Re: The Strange True Story of a Radio Station's Transmitter in New York State

Grumpy The Mule wrote:
Cecil Moore <nospam@xxxxxxxxx> wrote in
news:_0czk.235$fD.114@xxxxxxxxxxxxxxxxxxxx:

Mike Y wrote:
And while I realizeit's quite possible to get 'shocks' off an
induction
coupling that essentially goes to a high impedance, it's a far cry
from being
able to 'power a house' with a broadcast transmitter that wasn't
designed for the purpose.
The original story that I heard about 40 years ago is
that it involved 60 Hz high-voltage power lines. A
farmer is supposed to have built an induction coil
in a shed directly beneath the power lines and picked
up free energy.

Hmm.. a bit of physics..

Induced voltage is Nturns*dPhi/dt
dPhi/dt -> change in flux (Webers) per second

Flux is area of coil * B field.

AC field under a HV power line is typically around 1-10 microTesla.

So, the peak flux through a 1 square meter coil is about 10 microWeber.
At 60Hz, the maximum slope is 2*pi*frequency, or 377, so now, we're up to 377*10E-6, or 377E-5 or 3.77E-3.. about 4 millivolts..

Now, lets assume a coil that's 10x10 meters.. that's 100 square meters, so we're up to 0.4 volts, open circuit voltage, for one turn.

Now, let's say our ambitious farmer winds 100 turns.. now we're up to 40 Volts. But, that coil is 4000 meters of wire (100 turns * 40 meters/turn), and will have non-zero resistance. Let's say our farmer used AWG 10 wire. about 1 ohm/1000 ft, so call it 13 ohms all told (4000 m is approximately 13000 ft).

So we have a source with 40V open circuit output voltage and 13 ohm output Z. If we hook up a matched load (another 13 ohms), it will have 20 Volts across it, and dissipate about 30 watts in the load and 30 watts in the loop.

Now, at $0.10/kWh, and 0.03kW, that's about $26/year

Of course, there's the labor in building that coil.
And, the cost of the wire. (400lb of copper at $3/lb is $1200)

Sure, you'd use aluminum wire, so you could cut that down by a factor of 3 or so.. So, invest a lot of hours stringing up that coil, and a few hundred bucks in aluminum, and save $30/year...

Excellent economics there..

.

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