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Topics - Laci

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1
Dual Resonant Solid State Tesla coils / DRSSTC Driver Logic
« on: March 10, 2019, 04:40:30 PM »
I start this topic to understand the logic part of the universal DRSSTC drivers.The idea is to build the well known UD1.3 then upgrade it with digital phase lead control and freeweeling current limiter.In addition I'd like to make a bluetooth or ethernet interrupter.

The core of my design is a CY8CKIT-059 prototyping kit.

So far my driver looks similar to the UD1.3,expect one little bug:overcurrent has on direct effect on the output.Basically whatever I do at the CLR pin(13)it doesn't change the output.Only interrupter input at CLK pin(11) changes it,while I thought a logic high at CLR(overcurrent)should immediately turn off the drive at least for the set time constant(100us in my case and in case of the UD2.7).Is my theory right and my schematic wrong?
I think my code has no problems as it's really simple,just starting the DACs,comparators and the interrupt for the time constant.

My driver:



The internal of FliPC,which I made as a 74HC74 equivalent:



...and the UD1.3:

2
Dual Resonant Solid State Tesla coils / My first DRSSTC on bricks
« on: February 18, 2019, 05:17:53 PM »
I started the building of my first DRSSTC using two used SKM400GB126DH2 modules.Had some problems because not getting what I ordered,but eventually I got generously what I ordered.

The busbar is made out of two 135x22x2mm aluminium rails,with the large DC bus capacitor in the middle for good current sharing.Two 1uF 1250V snubber capacitors are coming,an aluminium heatsink soon and the gate drive components on perfboard/PCB left to do.I'm also trying to modify an ATX PSU for higher voltage and current for proper gate drive supply.

The MMC is rated 0.094uF,4000VDC using 2 in series,4 in parallel WIMA FKP-1 capacitors mounted on a painted piece of tough cardboard(hopefully good enough insulation).Soldering to aluminium was impossible,so soldered the capacitors together using a large solder joint,with a copper wire in the middle.This is probably the weakspot,we'll see how it turns out to be while operating.

Some pictures about the inverter and MMC:




I have a question regarding the inverter and another about the UD3. I see everybody hooking up the CTs between the inverter and the MMC.My MMC fits perfectly on the inverter and that would be satisfying and also really low inductance.Is it possible to connect the CTs to the other side,between the inverter and the primary?
About the UD3:does it uses internal comparators in the Cypress chip instead of external ones,like the TL3116?In this case the expensive comparators are omitted,but is the chip fast enough?(in my case about 150kHz)

3
Dual Resonant Solid State Tesla coils / Choosing IGBT module
« on: January 29, 2019, 09:55:57 PM »
I've benn watching IGBT modules for a while now and found two,but not sure which one is better for my ~150kHz coil.

First,the MG150J2YS40 TOSHIBA module,which is the faster one,with Fmax1=307kHz in the worst case.I planned a full bridge with EU mains rectified to run around at 500A.The datasheet doesn't mention the switching losses so I can't calculate else.



The second is the SKM400GB126DH2 Semikron module (what is the meaning of the H2 suffix?) which is larger than the previous.I calculated Fmax1=350kHz.Sadly,the turn on- and off energy is large ,Eon=29mJ and Eoff=48mJ ,so  Fmax2=20kHz at Tj=80 and Tc=50.This frequency limitation is a bit scary,as I'd like run it at 150kHz.Is it still possible?If the Semikron modules can run at my frequency,a half bridge of it or a full bridge of TOSHIBA modules is more efficient?



Netzpfuscher used similar modules in his Next Gen DRSSTC with lower current rating,but at lower frequency.I bet a medium size coil like mine could produce huge sparks with a compatible Semikron driver and freewheeling,like Philip's DRSSTC V.

The prices are close,two TOSHIBA modules 80 euro,two Semikron modules 105 euro.

Datasheet for the MG150J2YS50,which is newer than what I mentioned,but the same speed:
https://datasheet.octopart.com/MG150J2YS40-Toshiba-datasheet-10733651.pdf

Datasheet for the SKM400GB126D(without H2 suffix):
https://www.semikron.com/dl/service-support/downloads/download/semikron-datasheet-skm400gb126d-22890635.pdf


4
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!

5
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:


6
Dual Resonant Solid State Tesla coils / (DR)SSTC II
« on: November 17, 2018, 01:05:45 PM »
EDIT: Background material from original SSTC thread: https://highvoltageforum.net/index.php?topic=455.0

I did some basic double resonant tests at 50V.So far everythings seems to work.The OCD is doing it's job,I don't know if it activates at the right currents-should check it with the scope.It has a small problem though,since at the lowest potentiometer range,when the blue 7-segment display shows 0.00,it stops activating.



JavaTC shows an accurate result:the secondary has a bit too high resonance frequency,which should decrease at spark loading,but at 50V it performs better with two toroids,like here:
(An older picture)



The static load test was made,the water in a can heats up.I calculated a maximum of 6 half cycles to charge the MMC to about 1920V,where the peak current is around 200A.The MMC is weak yet,just two PHE450RD6220J capacitors in series.
And here are some noisy primary current waveforms through the OCD CT:







...and inverter output:







Is it rectified mains ready? :)



7
Solid state Tesla coils / SSTC II
« on: August 16, 2018, 09:52:20 PM »
After spending a few days with the testing of the driver and assembling the new coil,today I finally hooked it up to rectified mains.The results are amazing!I had no time to make a proper video,but here is a shot from a pretty breakout at a LOW on time.





These are the differences from the previous coil project:
-Smaller secondary coil(40 cm)
-Fullbridge of IRG4PC60U
-The enclosure of the driver(UD 1.3 with antenna feedback)and the inverter's heatsink is grounded
-Feedback from the secondary is received by a real antenna
-Primary coil by 6 and 1/4 turns of thick wire(0.8 cm diameter)for high coupling

The first question is how to calculate the maximum primary current?My IGBTs are rated for 300A peak and I want to keep the current under 200A for safety.

8
Solid state Tesla coils / Slow rise & fall time
« on: August 08, 2018, 10:08:48 PM »
Hello everybody!
Recently I got myself some IRG4PC60U IGBTs and made a fullbridge of them,which will hopefully power my new coil.The problem is the same as always before when using IGBTs:slow rise and fall time.I'm not sure if the waveforms are good or not,but a short try on the actual coil at 20V input was not that good.

Here is a picture of the GDT type TX42/26/13-3E25 with 11 turns on it:


...and the driver board:




I have a 1000uF electrolytic in combination with 1uF WIMA MKS-4 in parallel with a 10uF tantalum capacitor at the both driving MOSFET pairs.The GDT is connected experimentally with resistors and capacitors.

Here are the waveforms:




Is there any way to make the rise and fall times faster to be able to run the driver up to 170kHz?

9
Electronic circuits / Attempt to repair a welder
« on: May 06, 2018, 02:51:07 PM »
A couple of months ago I got a welder from a friend of mine to repair.



It is the awelco arc250 type switch mode welder.
My friend said that he used bad electrodes,so at a moment it exploded with a cracking sound and smoke was coming out of it.



After opening the case,the first problem was obvious:the output filtering inductor blown up.



The welder is made out of two identical power supplies in parallel.



When I turned it on for the first time,the room breaker immediately popped and I've seen some sparks at the driver circuit.





After taking it completely apart,some new problems show up.The inverter section was completely melted:the switching IGBTs,their gate resistors,the filtering ceramic capacitors and even two of the output rectifiers.






(The bottom side of the driver circuit,over the dead IGBTs.)

Thankfully this was one power supply so I could test things accordingly to the working one and turned out that the driver circuit also had problems.The working driver circuit was producing a square wave at the connectors to the IGBTs,but the other one not and the voltages were lower at the damaged board.Also the power resistor of the bootstrapping IC was getting hot so the first thing I did was to remove the L6386 bootstrap IC.



The next thing I want to do is to order a new IC and test the driver circuit.Hopefully the output stage of the BJTs at the bootstrap IC is not dead.Then I should repair the inverter.I already removed the burned gate resistors and got into the first trouble.The inverter board has a thick aluminium plate on the bottom,which is connected to a large heatsink.This makes almost impossible to solder anything on the board,because even the plate conducts the heat away.The legs of the IGBTs came out by heating and pulling them strongly,but their tab(collector)is soldered under them so I can't heat them up enough to be able to remove them.What should I do?By the way here are some pictures of the other inverter,which was already repaired in a service and there were replaced some of the output rectifiers which are the same package as the IGBTs,so it's definitely possible to replace them!






10
Solid state Tesla coils / How to ground a Tesla coil?
« on: March 10, 2018, 08:59:15 PM »
Many times when my coil was arcing to the base of it(which was connected to ground)transistors died.Up until today the base was connected to mains ground,which was connected to the neutral to the full bridge rectifier to the transistors,so any ungrounded high voltage could easily go to the transistors,causing them to break,probably short internally.I was working today to solve this problem with no results.I connected the base of the coil to a long wire and its other end through the window to a 4m long steel rail,which is completely fixed vertically in the soil to keep it stable at around 7m distance from the river.The weird thing was that the multimeter showed 0.000ohm resistance(no resistance) from the new grounding to the house grounding,which is at around 6m away from the new grounding.The first transistor died with this setup so it is obviously wrong,probably the same thing as connecting the base of the coil to the mains ground.I tried other things,like disconnecting the house grounding or running the coil from another wall socket with different grounding but the base(with the new grounding) is always shorted to every ground.How can I ground my coil to be able to arc to grounded objects for longer arcs and not killing the transistors?

11
Solid state Tesla coils / Best primary coil for SSTC/DRSSTC?
« on: March 03, 2018, 10:30:34 PM »
After experimenting a bit with my coil,I wanted to to change the primary,because right at the beginning Mads said that it has too low primary to secondary coupling for SSTC.So now I bought 3 meters of 0.5cm litz copper wire and made 6 tight turns on a plastic cylinder at the bottom of the secondary.The distance between the secondary and primary is 1.5cm.
I tested this setup on a full bridge of mosfets at around 150v,interrupted.It was interesting to see,that the arcs are not longer with this primary than with the "too low coupling" coil.Before this 6 turn primary I also tried more turns of around 0.2cm wire.
I tried different capacitors with the primary.With the 6 turn primary the best output is with 2x220nf caps in series,but not as good as the low coupling coil tapped at around 5 turns,and 3x220nF caps in series,which produced up to 35cm arcs at 150v with high on times!

In conclusion the new primary coil is worse as SSTC and also as DRSSTC setup,while it should be really better at least as SSTC due to lower inductive reactance.What do you recommend to improve on this primary?Should I go back to the lower coupling primary?

12
Today I received the latching connectors(HFBR-4513Z and HFBR-4503Z)for the optical transmittter & receiver.The first problem a have noticed was the mounting of the cable(MIKROE-1473) to the connectors.The datasheet says to use a special crimping tool to press the metal crimp to the optical cable.I used a small flat,thin piece of metal instead of the crimp,but it keeps the cable tight enough.
I left about 5mm of the optical cable at the end of the plug,the datasheet says to use a polishing kit to remove that ending,I just cut it off  not completely,and that short ending probably broke into the transmitter and into the receiver,since I no longer see that short ending.

When I hook up the receiver accordingly to the datasheet's test circuit(1.pin-->4.pin-->scope,2.pin-->GND,3.pin-->+5V)around 300mA starts to flow without any load,or input signal.Is this normal,or I have a broken receiver?

13
I would like to try out this interrupter :) Can you please tell me some informations about your interrupter?Can it play songs from SD card or has it got MIDI input?Do you have a schematic about it?

14
Dual Resonant Solid State Tesla coils / Highway to DRSSTC
« on: November 26, 2017, 01:09:10 PM »
After a short pause I'm back again :)
The concept is simple:make a working DRSSTC.

I've analyzed some DRSSTC circuits.The first question is about the CT feedback.Is this simplified schematic capable of doing a CW mode operation?Or it cannot start the oscillations without an interrupter?Then a simple 555 oscillator connected the the UCC's 3'rd pin will work?

15
Solid state Tesla coils / SSTC (Not) Working Correctly
« on: September 03, 2017, 08:25:15 PM »
Hello Everybody!
I recently upgraded my half bridge SSTC to a full bridge,from an IR2153 to 2xIR2109.The half bridge worked very well almost 10cm long arcs to not grounded objects at rectified mains.
With the full bridge i get pretty weird results;it lights up a CCFL lamp bright,at every frequency-around 100kHz-400kHz(andjusted by the pot at the 555),but very tiny arcs.The current drawn is also the half of the half bridge current drawn(1A-half bridge,+-0,4A-full bridge).
I tried to change the number of primary turns,changing polarity,adjusting frequency,everything I could,but the results are at least half or less as good as the half bridge.
I checked every frequency at the gates of the mosfets,with a frequency counter and they are the same.Sadly,I do not have an oscilloscope so I think that it is pretty hard to find out what is making the problem.
As I said,the driver circuit changed,so I'm sure that the problem is with that,but do not know what...The mosfets are also heating up simultaneusly,so they should work correctly...
If you have an idea,how can I improve this design to work correctly,please reply :)
Thank you very much!

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