I have found that using regular magnet wire with teflon tubing slid over
the wire will easily handle 2KW. I have wound a number of 4:1 transformers
as well as 49:1 transformers for EFHW using this method. All the balun
designs use a similar scheme; most likely due to the cost and difficulty in
obtaining silvered wire.
Ken WB6MMV
On Wed, Jan 27, 2021 at 2:10 PM David Eckhardt <davearea51a@...>
wrote:
I was also surprised it broke down, but every CMC I wound with solid #12
enameled wire broke down between 400 and 700 watts. I believe it has a lot
to do with the impedances in which the CMCs are installed. My W/C is on
40-meters where I measure 1161 - j1110 at 7.0 MHz. My lowest impedance is
at 2.0 MHz and measures 19 - j288.
I have not tried or thought of using teflon coated silvered conductor. I
need to find it and, if not too expensive, give it a try.
I rewound the 400-31 single core with the DavisRF 'antenna' wire with no
problems to at least 1.2 kW. It is certainly better at CM impedance than
the 43 material especially on 160 and 75 meters but 43 is a bit better on
the higher bands - as expected.
Out of all the CMCs I've wound and tested, I have three that I can use, all
wound with the DavisRF #14 stranded and insulated antenna wire: 1)
240-31, 15 turns, 2) 300-43, 16 turns, and 3) 400-31, 21 turns. Those
remaining do not perform well under DM loss (rejection) or phase balance
(¦Ð-radians out of phase) and/or amplitude balance on the DM side. I'm
going shopping for Teflon coated silvered solid conductor.
Dave - W?LEV
On Tue, Jan 26, 2021 at 11:26 PM Jim Lux <jim@...> wrote:
On 1/26/21 3:04 PM, n2msqrp wrote:
Dave,
Have you tried teflon covered silver plated wire?
Mike N2MS
The silver doesn't help much for RF conductivity, but it is a LOT easier
to solder to.
I'm kind of surprised that magnet wire broke down. Most magnet wire is
good for a kilovolt or so, because motors and transformers get hi-pot
tested at 2-5kV.
Decent insulated magnet wire
Catalog here:
AWG 12 copper bare is 0.0808 (nom)
single build is 0.0825 (i.e. the insulation is 8.5 mils (0.2 mm) thick
heavy build is 0.0842 is twice as thick. (0.4mm)
most plastics have breakdown strength of 20 kV/mm or more, especially
for thin layers.
PTFE (Teflon) and Polyimide (Kapton) are a lot better (100 kV/mm)
Polyester (Mylar) is in between (50kV/mm)
Note that thinner layers have a higher breakdown voltage per mm (that
is, you might find that a layer that's 0.1 mm and 1mm have almost the
same breakdown voltage)
Formvar is about 11kV as typically applied to wire.
On 01/26/2021 3:30 PM David Eckhardt <davearea51a@...> wrote:
Those wound with the #12 enameled solid conductor do not take power
with
my ant/feedline impedances resulting in discharges between bifilar
pairs
(not between individual bifilar windings). Also, the green wire of
unknown insulation does not take power. So, those CMCs wound with
solid
conductor are coming apart and being rewound in some fashion or
another
with the DavisRF "antenna" wire which seems to take power to at least
1.2
kW. Your mileage may vary with different impedances presented to the
chokes.
Those frequencies on which I tried the CMCs at power are:
3.8 MHz 24 - j56
7.15 MHz 493 - j740
Impedances noted are measured at the shack end of the parallel wire
feedline.
Dave
--
*Dave - W?LEV*
*Just Let Darwin Work*
