Is RCA's Airnergy Snake Oil? 271
Posted
by
kdawson
from the deepness-in-the-sky dept.
from the deepness-in-the-sky dept.
Ben Newman writes "Of all the tech that's come out of CES this week, nothing has gotten the blogosphere more excited then the RCA Airnergy. A lot of people love the thought of an ever-recharging cell phone, and the Airnergy promises to constantly charge its internal battery through 2.4GHz wireless signals. Neat idea, but as some commenters have pointed out the energy just isn't there to make this work — BOTECs for a full charge range from 100 days to 32 years. Plus, don't let the RCA brand fool you into thinking this must be from a legitimate company: RCA hasn't existed as anything more then a licensed brand name for a couple of decades. So what do Slashdotters think — real deal or 21st century hokum?"
Remote Charging (Score:1, Informative)
Let's say this RCA product isn't snake oil.
Do you know how much energy it must suck from the 2.4 GHz spectrum to keep it perpetually charged?
Multiply it by the hundreds to thousands of cellphones within one cell ... can you imagine how much power the cell tower much emit in order to charge all those phones?
And the effect of so much energy floating in the air --- what about the effect on human body?
Re:Yeah, tens of meters from a 50mW power source.. (Score:3, Informative)
the mythbusters tried to get power from the em radiation from a high voltage line. That doesn't work nothing will.
Re:Yeah, tens of meters from a 50mW power source.. (Score:5, Informative)
Not necessarily, frequency is just as important as voltage and current.
Re:Yeah, tens of meters from a 50mW power source.. (Score:5, Informative)
I think it is the _change_ in magnetic flux that generates a current in a conductor, not just the presence of magnetism.
Re:Yeah, tens of meters from a 50mW power source.. (Score:5, Informative)
Yes. Solar power from visual light (EM radiation) works very well. We know that.
Back of the envelope... (Score:5, Informative)
Re:Yeah, tens of meters from a 50mW power source.. (Score:5, Informative)
A *changing* magnetic field generates a current. If you just take a coil with some wires attached, and hook up a voltmeter, nothing will happen. Only when you start moving your coil through a magnetic field will you start to see volts. (Earth's field is extremely weak, but with a big coil and a sensitive meter you could see a small current.)
The reason this can't be used for infinite power generation is that the coil will resist movement. Any flow of current generates a magnetic field of its own, and if you do the math, it turns out that the induced current in your coil creates a field in opposition to the field it's moving through. It works against you like a kind of friction, or like air resistance. If you just give the coil an initial kick, it will quickly run down to a stop. In order to generate power you have to keep putting energy into the system.
In other words, you're not draining energy from the magnetic field, you're just converting the kinetic energy you put in.
This is in fact how generators work. A big conductive coil is spun around inside the field of some permanent magnets. If your generator is connected to a water turbine, you're converting the kinetic energy in falling water into the kinetic energy of a spinning coil and thence to electrical energy in a wire.
Re:30 seconds on full power (Score:3, Informative)
Snake Oil (Score:4, Informative)
Not enough energy available. Would probably not even offset self-discharging unless a pretty large antenna is used. You can fake a demo though with a highly directional antenna to beam in a wireless signal. Not realistic at all and inefficient as hell.
I am constantly amazed at what people are willing to believe.
There ain't no RCA (Score:3, Informative)
Plus, don't let the RCA brand fool you into thinking this must be from a legitimate company: RCA hasn't existed as anything more then a licensed brand name for a couple of decades.
You got that right. Neutron Jack cannibalized RCA in the late 80s, selling the consumer electronics division to Thompson. About 12 years ago, they sold chinese company TCL the right to use the RCA name on TVs and other products.
They ought to replace Nipper with one of those chinese hounds with all the extra folds of skin. HIs master's voice is in chinese.
Re:Yeah, tens of meters from a 50mW power source.. (Score:1, Informative)
Re:Yeah, tens of meters from a 50mW power source.. (Score:4, Informative)
Now, if you figure that we can improve power conductivity by, oh say, 50%, and can cut power utilization by 100x, (1/10th the amount claimed by Bell Labs) then suddenly, the charge rates from a 150 mw 802.11 radio source 5 meters away actually seems reasonable!
It won't happen today, or tomorrow. But in a few years? Not only possible, but likely!
Not at all. Cellphones need something like 100mW...2W RF output to cut though background static and get a signal to the cell tower. And by conservation of energy that means even if nothing at all besides the RF emitter consumes energy, the power consumption will be at least 100mW...2W.
Nokia's working on this too (Score:3, Informative)
Nokia proposed a power-harvesting (and power-sipping) handset over the summer last year, to derive its power from cellular signals rather than wi-fi. Although their target amount of 50mW is way off, they claim to have a prototype that can pull in a few milliwatts, which inspired a mixture of scepticism and existential terror from researchers in the field.
Re:Remote Charging (Score:2, Informative)
Actually, the article says "At CES, the device's battery, which I believe was precharged with Wi-Fi power, was able to charge a BlackBerry from 30% power to full power in about 90 minutes." Note the "which I believe was PRECHARGED" part. So they managed to charge a Blackberry from a pre-charged external battery in 90 minutes. Yay. But they never actually said how long it takes to charge the battery in the Airnergy device via wi-fi signals - probably for a good reason, because that would take probably a couple hundred days or more.
Re:Yeah, tens of meters from a 50mW power source.. (Score:2, Informative)
I suspect the sun is putting out slightly more than 50mW, though...
Re:Yeah, tens of meters from a 50mW power source.. (Score:5, Informative)
The greek nu is the standard notation for frequency in physics, or at least it generally was when I did that kind of thing. f is sometimes used, though less commonly. However, photons are not relevant for RF - the photon energy is so small that the quantum nature of the radiation is not apparent, and it behaves for all practical purposes as a classical wave.
Re:Yeah, tens of meters from a 50mW power source.. (Score:3, Informative)
Well, try standing next to a microwave antenna.
Re:Well two things (Score:2, Informative)
According to Nasa's "Advanced Energetics for Aeronautical Applications: Volume II" Tesla did get it working:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050170447_2005172301.pdf [nasa.gov]
"However, Tesla's claims were backed up with documented experimental demonstrations rather than mathematical equations. In the following quotation, Meyl describes one of Tesla's demonstrations and states that Hertz's technology could not have accomplished such a demonstration:
In Colorado Springs he had built a 10 kW transmitting installation and lighted
200 fluorescent lamps of 50 Watt each on a mountain in the Rocky Mountains in a
distance of 25 miles. With that he had completely transmitted the transmission
power of 10 kW, as can be inferred from the press reports at that time. With
Hertzian waves, which propagate spatially, this experiment even today, after over
100 years, wouldn't be realizable technologically. According to the law of the
square of the distance one isn't even able to let glow a tiny little lamp in such a
distance.
Meyl helps resolve the controversy between longitudinal and transverse waves by explaining that the high-voltage "spark" transmitters used in the early days of radio actually transmitted both longitudinal and transverse waves (Ref. 33, p. 459). The characterization of the type of radio technology employed was in the receiver, not the transmitter. Tesla's equipment would only receive longitudinal waves, whereas the equipment of Hertz and other pioneer radio inventors (such as Marconi) were designed to receive only transverse waves. Because both types of waves (longitudinal and transverse) were being transmitted, both viewpoints of how the technology functioned were correct."
Re:Yeah, tens of meters from a 50mW power source.. (Score:4, Informative)
Mythbusters isn't always right. For example, they busted the "myth" of an ancient Greek "Death Ray" by making one that didn't work. Some MIT kids showed it was possible (this was discussed on slashdot last year).
They had busted the "myth" of a sniper shooting another sniper through the second sniper's scope, and the US Army showed they were wrong, by giving them some better ammo. They covered this on the show itself.
I saw the episode you refer to, IIRC they used a device they bought from the internet. Just because that device wouldn't work doesn't mean none would. You should be able to get voltage from stray EMF from your house current; a crystal radio has no power source and is powered only by the transmitter's signal. But it takes tiny amounts of current for headphones to work, a phone takes quite a bit of juice.
So I'm skeptical. I'll believe it when I see one. I do think you could probably make an LCD clock without a power source, you can run an LCD watch from a potato battery.
Re:Yeah, tens of meters from a 50mW power source.. (Score:5, Informative)
Re:RCA (Score:3, Informative)
And Maytag and Zenith. They're both made in Mexico now.
Sun ~ 1 kW / meter^2 (Score:3, Informative)