Free Electricity from your Phone Line

While researching the last book, I became interested in electronics and built a few simple projects in my spare time. This one in particular might be of use to folks out there, and is worth mentioning.

One of our relations lives off the grid and I've been helping him install a solar PV panel system. It occurred to me that while he had no grid electricity, he does have a phone line. Phone lines carry their own power. It's not much, about 1 watt, but that's better than nothing. I measured 48volts at about 20 milliamps. It's AC, so you need to rectify it. The following simple circuit works well enough.

You'll need to buy a phone extension cable. I got mine for £1. Then strip the wires. Black and Yellow carry the power, so connect those to your bridge rectifier, and you're set. 48V is good for 12 LEDS, which use about 3.8V each. The larger the resistor, the less light you'll get from your LEDs. But if your resistor is too small, the phone won't work. So you'll need to strike a balance. A 1k resistor worked for me. The phone sounds odd, but it still works.

My picture here really doesn't do the light justice. It's easily bright enough to read by, and dimly lights up the whole room at night.

But this isn't a very efficient circuit. LEDs don't need a constant supply. You can use a transistor to quickly pulse the DC current and get more light output for less amps. I think the next step would be to build a little transformer to step the 48v AC down to say 5 or 6 volts and then split the current between a series of mini Tesla coil circuits and use those to power CFLs wirelessly. I'll see how that goes, but in the meantime, I have a cool wee light - for free.

As far as I know, there's no law against using the power from your phone line.