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Is a pancake coil primary necessary?

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hsieh

Fri Feb 11 2011, 02:12PM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

I have difficulties building pancake coil primary.Can I use a helical primary and increase the distance between primary and secondary to reduce coupling?

Thanks

radioman

Fri Feb 11 2011, 03:48PM

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

My first attempt at a Tesla used a helix coil with poor results: either there was overcoupling or not enough power transfer. I made my â€œpancakeâ€ coil in a simple way: I arranged five 12 inch pieces of pvc pipe in a radial pattern secured to a plywood board, then slowly uncoiled a 50 foot coil of 1/4 inch, copper refrigeration tubing from the inside of the radial pattern out. The copper tubing was held in place by simple wire tie downs -- which also provided the spacing between the turns. I think this is the simplest way -- no notches to cut.

Good Luck,
Radioman

quicksilver

Fri Feb 11 2011, 06:49PM

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

+ 1
I also tried a helix and actually only got it to preform on a VERY small secondary. I would unquestionably go with the pancake primary.

I had thought that the issue lay in a very narrow margin of tuning with a Helix from reading a great deal of old posts, etc. All the areas of adjustment in a pancake appear to be in place for a helix as well so you have space from coil to coil, coupling space and movement of the tap. After making 4 of differing sizes I gave up. as I would have to find a source of tubing size "cores" that had as little as =<1cm difference, and a method of expanding the coils just slightly (beyond the tap insertion point) that's a lot to account for: at least this was my experience.
When I made a very tiny coil this was MUCH less of an issue. I don't know the reason for this but I found that I was either very lucky or - the smaller powered coil simply didn't have the primary tuning issues of even a small-mid size TC.

Kingpin

Sun Feb 13 2011, 05:49AM

Registered Member #3594 Joined: Mon Jan 10 2011, 04:19AM
Location: Buffalo,N.Y. USA
Posts: 3

My first coil had a helix coil. As I changed the tap point I was also changing coupling and it was over coupled, not good. Take quicksilvers advice and build it like
he did. Buy the tubing full soft, bending it is easy. Pancake coils look good to.

quicksilver

Sun Feb 13 2011, 09:19PM

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

IF you have a nice touch (& a great deal of patience) you can sit and listen to music or whatever and start the could (pancake) so that you already HAVE a spiral design. This makes insertion and lash-up much easier and faster. Occasionally some tubing IS already in a spiral but all too often it is in two or more separate segments of 4 (+ or -).
Do NOT straighten the material. But the 1st anchor point should be substantial and the next and the next; until the coil is "feeding itself" to a spiral design. The above example with anchor points to PVC is a good one. I have tried several and using acrylic is not too difficult. You may want to cut your sections and drill out the holes for number of turns and then cut that in half so that you have a "U" shape on each side. Yet this still takes some care, in that the coil may want to "pop out" of the form. Obviously the holes need to be wider than the tubing but not too much; this makes the center cut critical t make an even division on each side.

I have a young cousin who simply formed the coil in a spiral and hot glued it to a acrylic square foot base. It doesn't look that pretty but it DOES work very well IF you wait for the first few section to harden completely and form the rest with slow care (not to easy for those with less patience). Remember that your tap must have room enough not to touch adjacent coils; therefore you need to project your tap width and allow some extra room as the tap could also tip sideways; thus contacting adjacent coils as well.
Take your time and review all elements before you begin. Speaking only for myself, it was easier to form the thing prior to lashing it to the form.
I have noticed that there ARE several makers of tubing and some ARE harder to bend than others; some microscopically thicker or thinner, etc. Examine before you buy. I once got a VERY good deal of some tubing that turned out to be almost annealed, it was so tough. It's better to pay a bit extra & get just what you want. IF I had a choice between a "preformed" spiral and had to pay a bit more for it: I would.

Matt Edwards

Mon Feb 14 2011, 05:10PM

Registered Member #2838 Joined: Fri Apr 30 2010, 07:55PM
Location: tehachapi, CA
Posts: 333

Using a drill press and a saw or dremmel you can make some supports like these.

It takes a bit of time but it is worth it in the end.

I read somewhere that a pancake is better than a primary for a few reasons. One of which is to avoid primary to secondary strikes. Try searching online for pancake vs helical.

quicksilver

Tue Feb 15 2011, 03:51PM

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

That IS really nice. Was that wood or polymer? End result is something I really like; so that it can stay in existence without the wife complaining.....

Matt Edwards

Tue Feb 15 2011, 07:03PM

Registered Member #2838 Joined: Fri Apr 30 2010, 07:55PM
Location: tehachapi, CA
Posts: 333

Haha, the base is a 16" round tabletop from Lowes that costs $6. The supports are cut from HDPE. Actually the marine stuff because I liked the black. Vary vary cheap from tapplastics.com. Think I paid like $20 for 10 pieces 1.5"x10" which was enough for two coils and a few mess ups ;)

Goodchild

Tue Feb 15 2011, 11:48PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I find that flat a primary is easier to build that helical. You just mount the supports and then snap the tube into them working your way from the center out in a spiraling fashion.

HDPE is great for primary supports, my personal favorite is lexan (polycarbonate).

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