BU-412: Charging without Wires

Find out about energy loss and higher temperature when charging on a pad.

Wireless charging may one day replace plugs and wires, similar to how Bluetooth and Wi-Fi have modernized personal communication. The concept rests on inductive coupling using an electromagnetic field that transfers energy from the transmitter to the receiver.

Wireless transfer of power is not new. In 1831, Michael Faraday discovered induction by sending electromagnetic force through space. In the late 1800s and the early 1900s, Nicola Tesla demonstrated wireless broadcasting and power transmission. The experiments in Colorado Springs in 1899 lead to the Wardenclyffe Tower in New York. Tesla wanted to prove that electrical power could be transmitted without wires, but lack of funding halted the project.

It was not until the 1920s that public broadcasting began. Europe built massive transmitters that covered many countries. The station at Beromünster in Switzerland could have transmitted radio signals at 600kW, but legislation on electro-smog and protests from the local population limited the power to 180kW. Smaller FM stations have since replaced these large national transmitters; cellular repeaters and Wi-Fi stations transmit at a fraction of this power and many are in single watt digits.

Wireless charging shares similarities with radio transmission. It sends signals in a near field condition in which the primary coil produces a magnetic field that is picked up by the secondary coil in close proximity. The radio transmitter, on the other hand, works on the far field principle by sending waves that travel through space. While the receiving coil of the wireless charger captures most of the energy generated, the receiving antenna of the radio only needs a few microvolts (one millionth of a volt) to recover a signal that becomes intelligent when amplified.

Types of Wireless Charging

Wireless charging is classified as inductive charging, radio charging and resonance charging. Most of today’s wireless chargers use inductive charging with transmit and receive coils in close proximity. Electric toothbrushes were one of the first consumer goods to adopt this method.

Radio charging serves low-power devices operating within a 10-meter (30-foot) radius from the transmitter to charge batteries in medical implants, hearing aids, watches, entertainment devices and RFID (radio frequency identification) chips. The transmitter sends a low-wattage radio wave and the receiver converts the signal to energy. Radio charging resembles radio transmission the most; it offers high flexibility but has a low power capture and exposes people to electro-smog. Radio charging is not in common use.

Larger batteries for the electric vehicle use resonance charging by making a coil “ring.” The oscillating magnetic field works within a 1-meter (3-foot) radius. To stay in the power field, the distance between transmit and receive coil must be within a quarter wavelength (915Mhz has a wavelength of 0.328 meters or 1 foot).

Resonance charging is not limited to high-wattage wireless chargers; it is used at all power levels. While a 3kW system for EV charging achieves a reported efficiency of 93–95 percent with a 20cm (8 inch) air gap, a 100W system is better than 90 percent efficient; however the low-power 5W system remains in the 75–80 percent efficiency range. Resonance charging is still in the experimental stages and is not widely used.

Wireless charging needed a global standard and the Wireless Power Consortium (WPC) accomplished this in 2008 by introducing the Qi norm. This opened the door for device manufacturers to offer chargers for Qi-compatible devices with 5 watts of power.

Powermat, a Qi participant, sprung loose over a disagreement and in 2012 started PMA as a new competitive norm. PMA is similar to Qi but runs at a different frequency. Also in 2012, A4WP announced resonance charging that allows freedom of movement while simultaneously charging several devices. A4WP has not yet been approved as a standard. Table 1 summarizes the three norms.

  WPC or Qi (Wireless Power Consortium) PMA (Power Matters Alliance) A4WP (Alliance for Wireless Power)
Established 2008, Qi was first wireless charging standard 2012, Procter & Gamble and Powermat 2012 by Samsung and Qualcomm
Technology Inductive charging,
coil distance 5mm;
Inductive charging,
similar to Qi
Resonant charging, loosely coupled; serious emission issues remain.
Markets Qi  has widest global use; Over 500 products, more than 60 mobile phones Tight competition with Qi, gaining ground, 100,000 Powermats at Starbucks, A4WP and PWA merged, no product available
Members & companies Samsung, LG, HTC, TI, Panasonic, Sony, Nokia, Motorola, Philips, Verizon, BMW, Audi, Daimler, VW Porsche, Toyota, Jeep Powermat, Samsung, LG, TDK, TI, AT&T, Duracell, WiTricity, Starbucks Teavana, Huawei, FCC, Energy Star, Flextronics Qualcomm, TediaTek, Intel, LG, HTC, Samsung, Deutsche Telecom. No commercial products

Table 1: Recognized standards for wireless charging. Qi and PMA are in completion while A4WP has no standard and no commercial products. Emission issues must be solved first.

While the A4WP format may not be available soon in a charging station, a war is being fought over Qi and PMA. To accommodate both systems, some manufacturers offer chargers and mobile devices that serve both standards. This is a repeat of when Columbia Records released the 33 rpm LP (Long Play) in 1948 and RCA Victor promoted the 45 rpm record featuring a large hole. Dual-speed gramophones and an insert solved the problem.

In 2016, SAE International released SAE TIR J2954 for the electric vehicle. Standardization enables drivers to simply park their vehicles in spaces with TIR J2954 equipment without having to take further action to initiate the charge. SAE TIR J2954 runs at a frequency of 85 kHz (81.39 – 90 kHz) and comes with Wire Power Transfer (WPT) levels 3.7kW (WPT 1) and 7.7kW (WPT 2). Future releases will include 11kW (WPT 3) and 22kW (WPT 4).

TIR J2954 compatible systems are currently being tested with the US Department of Energy and the Argonne National Labs. Rollout with finalized standards will be in 2018.

Modern wireless charging follows a complex handshake to identify the device to be charged. When placing a device onto a charge mat, the change in capacitance or resonance senses its presence. The mat then transmits a burst signal; the qualified device awakens and responds by providing identification and signal strength status. The signal quality is often also used to improve the positioning of the receiver or enhance magnetic coupling between mat and receiver.

The charge mat only transmits power when a valid object is recognized, which occurs when the receiver fulfills the protocol as defined by one of the interoperability standards. During charging, the receiver sends control error signals to adjust the power level. Upon full charge or when removing the load, the mat switches to standby.

Transmit and receive coils are shielded to obtain good coupling and to reduce stray radiation. Some charge mats use a free moving transmit coil that seeks the object placed for best coupling, others systems feature multiple transmit coils and engage those in close proximity with the object.

WPC calls the transmitter the TX Controller, or Base Station, and the receiver on the mobile device the RX Controller, or Power Receiver. There is a resemblance to a transformer with a primary and secondary coil. Figure 2 illustrates an overview of a Qi wireless charging system.

Overview of Qi wireless charging system
Figure 2: Overview of Qi wireless charging system.
Several systems are competing that may not be compatible. The three most common are Qi, PMA, A4WP.

qi logo Qi logo, Chinese word meaning "natural energy"


Pros and Cons of Wireless Charging

Wireless charging offers the ultimate convenience for consumers and enables safe charging in a hazardous environment where an electrical spark could cause an explosion. It further permits charging where grease, dust or corrosion would prevent a good electrical contact. Eliminating electrical contacts also helps doctors in sterilizing surgical tools. Wireless charging is durable and does not wear out the contacts on multiple insertions.

Makers of electric vehicles seek convenience in charging, and this is elegantly solved by parking the vehicle over a transmit coil. Engineers talk about embedding charging coils into highways for continuous charging while driving or when waiting at a traffic light. This is technically feasible, but high cost, low efficiency and field emission when transmitting high power remain insurmountable challenges.

For household and business use, the California Energy Commission (CEC), Level V, mandates that AC adapters must meet a minimum efficiency of 85 percent; Energy Star Level V requires 87 percent (European CE uses CEC as a base). Adding the losses of the AC adapter to wireless charging brings the overall efficiency down further as the inductive transfer efficiency of inductive charging is only 75–80 percent. Such a loss adds up when considering that an estimated one billion mobile phone chargers are plugged into AC outlets worldwide. To improve efficiency and comply with the Energy Star requirements, WPC combines the power needs into a single power conversion.

Lost energy turns into heat, and a wireless charger can get quite warm during charging. This causes stress on the device’s battery as it sits on the mat. It should be noted that the heat buildup only occurs during charging; the charging pad cools down once the battery is fully charged.

WPC was very careful when releasing Qi; the first version has a power limit of 5 watts. A medium-power version of up to 120 watts is in the works, but this norm must meet stringent radiation standards before release. Radiation prompts health concerns and these are raised by folks living next to mobile phone towers and Wi-Fi stations.  

Electromagnetic energy from radio towers, mobile phones, Wi-Fi and now wireless charging are categorized as non-ionizing radiation and are said to be harmless. Ionizing rays from x-rays, on the other hand, can cause cancer. As the number of non-ionizing devices grows, folks begin to question the safety of this form of radiation as well. Regulatory authorities are observing possible health risks and will impose restrictions if harm can be proven.

Health problems caused by electromagnetic waves are inconclusive; however, carrying a mobile phone close to the body is a concern. In standby mode the device is constantly seeking contact with a tower by transmitting signal busts. The transmit power is adjusted to the proximity of the tower and is higher in remote areas.

Going wireless demands a 25 percent cost premium on the charging station, a burden that also affects the receiver. For consumers who don’t want to pay the price, charging by wires remains a workable alternative. Birds looking for the missing wires will appreciate this move.

Birds on a Wire

Figure 3: Pros and cons of wireless charging
Wireless charging provides convenience but wires offer a practical alternative which the birds will support.

Anonymous source

Last Updated 2017-09-28

*** Please Read Regarding Comments ***

Comments are intended for "commenting," an open discussion amongst site visitors. Battery University monitors the comments and understands the importance of expressing perspectives and opinions in a shared forum. However, all communication must be done with the use of appropriate language and the avoidance of spam and discrimination.

If you have a suggestion or would like to report an error, please use the "contact us" form or email us at: BatteryU@cadex.com.  We like to hear from you but we cannot answer all inquiries. We recommend posting your question in the comment sections for the Battery University Group (BUG) to share.

Or Jump To A Different Article

Basics You Should Know
The Battery and You
Batteries as Power Source

Comments (61)

On January 27, 2011 at 1:24pm
Serge wrote:

typo: the word in asterisks needs to be removed from the text:

Detection occurs by noticing a change in capacitance or resonance when placing an object ***is*** on the mat.

On February 2, 2011 at 7:14pm
Lalit Singh Rawal wrote:

nice article. Yes in future wireless power transmission could be the most important achievement of engineering

On April 1, 2011 at 11:04pm
amol wrote:

i m using compaq latop.. my latop battery discharges very early .. wen i remove power it discharges is half hr…. 5 years to finish… wat i should do

On October 17, 2011 at 12:17am
Moustafa Magar wrote:


Just wondering if this technology could be used in a high temperature environment.

Thank you

Moustafa MAGAR

On January 11, 2012 at 11:47pm
Hashan Gayasri wrote:

Any explanation why the antenna of the mobile phone doesn’t induct the transmitted power and burn the signal amplifier?
Is it because resonance frequencies are different ?

On February 6, 2012 at 5:30pm
Gerry Schreiber wrote:

Ok, so how difficult i it to actually plug in a charger be it for a cell phone or a car…...c’mon, this is getting crazy.  The scary part is that in a world of necessary energy conservation, global warming etc etc etc we are prepared to set our concerns aside to save about 5 seconds of time?  Our drive for convenience really just exposes our laziness.  I think there a lot more important things to spend money on in the world than developing increased convenience.  ...put your minds and money to that for a star.  While I have been writing this about 50 children have died from starvation induced illnesses…meanwhile we wring our hands over the possibility of getting a little extra radiation we think might harm us.  Just because we can, doesn’t mean we should

On February 6, 2012 at 7:27pm
Sara wrote:

Wireless charging is just a waste of energy.  We look for efficiency in electronics, not putting out a large emf for a small pickup.  Not needed as stated elsewhere.

On February 22, 2012 at 10:25am
шкурило wrote:

молодцы это очень хорошо даже. ну можно ж придумать более мошне батарейки с таким внешним видом. например заряд от обычного  батарейка от телефона хватает на один день так вед. если заделать их так чтобы один раз зарядил и забыл на один год ну хотя бы на пол года и ни надо думать и ни надо придумывать всякие способы зарядит телефон. конечно такие штучки хороша когда под рукой нет зарядное устройства или нет электричество. ну все равно это к лучшему.

On March 7, 2012 at 10:44am
patjasiu wrote:

As stated in article great technology for hazardous areas (no spark allowed) and also for 100% water/dust-proof devices (no contacts & no slots = no leaks & no corrosion & no short circuit risk). One could safely get device or EV charged outdoors even in rainy weather or on ships deck in salty corrosive mist - which isn’t so easily done with plug-in technology. Going further I wonder how mass of water affects inductive power transmission - and I guess it hardly does, so You could “push current” fully underwater - try to “plug-in” something this way!
Maybe charging phone on desk this way is luxury, but technology is hard to beat in some areas!

On November 5, 2012 at 10:43am
cody wrote:

Funny how so many of these Comments are based on opinions and are sooooo wrong…lol…...This betters the planet….....technology reaching to be battery free….HOW IS THAT A BAD THING??????

2. waste energy????  in the short small brain it does…....you have to compare a usb adapter plugged in 24/7, YES it uses power…...and many other factors and this wireless charging ends up in the long run using less and cost less to use etc etc….

On December 10, 2012 at 1:29pm
thumar rushik wrote:

please give me information about voltage at mobile usb port

On January 3, 2013 at 9:23am
Wm. Cerniuk wrote:

Nice article.  Great reference and well written.

On January 3, 2013 at 1:35pm
cody wrote:

Funny how that used a product of one of the Huge Companies In Wireless Manufacturing and that Company is Not Qi…LOL…and Qi didn’t start their so called Standard until This year…
And you the Guy talking about Global Warming etc, This has and is Proven, if not by just Common Sense but proven by test and use. The Traditional way of charging with a a/c wall adapter and plugging into phone causes a person to be Lazy when it comes to using it. Do you watch for the charging to reach 100% and unplug the phone then unplug the Adapter? If you do, you are one in a count of less then 1%....before you beat it down, do some research of test etc.
Also when was the Last time you saw a charger Adapter get qualified for Energy Star? Prob haven’t because the ones that do exist are so far out of acceptable cost no one can afford them. These chargers are down to a 0.0001 kwh draw on standby and it has already been proven it will reach down to Zero draw…

On March 5, 2013 at 9:02pm
kaisen wrote:

AD time, wireless induction charger/pad etc…
we are looking for wholesalers, distributors…  we have our own compatible standard. Also we are producing Qi standard charger/pad…  welcome to ask for an inquiry…
thanks for your time


On March 5, 2013 at 9:04pm
kaisen wrote:

oh, forgot to leave my contact info: weinaisong@gmail.com

On March 5, 2013 at 9:20pm
cody wrote:

PowerMat or Duracell Powermat are not Qi . In fact they have their own group which wasn’t mentioned and have the who’s who of Big Corps in their group..
1.Vinton G. Cerf, Honorary Chairman
Vinton G. Cerf is vice president and chief Internet evangelist for Google

2.Mani Parmar, Duracell Powermat, Procter & Gamble

3.James E. Snook, Starbucks
James is the Vice President, Emerging Platforms & Innovation in Stabucks

4.Jeff Howard, AT&T Mobility
Jeff Howard, Vice President, Mobile Device Portfolio in AT&T

5.Katharine Kaplan, Energy Star (Board Observer)
Katharine Kaplan, Chief, ENERGY STAR Product Development and Program Administration Grou

6.James Miller, FCC (Board Observer)

Fcc and Energy Star on the team…lol…that’s the people who matter…lol

On May 23, 2013 at 5:56pm
Thomas Tsoi wrote:


On August 7, 2013 at 10:12pm
nithin wrote:

Why we are not using wireless charging in new mobile phones ?

can we make charge the battery using signals.?
How ?
Pls explane…..

On November 10, 2013 at 5:31am

can you say ? , somebody get pattern for it ?

On November 30, 2013 at 9:15am
gayatri wrote:

i want different modes of charingggg

On December 13, 2013 at 1:19pm
Frank Cohen wrote:

Thanks for the good article and the great Web site. I am designing a new mens luxury watch - see http://votsh.com - that uses epaper displays. Using inductive recharging seems like the best way to go. -Frank Cohen

On February 5, 2014 at 11:37pm
Glenn Crosby wrote:

Microwave ovens operate 2400 MHz, not 915 MHz as stated in the article.  2400 MHz is near the resonant frequency of water molecules so the cooking is efficient.

On March 30, 2014 at 11:53pm
Rashi wrote:

plese give me diagram (wire less charger)

On April 29, 2014 at 10:03pm
Katline wrote:

Just got the Nexus wireless charger from Amazon and they are going absolutely crazy with the discounts with these brands. If you don’t have a promo code, you can use this one: http://amzn.to/1iyFZfq - before they take it down.

On April 30, 2014 at 4:21am
hallary wrote:

First of all let me tell you, you have got a great blog on topic Charging without wire .I am interested in looking for more of such topics and would like to have further information. Hope to see the next blog soon.

I have recently posted on topic SMS Gateway visit link http://www.experttexting.com/sms-gateway/

On May 29, 2014 at 5:08am
RAY wrote:

Hadan gayasri the two interfering waves would have to be in very close frequency..called resonance. This is where as in hearing or signal distorted.  Actually only effects human more than to electronics..aka cancer cause or possible reverse as an cure (if possible… Thats whole different suvject but read fcc snd cell phone manual where legal disclamer printings in tiny letternso peoole dont really read the Fscts)

On May 29, 2014 at 5:19am
RAY wrote:

Amol buy a fresh notevook battery..google the battery part no. You will fine hope there if no longer available then your notebook is tine tilo burry it..but inbthis site there isnabway to re-trigger battery by hot wire the battery side of the nb bsttery terminals using 100ohm resister but look in left index. A link will bring you to show you how to try it (no guarantee)

Here. http://batteryuniversity.com/learn/article/how_to_repair_a_laptop_battery

On September 27, 2014 at 2:59am
Nathan wrote:

Hi I just was wondering this and looked it up!
but it sounds possible for an app to be made with this sort of re-charge ability.
I am also thinking going onto the app at times of low battery to charge while away from charging devices is possible!
Could you please send my email more info of new inventions in this area.
Thanks nathan

On October 13, 2014 at 12:02am
Ray wrote:

GOOGLE = noteobok battery revival
GOOGLE = lithium polymer cell battery circuit diagram
GOOGLE = lithium polymer cell battery circuit chip manufacturer

please be advised that proceed at your own risk..

On November 27, 2014 at 11:04pm
orderplz wrote:

Thank you for the info. It sounds pretty user friendly. I guess I’ll pick one up for fun. thank u.

Home Delivery Restaurants in Chennai

On December 1, 2014 at 5:15pm
Kyle Hobbs wrote:

I am wanting to create one, but i need a list of materials to do so. Contact me please at kylejhobbs@gmail.com

On December 2, 2014 at 10:53pm
Nathan wrote:

Good luck Kyle u need cash to make things I got plenty of great ideas myself but I’m a poor guy!

On December 4, 2014 at 12:00am
Puja Pansare wrote:

Great idea!..  Can you plz mail me more information related to it.

On December 12, 2014 at 11:21am
Fred wrote:

Are wireless chargers a hazard to those with cardiac pacemakers, automatic defibrillators and the like?

On January 5, 2015 at 10:29pm
kathun wrote:

why we can’t transfer charge from one mobile to another via bluetooth or wifi?

On January 30, 2015 at 7:31am
Phil wrote:

The Yagi-Uda array (TV aerial) was designed as a means of wireless power transmission in the 1920’s.

Although it did work it was impractical and inefficient but it did give us high gain antenna’s

On March 19, 2015 at 9:37pm
S Howell wrote:

I have a $400 wireless option in my 2015 Dodge Dart, an induction mat for a cell phone, my Android, to recharge while I am driving and making voice activated calls. Nice feature right? I thought so, but, WTH, nobody has a clue how to make it work? I was told I could obtain something to match the phone to the wireless mat to activate the transmit/receive for charging, but there isn’t anywhere to find out what I need! Not even the Dodge Homepage has anything about it except to say it is an option- nor do any Dodge Dealers have a clue. So I paid for the technology and cannot use it? Anyone know anything about how I can use this mat charger?

On March 24, 2015 at 8:32am
Steven | Intercel Battery Warehouse wrote:

Interesting development! However, I am always a bit sceptical when it comes to such technologies. Most of the time it will take several years before the technology is ready for mass production and we can use it in our daily products.

On April 7, 2015 at 5:27pm
Alfons Peter Johann wrote:

Thank you for picking up Wireless charging and your professional article.
I consider wireless charging as one of the things which the world doesn’t need. I’m wondering how these systems pass CEC level IV or V. How to sell this devices in California? How in Europe?
One has to leave the device at a precise location and it charges slow. Why not plugging it in and charge fast or QC fast charge? It does not work well with a case on your phone, except it is is a special charging case.
Why would we need another transmitter of high frequency EM noise in our private rooms? Is GSM, WiFi and radio in general not enough?
And one more thing before I forget it: These wireless charging systems are perfect in erasing your credit card placed on the charging area.


On May 21, 2015 at 3:47am
jerry roach wrote:

thank you

On June 28, 2015 at 10:19am
vinay wrote:

this is a good article which appreciates the engineers to the next level in electcronics

On August 18, 2015 at 2:27pm
Stratis wrote:

We are looking to purchase a wireless charging system for a historic landmarked restaurant in nyc

On October 31, 2015 at 5:09am
Anthony wrote:

Why the fuss about efficiency? Simply design in an auto detect mechanism and remain in standby mode. This can be done wirelessly using the same coils, and also the receiver itself can turn off its own coil when finished so the transmitter autodetect also goes back to standby.

On February 2, 2016 at 12:29am
rahul vadam wrote:

hiii guys,

  i m trying to share energy withought physical media with no limit of distance between source and destination.
if anyone doing such things please contact mi with my mail id.

On March 13, 2016 at 4:27pm
Jennifer wrote:

I would be sooo grateful if someone out there knows an alternative to the 2 options I know of to charge the phone. I dont like the idea of having to buy more accessories like the base station, the correct battery cover and eventually a new battery since the wireless puts more stress on it. However, all of those accessories would be cheaper than buying a new phone or paying to get the current phone repaired! I was looking into wireless charging because the phones that ive had (not just me and my husband, but friends and family members) all seem to eventually stop accepting/recognizing the charging cord. The male end that plugs into the phone seems to get looser and looser until no amount of re-positioning works. I really dont think its a problem with the cords, because i can successfully charge other devices with the same cord that wont work on the phone. I did go buy a replacement cord even though the ones i were trying to use werent kinked or stripped of insulation, and the brand new one didnt fit snugly into the phone. I know these things arernt built to last forever, but c’mon, a new phone every couple of years?! PLEASE, if someone is reading this and knows a way to remedy the problem, i beg of you to say how.

On July 29, 2016 at 8:57am
Ayush Maurya wrote:

Is this wireless charger work in j5

On August 13, 2016 at 11:24am
Dave Pickell wrote:

Making a podcast about new horizons in electrical tech, with emphasis on getting cables to a minimum. Great article and comments, all.

Trying to discover a way for users and purchasers of future tech to be given a stronger voice in the usability standard.  Apparently , e.g., the new USB plug/receptacle, for example, will be flippable and follows the vision of Ajay, the original team leader for the USB standard.  Little things add up in the electronic world.

On October 22, 2016 at 3:29am
gayathri.s wrote:

Is it possible to inbuilt a circuit within a laptop which absorbs near frequencies and convert it into energy for charging the laptop automatically?

On January 25, 2017 at 3:15pm
Jason wrote:

I’m curious: are there any manufacturers out there actually producing wireless rechargeable batteries that I can actually, like, buy? This ( https://powerbyproxi.com/applications/wireless-battery-charging/ ) might be the only one I can think of, and even then it’s not the actual batteries you’re buying. Basically I just really want consumer-level wirelessly rechargeable AA batteries already. They can’t be that far off, right?!

On February 12, 2017 at 1:11pm
HARDEV kalyan wrote:

I want to make an app.
That will make wireless charging.
I can let you know more about it .
Can you give me the person to go .to .
Or a company.
Thank you.




On June 9, 2017 at 6:37am
Vortexian wrote:

Wireless charging really shines in sealed-body applications like zero element ingress devices (waterproof watches, digital diving gear, tech intended to be used in an explosive atmosphere) or medical implanted tech, where exposed contacts would be a weak structural point or just be unsafe.

Regarding the emissions, people are already being exposed to enormous values of wide-spectrum non-ionizing EM radiation for at least 60 years, generated by electrically powered trains and electrical stoves.

On June 28, 2017 at 10:08pm
Jean Saraque Cius wrote:

Where can I this wireless battery charger for my cell phone?

On August 30, 2017 at 12:49am
Zohair wrote:

At this point, the work is still theoretical, but researchers are trying to create a prototype system that can be patented over a year.

On September 19, 2017 at 8:17pm
Awesome Academy wrote:

This is a good summary of wireless power but I do have one critique about this section:

“Larger batteries for the electric vehicle use resonance charging by making a coil “ring.” The oscillating magnetic field works within a 1-meter (3-foot) radius. To stay in the power field, the distance between transmit and receive coil must be within a quarter wavelength (915Mhz has a wavelength of 0.328 meters or 1 foot).”

This kind of implies that electric vehicles charge with 915MHz but this is not true. Virtually all wireless charging systems in existence today operate at 7MHz or less. Also modern resonant inductive power transfer systems do not transfer power via the far field so the standard calculations for 1/4 wavelength antennas etc do not apply here. The power is transferred in the near field region by magnetic waves whose effective range is largely determined by the diameter of the transmitting and receiving coils and the current flowing through them.

If anyone is curious to learn more about wireless power I offer an introductory course at http://www.awesomeacademy.ca

On December 19, 2017 at 11:41pm
CVZalez wrote:

I don’t recommend it, I bought one wireless charger, is a cool thing and it would hide all my cables, BUT, it does not work well. It take ages to charge, I know I have used a wired fast charge and the comparison is unfair, so I decided to put the wireless charger on my bed desk, so it can charge overnight, but it’s very unreliable, it gets hot, even more than my wired far charge, and I actually measured it with a battery temperature logging app, but what really made me give up wireless charge for my mobile is the fact that it intermittent charges ask the time, while my wired charge goes all way up to 100% and then uses the home electrify wine not unplugged, the wireless charger, charges and discharge all the time, and with the time it takes to get to 100% charge and then keeps charging and discharging, I estimate a bad battery in a fraction of the time of a wired charging. I guess the problem is on low wattage, to be safe to human contact the wattage is too low and makes the charging unreliable. It can be a solution for cars charging where is a good safe distance and then the power output is big enough for a reliable wireless link but right now, definitely not for mobile phones.

On December 20, 2017 at 11:57am
CVZalez wrote:

I do not recommend it, I did bought one wireless charger, is a cool thing and it would hide all my cables, BUT, it does not work well. It take ages to charge!

I know I have used a wired fast charger and the comparison is unfair, so I decided to put the wireless charger on my bed desk, so it could charge overnight, but it’s very unreliable!

It gets hot, even more than my wired fast charger, and I actually measured it with a battery temperature logging app, but what really made me give up wireless charge on my mobile phone is the fact that it intermittent charges all the time.

While my wired charge goes all way up to 100% and then uses the home electricity until it’s unplugged, the wireless charger on the other hand charges and discharge all the time until it slowly get’s to 100% charge and then keeps charging and discharging, I estimate a bad battery in a fraction of the time of a wired charging method.

I guess the problem is on low wattage, to be safe to human handling the wattage must be low and it makes the wireless charging unreliable. It can be a solution for electric car charging where is a good safe distance and then the power output is big enough for a reliable wireless link but right now, definitely not for mobile phones.

On January 18, 2018 at 2:33am
Steve Calvert wrote:

A fella that went by the name of Nikola Tesla had quite a run with ruminations towards the widespread use of wireless transmission of power, doomed from the start because any truly groundbreaking and inexpensive advancement in technology must be immediately buried to keep the planet consuming rich in the money.

Batteries are coming along nicely with new developments about to be released offering tremendous increases in safety and efficiency (changing the catalyst in LiPO battery packs for example) and with fresh eyes and new views we will see this stuff become much more reliable and if not shot down by existing big guns will make everyone much much technically comfortable campers, oir just generally happily mobile. ]:o) 2 cents..

“The scientists of today think deeply instead of clearly. One must be sane to think clearly, but one can think deeply and be quite insane.” - Nikola Tesla

I’d add to that, in so many cases also thinking simply KISS and Axoms Razor style rather than overthinktanking solutions is another thing needed in this industry in all areas.

73’s and peace

On April 22, 2018 at 7:46pm
Brendan LaCorte wrote:

What needs to be done to the battery for it to be able to receive the charge from the mat?  Can I just put my phone on the mat or do I need to do something?

On April 26, 2018 at 8:35am
Brendan LaCorte wrote:

How does wireless battery charging work and what needs to be done to both units for it to work?

On May 12, 2018 at 2:45pm
David M Schaeder wrote:

Hashan Gayasri - Because the received signal is so much less. You need an amp to read th signal.

On June 12, 2018 at 12:09pm
Steve Calvert wrote:

By the way, just wanted to say “thank GOD I don’t have any issues with birds resting on my usb charging cables!, the wife’s eX does have a parakeet tho, poor bloke.