Inductive Power through Floor?

Had an idea today, while trying to figure out how to power a low voltage item built into my coffee table.

I was wondering if any of you thought it would be possible or feasible to build or buy some sort of induction plates that would work through a floor and preferably a layer of carpet.

I imagine this would be great for floor lamps and other things which need power but which aren't always able to be close to an outlet.

Any ideas?

Reply to
E. Lee Dickinson
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Theoretically possible? yes. Practical? I don't think so. Safe? maybe not.

For efficient transfer of energy via induction, the driving coils need to be fairly close to the driven coils, and the alignment needs to be somewhat well controlled. Ordinary transformers are examples of inductive devices that are designed for efficiency where the engineers can easily control the relative placement of the coils. But they still put out a lot of heat, indicating they're not terribly efficient.

My toothbrush is charged by an inductive arrangement. It gets quite warm, indicating a low efficiency, but the power needed to charge it is very low. The advantage is waterproof sealing with no cords or sockets to corrode. But it still requires the toothbrush be nestled in the right position in its base for charging. It's no more convenient than the metal contact arrangement used for charging a cordless phone, and it's less efficient, but it's less prone to corrosion.

If you put an ordinary piece of metal on top of the driving coils, it will introduce eddy currents in the metal, producing lots of heat. That's how inductive stoves work, by inducing currents in the pans. You don't really want strong coils all over your floor sending power out to all nearby metal objects. A kid's metal toy could get hot enough to cause a burn. So for safely driving things as power-hungry as a 50 watt lamp, you'd want to have local power outlet coils that are only energized when a desired load is "plugged in".

There still might be concerns about the EMF fields from this kind of arrangement. There are enough health concerns already about 60 Hz EMF without introducing something that's explicitly designed to create more EMF into your home. Although I think many of the EMF concerns are unfounded and not based on sound science, I imagine it would be difficult to convince investors to develop products with such a huge lawsuit potential. I'd be hesitant myself to invest in something like this, because even though I don't believe 60Hz EMF is a huge health concern, I DO believe it's possible for a jury to find otherwise, so I think it's a huge lawsuit concern.

For small low power devices, if you can align the driven coils precisely over the driving coils in the floor, you might be able to make the technical side of this work. But I can't see it being nearly as efficient or practical as just putting ordinary outlet boxes in the floor.

Reply to

Hello Lee,

It is possible. You'd have to read up on series resonant power transfer and stuff like that. IIRC there was an experiment outlined somewhere on the web where they did that on a road in New Zealand. They could move illuminated lane boundary markers around by just sticking them onto the road surface anywhere there was inductive power, and they'd light up.

BUT: This can violate agency limits for RF emissions and could create a hazard for people, especially those with pace makers. Or imagine an ankle bracelet that slowly burns itself into the skin.

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