[Pumblechook (OP)]

This article seems to be full on inaccuracies and nonsense.

http://news.bbc.co.uk/1/hi/technology/8165928.stm

[lyner]

Amazing. I couldn't find a single performance figure in the article. Very naughty as one picture implies you could run / recharge a car with the system.  His description of the "near field" was suspect, too.
I wonder if he'd get money in The Dragons' Den.

[BenV]

I think TED vet their speakers fairly well though, so I suspect this may be a reporting fault rather than a story fault...

[Pumblechook (OP)]

Efficiency is poor..  Always will be. 

The bigger the gap you want to bridge the worse it gets.

I suspect the overall AC - DC efficiency over 2 metres (which requires large...60 cm coils) is 15%.

Seems to refer to far field in the text. 

I don't see how they can dress this up as being something new? 

People were used tuned loops in the 1920s.

[Pumblechook (OP)]

A bloke on another talkboard reckons a pal of his is working on charging mobile phones with stray wifi signals.   

I have worked out that it would take 3000 years to charge a phone if you were 10 metres from a 100 mW transmitter will no walls in the way. 

[lyner]

You could always bump up the power of your router. Hear it all over Sussex.

[Edster]

It does actually say the important word "resonant" so it may get near or even exceed the efficiency of the lapsed Tesla patents for the same things.

I know many people who think he is a charlatan, but read the patents and they aren`t smoke and magic, the language is archaic but still english. And all his stuff built to his drawings works.

[Pumblechook (OP)]

No.

It is rubbish.

There is nothing new in resonant coils.

It is 1920s technology.

[lyner]

Resonance only solve the impedance matching problem. It doesn't solve radiation or resistance losses.

[Edster]

That is the problem, there is no specific info on their site or in a patent seach ( so far). I would guesstimate 80% transfer top whack, but if you go back to previous work and add critical deratings from experience then anything over 50% is good.

It is however a resonant system, and I wouldn`t be comfortable dismissing efficiencies higher than this over limited ranges.

I certainly wouldn`t express my ignorance as comprehensively as pumblechook has.

Teslas patents are full of hyperbole, but the basic ones we still use the fruits of today are worded similarly to the more out there ones.

There are more questions raised than can be answered so far.

[Pumblechook (OP)]

The transfer over 2 metres (with thumping big 60cm coils) is 45%.

But I stick with the overall AC - DC of 15% - 20% = waste of time, money and energy.

[lyner]

It strikes me that the problem is not that the system is not efficient; One could live with that in the appropriate situation.
The worst thing about it is the potential for wideband interference / spectral pollution.

[Pumblechook (OP)]

I think they have been experimenting at 6 and 9 MHz.  A highish power at those freqs will get into all sorts of things.  It is hard to filter out. 

[lyner]

Harmonics would hit pretty well everyone. Even Band 2 Radio.

[Pumblechook (OP)]

That could be a problem as well.

All in all sounds like a really inefficient and complicated way or doing away with a short bit of wire and a plug and socket.  You would use more wire in the coils.

[wolfekeeper]

Yes, it's 100 year old technology.

But the point is that people are now carrying around batteries in their cell phones and laptops that need charging. The battery energy capacity by normal standards is really tiny- we're talking watt-hours, whereas energy is sold in kilowatt-hours, so efficiency is largely irrelevant provided it's not obscenely inefficient.

And you're seriously underestimating the efficiency anyway. With resonant energy transfer it's to do with the q factor; basically when you put energy into a resonant coil it starts to ring, and with care, you can get q really high.

Provided the amount of field energy that the secondary coil sees is more than the fraction of the primary's energy resistively lost over each cycle, then most of the energy will end up in the secondary, and can be tapped off. You're looking at efficiencies of 10-90% at say, up to ~6 times the coil diameter.

In practical terms, you could lay a few coils around the room under the carpet and cover the whole room, or have recharging zones around the house on your desk and so forth.

It doesn't seem to be at all stupid.

You'd want the power system to be smart though, the coils need to turn off when there's nothing that needs powering, and ideally you would authenticate the devices as well, you don't particularly want your neighbours charging their phones off your power(!)