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Messages - Laci

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1
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: January 07, 2019, 08:53:32 PM »
I made a new ugly looking,but low inductance bridge using only thick copper plate.Coincidentally the primary current with 10 ohm burden is noisy again,the bridge output now became noisy sawtooth... :-X
I should leave the thing as it was and move on to a more professional thing with newer driver and brick inverter.No way it gonna repair itself by a snap,just started to make me angry.




2
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: January 07, 2019, 12:43:26 PM »
About the IGBT bricks you found, you will have to do some guesswork/extrapolation of the available data, you do know these IGBT calculations? http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/
I found no informations in the datasheet about the switching losses,so I mainly compared the switching speeds with CMx00 modules and calculated a Fmax1 of 307kHz.The oneTesla bridge design accentuates the turn-off delay time,which is better than the CM200DU-24F's used by loneoceans at 120kHz in his DRSSTC 2.


Twisted wires will only have a low inductance if it is the two opposite currents flowing in each their wire, the same potential in two twisted wires does not have any effect on inductance. I got some information on busbar, primary circuit and low inductance design collected here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/busbar-and-primary-circuit/
At first I wanted to use twisted cables for bus connections to lower the DC resistance,eventually used up the remaining twisted cable for the other connections.

I assume that the "saw tooth" output is due to too much ESL/ESR in the DC link/bus capacitors - I have seen similar (though not as bad) on my larger coil at high currents.
I desoldered the two 1uF 400VCD polypropylene "snubber" capacitors and made a ESR test on them,on the MMC and on the DC link capacitors accordingly to this video: https://www.youtube.com/watch?v=115erzCCxgE
Interestingly the "snubber" caps and the MMC shows a triangle/sawtooth waveform at 150kHz,but without the "snubbers" and changing the MMC to variations of other capacitors rated for high enough voltage the waveforms are the same,just the frequency changes.
The large DC link capacitors are fine,I don't think they have too high ESL/ESR,they were designed for this kind of purpose.

I feel bad for sweating with such an uncommon bug for weeks.Of course it would be easier to buy a kit and press a button to turn it on.:)

3
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: January 06, 2019, 09:23:19 PM »
@flyglas
Thanks for the advice.I connected both of my large capacitors with short wires to the two half bridges.Unfortunately they made no difference,maybe the twisted wire has low enough resistance.





@Uspring
I think you are right.Across a large 470 ohm burden resistor the primary current waveform is perfect.The noise is probably constant at every voltage and it's a lot more significant in case of a low amplitude signal.The reason I care so much about the noise is the previous test with secondray,when the OCD kept kicking in.With the 470 ohm burden I measured 95V peak-peak so about 200A in the primary.With the OCD CT connected to the driver(which has a 12 ohm burden)the OCD trips at 1.08V,which shows just 90A in the primary!The ZCS is not perfect,but acceptable.



The two voltages at the LM311's inputs when it starts tripping(yellow:the disgusting primary current-rectified,loaded with the burden resistor-,blue:OCD setting potentiometer):




Primary current with 470 ohm burden resistor:




ZCS(470 ohm burden resistor):



4
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: January 06, 2019, 11:55:09 AM »
The top section is the primary coil support,which is made out of a wooden frame screwed together and a sheet on the top to secure the secondary coil tight.The bottom section is for the driver circuit with a switch for half/full wave rectification and another for bypassing the DC bus capacitor charging resistor.I use crocodile clips with twisted wires for lower resistance as primary-inverter connection.








The mechanical side is good,but the electrical part still has problems to solve.I'll try phase lead,since the horrible waveforms are not going to stop.
As I said,I'm still looking daily for IGBT bricks and found some,however they don't have informations about switching losses.Can they be calculated or estimated?

Some more pictures about the testing progress:





I wound a CT with thicker and not twisted wire,no better waveforms:




5
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: January 05, 2019, 09:51:10 AM »
I went down to 15 ohm resistor across the inverter,which started heating and also showed a little change in the waveform.The spikes got smaller,the amplitudes too.The switching looks great,at zero current with,and without the MMC discharge resistor.I will take the bridge apart soon.Here are some waveforms:

Primary current + inverter output WITHOUT MMC discharge resistor:





Primary current + inverter output WITH MMC discharge resistor:





Primary current WITHOUT MMC discharge resistor:




By the way what do you think about the TOSHIBA MG150J2YS40 module?I didn't make the calculations yet,but the switching speeds looks promising.Datasheet: https://www.tvsat.com.pl/pdf/m/mg150j2y_tos.pdf

6
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: January 03, 2019, 08:38:15 PM »
I have a lot more issues with the primary current noise.During just a static load test the primary current is really noisy,like I posted the scope shots before,with just a 10 ohm burden across the CT's output and not connected to the driver.I thought my wirewound burden resistor causes a phase shifting by it's inductance,but the signal is the same with a metal oxide resistor.The driver seems to switch at zero voltage,but there's a long delay,which probably makes the IGBTs to switch hard.

The large primary current spikes,which forms when the inverter switches are way over the limitations,for example at this picture they are over 10V on the scope,so over 1000A in the primary!



I was also thinking about the twisted(paralleled) wires from the inverter output to the primary,which might create a delayed magnetic field(noise),however the problem is the same with simple wires.
The MMC is weak,just two PHE450RD6220J capacitors in series,I hope they aren't causing the problem...I found around 10 WIMA FKP-1 capacitors in a local store,I will buy them next time.

Sadly I found no similar problems to mine,everybody has almost clear primary current on the web.Taking the whole thing apart and testing everything would be great,but then the coil is ruined again.Pretty frustrating!

Its hard to tell if the current is actually ringing up, as you only show the first part of the ring-up/-down.
The primary current is ringing up,then down nicely,interestingly,the inverter output voltage too!

7
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: December 30, 2018, 12:35:21 PM »
Adjusting the OCD does not mean that you have more current flowing, the idea of the OCD is that it should not trip unless you have a hard ground strike, all energy should be transferred to the secondary circuit and result in sparks. If you have little sparks and continuously have OCD trip, its out of tune, the current just circulates the primary circuit and too little of it is transferred.
That's exactly what I wanted to know,thanks for it!

I only changed the primary coil to a flat one for lower coupling.The scope is hooked up to the OCD CT's outputs,which are connected to the driver via the rectifiers and then the burden resistor.Sadly I have no more CTs right now.The primary coil's wire is also insulated,so no tap points. :/ A tunable primary would be nice not for this coil,but for the bigger,with some bricks.

8
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: December 26, 2018, 08:51:36 PM »
Turned out JavaTC was almost accurate(12kHz primary difference).Measured one IGBT gate and the frequency was 147kHz,which explains why the coil runs better with the second topload on.The primary current waveform is still ugly as well as the inverter output(which I can only measure at low voltages with my 1:10 probes).I thought the sparks lenght increases continously with the current,but as I said,cranking the OCD to almost 300A still leaves puny output.Is this normal behaviour?

Primary current + Inverter output:


Primary current + Gate waveform:




9
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: December 25, 2018, 12:52:25 PM »
I turned the OCD up to 300A,still no decent sparks.I think either JavaTC fooled me,or I tuned badly.I was thinking about the capabilities of a not paralleled TO-247 full bridge at the beginning with this medium sized coil.
Can I measure the primary current with my oscilloscope on the OCD CTs?Will the probe put unwanted noise into the driver?

The UD3 spits out the peak current, which is very handy.
I'm going to build the UD3,but without a powerful inverter a QCW coil is the best I can make for now.

10
General chatting / Re: Merry Christmas and Happy New Year to everyone!
« on: December 24, 2018, 05:06:55 PM »
Merry Christmas,and I wish you all a Happy and Successful New Year too! :)

11
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: December 22, 2018, 08:29:46 PM »
Use the proposed 0.13-0.15 coupling from JavaTC, any experiments with higher coupling than that will have to take extraordinary care of insulation between the coils to prevent flashovers.

Mads,you were right about the too high coupling,racing sparks appeared while I tested on rectified mains.Due to this I made a flat primary which now has 0.17 coupling at 159kHz(secondary at ~166kHz).It works,but I'm afraid of turning the OCD over 2.3V(1:1000 CT, 10ohm burden resistor, so 230A of peak primary current).Should I go higher with my HGTG30N60A4Ds or maybe a static load test would be helpful?Can I measure the primary current with my oscilloscope from the OCD CTs while operating?

12
I built the interrupter myself :D It uses a microSD SPI module,but the LCD screen glitches when I accidently touch it's metal screws while the coil is working.I hope the microSD module hasn't died, although the screen displays "No card found" everytime.The interrupter is already a big mess,so it'll be hard to desolder it I guess...

13
Thanks for the advices!
Sadly the store went on vacation and I can't order the parts until 20 January :( .I will try to run dual resonant with my current HGTG30N60A4D full bridge,but just carefully not to destroy them(under 250Ap)after I repair my oneTesla interrupter's SD card function,which isn't working.Another interesting experiment would be a IRFP460 bridge ramped,maybe buck modulated with high primary impedance to keep peak currents low.I will try that out with my small coils!

14
Hi,Guys!
I found some pretty nice IGBTs,but I'm not sure which ones are the best in a full bridge alone and paralelled for a high frequency coil(maybe QCW,250kHz-400kHz).

*FGH60N60
   180A peak,198W maximum power dissipation,0.33°C/W
   https://www.mouser.com/ds/2/149/FGH60N60UFD-889110.pdf


*FGA60N65
   180A peak,600W maximum power dissipation,0.25°C/W
   https://datasheet.octopart.com/FGA60N65SMD-Fairchild-Semiconductor-datasheet-68791176.pdf

*IRG4PC60U
   300A peak,520W maximum power dissipation,0.24°C/W
   http://www.irf.com/product-info/datasheets/data/irg4pc60u.pdf


The last one seems to be the best,but I never saw other coilers using it.Does anybody have experience with them,or knows other better IGBT?Any help would be greatly appreciated!

15
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« on: December 08, 2018, 12:52:41 PM »
I think 0.1uF of ceramic capacitor is not enough for UCC decoupling,since the electrolytics are bad for high frequency filtering.I always used at least 1uF polypropylene capacitors,but ceramic capacitors are also good.

16
Thanks for both useful answers!I was hoping that an Arduino can do the job,since I have 0 experience with PSoC boards.I'll get a CY8CKIT-059 development board anyways from tme.eu as soon as possible! :)

17
After Analyzing the newest DRSSTC drivers,I realized that they have quite a few interesting features.As I've seen,all of the UD3 drivers uses PSoC chips(or boards),but what about the good old Atmega328 microcontrollers?Can they compete with those PSoCs?What are the weaknesses of the Atmegas in comparison to the PSoCs?Are their operation influenced by Tesla coils magnetic field?

Here is my basic hardware idea of a UD1.3 logic with an Arduino Nano:


18
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: November 20, 2018, 09:31:12 PM »
Thank you for the help!I couldn't calculate the RMS current as I wanted,however that's pretty useless since while it runs as SSTC,the duty cycle isn't constant.The only reason was to know if a simple 2A fuse can handle this load,because any higher current fuse will break slower,than the mains automatic fuse if something shorts and that would be a big shame on a presentation.So I just cross my fingers and beleive in the power of silicon! :D

I will countinue testing in dual resonant mode,but I don't want to ruin the current driver,since I have to bring it to many places these days.If this "season" ends well,I will definitely look around for some bricks/minibricks and newer drivers,like the UD2.X or UD3.I'm already digging into freewheeling and complicated stuff like that. :) Until then I'm going to return to the old coil(which also had a better 1:4 diameter to height ratio for dual resonant mode)with a IRG4PC50W full bridge.

19
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« on: November 20, 2018, 07:14:56 PM »
Hi,sjsimmo!
Did you try swapping the feedback polarities or the IC's blew up before you could?I also see a few things to complain about,like the OCD full bridge rectifier,which seems to be mains rated frequency for me(am I right?)and the capacitors around the UCC driver IC's.Another possible problem can be the way you added the R6 resistor to the feedback,because the interrupter and the Q1 OCD MOSFET might influence the signal.Also just one pair of those MOSFET drivers is probably not enough to properly drive a full bridge,maybe try paralleling them only if you find a solution to the problem.I definitely recommend the MOSFET output stage driving system of the UD's! :)

20
Dual Resonant Solid State Tesla coils / Re: (DR)SSTC II
« on: November 19, 2018, 09:24:54 PM »
What about the static load test?Since the first snow arrived today,I'd like to make tests inside,without the counterpoise. :)
Is there any RMS current formula for a DRSSTC,just to make sure that it will not blow any fuses?!

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