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Powering a device from radio waves? Answered

I was just curious, but I was told someone was arrested fpr powering their house from a tv signal (illegal I know), but I was wondering if there would be any case where it would be legal to utilise my own RF signal as the source of power for some devices, and how is it possible?

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LasVegas

11 years ago

What you were told wasn't exactly true. I have seen experiments where about 3v was acheved drawing power from regular radio waves. Yes. It's possible, but not much. It would be kind of cool to build something like this to light an LED. I doubt if enough current could be generated though. There is also a technique used illegally to draw power directly from high voltage lines. This takes a tremendous amount of copper wire and very close proximity to the lines. It would also be detected as an unusual drain at the switching station. Yes. This has been done. I've never heard of anyone getting away with it though.

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photozzLasVegas

Reply 11 years ago

Had a response ready, but Vegas said it perfect, so DITTO. It's not illegal to siphon the power. What is illegal is the proximity you need to be at to do this effectively. If you can get a coil arrangement you could keep off federal land and at least 18 feet away from any public utilities, you could do it. I will reiterate though that you will get such a weak signal as to be really not worth it.

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photozzVIRON

Reply 11 years ago

No... I would say it's fake.

Wikipedia:
For operation from AC mains voltage, the use of simple inductor (a so-called "magnetic ballast") is common. In countries that use 120 V AC mains, the mains voltage is insufficient to light large fluorescent lamps so the ballast for these larger fluorescent lamps is often a step-up autotransformer with substantial leakage inductance (so as to limit the current flow). Either form of inductive ballast may also include a capacitor for power factor correction.

http://en.wikipedia.org/wiki/Fluorescent_lamp

Now this could be a trick of the magnetic field surrounding the wires, but it's my understanding that you need high voltages, in the kv range to light up free-standing tubes.

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trebuchet03photozz

Reply 11 years ago

Transmission lines are in the kV range -- 100+ kV is very common (in fact, 100kV is "low" for a transmission line. The picture could be fake, but this is possible and stupid people have done it....

Transmission exits (sub station) are less than that, but are still in the kV range. Then voltage is dropped again at distribution stations (still in kV range) and then dropped one last time near the point of service to municipal level (110 - 220 etc.).


Fluorescent tubes will do that near transmission lines. It's also incredibly dangerous.

This guy does it (and the light bulb in the microwave trick). He makes some bad conclusion (just a fallacy) - but it's an example.

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photozztrebuchet03

Reply 11 years ago

OK, so I learn something. are there any electrical engineers in here who can explain the proximity/power ratio we are talking about? how many amps at what Kv are you exposed to at, say, 3 feet. I'll also say that going waaaayyy back to the original point, you would still have to be way too close, illegally close I would bet, to draw enough juice to make it worth it.

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trebuchet03photozz

Reply 11 years ago

Coulomb's law ;)

I know for a point charge the electric field decrease is by the inverse square of the distance from the charge. For a line of charge... I remember it's goofy -- well, I remember that we derived it in my phys2 class, and it was a rather painful integral. I think it was something like (L2+l2)-1/2 where L is the length of the line and l is your distance from the point. That's NOT the equation to find the charge. That's just how it's related to distance (I don't have the equation in front of me and I can't remember it exactly). Of course, that could be wrong :P

Current depends on either the potential gradient or how fast a conductor moves through the field (move faster, more current -- just like a dynamo). Which makes me wonder -- if you hold a F. tube parallel to the transmission line, will it light up? In theory, no -- because there's no potential gradient parallel to a line of charge. I'll have to hit up the physics forums and see what happens :)

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photozztrebuchet03

Reply 11 years ago

all that, or we could just get some brave and stupid (has to be both) soul to go out with a multi meeter...

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LasVegasphotozz

Reply 11 years ago

Also, it takes very little current at very high voltages to excite florescent gasses. This is why Cold Cathode lamps are relatively safe.

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akimbo m

11 years ago

You can infarct power something near substantial (If Led lights is substantial) with radio waves. Just go to your nearest phone shop! They may still sell those batteryless phone flashing stickers. These stickers uses the phone antenna while it is calling to power it led. However i have a question myself, >>>> Do anybody know how to make a phone batteryless led sticker? (Does not need to flash, only just glow) <<<<

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trialex

11 years ago

There is an AWESOME conspiracy theory that involves the US Pine Gap facility, which is located in Alice Spings, which geographically is about as close to the centre of Australia as you can get. Supposedly the facility has a MASSIVE underground antenna, which outputs RF energy that US submarines use to recharge their batteries when they are somewhere nearby. When you think that ALice Springs is AT LEAST 1500km or so from the cost in any direction, and how much power a sub would use, imagine how impressive the antenna would have to be. Still, nice theory though.

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jtobako

11 years ago

NASA was testing something like this, but it took several miles (or more) of antenna to get any power out. any RF signal has to meet FCC regulations, and any appreciable amount of power is going to make a huge noise. other than that, look into some of the old Tesla power broadcasting ideas.

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wischi

11 years ago

It would be cool to have something which is charging your phone form RF Energy. Of course this would be very slow but it's charging 24 hours d day and 7 days a week !! wischi PS I'm not sure if this is possible at all ;-)

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trebuchet03

11 years ago

Sure :) Check out a crystal radio ;)

Crystal Radio

It's powered off RF energy. Keep in mind, this isn't free energy if that's what your going for.

Theoretically you could build a rather inefficient, enormous and expensive array to collect, store and transform the energy to power a small light bulb... But solar energy is more abundant and cleaner (and cheaper) than doing that ;)