Author Topic: Phoenix's Large DRSSTC II  (Read 1723 times)

Offline Phoenix

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Phoenix's Large DRSSTC II
« on: April 08, 2019, 01:12:14 PM »
Hello everyone  :)

About one year ago, I have finished my 160mm DRSSTC. Now, i am planning a 315mm DRSSTC. I have already ordered 6 large GTO Snubbers with 6µF and 3200V DC. I will put them in series to get 19200V DC @1µF. The capacitors can handle up to 2200A peak and 100 A RMS. Here is the ebay link: https://www.ebay.at/itm/Electronicon-6uF-660Vac-3200V-DC-1050V-AC-Cylindrical-Film-Capacitor/362555302076?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I got them for 35€ each, which is not too bad.

Here are my JAVA TC calculations: 


Secondary Diameter: 315mm
Wire diameter: 0.8mm
1800 Turns
158cm winding length

Primary inner diameter: 385mm
outer diameter: 865mm
15mm Copper tube
15mm turn spacing
8 turns in total
tapped at around 4.8 Turns including spark loading

Topload:
40cm Aluflextube
150cm diameter

I am planning on using a fullbridge made out of cm600du-24nf Igbts. The coil is going to run on a DIY 3 Phase variac that can deliver up to 30kW for one minute. This will give me up to 660V DC Bus voltage. What do you think about this specs?

Here is another question: Is there a big difference in terms of performance between DC Link and electrolytic capacitors? I know that you need less dc bus energy if you use dc link capacitors. How much less energy do i need?

Greetings
Phoenix 
« Last Edit: April 08, 2019, 04:06:11 PM by Phoenix »

Offline Mads Barnkob

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Re: Phoenix's Large DRSSTC II
« Reply #1 on: April 23, 2019, 09:39:04 PM »
Get ready for the ride of your life, a big coil is just a whole other game, the sound, the weight, the noise, the sparks, everything is just mindblowing.

All your specs looks fine, well specified and thoughtfully planned.

I ran my large DRSSTC on a 3 phase stack of mere 10A variacs and pulling 15kW through those did not make them heat up one bit, tough little transformers :)

I am not sure about the capacitance ratio when comparing electrolytics and dc link capacitors, but maybe you can get an idea from looking at the dV/dt times and ESR to see how much faster it can deliver some peak current.

Looking forward to see this monster :)
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline Phoenix

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Re: Phoenix's Large DRSSTC II
« Reply #2 on: April 25, 2019, 11:14:32 AM »
Hello Mads

Thank you for your advice  :)

I have found a good ebay offer on new 10000µF 350V electrolytic capacitors, so I bought 6 of them to get 700V @ 15000µF for the inverter. This gives me around 3600 Joules, which is more than enough.

I also found a good offer for large IGBT Bricks, so I bought 4× FZ800R12KF4 from Eupec/Infineon. These Bricks are not based on the newest technologies, but i believe they are still suitable. According to my calculations, they should easily handle up to 3000A. I really like that these Bricks only have 55nF gate capacitance, which is really low for a 800A IGBT. This low capacitance enables me to use a GDT instead of a direct drive IC. Here you can download the data sheet: https://www.mouser.at/datasheet/2/196/fz800r12kf4-93487.pdf

Here you can see the electrolytic capacitors and the GTO Snubber Caps:


Here you can see the MMC. I will try to get more of these caps to increase my RMS and Peak current capability. Right now, i am limited to 2200A, because of the maximum peak current of the capacitors.


I have got another question about the RMS current capability of these large GTO snubber capacitors. According to the datasheet value, they can handle 100A RMS. But according to my own hotspot temperature calculations, they should be able to handle around 180A RMS. I think the capacitors are only rated as 100A because of the terminals. I saw on your website that the capacitors in your large DRSSTC III are rated for 80A RMS. Did you run into any heating issues because of that?

Have you seen my comment about the IGBT calculations on your website? I think I found a mistake there, but I am not sure.

Greetings
Phoenix

 
« Last Edit: April 25, 2019, 11:42:37 AM by Phoenix »

Offline Phoenix

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Re: Phoenix's Large DRSSTC II
« Reply #3 on: April 29, 2019, 08:21:26 PM »
The IGBT Bricks have finally arrived and they are way bigger then expected ;D

The SKM200 looks tiny next to them:



They are the same size like the CM600DU24NF Halfbridge Brick, but I need 4 of them, because this are single IGBTs.

Offline Laci

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Re: Phoenix's Large DRSSTC II
« Reply #4 on: April 29, 2019, 08:42:52 PM »
...and I thought my SKM400s are huge...
I wonder how big your heatsink will be too. :D

Good luck for the building and looking forward to steal some techniques.  ;)

Offline Bambinz

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Re: Phoenix's Large DRSSTC II
« Reply #5 on: April 29, 2019, 08:50:58 PM »
This is an awesome project.
I'am an electronic Engineer but I haven't the competence to develop an so high power device.
You are crazy xD please pay attention because a failure will results in a new years show xD

Offline Phoenix

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Re: Phoenix's Large DRSSTC II
« Reply #6 on: April 29, 2019, 09:05:38 PM »
Hello Laci and Bambinz

Thank you for your compliments and the nice replies  :)

@Laci

I have yet to find a heatsink that large, but there are quite frequent ebay offers for such heatsinks.

I think you can't steal techniques from me, i have seen your thread and you definitely know how to build a DRSSTC  :)

@Bambinz

It really means a lot to me to hear something like that from an electronic Engineer   :D

I know the components may look intemidating, but it really isn't more difficult to build a large DRSSTC than a medium DRSSTC. Everything just needs to get scaled up, the basic working principle stays the same. But as you already said, you have to be way more careful with a large DRSSTC. The arcs could strike further than you might expect and a crash of the fullbridge could cause a lot of shrapnell to fly around. 3600 Joules is definitely more than enough to really blow something up.

Greetings
Phoenix

Offline Bambinz

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Re: Phoenix's Large DRSSTC II
« Reply #7 on: April 30, 2019, 06:34:07 PM »
It is a very difficult project also for an Engineer, because handle an so high current/voltage is not obvious. Theoreticaly, probably, is not very complex but in practise there are many things to take care: Layout, Power dissipation, ...
Requires many experience in the field, I think that you have certainly build many DRSSTC in various size.

To reduce the thermal resistance, I know that in generaly, the heatsink is polished to have a perfect planarity to increas the contact area. In addition, you should respect the mounting torque to have the best possible contact.  ;D

Offline Phoenix

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Re: Phoenix's Large DRSSTC II
« Reply #8 on: May 01, 2019, 08:31:05 PM »
Yes, you are right, there are quite a lot of things to consider when building a DRSSTC. You need to keep the stray inductance of your bus layout low, you have to make sure that no components get overloaded via calculations, you need to take care when winding the secondary to avoid flashovers, you need to keep the distance from the primary coil to the secondary coil high enough to prevent flashovers between them, ....

Here you can see the primary coil I designed with a computer software called "Geogebra". The red lines are the primary supports and by measuring the points via the software where the spiral crosses them, I get the distance and I know where to drill without any annoying calculations and possible mistakes. The x and y scales are in mm.



Greetings
Phoenix


Offline Bambinz

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Re: Phoenix's Large DRSSTC II
« Reply #9 on: May 03, 2019, 07:45:13 PM »
Very good!
Geogebra is a good software. I have used it during the Bachelor for the mathematics and physics :)

Why in the big teslacoil is used almost always a flat spiral for the primary?  To maximixing the distance between the primary and the secondary and to not have a too high coupling?

Offline Mads Barnkob

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Re: Phoenix's Large DRSSTC II
« Reply #10 on: May 03, 2019, 10:26:23 PM »
I have got another question about the RMS current capability of these large GTO snubber capacitors. According to the datasheet value, they can handle 100A RMS. But according to my own hotspot temperature calculations, they should be able to handle around 180A RMS. I think the capacitors are only rated as 100A because of the terminals. I saw on your website that the capacitors in your large DRSSTC III are rated for 80A RMS. Did you run into any heating issues because of that?

Have you seen my comment about the IGBT calculations on your website? I think I found a mistake there, but I am not sure.

Greetings
Phoenix

I assumed their RMS rating to be 80A compared to similar sized GTO snubber capacitors where the value was given in the datasheet. It is properly higher as they have rather large terminals.

GTO capacitors large physical size and if they are connected to heavy copper busbar will help them dissipate the losses fast and thus the dooms day prophecies of my MMC calculator wont come true, as it predicts I run them at 195 degree Celsius temperature rise :)

I saw your comment the day you wrote it, thought about it, looked at my calculations and had to check my spreadsheets on the PC to find out why I did as I wrote. I have concluded that the shown graph certainly isn't from the CM600. So I updated the article with a note about it being an example and that the 0.081 used for the CM600 is the thermal impedance multiplied with the single pulse normalized transient given in the datasheet, at 0.02 duty cycle that corresponds to 1, so I left that out in 2015, but added that now as there might be other cases where duty cycle is lower or higher.

So it was just a worst case scenario that apparently aligned up with a number from the example by coincidence. 
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline Phoenix

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Re: Phoenix's Large DRSSTC II
« Reply #11 on: October 21, 2019, 07:07:43 AM »
Hello Mads

Sorry for my late reply, it has been a long time and I have been quite busy lately  ;)

Thank you for always updating your design guides, they provide very useful information.

So I was finally able to get proper capacitors for my MMC.



The MMC can theoretically do 9kA Peak, 12kV and 225ARMS at 85°C. But if the MMC ist still colder, it could handle up to 350ARMS. These caps are very robust, they have a peak dc voltage rating of 2400V and they can do up to 3500VDC for 10s/day, which equates to around 8 minutes of DRSSTC runtime per day. Of course the 9kA are only theoretical because of the voltage rise, but my planned 3kA are no problem. With my MMC design, I also ensured proper current sharing between the caps.

I also found a good deal on way better Bricks, I will be using very modern FF1400R12IP4 Modules from Infineon. They can do 1400A Hardswitching, but are way faster and better in every aspect than my old 800A modules from the pre 2000 ages. These modules will laugh if I throw 3000A Softswitching in a DRSSTC at them  ;D

The bus layout also gets way easier with this modules, they are halfbridge modules. Here is the DS: https://www.google.com/url?sa=t&source=web&cd=1&ved=2ahUKEwjaxPiEyqzlAhWRJVAKHbQ6BZgQFjAAegQIBhAC&url=https%3A%2F%2Fwww.infineon.com%2Fdgdl%2FInfineon-FF1400R12IP4-DS-v02_04-EN.pdf%3FfileId%3Ddb3a30431f848401011feb7645573e9f&usg=AOvVaw1uqJS7NSpx5lVx8c3jLFJh

Greetings
Phoenix

Offline shrad

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Re: Phoenix's Large DRSSTC II
« Reply #12 on: October 21, 2019, 09:03:49 PM »
if I may just give a small advice from a guy I met who did high power laser PFN, this would be more efficient by connecting the series strings along with bits of threaded rods (no busbar, direct head to tail) and all three legs in parallel on triangle copper plates

his devise was "coaxial or it is not capable"... he did coaxial deionized water capacitors which served as spark gaps with dielectric breakdown, self discharging into a coil wound around the capacitor itself to reach picosecond pulses

not applicable there, but I though it would be more efficient to try this physical topology

Offline Phoenix

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Re: Phoenix's Large DRSSTC II
« Reply #13 on: October 22, 2019, 12:13:05 AM »
Connecting GTO Snubbers directly head to tail is a bad idea, because most of the heat losses in the capacitor get dissipated by the terminals. The thermal impedance is very low between the screw terminals and the inside of the capacitor, this is also stated in the DS. So if you screw them head to tail, the capacitors will heat up each other even more. I designed my MMC like that on purpose so there is copper busbar in between the capacitors which acts like additional thermal mass and as a heatsink.

Celem even states that screwing their power capacitors head to tail is an absolute no go.

Greetings
Phoenix

Offline shrad

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Re: Phoenix's Large DRSSTC II
« Reply #14 on: October 22, 2019, 09:48:57 AM »
ok then this makes sense, what about 3p3s with alternate disposition on copper discs then? wouldn't it reduce inductance ? :) just thinking, not criticizing your design, I love to learn from others designs so I challenge them

Offline Phoenix

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Re: Phoenix's Large DRSSTC II
« Reply #15 on: October 22, 2019, 11:38:31 AM »
Stray inductance does not really matter here, my tuning point will just be a little different (less turns). 3p3s is not possible, I will get to much capacitance for the MMC.


Offline shrad

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Re: Phoenix's Large DRSSTC II
« Reply #16 on: October 22, 2019, 12:26:39 PM »
meant 3p5s sorry

Offline Phoenix

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Re: Phoenix's Large DRSSTC II
« Reply #17 on: October 22, 2019, 12:38:33 PM »
 Yes you are right, it should reduce stray inductance a bit, but stray inductance is no problem here. Copper Disks in this size are also way harder to get and cost a lot more then simple busbar.
« Last Edit: October 22, 2019, 01:17:41 PM by Phoenix »

Offline davekni

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Re: Phoenix's Large DRSSTC II
« Reply #18 on: October 23, 2019, 04:03:42 AM »
I'd agree that primary stray inductance isn't a "problem", but it is at least slightly undesirable.  Stray inductance reduces the coupling factor, by the ratio of primary_coil_inductance / total_primary_inductance.  The less stray inductance, the further the primary can be spaced from the secondary, reducing arcing problems (for a given coupling factor).

The effect of stray inductance is a bit more significant in designs with low primary voltage (few primary coil turns), as I've built.  With only 3 and 4 turns for my SRSGTC and DRSSTC primaries respectively, minimizing stray inductance was worthwhile.
David Knierim

Offline Mads Barnkob

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Re: Phoenix's Large DRSSTC II
« Reply #19 on: October 28, 2019, 08:45:18 AM »
Nice to see some progress on the project! It is no shame to spend a few year building a large Tesla Coil (my large one, 4 years)

I am actually guilty of mounting my 5x GTO snubber capacitors in my large DRSSTC head to tails and the amount of room in my box would properly dictate that I try to install heat sink discs between them, I do after all have room for 6 mm more :)

What are your future plans to construct and keep the project rolling?
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Re: Phoenix's Large DRSSTC II
« Reply #19 on: October 28, 2019, 08:45:18 AM »

 


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