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Poor SGTC results Problem

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Michael W.

Thu Jun 22 2006, 04:31PM

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

I have a (semi first) tesla coil with very poor arc production, max 1 inch. I have a 1 3/4 " X 6.5" Secondary, 26 Gauge wire, 4 Beer Bottle Capacitors, A dual mot power supply (and tried a flyback, same results) and the primary tapped at about 3 turns (I've moved it around, it only gets worse) What Could Possibly be wrong? I'm becoming very tempted to throw it all out...

Nik

Thu Jun 22 2006, 04:47PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Try raising the primary a bit, it will change the coupleing and could help.

Michael W.

Thu Jun 22 2006, 05:01PM

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

I tried that and it increased the output a bit but not anything substantial....

Terry Fritz

Thu Jun 22 2006, 06:48PM

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

Hi,

I think I have heard of this type of problem before

Yeah!! like hundreds of times!!! (literally)...

There are two problems.

First and biggest is that the resonant frequency of the secondary coil and top load does not match the resonant frequency of the primary coil and cap. That is 80% of the problem. Having the primary and secondary matched to the same frequency is "important"!! Otherwise the coil is a space heater.

There are many Tesla coil design programs out there and lists of formulas:

I would be happy to work the numbers for you so you can see how to do it. Let me know, and I can do it latter. I should just make a web page on this...

Parts of the above problem but a problem too is that beer bottle are far better for beer than caps. Modern MMC type polypropylene caps will perform vastly better. But for now, fix the tuning. Bottle caps like yours are about 800pF each.

I assume you are putting the caps in salt water too when you run it. If you run it out of water as in you picture, that is another problem

Cheers,

Terry

Marko

Thu Jun 22 2006, 07:58PM

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

How's your spark-gap?

Single stage gaps usually quench poorly even on small power levels, and you get more of arcing than regular banging there.

Try something simple like nut gap (with flyback of course, you don't need 3kW for this one)

Try using a topload, maybe a chrismas ball wrapped in foil or something. SGTC's generaly don't do well without a topload.

I assume you are putting the caps in salt water too when you run it. If you run it out of water as in you picture, that is another problem

If you look closer bottles are wrapped in foil and then with plastic tape around.

Hazmatt_(The Underdog)

Fri Jun 23 2006, 12:00AM

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

You will also notice improved performance with a somewhat large sheet attached to the RF return from the secondary. This adds some capacitence referenced to the secondary, which helps control your frequency. For my ~700W coil I used a 4' x 4' with pretty good results, but I would think you could get away with a 1'x 1' or 2' x 2' sheet no problem.

Michael W.

Fri Jun 23 2006, 12:47AM

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

I actually have "RF Ground" made of Coiled chicken wire for that part, but I did suspect the fact thats its horribly out of resonance. How would I go about Transformer/Capacitor matching with bottle caps? and then taking on the daunting task of trying to tune the primary? (I do have a Func. Generator and an O-Scope)...

Marko

Fri Jun 23 2006, 01:21AM

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

Use wintesla to calculate your coil, you'l usually be about the range but tuning is best done by trial-and-error.

You can use mains ground for coil of such size, and it is necessary.

Topload is also going to pump the performance up.

Spark gap is pretty important thing but you said nothing about it.
Give some more info about the coil.

Desmogod

Fri Jun 23 2006, 01:30AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

Yeah, make sure you ground the coil properly as stated, I would also say that it's way out of tune, as you are only tapped on the second turn of your primary.
You also might not have enough capacitance in there.
Can you measure the C of your cap at all?
Definately use wintesla and go from there. Can you post specs? Secondary specs? C, spark gap etc etc?

Michael W.

Fri Jun 23 2006, 01:58AM

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

Secondary Specs are as previously stated : 1 3/4 " X 6.5" Secondary, 26 Gauge wire. For a spark gap I've tried many variations; Pointed Electrodes, Pipes, nuts etc. No Change. I've always wondered about the Capacitance though. For two MOT's would 4-5 bottles be enough? I've tried trial by error tunning and at about 3 turns I get the best performance but its still only like 1 inch arcs.

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