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Re: an interesting mechanical engineering problem (60ft TC)
Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>
Sounds like a nice toy...
An idea for a high current flexible "hinge": I acquired from a scrap
meta; yard, a high current connector that is two copper blocks joined
by at least 6 braided copper straps of about 1 1/2 inches across. It
would swing from being a straight connector through much more than 90
degrees with only finger pressure. I don't have a use for this huge
conductor but I used just one of the straps as the flexible switch
connector on my cap bank. Works fine to 100kA pulses.
The braided straps in parallel should be low resistance without the
problems of a "connection" and you just design the size and
configuration you want, to hinge where you want. Much more flexible
than multistrand cable. The braid layers need to have a short inner
braid for the inside diameter and progressively longer as you go out
I am interested in the 10kHz Fres from a couple of points of
view. Firstly you will drive away all the teenagers and kids that
can hear this frequency. (High frequencies have been used in train
stations to make it unpleasant for vandals I gather). Secondly, do
you have information on spark growth at this low frequency. You may
not be aiming for 3 times secondary length but you don't want to be
left with an underperforming coil in terms of spark length even if
all the power is being delivered. 100kHz seems to be fine but 1Mhz
seems too high and 50 Hz too low.
I personally like the use of double toroids to prevent ground strikes
to the strike rail (or worse in a DRSSTC, to the primary).
Original poster: "D.C. Cox" <resonance@xxxxxxxxxxxx>
I'm presently in the process of designing the "world's largest
portable Tesla transformer". It will be a 60 ft tall unit x 7 ft.
dia sec coil, running as a DRSSTC, 160 kW continuous input, crowned
with a 8 ft dia. toroid and above that, a 20 ft dia toroid. Our
present design target, using 24 pcs of PowerEx 2400 Amp, 1700 Volt
IGBTs, all carefully linked together in a low inductance
configuration, with 3 inch wide x 1/4 inch thick copper plate
(H-bridge with 6 of these massive IGBTs on each corner).
Planned buss voltage is 800 VDC. Solid state control of the 440
Volt, 3 phase, 400 Amp inputs with very large SCRs --- similar to
the smaller control system we are developing for our dual MOT coil
with 7 - 7.5 ft long sparks running off a 120 VAC circuit.
Pri cap, with res. freq of 10 kHz, works out to 6 uF, 10 kV Maxwell
pulse cap, with a 3.1 turn pri (thanks again to Bart's great JAVATC program).
The base will be 26 ft in dia. and can be disassembled for
transport. The sec coil is going to have the winding, 31,000 ft of
# 6 AWG wire, glassed inside after winding. This unit is 7 ft in
dia and 44 ft long, but still transportable on a lowboy truck.
The primary is 3.1 turns, tapped, with a total of 3.5 turns. Our
original design was to use 4 inch copper tubing to form the pri, but
this is where the problem is coming into play. If we build a 26 ft
dia coil, 3 turns, of 4 inch dia copper tubing, how do we
disassemble the beast for transport.?
So far, a few ideas we are tossing around:
1) Use 1/4 turn sections of the copper tubing and link each 1/4 turn
section together with massive copper blocks, 5 x 5 inches square x 6
inches long. Butt the primary 1/4 turn sections together and use a
lot of brass setscrews to firmly capture the 1/4 turn sections in
the brass blocks. I'm worried the resistance might become an issue
with nearly 12 "copper connectors" joining the pieces together. I
would like to use he large 4 inch copper tubing but it seems joining
them together might be a problem, and trying to haul it assembled
just will not work as the height would be too much for interstate
bridges and city streets with cross-wires, etc.
2) It's not possible to use 2-3 inch dia. copper cable as the weight
would be too high for assembly handling.
3) Perhaps use 1 inch dia copper cable and then wind 4 of these 1
inch dia. lengths in parallel to form the 3.5 turn
primary. Handling 1 inch dia. copper cable should not be too much
of a problem for a crew working with a small crane (which we will
have onsite to erect the sec coil and attach the large toroids).
With this idea, I probably would join the 4 cables together every
1/4 turn with some solid machined copper clamps to insure even
current distribution in the primary.
I know there are some great thinkers on this list and a few good
machinists, so ideas please!! We are open to consider every idea
and try to adopt the one we think will work best.
Resonance Research Corp.