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Re: [TCML] Small tesla coil design

On 12/28/18 8:32 PM, Dirk Schmidhofer wrote:
Greetings TCML'ers!

I can't exactly declare myself a long-timer, but have been lurking the list
for several years.  I haven't built my first TC yet, but am on the verge.
I was wondering if there might be a reliable design I can sort of mass
produce for an art project I'm working on.  I've been making various art
installation contributions to Burning Man for a dozen years now, and I have
the prototype for what I call the Kosmik Kalliope (Kosmik Dust is my
Burning Man theme camp, so please pardon the awful spelling abuse).  The
Kalliope currently is a flame effect piece; please see the prototype 13
second video here:


I have a custom microprocessor that receives MIDI and switches the solenoid
valves accordingly, 12 pipes for the 12 notes of the chromatic scale (it
rolls over and plays regardless of the octave a la MOD 12 calc.).  I've
fashioned a custom igniter so I don't need pilot lights.

I am licensed by the Nevada State Fire Marshal to operate flame effects as
well as a pyrotechnics license and I do commercial stuff but my true love
is to take art to Burning Man. (o:

I've been gathering parts for awhile now (NSTs, MMC and Terry Filter parts,
etc.) and I know it is highly recommended to build a SGTC before tackling
the solid state stuff, but I've also finished building several of Eric
Goodchild's UD2.5 boards I've had laying around for awhile because
sometimes I don't work linearly (o:

My question:  (Sorry for long windedness); I would like to build 12
relatively small Tesla Coils (or 24), and was thinking they might be static
spark gap units that could be displayed either above or alongside my Kosmik
Kalliope pipes and switch them on and off reliably, like I do the flame
effects?  Not looking for massive streamers (6-12"?), but I would like them
noticed by the audience.

Is there an available design out there that might meet my intentions, or is
this just a crazy idea, whereby the things will strike my stuff and blow up
all my other electronics?? (o:  They would of course be on stands far away
from audiences.

I would like to switch them quickly but I'm not interested at this time in
actually doing the MIDI modulation; just turn them on and off, as there's
lots of other music playing already.

I have ten Allanson NSTs (12K 30mA) that are unfortunately GFI and potted,
but perhaps could use them the way a previous TCML contributor used them
with that resistor network he described?

I also have three other NSTs (nonGFI) larger and smaller.

Or perhaps MOT TCs would be the way to go?

Or a simpler solid state design whereby I could power them all off one
large power supply?

I have a modest machine shop with lathe, 2 hp CNC mill and 3D printer so
I'm not afraid of fabricating.

I've toyed with the thought of designing, but as a first-timer, I seem to
get stumped with a chicken or the egg thing as far as where do I start?

this is a way cool idea..

One thing you might be interested to know is that flames are electrically conductive, so you've got some interesting effects you can do combining flame and HV, aside from the tesla coil thing - for instance, a jacobs ladder with a flame is very interesting...

For just keying on and off, a suitable relay in the line voltage supply is probably the easiest way. I'd try a decent industrial application Solid State Relay first (because it gives you optical isolation from your MIDI equipment), but it's possible that HV RF spikes coming back on the power line might kill it. A bit of experimentation is needed.

With this you can do effects, oh, like the Bellagio fountains, turning different coils on and off in patterns, and you could probably figure out a way to change the power level for the coils too.

One other idea that's been bandied about over the years is to have an array of DC tesla coils run by rotary gaps, with different numbers of electrodes on the rotor, or running rotors at different speeds, so that the coil's audible buzz frequency is tunable in a scale. For instance, rather than all your coils buzzing at 120 Hz (typical for a static gap running off a NST), you could have a coil running at 110 Hz (A2) one running at 130.8 HZ (C3) on running at 164.8 (E3) and so on..

To make this work, you'd need a nice DC power supply to feed all the coils and a way to turn individual coils on and off - a air operated mechanical switch would work nicely.

You might also be able to figure out a way to make inverters that can drive NSTs at different line frequencies - Nothing's sacred about 60Hz, after all.

Most of the "musical coils" you see out there use solidstate drivers to accomplish this. There's a lot more complexity in a SSTC, but they do work well.

Finally, another way to fire the coils is with a triggered spark gap - that lets you fire at a specific rate (for the musical note)
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