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Poor SGTC results Problem

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GimpyJoe

Fri Jun 23 2006, 06:38PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Also try a primary with WAY more turns. I recommend going to Home Depot or some similar store and buying two rolls of spring bronze weather stripping and two rolls of 1/4" foam adhesive weather stripping tape. All of these should be seventeen feet long each, at least that's what they carry at my store. Solder the ends of the two pieces of bronze weather stripping together to form one long strip, then remove the adhesive backing from the foam strips and stick them along the length of one side of the bronze. Wind this into a spiral and secure it with hot glue. Voila! A perfect bronze primary with 1/4" turn spacing. To tap it, use a flat piece of copper wedged between the bronze and the foam. While you're at it, make a bigger secondary. 3" diameter by 18" should be fine.
Your bottle caps will work fine with your MOT's, but you're going to have an insanely high break rate. To compensate you need excellent gap cooling. I like the inside-out sucker gap design from Greg Hunter's Hot Streamer site. Use the biggest vacuum or blower you can find.
With all those primary turns you'll be able to put a decent sized topload on your coil. Make a 4" aluminum duct toroid maybe 15"-18" diameter and use a break point.
With these improvements I wouldn't be surprised to see you get 18"-24" sparks at least from your MOT's and bottle caps.

Terry Fritz

Fri Jun 23 2006, 09:31PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

Let's see what we have now...

I have a 1 3/4 " X 6.5" Secondary, 26 Gauge wire, 4 Beer Bottle Capacitors

The secondary has 377 turns of wire on it. The inductance is 1.49mH.

I'll guess that the top terminal is about 2.5 x 7 inches so the resonant frequency is 1.35MHz.

You have six bottles (the picture looks like six) at say 800pF each so 4.8nF or primary capacitance. Thus you need a primary coil of 2.89uH. If your primary is 3 inches ID with a pitch of 0.5 inches, it should tune at about 4.5 turns. The wiring from the caps and gap will lower that some to maybe 4 turns.

You caps seem to be made fairly well so that is probably not a big problem.

If you can fire the coil 120 times per second at 8kV, it should put out 7.3 inch sparks "theoretically".

The very high frequency will add losses especially in any ferromagnetic metals and aluminum has poor skin depth properties. You are loosing some there for sure. Copper only conducts in the outer 0.002 inches at that frequency. Steel might as well be zero...

But I think it should be able to do 3,4...5 inch sparks. If you can fire faster at say 240...480 BPS that will help some. That should be the case anyway since two voltage doubled MOTs will charge the little cap very fast.

I'll make a new spark gap, and I'm going to try and tune the LC Circuit with an O-scope/Sig. Gen. this weekend...

That sounds like a good plan!

I have a top load suitable but I thought since with out a topload the max arc was about an inch, what would a larger topload do...I'll try it

You always want a topload! The one you have should be fine.

Fiddle with the gap and tuning and it should work.

Hope this helps

Your first coil is 10,000 times better than "my" first coil was

Cheers,

Terry

Michael W.

Fri Jun 23 2006, 11:14PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

UPDATE: 3 inch arcs to screw driver; Door Knob Topload, 5 bottle Capacitors, Eyeball Tuning, Flyback Power Supply and to top it off, a rotary Spark gap. I tried a gap using 4 brass nuts as suggested, but the rotary one gave 2X the results, hopefully I can pump more out of this hodgepodged mess....

Marko

Fri Jun 23 2006, 11:37PM

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

I think now you just need a much bigger topload.
Make yourself a nice sphere or toroid, that one from avatar looks good.

Rotary is an overkill for coil of this size but you'l have a good quenching at least.
Can you post a pic of it?

Michael W.

Sat Jun 24 2006, 12:35AM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

I've tried a 3X7" and a 3X10" Toroid with horrible results, >1" arcs opposed to the 3 inch arcs I get off of a doorknob. My spark gap is just thrown together....:

Hazmatt_(The Underdog)

Sat Jun 24 2006, 04:43AM

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

thats because you have to retune when you put a topload on top!

when in tune with your topload, you should have 4-5" sparks if you have 3" sparks with a free terminal.

My system gives me about 2' without topload and almost 4' with, but its all in tune. I also use a rotary with safety gapping. The system power is small in comparison to what you're using if you can believe that! I'm using a 12/60 NST and 16nF (should be 18nF from my calculations and simulation), and that gives me a 4' spark. So I would strongly suggest go back and do some calculations and some work insted of throwing everything together.

Steve Ward

Sat Jun 24 2006, 06:22AM

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

Well, a topload can in fact hurt performance on very small coils if the topload is too big. Remember, energy is conserved, so you can only charge that toroid so much, and if its a bigger C, then V will be lower. Bigger coils have enough power to form streamers, so top voltage isnt as useful as having more capacitance there, but on little coils that can hardly break out, you dont want to load it down too far (or else the voltage is too low to get good streamers forming). I would think a 2"x8" toroid or maybe a 4" sphere would be about the right size for this coil.

Terry Fritz

Sat Jun 24 2006, 11:17PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Steve brings up a good point! Let's figure it out...

The top terminal, and all, capacitance is 9.33pF. The primary is 4.8nF at 8kV.

So the primary energy is 1/2 x C x V^2 or 0.1536 joules.

Only 1/2 that will make it to the secondary with a high frequqncy spark gap coil so:

1/2 x 0.1536 = 1/2 x 9.33pF x V^2 V = 128kV

A 2.5 inch diameter top terminal should break out at 95kV. So if the losses are a little higher than I calculate here (easily), it might not have enough voltage to break out. But simply using a pin or sharp point on the toroid will fix that.

So if it is not making sparks with the toroid, add a sharp needle or pin preakout point to insure the sparks can get out. Also, the primary will certainly have to be retuned for any change in the top terminal. Having the toroid on the top, should make better sparks than no toroid at all. But your 3 inches off the door knob is pretty good!! There is a saying, "if it works, don't fix it" :o)

Cheers,

Terry

Michael W.

Sun Jun 25 2006, 01:01AM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

Now that its working, what is a reasonable expectation of when I can stop hoping for longer arcs? Right now I'm using a flyback to power, rotary gap and 6.5 Salt water Caps and I can get a "Good" 3.5-4 inches...Primarys tapped at 5 which seems to get the best results.

...

Sun Jun 25 2006, 01:54AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

how much power are you running into the flyback? There is sorta a standard formula of spark length=[square root (power in)] *1.2

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