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building my first sgtc

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ArcLight

Tue Feb 05 2008, 12:07AM

Registered Member #341 Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69

SilentPhoenix,

I don't think that your sparkgap as pictured is up to the job that you've assigned it. With a ground added it would make a great safety gap, but I believe that you're going to need something to blow the ionized gases out of the gap and cool the electrodes. Otherwise it will just power arc until it melts/vaporizes.

If you have a shop vac maybe you could put the hose on the exhaust and blow it on the gap, that might get the job done. Some guys have used an air compressor, but I'm not sure that pressure is as important as volume.

On my machine, the difference between having the blower running or not is startling.

Regards, ArcLight

Coronafix

Tue Feb 05 2008, 01:12AM

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

Nice work Ultra, I see you've used the Terry filter.

SilentPhoenix, your spark gap will be fine as a safety gap, but it will decrease the efficiency
of your coil as the primary gap. The difference a good gap makes is quite astounding,
and people have been researching them for ages. The Sucker gap seems to do a good job,
I just hate having my big vacuum cleaner going at the same time as the coil, but the sparks are longer
than my static gap.

Edit: I see Arclight got in first.

SilentPhoenix

Wed Feb 06 2008, 08:00AM

Registered Member #1258 Joined: Wed Jan 23 2008, 11:52AM
Location: Haarlem, Netherlands
Posts: 20

@ hazmatt:
the setup in the pic has been altered after i re-read what ultra wrote earlier...
according to the calculations, my 1,320 nF cap would need tuning at 15 turns when i use 60 degree angle primary, if i use 300 degrees it tunes at 5-6, that's why this was the initial setup.
but as ultra pointed out, it would be easier to raise the capacitance to 8-9, that way i can keep the pri anlge at 0 and tune at turn 7-8.
you're saying that i should start out with my secondary about an inch above my primary? that's something to keep in mind when i'm putting it together!i have already placed the primary inner turn diameter two inch wider than the secondary diameter so i have 1 inch of space on all sides.

@ arclight/goldsphere:
is it possible to use this gap just for proof of concept and upgrade it later on? i have been thinking about the suckergap style but i have no idea on how to tune the distance between the electrodes... so i would need to rread some more about that.
is it an option to just put the hose of the vacuÃ¼mcleaner next to the gap? this way it will provide some airflow and quench and cool it at least a little...

thnx for all the feedback! grtz

Coronafix

Wed Feb 06 2008, 09:39AM

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

SilentPhoenix wrote ...

i have already placed the primary inner turn diameter two inch wider than the secondary diameter so i have 1 inch of space on all sides.

That's right, what Hazmatt is saying I believe is to raise the secondary an inch above the first primary turn.
I would start with first turn on secondary equal with first turn on primary and raise it if you get racing arcs, but you could start the way that Matt suggested.

SilentPhoenix wrote ...

@ arclight/goldsphere:
is it possible to use this gap just for proof of concept and upgrade it later on? i have been thinking about the suckergap style but i have no idea on how to tune the distance between the electrodes... so i would need to rread some more about that.
is it an option to just put the hose of the vacuÃ¼mcleaner next to the gap? this way it will provide some airflow and quench and cool it at least a little...

Of course it will work for proof of concept, but it would be much better to make a half decent spark gap to begin with.
Even if you drilled some holes in some timber and set about 5 or 6 bolts 1/8" apart from each other, therefore making a multiple static gap, it would be better than the current one you have.
Crucial though is the safety gap, it is the difference between life and death of your NST.

ArcLight

Wed Feb 06 2008, 10:02PM

Registered Member #341 Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69

SilentPhoenix,

I'm not confident that your gap will even work as proof of concept. Goldsphere's suggestion of multiple bolts is quite inspired for its cost/simplicity/ease of construction and is far more likely to provide your proof. But, once you have your proof, you're still going to need a real gap. I ended up with the gap that I have because after taking inventory of the junk that I had, a blower from an old microwave oven and some leftover plumbing parts from a home improvement project, it was what I could build. It's difficult to offer suggestions without knowing what stuff you have in your junk drawer or what tools you have.

The gap that Ultra7 (up thread) has is relatively straight forward to build if you have a drill, some copper tubing, some PVC, and something to move air. If you have a propane torch, a PVC "T", some copper elbows, and a shop vac/leaf blower/squirrel cage/almost anything you could easily build a sucker gap or one like mine. Either one would only take an hour or two to build and will make the difference between a few little wimpy sparks or a machine that roars.

I'm not sure what you mean when you say that you "don't know how to tune the distance between the electrodes". If you mean setting the gap opening, no problem. Just connect your gap to your NST with nothing else. Start with a very tight gap (maybe 5mm/.2",) then keep opening it up until it starts to run ragged (you'll hear it,) then close it back until it's smooth again. You may wish to close it a little bit more to just be sure (temperature variations, erosion, etc.) To set the safety gap, with just it connected to the NST, keep opening up the gap until it just won't quite arc anymore and you're good to go.

Regards, ArcLight

Hazmatt_(The Underdog)

Thu Feb 07 2008, 02:00AM

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

So you're going with a flat primary now?

It's okay to have your primary with a 60 or 30 degree pitch, or whatever you like, its just going to be an issue with overcoupling and dielectric breakdown. I even made an exponentially curved primary for fun! It looked neat but the coupling caused havoc! I had racing arcs midway up the coil, don't ask how, I don't know, heh, it just happend to be seriously overcoupled, which is what I was going for just to see what would happen.

Anyway, the idea is that if you balance the coupling and have a good spark gap like everyone is suggesting, you'll have decent performance. If you overcouple your coil or the gap is poorly constructed the performance will be poor, but a lot of this is just trial and error.

Coronafix

Thu Feb 07 2008, 03:57AM

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

By the way, coupling is just adjusted by raising or lowering the secondary.
You get racing arcs, no problem, just raise the coil until it stops.

SilentPhoenix

Thu Feb 07 2008, 04:19PM

Registered Member #1258 Joined: Wed Jan 23 2008, 11:52AM
Location: Haarlem, Netherlands
Posts: 20

yeah i'll probably go with the flat primary for now.

i meant that i don't know how to adjust the distance between the pipes in a suckergap?
but i like the sound of the multiple bolts-in-wood gap that goldsphere describes. that's pretty low cost and i can build it with the stuff i have lying around. would it be an option to make a small plexi casing (my classmate has some i think) for the gap with two openings and have my vac suck air through it? i also bought a small cutting board (the kind that my gap's mounted on) maybe i can use that for the support of the bolts instead of wood...

i have a test week in school next week so i don't know how much i can do but after that is a week of vacation so i hope to finish building then and maybe even have a first test run!
maybe i can make some movies of the gaps when they're done to show how they're running.
question: if i set my safetygap just close enough to arc when on my nst, won't it arc all the time when i connect my cap? (because it raises the power)

Ultra7

Thu Feb 07 2008, 08:28PM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

SilentPhoenix wrote ...

if i set my safetygap just close enough to arc when on my nst, won't it arc all the time when i connect my cap? (because it raises the power)

No, you want your safety gap set so it just barely doesn't fire.
Your main gaps will be set closer than your safety gap, so it will arc there instead.
Your safety gap will only fire when the main gap has saturated and can't take any more.

Alexandre

Fri Feb 08 2008, 12:45AM

Registered Member #1228 Joined: Tue Jan 15 2008, 01:08AM
Location: Curitiba, Brazil
Posts: 162

the NST with in paralels or in series?

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