Author Topic: A few questions regarding design of DRSSTC (medium-sized)  (Read 122 times)

Offline markus

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A few questions regarding design of DRSSTC (medium-sized)
« on: May 03, 2021, 06:20:47 PM »
Hi Guys!

Though this is my first post, I have been lurking in this forum and the others for some time now and already built some smaller coils.
The first was an SSTC (after Steves mini SSTC / Gaos SSTC2), with which I had a lot of fun - though it mysteriously stopped working at some point, even after completely replacing all the electronics...
After that, I continued with a small DRSSTC (taken after Gao's DRSSTC1 / Mads DRSSTC2) with ~220kHz fres, a FGH60N60 half bridge, 66nF MMC, reaching a good 60cm at maybe 280Apk, running very reliably unlike the first coil.
It uses Steves 1.3b driver, but later on I added some phase shifting from the UD2.7 schematic.

Now that I have some time on my hands again, I have thought to take a step up and build a medium-sized brick-based coil. This was initially inspired from the loneoceans DRSSTC2, but has somewhat diverged from it.


The design goals so far:
  • I very much would like to test the more modern drivers like the UD+ or the UD3 (I do have experience with embedded software and some VHDL anyways) and use this coil as a platform for this.
  • Therefore, it obviously needs to run a full bridge for features like pulse skipping.
  • It should be somewhat compact (needs to be stored somewhere...). At the same time, it also should be larger than loneoceans coil as to not limit the output through the secondary length.
  • It should be robust and powerful. I would be satisfied with performance similar to loneoceans coil, but it should be able to run longer on-times with pulse-skipping. At the same time, while robustness is great, it is not really intended for shows or anything like that.
  • The coil must be able to run from a normal 230V / 16A single phase input (if later on more power is needed, I would have a 3 phase outlet available somewhere in the house, but this should only be optional with regard to single phase input).

The bridge will use BSM200GB120DLC Bricks (I managed to obtain 3 of them together with a  pile of 150A bricks quite cheap at ~10EUR for a 200A and ~5EUR for a 150A module) with a peak current of 450A - though during the test phase I might use a pair of the 150A modules initially. Datasheet: https://datasheet.octopart.com/BSM200GB120DLC-Infineon-datasheet-13708590.pdf
The driver will be a UD+ for now (still waiting for the PCBs).
The bus voltage would be 320V with a single (used) 4700uF 450V Kendeil electrolytic cap. If for some reason 640V (doubled) or 560V (3 phase) would be better, I have 2 more matching caps that could be used (e.g. two in series).
The primary f_res is supposed to be below 110kHz, with a calculated f_max2 of 138kHz this leaves room to spare and might also allow experiments with upper pole operation. Regarding the calculation of f_max2 I am somewhat unsure about my result - does it look reasonable for these bricks?


As of now, there are no clear designs on the primary circuit yet and I still have some important decisions left to make first in that regard (high / middle / low impedance, MMC, ...).
For now, I am in the process of designing the secondary / overall dimensions, as well as the bridge itself.

For the secondary design I am as of yet somewhat unsure about the exact dimensions (mainly height / diameter / wire size) I should choose. Right now, these are the designs I am playing around with:

First design, 0.25mm wire on 125mm form:
Code: [Select]
J A V A T C version 13.6 - CONSOLIDATED OUTPUT
5/3/2021, 4:38:34 PM

Units = Centimeters
Ambient Temp = 20ºC

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
6.4 = Radius 1
6.4 = Radius 2
50 = Height 1
110 = Height 2
2000 = Turns
0.025 = Wire Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
97.24 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
60 [cm] = Length of Winding
33.33 [cm] = Turns Per Unit
0.05 [mm] = Space Between Turns (edge to edge)
804.25 [m] = Length of Wire
4.69 [:1] = H/D Aspect Ratio
280.1664 [Ohms] = DC Resistance
60256 [Ohms] = Reactance at Resonance
0.351 [ kg] = Weight of Wire
98.622 [mH] = Les-Effective Series Inductance
101.645 [mH] = Lee-Equivalent Energy Inductance
99.194 [mH] = Ldc-Low Frequency Inductance
27.163 [pF] = Ces-Effective Shunt Capacitance
26.355 [pF] = Cee-Equivalent Energy Capacitance
40.126 [pF] = Cdc-Low Frequency Capacitance
0.2466 [mm] = Skin Depth
22.379 [pF] = Topload Effective Capacitance
348.6211 [Ohms] = Effective AC Resistance
173 [Q] = Quality Factor


----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=12, major=60, height=118, topload


Second design, 0.3mm wire on 160mm form:
Code: [Select]
J A V A T C version 13.6 - CONSOLIDATED OUTPUT
5/3/2021, 4:40:44 PM

Units = Centimeters
Ambient Temp = 20ºC

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
8 = Radius 1
8 = Radius 2
50 = Height 1
110 = Height 2
1666.7 = Turns
0.03 = Wire Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
92.07 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
60 [cm] = Length of Winding
27.78 [cm] = Turns Per Unit
0.05999 [mm] = Space Between Turns (edge to edge)
837.77 [m] = Length of Wire
3.75 [:1] = H/D Aspect Ratio
202.6707 [Ohms] = DC Resistance
60805 [Ohms] = Reactance at Resonance
0.526 [ kg] = Weight of Wire
105.11 [mH] = Les-Effective Series Inductance
108.094 [mH] = Lee-Equivalent Energy Inductance
105.121 [mH] = Ldc-Low Frequency Inductance
28.429 [pF] = Ces-Effective Shunt Capacitance
27.644 [pF] = Cee-Equivalent Energy Capacitance
43.344 [pF] = Cdc-Low Frequency Capacitance
0.2534 [mm] = Skin Depth
23.244 [pF] = Topload Effective Capacitance
273.2056 [Ohms] = Effective AC Resistance
223 [Q] = Quality Factor

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=16, major=60, height=120, topload

Third design, 0.25mm wire on 160mm form, slightly shorter at 55cm winding length:
Code: [Select]
J A V A T C version 13.6 - CONSOLIDATED OUTPUT
5/3/2021, 4:42:31 PM

Units = Centimeters
Ambient Temp = 20ºC

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
8 = Radius 1
8 = Radius 2
50 = Height 1
105 = Height 2
1833.3 = Turns
0.025 = Wire Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
80.27 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
55 [cm] = Length of Winding
33.33 [cm] = Turns Per Unit
0.05001 [mm] = Space Between Turns (edge to edge)
921.52 [m] = Length of Wire
3.44 [:1] = H/D Aspect Ratio
321.0182 [Ohms] = DC Resistance
70315 [Ohms] = Reactance at Resonance
0.402 [ kg] = Weight of Wire
139.417 [mH] = Les-Effective Series Inductance
141.801 [mH] = Lee-Equivalent Energy Inductance
137.45 [mH] = Ldc-Low Frequency Inductance
28.198 [pF] = Ces-Effective Shunt Capacitance
27.724 [pF] = Cee-Equivalent Energy Capacitance
42.335 [pF] = Cdc-Low Frequency Capacitance
0.2714 [mm] = Skin Depth
23.976 [pF] = Topload Effective Capacitance
414.3165 [Ohms] = Effective AC Resistance
170 [Q] = Quality Factor

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=16, major=60, height=110, topload

These designs should all be sound, but I cannot really decide between them. While the 160mm forms do give lower fres, they also somehow look quite fat and do require more space... I am also a bit unsure about the wire size needed - esp. with pulse-skipping -  as well as whether to go with a 60cm height or lower (while too small will limit the output, too large will require more storage).

Do you have any recommendations with regard to the secondary design in the context of my design goals?
Are there any rules of thumb for secondary wire thickness?
If a 0.25mm wire and ~100kHz fres appear reasonable, I might prefer the 125mm form.


Another thing I would be tempted to try is running the thing on the upper pole for music / better controlled sparks. Does this seem possible with the bricks used (where would the upper pole be, anyway - taking the first design, rather 110kHz or rather 120..130kHz)?

I will have some more questions in the future, but the secondary dimensioning is the most important for now.

Thank you very much!
Markus

Offline Mads Barnkob

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Re: A few questions regarding design of DRSSTC (medium-sized)
« Reply #1 on: May 05, 2021, 08:29:59 PM »
Hi Markus and welcome to HVF!

Running the BSM200GB120 bricks at 110 kHz and pulse skipping, while your Fmax2 calculations says 138 kHz (under which temperature and run mode conditions?), you could face other problems like needing a heavier driving circuit. Those gate charges at 2100nC could pose a challenge that you should look into ( https://kaizerpowerelectronics.dk/calculators/igbt-gate-drive-calculator/ )

I would go with the second design, large gauge wire is better here to handle the continues current load in long pulse skipping on-times. Designing for low impedance could make you able to use fewer primary turns and by that make a smaller base and then still use a 160mm diameter secondary coil form.

My recommendations for secondary coil design are all in the tables here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/secondary-coil/

110kHz or rather 120..130kHz is the same, heavy spark loading could be detuning it about as much as that :) Remember this is a hobby with +/- 3dB tolerances

To really determine on a design, make storage and a place to actually run the coil your priorities! I have a very large Tesla coil that I have a hard time to find good places to run and it takes up a lot of storage :)
https://kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics
https://www.youtube.com/KaizerPowerElectronicsDk60/join - Please consider supporting the forum, websites and youtube channel!

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Re: A few questions regarding design of DRSSTC (medium-sized)
« Reply #1 on: May 05, 2021, 08:29:59 PM »

 


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