[TowerTalk] Voltage Breakdown For Enameled Wire

[jimlux]

On 1/30/18 8:37 AM, Jim Thomson wrote:
> Date: Sun, 28 Jan 2018 18:02:55 -0800
> From: Jim Brown <jim at audiosystemsgroup.com>
> To: towertalk reflector <towertalk at 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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