Kaizer SSTC III

Introduction

The idea was to build a very small and compact Tesla coil as a gift for my mother that works in various science classes for the lower grades in public school.

This driver circuit is very similar to the one used in Kaizer SSTC I. This time I have made a PCB containing both driver circuit and bridge.

 

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

I knew this would get claustrophobic with so little space for a complete interrupter, driver and bridge.

Using the enclosure as the heat sink is the reason why a low break rate is chosen, to avoid excessive heating.

 

Specifications

Bridge 2x IRFP460 MOSFETs in a half bridge configuration
Bridge supply 230VAC directly from the wall, 4A rectifier bridge and 330uF smoothing capacitor
Primary coil Rev 1: 55 mm diameter, 1.38 mm diameter isolated copper wire, 10 windings.Rev 2: 80 mm diameter, 1.38 mm diameter isolated copper wire, 10 windings.
Secondary coil Rev 1: 50 mm diameter, 200 mm long, 1430 windings, 0.127 mm enamelled copper wire.Rev 2: 75 mm diameter, 165 mm long, 1500 windings, 0.1 mm enamelled copper wire.
Resonant frequency Rev 1: Self tuning at around 470kHz.Rev 2: Self tuning at around 180 kHz.
Topload Rev 1: Made of two bottoms from beer cans, 65mm diameter and 30mm in height.Rev 2: 45 x 152 mm turned aluminium toroid.
Input power Interrupted mode: ?W at 230VAC input voltage.
Spark length Rev 1: up to 140 mm long sparks.Rev 2: up to 250 mm long sparks.

 

Schematic and PCB files

PCB file for ExpressPCB

 

Construction

21st July 2009

I designed a compact single sided PCB that contains both driver and bridge section on a mere 65 x 75mm board. Here is newly etched board, traces are a bit shaky as I have drawn them all by hand.

The MOSFETs uses the enclosure as a heat sink, I sanded down the paint for metal contact and use pads to isolate between MOSFETs and enclosure.

BPS is kept low, but can be varied from 4 to 20 BPS, to avoid excessive heating as the enclosure is not an optimal heat sink.

In the bottom of the following picture you can see the bridge rectifier mounted to the enclosure and the input filter for 230VAC in. The red wires lead to the 330uF/400V smoothing capacitor and the 100nF/1600V Rifa capacitor is the DC blocking capacitor in the primary circuit.

The coil is connected directly to 230VAC without any kind of voltage regulation and also requires a external 12VDC supply for the driver.

Antenna and primary coil connections are temporary solutions for the sake of demonstrating the Tesla coil in working order. A fold out antenna from a small radio or such will be added later. Some kind of support with banana jacks with a secondary and primary coil mounted on will be added, to avoid wrong phasing of the primary coil.

Here the complete setup is size compared to a 330ml beer can

 

Sparks

Here is one of the more spectacular spark pictures I have taken, in my eyes it looks like a demon waving its arms over the head which also have a distinct face with glowing eyes and a open mouth, or maybe I am just seeing things from inhaling too much ozone 😀

24th July 2009

I borrowed a expensive macro lens for my Canon 350D camera and took some pictures with great details of the sparks, very sharp pictures!

 

Revision 2

1st August 2009

Doing a short demonstration I adjusted the antenna with my hand while the coil was running, this resulted in unstable oscillations and the bridge was short circuited. I am now replacing the destroyed MOSFETs and here I can feel the disadvantage of servicing on a compact design.

A new secondary coil is in the making, it is wider, shorter and have half the resonant frequency of the first. It will be fitted nicely on a piece of acrylic for a complete look.

 

19th August 2009

The new secondary is finished, it took me about 8 days to do the winding as it is very intensive to wind with such a thin wire. Keeping the wire tight, windings close to each other, not pulling the wire too hard from the spool, watch for jams and overlaps and it all have to be done with a bright light very close to get a good view.

It uses the topload from my VTTC I, a 45 x 152 mm aluminium toroid, with this it have a new resonant frequency around 180 kHz.

Top of secondary was filled with epoxy to insulate the brass bolt from the inside of the secondary and the bottom earth connection is fastened with a nylon bolt.

It is all fitted onto a piece of acrylic with additional protection around the primary connections so it no longer possible to touch any conducting part of the primary circuit.

 

Audio modulation

I use a audio modulator made by the user Reaching (Martin Ebbefeld) from 4hv.org.

For sound input I use a cheap children’s keyboard from a toy store, its far from perfect for the job, especially because its waveform is highly distorted and its not clean tones but seems to involve a lot of modulation inside it to simulate different instruments. But its cheap and expendable.

Watch the film and look at the schematics for more about the audio modulation.

 

Conclusion

I am very satisfied with the final result, that I got to fit everything and use the enclosure as a heat sink turned out real good. Heating is not a problem with run times at about 2-3 minutes which is also the durations its been built to be demonstrated for.

Enclosure dimensions are 125W x 80D x 50H mm.

Revision 2 looks even better, performs better but was also a lot of work to wind the new secondary with such a thin wire.

Demonstration

Revision 1

Revision 2

66 Responses to Kaizer SSTC III

  1. CJ says:

    Very nice work. I hope to have my minni sstc going soon.

  2. CJ says:

    Please help. I need a little info. I cant get this coil to fire without touching and holding the antenna first.
    I used your schematic to a tee. I also tried switching the antenna coupling diodes to 5 v zeners, Still no luck.

    Thanks again. CJ

  3. Mads Barnkob says:

    Have you tried moving the antenna closer to the secondary coil?

    My antenna is often within 6 – 8 cm from the coil and will occasionally have a bit of corona at the end

  4. CJ says:

    Thanks, I will try that tonight.

  5. Kembrik says:

    You can find out the size and type of ferrite rings in the GDT?

  6. Mads Barnkob says:

    Hey Kembrik. Its a N30 material ferrite toroid, properly around 30 mm in outer diameter. Find one with a permability above 4000.

  7. Kembrik says:

    Thanks.

  8. shahar says:

    I will try to build 1
    can I add audio modulation circuit to this design? or will it cause a problem?

    thanks in advance
    Shahar

    p.s
    sorry for my English level

  9. Mads Barnkob says:

    Hello shahar

    If you look at the schematics for the SSTC II, you can see how it was audio modulated. You can use the exactly same design for this smaller Tesla coil.

    Kind regards
    Mads

  10. shahar says:

    Thank you for the fast replay
    Shahar

  11. Unleashed says:

    Hello Mads.

    What is the GDT core you are using in that?
    Thanks.

  12. Mads Barnkob says:

    Hey Unleashed

    Look at my comment from June 25, 2012 at 6:53 pm

    Kind regards
    Mads

  13. frogger says:

    Hello,
    I’m very interesting in your project, so I decided to build it. I have a question to you, namely how many turns is on the GDT transformer?

    Thank you very much.

  14. frogger says:

    Sorry, this is not actually, I saw “15 turns” on your scheme.
    Greetings.

  15. shahar says:

    hello again
    I have hard time finding 75m”m tube for the secondary coil
    if i use 70m”m tube instead what are the constants i should keep?(secondary coil frequency, turns ratio, diameters ratio etc)

    Thanks in advance
    Shahar

  16. Mads Barnkob says:

    Hey Shahar

    There are no constants in designing a Tesla coil, but there are some general rules of thumb to stay within. There are many guides about this elsewhere, so I will not get into details.

    You can without any problem use a 70 mm tube instead of 75 mm, if you want to keep the same frequency, wind some more windings on it 🙂

    Kind regards
    Mads

  17. shahar says:

    thank for the fast replay
    ill start ordering the parts i missing 🙂

  18. shahar says:

    hello again
    sorry for having too many questions but i have few more:
    -can i plug it to the house grounding or should i try to find another option?
    (i am at 3rd floor and the water pipes are mostly insulated so only the water will be used as conductor if i plug it to them)

    -i done making 1500 laps on the coil and it is shorter than it should have been
    after a good look i saw there was some overlaps once a while. is it good enough or should i start over and work slower so there will be no overlaps at all or only few of them?

    -can i plug the audio trough optocopler to protect the player or will it add more noise or something?

    and last one:
    -i tried to plug the main circuit to power to test it and the second i plug it the transistors burn and short circuited can it be caused by plunging it before i turned on the driver so they was off for too long? and if not do u got another idea that can cause it? (my transistors rated for 16amp and 500V)

    thank you in advance (again….)
    shahar

  19. shahar says:

    i found that i excellently switched the source and drain of the mosfets so that’s probably the reason they blown
    so the last question is irrelevant

  20. Mads Barnkob says:

    Hey Shahar

    For a small Tesla coil you could use the house grounding, just not use any or make a artificial ground plane beneath the coil out of aluminium paper or other metal sheet.

    Over lapping windings are not good because they break the even surface of the coil and you could get problems with corona forming at these points. But in a small Tesla coil you should not worry about this and if you see it as a big problem, add more varnish to insulate the spots even more.

    You could use a opto coupler circuit to protect your audio source, I should also have used one on all my projects as I killed a little iPod shuffle with a flyback driver 🙂

    See if you get hold of a variac or a step down transformer so you can test your circuits at lower than full power, there are often small problems that you can discover at lower voltage and its hard to find faults after it all went BOOM!

    Kind regards
    Mads

  21. shahar says:

    thank you for your help
    variac is much over my budget but i will try to test it with step down transformer
    about what voltage should i test it on?

    thank you again in advance
    Shahar

  22. Mads Barnkob says:

    Hey shahar

    At about 30-50 Volt AC in, you should be able to lit up a flourescent light bulb or tube. At 100 Volt AC in you should begin to see break out and sparks.

    Kind regards
    Mads

  23. shahar says:

    i add a 3.5A fuse to protect the rectifier and it burned quite fast
    should it use mire than 3.5A with the 4A rectifier?
    and i tried to use old step sown i had to test it but it burned aswell. so ill try to get better one.
    and is there any way i can test the control circuit with out the main circuit?(i tried but got no output probably because there was nothing for the antenna to receive)

  24. zak says:

    why did you use 150nf caps on the half bridge

  25. jass says:

    can i use .47uF 400v capacitor instead of 150nF in the half bridge? if not what changes should i make, also in the driver section i’m using .47uF instead of the .1uF(C4) near the GDT.

  26. Mads Barnkob says:

    Hey Jass (and zak)

    I used 150nF because of the limited space in the small box. If you calculate the reactance of the capacitor at the frequency you run the coil at, you might find that several, maybe 3-5uF gives a much lower resistance to the primary current.

    The AC filtering capacitor C4 in series with the GDT can be sized between 0.1uF to 1uF at the power levels and frequency used for driving a Tesla coil bridge.

    Kind regards
    Mads

  27. jass says:

    I made all the circuit part exactly as your, the secondary is 3.5inch in diameter and 12inch long, the power supply is using a SMPS line filter connected directly from mains(220v AC) to half bridge.
    The problem is the MOSFETs get hot even after just 3 sec of running.
    Is the input voltage too high? if so is there a more powerful MOSFET i could use? I need
    to run it for atleast 15 min continuous.
    Thanks for help

  28. Mads Barnkob says:

    Hey jass

    Are you saying there is no rectifiers in between the line filter and half bridge? You need to supply it with either half- or full-wave rectified DC.

    Kind regards
    Mads

  29. jass says:

    Of course there is rectification and the tesla coils works but the MOSFET gets hot pretty fast. I’ve put 10 turns on the primary.

  30. Mads Barnkob says:

    Hi jass

    Could you upload some pictures of your tesla coil, it would make it easier to help you, there could be a million causes to why the MOSFETs heat up. You can now upload attachments directly in your comment here on the site.

    Which value gate resistor are you using? It could be that if it is too large the MOSFETs switches too slow, spend too much time in the linear region where it dissipates a lot of energy.

    Kind regards
    Mads

  31. jass says:

    Here are some pictures.
    The gate resistors are 4.7ohm 2W.
    Thanks for help

  32. jass says:

    Sorry, i’m not able to send pictures so I’ve uploaded it as a question in instructables.
    It includes a PCB schematic which i referred for making it.
    LINK: http://www.instructables.com/answers/SSTC-MOSFET-over-heating/

  33. Mads Barnkob says:

    Hey jass

    You tried to upload pictures that were bigger than 2MB, then it will fail and not show up.

    I took a look at your pictures and two things come to mind

    1) Do you know what kind of ferrite core you have used for the GDT? Is it a high permability ferrite core or is it some powdered iron core you pulled out of a power supply? A powdered iron core will not work at these high frequencies and thus it will only drive your MOSFETs in the linear region due to saturation of the core, not enough current can pass to the gates.

    2) It looks like your antenna is used as strike rail towards the wire from the topload, you should move the antenna so far away that there is not even corona showing on top of it at full input voltage. You just risk damaging the feedback circuit. You could also make a little distance between the antenna wire and the primary leads.

    Kind regards
    Mads

  34. jass says:

    1)The ferrite core was taken from a SMPS(computer power supply) and 22AWG wire was wound on it by me.
    2)The output from the coil is feeble like 2-3cm so i kept the antenna near.

    I’ll look for a better ferrite core.
    also does the gate resistor affect the bridge, because i’ve used a 2W instead of 1/4W?
    Thank you

  35. jass says:

    Also I’ve a ferrite core taken from a flyback(two ‘C’ shaped ones) could i use it as my GDT? if so could you please explain how?

  36. Mads Barnkob says:

    Hey jass

    The flyback core will be much better, despite it is much bigger than needed and not optimal at all, but it will however work. Put the two cores together so it forms a “circle” and wind your GDT as you normally would, if you have 15 turns, spread them out so they cover all the window area all the way around the “circle”.

    The core you found in a SMPS is most likely a iron powder core used as output inductor, they are absolutely no good as GDT.

    4R7 2W is good, when I have used 1/4W it is my experience that the gate resistor also blow up if you blow up the MOSFETs.

    Kind regards
    Mads

  37. jass says:

    Thanks for all the help, and by the way very nice tesla coil.

  38. jass says:

    Sorry for the inconvenience, but i’ve got one more question.
    i’ve got a ferrite transformer(i’ve uploaded photos), could i use that as my GDT if so which meathod is workable? or is it better to stick with the flyback core?
    On the transformer these are written “8250 GA6” is its permeability(8250)?
    Thank you

  39. Mads Barnkob says:

    Hi jass

    Just use the transformer core like if it was a normal transformer, do a trifiliar winding on the plastic bobbin around the centre leg. Like on the edited picture I attached.

    I think those numbers and letters on the plastic bobbin is just the model number of the plastic bobbin and has nothing to do with the core materiel.

    Kind regards
    Mads

  40. Kishan Jhaveri says:

    hi, any way i can get the pcb circuit trace for this build? the gerber or eagle files?

  41. Mads Barnkob says:

    Hello Kishan Jhaveri

    I added a link to the PCB file where the schematic is.

    Kind regards
    Mads

  42. Kishan Jhaveri says:

    Hi,
    Thanks for the PCB file. I have one question, on the PCB layout i didn’t find the bridge rectifier. Is it not needed? or is it being run off the board with the atx line filter? I see it in the schematic is why I’m asking.
    Thanks!

  43. Mads Barnkob says:

    Hey Kishan Jhaveri

    The bridge rectifier was mounted directly after the mains input socket, if you look close at the pictures you can see it is mounted with a screw into the side of the box, just behind the line filter. It is needed with either half wave or full rectification, you can not feed this circuit AC.

    Kind regards
    Mads

  44. Hello Mads,

    I was trying to find a hint in your posts and in the comments how the variac should be rated, but I could not find any specifications. You have used a 4A rectifier (or 8A in earlier versions), so this means 1kW (2kW) for the variac? Or could it be much smaller rated?

    You know, the higher wattage a variac has, the more it costs 🙂

    A reply would be much appreciated!
    Thanks
    Matthias

  45. Mads Barnkob says:

    Hello Matthias

    With this little coil you could do fine with a 4A variac, the variac you can see I use in the video is a 10A.

    Do not buy a completely new, there are plenty to be found used from old work shops, radio amateurs etc.

    Kind regards
    Mads

  46. Teemu says:

    Do you have idea how much current the mosfet circuit draws?

  47. Mads Barnkob says:

    Hey Teemu

    I have not measured the primary current in a SSTC yet, but you can calculate it using Ohms law. Divide the DC bus voltage with the reactance of the primary coil. The result should be your primary peak current.

    Kind regards
    Mads

  48. Prabodh says:

    what should the output be after c4? i dont seem to be triggering my mosfet gates. when i power up nothing happens.

    red dots are sites in question

  49. Mads Barnkob says:

    Hi Prabodh

    Adjust your antenna, maybe more it closer.

    Across the primary of the GDT you should see a square wave and on each of the secondary windings it should be the same signal, just inverted for one of the MOSFETs.

    Be sure to have the GDT connected to the MOSFET gates when testing, you need a load on the GDT to see the proper wave forms.

    Kind regards
    Mads

  50. Athos says:

    Hey,

    I built the SSTC exactly like the schematic, but nothing works. If I invert the UCCs, putting the 37322 in the place of 37321 and 37321 in the place of 37322 it works, but only in CW. What can I do to fix it?

    Thanks!

  51. Mads Barnkob says:

    Hi Athos

    By changing the MOSFET driver ICs around you are changing the phasing of driving the bridge and thus the secondary coil. Normally you just change the phasing of the primary coil to get it to oscillate in phase with the feedback antenna phasing.

    I am not sure what should not make the interrupter work, as it is only a matter of pulling a signal high on the MOSFET driver ICs.

    Kind regards
    Mads

  52. Saattvik Thourwal says:

    Can I still use this gdt ?? I broke the core in half……

  53. Saattvik Thourwal says:

    It is or was a flyback core. Which I broke in half accidentally and wound the trifler coil around it.

  54. Mads Barnkob says:

    Hi Saattvik

    You can use it if you have the other half, you need to complete the magnetic loop in order for enough flux to be a good and working GDT. You can “repair” it with a thin layer of super glue, but that will act as a air gap in the core and limit the performance. But it will work.

    Kind regards
    Mads

  55. MaxEletron says:

    Can I use this setting? No mur1560 and 150nf capacitor to 2u2.

  56. Mads Barnkob says:

    Hi MaxElectron

    You can use 150 nF, but you might experience that the sparks are more like full wave rectified unsmoothed, with a low enough capacitance you will see larger voltage sag.

    You need the ultra fast diodes to bypass the internal slow diode of the MOSFET, to unnecessary losses.

    Kind regards
    Mads

  57. magnus says:

    Hi again Mads! (i commented on your sstc 2)

    I have all the parts fitted together, and just 1 part left to place on the pcb.
    I noticed that there is no space for the r1 (100k resistor that comes right after the variable resistor) on the pcb, so do you place it outside the pcb?
    And why did you decide to change your 555 circuit?

    Have you tried to run it on full bridge? 🙂
    King regards
    Magnus

  58. Mads Barnkob says:

    Hi magnus

    You found an error in my PCB layout 🙂 I added the 100K resistor later to get a even slower maximum BPS of the 555 timer, you can see on one of the pictures that the 100K resistor is soldered directly onto one leg of the potentiometer in the enclosure side.

    I changed the 555 circuit to get 1-10 sparks per second, so I was sure it would not over-heat when only using the enclosure as heat sink.

    It was only my SSTC2 that was a full-bridge.

    Kind regards
    Mads

  59. magnus says:

    Hi Mads!
    I got it working!
    It worked for a couple of seconds, then the mosfets blew up.
    Maybe a bad ferrite core or some signale interferance from the coil?
    I am currently working on a new brige circute, so hopfully i will get it working again.
    You dont supposedly want to share your musical interupter pcb with me? Would save me the truble of making one 🙂
    Thanks for your help 🙂

    Kind regards
    Magnus

  60. Mads Barnkob says:

    Hi Magnus

    Great that you got first light! How did they blow up? Did they actually explode? where the MOSFET came apart, did it just have a crack?, did it spew a hot flame out through a melted hole? or was it just a silent death?

    Ii is my experience that interference will make a coil run unstable, but not explode. It is more likely that you had inadequate gate drive or that the GDT delivers a distorted signal.

    But for the MOSFETs to really explode, corss conduction is needed so that they short out the DC bus and thus the energy in the DC bus capacitor will be burned across the MOSFETs.

    I made the musical interrupter on a veroboard, so I do not have a design to share 🙂

    Kind regards
    Mads

  61. magnus says:

    Hi again 🙂
    One MOSFET came apart, and the other one looked like nothing had happend (it to was not working). More like a small bang, not that loud. The transistors and rest of componets where unharmed.

    My ferrite core is made of N30 grade material, so i dont think the ferrite core is at fault.

    My only idea is that maybe a shorted out somehow, or a unstable signal from the antenna ;(

    I think i will try to make a full bridge circute when i have time 🙂

    Kind regards
    Magnus

  62. Mads Barnkob says:

    Hi Magnus

    Even a unstable antenna signal should be corrected by the hex Schmidt trigger IC to a nice and clean square signal, the GDT protects against cross conduction, so the only thing left could be failing/too low gate drive voltage so that one MOSFET, the one that exploded, conducts a full short circuit current and the one in the linear region just burns up a lot of energy, while it has a higher RDS(on), and will get very warm, but properly not explode like the other did.

    Chances are that they are both damaged, gate resistors might also be damaged, be sure to solder them out and measure them, or just change them out to be sure.

    Kind regards
    Mads

  63. MaxEletron says:

    Which finish is correct?

  64. Mads Barnkob says:

    Hi MaxEletron

    I only use the twisted pair of same colour method.

    Kind regards
    Mads

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