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Re: strike rail??
Subject:
Re: strike rail??
Date:
Fri, 11 Apr 1997 08:06:36 -0400
From:
"Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
To:
"Tesla List" <tesla-at-pupman-dot-com>
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: strike rail??
> Date: Wednesday, April 09, 1997 11:20 PM
>
> Subject:
> strike rail??
> Date:
> Tue, 8 Apr 97 05:12:31 UT
> From:
> "William Noble" <William_B_Noble-at-msn-dot-com>
> To:
> "Tesla List" <tesla-at-poodle.pupman-dot-com>
>
>
> please explain "strike rail", and when one is needed. I presume it's a
> grounded ring above the primary to protect the "low voltage" side of the
> coil
> from strikes from the secondary - do I need to know anything else???
>
> I'm slowly building a small coil to run on a 15KV or less neon sign
> transformer - I've just about finished winding a primary using 1/4
> copper
> tubing in a flat spiral affixed to an acrylic base - 50 ft of copper
> starting
> with a 6" inner diameter and spaced with 1/4" acrylic bar stock glued at
> intervals throughout the spiral - my plan is to tune the coil and then
> invert
> the primary so that the acrylic (1/4 inch acrylic base) is between the
> secondary and the primary to further reduce arcs from primary to
> secondary
> (and to keep all that nasty dust off my nice looking copper spiral)
William,
The strike rail is indeed used to prevent strikes between the secondary
and
the primary. The strike rail should *NOT* be a complete, closed turn.
Instead, the strike rail is an open turn so that it will not remove
energy
from the primary. The strike rail should be connected directly to your
RF
ground.
It is needed whenever you find discharges are striking the primary coil.
This is normally related to coupling and power. Changing the coupling
can
sometimes cause strikes to be initiated from parts of the secondary
*other*
than the top.
The toroid at the top helps a lot to prevent primary strikes by creating
an
e-field that is shaped such that the discharges are directed upward and
outward rather than downward. But primary strikes are still a
possibility
even with a well-designed toroid, so the strike rail is good insurance.
It
is more often needed in the case of the saucer-shaped or rising spiral
primary, but it is useful even with the flat spiral primary.
Try to reduce corona loss from the strike rail, especially at the gap in
the strike rail. The ground wire that connects it to the RF ground
should
have as low an RF impedance as possible. Avoid excessive twists and
turns
in the ground wire, or anything else that would raise the AC resistance
of
the connection. Keep the ground wire as short as possible. Be aware,
however, that Tesla coil discharges can do some really crazy things, and
do
not be suprised if occassionally a discharge bypasses your wonderful
strike
rail and hits the primary anyhow.
Fr. Tom McGahee