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Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
What size doorknob caps do you need? I have some here I could contribute to your experiments. I have some 30KV and 50KV caps. I dont mind contributing you have contributed a lot so I could certainly hook ya up with either 2700pF or 1700pF, 30KV and 50KV respectively.
Very generous offer! But sadly, i have a bunch of similar doorknob caps and they are simply too much capacitance. My MMC added just 17pF total.
What are your secondary self-capacitance without the MMC, and your topload capacitance ? (to give me an idea of the secondary MMC value I should start with).
Im not sure if i remember that. Its a 3.3"x6" winding of 28awg with a 2"x8" toroid. I want to say ~8pF for the coil and toroid together.
Registered Member #3806
Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
Thanks Steve for the additional info So basically twice the secondary+topload capacitance seems a good value to start with.
Steve Ward wrote ...
Hopefully thats enough info for you to recreate it for your VTTC. Im not sure if a coil will benefit from the added capacitance unless its streamer capacitance starts to exceed the self-capacitance of the coil. But, i think its a worthy experiment still!
I recently measured my VTTC resonnant frequency (during operation) at 1.948MHz
Then I tried to measure the resonnant frequency of primary and secondary using the Grid-Dipping method
I found the primary resonant frequency to be 1.946MHz, so almost equal to the coil operation frequency.
When I mesured the secondary free resonant frequency, I found it to be above 2MHz (dunno the exact value cause my signal generator max frequency is 2MHz )
Then I added a piece of 15cm lenght (my coil's streamer lenght) copper wire to my topload, pointing outwards, and my secondary resonnant frequency was down to the expected 1.950MHz !
So I think we can say any spark lenght will detune the coil.
And as you suggested in you first post there might be other benefits in adding capacitance to the secondary. I'm really curious about this and will try it on my VTTC as soon as I get suitable caps
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
A useful trick is to use a very fine nozzle and helium supply to make the arcs longer. This particular method was pioneered by He-Who-Shall-Not-Be-Named but works well.
Registered Member #3271
Joined: Mon Oct 04 2010, 02:29AM
Location: Canada
Posts: 159
interesting photo. Awesome. 1) would a small fan blowing forced air in the center of the coil help make the sparks and discharge more straight? You probably dont want to carry an inert gas tank too.
2) hope you have not tried this with someone that has a pacemaker, or insulin metering device, or...... you get the picture!
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ArcAttack! Tesla Gun
So basically twice the secondary+topload capacitance seems a good value to start with.
)
