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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Is there any benefit or disadvantage with regards to streamer length by using larger toroids for a top-load? I understand that changing the dimensions affects the capacitance and that the capacitance affects the secondary self-resonant frequency.
For example, I have a six inch secondary that is thirty inches tall. I can use a toroid that is a 4" diameter tube and vary the wheel diameter from 8" to say 12 or 15". Or, I might want to use a 6" diameter tube. How do I determine which is best?
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
I think the mentality behind toploads increasing streamer length is that the topload acts A) as a capacitor and B) to suppress breakout.
The topload, as a capacitor, can swing with the secondary and 'charge up' (resonate) over a few cycles, storing energy. Where the top turn of the coil would otherwise discharge to air, the size (assuming it's smooth) of the topload will inhibit streamer formation until it reaches a much higher voltage.
When a streamer eventually grows from the topload, it's longer, because premature breakout without a topload from the secondary alone would occur at a lower voltage.
If the power of your coil is appropriate, I suppose bigger is better... assuming it doesn't inhibit breakout completely.
The gurus will have much more useful things to say. :P
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
I find that generally, the toroid outer diameter should be about the same as the secondary height. But in you can probably get by fine with a little less, maybe 24" diameter. If the toroid is too small, you dont get enough energy stored in the topload, and this seems to limit spark length. If the toroid is too big, then the capacitance is too large and you limit the voltage too much to grow the sparks out.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
this is just speculation but...
Terry has shown in his drsstc work that streamer length is limited by 2 things, voltage and current; whichever is lower. We know that bigger topload = higher voltage, until the point where it won't break out anymore. And we know that streamers have a fixed resistance, which would imply that the current for the streamer is inversely proportional to the voltage. So there should be a 'sweet spot' where the streamers are longest...
For maximum streamer length, nothing is "too big" as long as you can break out from it. My SISG coil does not break out without a "point" at its "present" limited power level.
But it might be cooler at higher powers without a point:
I "know things" to sort of drive towards "optimal"... But nothing concrete or useful "yet"... Now that I have been "fired" buy that mean old Tesla list moderator I hope to have more time to work on such "cool " things
But at maximum top voltage, the added current from the secondary coil is "zero". It is "all" stored energy in the capacitance of the top load... Bigger top load = lower voltage but more current. Smaller top = more voltage but less current... Probably a "perfect" impedance function there... Complicated by streamer growth...
Hmmmmm....
Cheers,
Terry
BTW - If you are not usng ball terminals, you are way behind
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Interesting you mention ball terminals Terry, I was dabbling with 6" ball electrodes back in 2000 and I had terrible performance compared with a toroid. The performance was such that I just threw the spheres away.
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Top loads
I hope to have more time to work on such "cool " things 
