A reader was asking to buy different colours of teflon coated wire to make a balun. This is my practical answer.
Thank you for asking about teflon wire to make a balun. I’m sharing my response on a Radio-Shop page for other users to read too.
I don’t stock teflon wire for baluns, and more importantly I don’t use teflon wire. It is a weird American habit that is seen in some amateur YouTube videos, maybe to identify the wires. The issue is the thickness and heat resistance of the teflon insulation.
Commercial transformers, baluns, chokes, etc are wound with enamelled copper wire (also called _transformer wire_) for a host of good reasons. I use 1.8mm, 1.2mm, 1mm, 0.7mm and 0.2mm enamelled wire. The American 18AWG (18SWG is a different and long discontinued size) happen to be in the 1mmØ range, which is the about the correct size for a 1KW transformer or balun. I’ll copy a portion of the conversion table for you.
A quick calculation will show that for an amateur radio delivering 100 watts to a balun/unun/transformer into a 50 ohm load, the respective formulas are Volts = Sqr (Watts x Resistance) and it works out to a nice 71 volts at slightly more that 1.3 amps. Considering that the standard for household wiring is around 10 amps for 1mm wire (and that already includes a generous safety factor) you can very comfortably use 1mm wire in your device.
Copper wire or transformer wire is sold by the kilogram, not length, but I can always wind off a piece for you if you are interested in making your own.
Hi Leon,
One thing that should be taken into account at higher frequencies (not applicable at mains), is skin effect.
As frequency increases, so the current tends to be at maximum near the surface of the conductor and
decreases exponentially towards the centre.
This then, makes the conductor appear “thinner” than it actually is and thus contributes to losses and heating effect.
To be on the safe side, always use a slightly larger diameter for conductors then needed at higher powers on RF.
Hope this helps.
Hi Paulo,
Thank you for reaching out. Indeed, you are technically correct about wire sizes, but at the same time going overboard (too thick; too close; etc) leads to other issues that can cancel out any gains made by increasing the diameter. My advice is always: Use the correct size, no more and no less. At least then you know what you are dealing with and you can calculate any required compensations.