh Dwivedi

  53. Daniel says:

    Dear Mads,
    One year ago I built a DRSSTC, with a UD2.5 and a full bridge of IXYS IXGN60N60C2D1. The specs were like your DRSSTC 1, and the full bridge is based on the combination of two flexiBrute DRSSTC Half Bridge modules, from EVR. About one week ago, I bought a new digital oscilloscope, a Hantek DSO5072P, and decided to try out phase lead, since I could finally scope the bridge outputs. Well, I found out really high spikes, in the order of 300V with only 80VDC on the +- rails.. I attached a scope shot. Probably the problem is because I used a too much small Snubber Cap, but.. I changed the 0.2uF 2kV one for a 20uF 400V snubber, but nothing changed.. I tried with lots of values for the Phase Lead, but seems that I cannot get rid of those nasty spikes.. Maybe I need a bigger Snubber Cap? How can I scope correctly the full Bridge? I’m not sure either if I’m using it well.. (the DRSSTC is being tested with a isolating transformer put between main’s AC and the Variac)
    Thank you
    Best Regards,
    Daniel Rinni

  54. Mads Barnkob says:

    Hi Daniel

    First off, be careful not to damage your oscilloscope inputs from over voltage, you are about right on the edge of what it can take.

    You need to buy a differential probe in order to get a fairly calibrated measurement, if you just add a resistive divider to your probe it might result in loss of accuracy in terms of phase shift and other anomalies that would make the signal appear different from what it really is.

    You might be driving your IGBTs too hard, what value gate resistors are you using? If you use 4R7 try using higher values like 5R1, 5R6, 6R2 and so on, up to 10R+.

    Do you have long leads or in other ways large inductance in your primary circuit?

    You could try to add a 2 to 5K resistor, remember sufficient power rating, across the inverter output, this can some times help phase lead drivers relax a little bit as residual stored charge in the primary capacitor can disturb the frequency locking.

    Kind regards
    Mads

  55. Saattvik says:

    In the stress test video, there were arc coming from the middle of the secondary coil

  56. Mads Barnkob says:

    Hi Daniel

    Here is a important update on your switching spike problem “As you can see the IGBT open state capacitance is largely depending on the voltage that is applied over Collector-emitter! And imagine what happens at your bridge when for example high side transistor turns on and low side transistor turns off. The emitter of the low side brick is tied to negative bus rail, and collector is quickly whacked to the full bus voltage which means the parasitic capacitance inside of the brick will be charged to your dc bus voltage at very high voltage rise time. And that charge current must travel through all parasitic inductances that your bridge has.

    As you increase your bus voltage, your parasitic capacitance will decrease and amplitude of these transients related to the bus voltage will go down. My big coil does that too, at 100V bus the transients are almost 200% above bus voltage. But at 650V they are only maybe 20% over.”

    From Kizmo on 4hv: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?176619.post

    Kind regards
    Mads

  57. Mads Barnkob says:

    Hi Saattvik

    Yes, there were a few racing sparks, but nothing too bad. It was simply a result of the coil not being tuned properly and maybe too high coupling.

    Kind regards
    Mads

  58. cooling heatsink for both igbt is not enough, they will overheat. either separate them on 2 heatsinks or use coldplate for both on 1 plate

  59. Daniel says:

    Hi Mads,
    Thank you very much for the answers. You were right, the connection between rectifier capacitor and the IGBTs is too weak, I used a 85A cable, but looks like it’s too less. I found a 2uF capacitor, 800v, 30Apeak for snubbing, I’ll do a full copper or aluminium bus bar, and rebuild completely the connections.. One last question, I’ve put the MMC in a open-sided plexiglass enclosure, with connections on side, like a sandwich of plexi, but it overheats on the bolts, melting it and making the connection lossy.. I’ve put two pieces of teflon, Tmax=260°C, in both connections,should I improve also the cables? I used the same cables of the busbar, a 25mm^2 one..
    Thank you for your help!
    Kind regards
    Daniel

  60. Mads Barnkob says:

    Hi Daniel

    To avoid over heating at the MMC terminals you must be sure to only use copper wire shoes, brass bolt / nuts and remember that you have the same amount of current flowing through here as in the primary coil, there is no room for weak points in the resonant primary circuit! Due to skin effect it is better to use 2-3 thinner cables than 1 thicker.

    Kind regards
    Mads

  61. Zach says:

    Hi Mads,

    How sensitive is the current transformer to material type? Is it ok to use the same cores for the current transformer as the GDT? I don’t see much talk about designing the current transformers aside from turns ratios.
    Thanks!
    Zach

  62. Mads Barnkob says:

    Hi Zach

    You need a CT that is capable of working at the high frequency that the coil runs at. Typically you can use the same core as used for the GDT, but in larger coils a larger GDT ring core would be used, to have enough drive current for large IGBT bricks, so here you should still only use smaller cores for the CT, it would be a waste of money on large cores, unless your large conductors can not pass through it 🙂

    Kind regards
    Mads

  63. Zach says:

    Hi Mads,

    I’ve been doing tests at low power (Vbus ~ 40V) and I’m experiencing a small oddity. I’m using the half bridge topology with the UD2.7. If I try to run the coil I hear the buzzing of the GDT, but no light. When I hook a 10M 2.2pf scope probe across the high side IGBT, the coil lights. If I scope the low side gate instead, again, no light. I’m not sure what could be causing this. Do you think I should connect a 2.2pF 10Mohm resistor across the gate or is there some other more insidious problem I need to fix? Perhaps it will just go away by itself at higher bus voltage? I’m a little leery of that, however, because throwing more power at a problem usually doesn’t turn out well.

    Thanks for your help.

  64. Mads Barnkob says:

    Hi Zach

    Did you measure the current drawn from the DC bus? Or AC supply to the DC bus? If there is no current drawn, the problem could be wrong phased GDT, feedback CT or opto receiver that has a different level output.

    If the current drawn from the DC bus is rising very fast, the problem is the bridge shorting out from wrongly switching IGBTs or there is a short from the bridge to ground.

    Testing at low voltages can give weird results that show huge switching voltage spikes, but this has to do with ratios of the voltage spikes from capacities of the IGBTs towards the DC bus voltage. The higher DC bus voltages, the ratio increases dramatically and switching spikes are much smaller.

    Kind regards
    Mads

  65. Zach says:

    I’m using an old Harrison 6824A power supply which is limited to 1A supply. I believe the phasing is correct. With the current setup, I have been able to get ~3″ sparks. I have not tried a higher bus voltage yet because I wanted to make sure everything was in order first.

    This supply uses a needle to indicate the voltage output, and in the past when I have inadvertently shorted the output, the indicator dips because the supply hit its 1A delivery limit. I do not witness the indicator dropping out in any of my tests, however it could be that my interrupter pulse widths are short enough (200Hz, 200us on time) where the supply isn’t being overdrawn.

    I uploaded a small picture with the 3″ sparks. My camera isn’t very good at low light, so it’s not a great shot. I appreciate the feedback!

    Zach

  66. Mads Barnkob says:

    Hi Zach

    So you can only get sparks with a probe connected on the high side? And thus you can not run higher voltages since you would ruin your scope.

    I think the scope probe + cable acts as a antenna and helps start the oscillation of the bridge. So adding a 10M resistor will properly not help.

    Try it with 100 VDC on the bus and see what happens.

    Kind regards
    Mads

  67. AndreaF90 says:

    Good evening
    Instead of your two smoothing capacitors can be fine No. 3 HCG F5A (Irms = 25A, 50 ° C) so about 75A with all three.
    The IXGN60N60C2D1 IGBT can go well anyway if well cooled for this type of DRSSTC?

  68. Mads Barnkob says:

    Hi AndreaF90

    You can use 3 capacitors in parallel, but I am not sure if it is needed, only if you are planning to run extraordinary long on-times, extending above 250-300 uS.

    I am not sure what you mean about the IGBTs, it was the IXGN60N60C2D1 that I used in this build, so yes you can use them.

    Kind regards
    Mads

  69. AndreaF90 says:

    Hi Mads Barnkob
    I’ve bought n°2 PP capacitors http://it.rs-online.com/web/p/condensatori-in-polipropilene/1235122/ .
    Can I use this caps for C3-C4 capacitors? that are 400v 10uF.
    Thank

  70. Mads Barnkob says:

    Hi AndreaF90

    As they are polypropylene capacitors and their rating is above the DC bus voltage, they should work fine as snubber capacitors, be sure to mount them with as short as possible leads to the IGBT terminals.

    Kind regards
    Mads

  71. AndreaF90 says:

    Hi Mads Barnkob
    It’s ok the schematic that i’ve done?
    It’s PCB for the full bridge IGBT and C3 and C4 that i’ve said before (On the mid of schematic).
    Andrea

  72. AndreaF90 says:

    Hi Mads Barnkob
    https://www.amazon.it/elettronica-regolatore-Governatore-controllore-termostato/dp/B00HPTLZO4/ref=sr_1_6?ie=UTF8&qid=1488992153&sr=8-6&keywords=regolatore+di+tensione
    Can i use this component for regulate the imput tension of the DRSSTC instead the variac?
    The variac costs too much and I wanted to find an alternative way.
    Andrea

  73. Mads Barnkob says:

    Hi AndreaF90

    A SCR/thyristor controller only works for a purely resistive load, a DRSSTC is a highly capacitive load to the power supply, without a variac in between the power factor is as bad as 0.45, which would overload this little controller so much, that using it at more than 40% of its ratings would damage it.

    I hope you will sign up at our new forum at http://www.highvoltageforum.net and show us the progress of your Tesla coil 🙂

    Kind regards
    Mads

  74. AndreaF90 says:

    Hi Mads Barnkob
    I’ve tested the SCR with in series a microwave transformer for current ballast ad it work fine, i’ve tested it for charging capacitors of my DRSSTC and the current is near 7-8 amperes max,
    With this current the SCR in cold, i’ve tested it with 2500W load ad it work very well.
    Have you seen my PCB schematic?
    AndreaF90

  75. Mads Barnkob says:

    Hi AndreaF90

    That sounds great, I look forward to see the results.

    The PCB layout looks good, if you want to improve it further, lessen the distance between upper and lower switches, it could get closer together to bring down the stray inductance of the long traces.

    Did you want to show off your project on the forum?

    Kind regards
    Mads

  76. AndreaF90 says:

    Hi Mads Barnkob
    When i’ll finish it I’ll show you my DRSSTC.
    Thank you for your advices 🙂
    AndreaF90

  77. AndreaF90 says:

    Hi Mads Barnkob
    I’ve a problem with my DRSSTC, yesterday i’ve built the primary coil and after that i’ve tested all.
    When i turn on DRSSTC the differential (30mA) of my house brake-out.
    After various tests i’ve seen that the problem is capacitor C6 that i’ve connected from negative rail to ground of my house together strike rail, RF, ecc. (i’ve used one 0.15uF 2000VDC 942C20P15K-F). If i disconnect C6 all work fine and when DRSSTC turn on i listen a beep beeep from MMC and primary coil. So i think it works ok…true?
    Do you think I was wrong to use that type of capacitor?
    In your video I see that by connecting it to the ground works, I can not understand.
    Thank you
    AndreaF90

  78. Mads Barnkob says:

    Hi AndreaF90

    You could try to use a smaller value capacitance, if the leakage current is too high in the capacitor, you actually do have earth fault conditions and your breaker should trip.

    Some of the best advices are in this thread: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?163880

    Kind regards
    Mads

  79. AndreaF90 says:

    Hi Mads Barnkob
    I try with 0.1uF 2kV.
    Can i test with two cap in series? For reduce the total capacitance.
    Thank you
    AndreaF90

  80. AndreaF90 says:

    Hi Mads Barnkob
    Can i change the diameter of the secondary wire? From 0.25 to 0.2mm with same number of spires.
    Through the calculators on this site the resonant frequency is 76khz and if i tapped primary wire ou 4 turn the resonant frequency is near 75khZ.
    Thank you
    AndreaF90

  81. Mads Barnkob says:

    Hi AndreaF90

    Yes you could try two capacitors in series and you can also make a secondary with a thinner wire, for a lower resonant frequency, but check the secondary part of the DRSSTC design guide on the page to get an idea of the result of the changes.

    Kind regards
    Mads

  82. Andreaf90 says:

    Hi Mads Barnkob
    in order to isolate secondary coil can i use this product?
    http://www.tme.eu/it/details/pvb60-50ml/rivestimenti-di-protezione-e-schermatura/ag-termopasty/lakier-pvb-60/
    For secondary wire i use 0.25mm with enamelled with two layers.
    Andreaf90

  83. AndreaF90 says:

    Hi Mads Barnkob
    Can I install a 1Megaohm resistor 0.5W on the power rail in order to dicharge C2 and C3 capacitors?
    Andreaf90

  84. AndreaF90 says:

    Hi Mads Barnkob
    Sorry for the disturb.
    What varnish can i use for protect the secondary coil?
    AndreaF90

  85. AndreaF90 says:

    Hi Mads Barnkob
    The RF Ground of the secondary coil is the same with Stricke rail, ecc.?
    I’ve connected all on my home ground.
    AndreaF90

  86. Mads Barnkob says:

    Hi AndreaF90

    The PCB varnish seems too expensive to use on a secondary coil, find some polyurethane varnish, its made for both furnitures and boats. Read my guide for the DRSSTC secondary for my advices on varnish.

    You could connect a 1M resistor across each capacitor, that would also help them divide the voltage more accurate.

    It is correct that all grounds on the Tesla coil should be connected together, I do not advise on using house ground! I have had bad experiences with arcing between ground and phase. Use a separate ground rod or you could make a artificial ground plane from sheet metal, mesh or aluminium foil spread out on the ground underneath the coil.

    Kind regards
    Mads

Leave a Reply

Your email address will not be published. Required fields are marked *