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building my first sgtc

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Ultra7

Wed Jan 30 2008, 06:01PM

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

There is an MMC calculator on Teslamap.

Beer bottle caps are notorious for having crappy values.

ArcLight

Wed Jan 30 2008, 07:08PM

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

My first coil used a bottle cap with a MOT 4-pak. If I read correctly what you wrote, you have confused the effect of series vs. parallel when working with capacitors. If your caps are parallel as you state then the reading you got would be correct ie. one bottle measures .5 nF so 3 should be 3x or 1.5 nF. If you had 3 in series then the capacitance would be .5/3 or .166666 nF. but at 3x voltage rating.

My bottle cap consisted of two 5-gallon buckets with eight 750ml wine bottles each. Very bulky, but priced right, and it proved to be quite reliable.

Once you get your machine running, you'll want to build an MMC, but the bottle cap will serve you well as proof of concept,.

I had the same experience as Ultra7 when I got my topload too high above the top winding of the secondary ie. lots of corona and reduced arc output. I now try to keep the bottom of the topload about even with (or slightly above) the top of the secondary.

As for topload material, I just used some cheap plastic drain tile (it's what I had) with a piece of baling wire inside. I warmed the plastic in the sun and then had a friend muscle it into a ring, then I twisted the ends of the wire together to keep it in a circle. The whole thing was covered with duct tape and then aluminum tape. A piece of foil covered plywood was wedged into the center, and I had a topload. Not very pretty, but it gets the job done and is priced right.

Two second exposure of my machine with bottle cap and MOT 4-pak (using old Fujifilm camera.)

Two second exposure of same coil with CDE 942 MMC, NST, and a bit more topload (using newer Panasonic camera.)

Regards, ArcLight

RogerInOhio

Fri Feb 01 2008, 01:59AM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

Hay ArcLight, I like your wine bottle capacitor, that's petty neat. I was just thinking that if you had any corona around the bottle tops you could pour some oil in there. It would float on the top and help prevent the corona from forming.

Anyway I bet that thing looks cool when the coil is running.

Roger

ArcLight

Fri Feb 01 2008, 05:07AM

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

Hey RogerInOhio,

You are completely correct, there was corona around the neck of the bottles and it was fun/interesting to watch. I avoided using oil only because the bottle cap for me was simply proof of concept and oil would have made a bigger mess than I already had. The MOTs had plenty of power so I didn't worry about some corona leakage. I did however learn to keep the sides of the buckets clean. I once slopped some saltwater up the side of a bucket leaving a salt residue. With a lid on the bucket, the humidity got high enough that it would arc down the side of the bucket between the discharge bolt and the surface of the water. It looked like a camera flash going off inside the bucket once or twice a second. If I took the lid off it would quit, I'm kind of slow, but I finally figured out that I needed to clean the side of the bucket.

I also learned to not use stranded wire with saltwater. The saltwater capillaries up the wire and finds its way out of the bucket, leaving a pile of salt beside the bucket and corroded connectors on the side of the bucket.

I originally used polypropylene liquor bottles (starting to see an ethanol trend here) with marbles in them to keep them from floating. The poly worked better than glass for a short time, but the corona killed (perforated) them fairly quickly. In all the hours that I ran the coil I never had a glass bottle fail.

SilentPhoenix,

In reviewing this thread, I realize that I haven't seen any mention of what you're using for a sparkgap. Regardless of everything else, the sparkgap is what will make or break the performance of your coil. Without a good sparkgap your coil will never produce a decent arc.

I picked the inverse of the famed sucker gap because it doesn't suck the heat and volatile gases into the gap, but instead blows these byproducts out. This particular gap has many hours of runtime with very little erosion and virtually no fouling. When the gap runs, it hisses like an arc welder and looks like the burner on a gas range-top with hot gas plumes blowing out in every direction.

I originally used this gap for a MOT 4-pak (that would occasionally pop a 15 amp. breaker) and today use it for a 15k/60mA NST. I don't know if I will ever go to a rotary gap (at least at this power level,) because this gap is simple and has never failed to perform.

[Moderator edit: Removed double post]

Moderators, my apologies. I was responding to two different persons, hence the double post. No offense intended.

Regards, ArcLight

SilentPhoenix

Fri Feb 01 2008, 03:12PM

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

i'm kind of in the middle of all the theoratical B***S*** that i need to write for school (bleh) because for some reason they won't believe i have all the knowledge and info stored in my head :P but i'm planning on finishing the bottlecap upgrade this weekend and i'll try to post some pics.
i don't use a bucket of water for my cap, i wrap them in alufoil and tape them together, it looks pretty good and isn't very hard to transport. i also thought of putting oil on top of the salt water to prevent corona.
the SG consists basically of two screws with the heads towards eachother. i chose this design because it is easily adjustable and because i had no idea on how to adjust the copper pipe type SG that you see often...
pics of the parts will come soon.

Ultra7

Fri Feb 01 2008, 03:48PM

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

here is copy of my Spark gap.

It's one of those copper pipe ones.
My buddy had an old mini vacuum cleaner he was throwing out and when I saw it, I knew exactly what it was good for.

The 4 inch PVC pipe fits like a glove in the tunnel part of the vacuum cleaner and keeps the whole thing running cool.
Here is another pic of it half-assed mounted into the coil.

You can see I have since added 1 more electrode to increase the distance.
I measured the distance between the electrodes with this metal ruler I found in the garage. But only with the width of the ruler, I would just cram it in there between the pieces of pipe and tighten down the nuts on the outside and then pull out the ruler.

Coronafix

Fri Feb 01 2008, 09:57PM

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

Hey Ultra, 2 things I see in your pic.
You don't seem to have a safety gap, and the wires coming off of the NST secondary don't need to
be anywhere near that big. It will only carry the NST rating current, ie 60mA or whatever you have.
The large wires are only needed in the tank circuit.
Safety gap is crucial though, I set mine once and never touched it again, never burnt an NST yet.

Ultra7

Fri Feb 01 2008, 11:49PM

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

Sorry bout that Goldsphere, those were old "Proof of concept" photos.
Here is how it looks as of today.

One of the spark gap.

and one last one of the whole thing.

SilentPhoenix

Mon Feb 04 2008, 01:04PM

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

i had the chance to make some pics and upload them...
here's the Spark Gap, i'm planning on making another one as a safety gap:

here's my capacitor:

(looks more like a suicide bomb :P)

the setup for my primary base:

(i know wood isn't a very smart idea, i'm looking around for free alternatives)

and here's the whole batch of pics&vids (there are some vids of my 8kV jacobs ladder but it needs a lot of improvements...

i hope you can give some fedback based on this so i can improve my project. the text that i wrote for my schoolproject is only available in dutch so i won't bore you with that. it's available for those who understand/care and maybe i'll write it in english too someday...

Hazmatt_(The Underdog)

Mon Feb 04 2008, 11:40PM

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

I probably would have inverted the primary the other way because what you have there is going to give you a lot of primary to secondary arcing, that is if the first secondary turn goes all the way down to the bottom of the coil form.
Now if your first secondary turn is 1-2" above that primary inner turn you could still get pri-sec arcing because the base lead is grounded and the high voltage ringdown tries to arc to ground. I have this problem when I'm playing with overcoupling because its dielectric breakdown of course.
So basically what I'm getting at is you'd want your first primary and secondary turns at equal height for the most coupling you could achieve in a SGTC.

For best performance you would want critical coupling of the coils where the secondary is adjusted so that your coupling coefficient is K = .14, but that comes much later, so don't worry about that too much. First step is sparks ^^. So just turn your coil supports around the other way, have about an inch or a little more distance between the secondary and primary inner turn, you will probably want the secondary first turn to be about an inch above the primary first turn to lower your coupling so you don't get overcoupling acring, and you'll be fine.

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