Can a Tesla secondary be wound on something metal like a water heater flue pipe or such? I always see plastic, wood or cardboard tubes, but, since it is a transformer, wouldn't the metal help (and, since it's hollow, would it still be considered "air core"?)?
Just curious.
Gary S.
Hmmm... Well, after taking stock of available resources (and abilities), I'm now started on my own Tesla coil -BUT- It'll be "different". Remember, this is Cheyenne, Wyoming - parts and materials are not as readily available as everywhere else (yep, it's primative here). Sadly I can't go out and buy a roll of magnet wire, or a 6kv neon sign transformer, etc. OTOH, I do have accumulated resources of my own to draw from.
One thing that was hindering me is the thinking that certain things had to be that certain way and nothing else (even the heavy math), but I have recently realized that EVERYTHING is highly variable. For example: It does NOT take 6kv to get high v from a Tesla. When something like a Slayer Exciter can get HV from 1.5 vdc, I'm convinced just about anything (like a 1.2kv fence charger I have) can be used to excite the primary.
So, for the secondary, I have a stout 3 1/8" cardboard tube, 24" long. For wire, I have 15 lengths of approx. 22 ga. stranded (7) computer cable wire, 15 ' each: 240' when spliced. It has some pretty tough double-insulation on it. The outside burns but the inside is still impossible to strip with thumbnails.
For a primary (since I used all my Romex on the last job before I broke the screw in my wrist plate), I have no choice but to use steel baling wire (!)(?). I've been noticing that some primaries consist of no more than about eight turns of heavy wire, well spaced and thus, well insulated (sort of). I can certainly accomplish this with steel wire (especially since the fence charger can't jump very far at all).
I had asked what a metal-core primary would do - well, we'll sort of find out, huh?
For the upper load, a pair of cheap stainless steel mixing bowls, inverted one on another, held together by spring clips ought to do it.
The secondary wire I have ought to give me a coil about 19" tall. I want to make it so primary coils can be easily interchanged.
Sound like a plan? Well, that's my story and I'm stickin' with it! :D
Gary S.
It works. 240' of 15 pieces of wire spliced for a secondary, about 5 1/3 turn of 12 ga. romex (also spliced), rolled on a cardboard tobacco can (same size as a small coffee can) for a primary. The braid shield that came off the secondary wire I used (computer wire) makes a great, long ground wire (clipped to my bicycle for a ground). The primary is centered and supported with small pieces of foam rubber; works perfectly. The top load is two steel (not stainless) bowls inverted on each other, held together by three spring clips. Not wanting to make holes in a perfectly good bowl, I opted to make the electrical connection via a *magnet I have.
Driving the primary is a 1.2 kv fence charger. I need to make a spark gap. I am using a jumper wire clipped to the end of a mini-blind twirly rod thingy to make a temporary spark gap by bringing it near the charger terminal. This thing is 30" tall which puts it up in the flourescent lights on my work bench, so I have to keep it slid forward some. It is making sparks at least 2" long to the reflector (that I can see), and it makes the lights flicker on the ends. I know that's not much, but it's a start. Since the top is easily removable, and since I have a bunch more cardboard coffee cans (tobacco), I can now start making various types of primaries, as well as different ways to drive them.
* This little magnet I use for my electrical connection to the top load is amazing. It is a very weak ceramic magnet nested in a "cup" just a little bigger. When it's in the cup, all that weak force is focused around the edge of the cup, making it remarkably strong!
Wave forms: I've not seen anything written about waveforms used in driving a Tesla coil. Sine? Triangle? Square? Any combination thereof? Does anyone know anything about that?
Later,
Gary S.
Ok, here's one photo. The camera is junk so the pic is lame.
I took one look at all the fancy math involved in "doing it right" (math I can't do) and decided that it can't be that (overly) complicated. Sure, if you want to custom make it to be optimum at a certain resonance, then maybe you would need such math, but not usually. The basic facts remain and that's what makes this basic device work. "Crude but effective", Spock would say.
Gary S.
BTW, I have a number of TV sets here, one of which is ripe for canibalism, but, again, my wrist/arm just isn't strong enough to handle it. Just too big for me to move right now. I wouldn't be able to even get one on the coffee table, let alone all the way up to my workbench (and I'm not workin' on it on the floor). I also have an assortment of chokes and coils that I could get wire from, but they are rather unique and I don't want to sacrifice them. Besides, again, I don't think I can apply the strength needed to disassemble one.
But, right now I want to start making different primary coils. Which is better, tubular or pancake? I also need to start digging through my junk to find some boxes of capacitors I have. Gonna also start working on different driver circuits.:)
Gary S.
As we all know, an inherent part of invention & discovery is finding out what all does not work. I can confidently say that steel baling wire does not work. I made a "coil-coil" sort of, by winding 20' of baling wire into a coil resembling a screen door spring, stretched it out to about 6', then wrapped it around a cardboard coffe can. It does NOTHING (looks cool though).:blush:
Gary S.