Why use Teflon wire in HF power toroid ?

Discussion in 'Homebrew and Kit Projects' started by AA7EJ, Sep 15, 2012.

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  1. AA7EJ

    AA7EJ Ham Member QRZ Page

    I am gathering info and material for my home-brew ATU. The design I am using recommends to use Teflon wire in the autotransformer toroid converting the 50 ohms to 12.5 ohms.
    It uses 14 gauge wire for “high power 1kW” coupler.
    I am going for 100 to 250 W.
    I am trying to find out what would be the advantage of using Teflon, especially when from experience I know it is not that easy to work with and string thru even 2 inch toroid and is relatively hard to find in small quantity.
    The electrical properties may have something to do with it, but I am really not in favor to use “an exotic” part just because it has .01 db less loss than using other insulation.

    Any to the point commentaries are as always appreciated and welcome.
  2. AB9LZ

    AB9LZ Ham Member QRZ Page

    The wire provided in my elecraft BL1 balun kit ( for winding the balun) was plain old doorbell wire. "Carol 20awg CL2 sunlight resistent" to be specific. I just pulled it apart to re use the core in another project.

    73 m/4
  3. W9GB

    W9GB Ham Member QRZ Page

    TEFLON (PTFE) insulation or sleeping is often used in BAL-UN and UN-UN construction for legal power limits (and HV) --- and addresses the Clueless Ham issues (destroying cores with excessive power and mismatches that produce HV points).

    I understand the difficulty in finding small qty. of PTFE wire for balun winding.

    I took a "hint" from Bob at Balun Designs.
    He uses Teflon (PTFE) sleeving, specifically --
    Bob constructs his windings with Thermaleze wire inserted in Teflon tubes (PTFE sleeving)
    which provides a breakdown voltage of 10,000 volts.

    Teflon sleeving is easier to acquire from a number of sources.



    Mark, AB9LZ is correct that you can used common copper wire (insulation typically rated to 300 V) for QRP power levels and for the Elecraft BL1 kit, up to 150 watts RF.
    Last edited: Sep 16, 2012
  4. G4COE

    G4COE Ham Member QRZ Page

    The real reason silver plated copper conductors is used in Teflon coated insulation is that teflon requires a high temperature to extrude, the temperature being that high copper would instantly oxidised.... and we should know the advantage of silver plating.

  5. G4LNA

    G4LNA Ham Member QRZ Page

    Newark seems to have plenty. I buy mine from its sister site Farnell Electronic Components in the UK.
  6. G4LNA

    G4LNA Ham Member QRZ Page

    Or, if you want the stranded stuff from Newark, scroll down the page a bit.
  7. K8ERV

    K8ERV Ham Member QRZ Page

    I didn't know TFE insulation was used for sleeping. I'm gonna try that.

    TOM K8ERV Montrose Colo
  8. AA7EJ

    AA7EJ Ham Member QRZ Page

    Thanks for all replies, I do appreciate most of it.
    I am still struggling with QRZ discussions which turns into jokes, sermons or otherwise highjack the thread. Despite being very opinionated I still believe in freedom of speech and opinion, so be it, I live with it.

    The coupler / tuner I am building was published long time ago and is basically LC filter with autotransformer ( 50 to 12.5 Ohms) at the input, not a balun. The design goal was to couple TX to short ( whip type) antennas with minimum adjustments.
    The design calls for using twisted pair and Teflon tape to cover the toroids. It uses stack of toroids. ( Increase power handling capacity of the transformer?) One of the design requirements is to maintain physical positions between the wires to maintain desired characteristic impedance. Since the characteristic impedance depends, besides wire dimensions, on distance between the conductors, the insulation thickness is important.

    BTW. I did try to twist unknown (Aircraft?) stranded wire of 22 gauge and managed to break the outer insulation so the inside brownish tape poked thru.
    After much search I found scrap of 22 gauge “appliance wire “ with TFE insulation. Will try it next.

    As far as what wire size – I need to do some search on how to calculate voltage and current on the output of 100 W TX at resonance, or just put a scope on dummy load with known PA setting on my Ft 857.

    Or maybe there is something like that on the web HI HI HI .

    But I need a refresher course on transformers in general , anyway.
    And not on the type my grand kids play with.

    Cheers Vaclav
  9. AD6KA

    AD6KA Ham Member QRZ Page

    For Teflon insulated wire, I go to Apex Electronics.
    It's a BIG surplus place about 30 minutes from
    my QTH. They have pallet racks piled with spools
    ofany size & color of Teflon and almost any other
    wire you want.
    Price is $5.00 per pound plus shipping.

    Their stock is NOT all in their online catalog,
    so give them a call or email with your needs.

    If you are ever in the area, drop in, it's a FUN
    place to poke around in. Don't tell the XYL
    "I'll only be there 20 minutes" because I guarantee
    you will get distracted by all the cool stuff they have there.
    73, Ken AD6KA
  10. K7MEM

    K7MEM Ham Member QRZ Page


    Just a little warning on working with Teflon insulated wire. Teflon insulation is very heat resistant and doesn't burn or disfigure when it is being soldered. But Teflon is not resistant to pressure. Too much pressure during winding or bending will cause the Teflon insulation to be displaced (cold flow).

    Years ago, we used Teflon insulated wire for the power to a rack of PC/hand wired boards. The wire was used to connect the +10 volt power and grounds. Each cable cable bundle consisted of 10 - #10 Teflon insulated wires. At one end they were grouped into a very large solder lug and at the other they were distributed across the card rack to the board connectors. We had about 24 of these racks and when QA inspected the harnesses, they found that all of them had cracked and had to be replaced. That kept me busy on a third shift for several weeks.

    We also used a #30 Teflon insulated wire for some board building. The wires were generally routed from chip to chip in the gaps between the chips. To keep everything neat and secure, the wire was bundled at intersections, and during long runs, using waxed nylon lacing string. If you made the tie up too tight, you could easily introduce shorts that were very difficult to find.

    Just take care when using Teflon insulation.

    Martin - K7MEM
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