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My First SGTC project

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Kristian

Wed Apr 18 2007, 12:23AM

Registered Member #611 Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79

Hey all,

I have been working on a SGTC project. My first, in fact. I just thought I would list what I have and show you guys what I have done so far.

The coil will be powered by two 15,000 volt 30mA neon sign transformers.

Transformers
Transformer Plate

The safety gap is two solid brass cabinet knobs. I replaced the bolts with longer brass ones and put them through a piece of 1/4 inch copper tube. This was then mounted to HV stand-offs via 1/4 inch mechanical lugs. Each electrode has about a half inch of travel distance for adjustment. In the final installation, the center electrode will be replaced by a 5/8 inch brass ball. Notice that the heads of the bolts needed to be ground almost off to allow clearance for the copper tubes and the lugs where ground down some as well.

Safety Gap
Gap Detail

The MMC is a single string of 10 Cornell-Dubillier 942C20P15K-F capacitors. The caps are rated at 2000V .15uF each. I know what some of you are thinking, and to be honest, I'm thinking the same thing, the voltage is too low. I searched out info on these caps. I have been assured by people with much experience with these caps that they are nearly indestructible and that this MMC will out live my coil. We will see. I bought two extra caps, just in case, and I can buy more in quantity, if need be.

MMC
TopView
BottomView

The main spark gap will be a multiple electrode, cylinder style gap. I have cut, cleaned and drilled seven 1-1/2 inch diameter x 3 inch copper tube electrodes. I would have liked to go with more electrodes at a smaller diameter, but with the fact that I had a 4 foot length of 1-1/2 inch copper left over from my home distilling project from years ago, and the price of copper these days, I decided to go with what I had on hand.

Gap Electrodes

I purchased a 6 inch diameter PVC coupler to mount them in. I also bought a fan for quenching the gaps and cooling the electrodes.

Coupler and Fan

That's as far as I got with the gap. I think I might have to find something else to mount the electrodes in. The wall of the coupler is fatter in the middle inside and out. I hope that makes sense. I am having a hell of a time figuring out how to drill this thing. I think it might be easier for me to source a new piece of pipe with straight walls than to try to accurately drill this thing with a cordless hand drill.

The control box is in the works. It contains a 0-140 volt variac fused at 10 amps, a dimmer style switch for a ceiling fan fused at 5 amps and a 120 volt through off the main switch. It has a voltmeter that is switchable between the two variable outputs. I also incorporated a florescent "under cabinet" light that goes on and illuminates the face of the panel when the power switch is thrown (not installed yet). It also contains a 30 amp RFI filter and a 120 vac 65cfm muffin fan to keep it cool.

Control Front
Back
Control Schematic

The box is made from some left over scrap MDF board I had and the front panel is made from a cheap cutting board. It looks a little rough right now, but I think after a couple coats of paint it will look decent. I left space on the panel for an ammeter and a safety switch of some sort. I have not acquired those two items yet. The wiring is going very slowly. I'm not very good at soldering, yet. I'm not too happy with the way it is turning out and I will probably redo the whole thing in the future.

I bought a 6lb spool of 22 gage wire from a local motor repair shop and I have ordered a 6 inch x 36 inch acrylic tube for the secondary form. It should arrive in the mail this week. I have a 50ft roll of 1/4 inch od copper tubing for the primary coil.

I also have a 3ft x 8 ft piece of 1/2 inch HDPE sitting at a friend's house I have yet to pick up. It is a used cutting board from a market. I don't know if I will be able to get it cleaned and sanded smooth enough to be acceptable by my standards to use for the stand and stand offs. If not, I will have to find other options.

I still have to buy stuff for the NTS filter and the toroid.

Thats the project so far. I hope to have it up and running by the end of May. Any comments or criticisms would be appreciated. I will update this post once I have the construction complete.

*Update*

Its been awhile since I have updated this, so I thought I would put up a few more pictures of what I've gotten done since I made the original post. I've finally finished the primary, secondary and topload. I also finished the primary spark gap and made a Terry filter. Its starting to look like a coil. All the components are complete. I just need to build a stand to mount everything to and wire it up.

The spark gap was a challenge. I drilled 1/4" holes in the copper tubes on a drill press and drilled 5/16" holes in the coupler with a cordless drill. The electrodes are held in place with 1/4" brass bolts. The gaps took three days to set by hand and are four hundredths of an inch between each electrode, give or take a couple thousandth of an inch. Blade style spark plug gappers were used to set the gaps and each nut on each bolt was tightened and loosened at least a hundred times by hand to get it set. What a hassle.

I bought the components for the Terry filter as a package off ebay, grabbed a board from Radio shack, and mounted the whole thing to a cutting board along with the safety gap.

I put the 6" acrylic form and the 22 gauge on a shelf until I get some practice winding. I don't want to mess it up after spending that much for the secondary materials. I scrounged some stuff for cheap or free so I wouldn't be too upset by mistakes made while taking the trial and error approach to learning how to wind a coil.

The secondary ended up 19.75" of 26 gauge wire on 4" PVC form. I made press fit end caps out of 1/2" plywood discs and drilled 1/4" holes in there centers. The turning rig went through a few design phases until I finally got it to work right. Here's how it turned out. Notice the finished control box in the picture as well.

The primary is wound on lexan stand offs and mounted to a 30" diameter disk cut from the big old cutting board my friend gave to me. The stand offs are drilled and tapped and held in place with nylon screws. The caps across the tops of the stand offs are epoxied down. Turned out pretty good.

The topload is two stacked toroids made from flexi duct wrapped around a flower pot. The pot was covered with aluminum tape and cut down for hight. The toroids are 4.5" minor 16.75" major on top of 3.25" minor 14"major. Here is the primary, secondary and toroid components all together.

Just to satisfy the itch, I broke out the Jacob's ladder and hooked up the transformers. I took a pic with the shudder open for a few seconds.

Thats where I'm at. Hopefully the next update will include some sparks being produced from the coil instead of the Jacob's ladder.

Vaxian

Wed Apr 18 2007, 03:31AM

Registered Member #635 Joined: Tue Apr 10 2007, 01:56AM
Location:
Posts: 85

I am very impressed you are spending this much time and effort on your first SGTC!

I took the time to look at most of your pix and it looks like you are well on your way to having a very nice setup!

My first coil was a bodged together mess but it worked.

I await first light with interest.

Good job!

Coronafix

Wed Apr 18 2007, 03:56AM

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

Excellent looking work!
Keep it up.
Someone here talked about coating their mdf
with aquadere before painting it, otherwise it just
absorbs too much paint, might help you.
Look forward to seeing the primary and secondary.

Kristian

Fri Jun 29 2007, 02:40AM

Registered Member #611 Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79

I updated the first post with my progress so far.

Kristian

Sun Aug 05 2007, 03:17AM

Registered Member #611 Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79

First light was a tremendous success. I threw the wiring together with 8 gauge with the components on a pair of saw horses. I guessed 12 1/2 turns tapped and I was almost dead on. I found the sweet spot at about 12 1/4. The very first run was 2 gaps for .08" and it started firing the gap at about 30 volts on the variac. I got 6" arcs to ground from the break out as soon as the gap started firing. After about an hour of tuning and slowly ramping up the voltage, I maxed out the gap and the voltage for 32" strikes to grounded rod. Without the break out there was up to 8 streamers at a time, ranging from 18" to 30". There was no sign of trouble at all. After a couple of 1.5 - 2 minute runs, everything, including the main gap, stayed cool to the touch except the power resistors, which were slightly warm. There was no arcing except where there should be.

Ill be on vacation for the next few days. I'll post some pics and vids when I get back early next week.

GimpyJoe

Sun Aug 05 2007, 08:34AM

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

:)
great job! I wish I had taken that approach with my first coil instead of throwing things together.
Have you considered building a synchronous rotary gap?

Sulaiman

Sun Aug 05 2007, 09:35AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Congratulations!

Looking really good, great work.

Kristian

Tue Aug 07 2007, 06:44PM

Registered Member #611 Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79

Funky wrote ...

:)
great job! I wish I had taken that approach with my first coil instead of throwing things together.
Have you considered building a synchronous rotary gap?

I have considered a synchronous gap. I have 6 old electric motors ranging from 1/8th horse to 1/2 horse. They are from the 50's and early 60's. They all work but need to be cleaned up inside and out. None of them are sync, but I have heard that they can be modified. I was going to investigate that mod process once I tear them apart and get them cleaned up. Just one more thing on the projects list that I don't know when I'll get around to doing.

For this coil, I still need to make a stand, mount the components, and I'm kicking around the idea of using 1/4" copper tube to "wire" it up, instead of the 8 gauge. I would also like to rewind the secondary. I got shorted on the wire I bought for this coil and came up a few inches shorter than I was shooting for. It also took a couple of diggers when the first winding rig I made failed horribly. Then, I put about 10 coats of poly on it and I still couldn't get it smooth, so I sprayed it with some acrylic and the whole damn thing bubbled and peeled. Then the lead to the top load broke and I had to solder it back on. Hey, it was a learning experience, I think I got it figured out now. I bought a couple pounds of 26 gauge and I just need to pick up another 4" tube and get to it.

I'm also working on getting materials together for an asynchronous gap DC coil. So far I have a 6" x 36" acrylic form, about six pounds of heavy insulated 22 gauge I bought from a local motor repair shop, 8' of 6" dia. aluminum duct for the top load, a couple of angle grinders to choose from for the gap, and the MOT's, caps and diodes from 12 microwaves to build a power supply from. Also I'm installing an 240V 100 amp breaker in the garage to run the thing on. I have the breaker, I just need to get enough wire to make it from the main box to the garage. This project definitely won't be done any time soon, maybe by next summer, maybe.

Hazmatt_(The Underdog)

Tue Aug 07 2007, 06:57PM

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

woah...hold on a sec. I've been investigating the wire gauge situation with a spread sheet calculator and for a 4" coil form dont go with less then 24 gauge. The losses/ unit inductance get higher after 24 and the optimum is about 22 or 23 AWG with a 4-5 H/D ratio.

For 6" form you're going to need 21 or 20 AWG for a 5:1 ratio, but don't go over 5:1 because the losses really start adding up. And if you're going with CW I would probably lean toward 18 AWG if you're planning on pumping a lot of power through it >2KW.

Anyway..that's what my calculator tells me.

Kristian

Wed Aug 08 2007, 06:40PM

Registered Member #611 Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79

I've took some video of the coil and uploaded it to youtube.

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