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Small spark gap TC question

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Josh

Wed Apr 20 2011, 09:21PM

Registered Member #938 Joined: Sat Aug 04 2007, 05:39AM
Location: Honokaa,HI,USA
Posts: 65

I'd like to power a small tesla coil with a modern flyback transformer.
I can pull 1.5 arcs from the flyback.
The arcs seem rather intense...
Roughly speaking what specifications should I use for my primary and secondary coil?
I realize it won't be precise, however I just want to get some form of results.

quicksilver

Thu Apr 21 2011, 04:41PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

It would be fairly impossible to respond to the question because "roughly" engineered TC are actually close and require tuning. But to START building one, certain issues need to be fairly precise. The length of an arc gives very little indication of what it is. Is the LOPT unit AC or DC? The type of energy has a bearing on topology. You would need to know with fair accuracy what voltage and current you are beginning with. So even rough work HAS to have specifics.
That is one very good reason to begin with a NST rather than a LOPT (flyback) - you'll KNOW what voltage and current you're starting with! Without those bear minimums everything else is an exercise in futility.

Please take a look at the JAVATC web page. That will give you wonderful examples of what information is needed to start. it is a computational page that calculates what length, diameter, etc of coils are needed but it also has to have some INPUT. This will clue you in on what's vital to starting on a TC.

Many people HAVE made effective coils with a LOPT! But they had means of determining the voltage and current. To simplify this, many beginners get a NST because it has that information reliably supplied & it's at a level that MANY coils are built. Meaning that you will not be required to build a MICRO secondary with substantially thin coil wire or design a spark-gap that is very tough to adjust becasue it would need to be within a few 10,000th of an inch, etc......as would a TC built with a LOPT as a starting point.

So make life easier on yourself and begin with a power supply whose parameters are known to you! It will save time, headaches, & some guesswork out of the construction. Most people here are happy to help but you must have actual numeric data as a starting point.
If you have some concerns about safety & that is one of the reasons for using the LOPT; it makes more sense to take time and learn specific aspects of keeping yourself safe so you can explore other areas in the future. If it's a question of money; if you look for them, NST's are equally available as flyback units. Either way, starting with a small NST will make this a great deal easier & fun.

Josh

Fri Apr 22 2011, 02:53AM

Registered Member #938 Joined: Sat Aug 04 2007, 05:39AM
Location: Honokaa,HI,USA
Posts: 65

Thank you very much for you input regarding my question,
and helping me avoid the headaches of using a LOPT
I understand what you mean by needing some form of specifics.
I've never done much with electronics other then follow schematics, and I've never really appreciated or understood how specific things need to be.

I'll get a non GFCI old style NST off of ebay. Safety is a concern, I've read a decent amount regarding safety(the primary can be deadly, proper grounding, etc) and tesla coils over the years of wanting to build one but not getting around to it.
My primary reason for using a LOPT is because I have it on hand, although the idea of a small tesla coil did interest me to a certain extent.

Ash Small

Fri Apr 22 2011, 11:05AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

What you want to do should be do-able, using a home-made capacitor, a non-suppressed automotive spark plug, a length of suppressed automotive ignition lead as an HV resistor, and an effervescent vitamin C tablet tube (with the paint/ink scrubbed off) as a coil former (Polypropelene).

I'm planning to try this once I get another unsupressed spark plug, not sure what I'll use as a topload though, but this should work with a modern DC flyback.

I don't think I'm talking complete bo**ocks, can anyone else comment?

(I think this would be the simplest/easiest/cheapest way to build a small SGTC)

quicksilver

Fri Apr 22 2011, 05:14PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Home-made items are a very good & workable alternative. A great deal depends on what you want the final result to be...
Cost is a universal factor that may rest on what level of design parameters, "looks", and elements of the finished product [if they are something that are valued]. A transformer from any source may lead to a beautiful enclosed coil with a turned top-load, enclosed with high grade wood or well-engineered acrylic; pushing the several hundred dollar / pound mark or he could work with surplus and home-made items keeping the price nearly free.
If the TC would be a display item, the likelihood will be that some money will be spent. if it's simply a hobby of engineering one for the first time, the proposal of automotive parts could actually keep it in the 'nearly free" category. To some, the looks of the finished product have a strong appeal.
Having purposely built one as an example of a "free" TC I can attest that the criteria for "looks" rests with the creativity of the builder & his ability to take time and effort to clean up any less-than-clean workmanship. It certainly is possible to make a nice looking one for free.

From a standpoint of simplicity; I've found that getting all my parts together and having my design working was the best way to go since then if I had the money & time I could then make it as pretty as those variables would allow. It seems automotive items could be the cheapest way to go; unless a source is found for NST's (as they can often be free or nearly so). The measurement issue with an automotive coil may still exist (depending on input) a HV probe may still be needed. Perhaps another way to go would be to simply study the various designs of TC. The AC/DC topology issues would need to be addressed & having all the background may help a great deal in decision making.

One thing I have not tried was using an old Model T Ford coil. From my understanding they have some unique properties & are very strong.
Just playing the "Devil's Advocate" it might be possible to have all the needed solid state parts from a free or nearly free source to make that an option.
I think a great deal of study helps trim the time and work-load in the end.

One issue with a top-load I learned early on was that a toroid will allow sparks to travel horizontally & that's a real plus. Toroids are tougher to make (& look pretty). Spheres often will have their output moving vertically (& often down to the secondary & beyond). They are easy to find but shielding is a consideration I have come to expect if I use one.

Josh

Fri Apr 22 2011, 09:36PM

Registered Member #938 Joined: Sat Aug 04 2007, 05:39AM
Location: Honokaa,HI,USA
Posts: 65

I do like enjoy nice looking things.
It's always a tossup between nice looking and function for many things I'm into.
Currently I have $1400 into a reef setup,
it's not pretty(diy stand, mh light retrofit, lots of hang on back equipment), however the fish and coral love it(it works well).
I've gained enough confidence, experience, and desire that I want to do a tank 3 times the size that will look nice, while not costing a whole lot of money.
Well the cheap is relative to my current experiment tank that I've had for 3 or so years

I'm thinking I'll get myself a $25 NST from ebay,
build a decent tesla coil then go for something made from cast acrylic that looks good and works. Then perhaps a SSTC or better yet an audio modulated one?
Who knows....

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