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Re: [TCML] Twin coils primary lead design
I'm running my little twin UBTT:
with heavy gauge (10mm^2 cross section) ultraflexible car-loudspeaker
cable (the one HiFi-Freaks are using) as connecting line between the 2
primaries. This parallel-line cable can easily take the primary voltage
stress, and keeps the cross-sectional area of the of the current loop in
the primary low, in order to have low stray inductance. In my example:
The seriesed primaries have a total inductance of 23.2uH, of which
the cable was responsible for about Lcable=2.6uH(Ccable=88pF). This
was when I used a "T" for the feeder (unfavorable), which was later
corrected to a shorter, direct "---" connecting parallel-line only(better).
Data with the "T" are in the above report PDF on page 22/23.
I can make Pic's of the primary lead system, if desired.
Peter Terren wrote:
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.
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