Author Topic: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors  (Read 3151 times)

Offline TiagoBS

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Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« on: November 26, 2021, 07:44:25 PM »
Hello everybody. Since the beginning of the Covid-19 pandemic I have been more interested in electronics. Since then I have had success building some SGTC and decided it was time to try building an SSTC. That's where my frustration starts. The only thing I've managed to build so far is an slayer exciter with TIP31c. After that I tried several times, several different schemes and nothing worked. But I didn't come to complain about my lack of skills and knowledge, but rather to bring up a problem I'm having with an attempt to build an SSTC.
A few days ago Zach from LabCoatz channel released a video with a tutorial for a Half Bridge SSTC (2.0) and I decided to give it a try. Well, I had already tried to build the first version, but I was unsuccessful.
Follow the circuit diagram below.
I had the PCB made and bought all the components (Some with slight differences, but I believe within tolerance) and assembled everything on the board.
I used mains voltage (127vac) rectified (170vdc) as in the scheme and I only had a small fuzzy plasma on the break point. I was using a 16cm high by 7.5cm diameter AWG35 secondary with approximately 1100 turns (>400khz). On the primary, 5 turns AWG18 insulated wire with the coupling at 0.41. As the system requires a lower secondary frequency, I put a top load which left it with a frequency of 301khz (JavaTC). From there I try to turn the interrupter switch on and off but nothing different has occurred. I figured it could be the signal from the antenna, I tried to reduce its size but nothing changed. I moved the antenna away and closer with only a small difference in the plasma that formed at the break point.
So I tried to change the polarity of the primary. When I did this I immediately pop my transistors and one of the tracks that connects the live phase into one of the Full Bridge Rectifier connectors.
I fixed the track that had pop and changed the transistors to two IRFP460s to test and save my FGA60N65. I also changed the coils, using a secondary 15.5cm high by 7.5cm in diameter AWG32 with approximately 770 turns. On the primary, 7 turns AWG18 insulated wire with coupling at 0.222.
When turned on, again pop the transistors. I put in two new ones and tested it by reversing the primary polarity again, this time nothing exploded, but I had no output and the transistors became very hot in a matter of 1 or 2 seconds of operation.

I would like help understanding what might be going wrong. I don't have access to a lot of testing tools, just a multimeter. But I have all the documentation I used, the recommended parts list and the parts list I used, I have some spare parts for further testing.


Offline Mads Barnkob

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #1 on: November 27, 2021, 07:47:23 AM »
Generally SSTCs needs a very high coupling to get a efficient energy transfer. This will affect your feedback circuit as the feedback gets weaker as well and it might not even start oscillating.

What happens if you touch the antenna with a screw driver while its on? Some external disturbance can normally kick it into gear.

Did you make the PCB layout yourself, from the schematic? Did you double/tripple check for errors?

The schematic is based on Steve Wards SSTC5, so it is a very well-proven circuit, I would concentrate on the points/parts where this differs from Wards schematic.

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Offline davekni

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #2 on: November 28, 2021, 12:16:04 AM »
I'd keep your later secondary for lower frequency.  Wind a new smaller-diameter primary to get coupling high as Mads suggested.  Do double-check circuit implementation too as per Mads.

Quote
From there I try to turn the interrupter switch on and off but nothing different has occurred.
The circuit you posted doesn't show an "interrupter switch".  If you are setting UCC27425 enable continuously high with a switch, failure is likely.  This circuit is designed to run at limited duty cycle controlled by the 555 timer chip.  Test at very low duty cycle (0-2M variable resistor set to 2M) until everything is working correctly.

For further protection during initial testing, I'd run at lower voltage or current.  If no variac is available, add a power resistor (incandescent light bulb) in series with the +IN power terminal.

An additional capacitor between +IN and -IN at the ECB may help with any voltage transients there, caused by long wiring inductance back to bulk capacitors.

I've seen this circuit variation several times, but it isn't quite as good as Steve's original versions.  See these links:
https://www.instructables.com/Building-a-solid-state-tesla-coil/
or with additional startup aid:
https://www.stevehv.4hv.org/SSTC5/miniSSTCsch.JPG
The key difference is around the antenna input.  The original versions use 1N60 germanium diodes directly on HC14 input.  The new circuit's added 1k resistor is good, but the added 0.1uF capacitor and change to 1N4148 diodes causes issues.  The 1N60 diodes have enough leakage current to bias HC14 input to roughly center-supply voltage, making it more sensitive to antenna signals.  1N4148 diodes have very low leakage current, and the 0.1uF capacitor isolates any bias voltage from getting to HC14.

There's an even better fix than changing diodes:  Add two identical resistors (1Meg to 10Meg) across the two 1N4148 diodes and replace the 0.1uF capacitor with a piece of wire.

My guess is that the primary connection polarity that "explodes transistors" is the correct polarity.
David Knierim

Offline TiagoBS

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #3 on: November 29, 2021, 03:08:58 PM »
Guys, first I would like to thank you for your time and willingness to help me!

Generally SSTCs needs a very high coupling to get a efficient energy transfer. This will affect your feedback circuit as the feedback gets weaker as well and it might not even start oscillating.

What happens if you touch the antenna with a screw driver while its on? Some external disturbance can normally kick it into gear.

Did you make the PCB layout yourself, from the schematic? Did you double/tripple check for errors?


Alright, I'm going to build a new primary with the coupling coefficient within the ideal values.

When I touch the antenna with a screwdriver (in the original configuration, where there is a fuzzy plasma output) nothing happens.

About the PCB, I used the provided gerber files designed by Zach. Available in his video description.



Quote
From there I try to turn the interrupter switch on and off but nothing different has occurred.

The circuit you posted doesn't show an "interrupter switch".  If you are setting UCC27425 enable continuously high with a switch, failure is likely.  This circuit is designed to run at limited duty cycle controlled by the 555 timer chip.  Test at very low duty cycle (0-2M variable resistor set to 2M) until everything is working correctly.

About the Interrupter Switch, I attached some images, indicating where it is.
During the initial tests I turn the two potentiometers position. But now I'm going to leave the duty cycle at very low (2M).


For further protection during initial testing, I'd run at lower voltage or current.  If no variac is available, add a power resistor (incandescent light bulb) in series with the +IN power terminal.

An additional capacitor between +IN and -IN at the ECB may help with any voltage transients there, caused by long wiring inductance back to bulk capacitors.

I'm going to add the light bulb. What is the capacitor specification?

The key difference is around the antenna input.  The original versions use 1N60 germanium diodes directly on HC14 input.  The new circuit's added 1k resistor is good, but the added 0.1uF capacitor and change to 1N4148 diodes causes issues.  The 1N60 diodes have enough leakage current to bias HC14 input to roughly center-supply voltage, making it more sensitive to antenna signals.  1N4148 diodes have very low leakage current, and the 0.1uF capacitor isolates any bias voltage from getting to HC14.

There's an even better fix than changing diodes:  Add two identical resistors (1Meg to 10Meg) across the two 1N4148 diodes and replace the 0.1uF capacitor with a piece of wire.

My guess is that the primary connection polarity that "explodes transistors" is the correct polarity.

About the changes in the antenna circuit, I drew a picture of what I understood. Is it correct?

I also attached some images of the board without the components and the GDT.

Other information: When I turn on the system only with the low voltage circuit, I hear a noise like a vibration, but when I turn the potentiometers, nothing changes.

I also posted an output image. It just produces a soft hissing like an exciter slayer.

Offline davekni

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #4 on: November 30, 2021, 05:58:42 AM »
Quote
About the Interrupter Switch, I attached some images, indicating where it is.
During the initial tests I turn the two potentiometers position. But now I'm going to leave the duty cycle at very low (2M).
Thank you for the schematic.  When the switch is open, the driver is continuously enabled.  UCC27425 enable inputs have internal pull-up resisters.  Open is enabled.  If you want a switch to disable the coil, short enable to ground after the 5k series resistor.  If you leave the existing switch in place, make sure it is always closed during testing.  Yes, low duty cycle (2M) is good.  Of course, you won't get long sparks at low duty cycle.  It is still better for experimenting with primary coil polarity and antenna placement without frying transistors.  Then carefully increase power.

Quote
I'm going to add the light bulb. What is the capacitor specification?
To first order, whatever you have around that can handle 170Vdc and be mounted at the ECB.  (Not a small electrolytic, however, as that will have problems with RMS current being too high.)  I was thinking of a 1uF to 10uF film capacitor.  Or, a larger electrolytic.  The large electrolytic will support higher performance during testing with the light bulb, supplying peak current during the infrequent enable pulses.  However, that also increases risk of frying FETs/IGBTs.  So, at least initially, a film capacitor is lower risk to your FETs/IGBTs.

Quote
About the changes in the antenna circuit, I drew a picture of what I understood. Is it correct?
Yes, exactly.  The two resistors need to be the same value.  (Actually, the upper resistor to +5V could be ~20% higher value than the resistor to ground, since HC14 input thresholds are typically a bit below half supply voltage.)

Edit:  I forgot to mention an alternative to these two resistors.  You can instead add a single resistor, ~1Mohm, between 74HC14 pins 1 and 2.  This is actually better than the two separate resistors.  It will make the 74HC14 oscillate at a low frequency even without antenna feedback, which will kick-start the feedback.  You can experiment with lower resistor values to make the kick-start frequency close to coil operating frequency for even more certain startup.  BTW, likely easiest to add the resistor to ECB back-side, from 74HC14 pins 2/3 to one lead of the 1k resistor.

Quote
Other information: When I turn on the system only with the low voltage circuit, I hear a noise like a vibration, but when I turn the potentiometers, nothing changes.
Perhaps makes sense if that is with your existing enable switch open, so driver continuously enabled.  Might be line-frequency hum being picked up by the antenna.  If it still occurs with the 555 connected to enable and the 2M resistor set to 2M, then I'd be a bit concerned.

Quote
I also attached some images of the board without the components and the GDT.
Based on a quick review, layout looks reasonable.

Good luck!
« Last Edit: December 01, 2021, 04:40:41 AM by davekni »
David Knierim

Offline TiagoBS

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #5 on: December 10, 2021, 09:40:35 PM »
Hello again!
New: I redid all the solders on the board and replaced all the ICs, reduced the size of the high voltage cable and placed a light bulb in series with the positve.
Made a new set of primary and secondary coil. There are now 1377 turns of 32AWG (0.2019mm) wire on a pvc pipe 101.6mm in diameter by 270mm in height. The resonance frequency is around 285.96kHz. Primary: 5.5 turns 18mm in height of 18AWG cable resulting in 11.37658 Total LC Impedance and Coupling Coefficient of 0.25. Stretching the primary to 48mm in height, Total LC Impedance is 7.38 and Coupling Coefficient is 3.83.
Tests using the 18mm primary, I left the potentiometers at 2M and 50K, the Interrupter switch turned on and a light bulb in series with the high voltage input. With the two primary polarities the result was the same. A stronger fuzzy plasma coming out of the spike. The coil also produced a field capable of lighting fluorescent lamps. When I touched the metallic part of the 2M potentiometer it arcs to my finger. Changing the value of the potentiometers did not change the output either. The two transistors don't heat up much, however when I touch the plasma with a screwdriver they heat up faster. After that I removed the lamp and tested it using both polarities, the plasma was even stronger in one of them, in the other there was no output and the transistors warmed up very fast. It was also possible to hear a noise, like a transformer working.

--
Add:
I did new tests with better light. It is now possible to see the output. I stretched the primary to 48mm.
In one of the polarities of the primary I have this fuzzy plasma on the output, in the other polarity I have no output, but it is still possible to turn on a fluorescent lamp near the secondary coil.

Add2:
changing the distance from the antenna it seems that the output changes. I just don't know yet which side of the primary is correct, which has output or which doesn't. (On both sides the coil can light a light bulb) gif2
« Last Edit: December 10, 2021, 11:32:39 PM by TiagoBS »

Offline davekni

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #6 on: December 11, 2021, 04:42:02 AM »
Quote
After that I removed the lamp and tested it using both polarities, the plasma was even stronger in one of them, in the other there was no output and the transistors warmed up very fast. It was also possible to hear a noise, like a transformer working.
Now that you are testing in lower light, I'd say that the polarity where you see plasma is likely the correct polarity.  If your multimeter can measure frequency and measure up to 300kHz, measuring frequency would be useful.

Do you have heat sinks on the IGBTs or FETs?  That is necessary for operating at any significant total power.  Even when working properly, these power devices generate significant heat.

Quote
Primary: 5.5 turns 18mm in height of 18AWG cable resulting in 11.37658 Total LC Impedance and Coupling Coefficient of 0.25. Stretching the primary to 48mm in height, Total LC Impedance is 7.38 and Coupling Coefficient is 3.83.
I presume you intended to say 0.383 coupling.  Yes, that is better.
Not critical, but I'd also recommend completing the 6th turn and bringing the primary wires out to the half-bridge as a pair (twisted or taped together).  Lead inductance reduces effective coupling a little, so it is good to minimize lead inductance.
David Knierim

Offline TiagoBS

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #7 on: December 13, 2021, 08:35:32 PM »
Today I did new tests. Again I checked the entire circuit and everything seems to be correct. I completed the sixth turn on the primary coil and brought the wires taped together to the half bridge.

The antenna is cut to approximately 2cm in length. When I turn on the coil away from the antenna/PCB it has no output, however the transistors heat up anyway (I added the heatsinks and a cooler fan). When I increase the antenna size with another piece of wire, the coil starts to have output. Tapping the antenna with this piece of wire results in multiple types of outputs, like in the attached photo, not just a fuzzy plasma.


Quote
Other information: When I turn on the system only with the low voltage circuit, I hear a noise like a vibration, but when I turn the potentiometers, nothing changes.
Perhaps makes sense if that is with your existing enable switch open, so driver continuously enabled.  Might be line-frequency hum being picked up by the antenna.  If it still occurs with the 555 connected to enable and the 2M resistor set to 2M, then I'd be a bit concerned.

The noise continues even with the interrupter switch closed (allowing the 555 signal to reach the ucc enable pin) and the duty cycle potentiometer at 2M. Touching different parts of the pcb (heatsinks for example) with my finger makes the noise change in intensity, even when I touch the antenna with my finger or another piece of cable. However, turning the potentiometers does not change the noise.

I still haven't performed the suggested changes in the antenna circuit.

My multimeter is capable of measuring frequency, however I don't know where to measure it.

I'm in doubt about the UCC27425. The model I managed to buy is written: 51AC5AW UC27425 G4, as in the attached photo. Is this model correct?



Offline davekni

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #8 on: December 14, 2021, 06:17:23 AM »
Quote
I'm in doubt about the UCC27425. The model I managed to buy is written: 51AC5AW UC27425 G4, as in the attached photo. Is this model correct?
I can't tell by looking.  However, there have been counterfeit UCC37322/21 chips around with non-functioning enable inputs.  Based on your results, I'm suspecting you have a counterfeit UCC27425 chip with non-functioning enable inputs.  One option is to replace 74HC04 with 74HC132 (quad schmitt trigger NAND gate) and use that gate for enable.  Or find genuine UCC27425 chips.

Quote
My multimeter is capable of measuring frequency, however I don't know where to measure it.
Debugging is difficult without a scope.  One use for frequency measurement is to measure the 555 output (pin 3) to see if that frequency changes with changes in the 2M POT.  If it does, but sound does not change, that is proof that the UCC27425 chip is fake.  Or, just tie the enable inputs (UCC27425 pins 1 and 8\) to ground.  If the coil still runs, the UCC27425 chip is fake.

You can also measure UCC27425 outputs (pins 5 or 7) to see coil operating frequency.  That will work only when running continuously.  If UCC27425 is bad, it is already running continuously.  Or bypass the enable with your switch.

Quote
The antenna is cut to approximately 2cm in length. When I turn on the coil away from the antenna/PCB it has no output, however the transistors heat up anyway (I added the heatsinks and a cooler fan). When I increase the antenna size with another piece of wire, the coil starts to have output. Tapping the antenna with this piece of wire results in multiple types of outputs, like in the attached photo, not just a fuzzy plasma.
Yes, I think 2cm is too short.  May be picking up voltage from primary or part-way up secondary so oscillating at a too-high frequency.  Great to see some reasonable performance with a reasonable antenna length.

« Last Edit: December 14, 2021, 06:19:51 AM by davekni »
David Knierim

Offline TiagoBS

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #9 on: December 22, 2021, 12:46:23 AM »
It finally worked!
The problem was the ucc, which probably didn't have the enable pin. I ordered some from Mouser, and everything worked, the only problem is that I had to pay the import fees and it was very expensive.  :-\
Today I managed to do several tests, all with 170vdc. With the 6-turn primary the transistors (IRFP460s) worked well and didn't heat up. However I had several racing sparks arcing between the primary and secondary and they burned the wire insulation. So I lowered the height of the primary and my transistors arced on the pcb tracks burning with smoke and sparks.

What should I do, increase the distance between primary and secondary, lower the height, or increase the number of turns?

Doing the tests I realized that the 2M potentiometer controls the frequency and the 50K the duty cycle, is that right?

Offline davekni

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #10 on: December 22, 2021, 05:40:53 AM »
Quote
It finally worked!
That part is nice.  I noticed in your GIF that some Christmas lights flash at one point.  (Depending on the nature of these presumably-LED lights, stray fields can fry them due to excess reverse voltage.  I've experienced that with my Marx generator running in my garage frying LED Christmas lights hung outside my garage.)

Quote
With the 6-turn primary the transistors (IRFP460s) worked well and didn't heat up. However I had several racing sparks arcing between the primary and secondary and they burned the wire insulation.
I noticed what looks like a hole and nylon tie at the top of primary form.  Was the arc there?
With your relatively small-diameter top load, one possibility is that the antenna is coupling more to the center of the secondary coil rather than to top.  That might cause oscillation at a higher mode of the secondary where peak voltage is near the center.  Without a scope that will be hard to tell.  Do you have a picture showing antenna size and placement?  What antenna input circuit do you have now (parts around HC14 input)?
What material is the primary coil form?  Is it 3D printed?  Making the form slightly larger diameter and extending slightly higher above the top of primary winding should help.

Quote
So I lowered the height of the primary and my transistors arced on the pcb tracks burning with smoke and sparks.
Likely the IRFP460 FETs fried first, then overheated the adjacent trace. Did you have a heatsink on the IRFP460s?  If so, how did you handle electrical insulation so the heatsink doesn't short the two FET drains?  If no heatsink, FETs may have overheated before you noticed.
Location of burn spots on IRFP460's looks unusual.  I don't know burn patterns of that specific FET, but IRFP460s are commonly counterfeit.  If you purchased them cheap from China, I'd guess they are not genuine.  Generally work, but can handle less current than real parts.

Quote
Doing the tests I realized that the 2M potentiometer controls the frequency and the 50K the duty cycle, is that right?
2M controls the off-time (time between enable pulses) and 50K controls on-time (width of enable pulses).  Period is the sum of those two times.  Frequency is 1/period.  Duty cycle is on-time/period.
David Knierim

Offline TiagoBS

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #11 on: January 10, 2022, 03:13:08 PM »
Happy 2022 to everyone!

Well, for the past few weeks I have been working on my Tesla coil and almost finished my project. I managed to fix all the problems I had and also got some new ones.


I designed and 3D printed all the case components, and even tried to make a toroid (To be improved. A 3D printed one, totally without supports. The maximum size I can print is 22cm in diameter or 8.7 inches, so this toroid will be used for another project).

Unfortunately during my tests a spark hit the antenna and I had to change several components on the pcb, I ended up burning my last two 60n65 and went back using IRFP460 temporarily while waiting for the new igbts to arrive.

With the Chinese IRFP460s half-bridge, 170vdc and a top load made of a stainless steel bowl I got 22cm - 8.6 inches sparks.

-


So far I've only connected the pcb using 170vdc, my circuit has a voltage doubler, but I haven't used it yet as I don't know if the IRFP460s can handle 340vdc (Would they work?).

In the long-run tests the transistors barely warmed up.
The primary has height adjustment to adjust the coupling, however in the current configuration I raised the primary height to 5.5cm, the maximum I can go without needing to print a new support, and I had no problems (Maybe I can raise it a little more?).

What antenna input circuit do you have now (parts around HC14 input)?
I haven't made any modifications to the antenna circuit as it seems to be working fine now (Does the addition of the resistor between pins 2/3 of the 74HC14 and the 1k resistor mean a performance boost, improvement or something?).

Sometimes when I bring something closer to the output, the spark becomes very thin as if it lost power. After raising the primary height this behavior started to happen less often but still present sometimes when I bring things closer to the output. What is the reason for this to happen?
A proper toroid can solve this problem?

I noticed in your GIF that some Christmas lights flash at one point.  (Depending on the nature of these presumably-LED lights, stray fields can fry them due to excess reverse voltage.  I've experienced that with my Marx generator running in my garage frying LED Christmas lights hung outside my garage.)
Well, that was the last time my Christmas lights worked.


Offline ZakW

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #12 on: January 10, 2022, 07:50:13 PM »
Awesome 3D printed case and overall beautiful coil! I plan on printing a case for my coil as well, its nice to see your design.

I like the adjustable primary height. Does it normally move freely but can be held in place using zip ties?

Quote
I haven't made any modifications to the antenna circuit as it seems to be working fine now (Does the addition of the resistor between pins 2/3 of the 74HC14 and the 1k resistor mean a performance boost, improvement or something?).

It is probably best if others weigh in but I have found when testing my HC14 feedback at different frequencies (sweeping from 200kHz to 500kHz) that the resistor value from from pin 1 and 2 is important. For me I noticed anything under ~8kohms caused the 74HC not to lock onto the secondary signal and instead oscillate via the resistor. The resistor from pin 1&2 helps restart the oscitation if feedback becomes interrupted or is too weak. In my case, I was able to use anything above that 8Kohm value, I think I went with 15kohm.

Quote
Sometimes when I bring something closer to the output, the spark becomes very thin as if it lost power. After raising the primary height this behavior started to happen less often but still present sometimes when I bring things closer to the output. What is the reason for this to happen? A proper toroid can solve this problem?

I have also observed this issue when using a current transformer instead of an antenna. I am not sure what the causes it so I hope someone has more information. I assume it is feedback related i.e. detuning the coil when something comes near it, possibly preventing the antenna from receiving a proper signal. However, since the driver should always be in tune with the secondary coil you would think this wouldn't happen.

Sorry I could not help more. Great coil!


Offline davekni

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #13 on: January 11, 2022, 06:24:13 AM »
Quote
Quote from: davekni on December 22, 2021, 05:40:53 AM

    What antenna input circuit do you have now (parts around HC14 input)?

I haven't made any modifications to the antenna circuit as it seems to be working fine now (Does the addition of the resistor between pins 2/3 of the 74HC14 and the 1k resistor mean a performance boost, improvement or something?).

Sometimes when I bring something closer to the output, the spark becomes very thin as if it lost power. After raising the primary height this behavior started to happen less often but still present sometimes when I bring things closer to the output. What is the reason for this to happen?
A proper toroid can solve this problem?
This Labcoatz SSTC 2.0 circuit has problems when used with current transformer feedback.  Yes, it may function some, but it could also be your issue here.  I'd fix this before exploring anything else.  See this post for examples:
https://highvoltageforum.net/index.php?topic=1888.msg14153#msg14153
David Knierim

Offline Mads Barnkob

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #14 on: January 17, 2022, 07:45:48 PM »
Happy 2022 to everyone!

Well, for the past few weeks I have been working on my Tesla coil and almost finished my project. I managed to fix all the problems I had and also got some new ones.

Congratulations on having a good looking and working Tesla Coil! You did a great job on making all those parts from scratch. Happy new year!

Well, that was the last time my Christmas lights worked.

 ;D :D ;D :D
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Offline TiagoBS

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #15 on: January 20, 2022, 06:56:35 PM »
Hey guys!
I modified a few more things on the coil and had some issues.
I also finished the toroid!



IGBTs have finally arrived. I replaced the IRFP460s and put the FGA60N65SMDs in place.
In the first test I didn't use the voltage doubler, so it was 170vdc on the IGBTs.

The first thing I noticed was the different sound of the sparks, the second thing was the sparks between the primary and secondary (which did not happen when using the IRFP460s with the same voltage).
I lowered the height of the primary to reduce the coupling and the sparks stopped happening (However, when I brought my hand closer to the output, sometimes sparks would happen between the primary and secondary).

I did a few more tests and played with the coil for a few minutes, no problems.
So I decided to use the maximum power, 340vdc. I turned on the voltage doubler and for a few seconds everything was amazing. The coil worked wonderfully, the sparks were huge!
The duty cycle potentiometer was at approximately 60%. When I increased it to 100% the coil ran for a few seconds and something went wrong.
The on/off switch seemed to have sparks inside. The coil has stopped working. I immediately turned off the switch.
I did a quick inspection and nothing seemed to have any burn marks despite a little smoke and a smell of burning electronics (I figured this must be a problem with my on/off switch).
Again I turned the switch on for a second or two and I could see a light like an arc forming inside the plastic of the switch cover.

The third time I flipped the switch to try to identify the cause, my house breaker tripped and my extension cord melted completely!


I would like to understand a few things:
Why after putting the IGBTs I had problems with racing sparks even when using the same voltage as when using the IRFP460s?

Inspecting the coil, it appears that the problem is in the rectifier bridge, as the smell of burnt electronics is coming from it. If the problem is really there, could this have damaged my IGBTs or some other component on the board?

And what could have caused this problem?

The bridge model is:
KBPC-3510
Reverse Voltage: 1000V
Direct current: 35A

Congratulations on having a good looking and working Tesla Coil! You did a great job on making all those parts from scratch. Happy new year!
Thank you so much!

This Labcoatz SSTC 2.0 circuit has problems when used with current transformer feedback.  Yes, it may function some, but it could also be your issue here.  I'd fix this before exploring anything else.  See this post for examples:
https://highvoltageforum.net/index.php?topic=1888.msg14153#msg14153
After switching to IGBTs, during tests with 170vdc I didn't notice the sparks getting weak when approaching things to the output, however I couldn't do many other tests because I had other problems.

Awesome 3D printed case and overall beautiful coil! I plan on printing a case for my coil as well, its nice to see your design.
I like the adjustable primary height. Does it normally move freely but can be held in place using zip ties?
The zip tie is just for leveling the primary. But I already have plans to print a new primary model with tabs so I don't have any more leveling problems.

« Last Edit: January 20, 2022, 07:01:49 PM by TiagoBS »

Offline davekni

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #16 on: January 22, 2022, 04:27:38 AM »
Quote
And what could have caused this problem?
Are you using an antenna for feedback, or a current transformer on secondary current?
David Knierim

Offline TiagoBS

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #17 on: January 25, 2022, 01:48:02 PM »
Quote
And what could have caused this problem?
Are you using an antenna for feedback, or a current transformer on secondary current?

I'm using the antenna feedback.

Offline davekni

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #18 on: January 26, 2022, 05:17:03 AM »
Quote
I'm using the antenna feedback.
Thank you for the clarification.  Reviewing this thread, looks like you were using antenna feedback always.  (I was likely mixing this up with another thread where antenna and CT were both tried.)

Quote
The duty cycle potentiometer was at approximately 60%. When I increased it to 100% the coil ran for a few seconds and something went wrong.
At 100% duty cycle, the coil is likely drawing more wall-plug current than your outlet is rated for.  That may be the cause of both switch failure and later rectifier bridge failure.  (Possible that the IGBTs fried just before the rectifier bridge, drawing even more line current.)

Quote
The first thing I noticed was the different sound of the sparks, the second thing was the sparks between the primary and secondary (which did not happen when using the IRFP460s with the same voltage).

Why after putting the IGBTs I had problems with racing sparks even when using the same voltage as when using the IRFP460s?
Difficult to tell just what is happening without a scope.  IGBTs have more delay than FETs, so will add a bit of phase lag.  That could be significant enough to change performance.

Quote
I lowered the height of the primary to reduce the coupling and the sparks stopped happening (However, when I brought my hand closer to the output, sometimes sparks would happen between the primary and secondary).
Reduced coupling with an SSTC tends to increase primary current at half-bridge switching times.  It is possible that current increase caused later IGBT frying which then fried rectifier bridge.  You'll know more once IGBTs are tested with a new diode bridge.  It is necessary to avoid primary-to-secondary sparks.  Might be better to primary to 5 turns spaced farther apart to get coupling back up while keeping primary inductance roughly constant.

Quote
Inspecting the coil, it appears that the problem is in the rectifier bridge, as the smell of burnt electronics is coming from it. If the problem is really there, could this have damaged my IGBTs or some other component on the board?
Rectifier frying isn't likely to have fried anything else.  However, the reverse is quite possible.  IGBTs may have fried slightly earlier, which then fried the rectifier bridge.

Quote
And what could have caused this problem?

The bridge model is:
KBPC-3510
Reverse Voltage: 1000V
Direct current: 35A
I have no information specific to KBPC-3510.  However, I have purchased similar-sized rectifier bridges on EBay that burn out way below their rated current.

Overall a nice project.  Impressive what you have achieved without a scope to aid in debugging!  Good luck with fixing it.
« Last Edit: January 26, 2022, 05:19:22 AM by davekni »
David Knierim

Offline TiagoBS

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Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #19 on: January 26, 2022, 07:26:22 PM »

At 100% duty cycle, the coil is likely drawing more wall-plug current than your outlet is rated for.  That may be the cause of both switch failure and later rectifier bridge failure.  (Possible that the IGBTs fried just before the rectifier bridge, drawing even more line current.)

The breaker for the room I was in is rated for 40A.
I believe my extension melted due to the short circuit caused by the power switch failure and that made the breaker tripped. The switch I was using is rated for 15A.

I'm going to replace the rectifier bridge with a 50A one that I have available and also change the power switch for a 20A one. I hope it's enough.


Reduced coupling with an SSTC tends to increase primary current at half-bridge switching times.  It is possible that current increase caused later IGBT frying which then fried rectifier bridge.  You'll know more once IGBTs are tested with a new diode bridge.  It is necessary to avoid primary-to-secondary sparks.  Might be better to primary to 5 turns spaced farther apart to get coupling back up while keeping primary inductance roughly constant.

So could the fact that I lowered the primary height to avoid racing sparks caused the problem?

Is there any difference between 5 tight turns and 5 spaced turns in a scenario where the final height of the two is the same?
I simulated these scenarios in JavaTC and there was little variation from the coupling coefficient.

If that's the case, wouldn't just raising the height of my primary with 5 tight turns be enough to raise the coupling?

Overall a nice project.  Impressive what you have achieved without a scope to aid in debugging!  Good luck with fixing it.

Thanks! I definitely did it with your help!

High Voltage Forum

Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
« Reply #19 on: January 26, 2022, 07:26:22 PM »

 


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