Fry-kun wrote:I have a house with built-in coax cabling to each room (2 cables per outlet, all coming to a single junction box on the other end). I don't use them for anything, so I had a [potentially] stupid idea -- would it be reasonable to use those cables for some DC power? Perhaps I could install a USB outlet everywhere there's a coax plug right now (to charge various devices).
How much power could I transfer over those cables? What other considerations are there?
You could but you can't use any house current voltages like 110 V in USA or 220 in other countries. I would keep it at a low 12 volts. But of course you realize that there is an intrinsic resistance in 75 Ω cable TV coax. Of course that is impedance for AC voltages. But there is a much smaller DC resistance present too. Couple that with the intrinsic resistance for long runs you can expect your resultant output voltages to be much smaller than 12 volts. So you will need a variable power supply that can compensate for the resistance.
What I would do with it would be to use it for a CCTV system to watch for burglars or check on the kids in the play room. You could use it for a closed circuit room-to-room simplex video intercom. You could use full-duplex if you use surplus Ch 3 and Ch 4 RF modulators. You can't run several CCTV cameras without a video sequencer or variable RF channels.
You could also use it for a extension for your POTS telephone - to a hard to wire room that already has coax but no telephone wiring. They use about 5-9 volts DC for speech and dialing. About 48 volts AC for ringing.