[RFI] Choke questions

[k9yt at yahoo.com]

Don't see a specific reference to failure.

72/73,

San K9YT

Creep and Cold Flow
http://www.rjchase.com/fep_handbook.pdf

Wire Insulation Selection Guidelines
https://nepp.nasa.gov/npsl/Wire/insulation_guide.htm

Electrical Engineer's Reference Book edited by M. A. Laughton, D.F. Warne
https://books.google.com/books?id=5jOblzV5eZ8C&pg=SA7-PA28&lpg=SA7-PA28&dq=Teflon+would+"cold+flow"+inductor&source=bl&ots=tZqQ9EReLS&sig=ACfU3U3TGv9Vou9O1vYgrU3fEZ5NUHhR8A&hl=en&sa=X&ved=2ahUKEwjSv8rgypXnAhVIOKwKHeGqAsUQ6AEwAXoECAgQAQ#v=onepage&q=Teflon%20would%20"cold%20flow"%20inductor&f=false

AI Techniques for Reliability Prediction for Electronic Components edited by Bhargava, Cherry
https://books.google.com/books?id=RMO4DwAAQBAJ&pg=PA20&lpg=PA20&dq=Teflon+would+"cold+flow"+inductor&source=bl&ots=a4PvXwAjQr&sig=ACfU3U1Qz4WYTBjEdrd6IU1lsfwKvTzKjQ&hl=en&sa=X&ved=2ahUKEwjSv8rgypXnAhVIOKwKHeGqAsUQ6AEwAnoECAoQAQ#v=onepage&q=Teflon%20would%20"cold%20flow"%20inductor&f=false

Alan Douglas
 Post subject:PostPosted: Mar Wed 23, 2011 7:22 pm
Member

Joined: Jan Thu 01, 1970 1:00 am
https://www.antiqueradios.com/forums/viewtopic.php?t=160894

Posts: 30698
Location: Pocasset, Cape Cod, MA
The purpose of inter-layer insulation is to keep the windings level. Teflon is much too soft, and it flows under pressure. Given its original use, that should not be a surprise.

Glassine paper was used originally, but that's hard to find, if it's even made at all now. Most paper is too thick. Given the excellent dielectric strength of modern wire enamels, scramble-winding works fine, unless the distributed capacitance is a real concern.

Thin mylar might work, but it's too slippery to hold the wire while winding. It's good for inter-winding insulation. Kapton is better as it has excellent resistance to cold flow. Pressure-sensitive adhesive won't make a very stable base for additional layers.

Power transformers ought to be varnish-impregnated and baked, otherwise vibration (hum) will wear through the wire insulation.


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On Tuesday, January 21, 2020, 2:47:53 PM CST, K9MA <k9ma at sdellington.us> wrote:


Back in my spacecraft hardware building career, it was well known that
Teflon would "cold flow". Great care was taken where wires went around
corners, etc., that there was no pressure on the insulation. Has anyone
heard of such issues with chokes?

73,
Scott K9MA


On 1/21/2020 12:21, Jim Brown wrote:
> On 1/21/2020 9:32 AM, EDWARDS, EDDIE J via RFI wrote:
>> Use coaxial cable when making RF chokes for antenna systems.
>
> Parallel wires work fine for winding chokes. There's no need for
> shielding -- the field from the choke is confined to the core.
>
> At least half of the chokes in my station are wound with a pair of
> Teflon insulated #12 stranded silver-coated copper wire. The rest are
> wound with RG400. The Cookbook includes data for #12 THHN as a lower
> cost alternative.
>
> http://k9yc.com/2018Cookbook.pdf
>
> 73, Jim K9YC
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi


--
Scott  K9MA

k9ma at sdellington.us

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