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Registered Member #2273
Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37
Hey guys,
I am trying to get my second DRSSTC working one more time.
I use Steve's newest driver, it's shielded with a metall case. The secondary is 15*50cm with .3mm magnet wire. The toroid is about 40cm is diameter and 15cm thick. The fullbridge consists of two semikron SKM300GB12V IGBT's.
The driver seems to work fine, I have a constant feedback signal.
At the moment, it runs off 30V from my variac and I get about 1,5cm sparks to the ground.
The problem is that i can't get any streamers into the air.
Do you guys get streames from a comparable DRSSTC at this voltage? Is it problem of the tuning? How exact do I need to tune the primar? Any other suggests?
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
For me with a fullbridge of IRG4PC50UD I got about 10cm of sparks at 30V (and even more some times).
Do you toroid has a breakpoint? that is important for low voltage output.
Also it maybe tunning problem. The primary frequency needs to be a little lower (or higher) (about 10% or less) from the secondary frequency to compesate the frequency poles.
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
The size of toroid matters, there is a formula to calculate the breakout voltage of the toroid, but if you have a breakpoint on it, it doesnt matter, the breakout point will direct the sparks when it has enough voltage to breakout air.
You can calc the breakdown voltage here:
How much a cm of primary matters depends how big is your primary coil, also the ressoant frequency. It can matter much.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
hv-friekie wrote ...
My primary is about 25cm in diameter, the resonantfrequency is around 80khz.
So you really tuned you DRSSTC centimeter by centimeter?
Finn Hammer and Daniel Uhrenholt built DRSSTCs that could be tuned while running, Daniel said at some point that the sweet spot is within a few centimeters on the coil, it is a lot of experimenting to find the best tuning point when you have to turn on the coil, measure spark output, adjust primary tap, rinse and repeat. But it is worth the effort.
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Also remember that the stuff that is near the coil also changes the ressoant frequency. The ideal is to run the coil without anything with a few meters of it.
Registered Member #2273
Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37
Yesterday I tried tuning the teslacoil by tapping the primary coil centimeter by centimeter.
The thing is, it makes pretty much no difference where the best tap on the winding is! I get the same output, no matter where I tap this one winding. Seems like I have more like a 'sweet winding' than a 'sweet spot'. I get about 3 to 4cm sparks to ground at 30V, no streamers.
What to do? Maybe increase the input voltage or something liek that?
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
hv-friekie wrote ...
Yesterday I tried tuning the teslacoil by tapping the primary coil centimeter by centimeter.
The thing is, it makes pretty much no difference where the best tap on the winding is! I get the same output, no matter where I tap this one winding. Seems like I have more like a 'sweet winding' than a 'sweet spot'. I get about 3 to 4cm sparks to ground at 30V, no streamers.
What to do? Maybe increase the input voltage or something liek that?
Kind regards,
Philipp
What I normally do is setting a OCD limit within reason, f.ex. 300A if max for the coil was 500A.
Set the tap to the suggested tapping point from JavaTC simulation.
Turn up the voltage till the OCD starts tripping, note down the spark length, take pictures of it or record a video to study the behavior. But having some grounded object for it to spark against is good enough.
Tune the primary for a lower frequency by moving it maybe... 3-5 cm at a time, if I find a interesting spot I try to move 1 cm at a time in either direction to see which way to go.
What you will discover is that you can run with higher voltages, lower ontime, lower primary current for the same spark output as you come along in the progress.
Registered Member #2273
Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37
I tried tuning it without success. Now, I haveanother suggest:
Am I too worried about the On-Time? What is a typical On-time for a DRSSTC on decent power?
I say that because the old interrupter I am used is able to output fatal on-times if you aren't careful. Now I have Steve's interrupter (withe the two 555s) and have no idea how the on-times are compared to my old one^^
I measured that it can output a little more than 200µs on-time, so can I crank it up completely without running into some serious problems?
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DRSSTC - Problems
