Comments on: EEVblog #55 – RCA Airnergy WiFi Hotspot Energy Harvesting Marketing BS

By: Paul

Paul — Thu, 17 Mar 2011 10:54:22 +0000

Has anyone tried to put the airnergy in a microwave oven? There should be enough 2.4GHz energy in there to make it work…

It might even release the magic smoke.

By: EEVblog

EEVblog — Wed, 22 Sep 2010 02:14:01 +0000

The mobile phone charging is not a hoax. The device contains a high capacity lithium ion battery that is perfectly capable of charging a phone. The battery was pre-charged and hence was able to charge the phone. There is nothing off-camera, that’s just silly. The hoax part is about the harvesting of the wifi energy to charge the battery.
Dave.

By: Th3_uN1Qu3

Th3_uN1Qu3 — Tue, 21 Sep 2010 18:22:54 +0000

That circuit does capture energy from radio waves, and it could even get 50 volts or higher. However once you put a load on it it will collapse because the current available is next to none.

The mobile phone charging is just a hoax, he used an actual cellphone charger which wasn’t in the field of view of the camera.

By: nbsr

nbsr — Mon, 14 Jun 2010 16:56:55 +0000

Dave,

There are some real world applications of such energy harvesting but they are all limited to powering up things like autonomous single-chip systems (RFID’s, sensor networks etc).

Your calculations are actually fairly accurate. People generally use dedicated larger power (0.5~4W) dedicated RF transmitters, directional transmitter antennas, but then there are losses in the rectifier circuit, reflections, longer distance etc. The circuit I worked on could actually produce ~100uW of DC power at 4m range, which was enough for supplying a rather non-trivial system.

By: nbsr

nbsr — Mon, 14 Jun 2010 16:14:41 +0000

It’s an interesting project but not for powering up home appliances. Anyone who argues it can be used for such purpose is not very different from these RCA guys.

Both high-Q LC circuits are tuned so that their current phases are opposite. That cancels out (mostly, and only at a very near range) magnetic field between them. But, there is simply too much field being produced in the first place. Just think of how much energy has to be stored in the LC tanks so that after loading them with, say, 100W they still have a Q factor of ~100.

By: Kelvin

Kelvin — Mon, 26 Apr 2010 08:12:31 +0000

Dave this blog of yours sometimes remind me that having too much knowledge is bad. The majority of the people to stumble upon this product will probably say that the technology is cool and move along and never hear of it again due to the product failing before even hitting the mainstream.

My friends usually give me “great” ideas about projects that no one has ever done before and I’m always the one to deliver the news that the idea won’t work because of the concept and physics won’t add up to a working product.

I guess this is a disadvantage of being an engineer/scientist. Ignorance is a blizz as they say.

By: Dmitry

Dmitry — Thu, 04 Mar 2010 18:00:19 +0000

Take a look at this:

http://www.youtube.com/watch?v=csR8q5QttDw&feature=related

Could you comment it?

By: Brodieman

Brodieman — Fri, 12 Feb 2010 05:55:19 +0000

I hear ya AJ – this is absolute rubbish. I’m honestly amazed how these are allowed to be manufactured and marketed!

By: Sean

Sean — Sun, 31 Jan 2010 06:22:09 +0000

Two coils, essentially an air coil transformer, and in close proximity. And a bit more than 100mW input.

By: TrentO

TrentO — Thu, 28 Jan 2010 06:13:26 +0000

I’m gonna buy one just to try this.

No worries– I’m going to do it outside.

By: TrentO

TrentO — Thu, 28 Jan 2010 06:12:04 +0000

WTF is this?!!!

By: Mark

Mark — Thu, 28 Jan 2010 03:46:22 +0000

Thanks Dave,

For anyone else a little confused by capture area here is a good explanation: http://www.w8ji.com/capture_area_ae_effective_aperture.htm

Mark

By: John W.

John W. — Wed, 27 Jan 2010 01:45:41 +0000

If you want to charge it really fast, just throw it in the microwave.

By: Steven

Steven — Mon, 25 Jan 2010 05:37:55 +0000

Great video. ‘The free energy scams busted’ vidoes always bring a lot of negative comments from the ‘believers’ though.

It seems more and more commonplace that people get sucked in by ‘overunity’ scams and the like.

Another interesting one to look at is the EEstor cell, a 52kw/h ultracapacitor that can be charged in 3-5 minutes, apparently. It would be interesting if you could do a video blog on these sorts of technologies and their potential.

always watching, keep it up!

By: George Herold

George Herold — Fri, 22 Jan 2010 21:15:48 +0000

Yup, I thought about that too. The MIT thing works in the near field and has a ‘relatively’ low frequency… a large wavelength. In the near field (I think) you can have a cross section that is much bigger than the physical size of the antenna… Then in the far field the cross section can be as large as the square of the wavelength (With a factor of pi somewhere.) But that’s almost exactly 10 cm. The number that Dave used.

Well done Dave,

George H.

By: Hamed

Hamed — Fri, 22 Jan 2010 05:17:29 +0000

hi dear Dave
how are u today?
i need to be a circuit which derived the shave machine (Philips)
please sent its schematic
tanks a lot

By: blipton

blipton — Thu, 21 Jan 2010 17:56:05 +0000

What about the Palm Pre (induction?) charging?

It’s wireless and doesn’t require 7 years to charge! What’s going on here?!

By: Roy

Roy — Thu, 21 Jan 2010 17:28:04 +0000

Well done, sir. I have been telling RCA (a subsidiary of Audiovox) that their story is nonsense. I have also told a number of journalists, some of whom have quoted me. I do chair an International Standards committee on Energy Harvesting and am applled at the damage that these stupid stories do to companies that have energy harvesting products that really work. I did manage to get a retraction out of Nokia in June wityh their similar story but RCA are proving more difficult.
Please keep up the good work – bad science must be exposed

By: EEVblog

EEVblog — Thu, 21 Jan 2010 06:02:42 +0000

Correct, I was working with the ideal case just for argument.

By: Viewer

Viewer — Thu, 21 Jan 2010 05:41:00 +0000

Correct me if I’m wrong, but that isn’t even a constant 100mW. If you’ve got a digital signal, that’s intermittent by nature. Not to mention power is only present when a signal is being transmitted. An inactive router doesn’t give off much, if any, residual power.

By: EEVblog

EEVblog — Thu, 21 Jan 2010 01:37:44 +0000

Don

By: Mark

Mark — Thu, 21 Jan 2010 00:09:41 +0000

Dave,

If one were to build a perfect antenna that could absorb all frequencies of radio energy in the air, how much energy could one harvest? How much radio energy is in the air at any given time? Is there any way to measure this?

Mark

By: Mark

Mark — Thu, 21 Jan 2010 00:00:40 +0000

Dear Dave,

Don’t you mean cubic meters, not square meters?

Mark

By: Richard

Richard — Wed, 20 Jan 2010 08:50:27 +0000

Ont thing you didnt mention is that wifi accesspoints are not transmitting all the time – only when needed other than a beacon.

So unless you are downloading a lot (and not uploading, since that would mean it would be receiving more) the figures are gonna be even worse.

By: Neil

Neil — Tue, 19 Jan 2010 20:13:35 +0000

Dave,

There are a depressing number of these around at the moment. The BBC did an article on some device to bring the house mains voltage down to nominal volts. (In the UK that is 240V – generally the mains supply is a bit higher 247V typical).

They started quoting all sorts of savings. Apparently a switch mode mains supply will save 30% energy. Now I’m forced to explain to people who don’t know the first thing about it how it will never save that much if anything at all.

But it must do – it was on the news.

Neil

By: EEVblog

EEVblog — Tue, 19 Jan 2010 04:19:19 +0000

Yeah, I’ve seen it and it’s quite neat and seems great value.
Might have to get one just for the heck of it!

By: Norvog

Norvog — Mon, 18 Jan 2010 22:08:45 +0000

Hi, Dave!

Saw an advert and it looks interesting: TI’s programmable watches with wireless interface and some sensors in it.
http://focus.ti.com/graphics/tool/ez430-chronos_800.jpg
http://focus.ti.com/docs/toolsw/folders/print/ez430-chronos.html

The con I see is that you’re stuck with TI’s chips cause I guess they use SimpliciTI protocol for wireless connection. First time I’ve heard of it.
And their way of reprogramming device is crappy! You should open it! Why not have wireless bootloader out of the box!!!

So what do you think of it?

By: DaveL

DaveL — Mon, 18 Jan 2010 21:14:46 +0000

A research group at MIT has developed a functioning magnetic harmonic resonance induction system (shades of N. Tesla) that actually works. It is a long way from functioning on a broad scale. I did see a demo of the system that was used to power a wide screen plasma TV and an iphone. It can be done but perhaps not via WiFi.

By: Rastislav David

Rastislav David — Mon, 18 Jan 2010 15:59:05 +0000

I was browsing lt videos and found out this one:
http://www.linear.com/designtools/video/ltchannel_energyharvesting.jsp

Where different energy sources and how much can be extracted is explained. Starts on about 3:00

Rasto

By: AskJacob

AskJacob — Mon, 18 Jan 2010 05:03:19 +0000

If this thing even had a chance at being able to deliver, you would end up being torn limb from limb for creating a local blackspot for wifi around you, as it harvests a lot of the energy that was meant for distant wifi users….

Pure snake oil product. My theory is – if it can’t even light an led, it ain’t gonna charge anything!

They may as well sell us a super efficient solar panel with a light bulb for self illuminating perpetual electricity…

Or perhaps a thermo-electric generator powered by the hot air coming out of the marketing department…

Jacob

By: Stephen Woolhead

Stephen Woolhead — Sun, 17 Jan 2010 22:51:42 +0000

I was wondering what the internal discharge rate of the battery would be. Would be nice to have something like this you could charge from the mains, then throw in your bag and know that six months later when you need it it would still be charged.

The shear number of blogs that have reposted this as a good workable idea though is some what shocking!

By: Jo

Jo — Sun, 17 Jan 2010 19:33:08 +0000

Hi,
It could work if you put the antenna inside of a microwave at full power! :p
Kids don

By: Jonathan

Jonathan — Sun, 17 Jan 2010 18:38:34 +0000

I don’t know what the levels of a cell phone signal are but can this device harvest that?
I don’t personally believe it will work even then but perhaps they believe the sheer number of sources will charge it?

By: Kathy Quinlan

Kathy Quinlan — Sun, 17 Jan 2010 17:22:38 +0000

Hi Dave,

I had a problem up until 8 odd minutes, but then you started talking efficiency I doubt you would charge it in 8 years

Also once you get over about 60 days for nicad, not sure what the figure is for Li based packs, the internal self discharge would be higher than the charging rate

Sigh when will the snake oil merchants give up

Regards,

Kat.

By: Brian Hoskins

Brian Hoskins — Sun, 17 Jan 2010 10:53:34 +0000

This smacks of those silly You Tube videos you see, except this time someone’s actually made a product out of it.

I agree. Absolute crap.

By: Leon

Leon — Sun, 17 Jan 2010 09:20:52 +0000

I don’t doubt that the WiFi name was thought up by some marketing monkey, but I’m one aspect of this story interests me: What level of EM power, across *all* frequencies, not just 2.4GHz, could a small antenna pick up in an active 21st century household? I guess you’d have to assume that you had a magical rectifier. (You could be really cheeky and put your wire up against an active 50Hz household supply…)

By: EEVblog

EEVblog — Sun, 17 Jan 2010 07:55:21 +0000

RCA is mostly made by SGS Thompson, a French firm.

Yes, the name is owned by the Thomson group.
I in fact used to work for the Thomson group (Thales).
It’s a huge group, so could really be anyone, but probably TCL in China.

By: Jan

Jan — Sun, 17 Jan 2010 06:36:35 +0000

these are product trolls, best to ignore them.
all they want is what you just gave them: attention.

btw. the battery version is probably a ripoff of the very successful minty boost by adafruit. i bet my ass that this got the same circuits inside. http://www.ladyada.net/make/mintyboost/

By: Zach

Zach — Sun, 17 Jan 2010 05:48:00 +0000

I saw a vid with that device as well and immediately came to the same conclusion. Hopefully it might be cheaper than making a http://www.instructables.com/id/How-to-make-a-solar-iPodiPhone-charger-aka-Might/ which I made without the solar panel.

By: Tony P

Tony P — Sun, 17 Jan 2010 05:43:52 +0000

Great debunk Dave! Yeah, when I heard about this I wondered how they’d pull it off. I note it appears to have a USB plug on it. Plugging it into a computer would charge it at a reasonable clip, at least a couple of watts on the USB port.

And btw, RCA is mostly made by SGS Thompson, a French firm.