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Avalanche

Sat May 27 2006, 09:29PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

This started off as just a quick 'something to do with my flyback'.

I have become totally hooked now, and I have been playing around and improving this coil all day, and plan to build it into a proper coil eventually, so I think it deserves a thread on the project board! It's my first SGTC, after building several solid state coils. I can't believe how noisy even this small coil is, how do you guys cope with large coils

fRes = Approx 1.2Mhz
Tank Cap - 5 beer bottle caps (about 5nF?)
Primary - tapped at 6 turns
Secondary dimensions - 35mm diameter, 75mm winding length.
Topload - Foil covered table tennis ball

Anyway it all started out with a single beer bottle cap, and I noticed I was getting the most output with the maximum number of primary turns, so I simply started drinking more beer and slowly adding capacitors. I am now up to 5 caps, still tapped at the furthest turn - so I think it can do more!

Coil is running from a ZVS driven flyback, and has a 2 spark spark gap (whatever that is called!)

The setup has already been through a number of revisions, and I'm on my second ZVS circuit. See below for pic of latest setup, and a video. The post I made in the 'add your tc here' thread is already out of date...

The coil is doing about 4" to air, even though it looks less on the photos

Any suggestions on how I could improve it would be most welcome

Latest Video: 1.3MB MPEG1

ragnar

Sat May 27 2006, 11:01PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Aw, he's cute, Avalanche. I saw it last night in the "Post your TC here" thread, but no sparkies =P

I reckon you could improve it by constructing a rolled cap (for size reasons, compared to the bottle cap), lying it down next to the flyback, and bolting it all down to a nice little board. Mini SGTCs just don't have the charm unless they're portable and neatly finished (like your other coils

)

Are you losing much in the way of corona off your bottles? If so, for efficiency, perhaps you'd consider some corona rings.. =)

Wow, just saw the video - there's a lot of corona there! How does he perform with a single breakout point on the topload?

Marko

Sat May 27 2006, 11:32PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

My first TC ever was too a miniature SGTC.

It was powered by NE555 ignition coil driven from 12V (I didn't even have an adequate power supply), about 10kV, and it gave some 5cm sparks at maximum (but very hazy and barely visible).

Later I tried few times with flyback but I never got into something more than aligator clips and bunch of bottles on the table.

so I simply started drinking more beer and slowly adding

I hope you aren't going to build some 30nF cap this way.

Actually you don't have some special restraints in choosing tank cap since you are charging with DC.

For more bang energy you can simply set the gap more loosely so the cap charges to higher voltage.

Maybe you can later play with resonant charging, different cap types (MMC; rolled) etc.

The coil is doing about 4" to air, even though it looks less on the photos

It looks much less than that, it seems like 10cm arc would probably engulf secondary completely

For what I can tell sparks seem to be about 5-6cm long in the movies.

One thing I was dissapointed with samll SGTC's is that they seem to be quite poor EF transmitters. I could weakly light up neon bulb only by drawing an arc with it.

Resonators also didn't respond at all.

Mike

Sun May 28 2006, 02:04AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Awesome coil Avalanche, it is a beauty!
The primary and secondary together look great, and a cool arc picture. For a new cap may I suggest Polystyrene Plate capacitors

I have been hoping someone would test em on a SGTC, and these might just be what you need.
Well good job!
-Mike

Avalanche

Sun May 28 2006, 10:54AM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Thanks for the comments

wrote ...
I reckon you could improve it by constructing a rolled cap (for size reasons, compared to the bottle cap), lying it down next to the flyback, and bolting it all down to a nice little board.

wrote ...
For a new cap may I suggest Polystyrene Plate capacitors

Yes good suggestions for new capacitors. I will experiment with a rolled cap and plate caps (or similar), and post my results. The setup is very lossy, if I disconnect the coil and power up the flyback, everything hisses and it stinks of corona. I guess eliminating that would help! Might try an MMC also, I have some small caps but I'm not sure on their voltage.

wrote ...
I hope you aren't going to build some 30nF cap this way.

lol, I'm getting close. I'd better sober up before I wind the new secondary for that cap

wrote ...
How does he perform with a single breakout point on the topload?

Here's a few new pics, first up is a screw as a breakout point. The behaviour of this coil is totally different to any of my sstcs! The corona looks like it is liquid flowing off the top of the screw

The third photo is interesting, if you have a look at the full size photo you can see arcing between turns on the secondary! The voltage rise must be huge, it must take at least 1kv to do that?

1148813571 103 FT10264 Composite Blue Medium

1148813571 103 FT10264 Arc Between Turns

Marko

Sun May 28 2006, 11:43AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I like your streamers, especially in second pic. Mine were a lot thinner and hazy, probably because coil wasn't tuned properly.

I did also figure out that bottle caps are especially bad for low power because of corona losses.

It seems that you are already overpowering the coil since racing sparks are occuring.
You can maybe try bigger topload to prevent this.

Self Defenestrate

Sun May 28 2006, 03:04PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

For the between turn arcing, I would suggest finding some acrylic tube to fit over the secondary, sealing it in with hot glue, and filling the space inbetween with oil. I had beaten the secondary on my 1kv coil until it had no output from arcing to itself, but the oil fixed it up and it works great now. Your topload reminds me of TDU's 18 inch coil, but without four mot's worth of power behind it.

Marko

Sun May 28 2006, 03:11PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

would suggest finding some acrylic tube to fit over the secondary, sealing it in with hot glue, and filling the space inbetween with oil.

Noo

It would ruin the nice coil, and especially oil would be very messy, maybe poliester or epoxy would do if it's really necessary.

Since coil is not CW it will hardly set itself on fire or damage the top of secondary severely.

you can give it few more coats of poliurethane if you are really afraid of blowing it up.

Avalanche

Sun May 28 2006, 03:47PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Yeah it doesn't appear to be damaging the coil, so I will probably leave it for now.

I've been constructing roll up caps anyway, but I am not having much luck

The caps themselves are working really well, it's just that I don't have a clue as to their capacitance.

The one I'm using at the moment is about the size of an AA cell, and is made from 2 strips of aluminium foil, and 2 strips of overhead projector transparency. It seems to be tuned to the coil, in that altering the tapping on either way decreases output, but the output itself is anly about half an inch

I guess the coil is probably tuned to a harmonic.

At a very rough estimate, how would these caps compare to beer bottle caps in terms of capacitance? I get the feeling this cap is probably about 10nF maybe?

I made a really huge roll up cap, and the spark gap sounded like a machine gun with it connected

It must have been about 100nF

Once I sort out a capacitor I will start building this coil onto a base.

Steve Ward

Sun May 28 2006, 06:23PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

If you know the thickness of the plastic, and its dielectric constant (you can look it up), then you can figure out the capacitance.

C = (K*Eo*A*N)/d

K is the dielectric constant (around 2.0 for PP/PE).
Eo is the permittivity of air = 8.85 x 10-12 F/m
A is the plate area
d is the thickness of the dielectric.
N is the number of plates - 1 (so for a rolled cap, N = 1). Or the number of dielectric "plates", if you like.

Hope that helps.

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