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John Perzow

Wireless Power

John Perzow
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lcgallo
lcgallo
7/17/2014 6:05:58 PM
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Newbie
Power harvesting

Hi John,

Thank you for yor answers.

I am a student of history of technology and an electrical engineer no longer working for a living.

Over the years, Tesla has been in my line of interests, particularly because of his concept of wireless transmission of power. Very recently I got quizzed on how to best transmit energy at micro-watt level and also reminded that some individuals, particularly the sick ones, are discomforted already at micro-watt levels.

From here my interest in bringing my knowledge up to the state of the art.

While I see the convenience and the possibility of charging a phone wirelessly, I wonder is something more could be done by harvesting, for that purpose, the energy that is already around us.


lg

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JDPerzow
JDPerzow
7/16/2014 9:25:01 PM
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Re: State of the art
Ah, yes, the 100 MHz is a typo. The cutting edge is efficiency, not power. Receivers will appear after transmitters are available, so 30W receivers after 30W or greater transmitters are standardized.

For close-coupled systems, near-field techniques are used. For loosely-coupled systems, the transmitter and receiver coils are tuned to the same frequency to increase the power transfer efficiency over distance (Z-axis).

Any system that is released to the market will be safe for people to be around, and must meet government and safety standards.  Just like induction cook-tops, people can be as close as they want to the transmitter.

JP

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lcgallo
lcgallo
7/16/2014 8:19:45 PM
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Newbie
State of the art

Hi John,

The 100 MHz I was asking about is then a typo.

I see published information about transmitters but none of a 30 W receiver, is the receiver where the state of the art is found?

In a wireless "set up" is the magnetic field generated and radiated by the Tx coil like the near field of an ordinary AM transmitter antenna?

The 3KW transmission sounds very interesting, in that demonstration what was the distance Tx - Rx and how close could people be?

Thanks,

lg

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JDPerzow
JDPerzow
7/16/2014 7:48:28 PM
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Blogger
Re: Receiving power
Hi Icgallo,

Yes, transmission frequency for Qi is 105 ~ 210 kHz (they control power by modulating the frequency). PMA uses 200 to 300 kHz. The A4WP Rezence standard uses 6.78 MHz.  5W to 7.5W are the typical low-power standards out there today and this power level is great for cell phone charging. The standards groups are working on extensions to their spec to allow for higher power, which will charge tablets and notebooks more quickly. Those devices will indicate how much power they want back to the transmitter. So, for example, one may put a phone and a tablet in a charging area, and the phone will communicate a 5W need, the tablet may communicate a 15W need and the transmitter will provide power as appropriate. The WPC has just demonstrated a 2000 W system (transmitter and receiver) for kitchen appliances. The demo powered a food processor through a 30mm kitchen counter. 

JP

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lcgallo
lcgallo
7/16/2014 4:17:36 PM
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Newbie
Receiving power
Jon,

Did you really mean " The transmission frequency can be between 100 MHz and 6.78 MHz," ?

There seem to be information on transmitting energy up tp 30 W, what about receiving it?

lcgallo

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JDPerzow
JDPerzow
7/1/2014 9:22:35 PM
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Blogger
Re: Wireless concerns
RedDerek:

These are valid and central points. We will get into some of these topics in detail, but I'll address them at a high level one-by-one. But first, a note about releasing a responsible product into the market: All the companies I am aware of working on wireless power products or standards are top-notch and of high integrity. So it goes without saying that, despite design trade-offs that could impact efficiency or safety, any product or standard released will certainly meet regulatory and industry requirements for efficiency and safety.

1. Efficiencies. Wireless power can be transferred with almoast 100% efficiency (perfect coupling, no circuit or switching losses) all the way to 0% (no received power as described in the article). Distance between the transmitter and receiver, switching speed and the amount of the flux field captured by the receiver are the first-order factors that determine efficiency. Resonant techniques can compensate somewhat for distance. GaN and other semiconductor technologies can compensate for switching losses.  Coil design, coil arrays and magnetic shielding can help improve how much magnetic energy is captured by the receiver over the charging area. We are seeing tightly-coupled systems transmit power with over 80% total efficiency.  For purposes of discussion, we will define efficiency as power into the load divided by the power into the transmitter.

2. Health considerations. The International Commission Non-Ionizing Radiation Protection (ICNIRP) has set clear limits for safety and modeling techniques exist to enable accurate testing. Some topologies have inherently more EMI than others, but all systems released to the market will certainly operate well below ICNIRP safety limits. Operating frequency, coil design, waveform, distance, power levels and shielding all impact the design trade-offs required to operate below ICNIRP safety limits.  These are typical design considerations for any power system, but different wireless power implementations present different design challenges.

3. Conflicts of interests in standards development. I too was involved with 802.3at and af and witnessed individual companies vie for control of the I.P. Some standards are created by a single company and result in great benefit to consumers and markets. Some do not. When groups of competitors agree to work together to develop a standard on a level playing field (RAND terms), the result is often reliably good, but there are no guarantees, either. We will focus primarily on circuit design and system challenges, but stark differences exist in the composition and motivation between wireless power standards groups. It will be very interesting to see how this plays out.

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etnapowers
etnapowers
7/1/2014 8:13:04 AM
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Newbie
Re: Wire Charging Process
@samicksha, that's correct, the voltage of the receiving coil has to be converted by mean of a AC/DC converter to charge finally the device.

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yalanand
yalanand
6/30/2014 2:58:15 AM
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Newbie
Re: Wire charging process
The concept of wireless charging will be really ideal especially when it comes to car charging. The only thing that they should ensure is that it works in all devices. Cars operate differently depending with the brand of the vehicle. The wireless charging process should ensure that it takes this into serious consideration. This will enable drivers to comfortably charge their phones when they are driving and this will be a good boost to technology. All that needs to be done is just energy diffusion.

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RedDerek
RedDerek
6/26/2014 1:16:14 PM
User Rank
Master
Wireless concerns
Back from a three week vacation, I am catching up on all the discussions. Problems I see with wireless charging that I would like to see are:

1. Efficiencies

2. Health considerations, especially for the high-power charge applications. How well is the magnetic field generation kept within the charging device?

As for standards... I can understand the challenges of putting a standard together. When I worked with the 802.3at development, there seemed to be one or two companies pushing their method. Primarily because of patents in place to sell rights to. I suspect this is the same thing for the wireless standards.

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tzubair
tzubair
6/25/2014 11:06:27 AM
User Rank
Newbie
Re: Wire Charging Process
@JDPerzow: What about the normal range that is covered by these wireless devices? How big of an area can each device covere and what's the restriction when it comes to expanding the area?

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