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Re: Conical and Pancake Coil Arguments... (fwd)



---------- Forwarded message ----------
Date: Wed, 20 Jun 2007 00:32:39 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Conical and Pancake Coil Arguments... (fwd)

Hi Jeff,

Thanks for the information and links. Your site is a real wonder to 
behold! Thanks for pointing out the failure area of the coils. I 
experienced exactly the same on my smaller flat coil. The last time I 
ran it I shorted a few windings near the outer winding (about 1/2" 
inside). With my large flat coil, given such large spacing, I'm will 
likely run into quite a few problems that will be very different from 
closewound coils, but some the same.

I've also tried the plexi sandwich and that turned out horrible. That 
was actually my first flat coil (what a mess). It was so bad I tossed it 
out and wound a new one. I think the idea of potting the coil is really 
the best solution (at least for small flat coils). I've been working 
with Epic Resins for potting electrical components for work (UL94V-0 
ratings, high flexibility for surface mount components, high dielectric, 
thermal dissipation, and lot's of other tid bits needed for electronic 
potting). Something like this might work well for flat coils, but it is 
expensive (about $72 per gallon if 5 gallon quantities are purchased, 
"much" higher for lower quantities). The other downside is it isn't 
going to melt away like beeswax or similar compounds, so fixing the coil 
if it shorts could be nearly impossible. The upside is besides it's 
design for the electronic industry, it sure would make a mechanically 
strong coil. Epic Resins are great people to work with. I called on a 
lot of different potting manufacturers and Epic was amazingly responsive 
and had the products to suit any need. How I wish more vendors were as 
knowledgeable and responsive as Epic is.

Take care,
Bart



Tesla list wrote:

>---------- Forwarded message ----------
>Date: Tue, 19 Jun 2007 21:10:57 +0000
>From: Jeff Behary <jeff_behary@xxxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: Re: Conical and Pancake Coil Arguments... (fwd)
>
>Bart,
>
>Its great to see some interest in Pancakes and Flat Spirals.  Probably you 
>know about this, but there
>are a few things I forgot to mention that I probably should.
>
>"Pancake Coils" are used as a generic term, and include both multilayered 
>coils and flat spirals.  In the 1890s portable coils that Tesla formed the 
>basis of most of his circuit controller patents for, he always used the 
>multilayered variety.  Of course the beautiful flat coil from NY represents 
>the other style, which is basically "one turn per layer".  (The half scale 
>reproduction posted a while back is beautiful beyond words!)
>
>Oil insullation for these coils becomes tricky.  I made one flat spiral 
>Pancake this way:
>http://www.electrotherapymuseum.com/2005/KinraideAcrylic/index.htm
>
>I put a funky support on the acrylic forms to allow the oil to penetrate 
>everywhere.  I stole this idea from Kinraide.  It worked well for oil, but 
>when I switched over to wax it was a disaster.  (details below).
>
>Kinraide's original design:
>http://www.electrotherapymuseum.com/2006/KinraideSeeThrough/index.htm
>
>Originally Kinraide used glass rods as supports that were heated and smashed 
>on the end so that silk thread may tie them together and "sandwich the 
>pancake" as it were:
>This formed a patent for the first non-Tesla Pancake Coil.  Of course it was 
>still a Tesla Coil, and hundreds of other people patented them since then 
>just by getting creative too.
>
>http://www.electrotherapymuseum.com/_PatentLibrary/_KinraideInductionXRayCoil/index.htm
>
>The original coils made like this are here amongst some of the other 
>artifacts:
>http://www.electrotherapymuseum.com/2007/KinraideRecovered0207/index.htm
>
>My first attempts at making Pancakes & flat spirals were completely 
>worthless for the most part.  I attempted to make them by sandwiching the 
>wire between acrylic, as many people are doing today:
>
>http://www.electrotherapymuseum.com/2005/KinraideAcrylic/index.htm
>
>I can tell you now, that this method is not the way to go at all.  Once the 
>coils are tuned to resonance, they can produce an arc equal to their 
>diameter or greater.  Any chance of breakdown with these that can occur, 
>will occur.  Materials like plastic and rubber that may be good insulators 
>at low frequencies are lousy at high frequencies, and eventually a carbon 
>track will prevail and the output of the coil will dwindle to nothing.  I 
>have a movie of this for proof, a 100% goof fully documented:
>http://www.electrotherapymuseum.com/Films/675.wmv
>
>What you'll see is low power (30 watts, actually a Violet Ray circuit) with 
>about 2" sparks.  Then I close a knife to allow another coil in parallel 
>with the kicking coil to get 100 watts.  The sparks jump to around 6", but 
>immediately you see breakdowns in the coil.  After a short while one of 
>these occurs between two wires and shorts them, and the output of the coil 
>dies to less than when the 30W circuit was used.  Ouch!  That was a few 
>hours time lost in a few seconds!
>
>With any insulator, even wax, the wire itself must be held and positioned in 
>such a way to have the wax or oil be as close as possible to the only 
>insulation used, or a discharge will try to occur on the second best 
>insulation...if that makes sense?  For example, I tried to use that flat 
>acrylic star shape to emulate Kinraide's glass rods.  Despite the 1/4" width 
>of the acrylic, it was enough to eventually cause a short.  Kinraide's rods 
>look primitive, but the wire is touching only on the tangent so the actual 
>contact with the rod is reduced to a minimum.  This means the difference 
>between "life and death".
>
>Even with paper interleaves, you still must be careful if you raise the coil 
>above the ground surface .  I've placed 2" tall paper-interleaved 
>multi-layered and flat spiral coils on rubber insulators to get some extra 
>height to allow the wax to fully flow underneath the coil (good practice) 
>but used pieces too wide before and had an arc form through the wax and 
>around the rubber straight up through the wax again to another turn of wire 
>and short it out!
>
>The key is to have the thinnest supports possible, or better still (and wax 
>is about the only thing you can cast like this in two shots) pour the coil 
>once with wax in a form and then position it on supports, add your primary 
>coil, and then pour a second time to allow complete immersion in and around 
>both coils.  Impregnating the primary coils is also a good idea.
>
>Now, the surprise:  Where do Pancakes normally fail?  You might think (and 
>its logical to think this way) that the centre-most windings will fail 
>because of the high stresses and voltages raising higher and higher in this 
>area to its maximum:  In reality, most arc-overs and short circuits occur in 
>the outer 10% or so of the winding.  Its actually the lowest potential part 
>of the coil, but the windings are longer and have the most resistance.  In 
>coils I've made that "burned out", most 9" coils will burn out around 1/2" 
>or 1" from the OD, only a short distance from the ground.  Logical would 
>seem like the opposite way, but logic looses in this case.  It doesn't make 
>any sense at all until you consider the resistance.  Even one of Kinraide's 
>coils is burned out in about this very spot.
>If you check out that video again, you'll see what I mean!
>http://www.electrotherapymuseum.com/Films/675.wmv
>(of course this coil has no insulation at all, its just sandwiched between 
>1" acrylic discs)
>
>If you choose to wind a coil without interleaves, the easiest way is to pass 
>cotton or silk-covered wire through a trough of wax.  This automatically 
>glues it together as your winding.  I use acetate sheets in the form so I 
>can see through and also remove the coils easily afterward.  They are still 
>fragile, but try to do this without the wax and you'll have an exploding 
>"slinky" of wire everywhere.
>http://www.electrotherapymuseum.com/2007/5inKinraideCoils/index.htm
>
>A last minute thought, for interleaves, cash register paper works really 
>well and so does dry-wall seam paper.  Both are cheap and can be tossed in 
>some hot oil and let to sit overnight.  You end up with oiled paper that 
>sticks to itself nicely.  The oil seals nicely with hot wax too, and the 
>fact that its already soaked avoids many problems with air pockets.
>
>A final note is for small Pancakes - silicone baking pans make the best 
>molds imaginable.  You can simply turn them inside out and pop out the coil. 
>  Non-stick pans and other types of forms can get brutal when it comes time 
>to remove the coils from them.
>
>Jeff Behary, c/o
>The Turn Of The Century Electrotherapy Museum
>http://www.electrotherapymuseum.com
>
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