[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] Twin coils primary lead design

Good point. I have not seen any misbehaviour though and don't really expect to do so with this low power system. To stand off the primary 12kV, I have about 3mm of insulation in total with the wire plus the plastic tubing I put the wire in. So hopefully no sparks near the ends of the coax where Blumlein effects are usually generated.

----- Original Message ----- From: "DC Cox" <resonance@xxxxxxxxxxxx>

If you have any standing waves on the coaxial line, you could get "Blumlien"
effects which could damage the coaxial line in short order.  The breakdown
could also damage your capacitors, so be sure to use a protective sparkgap
on the caps if you try this experiment. It takes a lot of HV and energy to
puncture a 250 mil acyrlic plate.
Dr. Resonance

On Sun, Aug 2, 2009 at 5:52 PM, Peter Terren <pterren@xxxxxxxxxxxx> wrote:

The coax is easier to make using available heavy wire and copper tubing and
is more robust and compact. Hopefully it will be as efficient as a
transmission line. There is no risk of primary strikes in my application.
In my bigger coil I have to cover the HV feed lines with low profile
extruded aluminium "L" cornering particularly as some of my sparks from a
rotating breakout point cause a uniform ring of ground strikes.  I didn't
think of guttering - shame since we just had our house guttering redone. My
usual motto is never throw anything out.

Peter  www.tesladownunder.com

----- Original Message ----- From: "DC Cox" <resonance@xxxxxxxxxxxx>
You might also wish to try a "parallel plate transmitter waveguide" like I
used in the early 1960s.  It consisted of a wide strip of acrylic sheet,
0.250" thick, and, then on each side I affixed a wide flat copper ribbon,
thus forming a capacitive "transmission line" allowing me to transfer
to the coil base. It had an extremely low inductance (less than 2 uH) at
distances up to 30 feet.  Over a 10 ft. distance the inductance would be
very low. One drawback was an occassional flashover from sec HV terminal
the transmission line.  We were using very robust capacitors in our
oscillator so no damage was ever sustained by the transmission line
strikes. My acrylic was 8 inches wide and each copper strip was 5 inches
wide to allow a very long creepage distance.  All sharp edges on the
strip were deburred and the edges coated with G.E. Red Glyptal.

This was later abandoned when "common sense" dictated I place all the
components directly under the coil. I began using this design around 1971
and have used it ever since.  It ended the flashover problems except to
HV feed lines. Metal raingutter( lay out inverted) is cheap and prevents
this problem in large coils.

Dr. Resonance

2009/8/2 Peter Terren <pterren@xxxxxxxxxxxx>

Thanks for all the suggestions. I did switch to a coax setup for primary
lead wires with heavy wire inside about 50cm copper pipe to each primary
I think that it improved output over the parallel conductors.
Interesting about the coupling because using a single secondary, I could
induce racing arcs before if I tried to max coupling.. Not as twins,
however, although the 6-7 turns required probably puts the coupling range
back to "normal". I also have plastic wrap on the coils as well.
My application does not permit separate electronics at present and the
leads need to be almost 80 cm.
I am aware of the V-twin at Palais.  I already had the boards and
components for a standard SISG though but a triggered SISG sounds
attractive, particularly if I could use some of my IGBT bricks. The low
turns and high current would require the electronics to be separate and
local which is not suitable here.
So at present I have 80cm sparks between 50cm secondaries.  Certainly
nothing to write home about but is probably adequate.  I am awaiting
SIDACs as half were 200V rated and plastic packed so starts firing at
180V on the variac (out of expected 250V) Had to source them from China
the usual suppliers were out of them. Hopefully that will take sparks up
I did flame a MOT today with this arrangement so some voltages are
appearing when they shouldn't. Plenty more where that one came from.
Peter  www.tesladownunder.com

Tesla mailing list