Re: [TCML] Twin coils primary lead design

[Finn Hammer <f-h@xxxx>]

Peter,

One proven way to remove the lead inductance between twin SISG coils is
to make the sisg triggered, as in my designs. Each coil has independent
tank circuits, but are triggered from the same source, so the ringdown
starts in the same instant, If I remember right, only about 10-20nS
apart. So the secondaries ring up in anti phase and connect as if they
were sharing the same tank.

Another way is to use extra long secondary windings, and arrange them in
a "V" configuration. In this case, where the secondary′s almost meet at
the bottom, you can hook up the primarys in a "figure of eight"
configuration. This eliminates the inter coil lead inductance, and
allows you to use a common tank circuit, even without the added comfort
of triggering.

I have found that a "V" angle exceding 90 degreed is quite possible,
without primary strikes and I think it would be safe to go up to 120deg
btwn secondary coils.

I used the "V" configuration with separate triggered SISG tanks in the
coil that was delivering the spark effect for Roman Signers umbrella
installation at Palais de Tokio, Paris, this spring.
Since I was limited to 1100Vpri, I did not use "figure of eight"
primary, but instead, individual primary′s, to get as much bang energy
as possible within the voltage restraint.

If you should decide to go for a coaxial interconnect, a great source of
material is the coax used to feed the cell phone antenna′s. It is
basically 2 copper pipes separated by insulating foam. I have not tried
it, but keep some in stock for this very application.

Hope this inspires.

Cheers, Finn Hammer


Peter Terren skrev:
> I am working on a small twin coil system with a cylinder primary and
> small spherical topload. Using a single coil only, run by a single MOT
> SISG, it puts out a 60 cm spark for a 50 cm secondary winding.
> I am finding results a bit limited when run as a twin system due to
> the length of the primary leads. With a series primary arrangement I
> should tune to 3 turns on the primary but with loose leads this drops
> to about 1.5 turns which is not efficient and spark length is less
> than 30cm despite double the power.
> With parallel primary windings, I should tune to 6 turns but it is
> reduced to 3 turns with the lead in wire inductance. It seems like I
> am wasting half of my inductance.
> Best performance of 90cm sparks with 2 MOT SISG is with a reduced tank
> capacitance to allow greater inductance in the primary using 8 turns
> in parallel connected primaries with lead in wires taped together sort
> of transmission line like.
> My question: How can I minimise the effect of primary lead inductance.
> Should I use two close parallel conductors (sort of transmission line
> like) or would a coax arrangement be better? I can make up a coax
> system with copper pipe and plastic tubing covering 1/4 inch tubing. I
> don't really understand the concept of impedance matching as applied
> to Tesla coil primaries though or whether it is even likely to be
> relevant.
>
> Any thoughts?
>
> Peter www.tesladownunder.com
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