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Registered Member #2750
Joined: Sun Mar 21 2010, 08:47PM
Location: Poland
Posts: 46
Hi all. I want to show my first DRSSTC. I started to work on it a year ago. First I build classic Steve Ward's driver and add only 1uF snubbers on my IGBT bridge - I had no possibility to get bigger ones. Tank capacitor is like Steve's DRSSTC1 - 450n/4kV CDE 942C20P15K-F. Six parallel strings of two in series. My secondary and primary coil is like Steve's DRSSTC1 too. I thought that at the beginning is better not to try to do your own design of the coils. The first time I ran this version in September 2009. First run delayed due to waiting for the CDE - they are very hard to buy in my country. I had to import them specially from the U.S. I enclose a few photos of first version
I get some nice sparks but as the result of my lack of knowledge about operation of this coil, incorrect gate waveforms and a lot of things what I did wrong I blow two pair's of IGBT halfbridge's. After this the winter was began so it was not possible to do further tests on the outside but I had a lot of time to think about this project. I learned much more about everything that involves the DRSSTC. I understood that the cause of damage the IGBT's was current overload caused by a wrong setting of OCD and voltage overshoots (too small subbers, not suitable TVS diodes and big delays on the logic). Below is a video of the last test in 2009 ended by damage of IGBT's (not so good quality) In the meantime, I came to the Finn Hammer's project named "Thumper" and the mention of "predikter" driver. Next i found the Finn's video about idea of this driver where he shows how it works: one move of potentiometer in circuit and ringing, voltage spikes and other bad things was disappear I thought, this is not possible but if possible I want to build this driver. After some time Finn released a complete project and I ofcourse started to buid them:-) Great thanks to Finn Hammer for the relase of this amayzing driver. My finishingof new driver and rebuilding the bridge - I get big 5uF snubbers directly from Wima and beter TVS too. was coinciding with the beginning of the sunny days of spring. The first run was ended with destroyed GDT - my fault I had not noticed damage of the windings insulation. Fortunately this not damaged the IGBT's. I made new GDT and coli starts to work proper. Predikter is amayzing I don't have any spikes on bridge output. This is the greatest most cool and probably most expensive... project ever built! I planned construction of a second identical coil in near future. I have all component's now I must put all together and ofcourse I want to modulate them with music I have some experience with the modulation of SSTC. I interested in electronics for a very long time and write a program to allow the microcontroller to read MID files directly from SD card and play them on tesla coils is not a big problem for me. I intend to build a system to play mid files on tesla coils without the PC. Now I have some problems with tunning of my coil. I know i need to detune primary circuit to lower frequency than the secondary frequency. But I don't know how much is good. Last tests looks like detuning to 66,7kHz with secondary resonance at 68kHz was near to be good. I stil have notching on primary current but that current increases all the time. When the primary worked on the same frequency as the secondary primary current incerases only by 6 cycles next 7th cycle was lower current than 6. Here are the pictures after rebuilding of the driver.
Bridge output waveforms at low voltage ~40V: Without predikter - swithing after current 0crossing
With properly set predikter - swithing right at the current 0crossing
And video how it works now (stil not so good quality ) Im happy to read all comments and propositions of changes in my coil(s)
Registered Member #2750
Joined: Sun Mar 21 2010, 08:47PM
Location: Poland
Posts: 46
I don't have capacitors in series with GDT. Im using two stage driver like Finn Hammer and Daniel Uhrenholt in this project Output of predikter drives small gdt in small intermediate mosfet H-bridge. That bridge drive huge GDT and IGBT's. Nothing bad happens but I think I should add capacitors in series with GDT's primary.
Update 29.05.2010 Some new pictures
and new video: I think this is the maximum what I can safe do on this setup. Current ringup in 7-8 cycles. I have problem with measuring the current.
Registered Member #2750
Joined: Sun Mar 21 2010, 08:47PM
Location: Poland
Posts: 46
I do not use capacitors made by Black Gate (If I good uderstanding you Black Gate is a company that produces high quality audio capacitors). My caps are good quality lowESR electrolytic purchased in the normal electronic shop. made by Hitano or Jamicon. But they are looks like Black Gate caps
Registered Member #2750
Joined: Sun Mar 21 2010, 08:47PM
Location: Poland
Posts: 46
I cant do more with this setup. I have 320V in the bridge - rectified mains and get 59" - 60" sparks. Steve gets the same (60") with his setup. What do you thing is possible to get more with that setup without pushing capacitor and igbt's to extreme overload ?
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My first DRSSTC
I thought, this is not possible but if possible I want to build this driver. After some time Finn released a complete project and I ofcourse started to buid them:-) Great thanks to Finn Hammer for the relase of this amayzing driver. My finishingof new driver and rebuilding the bridge - I get big 5uF snubbers directly from Wima and beter TVS too. was coinciding with the beginning of the sunny days of spring. The first run was ended with destroyed GDT 
- my fault I had not noticed damage of the windings insulation. Fortunately this not damaged the IGBT's. I made new GDT and coli starts to work proper. Predikter is amayzing I don't have any spikes on bridge output. This is the greatest most cool and probably most expensive... 
project ever built! I planned construction of a second identical coil in near future. I have all component's now I must put all together and ofcourse I want to modulate them with music 
I have some experience with the modulation of SSTC. I interested in electronics for a very long time and write a program to allow the microcontroller to read MID files directly from SD card and play them on tesla coils is not a big problem for me. I intend to build a system to play mid files on tesla coils without the PC. Now I have some problems with tunning of my coil. I know i need to detune primary circuit to lower frequency than the secondary frequency. But I don't know how much is good. Last tests looks like detuning to 66,7kHz with secondary resonance at 68kHz was near to be good. I stil have notching on primary current but that current increases all the time. When the primary worked on the same frequency as the secondary primary current incerases only by 6 cycles next 7th cycle was lower current than 6. Here are the pictures after rebuilding of the driver.
