2017 DRSSTC completion and first light

Bud, Sun Jul 09 2017, 02:19PM

Hi all, I just finished my big TC using 4 CM600HA-24 IGBT's. The h-bridge was a duplicate "thanks to pictures" from Phillip Slawinski on the web. I was able to visualize the design from the pictures and re-engineer it into the bridge I built. From there I was able to construct the rest of the hardware required for the entire build. I did run into some electronic stumbling blocks which stopped me cold. They involved the CT ratio's and the CT material. Also the GDT arrangement. But I contacted Steve and he provided me with the correct basics to construct and test them myself. Thanks again Steve!

I had met Steve long ago on two different occasions at the Teslathon in NY at Ed Wingates. The first time was prior to any SSTC or DRSSTC's....only rotary spark gap. The second meeting was when Steve and another young man had brought their SSTC's to Ed's and ran them. It was this time that was so compelling that I had to build one of them for myself. I remember the arcs were so bold, blue, and thick and I remember being scared to death because it was so much more powerful than Ed's extra coil.


I have no formal education in electronics at all. I started 2 years ago teaching myself by doing. My background is in tool and die and Eng. and in business. I think the biggest asset to this build was that I had built 6 tesla coils previously thru a 15 year period. One of them was the minibrute from scratch. This construction was a huge education in IGBT switching but only on a half bridge arrangement. Going to a full bridge was a little bit different but now that I have completed it I see there is not much difference. Did not know one could drive 4 IGBT's with one GDT! Also did not know how to setup the OCD.

I know some of you are going to question the red stripe on the secondary.....I ran out of gold wire and had red. The toroid was a copy from Finn Hammer's picture on the web. Once I saw it I just knew I had to build it. The strike rail is a new design that I am willing to bet no one else has. It is one continuous switchback that does not overlap. This idea came to me from a total failure I had built and welded. It was a beautiful hinged arrangement that wrapped around the primary for easy disassembly. It looked like a big fence. I sent Steve a picture and he immediately wrote me back stated that this will not work and why. So after all that work, time, and material I made a sketch and built it by undoing all the welds and rebuilding it into what is seen now. It is really cool. It is made from 1/8 ridged electrical conduit. I bent the tubing on my #2 Cincinnati vertical mill then tig welded the assy together. I then used some plexi to maintain the gap spacing.



Video of the coil is found here:

Construction pictures found here:

I have encountered a problem with photobucket doing 3rd party hosting so I switched all the photos to Flicker. Seems to be working good.






I power this coil with a 90 amp 240vac variac. I am only feeding 240 to the coil which has an onboard voltage doubler which works fantastic. The coil only draws 40 amp. at 2400 amp on the primary. This has been verified by an additional CT "thanks again to Steve's suggestion". The primary is cooled by an aux cooler. The sec is wound on a sonotube and is lightweight and very easy to disassemble. The toroid is made from 1/8 alum plate with lightning holes and .040" alum tube. All tig welded and very light weight. I plan on taking it to Roger Smith's Teslathon in Chillicothe Ohio on August 19th.

I am fully retired now after 48 years and have plenty of time to pursue more projects like this. I consider myself fortunate to live close to CTR surplus and made off with several truckloads of stuff before they shut down. This kept the build price low. I am also fortunate to have a manufacturing background which makes construction a breeze. When I look back at where I started 15 years ago with this hobby I cannot believe how far my education has grown and how far I have come due to shear determination and hard work. I never stop wanting to learn and do. Too bad we cannot live for 800 years like Noah!

This project was way cool and so are the arcs!

Forrest "Bud" Mohrman