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I have an electric fence running around my farm. I would like to be able use this to power a number of 12V lights along the road so I have a ready source of light, especially since the electric fence is on continuously.

The specifications I can find for the fence is - DC 5000 V, pulse about 500 microseconds every 1 sec, 1.5 Joules (these vary for different energisers.) (As you can see I am no electronics or engineering buff.)

Can anyone help me with the electronics to convert this power pulse into a steady 12V power supply for lights?

JRE
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Andrew Coulton
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  • While it is doable, I think that doing it may damage the power supply, or more likely knock it into a over current mode. What happens if a animal touches it and stays on it, does it turn off within a few seconds? What kind of 12 volt lights are you planning on using, incandescent or led? – Garrett Fogerlie Dec 23 '12 at 12:15
  • Bad idea unless you want to use very dim 5mm LEDs with surge lightning protection in each one. and a choke for every LED to isolate impedance from 1 sec 0.5mS pulse widths – Tony Stewart EE75 Dec 23 '12 at 13:21

5 Answers5

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Run a separate cable along the fence.

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That's not a good idea, use a separate power supply for the lights.

1.5 Joule once per second means you have at most 1.5 Watt of power for your lights, which probably is too little for several lights (and then the electric fence wouldn't work any more).

And this is far too optimistic, because the huge voltage difference would cause big energy losses. And components for 5000V tend to be expensive.

Edit: Best is probably to use those inexpensive solar powered garden lights.

starblue
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    I have **NEVER** seen those solar powered lights put out anything even resembling a useful amount of light. Every one I have seen barely puts out enough light to make itself visible, let alone actually light up the surroundings well. – Connor Wolf Dec 23 '12 at 13:29
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    @FakeName: I agree completely. These solar garden lights are not only crap right after purchase, they're even more useless after one winter. They're all made in china, designed to be crappy. Let's not buy stuff that will just end up in the landfill after a few weeks. – Christoph B Dec 23 '12 at 15:22
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I would use a high voltage capacitor with a diode and a regulator on top of that. It would maybe be possible to power a small LED about it. I don't think you can power much from the fence, and even less if you want the fence to actually work as an electrical fence.

Gunnish
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The simplest way is probably a small neon bulb such as the fence testers use, but you won't get much light out of it. If your fence is current controlled (does it adjust the power to compensate for weeds, etc. touching it?) then you can get a bit more energy out, but in the end it's going to be limited to avoid killing people who touch it.

I can get a pretty bright glow from a white LED + 10k ohm resistor connected to my horse fence, but it's not really usable for anything. Remember that it's pulsing, so you get one flash about every second or so. I only built that circuit because I couldn't find the "real" fence tester and I needed to check a section of fence (gets painful repeatedly shocking yourself just to check the wiring).

Much easier to put a few solar powered lights on the fence posts and turn them on when needed.

lyndon
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I you're using a multistrand fence isolate two of the earth wires from the fence and use those to power low power led lighting. You can run them off a battery to give lighting when the power is down on the grid.

stheman
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  • Welcome to EE.SE! Could you clarify your answer a bit? Does your suggestion still work if the electric fence is operational, and would it survive something touching both the high voltage line and your isolated ground? If the answer is no, then you haven't really addressed the original question. – Joe Hass Dec 29 '13 at 13:34