Hey, just want to make an update of where I am with my BTC project. For those who don't know I proposed to my school to build them a big tesla coil that can make music. A budget was fixed and so I started building this coil.

You can find the precedent progress in this post:
https://highvoltageforum.net/index.php?topic=1654.msg12650#msg12650

First I built my H-Bridge:


It's a full bridge with 4700uF at 800V, it used two GD600HFY120C2S from starpower, the heatsink it's from semikron.

Then I assebled the base primary circuit:

I'm still missing some cable management but i wanted to make sure that a first prototype was working before continuing

Next step was having everything toghether just to make a cool photo:

There things that are still not optimized. For example I have too many turns right now on the secondary but it's easyer to take out turns then to add them so I will optimize that in the future. Also the space between toroid and coil it's not necessary and could be shortened.

Resonance check and regulation:
primary:

secondary:


In my school we have a bode100 impedence meter that i used to check for resonances, please note that the impedance is not rappresentative in the secondary circuit because of an added resistor for measures.

IGBTs gate check:

Before powering on the main inverter I checked the gate signals. here I found a problem on my GDT where I've taken the wrong pair of cable to connect to the IGBT.

First power up of the primary circuit:


This was the first test with real power where something could really go wrong. Fortunatly everything has gone as planed and I was able to tune my phase lead and check for things like temps, current waveform, current limit. In the oscilloscope you can see in yellow the bridge output at 600VDC and blue is the current (the distortion is due to my setup that wasn't optimal and the phase is wrong but the amplitude correct 1V=1A). The test was done with an OCD of 600A.

Finally was time to test the entire system:



First I tested the system with 600A limit but soon changed it to 800A limit because it was really wokring well. I still have to adjust the primary coil to check if I'm good tuned but I'm already very happy about the result! In this test I reached 1.3kA current limited using 7kW of 3 phase 400VAC out of a 15A variac.


Specs:
Primary:

• Full bridge GD600HFY120C2S 3phase 400VAC 4700uF
• 15x1mm copper flat ribbon for connections
• 4s2p of FPG86Z1254J for prim. capacitor
• UD2.7revC

Secondary

• 2200 turns wih 0.5 enmalled copper wire
• 30cm diameter PP tube (fu**ing to heavy)
• 75cm major / 20cm minor
• 40kHz resonance

Interrupter :USB midistick (it's awesome!!!)


Thank you:
Here I would like to thank you some people that made this possible:

• HEIA-FR school for the opportunity
• Steve Wards to start everything
• Mads Barnkob for the cool documentation
• Gao Guangyan for realaizind the UD2.7revC
• Thorben Zethoff for the awesome midi-stick

Video:

https://www.youtube.com/watch?v=u88nMUH2cQo

With the width of your bus bars you could probably increase the spacing quite easily by drilling one of the mounting holes off-center. That would allow you to move the bus bar on the outer terminal further out, increasing the spacing considerably.

You will also need a pre-charge resistor for the dc bus. The inrush current of charging up such a large capacitance directly from the mains is massive, and will very likely cause problems.

I also think that a 10A breaker for such a high power coil is a little small. I managed to trip the breaker on my 3 phase 16A outlet in a matter of seconds with my skm400 coil and I suspect your inverter might do the same
And a type C breaker won't help do mucht to protect the semiconductors. if anything goes wrong the bus capacitance is likely enough to kill them by it self. I'd recommend just not installing a breaker on your coil directly, since all it would protect is the cabelling and that is already protected by the breaker in the distribution box.

Thanks TMax that's actually a good idea, I'll take note and see what to do when my fat heatsink arrives. Actually the holes are already off-center but I forgot that the widht of the busbars was changed last minute bruh

For the circuit breaker it's true that it doesn't add a lot of protection. I think I will go with the 10A one for the test phase and that evaluate to skip it when everything work as it should if necessary.
 
I agree with you about the pre-charge resistor, there is no way it will work if I attach it to 400VAC directly. For now I will be using a variac to be able to run it at a lower bus voltage. When everything works I will put 3 pre-charge resistors that get shorted after some seconds by a relais and regulate power via on-time.

Thanks all for the suggestion for the aircooled primary!

I will take that into consideration, but I will wait the test phase to make some measurements about temps and see what are my necessities.

Quote from: SAMGO on July 05, 2021, 11:32:14 PM

Hey Mads, thanks for the reply. 

Quote from: Mads Barnkob on July 05, 2021, 10:28:05 PM

How are you getting 13.5kV from 3 in series of 2500V rated capacitors?

You are right  It's because 13.5kV would be the absolute maximum rating allowed 10s/day, actually the rms value as you pointed out would be 9.6kV_peak or 7.5kV_{n_dc}.
If I'm not wrong I've calculated that at 50kHz with R_s=3mΩ and 2000A I have around 8kV across the cap.
My thinking was that because the usage of such coil would be limited i could push the dielectric of these C a little bit further.

I think you are taking this to a extreme level of extrapolation.

In a real world application, we should calculate with the AC voltage, voltage de-rated according to load and frequency! In Tesla coil hobby, for ease of calculations, we assume that we can just use the DC voltage rating and use that to achieve a higher number than the expected peak voltage to develop across the MMC.

Shure ahahaha, I will re-design something with more margin... or may I say something WITH margin  I just have to check what I can find for snubbers.
I prefer spend the double for 1 bank and not double because the first is on fire 🔥...

Hey Mads, thanks for the reply. 

How are you getting 13.5kV from 3 in series of 2500V rated capacitors?

You are right  It's because 13.5kV would be the absolute maximum rating allowed 10s/day, actually the rms value as you pointed out would be 9.6kV_peak or 7.5kV_{n_dc}.
If I'm not wrong I've calculated that at 50kHz with R_s=3mΩ and 2000A I have around 8kV across the cap.
My thinking was that because the usage of such coil would be limited i could push the dielectric of these C a little bit further.

The capacitors FPG86Z1254J are nice and suitable, but you need more than 6 of them if your going for 2000Apeak

For the I_rms your are actually right, I had calculated this with 1500A_peak in mind and for that it would work, I will make a good revision of the calculations of the MMC, right now my focus is in building the inverter. To be on the safe side for the IGBTs I will probably restrain it at 1500A even if it can run more.

Bdw, I'm having a real hard time finding big snubber capacitors, I had designed a MMC with smaller Cornel Doubillier cap but it was really easier to find some good big snubbers because it was easier from a mechanical point.
For example these FPG86Z1254J are out of stock and i even contacted AVX but then don't have any stock either...

Interrupters and drivers, look at the free PCB packs ( https://highvoltageforum.net/index.php?topic=353.0 ) which has a regular interrupter and midi. Then there is also syntherrupter https://highvoltageforum.net/index.php?topic=1020.0 and MidiStick https://highvoltageforum.net/index.php?topic=1117.0

Thanks for the links! i will take a look at them, I've been contacted by Tmax for the midi stick and it seems very good !

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Just one more quick question for everyone, I still don't know if i have to implement a watercooling for the primary, I've tried to do some simulations with COMSOL but I'm not shure about the results, does someone have expirience in this field ? I know it depens on many factors but considering a normal use like: 100us-150us at 1500A peak 50kHz. Because I'm hesitant, I leaved the opportunity to easily watercool the system for now



Thanks for your time and have a wonderful day ! 🌟

Hi,

First off all, how big will the coil be, and how long do you hope the sparks will be?

My large coil is Around 2 meters tall and made 2.6-2.8 meter sparks, as I recall. ( being 10 years since last run )
I use a couple of SKM400GB124D running a full bridge running 550-600VDC on the bus capacitor using an 3 phase variac. And I have never had one of these IGBTs failing on this coil.

Cheers

Daniel

Hey you can see my new post "New BTC Project Big boy DRSSTC" is around 2m, and I think I'm aiming for your sime results. At the end I choosen to go with some GD600HFY120C2S from Star Power, I hope I didn't regreat it :,)

Where should I start ?
I received a proposal from my school to build a tesla coil so I started this project. I now decided to share my project here!
After building a small SSTC and a medium size DRSSTC this is the biggest and most powerful tesla coil I have ever built, so I am open to suggestions and improvements.

Specs:

• Power: From 3phase 400VAC variac max 15A aiming at something like 10-15kW
• Secondary: 2100turn for now but it will probably be less on 32cm diameter with 0.5mm diameter wire, epoxy coated on a PP pipe
• IGBTs: GD600HFY120C2S from Star Power 1000A continous and aiming for around 2000A ~1500A peak from my calculation they would perform good but I hesitate a little to go outside Infineon / Mitsubushi / and these big IGBT manufacturers
• Full bridge rectifier 3Phase 150A (yeah it's op but was free) with 4700uF 800VDC cap, lower capacitance because of "triple" the freq from 230VAC
• Primary: 10mm diameter 1mm wall copper pipe, I will try without watercooling but I will keep the possibility to add it
• Driver: UD 2.7 I love it <3
• Interupter: I was looking for the industrial one from eastern voltage but I open to new ideas
• MMC: 3s2p of FPG86Z1254J for 0.83uF at 13.5kV and 130Irms from datasheet (probably more huh )

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Where I'm right know ?
First I calculated and sized all components of my coil, here some of the main things.


note that the igbts are wrong and this schematics still miss the emergency discharge for the capacitors

I then proceeded to create a very specific budget to propose to my school. The budget was accepted for a total of around 4000CHF
I then started by making a CAD of the entire project:



I then proceeded by starting the construction with the base and now the secondary:




note that the toroid is probably too small, I will still try with this one but if the res. freq is to high I will ask to a bigger spooned one or I will build an alluminium rings one

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What next ? The next step is to buy all components for the big FAT inverter, and start mounting all the electronics. I will also to a emergency stop sistem that will discharge the capacitors in a matter of seconds (because 560VDC are bbbbad).

If you have question or notice something that doesn't make any sense  please respond to this post, as I said this is my first high power tesla coil and I'm sure I will miss some things BUT I would love to lern more and I'm determined to make this my greatest creation!

Thank you for your time by reading throught this post  and have a nice day!

I to everyone, I hope you are doing well!
I managed to get a contract on a giant tesla coil project with my school. I would like to use some CM600DU-24NF to be on the safe side, since they are already tested and proven components.
Would anyone know how to direct me on where to find them?
I'm looking around but the only place where I can find them is on ebay or cina.

I had also build a "smaller" DRSSTC for personal use using 2x CM300DY-24H for 41$ from cina and for now they have not yet become expensive fireworks, maybe worth the risk?

---

Any ideas on newer igbts? Many new igbts use springs and contacts systems that are good for pcb compact design but not for a project like a tesla coils.


Down here you can find some photos of my last tests which I imagine are always welcome.

Hi,
Recently I seen some video of TC blowing up in brust mode. There is something to take care of in this specified mode? Also what if I make only 1 pulse composed of 10 cicles ? Normally I would think that there is no problem at all but let me know if you have some personal experiences

Hi,
Maybe you can try to put the enable pin of both ic to gnd and with an oscilloscope or if you didn't have one with a multimeter watch that it's really 0 to max 1.7V  like is written on datasheet. Put the measuring tool direclty on the pin so that you are shure of the measure. You can also try to make the same thing with the tesla ON and OFF and search for difference between measurement.

Thank you for the suggestion on the attacheent of the cables to the busbar! I didn't ever thinked about that, bu I also can immagine that it didn't make so much of a difference. Yes, those red caps holding the ground ring are 3D printed and designed by me. Also the blue thing on the bottom of the toroid is a giant connector to easy remove the topload. i can share the 3D files if someone wants

bdw my MMC is barely warm to the touch ahahahahah it's good but I don't really understand how is it possible