Long range wireless charging feasible? - Page 1
Forum section: electronics / beginners

author: elliottveares
author_rank: Contributor
timestamp: January 22, 2017, 12:08:36 am
content: Just seen the below linked video from a tech person in the US. Talking about how the next iPhone could have wireless charging built in. (Not close coupled inductive charging but medium/long range wireless charging).Is this even possible or is it complete BS as I suspect? I don't know that much about electronics and RF related stuff, but seems rather impassible without having a massive energy loss involved in the process.Transmitting data/signals over long range is one thing, but doing the same with enough power to charge a smart phone!?Sure RF energy is all around us from AM/FM radio to Wi-Fi, but proportionally the power transmitted involved is minuscule in regards to Wi-Fi and is equally minuscule for the amount of power that can be absorbed by your typical TV Arial under a normal conditions.Should it be possible (Say to charge your average smart phone from 2-4 meters away), how much input power would be required at the transmitters end?Reagrds: Elliott.

author: orolo
author_rank: Frequent Contributor
timestamp: January 22, 2017, 12:34:25 am
content: If you place an isotropic radiator 2 meters away, with a power emission P, the power per square meter you get at a two meter distance is P/50 (inverse square law). If a phone has a cross section of 100cm^2 = 0.01 m^2, the power it will harvest from the radiator will be at best P/5000. So, to get 1Watt in your phone, the radiator must be rated for 5000W. Not practical. The only way to get some efficiency would be for the radiator to use a very directional beam, at extremely high frequencies (diffraction), which would not be very practical or safe, either.

author: Ian.M
author_rank: Super Contributor
timestamp: January 22, 2017, 12:50:50 am
content: Not possible. FCC limits for long term human exposure microwave band power density are 1mW/cm2(5mW/cm2short term peak under controlled circumstances). Assume a max pocket size of 10cm x 18cm, and a 90% efficiency rectenna, that's only 162mW under ideal conditions (phone directly facing power transmitter with clear line of sight). That's 1.6% of the output of a normal 2A USB charger, or about 4 days to charge an iPhone 6!

author: IanB
author_rank: Super Contributor
timestamp: January 22, 2017, 12:56:29 am
content: Very likely "wireless charging" means putting the phone on a special charging pad. This would naturally be very convenient since most people will put their phone on the nightstand next to the bed when they go to sleep at night.

author: The Magic Rabbit
author_rank: Regular Contributor
timestamp: January 22, 2017, 04:31:22 am
content: I don't think you can say "not possible" when it's already being done...https://youtu.be/GNgUdWW0y-sSent from my Moto G (4) using Tapatalk

author: JimRemington
author_rank: Regular Contributor
timestamp: January 22, 2017, 04:49:17 am
content: QuoteThe video does demonstrate short range charging/powering, like my decade old electric toothbrush.The rest is just talk.

author: amyk
author_rank: Super Contributor
timestamp: January 22, 2017, 01:20:01 pm
content: Feasible, yes.Safe, probably not.http://www.industrytap.com/florescent-bulbs-unplugged-and-shinning-tapping-electromagnetic-fields/1763https://en.wikipedia.org/wiki/File:TeslaWirelessIllustration.png

author: Ian.M
author_rank: Super Contributor
timestamp: January 22, 2017, 01:32:41 pm
content: Yes. I should have qualified that "Not Possible." as 'Physically possible but could not legally be sold in North America or other parts of the 1st world, so not commercially possible'You should note that in most developed countries it's not legal to build under or adjacent to overhead high voltage power lines. e.g. from theW.A. Powerlines, Electromagnetic Fields and Health, Environmental Health Guide:Quote

author: BrianHG
author_rank: Super Contributor
timestamp: January 22, 2017, 04:29:09 pm
content: Give me the patent number, I'll read it and tell you if it's possible, feasible & will pass FCC.

author: IanB
author_rank: Super Contributor
timestamp: January 22, 2017, 05:49:59 pm
content: Quote from: Ian.M on January 22, 2017, 01:32:41 pmHowever, this is not apparently the case in the UK:https://goo.gl/maps/bcSgwySzUfQ2Land is too expensive to have a "dead zone" underneath power lines. I have seen it here in the USA but in the UK power line towers just put their footings wherever needed and hop over whatever lies beneath.[Edit: fixed broken link]

author: Ian.M
author_rank: Super Contributor
timestamp: January 22, 2017, 06:04:10 pm
content: That's a good case for requiring either a well grounded metal roof or a well grounded wire mesh lining the rafters. You don't see a lot of overhead lines in UK urban and suburban residential areas as the high population density and high land values + perceived blight of overhead lines makes it economic to use buried HV lines.

author: BrianHG
author_rank: Super Contributor
timestamp: January 22, 2017, 07:51:51 pm
content: Quote from: Ian.M on January 22, 2017, 06:04:10 pmForget grounding your roof, I would use it as an antenna, put it though a step-down transformer and siphon power, use it + feed the surplus backwards through my houses power meter & have the power company pay me. If the power company wants to radiate my house, I'll use that radiation to my benefit & profit.

author: IanB
author_rank: Super Contributor
timestamp: January 22, 2017, 07:57:17 pm
content: Quote from: BrianHG on January 22, 2017, 07:51:51 pmIn the picture I linked the power lines were there long before the houses were built. I am frankly surprised they found buyers for the houses. I wouldn't want to buy a house situated like that.

author: james_s
author_rank: Super Contributor
timestamp: January 22, 2017, 10:28:31 pm
content: I'm not aware of any conclusive evidence showing harm to humans caused by EMR from 50/60Hz power lines. There has been some paranoia out there, but ask around and for anything you can think of you'll find someone who thinks it causes all manner of health problems.As far as wireless charging goes, sure it's possible to transmit significant amounts of energy over the air, I can light up lamps across the room with my tabletop tesla coils, but it knocks out radio reception all over the house and probably a much larger area than that. It's also extremely inefficient.

author: The Magic Rabbit
author_rank: Regular Contributor
timestamp: January 23, 2017, 01:02:03 am
content: Quote from: JimRemington on January 22, 2017, 04:49:17 amI doubt Apple would be in testing with them etc. if it was just talk.The power transfer on the short range transmitter is nothing like your toothbrush. The toothbrush chargers are essentially just magnetic induction.Sent from my Moto G (4) using Tapatalk

author: ConKbot
author_rank: Super Contributor
timestamp: January 23, 2017, 06:34:01 am
content: In the far field? Lol no, definitely not. Any wireless charging system for public consumption is going to be some sort of near field coupling, with some sort of antenna magic and fiddling to keep them physically small for their frequency.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: January 23, 2017, 06:47:30 am
content: Quote from: The Magic Rabbit on January 23, 2017, 01:02:03 amI think if people understood the inverse square law alot of these videos wouldn't be made. Its like how people think teslas wireless electricity is still viable. We rely on radio freq. spectrum distribution so much that these generators would reak havoc on communications, wifi, etc... Plus it seems like people would get RF burns when they touched metal.

author: The Magic Rabbit
author_rank: Regular Contributor
timestamp: January 23, 2017, 07:04:12 pm
content: Well I don't have the in depth understanding to give you the solution, but from the little I do know, it's about creating a highly focused beam, hence the need for so many aerials inside the unit.Sent from my Moto G (4) using Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: January 24, 2017, 04:55:50 am
content: Quote from: raspberrypi on January 23, 2017, 06:47:30 amI'm sure they would, I got a painful RF burn on my finger when it brushed the grounded screw that holds the cover plate on a light switch while I had my small SSTC running on the table. Tesla had some brilliant ideas, but he was also off his rocker, especially as he got older. He was under-appreciated for a long time but lately the myths surrounding him have grown to ridiculous levels.

author: DBecker
author_rank: Frequent Contributor
timestamp: January 24, 2017, 06:16:55 am
content: There is strong evidence that Tesla didn't quite 'get' EM waves. He apparently was very good at visualizing magnetic fields, and devising novel devices. But he didn't understand far-field behavior, and didn't have the mathematic skill to compensate. There is a big difference between rotating magnetic flux and wave behavior. Having an intuitive grasp of one doesn't automatically mean you understand the other.

author: Marco
author_rank: Super Contributor
timestamp: January 24, 2017, 07:28:10 am
content: Quote from: raspberrypi on January 23, 2017, 06:47:30 amWhat's the law for inductive coupling ignoring environmental/ohmic losses? Does the power which needs to slosh around in the primary tank increase by the square of distance too to transmit the same energy per cycle?

author: JiggyNinja
author_rank: Regular Contributor
timestamp: January 24, 2017, 03:14:06 pm
content: Quote from: raspberrypi on January 23, 2017, 06:47:30 amNot even RF burns, there would be a very real possibility of real burns too.The biggest downside to wireless power transmission is the same as for wireless information broadcasting: you can't control who can receive it. And before someone mentions "encryption", encryption does nothing to prevent the signal from being received, it only makes the received signal useless to the eavesdropper (if done right). You can't "encrypt" power in the same way you can encrypt information anyway.So the biggest flaw for wireless power transmission isn't transmission efficiency, but that you can't control what receives the power. And it's not a problem because of Big Business conspiracy theories about "not being able to bill for usage", because that's a solvable problem. Most countries already use taxation to subsidize building and maintaining infrastructure (such as roads, water, electric grid, and telecomms), and this would not be majorly different.No, the real problem is that now every piece of metal within range of the power transmitter becomes an induction heater. Your car. Building frames. Pots and pans. Metal cases. Jewelry.EVERYTHING. Not only is it doubly wasteful (extra greenhouse gases + directly heating the environment), it is dangerous. With that much power there would definitely be some pieces of metal with the right shape and orientation to get hot enough to burn things.Large scale wireless power transmission is astupid idea, and no amount of "OMG oppressed genius TESLA!!!11!" can change that.

author: rch
author_rank: Regular Contributor
timestamp: January 24, 2017, 09:55:32 pm
content: Quote from: Marco on January 24, 2017, 07:28:10 amQuick googling suggests an inverse cube law. My basic theory isn't good enough to know if this is power or current though!

author: rfeecs
author_rank: Frequent Contributor
timestamp: January 24, 2017, 10:10:12 pm
content: There was a lot of talk about this from MIT about 10 yrs ago. Marin Soljacic using wireless resonant power transfer. It looks like they went off and started a company called WiTricity:http://witricity.com/They demonstrated powering a 60 watt bulb over a distance of a few meters.Here's a TED talk about it:

author: rfeecs
author_rank: Frequent Contributor
timestamp: January 24, 2017, 10:19:58 pm
content: Quote from: BrianHG on January 22, 2017, 04:29:09 pmHere you go:https://www.google.com/patents/US9086864Edit. Seems like Google's images are messed up.From the US Patent office:US9008864

author: JimRemington
author_rank: Regular Contributor
timestamp: January 25, 2017, 03:12:47 am
content: QuoteObviously, you are convinced by the empty talk and the near field demo. The rest of us certainly aren't.

author: orolo
author_rank: Frequent Contributor
timestamp: January 25, 2017, 10:38:03 am
content: Quote from: rch on January 24, 2017, 09:55:32 pmTo first order, the magnetic field is dipolar, \$H \sim r^{-3} \$. So the magnetic flux also decays with the cube of the distance and, from Faraday's law, the induced voltage decays with the cube of the distance. That implies that power decays as \$ r^{-6}\$, which is also obvious from the energy density being \$\sim \vert H\vert^2\$.Anyway, magnetic coupling is good enough, and in fact better, for very short distances, where the inverse power law doesn't matter. At greater distances,bothsquare and cube laws aren't good enough. A very narrow beam is useless: if I have to be in a very precise position to charge my phone, I better use a cable or close magnetic coupling. As soon as you abandon theverynarrow beam idea, inefficiency gets overwhelming.

author: Marco
author_rank: Super Contributor
timestamp: January 25, 2017, 04:19:39 pm
content: They say they can do resonant transfer upto around 5 times the diameter of the coils.Might be able to make charging pads for under seat cushions which charge mobiles in your trouser pocket.

author: Ian.M
author_rank: Super Contributor
timestamp: January 25, 2017, 04:54:26 pm
content: Quote from: Marco on January 25, 2017, 04:19:39 pmWell at least that should improve the IQ of the general population, as male frequent users who haven't yet reproduced will be eligible for Darwin Awards!Seehttps://en.wikipedia.org/wiki/Diathermy

author: rfeecs
author_rank: Frequent Contributor
timestamp: January 25, 2017, 11:15:29 pm
content: Some market research based on supply chain, patent filings, claiming Apple is not going to incorporate long range wireless charging:https://www.scribd.com/document/337322317/Energous-Corporation-WATT-Game-OverQuoteEnergous is hyping the Apple connection to raise more money:Quote

author: Marco
author_rank: Super Contributor
timestamp: January 26, 2017, 01:33:39 am
content: Quote from: Ian.M on January 25, 2017, 04:54:26 pmDon't think double digit kHz magnetic field fluctuations can couple much energy into people.

author: Ian.M
author_rank: Super Contributor
timestamp: January 26, 2017, 01:48:43 am
content: Double Digit KHz wont get much energy transfer to small receiver coils at a range of 5 diameters. Increasing the frequency increases the number of flux reversals per unit time and thus the energy that can be received, but strong fields at even a few hundred KHz can cause detectable deep tissue heating.Then you've got the direct heating from losses in the under-seat transmitter coils . . .

author: JiggyNinja
author_rank: Regular Contributor
timestamp: January 26, 2017, 07:25:59 pm
content: You know what else is a coil? Rings. How many people are going to be happy getting fingers toasted by their wedding bands?

author: JimRemington
author_rank: Regular Contributor
timestamp: January 26, 2017, 08:42:16 pm
content: My wife's father was in the Navy in the 1940s.He said that the sailors often used to stand in front of the radar dishes on cold days, in order to warm up.

author: rfeecs
author_rank: Frequent Contributor
timestamp: January 26, 2017, 11:25:29 pm
content: There's the famous urban legend:http://www.snopes.com/horrors/techno/microwave.aspQuote

author: raspberrypi
author_rank: Frequent Contributor
timestamp: February 04, 2017, 03:54:27 am
content: Quote from: rfeecs on January 26, 2017, 11:25:29 pmIncreasing the power would not be wise to increase traffic. Reduced power and more site increases traffic. Plus the beer would be isolated from the microwaves.This sounds more and more like a solar roadways company. Get as much money as you can before people realize the idea doesn't actually work. What gets me is how people who have nothing to gain still will advocate that these BS technologies actually work. That or they do actually work but solve a problem thats a non issue; the spinning solar panels that reduce heat even though energy loss through heat is very small loss and easily dealt with by installing a small air gap, like on daves roof. If he really wants to get more power he should spin his whole house on those magnetic copper coils that made the tony hawk skate board, which is totally unrideable, and uses a huge amount of power. These companies take the money then say "Tried. Can't. Sorry, not sorry".