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Anyone know a commercial source for HV, HF transformer windings?

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Carl A. Willis

Wed Mar 06 2013, 11:15PM

Registered Member #9640 Joined: Wed Jan 16 2013, 07:53AM
Location: Albuquerque, New Mexico
Posts: 26

I'm looking for a reliable source of commercial off-the-shelf (or possibly custom, if affordable) pie-wound coils for high-frequency, HV transformers.

The pic below is an example of the inverter output transformers (one of four) in a 2-kW Glassman power supply. As you can see, this is a single-pie air-insulated magnet wire winding on a fiberglass tube. I have been using one of these same transformers (albeit with new core gapping and a new primary) in the 150-watt driver for my plasma tubes. The winding impresses me: insulated under oil, it generates an estimated 30 kV at resonance and shows no tendency to flash over. (In the Glassman air-insulated service, it probably only generates about 10 kV, maybe less, although it handles close to 500W and I never use it above about 200.) It's a much more robust kind of winding than those found in the typical CRT "flyback" transformer, and I'd rather use such an item as a standard power transformer for plasma than have to hunt through the ever-variable crop of trashy CRT transformers.

So if you know a company that winds this type of coil, or you know where Glassman and Spellman get theirs, please give me a heads-up. I have data on the number of turns on the Glassman winding, the magnetizing and leakage inductances and SRF on the particular core that it's on, and some dimensions IF that is helpful, but really I'm looking for a potentially broader variety of such items to choose from.

Thanks for any assistance!

-Carl

Ash Small

Thu Mar 07 2013, 02:21AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

That is an extremely interesting photograph, Carl. Thanks for posting it.

As you're probably aware, I'm currently designing a 50kV, 5kW supply that I believe we discussed a few years ago on another forum.

Am I correct in assuming that the wire has plastic insulation?

I'm going to try winding one of these very soon, I assume the 'basket-weave' design reduces capacitance?

There is some duality/confusion as to the meaning of 'pie windings' on the internet, according to my recent research (this is mentioned in my thread on self resonance of HV transformers). One interpretation refers to these 'basket-weave' coils, the other refers to the placing of primaries between sucessive 'pancake' secondaries. I assume there are advantages in combining the two.

My main concern at the moment is in reducing leakage inductance, as I'll be driving a multiplier under vacuum (You are already aware of what I intend to use this for), but any reduction in stray capacitance will also be beneficial.

I could adapt my lathe to wind these, but I should probably try winding a few prototypes by hand first.

I'll look into obtaining suitable wire, and let you know how it goes.

Adam Munich

Thu Mar 07 2013, 08:08PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

If I had to wager a bet, I'd say glassman buys them special order from TRIAD transformer company. I have many AC flybacks just like that in a box somewhere, made by TRIAD in the 1940s.

klugesmith

Thu Mar 07 2013, 09:20PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Hi Carl.

Ash beat me to mention the name "basketweave" for the winding style in your picture.
You're probably a good Internet searchist. My own few minutes of searching found no coil- winding companies that feature basketweave, but several amateur approaches.

I like Gren's suggestion of checking Triad.

My coil-type search found this curiosity posted on an over-unity forum.

One of those experiments that can not or should not be repeated.

[edit] In response to Ash's post below, here is a video showing a homebrew coil winder doing basket weaving / pie making.

Now I know how those things are made! But sadly, Lindsay Press (source of many great amateur technology books in the pre-Internet era) appears to have closed down.

Ash Small

Thu Mar 07 2013, 10:29PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

klugesmith wrote ...

My coil-type search found this curiosity

Another interesting coil, Rich. I found a similarly wound coil on one of those 'audiophile' (sic) sites, it's creator called it a 'Pi' wound coil. (The explanation given stated that the diameter of the central wire was Pi times the diameter of the wire wound around it, apparently it was supposed to do something for low end (bass) response)

I've designed a jig to wind the coil in Carl's photo on a range of bobbin diameters, I hope to knock the jig up tomorrow (I have limited resources here at the moment). I also sent an E-mail to a coil winding company I did some work for a decade ago, asking if they could suggest anything. I've not heard back from them yet.

The LOPT from TRIAD's 1981 catalogue does look very similar to Carl's photo

Ash Small

Fri Mar 08 2013, 09:12PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Well, I've tried winding one using some PVC? insulated wire with an OD of 1.6mm, holding and turning the jig in one hand, and feeding the wire with the other, and the result isn't quite as tidy as it should be.

I'm going to have to fix the jig to a bearing carrier, and clamp it to the table, and rig up a tensioner, so that I can maintain the tension on the wire more easily in order to get a more tidy looking coil. I'll also need to get some thinner wire to practice with, before I get some expensive HV stuff.

It's looking quite promising as a 'proof of concept' first attempt, though.

I put a bit of glue on it to hold it all together when I removed it from the jig

paris

Sat Mar 09 2013, 04:16AM

Registered Member #3042 Joined: Wed Jul 28 2010, 12:36AM
Location:
Posts: 121

what the hell is that thing klugesmith put up ?
nice place for a solder join.
would the pri be 7 turns ?

its a crazy lookin object

Ash Small

Sat Mar 09 2013, 11:36AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I found this coil winding machine on Ebay for ~Â£200, but I imagine shipping from Canada won't be cheap.

I was hoping to be able to see how the adjustable traversing mechanism works, but there are no photo's showing the mechanism.

I also found this book on building your own 'universal' coil winding machine. It calls the 'basket-weave' type coil a 'honeycomb' coil.

As I only need ~300 turns on each of the six secondaries on the HV transformer I'm building (due to the ~20cm^2 CSA of the core), I could wind mine by hand, but a simple machine would still make life easier. Initial calculations indicate that a 300 turn basketweave secondary 5mm wide using ~0.5mm OD wire will be less than 20mm deep. I'm considering various wire choices, ranging from 30AWG silver plated single core PTFE coated wire @~Â£100 for 250 metres to 30AWG tin plated single core PVC coated @~Â£10 for 300 metres. Both have an OD ~0.5mm and are rated for 300-350V, and both seem to be tested to 2kV with AC, but this is probably only @ 50/60Hz.

I'll post some more details in the 'other thread' later.

EDIT: I found a free download of 'Build a Universal Coil Winding Machine' by David J Gingery (I assume the copyright has expired), but was unable to upload it here as the server seemed to 'time out'.

The link is here

but it does take a while to download (it took me two attempts).

It uses a cam for the traversing action, and friction drive, making it infinitely adjustable. Anyone who builds one of these would be able to wind Carl's coils for him. It could also be powered by an electric motor and drivebelt.

EDIT: An improvement might be to drive the coil spindle directly. This should allow for more tension to be applied to the wire.

Using a stepper motor with suitable driver could make it completely automated.

I'd also add supports for the 'other' end of the coil spindle and cam follower, and possibly use spindles of greater diameter, to make it more sturdy, if greater wire tension is required.

Hazmatt_(The Underdog)

Sat Mar 09 2013, 04:26PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Found a site with the video of your layout there.

The coil it winds is remarkably well done.

Ash Small

Sat Mar 09 2013, 05:10PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Hazmatt_(The Underdog) wrote ...

Found a site with the video of your layout there.

The coil it winds is remarkably well done.

That's a very interesting link, Hazmatt, especially the bit regarding the 'improved' heart shaped cam for the above 'universal coil winding machine'.

Some of the coils pictured in the link are pretty amazing too.

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