My friend just bought an inductive stove-very cool. My question, now that we have LED lamps(that just consume a few watts), why not wire them into inductive loops in the ceiling, and transmit the power via a nice big coil in the floors? If your radio and TV are properly shielded, you would have no interference problems. No more wall switches-just handheld RF controls!
Would it work?
would it work? yes.
does it make sense to do so? no.
you need less wire and less power if you wire directly. wireless switches already exist for wired devices.
i do have a toothbrush that charges inductively so it does work for some situations.
This is basically one of Tesla’s old ideas. Tesla envisioned power towers all over the place radiating power out through the air and devices would just receive the power and use it.
The problem is that you end up wasting a lot of power. You end up beaming power out in all directions and only a few devices in specific areas end up using parts of it. If you are beaming from a fixed point to another fixed point (as in a ceiling light) then you can make things a bit more directional and you won’t be quite as wasteful but as johnpost said it’s more efficient and less wasteful to just run a wire to the thing.
Inductive power transfer is being done more and more though. Electric toothbrushes and shavers have used it for years so that they could keep the device sealed from water and still be able to transfer power to it to charge it. Now a lot of small hand-held devices are starting to use it because the devices are small and thin and a power jack would either be too thick and bulky or too thin and fragile. You’ll note that most of these devices work over a very small distance. The electric toothbrushes and shavers pretty much have to be in their charging stand and the newer electronic things have to be sitting on a charging pad. The close distance helps reduce the amount of power lost through waste and keeps the devices relatively efficient.
A similar idea is to transmit the power via RF, as in a microwave beam instead of an inductive coupling loop. This is how RFID tags work. The RFID tag contains a tiny chip and a capacitor. The incoming RF beam is first use to charge the capacitor. Once it is sufficiently charged, the chip turns on and broadcasts its RFID code. These also work over a fairly short distance. Longer distance RFID systems do exist, but they usually use battery powered tags instead.
I would expect to see more and more uses of wireless transmitted power as time goes on, but it’s not going to replace wires for the bulk of power distribution around your home and probably isn’t going to be used for lighting systems either.
By the way, if you want RF controls, that already exists. From what I’ve seen they are more popular in Europe than they are in the U.S. I don’t know how true it is, but I was told that this was due to the fact that a couple of decades ago, when these RF controls started to be introduced, a lot of homes in Europe still had old fashioned pull chains on ceiling fixtures instead of wall switches, and these RF controls were a quick and easy way to convert the ancient systems over to a wall switch.
Maybe your switches wouldn’t interfere with your radio and TV, but how about with your cordless phone? Wi-Fi network? Garage door opener? Wireless keyboard? Or maybe the interference those items put out will mess up your switches.
Your house is full of little RF transmitters and receivers.
I thought most non-battery RFID used inductive coupling as well. Wikipedia says at least some do, but I can’t get any sense from there of which method dominates.
I was under the impression that an inductive power source is like the primary winding on a transformer. If no power is drawn from the secondary, these will be very little drain on the primary. So I don’t see it as radiating power in all directions the way a microwave transmitter would. Obviously there would be some losses, but I cannot estimate how large the losses would be if you just powered, say, some LCD lamps. How about if you used it only to power a few really cordless phones?
The difference is in near-field and far-field transmission. With a transformer the primary and secondary coils are close enough to each other to be directly coupled magnetically. The current on the primary induces a current on the secondary, and the load on the secondary causes an effective load on the primary, so the current draw on the primary is determined by the load on the secondary. For this to work you need to have the primary and secondary very close to each other. Broadcast power doesn’t work like that, the secondary is too far away to have much of an effect on the primary, so the primary has to be blasting out a lot of power that is wasted all the time.
I can tell you that 10 years ago, beam-powered RF tags by far dominated. I haven’t done much with RFID since then though and I don’t know the current market very well. I suspect that the flat tags used for things like badge readers and toll booths are still beam powered but the little grain of rice sized tags used to track pets are probably inductive.
Yes, but the OP is asking about a near-field situation, too. It’s sort of a distraction to bring up Tesla’s wildly impractical far-field schemes in this discussion.
That said, for the specific application the OP has in mind, there’s no advantage at all to inductive power, because you could do all the same things with wires.