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Light an LED by drawing power from high tension wires

Discussion in 'Electronic Basics' started by Owen Lawrence, Nov 16, 2003.

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  1. Hi. I bought one of those 1mH coils from solarbotics, and a
    supercapacitor, in the hopes that I could cobble together a little circuit
    to light an LED when I drive under those huge high tension wires. I figured
    if I choose the component sizes to make a tank circuit with a 60Hz
    fundamental frequency, I could somehow get a voltage and draw off power to
    charge up the supercap. Then it could be used to drive a blinkey light.

    But on paper, after I connect the coil and a capacitor of the right size
    together (in parallel?), I'm stuck. What do I do next?

    Do any of you know of a circuit that can do this, or can you give me
    some advice on how to proceed? Thanks.

    - Owen -

  2. I think you will have trouble getting the blinky light to run off any
    small sized circuit, regardless of design. This is because the energy
    density in the field at ground level under a transmission line is
    pretty diffuse.

    But you will learn some things from the exercise.

    Think of this resonator as just a very low frequency AM radio
    receiver. You need some sort of rectification to convert any resonant
    AC in the tank into a DC output to charge up the cap. Since you are
    working with very low power, you might start with a 1N4148 signal
    diode, or a small germanium or schottky diode (which will waste a bit
    less with forward voltage drop). There are lots of ways to connect
    the rectifier diode and cap to your resonator, but you might just
    connecting them in series, and paralleling that across the tank. You
    might get enough voltage to measure with a DC meter.

    I once stood under the 500 kV lines with an umbrella, and drew a thin
    spark between the metal and the tip of my finger. It might have dimly
    lighted a neon lamp.
  3. Disappointing. Maybe I can draw power from wires in my house, instead. I
    realize that the two wires in an extension cord, side by side, cancel each
    other at any distance, so I'll have to place it next to a single wire.
    (Correct me if I'm wrong.) I'll try the high tension wires, though.
    Do you mean something like this:

    | |
    ---| |---------
    | | Cap | |
    | ------||-----| |
    | |
    | |
    Supercap Diode

    I have a 1N34 diode; would that work better than a 1N4148?

    Do I then draw power off the supercap to whatever circuit I intend to drive,
    by just connecting where I put the '.'s in the above diagram?
    Somehow I don't find that very comforting. Pretty cool, though!


    - Owen -
  4. The same holds true for the high tension lines. That's why the three
    conductors periodically change positions on the towers. They
    transpose the wires to cancel out the field along long lengths.

    Was his name Ben Franklin, Jr.?

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