Yes Jason, you can do it by having the minor diameter large enough to hold
off breakout until almost full power is applied.
http://www.youtube.com/watch?v=3vKJyAycigQ#t=59 (That is an 8 x 34 inch
diameter)
The coil 'crackles' and buzzes until 80 - 85% + power is dialled in. Any
shortcomings in the coil will be exposed though, as it's under stress until
a streamer appears.
Phil
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Jason
Sent: Thursday, August 22, 2013 1:14 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] toroids instead of spheres - why?
While we are talking about toroids and spheres,
Whats the best way to work out size? and is there a way to only get the
break out at one point with a traditional spark gap coil? I am using a
break out point but still getting a dozen or so break outs
Cheers
Jason
On 22/08/2013 10:05 PM, Jim Lux wrote:
On 8/22/13 4:48 AM, Scott Bogard wrote:
I'm not sure which document you are referencing, but if I am not
mistaken,
a toroid typically has a larger capacitance for a given breakdown
voltage
does it not? IT also has far superior top turns shielding
characteristics
which is why we use them so much; I believe this has to do with the
E-field
shape though and not the capacitance.
Yes, toroids will give a more "uniform" field along the secondary. An
infinite flat plate would be ideal, of course, but a toroid is a nice
way to get an edge on the flat plate while keeping the field at the
edge high enough that breakdown doesn't occur too soon, allowing more
charge to be stored. You could have a Rogowski type profile on the
bottom of a sort of hemispherical electrode. That's a flat plate that
has a rolled edge, where the field is greatest in the flat plate part
and gradually decreases.
http://home.earthlink.net/~jimlux/hv/rogowski.htm
However, for a given diameter, a sphere has larger capacitance than a
toroid.
C(pF) for sphere is 4*pi*8.85*radius in meters.
An approximate formula from Bert Pool for a toroid (sorry for the
change in units to inches) is
C(pf) = (1 + (.2781 - d2 / d1)) x 2.8 x sqrt ( pi( ( d1 - d2 ) ( d2 /
2 )) / 2)
d1 = outside diameter of toroid in inches
d2 = diameter of cross section (cord) in inches
Some practical numbers.. a 36" diameter sphere has a C of about 50pF,
a 36" diameter toroid with 18" "tubes" has 35 pF capacitance. With 8"
tubes (and a 20" disk in the middle) about 39 pF
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