Re: Another toroid question

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Thursday, December 24, 1998 5:29 PM
Subject: Re: Another toroid question

>Original Poster: Esondrmn-at-aol-dot-com
>In a message dated 12/24/98 12:29:12 PM Pacific Standard Time,
>tesla-at-pupman-dot-com writes:
><< Original Poster: "Jon Rosenstiel" <jonr-at-pacbell-dot-net>
> Hi, I'm fairly new here, have been lurking for a couple of weeks, this is
> first post. I have been playing with a couple of small coils, (1.75 inch
> now 4 inch secondary). I am powering them with a 15kV, 60mA neon, but I am
> not using any higher that 40Vac input to the xfmr due to my inadequate
> capacitor, (correct capacitance, just not enough dielectric).
> I have been following the discussion on toroids, has been quite helpful to
> me.  My question is: What is the effect on total capacitance of stacking
> toroid on top of another? Do you add the two capacitance's? It would seem
> that some surface area is lost where the toroids contact and that would
> the total capacitance somewhat less.
> On my 4 inch coil I have achieved best performance so far, (15 inch sparks
> to a grounded wire), by stacking a 6" x 19" on top of a 4" x 15.5" toroid.
> wanted to know the total capacitance.
> This stuff is really exciting, I'm having a ball!
> Thanks, Jon Rosenstiel
>    jonr-at-pacbell-dot-net
>  >>
>Congratulations, sounds like you have the addiction now.  Your 19" toroid
>probably adds about 20 pf of capacitance to the secondary, the 15.5"
>probably about 15 pf.  If you lay one on top of the other, the new total
>be much higher than the original amount for one - my guess would be the
>for both laying on top of each other would be 25 pf.  I use dual toroids on
>both of my coils, one reason is to yield larger capacitance but an equally
>important reason is that it increases the distance between the primary and
>where the sparks come from, which will be the upper toroid.  On my 3.0" dia
>coil, the two toroids are separated by 6".  On the 6.0" dia coil, that 33"
>40" toroids are separated by 16".  My notes say the total for this type of
>configuration will be 65 to 75% of the combined total of both toroids.  I
>can't find the source for this number but I believe it.
>Ed Sonderman
Your reply got me thinking of a way to measure the capacitance change when I
add the second toroid. I worked backwards through the formula, (using
WinTesla), inputting the change in tuning to arrive at the change in the top
load capacitance. This roughly gave me the following: When I added the 6 x19
toroid on top of the 4 x 15.5 one the primary tap changed 1.3 turns. This
works out to about a 9pf increase in capacitance, a total of 28pf. Does this
seem right to you? I am going to try attaching the second toroid as you
The coil was a big hit with all of our Christmas party guests, (inlaws),
they were quite impressed!