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Re: 2 toroids

Subject:  Re: 2 toroids
  Date:   Sat, 19 Apr 1997 10:04:27 -0400
  From:   "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
    To:   "Tesla List" <tesla-at-pupman-dot-com>
    CC:   <Esondrmn-at-aol-dot-com>

> 
> Subject:  2 toroids
>   Date:   Fri, 18 Apr 1997 12:38:20 -0400 (EDT)
>   From:   Esondrmn-at-aol-dot-com
>     To:   tesla-at-pupman-dot-com
> 
> 
> I was doing some experimenting last night with my small 3" coil.  I have
> been
> running one 12 kv 30 ma transformer and wanted to add another one in
> parallel.  Since the secondary is not very long, I was concerned about
> getting strikes down into the primary - and have been too busy to build
> a
> strike rail as of yet.  I mounted the smaller of two toroids (10") on
> the
> coil and then set an aluminum cylindner 6.4" dia x 6" high on top of it
> then
> placed the 12" toroid on top.
> 
> The thought here was to get all the discharges to leave from the upper
> toroid
> and thus stay away from the primary.  I have this problem in spades with
> my
> larger 6" coil.  I contunually get white hot, thick bolts hitting the
> strike
> rail on this coil at 5kva and higher.  So, I thought I could apply what
> I
> learned here to the larger coil.
> 
> When I fired the coil when set up as described above, most of the
> discharges
> left from the lower (smaller toroid) and tended to go mostly down.  This
> was
> a surprise.  Then I reversed the two toroids so the larger was on the
> bottom
> and smaller on top.  It worked now just as I had planned but required
> the
> larger toroid on the bottom.  I thought the theory was to have just
> enough
> lower toroid close to the coil to prevent corona and then go as large as
> possible on top.  This seems not to be the case.  Can anyone explain
> this?
> 
> Ed Sonderman

Ed,
The radius of curvature of the smaller toroid made the e-field more
intense
at this toroid. The larger toroid was not able to shield the lower
toroid,
and so discharges broke out first on the lower toroid. By the way, by
putting the smaller toroid on top of the bigger one you not only
increased
the effective capacitance, but you also re-shaped the e-field so that
discharges preferred to leave from the top toroid. To further increase
the
effective capacitance of the top (smaller) toroid, it would need to be
positioned several inches to a foot or more above the larger toroid. The
capacitance is a function of the *exposed* surface area, not the surface
area of each toroid taken by itself. For initial experimentation you can
use a wood block to position the top toroid, or suspend the top toroid
from
below a ceiling using heavy duty monofilament
fishing line or lacing cord, or any other decent insulating material.
You
can use almost any conducting material to attach the two toroids
together
(even aluminum foil strips) as long as the material stays somewhat
centered, as the two toroids will effectively shield it. If the cord you
use to suspend the top toroid is really strong, you can even try raising
and lowering the top toroid while the Tesla coil is operating. Just be
cautious and make sure everything else is secure before attempting such
a
thing. As the toroids get further away, you will reach a point where the
toroids no longer shield the conductor that joins them together, and
discharges may break out along the conductor.

The same experiment done with just a single large toroid may help you to
find the most advantageous height above the secondary to mount your big
toroid. As you raise it, you will reduce the shielding effect, and
beyond a
certain point you will get corona and discharges from the top of the
secondary. But many folks have their large toroids down too far in
relation
to the top of the secondary. Raise the toroid to the point where it
effectively shields the secondary, but go for the extra height, as this
can enhance the size of the discharge that can be thrown by several
inches.

Fr. Tom McGahee