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From: roger@telesoft.UUCP (Roger Arnold @prodigal)
Newsgroups: sci.electronics
Subject: Re: Living near high tension lines
Message-ID: <112@telesoft.UUCP>
Date: Mon, 9-Nov-87 21:06:09 EST
Article-I.D.: telesoft.112
Posted: Mon Nov  9 21:06:09 1987
Date-Received: Thu, 12-Nov-87 23:38:42 EST
References: <9312@tekecs.TEK.COM> <1718@bloom-beacon.MIT.EDU> <1913@frog.UUCP> <2209@kitty.UUCP>
Organization: TeleSoft Inc., San Diego, CA
Lines: 44
Summary: insert foot in mouth..

In article <2209@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes:
> In article <1913@frog.UUCP>, die@frog.UUCP (Dave Emery) writes:
> 
> > 	I have heard a similar story about farmers in the Midwest using
> > long stretches of barbed wire fence near long distance power lines for the
> > same "free" power gambit.  As I understand it the power companies were able
> > to sucessfully prosecute some of them for stealing power.
> 
> 	The above situations sound like rural (as opposed to urban) legends
> to me. [..]
> 	Now, let's look at this situation and apply a bit of electrical
> engineering.  Let's assume the following:
> 
> [back-of-envelope analysis omitted]
> 	The above assumes an iron core in the "receiving coil", which at
> 4 x 40 feet in dimensions is pretty impracticable.  Without actually doing
> the calculations, an air core would be at least an order of magnitude less
> efficient.
> <>  Larry Lippman @ Recognition Research Corp., Clarence, New York
> <>  UUCP:  {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry
> <>  VOICE: 716/688-1231       {hplabs|ihnp4|mtune|seismo|utzoo}!/
> <>  FAX:   716/741-9635 {G1,G2,G3 modes}   "Have you hugged your cat today?" 

I'm probably sticking my foot in my mouth, since I haven't really thought
about the problem, and Larry isn't often wrong.  However..

I don't immediately see what iron core vs. air core has to with the amount
of power that can be extracted in this situation.  There's a certain
induced EMF in the pickup loop, and the power extracted is a function of
the integral of the product of this EMF and the current in the pickup loop
over one cycle.  If you assume a simple resistive load in the pickup loop,
then you get one answer.  But if you were serious about extracting power by
this method, wouldn't you use a resonant circuit, or something that gave a
high current in the pickup coil, properly phased against the induced EMF?

Hmm, the process is still limited by resistive losses in the pickup loop.
Doesn't do any good to push more current through to extract more power, 
if the increased resistive losses more than offset the additional power
extracted.  Probably optimizes out to about what Larry calculated...
unless, of course, what you're INTERESTED in is heating the barn.

Well, back to the drawing board. :-]

- Roger Arnold				..sdcsvax!telesoft!roger