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Registered Member #4532
Joined: Sun Apr 22 2012, 03:16AM
Location:
Posts: 3
I've been finishing up a new small sized DRSSTC inspired by Steve Ward's DRSSTC.5, however I've encountered a strange issue with its operation! Here's a video of it:
The issue is that it only produces sparks like a DRSSTC should (sometimes) for a moment when it is turned on and (every time) for a moment when I turn it off. The rest of the time it gives off maybe an inch or two of thin sparks (OCD is set at about 100A). I also noticed that if I adjust the pulse width nothing happens during the thin spark operation, however it does change the "moment" sparks when I turn it on and off.
Any thoughts on why this might be happening? I'm thinking it has to do with my driver board.
Here are some specifications of the coil: Secondary: 6.5 inches of 36AWG wound on a 2.5x7 inch PVC tube. 1125 turns. Toroid: 6 in major/ 1.5 inch minor. Fres of secondary with the toroid is ~370kHz Primary: 5.1 turns of 12 AWG standed wire on a 3.5 OD piece of PVC. Primary MMC: 4x 942C20P15K-F in series. 37.5nF 8kV. Primary circuit Fres is about 340kHz Half H-bridge of IRG4PC50UD's. 340 V bus supply (from voltage doubler with two 1000uf/200v caps) Steve's UD (based on version 1.3b), 100:1 triad CT's GDT: 10:10:10 with 24AWG. The ferrite core is from EVR
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I agree. This sounds like an interference issue. Try keeping interrupter away from the DRSSTC during operation and make sure to route your interrupter wire (assuming you're not using fiber optics) away from the coil and power line.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
That is eerily similar to a problem I had with a MUCH larger DRSSTC.
The problem was indeed interference like the before mentioned. In my case it was interference on the feedback transformers, not the interrupter. But your problem definitely appears to be interrupter and interference related. Like previously said, more distance between your interrupter and the coil, and I can't quite tell form the video but use shielded enclosures. I'm sure you probably know that though
Registered Member #4532
Joined: Sun Apr 22 2012, 03:16AM
Location:
Posts: 3
I solved my issue (it turns out it wasn't interference, more so impedance)!And what was the solution? I dropped the bus voltage to ~120V (while keeping OCD at 100A). The reason this worked: impedance. Originally with my bus voltage at 340V, too much current could flow per cycle. This would cause the primary circuit to hit the 100A OCD limit after as few as 4 cycles and then disable the coil for the rest of that interrupter pulse. That was a very bad thing! Not enough enough energy could be transferred to the coil in so few cycles to properly form sparks. Cutting the bus voltage in half effectively reduced by 2X the amount of current that go through the primary circuit per cycle due to ohms law and the fixed impedance. This allowed for more cycles to add energy to the coil before hitting the current limit, being sufficient to form "good" sparks. I then amped up the OCD limit to about 250A and increased the bus voltage to get some decent 14 or so inch sparks. Hopefully with some fine tuning I can get better!
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Put your scope on your interrupter line and find out for sure if it's the interrupter. Although it sounds like the issue do check before you rip apart something based on a hunch.
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Odd DRSSTC problem
