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Winding multilayer coils is a big PITA...

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hboy007

Fri Apr 16 2010, 10:19AM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Posts: 374

just a thought: why not use 0.2mm bifilar wire wound with an additional nylon fiber (Cu - Cu - Nylon) and use a multiple of your layer insulation sheets? This will noticably shrink your fill factor but help reduce the parasitic capacity and distribute the current a little more (I don't think litz wire is mandatory at this frequency).

that's what you would end up with

jpsmith123

Fri Apr 16 2010, 02:41PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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@Patrick

I'm pretty sure I'll ultimately be able to get what I want from this core: 20 kv center tapped, at 27 kHz or so.
It's a matter of getting the right combination of materials and geometry...and my latest experiment rules out (once-and-for-all IMO) a conventional layer-wound coil with magnet wire.

@hboy007

That's similar to one idea I was going to try. I was going to try using teflon coated wire, which would add space and thus lower the electric field and the parasitic capacitance. In fact I have a crude prototype coil wound already. Hopefully later today I'll be able to test it a little bit.

Patrick

Sat Apr 17 2010, 05:52AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

yeah ok please post again Jpsmith123 my transformer design is similar to yours, so i would appreciate your results

TY

-Patrick

jpsmith123

Sat Apr 17 2010, 09:40PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Patrick,

I didn't get a chance to test the other coil today...hopefully tomorrow I'll have time.

Steve Conner

Sun Apr 18 2010, 04:19PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

According to the trusty old Radiotron Designer's Handbook, vertically sectionalized winding has lower self-capacitance than regular multi-layer arrangements. It's also known as pie winding: imagine a bunch of wide, flat discs like the windings on old flybacks, connected in series.

jpsmith123

Sun Apr 18 2010, 06:48PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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I'd like to experiment with pie windings. One reason I haven't yet is because of issues with materials.

Maybe I'm being too anal about it, but I see cpvc as being too lossy, and polyethylene, while having good electrical properties, has such a high coefficient of thermal expansion that you could make a nice thermometer out of it, and of course there's the problem of nothing-sticking-to-it.

I'd like to try making a pie type coil-former out of polystyrene, which seems to have a reasonable set of properties for this application, but unfortunately I haven't been able to find a (reasonably priced) source for 2.25" to 2.5" diameter polystyrene rod or thick-walled pipe or something.

Edit:

Well I just swept the multilayer coil (wound with teflon insulated wire), and it starts rolling off at about 25 kHz.

If I had wound this coil starting each layer from the same side, it might have been usable at 30 kHz, but on the other hand, this coil only had about 350 turns - not the 400+ I would like to have; so it's questionable whether any kind of layer winding will work the way I want it to.

hboy007

Sun Apr 18 2010, 08:28PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Posts: 374

now I get the point. How embarrassing. Seems like I vastly underestimated the voltage swing between the layers produced by zig-zag winding of the wires.

How about this: build a coil form to make pie windings but also add a base cylinder before closing the form, then add strips of tape that fan out in radial directions. You stabilize each completed layer with double-sided adhesive tape and a strip of glass fiber mat, followed by another adhesive layer. Once finished, fold the strips you started with inwards so you get a donut-shaped coil with wraps of tape around the windings that should keep its structural integrity.

In case you would rather reject the idea of constructing a coil of sticky tape with some copper content, you can still build a winding form out of polypropylene, wind your coil and pour some nice epoxy over it. This should also give you a self-supporting structure.
When you're through with waiting for all pies to harden, you can connect and stack them (with proper insulation spacers) and there you are!

Patrick

Sun Apr 18 2010, 11:50PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

yeah i might have to go the pie route too CRAP ON A STICK!

maybe polystyrene 7-11 slurpee cups will work , the clear kind... i willl try this.

-Patrick

jpsmith123

Mon Apr 19 2010, 06:07AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

McMaster has Polystyrene rod 2.0" (+ 0.015") diameter for $30/foot.

Let me think out loud: If I cut radial grooves, 0.125" wide by 0.125" deep, I could put 49 turns of 26 gauge wire in each groove (according to a wire table I'm looking at), which would amount to about 1100 v per groove. And if the grooves are separated by about 0.090", I could fit 10 grooves over a winding length of 2.25".

But then again, if I'm going to go through all that trouble, I might as well just add the two "I" pieces to the core, as per my first inclination, giving me two winding lengths of 6.25", upon which I could wind 400 linear turns of 28 gauge, and be done with it once and for all.

Patrick

Mon Apr 19 2010, 06:43AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

"once and for all" ... LOL the quest for the best HV transformer never ends!

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