DRSSTC design advise / Primary peak current calculation

[Martin]

Hello Everyone,

after watching too many videos on musical tesla coils I decided to build my own.
I found Mads Barnkob´s website and his guide on designing a DRSSTC was a gread read, lots of useful information in one place.

Currently I am trying to figure how big I want/can make it, I was thinking in the order of Mad´s DRSSTC 1.
I already have 2 SKM300GB123D igbts and 2 4700uF 450V for my primary DC filtering, I would like to build my tesla coil around these if possible.

I had a play around in JavaTC and tried to design a coil that I like.
But its just that, something I just made up based on the physical proportions I like.
I dont really know if it would work or how I would determine if it would be a good design.



A lot of the formulas for calculating the values of components for the primary circuit require me to know the peak primary current.
How do I calculate that? Or is is just something I make up and design my DRSSTC around that made up value?

Greetings Martin.

[Martin]

I found the answer myself, its in there, I just overread it.
https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/mmc-tank-capacitor/

[Mads Barnkob]

Hi Martins and welcome to HVF!

Going with 0.25 mm wire might get you a too high impedance coil, to be understood like this: The losses in the slow CM300 from the required longer on-time at high impedance, might be higher than the losses from a higher switching frequency from using a large gauge wire. Did you get through: https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/secondary-coil/ and did you find the almost hidden link to larger spread sheet? https://docs.google.com/spreadsheets/d/1TkpvH7e5geHCIhB_Gr3egwL_THJYqjZIU5INoo54nD4/edit#gid=482293335

I started working on this guide very long ago, so much to write and along the way I started re-writing it at a hardback book, but its a huge work and I never seem to find time to work on it. But its a lot of information with a somewhat red ling through it, in the online version. I would like to make that a very clear red line so its more like a proper design guide where you can choose a starting point

Looking forward to see your results!

[Martin]

So I want the AC Resistance of my secondary to be equal to the resistance of my spark. But the resistance of the spark varies a lot and can't be calculated well, so I should aim for the "magic 50k Ohms". Do I understand that correctly?

[Felix B.]

Pretty much. My coil has over 70k impedance and works fine but yeah it should work better with a lower impedance. 82k is pretty high for a DRSSTC. Around 2000 turns with a bigger topload will work fine. I would go for under 60k now but I only had a kinda small topload at the time and didn't wan't to make one (because I had a nice spun topload) and it works fine now but I assume with a lower impedance I could probably get 250cm+ instead of 230cm. Good luck with the build

[Martin]

So I increased the wire diameter and the size of the topload to keep the frequency down.
That thing just keeps getting bigger it seams. Hopefully the sparks will reflect that in the end.

Now to ordering parts and winding that secondary I guess.

[Felix B.]

Nice! Looks good now. I'm pretty excited to see how it turns out. Will you use the UD2.7 as the driver?

[alan sailer]

A quick question. The printouts for your JavaTC design have parameter inputs/outputs that I have not seen before. The "Calc Turns" entries.
How do you get to this information?

Cheers.

[Martin]

I have not given much thought to the parts beyond the IGBTs, as the drivers seamed quite generic. I am intending to use something that is already designed and proven to have something less that might go wrong. The UD2.7 looks quite mature and promising. I will look into that.

The CalcTurn Menu in JavaTC shows up, when I click the small blue calculator. Maybe there are multiple versions of JavaTC out there, I was using the first one that showed up on Google (http://www.classictesla.com/java/javatc/javatc.html).
 

[alan sailer]

Martin,

Thanks. I don't use many on-line simulators like this so I didn't even see the little
calculator.

Cheers.

[Mads Barnkob]

I think about helical coils in another way, so I made myself a helical coil calculators that is on my website https://kaizerpowerelectronics.dk/calculators/helical-coil-calculator/

Formulas are listed if you want to make it a spread sheet instead