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Winding multilayer coils is a big PITA...

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jpsmith123

Wed Apr 07 2010, 08:22PM

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

Maybe I had too much tension on the wire? Or maybe the polystyrene film I was using (for layer insulation) was too "slippery" and/or too stiff? All I know is, it's very difficult to get it the way I want it.

In my most recent attempt, I had just started winding the fourth layer, when it all went to hell.

For my next attempt, I suppose I'll try using glass-cloth tape as layer insulation.

Dr. Dark Current

Wed Apr 07 2010, 08:26PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Maybe you could try taping every layer down a bit with a transparent tape? just so that the wire doesn't slip before you wind the coil.

IntraWinding

Wed Apr 07 2010, 09:35PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Get the tension reasonable and reasonably constant and wind one layer. Use precut tape pieces to hold anything that moves in place whilst you apply a layer of insulation, and tape that (or just insulate with tape). Repeat. At worst you will have to rewind one layer.

Use thin tape suitable for the temperatures you expect (polyester or polyimide).
Make a simple winding mechanism so the wire is unwound under tension from the reel straight onto the core. Old Hard Disk Drives are a handy source of good rotary bearings.

Take steps to keep each layer + insulation smooth so the next layer winds on easily. Watch out for starting each layer at the same point around the circumference of the core or you'll probably end up with high and low spots to wind over after you've added several layers with the 'lumpy bits' all in the same place. If you plan to impregnate the coil with oil or whatever, design the winding to allow the liquid easy access to where it needs to go.

Good luck,

Alan

quicksilver

Wed Apr 07 2010, 10:09PM

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

[Depending on the size of the wire] I've used a bit of tape also w/ success. I've also tried a dot of super-glue and a plumber's tape (Teflon) between layers. If you know of a packaging place, they sell 2 sided transparent tape (Scotch) and starting with that ($1.59 well spent) makes a world of difference.

Patrick

Fri Apr 09 2010, 06:20AM

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

Uzzors and quicksilver say that scotch tape works well, do we know the max temp on this tape is?
i always try to keep my oil transformers at or below 140 degrees F. (peak at hotspot)and i guess oil resistence is irrelivent because once the core is finished it cant unravel even once the vacuum oil is drawn.

-Patrick

wylie

Sat Apr 10 2010, 02:34PM

Registered Member #882 Joined: Sat Jul 07 2007, 04:32AM
Location:
Posts: 103

How about teflon plumbers tape? I'll wind a layer, securing the start and end with a dab of CA-glue, then wrap a tight layer of teflon tape. Then onto the next winding. Then slather the whole thing in Minwax Polycrylic clearcoat a few times to secure the outermost winding. I've also tried putting the clear coat on each set of windings before the tape, but i'm not sure if there really a point. The tape grabs real well, both on the winding underneath and for the next winding on top of it.

I've had one HFHV coil burn through it, but i think it could just be that the method traps too many air bubbles (corona -> carbonization -> internal arcing). Someday I'll get a vacuum pump and try it again, winding the whole thing with wet layers of clearcoat and the teflon tape, then pumping down to remove the bubbles/airpockets.

EDIT: in my avatar, you can see some spacing in those red windings, particularly the bottom one. I was doing them quick and dirty to try that symmetric winding layout and skipped the clear coat. The windings were perfect when i made them but 15mins of fiddling later and i messed up a few spots. i SHOULD have put on some clearcoat, dag nabbit.

jpsmith123

Sat Apr 10 2010, 05:25PM

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

Being that this is my first attempt to wind a multilayer coil that will see high voltage at high frequency, all I can do is speculate as to what may work well (i.e. last a long time) and what may not (i.e. fail after a short time due to excessive power dissipation and/or corona, causing subsequent insulation breakdown).

I may be wrong about this, but it seems to me that, generally speaking, the more "stuff" used to hold the coil together while winding it (e.g., scotch tape, glue, acrylic spray, teflon tape, etc.) the more difficult it may be to get rid of entrapped air later on, when vacuum encapsulating or oil-immersing the coil.

Also (and I admit this is probably just me being "anal" about it) I hate to use anything in the construction for which I don't have a lot of information about its dielectric, thermal and even chemical properties.

Of course, some tape or a dab of something here or there is necessary, or you'll simply never get it done...and common sense tells me that most insulative materials will probably work ok if used sparingly and judiciously placed.

Anyway, as soon as I receive the 1.25" x 0.007" glass cloth tape I just ordered, I'm going to try it again.

clavius

Sun Apr 11 2010, 01:31AM

Registered Member #2798 Joined: Sun Apr 11 2010, 12:51AM
Location: NE Massachusetts
Posts: 3

Don't be afraid to tape the wire in to stabilize the windings. Use interlayer insulation that is thick enough to yield a flat, smooth surface for the next layer. Wrap a little "flag" of tape around your wire at the start of the layer, then fold it back such that it sticks to the layer insulation, then begin winding your layer over it. That way the subsequent turns of wire hold the tape down. When you get near the end of a layer, stop winding and place a strip of tape, sticky side up and long enough to hang off the end of the coil on the coil, and continue to wind over it. When you get to the end of the layer, fold the tape over the winding. Again this will anchor the ends of the layer and keep them from "popping out" of the coil margins. You can do this in several places around the coil.

When winding coils like this remember: Tape is your friend!

I've watched thousands of such coils being wound on hand feed machines. There is a definite knack to it, and getting the layers and wire tension right takes some practice. But it is certainly doable by a home-brewer. I used to work at a custom transformer company and had a crew of gals there that could whip these things out like crazy. We went through LOTS of tape.

For our HV stuff, the insulation was generally mylar or kapton. A cheap source of mylar is to cut up those clear films that office supply places sell. The ones you run through a laser printer to make overhead transparencies and the like. Some of the "sheet protectors" or those clear report cover things they have were also mylar. Kapton is nice but pricey.

You may know this already, but if you are in the USA, one source for everything you may ever need for making coils (wire, tape insulation, varnish, etc.) is a company called "EIS". Not sure if is OK to post a link here, but google it, you'll find them. They have branches all over the country, and most will sell to an individual if you pay by credit card. At least that was so a few years ago, I have not tried recently. Not bargain priced, if you need it, they likely sell it. (all standard disclaimers apply: I have no connection with EIS, nothing in it for me, just a past customer, etc....)

Hope that helps a bit. Good luck!

jpsmith123

Wed Apr 14 2010, 01:23PM

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

Thanks for the tips.

My latest effort uses two layers of 1.25" by 7 mil glass cloth tape as layer insulation. As of right now, I just completed the 5th layer. I'm going to try to put one more layer on.

Attached is a picture of what it looks like presently.

The winding is about 1" wide, and I was trying to maintain 0.125" margins. You can see from the picture that the margins on this layer are not exactly equal...they seem to shift a little bit from layer to layer. It's difficult to keep everything nice and neat and perfectly symmetrical.

jpsmith123

Wed Apr 14 2010, 03:19PM

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

Here's a picture of the finished coil #1:

The glass cloth tape seems to have been the main factor in successfully winding the coil. I guess it's now ready for potting. According to the manufacturer, this tape will absorb varnish, so hopefully it will also absorb epoxy, or whatever I end up potting it with.

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