On 1/30/18 8:37 AM, Jim Thomson wrote:
Date: Sun, 28 Jan 2018 18:02:55 -0800
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk reflector <towertalk@contesting.com>
Subject: [TowerTalk] Voltage Breakdown For Enameled Wire
<I'm once again considering winding high power chokes with enameled wire.
Zo of a closely #12 pair is about 53 ohms, which makes it desirable IF
breakdown voltage is sufficient. I would appreciate for sources of #10
or #12 enameled wire with published breakdown specs.
You're looking at motor windings driving the specs.
The wire insulation is defined by temperature class and "build" (single,
double, triple)
these folks probably have the info.
http://mwswire.com/
if it's not in the catalog, give them a call. They've been helpful in
the past when I've had weird questions about wire (I was buying thin
aluminum wire, and also building tesla coils, etc.). They've probably
answered questions about RF applications before (heck, they'll make you
some custom multi metal wire if you want, as well as stocking bifilar,
as well as tri and quad, usually used in inverter/switchmode
applications).
In general, I suspect you'll get voltage ratings for 60Hz and for some
specific pulse waveform (corresponding to spikes from an inverter) with
an "endurance" rating - how many hours can you run with that waveform
applied before it breaks down.
Some other data sheets I have laying around give breakdown voltages of
10 kV or thereabouts, but it degrades over time and high temp (300C)
Try this:
https://www.hitachi-metals.co.jp/e/products/auto/el/pdf/MagnetWire_en.pdf
I've found that THHN (about 93 ohms Zo) works fine for simple antennas
like dipoles, but some multiband antennas with complex matching/coupling
systems don't like that much mismatch. We had this problem with the
Force 12 C3SS, the choke is enameled #12 of unknown pedigree. No
breakdown issues with a 600W power amp and the antenna is a good match
to it, but the engineer in me wants to be conservative for legal limit
to an 80/75 dipole that I use from 3.5-3.9 MHz.
Yes, I know I could put the conductors in Teflon tubing, but that
increases Zo. I've measured #12 pairs with various Teflon insulation and
get values around 101 ohms at HF.
Suggestions?
73, Jim K9YC
## I bought a bunch of 10 gauge and also 8 gauge from SSON, on sale,
years ago. It used polyimide. Was rated for 15 kv, at least in the larger
gauges,
like 14-12-10-8. V rating was reduced with the smaller gauges, since if 15
kv
insulation used on real small stuff, like 18-28 gauge wire, then the
insulation would be super
thick compared to the actual small gauge wire diameter itself...and 28 gauge
wire would resemble
something like 20 gauge wire.
## In Orrs very last handbook, the blue covered one, they had a chart at the
back of the book, showing
3 different diameters for the SAME gauge magnet wire. The difference
between the 3 was the thickness
of the insulation used. This can have a profound effect when winding plate
chokes for tube amps, and explains
why 2 identical wound chokes can have series resonances on different freqs.
The turns per inch was less
when the thicker insulation was used.
## The stuff I bought hi pot tested to > 15 kv. And > 30 kv between
adjacent turns. If you really want to go crazy,
you can slide it into teflon tubing, but as you stated, for your application,
Zo increases too much. For my application,
I was just using it for bifilar fil chokes..and the 15 kv rating was gross
overkill anyway, but at the time, the price was right.
## What ever you end up buying, easy enough to hi pot test it, which is typ
done at DC..or 60 hz AC.
Jim VE7RF
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