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What is wireless charging and how does it work?

Qi charger
Qi charger (Image credit: Jerry Hildenbrand / Android Central)

Wireless charging, such as the Qi charging tech many Android phones use, isn't new technology. My Panasonic electric razor used it many years ago, and most of us have seen toothbrushes that charge wirelessly in a cradle. And of course, we can't forget Palm and the way it brought wireless charging to the masses with the Touchstone. Now that size, cost, and efficiency constraints have all eased up a little, putting wireless charging in something like your Android phone or watch makes more sense.

We get more than a few questions about wireless charging and how it works, so let's take a few minutes and talk about the basics; what it is, how it works and why you would want it in your next Android purchase.

More: The best wireless charging pads for Galaxy S8

What is wireless charging?

Wireless charging isn't magic — you still need a wire. The difference is that the wire is connected to a charging base instead of your phone, so you can just drop your Android onto the charger and things get to work without hooking anything up to your phone. The charging base can be almost any shape or size, and can even be in something like your car dash or the base of a lamp from IKEA. As long as you're able to get the right spot on the rear of your Android on the right spot on the base of the charger, it will work.

A good example would be having a wireless charging base on your desk at work. When you're not using your phone, you set it on the charger. When you need to use your phone, pick it up and it has a charge. Wireless charging isn't as fast as Quick Charge, but it's easy and something you're more likely to use to keep your phone topped off throughout the day (in our example). That's where wireless charging shines — ease of use.

How does wireless charging work?

Wireless charging uses two resonant inductive couplings to transmit low-power signals between two devices. These are specially designed to transmit electricity without touching each other like a normal wired connection does. The base station, which is plugged into the wall through its own power supply, has a transmitter coil and your phone has a receiver coil. The base station regularly sends a signal out, and when a receiver coil gets close enough, a resonance change (the base station changes the amplitude of its oscillation — it vibrates faster) happens in the signal. The waveform of the signal is then modulated (changed to let the coil in the phone know power is being sent) and inductive charging begins.

Wireless charging uses the same electrical theory as a generator: mechanical energy creates electrical energy.

Inductive charging uses those two specially designed electromagnetic coils to create a magnetic field between two devices. There is an intricate process involved that allows a magnetic field to produce electricity through the difference of potential and oscillation. Oscillation is a timed repetitive variation, and in the case of an electromagnetic coil, you can think of it as vibration.

The coil in your Android device is also connected to the battery charging circuit, and your battery is charged using the energy induced by the magnetic field.

Electromagnetic induction is really cool, and the basics are that if you move an electrically conductive material, like a coil or winding, in the presence of a magnetic field you make electrons flow. Things like a gas-powered generator also "create" electricity by using mechanical energy to create EMF (electromotive force). Electromagnetic induction is also used in transformers and current measuring devices.

Wireless charging isn't very efficient, but it is getting better with each iteration of the standard.

Excess heat is created as well, and that's part of why wireless charging isn't the most efficient way to transfer power from the wall to your battery. This is also why it takes longer to charge your phone on a Qi pad than it does to plug it into the wall. While new methods and materials use higher frequencies and thinner coils than past iterations, wireless charging is still less efficient and more costly than standard charging over a wire. It will stay this way for the foreseeable future.

To simplify:

  • Your Android and the charger each have special electrical coils in them.
  • When the two coils get close enough, they use magnetism to create small oscillations (vibrations) in the coil and an EMF is created by the coil inside your phone.
  • This EMF sends a small amount of power through the charging circuit in your phone and charges the battery.
  • It costs more and takes longer to charge than it would if you plugged your phone in, and creates more heat because this is less efficient than connecting wires the traditional way.
  • Faraday's law of induction is awesome and the Maxwell–Faraday equation is like mathematical chocolate: sweet and decadent. Wireless charging is also pretty awesome when you're using it, too.

A word about Powermat

Powermat

Qi is not the only wireless charging standard. Other standards like Powermat are used to build wireless charging solutions. These use a different standard than Qi but the science behind them all is the same. Powermat has partnered with companies like AT&T and Starbucks to provide base stations in public places, and using a special case or charging block attached to your phone lets you wirelessly charge. They are also partnered with General Motors and are working to bring built-in wireless charging bases in vehicles.

Powermat does some really great things (great if you're an electrical engineer, anyway) and some would argue that it's the better standard. In any case, Qi is more prevalent.

While the same basic electrical theory applies to both Powermat and Qi, the different standards mean they are not compatible. Your Qi-enabled phone won't charge on a Powermat base because the signals sent and received are different. If you have Powermat equipment, you'll need to be sure you're buying more Powermat equipment to get everything working.

There are exceptions, like Samsung Galaxy phones, which include both Qi and Powermat standards.

Why do I want wireless charging in my next phone?

Now that we have a widely accepted standard — we're talking the Qi standard here — we have to remember that any Qi charger will work with any device that is Qi-certified. That means the charger you buy, whether it's a $6 Chinese unbranded unit from Amazon or a name-brand like Samsung or Zens, will work with the device you have now and any devices you buy in the future.

You don't use wireless charging because it's "better". You use it because it's more convenient. A lot more.

Couple this with the convenience factor — and until you've bought a couple Qi chargers and put them in the places you're likely to set your phone you don't really understand how convenient it is. You might have a Qi charger at your desk, on the table in the living room, one in your car and one on your nightstand. Your Galaxy S8 will almost never have less than a 50% charge. Not because the battery life on the Galaxy S8 is great, or because Qi chargers work "better", but because whenever it's not in hand it's charging.

Of course, there's the initial cost of buying the charging bases, but they are pretty cheap — about the same cost as a good wall wart and USB cable. As more and more handheld devices and smartphones move towards the Qi standard, more and more devices will be able to take advantage of the chargers.

Wireless charging doesn't make your phone work any differently, but it can change the way you use it.

Update September 2017: Clarified some of the electrical theory and made sure the latest versions of the Qi standard were represented.

Jerry Hildenbrand
Senior Editor — Google Ecosystem

Jerry is an amateur woodworker and struggling shade tree mechanic. There's nothing he can't take apart, but many things he can't reassemble. You'll find him writing and speaking his loud opinion on Android Central and occasionally on Twitter.

37 Comments
  • Can't wait for Apple to invent wireless charging tonight :-)
    On topic; I still miss wireless charging on my 6p! Got hooked on it because of my Nexus 5. It's one of those things where it seems mildly convenient at first, but after a week of using it, you can't imagine life without it...
  • You joke but from I'm reading they're going to use a different standard to everyone else so iPhone users will have to use Apple wireless chargers or ones specifically licensed by them. If they miraculously come out tomorrow with the system they were supposedly testing where you only have to be in the same room as the wireless charger to charge the phone then I'll genuinely be blown away
  • havnt you heard apple invented wireless charging . ....well that's what they'll claim anyway . oh an they also invented face detection hehe
  • If true I would be one angry Apple customer. Some vehicles and furniture have wireless chargers built in, there are public places with charging pads as well. Besides Apple will charge a fortune for their own pads.
  • Their customers don't care. They never have when it comes to proprietary accessories....
  • True, but people are used to different charging ports, been that way for decades on electronics. Different wireless charge tech is almost as bad as having incompatible Bluetooth devices because they have their own wireless standard for audio.
  • Apple using a proprietary wireless charging method would not surprise me at all. then they get royalty fee's from whoever that makes a charging pad for apple
  • My wife works with all women...only one other is an android user. One of the iPhony ladies said to her yesterday, 'oh have you heard the iPhone X is going to be able to charge without plugging it in?' My wife, not exactly tech savvy said, 'do you mean, wirelessly? I've been doing that for 3 years now with my phone(s).' She looked at my wife and said no way, because iPhone is just now doing it. She said I don't have an iPhone and it seems like they're always behind. They then went on to discuss what her S8 can do and a little bit of my Note 8. She told me they were very confused. I thought it was hilarious!
  • Priceless. It sounds like trying to use logic with liberals.
  • Used wireless charging on my Nokia 820 more then 5 years ago. Phone is still working battery life is only about 30 minutes now though.
  • I love just dropping mine galaxies on the wireless charger . Got them all over the house
  • And today you will see Tim crook explain how wireless charging is so innovative and courageous. And the world's first company to invent it.
  • I just think it was courageous of them to develop the first smartphone, then the first touchscreen!
  • Excellent article, Jerry. Very clear and easy to understand for those who aren't electrical engineers. I don't have any Qi compatible phone yet, but hopefully someday it will be a standard feature amongst devices (like headphone jacks, bluetooth, etc.).
  • Any phone can be made Qi compatible. Just plug in a wireless receiver into its USB port
  • Face-palm :-)
  • I prefer built-in solutions, at least on phones. Accesory quality in Argentina is iffy at best, hazardous at the worst.
  • I have a Nillkin wireless receiver & a 3-coils Choetech charger. The combination of the 2 is excellent. I even charge my 9.6 inches tablet with them. You can get them from Amazon or Aliexpress
  • So glad Apple is rumored to be adding it. That means there is a chance for the Pixel 3. I miss my Nexus 5. It was so much better than the phones Google has released the past few years.
  • Totally agree! Nexus 5x should of had wireless charging since it was a plastic back. Google made a wack excuse of having USB type c you didn't need wireless charging
  • Ooh! I know I'm gonna like this write-up because: Jerry!
  • Nice article Jerry, of course. Has anyone done a charging test to give a perspective on times using the various methods, like regular wireless charging vs wireless quick charging vs USB from a computer port vs USB QuickCharge? If you decide to do the tests yourself (that would be cool!), you may want to cut the test range and make it from 10% to 80%. Not going to 0% (2.7 volts if I recall correctly), is easier on the battery, and stopping the test at 80 eliminates the last portion of charging where some technologies drop rates to preserve battery lifespan and allow cooling. Correct me if I'm wrong, but the Note 8 only has the older 2.0 QuickCharge, and not 3.0 like others have, correct?
  • PS: When I did my own tests, I went from 25% to 75% with the following results:
    Quickcharge version 2.0 - 37m 20s. Maximum temperature 110 degrees F.
    1.5 amp standard charge: 59m 32s. Maximum temperature 96 degrees F.
    0.5 amp PC USB port: 2h 39m 57s. Maximum temperature 81 degrees F. The peak charge rate per hour for each method was 82%, 54%, and 22%.
  • Sometimes I wish a media outlet would just man up and say, we aren't calling it wireless charging anymore. Things like wifi and Bluetooth are wireless. Inductive charging is not. This is how we get stupid terms like "True wireless charging" or "real wireless charging" which confuses everyone and the guy at Best Buy 5 years from now has to explain to your mom that wireless charging isn't actually wireless charging, but a marketing term that was coined and allowed to run rampant several years ago. Maybe I'm just touchy because I watched the Apple keynote that featured the iPhone X with a bezel-less display. Of course there is a bezel around the display, but who cares. It's not like the media is going to hold them to any of these claims. Wireless charging...woohoo!
  • Great post! 👍
  • @mikemick, since there are no wires directly connecting the two devices, technically it is wireless. The fact that it takes yards of wire to make the coils is not the point.
    The early radios were called wireless in years gone by, and they had miles of wire inside them... Same story... No direct connection, therefore... Wireless 🙃
  • So is a dock wireless? A qi charger and a dock are the exact same thing. Neither one puts a wire directly into the phone. A qi charger charges inductively through the back plate. A dock charges via the port. Neither one attaches a wire directly to the device. My idea of wireless is the same as "untethered". If your device has to be in physical contact with something it is tethered and therefore not wireless in my book.
  • That's a pretty semantically narrow view that stands at odds with the clearly observable physically differences between a charging cable and charging stand/plate. I can hold my old Nokia 930 so that it is not in contact - air gapped - with my Tylt Vu stand and it will detect and charge. That distance is small, maybe a millimeter or two, but it will work not being in contact, nor having been initially in contact and lifted, with the stand. The limiting factors in wireless charging are more safety and space related. Larger coils, higher voltages could be implemented, but would need to matched with more robust (taking more space) coils on the devices. The safety aspect becomes what projected electrical field density is acceptable for biological health and to avoid harmful interference in other electronic systems.
  • Wi-Fi and Bluetooth aren't wireless by your definition. They share many of the same components and have identical hi-side wiring in the transmit device as a Qi charging base does. They also have wires inside your phone and use the very same power supply conductors.
  • I guess I'm thinking of a more "common sense" approach to wireless. I'm not trying to create my own definition. I'm just trying use the same nomenclature that the mass public has used and has understood for decades. You kinda made my point. As you mentioned, there are wires in our phones, yet they are still called wireless phones. The term "wireless" really has less to do with the the lack of wires and more to do with something being untethered (like a wireless tv remote).
  • The term <wireless> actually means <cordless>.
    As in, there is nor cord tethering the device to a wall or a machine.
    Simple.
  • yeah, man couldn't agree more. great post
  • What case is that in the second pic?
  • I would like to hear more about how the heat generated from "wirelessly" charging your phone affects the batteries ability to hold a charge over time. I remember reading something about the detrimental effects of wireless charging, but haven't heard anything about the new standards being used.
  • Interestingly enough I used Wireless charging almost everyday on my Galaxy S7. Unfortunately my Galaxy S7 was temporarily down so I brought a Moto G5+. I thought I would miss Wireless Charging but I realize I don't. Definitely a nice bonus for me but not required.
  • It is good to have one wireless charger ,really convenient.
  • I am going to disappointed I know, but will teh PIxel 2 have Qi charging? Why does it feel like Google now is following in Apple Footsteps. Last i Phone was IP68, this year the PIxel 2 is IP68. This year Apple is bringing in wireless charging, (which I used to have on my Nexus devices) and is Google leaving it out again this year?