Power over WiFi: ‘Physics is Physics’ or ‘Dare to Dream’?

February 23rd, 2010 by Ben Smith

Our post about the RCA Airnergy device generated a bit if a conversation… both for and against.

To reflect many of the sceptical comments around the web I added a video from EEVblog which summarised much of the physics-based disbelief, but our readers can do better than that…

In the meantime Terrence Eden had been handing the believers their back-sides in physics-shaped hats…

- A WiFi access point can transmit a maximum of 0.1W.

- A WiFi access point radiates energy in a sphere - it does not direct the signal.

- A WiFi access point does not transmit all the time.

A typical USB charger supplies about 4.4 volts at 100 milli Amps. That’s about 0.44 Watts.

So, this magical devices would need to absorb ALL of the power produced by a WiFi access point with 100% efficiency with the WiFi transmitting ALL the time in order to get a quarter of the needed power.

And that’s the best case scenario. And it’s impossible.

…This is a nice idea - pick up lost power - but as Scotty says “You canna change the laws of physics!”

But Jonathan MacDonald says he’s also seen another firm working on this technology and believes we are witnessing a game-changer. He urges us not to fall into the trap of ‘The Fallacy of Certainty‘:

For the moment I remain a sceptic but am confused why a brand such as RCA - one which is used by a number of firms none of whom would be obvious sources of earth-shattering physics breakthroughs - would make this claim regardless if it’s true or not.

What do you think?

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  • NeilHoskins
    First reaction is to check the date. Not April 1, apparently. Did you ever see, RFC3251, "Electricity over IP", issued April 1, 2002?
  • lwsdm
    So the guardian reported last year that Nokia are working on something like this already.
    http://www.guardian.co.uk/environment/2009/jun/...
    But as you can see from the comments at the end of the article and on the last post here they are fighting an uphill battle against the laws of physics. What Johnathan is not really appreciating is that the laws of physics do tell you it's possible but as Terrence points out it's just not practical, at least using the WiFi source as alleged.
  • Kirk "Grumpy" Bateman
    If I remember rightly, part of the point of the Nokia article was the mention that they were NOT using specifically WIFI signals, but generically radio signals (thus increasing the possibility a tiny bit). However, still not going to be getting all that much from it .. from what I see. I don't realistically ever see this as a general means of charging a device, however even if it can provide a tiny amount of power that would be better than nothing. In some ways I suppose you could look at it as recycling energy (so not wasting so much of it ??) Just a thought.
  • jamesbody
    As an individual who hates to be told the 'it cannot be done' and who routinely operates on the edge of wht is possible I would very much like for the RCA spoof WiFi powered charging device to work.

    However (as Dvid Jones so eloquently pointed out) t- there is NO WAY that this device is going to be capabe of charging moble phones by 'harvesting' energy from WiFi APs.

    The science involved here is prety basic and is well established - such that any student wit GCSE Physics should be able to prove (as David did in his video) that this is going to work.

    Jonathan - I remain a firm member of your fan club - but asking me to believe in the chance that this product is genuine is just a little too much!
  • Thanks for your commitment to my fan club James (which is undoubtedly a lonely experience!).

    My point isn't about whether the product is genuine, but instead against the people who state that something is impossible, FOREVER.

    Just as people said the aircraft couldn't possibly work because the 'laws of physics' said that something heavier than air couldn't fly, my concern is that we are framing ALL future potential through today's lens.

    Thats all really - I couldn't care less whether the RCA development is real or fake - but I really do care that people accept aspects like the Chaos Theory and pretty much every other development that proves that random outcomes can come from something that is predictable as clockwork....
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