First Midi tests with our new DRSSTC

[Michael_DA]

Hi Guys,

finally the time has come. Yesterday we had our DRSSTC down to a few trifles (a bit cleaner wiring, thicker cables for the prime and some security mechanisms), we finished the coil yesterday and tested today. We only started again with a voltage of 200 V and worked our way up to 560 V. The results were already very impressive for us (this is our first Tesla coil):

                               

We have set the T_On time to 200 us. We have a current of approx. 500-600 A in the primary circuit (in the tests without secondary coil we were at the same T_on time already at approx. 1 kA) and a current of approx. 6A in the secondary coil. So in principle our IGBTs can switch a lot more current. According to the datasheet, they can have a pulse current of 800 A and we have 2 IGBTs connected in parallel. During the test, none of the elements was warmer than 23 °. But first we want do approach step by step, as none of us could accurately assess how the coil reacts. Here are our measurements during the test (yellow = primary current; magenta = secondary current; turquoise = bridge voltage:



However, there was something again, which disappointed us. Namely, in the MIDI playback mostly higher frequencies are not played. That all sounds then, for example. like here at "Imperial March" from Starwars.

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Does anyone know why that is? Our guess is that the Interupter will not pass these high frequencies to our controller. Therefore we want to try to lower the songs an octave and try it again. But that's just a guess ...

Here are a few other songs. A friend of us tried to play music via an electric guitar, which worked quite well. However, I would say the sparks were a bit smaller (at least on the video looks like), but in the high-voltage hall, the approximately 3.30 m high coil looks small in comparison to the rest, too.

Game of Thrones Intro:   

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Mario Theme: 

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Pirates of the carribean:   

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First tries with an electro guitar:   

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Kind regards,
Michael

[erdal]

Hi Michael_DA,
looks very good, electro guitar is fantastic.

However, there was something again, which disappointed us. Namely, in the MIDI playback mostly higher frequencies are not played. That all sounds then, for example. like here at "Imperial March" from Starwars.

What is the resonance frequency?
I think because of the low resonance frequency of the great DRSSTC. That's why the sound quality of class E tesla coils, which work in a few MHz, is much better. However, you may also have a problem with midi interrupter. Direct midi instead of analog input gives better results

very good result for initial tests

congratulations...

[Michael_DA]

Hello erdal,

aaah ye, that could also be a point, thanks for the hint!  The resonance frequency is designed low. It is arround 29 kHz.

[profdc9]

Which interrupter are you using?  Since the note seems to be totally absent and not just muted, it looks to me like either the interrupter has some sort of limit set in the MIDI note it will play.  It is also possible that the MIDI file is set up incorrectly.  For the oneTesla interrupter that I use, for example, all notes must be channel 0 or they will not play, and if more than 2 notes are played at once, one of the two notes are stopped (it only has 2 note polyphony).  If you want to examine this the MidiEditor program is very handy:

https://www.midieditor.org/

I also attached some music that I adapted for the oneTesla interrupter if that's what you're using.

If you want, you can look at the DRSSTC PCB Pack I made

https://github.com/profdc9/DRSSTC-PCB-Pack

The "interrupter" project is a multiple function interrupter and includes the oneTesla MIDI interrupter on it if you want to build one yourself.  You will need an ATTINY85 and an AVR programmer.

Dan

[futurist]

I agree with profdc9, it seems that the interrupter ignores second note if one is already playing and higher frequency notes are not causing the problem

[Uspring]

Impressive coil 

We have set the T_On time to 200 us. We have a current of approx. 500-600 A in the primary circuit (in the tests without secondary coil we were at the same T_on time already at approx. 1 kA) and a current of approx. 6A in the secondary coil. So in principle our IGBTs can switch a lot more current.

You can try to tune the primary somewhat lower, i.e. a bit more out of tune. That will reduce power transfer to the secondary initially, leading to higher primary currents. After the arc breaks out, its capacitance will lower secondary resonance frequency, pulling it into tune with the primary leading to an efficient transfer of primary energy to the secondary. You may need to increase burst time for this. Bad for high notes, but good for arc length.

[Mads Barnkob]

That is definitely a interrupter "problem", a low frequency coil will always be able to play high notes, just with shorter streamers as there is no time to ring up enough current.

Even a large and very low impedance primary circuit DRSSTC will play high notes just fine and spark length will not be limited as bad as Uspring makes it sound, sure you are not getting ground strikes with high notes, but it will still be impressive from a large coil and require ear defenders

Example of Kizmo's BiggerDR playing high notes. He run with a 1uF MMC.

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I am really envious of your access to a HV hall like that, I am so limited by my small work shop 

[Michael_DA]

Alright, thank you for the many tips!
We suspect that the Interupter has a security function at too high a sound, we will examine it more closely and see if we can disable it or at least partially bypass it. If necessary, we have another Interrupter, we still have to build, but that would be the alternative in any case.

I am really envious of your access to a HV hall like that, I am so limited by my small work shop 

Haha yes, the many space and possibilities in the high-voltage hall are very beneficial. However, there are also some disadvantages. With the large Marx-Generator in the background more often gas breakdowns in eg SF6 with lightning impulses around 1.5 MV are produced. At the beginning, unfortunately, we also have some small electronics, such as Receiver for optical fibers, broke because of the high EMI.

Kind regards
Michael

[Michael_DA]

Hi Guys,
we have solved our problem. Our interrupter has a protective function, so that it does not transmit any more signal from a certain pitch. But with the help of audio programs, we can simply lower the pitch of a song completely an octave, so actually every song should be possible.
Alternatively, we now have a second functional Interupter with which we can choose between 3 different protection functions. So all sounds are possible. Here you can also set the maximum T_On time for the highest tone, we have this (for fear of continuous tones) limited to 100 us.

Here is a video of a complete song, but only at 200 V bus voltage, because we did not want to break the fluorescent tube. (It still broke in second 12 )

Thank you for your tips!