- Sun Feb 19, 2006 1:09 am
#10070
Well, cesarsalad, I imagine that you have either done your experiment and moved on to bigger and better projects or killed yourself by now, but if not, here are a few thoughts.
You can run your coil off the line safely with a suitable series resistance and suitable insulation of all possible points of contact with hot terminals. Use electrical tape liberally.
Any large diameter coil you wind yourself will have insufficient inductance or resistance to limit current, even with a 12 volt transformer. A suitable and foolproof current-limiting resistor is a household light bulb in a hardware store surface-mounted ceramic socket. If you can wire it up directly across the line, you can wire it up with a series coil. Current is easily selected and changed by selection of the lamp wattage. (I presume you can calculate current from voltage and wattage.) The lamp also makes a pilot light that you can't ignore.
You won't find a ready-made coil in a hardware store, but you can easily wind your own. Without benefit of calculation or experiment, I would start out by winding a few dozen turns of, say, # 16 wire insulated for at least 120 volts around the grooved top of a plastic 5-gallon bucket for the primary and secondary. Alternatively, you could make a coil of any desired diameter by putting some nails into a piece of 1/4" plywood, insulating the nails with electrical tape, and winding the wire around the nail pattern. Note that there is no particular virtue of a circular coil as opposed to a square coil except economy of wire usage for a given enclosed area. (Square coils were often used by ham radio operators before they all went to VHF/UHF Walkie-Talkies.") (OW! OW! Just kidding, hams.)
Since a coil of these parameters would have negligible current limiting inductance at 60 Hz., the current in the primary coil will be totally determined by the wattage of the light bulb used. About 0.13 amps for a 15 watt bulb, 0.35 amps for a 40 watt bulb, and 1 amp for a 120 watt bulb - all well within safe current for #16 insulated wire, even if not to code.)
As a receiver I'd start out with an LED connected across the + and - terminals of a full rectifier bridge fed by the secondary coil ends and see how close I had to get to the primary to light the LED with and without some iron inside the coil(s). If you don't get enough sensitivity to light the led at the desired distance, you can very safely use many turns of fine, enamel insulated "magnet wire" in the secondary (NOT the primary!) You can buy enameled magnet wire at an electronics supply house. At a given distance, received voltage will be proportional to, among other things, the number of turns in your windings.
Have fun.
awright
