Comment by quesera | Hacker News Reader

Comment by quesera | Hacker News Reader

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> Dr. Hall, CTO WiTriCity: > "We just don't think about it anymore: I'm going to drive my car home and I'm never going to have to go to the gas station and I'm never going to have to plug it in.

Count me as a wireless electricity skeptic, in general. But this claim is astounding to me.

I believe that if you placed a properly resonant circuit into an MRI device, for example, you could charge a decent sized battery (but probably not a vehicle propulsion battery) at a reasonable rate.

But it would be horribly inefficient and your car (and everything else in your garage) shouldn't be made of ferrous metal.

Cell phone batteries on little charger pads, sure. Maybe even via ambient EM, though I'm not convinced you could get regulatory approval above a certain emissions level (which, critically, has an inverse-square relationship to available current delivery capacity at the device).

But the article also talks about lighting and televisions, and cars. WiTricity has investors to fluff, clearly, but is this not absolute crazy talk?

This is one of the fastest electric race cars on earth right now: http://www.draysonracingtechnologies.com/home.html

http://www.draysonracingfe.com/technology.html?Wireless-Char...

It gets charged via induction. Fifth Gear recently had a segment about this where you could briefly see the black flat device they park it over.

edit: pic: http://www.draysonracingfe.com/technology.html?Wireless-Char...

Of all the silly things one could do with "wireless" electricity, charging cars is probably one of the better applications.

I believe this is in use since quite some time for charging equipment like forklifts, busses on fixed lines, etc.

The claim on their wiki page was a light bulb at 90% efficiency at 3 feet. If it's more efficient when closer, you could put one in the bottom of your car and one just below the surface of your garage, and you'd probably only have a separation of about 1 foot.

> But the article also talks about lighting and televisions, and cars. WiTricity has investors to fluff, clearly, but is this not absolute crazy talk?

They've apparently already powered lighting, and the TED talk supposedly had them powering a TV [0]

[0] http://www.ted.com/talks/eric_giler_demos_wireless_electrici...

From what I've seen of their demos (going off memory), they focus on power transfer to a single device. Their efficiency drops to near 0% when multiple devices are being powered.

I have a hard time getting excited about these guys' work, but will readily admit they are excellent about generating publicity. There is a lot of _very_ closely related work in resonant energy transfer and use of time reversal or lensing currently being looked at around academia. Hopefully one day it will pan out, but it is never going to be as efficient as running a wire. For some applications wireless power is a great enabling technology, but powering a light or a tv in your home? That's a hard sell for the "convenience" of moving your tv versus the extra costs in energy inefficiency.

Ok, sure. If you can control the proximity carefully, you can achieve reasonable efficiency. Transformers work.

But it's still a super high powered magnet. There are more places than not where that's just a bad idea. Garages are high on that list. Also carports, kitchens, living spaces in general...offices, sleeping spaces..bathrooms. All bad.

LED lighting gets you pretty far down the current draw curve, but I don't see a small, easily moved coil generating enough resonant current to be useful in many common consumer electronics. That coil has to be plugged in to the mains, remember -- invalidating the promise of wireless power, even at three feet.

And ambient charging has all of those problems, squared.

Also, can't magnets interfere with pacemakers? "Oh, you have a pacemaker? Ya, don't come over or you will die... I don't want to have to plug in my lamps."

For cars is way more feasible just having two electrical-charged metal bars that always touch the underside of your car when is in the garage, and if they are far apart it's complete safe (i.e: children can't touch both at the same time)

Children may have pieces of metal such as bicycles, or they may walk across such bars while holding hands. I bet there are way more failure modes with such an approach (kids never drop buckets of water inside garages, for example)

I would put in a few more safety methods.

You can also have a 4 heavy switches under the 4 wheels, that way a very heavy object (the car) must be there over all of them to turn on the electricity.

And then you spill some water while the car is parked in the garage and bam, 440V right across the heart.

Are you serious? To touch the car the metal bars must be above the floor, unless you spill tons of water enough to fill the garage you should be okay.

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