Post by: Phoenix on April 08, 2019, 01:12:14 PM
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
Post by: Mads Barnkob on April 23, 2019, 09:39:04 PM
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 :)
Post by: Phoenix on April 25, 2019, 11:14:32 AM
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
Post by: Phoenix on April 29, 2019, 08:21:26 PM
The SKM200 looks tiny next to them:
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They are the same size like the CM600DU24NF Halfbridge Brick, but I need 4 of them, because this are single IGBTs.
Post by: Laci on April 29, 2019, 08:42:52 PM
I wonder how big your heatsink will be too. :D
Good luck for the building and looking forward to steal some techniques. ;)
Post by: Bambinz on April 29, 2019, 08:50:58 PM
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
Post by: Phoenix on April 29, 2019, 09:05:38 PM
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
Post by: Bambinz on April 30, 2019, 06:34:07 PM
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
Post by: Phoenix on May 01, 2019, 08:31:05 PM
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.
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Greetings
Phoenix
Post by: Bambinz on May 03, 2019, 07:45:13 PM
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?
Post by: Mads Barnkob 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.
Post by: Phoenix on October 21, 2019, 07:07:43 AM
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.
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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 (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
Post by: shrad on October 21, 2019, 09:03:49 PM
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
Post by: Phoenix on October 22, 2019, 12:13:05 AM
Celem even states that screwing their power capacitors head to tail is an absolute no go.
Greetings
Phoenix
Post by: shrad on October 22, 2019, 09:48:57 AM
Post by: Phoenix on October 22, 2019, 11:38:31 AM
Post by: shrad on October 22, 2019, 12:26:39 PM
Post by: Phoenix on October 22, 2019, 12:38:33 PM
Post by: davekni on October 23, 2019, 04:03:42 AM
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.
Post by: Mads Barnkob on October 28, 2019, 08:45:18 AM
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?