First Medium DRSSTC Build with Updates

[DJthefirst]

Hi, this is my first time designing a DRSSTC though I've built a spark gap TC and the OneTeslaTS kit and I want to double-check everything before diving too much farther in. The main goal of this coil is that it has room for later modification and a good platform to learn from and design on in the future. I hope to in college design my own driver and contribute back to the community. That being said I have already bought some parts online so here are my current plans.
Specs-
-Secondary I plan to wind 2400 turns of 30Awg wire 0.0116in diameter on 3.3125 Radius PVC with polyurethane coating
-Primary 1/4in Copper tube 10Turns for Tuning
-Topload whatever I can find
-IGBT CM400DU-12NFH I got a deal on 4 rated 60-70khz soft-switching 400amp 600v
-Snubber Two C4BSNBX4200ZBLJ rated at 1000volts 2uF
-Bus Cap "A bit overkill" 2 ALS70A 27000uf 250V dc KEMET caps in a voltage doubler
-Diode Bridge Rectifier KBPC5010
-MMC 8 940C20P1K-F 4 Parallel  2 Series for combined 0.2uf @4000vdc
-Primary Strike Capacitor 940C30S1K-F 3kV 0.01uF
-Bridge Bleeding Resistor B20J7K5E 20watt 7.5K 5% across IGBT output
-GDT 6.25UH T65 core B64290L0040X065
-Current transformer 6.25UH T65 core and two 75 TOROIDs 5975001401
-interrupter Loneoceans UD2.7
-midi controller Loneoceans duel MIDI Controller

*Other items I'm unsure about
-Noise Filter NBC-20-472
-GDT Diode 1N5819
-GDT Resistor 5.1ohm .5W
-GDT Zener 1.5kE30CA

Questions
-My MMC seems smaller than other coils. should I buy some more to get a higher power rating?
-What are the recommendations for IGBT protection currently I have the GDT specs from Loneoceans DRSSTC 3 but I haven't seen how one would calculate them? I expect my buss bar will have some voltage transients.

Again thanks for looking this over as it is my first coil any help is very much appreciated .

[zanikk]

hi, that mmc is probably for some 400A Peak current and those igbts are capable of handeling 700A/800A or more.
In your case i will go for some 942C20P15K-F caps , take a look at kaizer's mmc calculator http://kaizerpowerelectronics.dk/calculators/mmc-calculator/ .
Overall seems like a nice configuration .

[Mads Barnkob]

Hi DJthefirst and welcome to HVF

You seem to have done your home work and have come up with a good plan already.

The CM400 can take well above 1000A (CM300 have been pushed to that). Remember that all datasheet specifications are for hard switching and we do soft switching. If you want to calculate it, I wrote a guide on how to do that the easiest way with a few assumptions and guesses http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/

Your MMC is too small for such a powerful bridge and large secondary resonator. You need something to match that raw power. Do not try to save money on inverter or MMC, cutting corners will just lead to destruction and disappointment. If you do not wish to spend more money on the MMC, it is almost a waste to use CM400 bricks. You could go down to something like SKM100/200 bricks instead.

Your topload has a too narrow major diameter if you ask me. I usually go by the rule that secondary winding length should be the topload major diameter, gives you some good distance to the primary coil and bigger is almost always better here. Lower resonant frequency is only a good thing for your IGBT bricks! I made some tables with various configurations in my guide on secondary coil/topload ratios to impedance: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/secondary-coil/

-Noise Filter NBC-20-472: I guess this is just a noise filter on the input of the coil power or control electronics? Just a precaution to avoid as much EMI to wander around. Can be any suitable current rated filter you can find in many old machines or such.

-GDT Diode 1N5819: You can use any similar specified small signal diode

-GDT Resistor 5.1ohm .5W: I think you are talking about gate resistors, it is important that you try to match these to get even turn on/off times on your IGBT gates.

-GDT Zener 1.5kE30CA: To protect the IGBT gates from over-voltage / transient spikes. A IGBT gate can however withstand up to 80VDC, but gate voltage should be limited to limit highest possible C-E junction current.

Looking forward to follow your build progress

[DJthefirst]

The CM400 can take well above 1000A (CM300 have been pushed to that). Remember that all datasheet specifications are for hard switching and we do soft switching. If you want to calculate it, I wrote a guide on how to do that the easiest way with a few assumptions and guesses http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/

My thought process behind choosing to use CM400 was for future expansion. Several of the large coils I have seen also run on 240v dc with a voltage doubler but as I live in the United States with a voltage doubler I only get up to 170volts theoretically after rectification. After finishing the initial coil I plan to make several further upgrades to the MMC and enclosure.

All the being said, I purchased a few more 940C20P1K-F 3 series 6 parallel to keep my .2uf of capacitance with later plans to upgrade to a 4 by 8 grid. In the meantime how would I limit the current used by the coil? I saw you can change max gate current by changing the gate resistor external resistance but I'm not sure if that will interfere or damage my large igbts. UD 2.7 also has over-current detection but that still waits for the crossing point to turn off. I was hoping to run my first version of my coil at only 500-600 amps not the rated 700-900.

I'm also beginning to wind my secondary any tips on how to wind some extra coil on the ends in case it breaks or needs to be reconnected.