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Sulaiman's new Tesla Coil

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LAN_403

Sulaiman

Wed May 13 2009, 10:04AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

A few years ago when I was 'playing' with Tesla Coils
my son & daughter asked me what I'd like for a father's day present.
I asked for a couple of hemispherical stainless steel salad bowls from Ikea as a topload.
The idea came from other coilers. I never got the bowls (useless kids)
Yesterday my daughter whilst in Ikea saw the bowls, and bought two.
So now I have two 28 cm bowls

and I'm sort of 'obliged' to make a new TC.
This will be my last.

I intend to make it
A) Pack-away-able and get-out-and-run-able.
B) 12 Vdc powered for 'safety'
C) SGTC - some kind of 12 Vdc to kilovolts dc, to power a conventional SGTC
D) SSTC - or DRSSTC 12 Vdc powered.
E) Eventually - gardening, astronomy & amateur radio are hobby priorities.

I have a reel of 0.2mm insulated copper wire ('magnet wire')

and a 5" diameter by 12.5" high acrylic tube
that will make a nice coil former for the secondary,
so the secondary will be in the 100 to 200 kHz range,
(I may aim for 137 kHz to coincide with an amateur radio band.)

My previous TC's had aluminum ducting toroids
this one will have a stainless steel sphere. (and a breakout point)
This has raised a couple of questions in my mind,
none critical but as it's my last I'd like to be sure.

Bearing in mind -
the coil will be low-powered, hopefully 12" streamers, maybe 120 W dc input.
I suspect the steel will 'dampen' the magnetic field near the top of the scondary
the top turns of the secondary apparently 'suffer' corona etc. with spherical toploads
lower frequency is better for an SSTC

Which should I go for ?
H/D = 2.5 , fully-wound for maximum turns/inductance/impedance
H/D = 2.0 , space between top turns and topload

Of course they would both work,
but which is more likely to give the best performance ?

Extreme Electronics

Tue May 26 2009, 02:41AM

Registered Member #74 Joined: Thu Feb 09 2006, 09:17AM
Location: Nottingham UK
Posts: 99

Suliman, Id go for the H/D =2.5 and no gap, Ive never had any problems with steel or Alu sucking power and the thin wire you'l need for the secondary needs protecting. Spherical torroids need to be lower to give any protection at all to the top turns compared to a torroid.

Have you seen my Joan ?

maybe give you some ideas..

12v powered 12" sparks..

Derek

Hazmatt_(The Underdog)

Tue May 26 2009, 03:16AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Inductance is everything! V = L di/dt bud! Hope to see it soon.

Coronafix

Tue May 26 2009, 03:42AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

I always use 3 or 4 turns of space winding at the top, I never get any corona off the top turns. The 3-4 turns only take up about 1/2 an inch.
You can always raise the sphere higher if you have a problem.

Killa-X

Tue May 26 2009, 04:38AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Coronafix wrote ...

I always use 3 or 4 turns of space winding at the top, I never get any corona off the top turns. The 3-4 turns only take up about 1/2 an inch.
You can always raise the sphere higher if you have a problem.

This is a bit too late now as I varnished it. But, are you saying the reason my top coil has corona leaks is because I didn't space it? This was my first coil. The last top ring of magnet coil has a lot of corona. F I had done what you said, that would fix it?

Coronafix

Tue May 26 2009, 06:09AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Perhaps. Tesla used to do it with his coils and I've always followed suit. All I'm saying is that I have never had any corona issues with this design.
You can add a small toroid at the top turn to suppress the corona as well.

Sulaiman

Tue May 26 2009, 09:01PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I like the look of 'Joan' ... just the performance level I'd like.
I'm considering
- Using up to 10x 35kV TV flyback transformers in parallel for a separate hvdc psu,
(I already have them) then a standard sgtc setup (for long noisy arcs)
- A 2 or 4 turn primary with a resonant capacitor as a cfpr (zvs) direct-drive cw sstc
(as part of yet another project)

I will probably put (almost) one turn of 10mm wide copper foil tape top and bottom for termination/connection and as a sort of corona-ring,
just need to make the end/extension-pieces for the acrylic former,
so H/D will be about 2.5....may as well use all available winding height.

Dr. Dark Current

Tue May 26 2009, 09:15PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

10 transfomers for 120W? One should be enough

Sulaiman

Wed May 27 2009, 07:59AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

One of our component suppliers (cpc.farnell.com) sold off all their crt-related stock cheaply,
so I bought a range of flyback transformers, then I bought 10 of the 'beefiest' looking type,
I also bought 13 (3 to blow up!) HOT to match. All together it was about Â£5.
So a separate project is an eht psu, 230 Vac input, 0-30 kV @ 0-10 mA.
Hopefully everything will be conservatively rated for long life, possibly a serial interface to pc etc.

This eht psu will take a while,,,,,, so initially for the sgtc version I will be using my
one tv flyback dc eht psu. Only 10W at up to 20 kV.
I need to test with fairly low bangs-per-second (guess 5 to 10 bps) to see what happens to a rectified tv flyback directly connected to the sgtc primary circuit, across the spark gap.
....will the primary voltage oscillations destroy the flyback?
.... will I need to use dc resonant charging?

I just need to make end caps for the acrylic former and the rest of the sgtc will be quick..
I already have a nice tungsten-rod spark gap, a choice of mmc caps etc...
The only reason I started this thread early is to get members opinion on
winding the secondary so that it ends at a stainless steel 'sphere'
does the s.steel 'steal' energy that could have gone to the arc?

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