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LAN_403

Hazmatt_(The Underdog)

Wed Feb 15 2006, 01:19AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

If the capacitence lowers the resonant point, lower then the 1/4 wave, which it does, how do you bring the coil back up to the 1/4 wave resonant point then?

I'm under the impression that the Cself of the secondary is a series capacitence and the toroid being a parallel capacitence. Are you suggesting that by sizing your toroid to Cself it can be canceled?

WaveRider

Wed Feb 15 2006, 08:07AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

The electrical length of the winding at the fundamental resonance without a topload is longer than 1/4 wave. However, it behaves like a classic 1/4-wave open-ended transmission line (like a resonant circuit). Having built helical resonators in the past, I know that if they are loosly wound, they have an electrical length almost like an "unrolled" 1/4-wave transmission line...particularly if the external shield is not very large.. It's the close windings that make the difference in the TC case. To me, that's what makes this very interesting. I should probably shut up now and think about it some more!

Dr. Shark

Wed Feb 15 2006, 09:29AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Whohoo, my "What _is_ a tesla coil" thread lives again! Im sorry I was sleeping through the heat of the battle.
In case you did not find the paper Steve is referring to, it is here

. But I'm still not sure if it is worth understanding what is going on there, the trial and error approach seems to give you sparks at some point at least, whereas the theory is never going to do that .-)

Firkragg, most people seem to use the empiric Medhurst formula to calculate the capacitance, I am sure you know this, but just in case: C[pF]= k*d[cm] where the constant k depends on the aspect ratio of the coil and is about 0.7 for a 1:3 tesla coil. d is the diameter. This is supposed to be quite accurate, which I find surprising considering all the parameters _not_ entering the formula.

Marko

Thu Feb 16 2006, 07:15PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Firkragg, most people seem to use the empiric Medhurst formula to calculate the capacitance, I am sure you know this, but just in case: C[pF]= k*d[cm] where the constant k depends on the aspect ratio of the coil and is about 0.7 for a 1:3 tesla coil. d is the diameter. This is supposed to be quite accurate, which I find surprising considering all the parameters _not_ entering the formula.

LOL, formulae fails any mathematics but I used it and calculated 7,7 pf, TC CAD did 7,1 for my secondary... I dont understand, capacitance, our tesla coil 'constant' and diameter (now in centimeters)

dont have any basical linking in reality, but I calculated C well

Marko

Thu Feb 23 2006, 02:50PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Well few days have past so i hope I can double-post now

I made my micro-coil work using similar schematic, streamer is about the same size (only 20V supply)

Im using small topload and wire with spike far from it to promote breakout.
Using some half-baked calculations I guess it resonates at about 2Mhz (doh's formulae is strange but works quite well

)

Spark wields a lot of power, it easily burns paper, fingers, insulation...
Here is small movie that shows drawing arc trough insulated wire (insulation bursts and carbonises, making interesting fireworks)

Pictures of streamers are also added , nothing spectacular but I think wawerider (and me now

) are on very good way to accomplish something...

cheers...

ragnar

Fri Feb 24 2006, 05:09AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

*ahem*! lol

My oscilloscope might arrive next week, so by then I can have tried to build my own circuit finally!

Marko

Fri Feb 24 2006, 11:21AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

You really dont need osciloscope for this...

I ran it in ''interrupted'' mode, about 36 volts but halfwawe rectified.
It makes noisy, 2cm wide streamer.

Hanged 3 mosfets already, now usingIRFZ30 and IRFZ46 (very similar, results are same as with two 24's or two 30's)
So mosfet choice is not critical at all, just go for highest current and voltage about 50V (if you dont mind push it more)

When I tried to filter it mosfet blew instantly, obivously gate got overvolted by feedback.
I tought about to improve coil for higher voltage, most probably in interrupted mode.
For higher voltages gate zener will be needed.

Maybe some capacitors wisely placed at primary could make it resonate in class E (that would need LOTS of thinkering)

When I run it it f*cks my ADSL up

Jams heavily radio, TV, internet connection, cell phones hold but lose some signal.

While using 3 feedback turns streamer was smaller but incredibly hot, if you could watch that film (some people said download doesnt work

you could see what is it doing to wire insulation

Now I reduced feedback to 1 turn, it is more stable, bigger but weaker arcs.

Draws about 2A of current in this mode, but that depends lot on coupling, output power, etc...

WaveRider

Fri Feb 24 2006, 11:49AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

Excellent work.. Indeed, I also found the arcs very hot. You can feel the heat rising off them..

I couldn't get your film to work either.. Got directed to some crap page that wanted me to buy internet services..

You may find that enclosing the coil (and associated electronics) in a well bypassed Faraday cage will stop the intereference and actually increase arc size. (I found this to be the case..I was getting strong coupling into the power supply leads, and hence into my apartment's electrical system... This could have been sucking up a few tens of watts or so..)

The harmonic content is considerable (depends on biasing, feedback level, etc..). Even if fundamental radiation is weak, harmonic radiation can be significant and can wreak all kinds of havoc....

Marko

Fri Feb 24 2006, 12:14PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

The streamer itself is actually biggest mess-maker.
Ionised air emits whole specter of EM radiation that interferes with everything...
Other threat is strong electric field emmited from coil that lights neon bulbs and also causes havoc in instruments...

My coil is not grounded as it will cause it to couple and demonstrate its 'wirelles energy sending' capabilities, but on electronic devices.
It draws small current, mosfets are cool but secondary itself becomes very hot over time (thin wire and low thickness of skin at that frequency)

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