primary coil / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

primary coil

1 2 next

Move Thread

LAN_403

radioman

Fri Aug 27 2010, 02:32PM

Registered Member #3026 Joined: Fri Jul 23 2010, 02:46PM
Location: Los Angeles, California, U.S.A.
Posts: 54

How in the world do all you guys make those beautiful flat spiral primaries out of copper tubing without kinking it?? My present primary coil is a vertical spiral with seven turns and a seven inch diameter. Using a signal generator and a scope, moving the tap doesn't seem to make much difference in the resonant frequency. Can someone tell me how to form a flat spiral coil and what are the advantages of this kind of primary? Thanks!

porkcake

Fri Aug 27 2010, 08:07PM

Registered Member #3138 Joined: Tue Aug 24 2010, 05:20PM
Location: Herefordshire
Posts: 7

Hi, i may my primary with 8mm copper tubeing, it comes ready formed in a loop (25m).

after deciding how much i needed and cutting it off, i unravelled in and tweaky it from the centre out bit by bit. then i fastened it to a wooden frame with holes drilled for cable ties. it looks nice but is by no means perfect, the spacing is a bit off.

As this is my first TC i haven't tried anything else yet.

Hope this helps and good luck

Herr Zapp

Fri Aug 27 2010, 09:02PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

radioman -

Building a perfect flat spiral primary out of soft copper tubing is actually quite easy, IF you follow some basic guidelines:

1. Use ONLY a brand new roll of soft (fully annealed) copper refrigeration tubing, typically 1/4" diameter for NST powered coils.

2. DO NOT (REPEAT: DO NOT!!) try to straighten the tubing, or deform or flex it it any way prior to laying it onto your primary form. Annealed copper work-hardens dramatically when deformed even slightly, and will then be very difficult to form into a smooth spiral shape without kinking or forming irregular radii.

3. Build a series of primary supports out of some insulating material (LDPE, acrylic, polycarbonate, etc). that are notched to accept the tubing. Use a minimum of 5 or 6 supports, arranged radially around the base of the secondary coil. Remember that the notches need to be cut (or the supports offset on the base) so that the notches describe a spiral, and not a series of concentric circles. A table saw, or radial arm saw works great to gang-cut the notches.

4. After your supports are secured to the baseplate, get ready to position the copper tubing in the notches. Have a "helpr" hold the coil of tubing a few inches above the primary supports, and then gently pull one free end of the coil of tubing down and press it into each notch in the primary supports sequentially. I recommend starting with the outside turn of the primary, and winding inward.

5. At least in the US, 25' coils of tubing are sold as a single-layer spiral coil, while 50' coils of tubing are wound a little different, as a two-layer coil. Starting at the outside end, the tubing spirals inward, then takes a "jog" and spirals outward again. This complicates the transfer of the tubing into the supports, but only slightly.

6. Go slow, and if any pressure needs to be applied to the tubing to get it to align with the notches in the supports, make sure that the pressure is applied to as wide an area on the tubing as possible to avoid any local flat spots, etc.

The most inportant part of the process is the construction, alignment, and attachment of the primary supports. If you get the supports aligned correctly, actually installing the tubing is almost a no-brainer.

Herr Zapp

quicksilver

Fri Aug 27 2010, 09:03PM

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

I think I may be able to help you here. There are some things that make doing this a LOT EASIER! And if you want I would post some pictures if you want as well. The first thing is to obtain your materials. IF you are doing to make a flat spiral (let's start with that), it's important to note what is termed the "skin effect" which for lack of in-depth explanation means that the outside of the conductive material is where the majority of the energy flow exists; thus the use of copper tubing or even bands (or flat conductive materiel). The reason I mention this is that since you have some choices here you may make a very functional coil with less work using differing materials. However, they are often less common that simple copper tubing!

The next issue is to get a "form". To make a spiral form the most simple "bending jig" happens to be a CONE. Keeping in mind the direction of the wound secondary; wind your tubing starting from the lowest point on the form - to the highest. - From wide to thin: if that puts a picture in your mind. This will get you a winding of the cone whereas the spiral winds from wide to small.

It CAN be VERY IMPORTANT to anneal the copper by heating it with a torch and then rapidly submerging it in water as this will soften it to a GREAT degree and keep it from kinking OR just looking bad, as it now will bend to your form with few awkward bends or inappropriate shapes!

Once you have it bent to the cone shape you may choose to bend it slowly back into itself to form a flat coil OR you may choose to push it together to make an widening pattern or whatever your concept calls for.

At this point you would need to make some manner of insulation - but keeping in mind that you must be able to MOVE the TAP point. One way of doing this is to obtain some materials such as a polymer and as it would start in a strip for instance 2" wide by one foot in length; you would drill EVENLY spaced holes through it WIDER than the conductive materiel. So say you're using 1/4" copper tubing; your holes would be 3/8" and so forth.
Once you have drilled your evenly spaced holes; you then make a cut down the CENTER of the strip, through the holes, so that now you have supports for your tubing.

There are MANY different ways of doing this as there are different types of Primary coils. But I hope you get the general idea.
You will need a coil form and some form of supports or insulators: they can do double duty!

There ARE much less involved methods than using a clear polymer but if you want it to be nice looking the import things are that the copper MUST be soft - so annealing is a good idea! You want CLEAN coil shapes, so that a coil "form" is an important item as well.

I hope this gets you off to a good start. Conceptualize in your thinking what you want to accomplish. A clean primary is a good thing to work on as it gives you a very significant tuning mechanism. An "open access" to the coil allows the TAP to access incremental changes & this is also a very good thing.

I know that if you can visualize what I'm going on about, you'll see it's not too hard (neither is a secondary) but making it clean and neat are both aesthetically pleasing and functionally significant!

Go for it!

Herr Zapp

Fri Aug 27 2010, 11:14PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

quicksilver

I must ask, how many primary coils have you actually wound using your "wind-it-on-a-giant-cone-and-then-squash-it-flat" technique?

How on earth would you fabricate the LARGE cone you are proposing for use as a coil form?

As I noted in my previous post, the primary coil does NOT any sort of "bending jig", or need to be "pre-formed" in any way. The primary supports, which are a necessary part of the system anyway, serve as both the primary "coil form" AND the insulating support structure for the completed primary coil.

If you use a brand new coil of copper refrigeration tubing, is is already fully annealed and ready to go. If you try to use some "salvaged" tubing, regardless of any attempts to "torch anneal" it, you will likely end up with a pretty sorry looking mess......

The cost of copper has dripped significantly over the last year, and the cost of a 35' or 50' coil of new tubing is insignificant in comparison to the rest of the system.

Try it ........

Herr Zapp

quicksilver

Fri Aug 27 2010, 11:55PM

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

I think we had replied to the question at the same time & I didn't mean to imply that "my method" was somehow the answer or the de facto standard.... Far from it. It WAS something that worked for me when I met with some frustrating experiences.

Realistically, I don't think there is just one method that covers all bases. There are simply too many variables. If I had the source I would try some copper strips!
In my experience it's a lucky thing to find a coil that decreases in size. Those that I had seen were generally of uniform diameter.

I had made four in the method I proposed. It really did relieve me of some frustration and additional expenditures (heavier acrylic, etc).
I had a very frustrating experience with some (it was in-fact used tubing) & found that forming the basic shape prior to setting it into the spacers was a great help.

And I certainly agree: if a person is lucky to get a spiral (as you mentioned) the whole deal is a cake walk. I certainly agree that straightening them (the tubing) is the "kiss of death".
But the ones I've gotten were one sized loop! (HOME DEPOT!). I had wondered where you found some that were sold in a decreasing spiral! (As you can see, I'm in AZ).

The "cone" forming jig allowed the one size to be brought down to a spiral. That allowed design alterations aside from a flat-style to be used without depending on the supports for for "forming strength".

I think a lot depends on the distance and construction of the supports. If the coil exists as a proper spiral then generally, I can't see anything going amiss. But if one begins with a "single sized" loop,the "guides or supports" would need to not only be in place prior but also be quite strong at certain points depending on the demands of the spiral.

I've used quite a few things as "formers". I've used a wooden one; turned down on a lathe that was a fairly large thing at the base, traffic cones (some are too soft and needed to be filled).

The costs have I've seen with copper tubing varied, This may be an "application specific" issue. Some of which is certainly annealed; some however is a nightmare. The refrigerator material is obviously the best as it really was meant to be bent. Some of the rolled stuff was either (most likely) thinner walled OR was"hardened" during forming and showed flattening even with the most gentle touch. It needed annealing.
THAT tubing I have seen sold for water-spraying coolers ("swamp-coolers") that appeared not to be designed to handle as much pressure as a refrigerant tubing. This also may be where there is a price difference.

Just for discussion sake, out here - for new .25" tubing we pay not too far from a dollar per foot $18 per 20' roll. (Home Depot price). I had also bought "water cooler" tubing from another source whose OD was .25" but it was a very poor second to the new material (designed for higher pressure) and actually flattened when bent with care so the walls MUST have been thinner.

radioman

Sat Aug 28 2010, 02:59PM

Registered Member #3026 Joined: Fri Jul 23 2010, 02:46PM
Location: Los Angeles, California, U.S.A.
Posts: 54

Thank you, gentlemen!

I was not even aware that 1/4 inch copper tubing was sold in a coil! This really solves the problem. Now, can anyone tell me of an electrical advantage to a flat, spiral coil?
It certainly is more work.

Thanks,
John

quicksilver

Sat Aug 28 2010, 04:04PM

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

That's a bit unclear... A flat, spiral coil, as opposed to what exactly?
Do you mean using a flat strip instead of a tube? I imagine it would work out just fine provided there is enough attention paid to insulation, etc..
The concept of issues like the "skin effect" also allows you to understand why a tube is used in the 1st place......"Why not solid wire, etc"? People have used solid copper wire before: it would function. As you can see there are very individual lessons learned & they have value but the elemental science doesn't change: that where a self-study agenda is appropriate.

I will say this; that I have had a tough time finding strip copper in a gauge appropriate enough to use and a competitively price as tubing. IF you DO ever find a source: that would be GREAT!

Herr Zapp

Sun Aug 29 2010, 12:33AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

radioman -

Regarding flat Archimedes spiral primary coils, you wrote:

"Now, can anyone tell me of an electrical advantage to a flat, spiral coil? It certainly is more work."

More work than what other kind of primary coil configuration? A vertical helix? An inverted cone? Having built all of these primary configurations, I can assure you that the primary supports for a flat spiral are MUCH easier to fabricate than supports for other types of primary coils, and the primary supports are 96% of the "work" in building any primary. After fabricating the primary supports and attaching them to your base structure, actually "winding" the primary coil only takes a few minutes.

An appropriate primary - secondary coupling factor can be obtained with either a flat spiral, a helical, or an inverted cone primary.

So, the benefit of an Archimedes spiral is that it will provide the greatest distance from any part of the primary to the topload, which (if the secondary is of a reasonable length for the input power) greatly reduces the tendency for streamers to connect to the primary. A coils whose streamers are constantly arcing downward onto the primary is not nearly as visually appealing as a coil that is directing its streamers outward and upward. With a solid-state coil, a primary strike can be catastrophic, destroying the IGBT switches.

Herr Zapp

iceowl

Sun Aug 29 2010, 06:54PM

Registered Member #2834 Joined: Thu Apr 29 2010, 02:04PM
Location:
Posts: 22

I've wound two primaries now. One using 0.25" copper tubing through polycarbonate stanchions. I did not use the recommended method of cutting "c" shaped holes and laying the tubing in the holes. Rather, I threaded the tubing through the 6 stanchions (15 holes each), by laying the copper tube on top of the stanchions and then taking the outermost part of the coil of tubing (as it came out of the box from Home Depot) and threading it through the outermost hole in the stanchions, going round and round till the coil of tubing was completely threaded.

I heartily do not recommend anyone in their right mind try this process. While the results are quite pretty, the process is painful and excruciatingly difficult. After the first turn or so the tubing generally only wants to move a couple millimeters with each "twist" applied with the hands. My 15-turn primary took about 8 solid hours to thread. And, as someone has already mentioned, as the copper bends over and over, it gets work hardened, which makes it less likely to want to be threaded through ever decreasing diameters.

I liberally applied windex. Then I liberally applied WD-40. Then I nearly tossed the whole thing in the trash, several times over. It is possible to do (see pics below), and the results are quite pretty. But I'm not sure it's worth the pain. In fact, I'm pretty sure it's not worth the pain.

Over the course of my experimentation I had to splice in a couple more turns of copper to the outside, which didn't turn out as pretty as the original coil. And then, because I had some terrible overcoupling issues with a new secondary I wound, I had to cut out the inner 2.5 turns. In the end, I only wound up using 4.5 turns. Had I known at the onset I would be tweaking the coil from the point where i needed 15 turns down to 4.5 turns, maybe this method would have been the best way to get a good functioning, good looking result. But for 15 turns, I think you'd have to be a madman.

My second primary took about 10 minutes to wind. I used 1.5" wide spring copper, interlaced with 0.25" foam weatherstripping, as first noted on Terry Blake's website http://tb3.com/tesla/hugecoil/primary/primary.html. I wound mine differently. I cut a 12" circle of 1" UHMW with a router and mounted it concentrically on a 25" polycarbonate disk. Then I wound the interlaced spring copper and foam in a horizontal plane, with the wife's assistance. When finished, I topped the primary with an 18" concentrically mounted polycarbonate disk.

The results have been great, in fact, I would say superior to my tubing primary in terms of compactness and looks. It functions really well, too.

Cheers,
Joe

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob