Re: Off-The-Shelf chokes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

First, look at what sort of resistance that 500 ft will have...

about 1 ohm according to one table

now think about how much current... say 20 Amps...
I^2 R  = 400 W.... that's a fair amount of heat to dissipate in a small
volume.  You don't have much radiating surface, so, mostly, you're depending
on the 10 pound mass of the wire and the short actual run time to keep
temperatures reasonable..

Figure that the specific heat is around 0.25, and, there's probably around 5
kilos all told.. Each kJoule disspated will raise the temperature around 1
degree C.  At 400W, you'll dissipate that kJoule in 2.5 seconds...

Figure the wire is good for 90C, starting at, say, 30C, so you can tolerate
a 60 degree rise.  60 degrees => 60 kJ => 2 1/2 minutes...

This is a worst case kind of calculation... if you're only running 10Amps
through it, then the power is 1/4th.. there IS actually some cooling, etc.

You could stick the spools in a bucket of water... Break the spool flanges
off to let the windings increase their spacing a bit...

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, September 15, 2002 11:44 AM
Subject: Off-The-Shelf chokes


> Original poster: "Cajun Coiler by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<cajuncoiler-at-cox-dot-net>
>
> I recollect hearing of some personages using a
> 500 ft roll of #12 THHN as a current limiting
> choke on their NST, and it was found to get warm.
>
> I found such rolls of wire at the local Home
> Depot for $18(and something) a roll, and so I
> begin to ponder...
>
> Is there just that many amps being shot thru
> the roll to cause the heat? Or is this just
> normal dissipation?  Nobody mentioned if the
> warmth was a "abnormally warm", or just an
> average normal operation "warm".  Can we get
> an official description of operation?
>
>
>