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Hey everybody, I was reading up on a few quasi wave coils, and started to wonder how high the operating frequency could be. I wish to build one someday and was wondering how high the frequency could actually be. I was thinking that if I built one it would be small, like say with a resonant frequency of around 750kHz. How well do you think a quasi coil would work with a frequency that high? Obviously I have a lot to learn before I ever attempted one, just kinda curious and decided to ask now.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
As far as I know, it would work, but you would get shorter sparks for the same peak power. The "sweet spot" frequency seems to be somewhere around 300-500 kHz...
Interesting, anybody know how this topology behaves as you go smaller in coil size? Like 1" dia. small, I have no idea what the size limits would be. Anybody have any ideas?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I have some little IGBTs with 60 nC gates and turn on/turn off times below 100 ns, I think these could work at >>500 kHz with ZCS. But the peak output power will be limited of course... They are the FGP20N60UFD and are (were?) available very cheap on Ebay.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
From both the experiments that I have done and what I have seen of Steve Ward's work an increase in frequency seems to be more efficient. Being you can grow longer sparks with less top voltage. If you think of it from a physics point of view this makes sense in that the higher the frequency the more energy for the same given amplitude.
One thing that has to be watched out for though at high frequency is the Efield effect of the toroid. This effect is very important because it keeps the sparks straight rather than curving around the Efeild. I noticed this effect when I kept the same toroid size but raised the secondary Fres, the sparks started to cuve around the outside of the toroid's Efield due to the lower top voltage present.
This effect can be compensated for by using a larger toroid that projects the Efeild better. I had to switch from a 8x2 to a 3x12 when I went from 380KHz to 500KHz
Depending on the size of the sparks you want to make you can probably get away with a smaller toroid at higher frequencies, but there will come a point were it will be to weak to keep the larger sparks in line and a larger toroid will be needed.
I personally have only operated up to 500KHz I would expect this trend to continue somewhat at least up to maybe 1MHz. Although it's anyone's guess.
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Quasi Wave Coil Operating Frequency
