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Registered Member #1996
Joined: Wed Feb 25 2009, 03:56AM
Location: Blackburn South, Melbourne, Australia
Posts: 10
Greetings everyone, I'm attempting to build my first DRSSTC. I've come into trouble with the secondary calculations. I have a toroid topload that according to online calculators is 20pF. A tesla coil is basically two resonant tank circuits right? With 20pF topload and a frequency of 500KHz I need a 5mH coil, which is only 95 turns on a 75mm former, seems way to small...
Is my frequency too high? I wanted to use Tesla's "storm frequency"...
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
??? Yes, a Tesla coil is two resonant circuits that are tuned. 500kHz seems like a rather high frequency, not to say it's not possible because it totally is. It just suggests a small coil and fast IGBTs. Perhaps you could use a different topload or lower your frequency expectation. Chances of getting bang on 500kHz are rare anyhow.
Registered Member #1996
Joined: Wed Feb 25 2009, 03:56AM
Location: Blackburn South, Melbourne, Australia
Posts: 10
Thanks, good to know I'm actually on the right track.
Next problem:
I want to run it CW, so I'm going to need to monitor the current in the primary right? To stop the primary resonant currents from killing the IGBT's? My idea is to experiment with power transmission not create spectacular arcs...
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
If I'm not mistaken, it is not possible to calculate the resonant frequency of a Tesla secondary based just on the topload capacitance and secondary inductance. There are many calculators on the net, the most sophisticated one probably being
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
MOTVolt wrote ...
Greetings everyone, I'm attempting to build my first DRSSTC. I've come into trouble with the secondary calculations. I have a toroid topload that according to online calculators is 20pF. A tesla coil is basically two resonant tank circuits right? With 20pF topload and a frequency of 500KHz I need a 5mH coil, which is only 95 turns on a 75mm former, seems way to small...
Is my frequency too high? I wanted to use Tesla's "storm frequency"...
500kHz is much too high for your DRSSTC. Not to say it can't be done, but given your experience (you haven't built any before) and the limitations of switching devices (IGBTs), 500kHz is entirely too high.
I would recommend designing your coil for about 100-200kHz.
Download WinTesla. Your design will come out to be about 1000-1200 turns typically. (usually 26-30AWG is pretty common) on a 4" coilform.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I want to run it CW
Do you mean without an interrupter? This is not really possible to get the full spark length with CW, im sure you could somehow but there is no reason to try it. It would pull a *lot* of power, the IGBT's would be switching somewhere in the 100's of amps continuous, your secondary would heat, you'd need a hell of a cap bank most likely. If you look at drsstc's you will not find one without an interrupter. The tank cap, when resonant, makes the primary current much higher than if you where to have no capacitor.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
MOTVolt wrote ...
Thanks, good to know I'm actually on the right track.
Next problem:
I want to run it CW, so I'm going to need to monitor the current in the primary right? To stop the primary resonant currents from killing the IGBT's? My idea is to experiment with power transmission not create spectacular arcs...
Then you don't want to build a DRSSTC. You want to build a CW type coil.
Your best bet is to build a coil like my Plasmasonic, and not audio modulate it and run it at full duty. Doesn't create much arc, but generates an enormous field. Basically, can be built with some large MOSFETs in a half-bridge or full-bridge implementation and can be run at 500kHz, although above 300kHz, you start getting too many switching losses and parasitics really come into play for proper switching.
Also, Class-E coils can be run CW as well at much higher frequencies (>3MHz typically)
Registered Member #1996
Joined: Wed Feb 25 2009, 03:56AM
Location: Blackburn South, Melbourne, Australia
Posts: 10
Arrgh!, so I need to do more research! Ok so the CW coil is basically like driving a flyback... With the DRSSTC what exactly happens when the primary tank starts to resonate? I was under in impression that the current increased, what does the voltage do? I was thinking of having PWM driving the primary with current feeback to reduce the drive significantly, just enough maintain resonance... Instead of using an interupter, which has OCD anyway.
Just beeen reading the wiki on drsstc and answered all of my questions...
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First attempt at DRSSTC! Please help a newb...
