Re: true solid state Tesla coil >> with NE555!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Pyrotrons-at-aol-dot-com>

Hi all.

Thank you Rick, Tom, and others for the comments on our website. We've put 
quite a bit of effort into it, and we're always happy to hear that someone 
has found it beneficial.

Vladi: I have a good, solid design going for a NE555 powered SSTC, driving a 
300kHz secondary coil on a harmonic. I am getting a 1" discharge to air with 
it, could be just what you're looking for. At www.hvguy-dot-com, at the top in 
purple font, click on "FETdriver.html".  YES, this circuit was designed for 
driving flyback transformers, but it will also drive a primary coil in the 
conventional "Tesla Coil" setup. Inefficiently, yes, but it does work. Real 
live SSTC arcs, 330kHz of pure sine wave HVRF.

Although I will add, I have gotten 4" of foggy blue corona (no typo = four 
inches) off of a flyback with this thing. Strike an arc out to 2.5" or so, 
and draw it out to a little more. It pegs the needle on a 30kVDC HV probe. 
Flyback arcs are so much different than SSTC arcs though ; )

If you can get the 555 to work well at 300kHz, more power to you, literally. 
You'll get a significant amount more output, maybe 2" arcs to air, if you 
drive the secondary coil at its fundamental frequency. (which is what you 
would normally calculate using the "Wheeler" inductance and Medhurst 
capacitance formulae....)

I will say again, the circuit at FETdriver.html was designed by me to run a 
flyback transformer. Not a SSTC. But it will work to drive a real SSTC, with 
a low frequency secondary, driven on a harmonic.

The secondary coil I'm using is 2" O.D. x 12" long, wound with #37 gauge to 
get the frequency down as low as possible. The primary is 25 helically wound 
turns of #20, the coilform is PVC a little bigger than the secondary so it 
will fit inside. Simply connect one wire from the MOSFET drain to the primary 
coil, the other side of that goes to V+ of the external supply. Basically 
swap the flyback out with the Tesla coil..............!! Ground the base of 
the secondary.

I can get 1.5" arcs to my finger or a screwdriver or a grounded wire (lol), 
and 1" streamers to air. Switching 60V of filtered DC into the primary, at 
the secondary coils' fifth harmonic, via a single IRF840 MOSFET. Beautiful 
plasma displays in a 6" lightbulb, if tuned to a low harmonic (fifth or so), 
the plasma comes off the filament in 2 thick flames. If detuned to just above 
audio frequencies, the 2 thick flames turn into about 20 thin writhing deep 
violet colored streamers that flicker all over the place. Very interesting.

Because I have no $$ to buy decent protection diodes, the MOSFET usually dies 
quickly from voltage spikes at 60V input.

However, I put six 68V MOV's (from Aron,,,,,thanks again man,,,,,) in series, 
and put this string across the primary coil to clamp the voltage spikes. Now, 
I can run the little setup indefinately at 40VDC input. .5" arcs to 
conductive objects, and a little less to air (streamers). I'm sure I could 
run it at a higher input voltage, but the MOV's start getting warm at 60V 
input. Wow, I need some diodes..........................so I can reliably run 
the MOSFET at what it's rated current-wise.....)

>> As for the higher power SSTC stuff <<<
My best bud Aron Koscho has had a lot of success with a design originating 
from Richie Burnett of the UK. There is a LOT of excellent SS theory on his 
page, schematics, everything you need to know.

Richie's site is at:

www.richieburnett.co.uk

Aron built his design for a half-bridge MOSFET driven coil and has had good 
success. I just got off the phone with Aron, he mentioned it took 33 dead 
IRF840 MOSFET's to get there, however ; ) Richie does clearly state that the 
half-bridge design could use some improvement on the reliability side.

Happy SSTC'ing. Power electronics and Tesla coils together, it's fascinating 
stuff.

Justin Hays
KC5PNP
Email: pyrotrons-at-aol-dot-com
Website: www.hvguy-dot-com