Send 12vdc through the air?

T Chap

I had someone ask me today about how to connect DC to a moving object without the hassles of wires bouncing around or getting broken over time. I thought maybe there is a way to send AC through the air like those battery operated tooth brushes that charge on a stand with no electrical contacts. I assume they are just using a coil on each side and sending AC, then rectifying the AC. Does anyone know of a robust system to get <1 amp like this?

legoman132

I think you could do it, but it might be tricky. how far and in how many dimensions does the thing have to move? there could be a better (easier/more robust) way

ElectricAye

If you're talking about sending that kind of power across, say, a few millimeters, then you could probably use induction of some sort. But if you're talking about sending that kind of power (1 amp at 12 volts) across a room or farther via radio waves, then chances are you risk cooking the flesh of anyone who might be standing around the thing. If you use a laser or microwave to focus the energy into a beam, it's still a tremendous hazard, not to mention difficult for an amateur to do.

T Chap

ElectricAye wrote: »

If you're talking about sending that kind of power across, say, a few millimeters, then you could probably use induction of some sort. But if you're talking about sending that kind of power (1 amp at 12 volts) across a room or farther via radio waves, then chances are you risk cooking the flesh of anyone who might be standing around the thing. If you use a laser or microwave to focus the energy into a beam, it's still a tremendous hazard, not to mention difficult for an amateur to do.

Sorry I didn't make that clear, only when a door is in fully closed position so that a device is mounted on it and can come in contact with some other device mounted in the wall does it need to work. So that actually the two parts could be basically touching, but as far as electrical contacts, that is no an option, I think it would be asking for headaches. A coil on the door and a coil on the door where they can touch each other, that seems like a reliable method.

I heard rumors the Tesla had a system that would transmit energy and everyone could drive their cars off it :

Whit

T Chap wrote: »

I heard rumors the Tesla had a system that would transmit energy and everyone could drive their cars off it :

There was a show about this the other day on the History Channel. It was pretty wild.

ElectricAye

T Chap wrote: »

...
I heard rumors the Tesla had a system that would transmit energy and everyone could drive their cars off it :

Yes, I think Tesla believed it could be done, but I don't think it's a realistic concept. For one thing, living things are sensitive to electromagnetic fields, so it's more likely you'd cause some kind of damage to cellular functions. As Tesla got older, his mind reportedly evaporated into some kind of fantastic, otherworldly dotage and I sometimes wonder if his "visionary states" might have been caused by his years of exposure to strong damaging electrical and magnetic fields.

TheGrue

Well, as a Tesla buff I can answer you. He thought that he could improve his mind with high doses of X-Rays at one point in his life. That destroyed his photographic memory.

But before that time, he did transmit electricity about 20 miles away using a high powered coil at high frequency. There are pictures of him sitting on a chair in the center of that transmitter. Alas, such a transmitter, if turned on today, would fry everything electronic for several miles. I went through several computers and digital watches when I was building and testing large table top Tesla coils.

The chargers that you mentioned are simply a primary coil in the charging base and a secondary coil of the same frequency in the item to be charged. All at a low enough power and frequency so as not to bypass any voltage regulators by induction on the actual circuitry.

Tubular

Not really good for 1 amp, but here's an easy to digest article on wireless power transfer
http://www.economist.com/node/16295708

The 10 minute video link at the bottom is even easier to digest. They talk about harvesting 1mW from the local TV tower.

mctrivia

if wires are possible but it is wear and tear that is worried about use flexible PCB instead of wires. They do not break as quickly from repetitive motion and stay neater.