How does wireless charging work

Updated October 3, 2017, 12:53pm EDT

How does wireless charging work

Wireless charging is set to become more popular with the adoption of Qi wireless charging in Apple’s iPhone 8, iPhone 8 Plus, and iPhone X. It’s also found on some Android phones, like Samsung’s Galaxy Note 8, Galaxy S8, and Galaxy S7.

Most wireless chargers use magnetic induction and magnetic resonance. They offer the promise of being able to place a device on a surface and have it charge automatically—no fiddling with cables required.

How Wireless Charging Works

Wireless charging isn’t truly wireless, of course. Your phone, smart watch, tablet, wireless headphones, or other device doesn’t need to be plugged into the charger with a wire, but the wireless charger itself still has to be plugged into a wall outlet to function. When the iPhone 5 was released without the wireless charging feature found in competing Android and Windows phones at the time, Apple’s Phil Schiller argued that “having to create another device you have to plug into the wall is actually, for most situations, more complicated”.

Five years later, Apple has changed its mind. With the iPhone 8, iPhone 8 Plus, and iPhone X, Apple is including support for wireless charging using the Qi open standard. (It’s pronounced “chee” as it’s a Chinese word that refers to the “life energy” in living things.)

Wireless chargers typically use magnetic induction. The short explanation is that they use magnetism to transmit energy. First, you place the device–like a smartphone—on the wireless charger. The current coming from the wall power outlet moves through the wire in the wireless charger, creating a magnetic field. The magnetic field creates a current in the coil inside the device sitting on the wireless charger. This magnetic energy is converted to electrical energy, which is used to charge the battery. Devices must have the appropriate hardware in them to support wireless charging—a device without the necessary coil can’t charge wirelessly.

While the Qi standard was originally limited to magnetic induction, it now also supports magnetic resonance. This works similarly, but the device can be up to 45mm away from the wireless charger’s surface rather than touching it directly. This is less efficient than magnetic induction, but there are some advantages—for example, a wireless charger could be mounted under a table’s surface and you could place a device on the table to charge it. It also allows you to place multiple devices on a single charging pad, and have all of them charge at once.

When not actively charging, the Qi charger doesn’t consume the maximum amount of power. Instead, it uses a smaller amount of power and, when it detects a device is placed on the charger, it increases the energy output.

Competing Standards: Qi vs. Powermat vs. Rezence

Wireless charging is becoming more and more common, and even more standardized. And for once, Apple didn’t create its own wireless standard. Instead, it chose to support the existing Qi standard, which many other devices also support.

However, Qi isn’t the only standard around. The Qi standard, which is owned by the Wireless Power Consortium, is ahead, but it’s not alone. In second place is the Power Matters Alliance’s Powermat, or PMA, standard. It uses magnetic induction, like Qi. The two are incompatible, though. An iPhone can’t charge with a PMA wireless charger.

Some devices are compatible with both, however. Modern Samsung devices like the Galaxy Note 8, Galaxy S8, and Galaxy S7 actually support both the Qi and PMA standards, and can charge with either. Starbucks bet on PMA, but they may rethink things now that the iPhone only supports Qi. Apple is betting that airports, hotels, and other public locations will also choose to bet on Qi.

The Alliance for Wireless Power (A4WP)’s Rezence uses magnetic resonance instead, a feature Qi added later. This allows for greater freedom of positioning. You can have multiple devices on a single charger, move devices around, and even charge devices through an object like a book between the device and the charger. Rezence requires Bluetooth to communicate with the device.

As the second and third place companies here, the Power Matters Alliance and Alliance for Wireless Power have since rebranded themselves the AirFuel Alliance and are cooperating in an attempt to take on Qi.

How You Can Use Wireless Charging Today

All the technology aside, getting started with wireless charging is pretty simple. If you want to charge your smartphone wirelessly, you’ll need a smartphone that supports wireless charging and a compatible wireless charging mat to place your phone on. You can also purchase adapters to add wireless charging support to phones that don’t include it.

Popular smartphones that support wireless charging include:

  • Apple iPhone 8, iPhone 8 Plus, and iPhone X
  • Samsung Galaxy Note 8 and Galaxy Note 5
  • Samsung Galaxy S8, S8+, S8 Active, S7, S7 Edge, S7 Active
  • LG G6 (US and Canada versions only) and LG V30
  • Motorola Moto Z, Moto Z Play, Moto Z2 Force, Moto Z2 Play (with wireless charging mod only)

Android manufacturers have increasingly been abandoning wireless charging in recent years. Only Samsung has kept it on its recent high-end phones. For example, Google does not offer wireless charging in its Pixel smartphone, although earlier Nexus phones included this feature. With Apple giving the Qi standard a vote of confidence, wireless charging could become more common on Android devices once again.

If your phone doesn’t support wireless charging, you can add support for wireless charging with a special phone case or wireless charging adapter that you stick on the back of your phone and plug into its power port.

Once you have a phone or adapter that supports wireless charging, pick up a wireless charger that’s compatible with it. For most phones, you’ll want a Qi charger. Any Qi certified wireless charger should work with any Qi certified device. You can find them online on websites like or in electronics stores. Plug the charging pad into the wall and place your phone (or other Qi-enabled device) on it to charge. As long as your device and the charger support the same standard, it will just work.

In the future, wireless chargers will hopefully be more common in public locations, allowing you to just place your smartphone on a table to charge it.

In case you haven’t heard the news, Apple is rolling out a new version of its AirPod headphones. The new AirPods come with a slew of convenient new functions but there’s one that really stands out to me. One of the newest features of the second rendition of the AirPods is a Wireless Charging Case. This wasn’t offered with the original AirPods. So, you may be wondering, “How does Apple’s Wireless Charging AirPod Case work?” You’re in luck, because it’s actually really simple.

In a highly-anticipated announcement, Apple unveiled a new version of AirPods on Wednesday, March 20. For the most part, the new AirPods look the same as the original AirPods. But, there are some major differences like the addition of a Wireless Charging Case. Now, the case is optional. You can buy the new AirPods with the standard charging case for $159. It’s just like the case that comes with the first version of the AirPods. Or, for an extra $40, you can buy the latest version of Apple AirPods with the added bonus of a Wireless Charging Case. The cord-free case is also available for purchase on its own. It’ll run you $79.

If you’ve never used any sort of wireless charging technology before, you may be curious as to how it works. It’s really easy to use. Per Apple, the new Wireless Charging Case works with “Qi-compatible charging solutions.” If that sentence left you scratching your head, not to worry. Qi is simply the technology that supports wireless charging. You’ve probably seen (or at least read) about wireless charging pads. Many retailers like Amazon, Target, and Walmart offer wireless charging devices.

To power up your Wireless Charging Case, purchase a charging device that is suitable with the new Apple AirPods case. Just check out the product description to make sure that the wireless charging pad is Qi friendly. First, plug the wireless charging pad into an outlet. The pad needs power in order to charge your AirPods. What’s the benefit? Well, for starters, you can charge your AirPods and other devices without using multiple cords. The wireless pad serves as your one-stop-shop to help make sure your new AirPods are juiced up and ready to go. Once you’ve plugged in the wireless charging device, place your AirPods on top of the pad. The ear buds should immediately start charging.

You can check on the status of the charge by opening up the case. If you see a green light, this means that your AirPods are charged. If you see an amber color, this means that your AirPods have less than one full charge left.

If you have issues with the Wireless Charging Case, you may need to reset the connection. Try setting up your AirPods again to troubleshoot the problem. If you don’t have any luck, set up an appointment at the Genius Bar or contact Apple Support directly.

The standalone Wireless Charging Case is currently available for purchase on Apple’s website. You can also buy the new version of AirPods with the Wireless Charging Case online, too. Both options will be available in Apple stores starting next week.

Learn how to charge your iPhone 12 wirelessly with your MagSafe Charger.

How does wireless charging work

Set up your MagSafe Charger

Connect the USB-C connector on your MagSafe Charger to a recommended 20 watt (W) or greater Apple USB-C power adapter or compatible third-party USB-C adapter. You can also connect to a USB-C port on a Mac or PC.

Place your MagSafe Charger face up—as shown—on a flat surface, clear of any metal objects or other foreign material.

Get up to 15W faster wireless charging

The MagSafe Charger is designed to quickly and safely wirelessly charge your iPhone 12. The system intelligently adapts to conditions in order to optimize charging iPhone 12 at up to 15W of peak power delivery for faster wireless charging. The actual power delivered to the iPhone will vary depending on the wattage of the power adapter and system conditions. For iPhone 12 mini, the MagSafe Charger delivers up to 12W of peak power delivery.

It’s important to plug into a power source before placing your iPhone on the MagSafe Charger. This allows MagSafe to verify it’s safe to deliver maximum power. If you happen to place your iPhone on the MagSafe Charger before plugging into a power source, simply remove your iPhone from the MagSafe Charger, wait three seconds, and then put it back on to resume maximum power delivery.

The MagSafe Charger is designed to negotiate the max power up to 9 volt (V) and 3 amp (A) with a USB PD-compatible power adapter. MagSafe will dynamically optimize power delivered to the iPhone. The power delivered to the iPhone 12 at any moment will vary depending on various factors, including temperature and system activity.

All power adapters have different ratings for amount and rate of power delivery. The MagSafe Charger requires the following ratings to deliver faster wireless charging.

Compatible power adapters for up to 15W faster wireless charging

  • USB-C connector. USB-A is not supported
  • 9V/2.22A or 9V/2.56A and higher
  • iPhone 12 mini can get up to 12W for faster wireless charging with at least 9V/2.03A
  • Higher wattage adapters at or above 9V/2.56A will also deliver a maximum of up to 15W peak power to iPhone 12*

When Lightning accessories such as headphones are connected, charging is limited to 7.5W to comply with regulatory standards.

* The MagSafe Charger will also function with power adapters that provide a minimum 12W (5V/2.4A) of power, but this will result in slower charging.

Learn more

  • Your MagSafe Charger is designed for faster and most efficient charging with iPhone 12, iPhone 12 mini, iPhone 12 Pro, iPhone 12 Pro Max, and Apple MagSafe accessories.
  • When charging a non-MagSafe Qi-compatible device with a MagSafe Charger, power is reduced and charge times may be slower than on a typical Qi charger.
  • Don’t place credit cards, security badges, passports, or key fobs between your iPhone and MagSafe Charger, because this might damage magnetic strips or RFID chips in those items.
  • If you have a case that holds any of these sensitive items, remove them before charging or make sure that they aren’t between the back of your device and the charger.
  • If your iPhone is connected to both a MagSafe Charger and power via a Lightning port, your iPhone will charge via the Lightning connector.
  • As with other wireless chargers, your iPhone or MagSafe Charger might get slightly warmer while your iPhone charges. To extend the lifespan of your battery, if the battery gets too warm, software might limit charging above 80 percent.
  • If you keep your iPhone in a leather case while charging with your MagSafe Charger, the case might show circular imprints from compression of the leather. This is normal, but if you’re concerned about this, we suggest using a non-leather case.
  • Learn how to clean your MagSafe Charger.
  • Learn about the magnets in MagSafe products.

Information about products not manufactured by Apple, or independent websites not controlled or tested by Apple, is provided without recommendation or endorsement. Apple assumes no responsibility with regard to the selection, performance, or use of third-party websites or products. Apple makes no representations regarding third-party website accuracy or reliability. Contact the vendor for additional information.

Apple in March launched second-generation AirPods that include several new features over the original models, including the ability to wirelessly charge using third-party charging pads.

How does wireless charging work

How to Charge Your AirPods Wirelessly

New Apple ‌AirPods‌ usually come fully charged out of the box, but at some point during use you’ll hear a tone when your ‌AirPods‌’ batteries are low, and another tone just before they run out.

When that time comes, it’s time to charge your ‌AirPods‌. Simply putting them back in the case usually does the trick – the case holds multiple, full charges for your ‌AirPods‌, allowing you to charge on the go. But at some point the charging case will also become depleted, and then it will need charging too.

How does wireless charging work
Apple’s Wireless Charging Case and second-generation ‌AirPods‌ can be charged with almost any Qi-compatible charging mat or stand (although we’ve heard scattered reports of ‌AirPods‌ incompatibility with some Mophie chargers). If you don’t have a charging accessory and are wondering which one to buy, check out our roundup of the best Qi-compatible charging mats and stands for Apple devices. At any rate, here’s how the charging procedure works.

    Place the case on the charger with the status light on the front of the case facing up (or towards you if you’re using a stand). Note that you can charge your case with or without your ‌AirPods‌ inside.
    How does wireless charging work

  • The status light should turn on for several seconds, then turn off as it continues to charge.
  • If the light doesn’t turn on when you put it on the charging mat, try repositioning the case.
  • If you have trouble getting the case to charge, check that the cable is firmly plugged into the charging mat and that the other end is correctly plugged into a power outlet. If the case still isn’t charging, don’t forget that you can also charge it by plugging the supplied Lightning cable into the Lightning connector on the bottom, and the other end of the cable into a USB charger or port.

    Checking Your AirPods Battery Life

    You can check the battery status of your ‌AirPods‌ by opening the charging case lid with the ‌AirPods‌ inside and holding the case close to your iPhone. The charge status of your ‌AirPods‌ and their case should appear on the device’s screen, and if you take out an AirPod, you’ll see individual percentages for the two earpieces.

    How does wireless charging work
    You can also check the charge status of your ‌AirPods‌ using the Batteries widget in your ‌iPhone‌’s Today View, accessed by swiping right on the Lock screen or on your Home screen’s first screen of apps.

    A fully charged Wireless Charging Case will provide ‌AirPods‌ with more than 24 hours of listening time, or up to 18 hours of talk time. If you charge ‌AirPods‌ for 15 minutes in the case, you get up to 3 hours of listening time or up to two hours of talk time.

    The latest Apple iPhone doesn’t ship with a power adapter, but does support Apple’s new wireless MagSafe charging. Whether you use a cable or not, these are the fastest ways to charge the iPhone 12.

    How does wireless charging work

    With iPhone 12, power adapters will no longer be included in every box, as Apple moves to reduce package waste (and make some cash on accessories). The lineup also includes support for Apple’s new magnetic MagSafe charging. Here’s what you need to know about charging your iPhone 12, and what you might need to purchase.

    What Comes With the iPhone 12?

    Every iPhone 12 comes with a Lightning-to-USB-C cable, and that’s pretty much it. So out of the box, those who don’t currently have any Apple power adapters will need a USB-C power adapter to charge the iPhone 12.

    Plus, this is the first iPhone to ship without EarPods, so you’ll need to supply your own headphones to listen to music and podcasts. Apple sells its own AirPods wireless earbuds, but there are plenty of alternatives that won’t break the bank, not to mention our picks for best wireless headphones and those made with runners in mind.

    As Apple explained during its iPhone 12 event, excluding the power adapter reduces the size of the box. This means 70 percent more devices can fit on a shipping palette, which means more iPhone 12 devices can ship to users. Smaller boxes also allow Apple to reduce yearly carbon emissions by 2 million metric tons, it says.

    How Do I Charge the iPhone 12?

    How does wireless charging work

    Apple has not fully transitioned the iPhone to USB-C—which typically provides faster charging speeds—or removed ports altogether, so the iPhone 12 still includes the typical Lightning charge port. This means you can use an existing Lightning cable and traditional USB-A power adapter to charge your iPhone 12. With the included Lightning-to-USB-C cable, though, you can also plug your iPhone 12 into your Mac laptop.

    Additionally, the iPhone 12 is compatible with current Qi wireless charging pads. However, Apple’s main focus for charging the iPhone 12 (and likely future phones) is the new, built-in, fast charging MagSafe magnetic power connector.

    What Is MagSafe?

    Before Apple transitioned the MacBook lineup to USB-C charging and data transfer, Apple used the term MagSafe to describe its computers’ charging cable connectors. Their magnetized tips “snapped” into the magnetized MacBook charging ports—and snapped out if disturbed so as not to bring a Mac laptop crashing to the floor, for example.

    Apple brings a similar technology to the iPhone 12 lineup in the form of a magnetized “hockey puck” disc that looks like a big Apple Watch charger and snaps to the rear of the phone. This MagSafe connector includes a USB-C cord that plugs into a power source and charges at 15W.

    What’s the Fastest Way to Charge the iPhone 12?

    Since iPhone 5, Apple has shipped its iPhones with a 5W USB power adapter in the box, with the exception of the iPhone 11 Pro and Pro Max, which ship with an 18W USB-C power adapter. (Apple’s iPads also ship with 10W or 12W USB or 18W or 20W USB-C power adapters, depending on the model.) So unless the iPhone 12 is your first Apple device, you probably have one of them lying around.

    Since iPhone 8, meanwhile, Apple’s smartphones have supported fast charging, which allows for a 50 percent charge in 30 minutes. But for fast charging to work, you have to use an Apple USB-C-to-Lightning cable and one of these adapters: Apple 18W, 29W, 30W, 61W, 87W or 96W USB-C Power Adapter; or a third-party USB-C power adapter that supports USB Power Delivery (USB-PD).

    Apple iPhone 8 and above also support Qi wireless charging, which charges those iPhones at 7.5W via a supported wireless charging pad.

    With the MagSafe adapter, your iPhone will charge at 15W.

    So, if you have a 5W charging adapter, a Qi wireless charging pad, and the MagSafe connector, MagSafe will deliver the fastest charging times. The question is whether that’s worth an extra $39 for the MagSafe connector. If you’re always in need of a charge, the answer might be yes. For others, an existing power adapter or charging pad might do the trick, and that $40 is better spent on a rugged case to protect your pricey new smartphone.

    What Do I Need to Buy?

    How does wireless charging work

    If you already have an iPhone or iPad with a Lightning cable, you don’t need to buy anything. Plug the power adapter you own into the wall, plug the Lightning end into your iPhone 12 and you’re ready to go.

    If you want the new MagSafe charger to experience the “snap” effect that secures and charges your phone, it will cost an additional $39 for the charger and 1m USB-C integrated cable.

    For a faster charging experience than Apple’s 5W power adapter, a separate 20-watt USB-C power adapter can be used for both the supplied Lightning-to-USB-C cable and the MagSafe charger. Previously $29, you can now get it for $19.

    Though you will be getting a Lightning-to-USB-C cable with the iPhone 12, Apple also sells longer Lightning-to-USB-C cables; grab them in 1m or 2m lengths for $19 and $33, respectively. You can find cheaper ones on Amazon, too.

    Apple is also touting a foldable MagSafe Duo Charger that includes a dock for your Apple Watch, but no release date or pricing information is available yet.

    Does MagSafe Work With a Case?

    Short answer: Yes. But there are caveats.

    Those who want to protect their iPhone 12 with a case and make use of MagSafe magnetic charging will need a MagSafe-compatible accessory. Naturally, Apple is selling several MagSafe chargers and a magnetic wallet on Third parties, like Belkin and Otterbox, have their own MagSafe products, too.

    MagSafe leather wallet (Image: Apple)

    If you have a non-MagSafe case without the magnet, you should be able to charge it with the MagSafe charger as it’s Qi wireless compatible, but it won’t snap on to the case.

    Does MagSafe Work With Older iPhone Models?

    While the MagSafe charger was designed for the new iPhone 12 models, it’s technically compatible with older phones that support wireless charging, as well as AirPods models with a wireless charging case (see officially compatible models below).

    However, since these older phone models do not have the magnetic feature on the back of the device, you won’t be able to “snap” your iPhone into its ideal charging position. Only the iPhone 12, iPhone 12 mini, iPhone 12 Pro, and iPhone 12 Pro Max support that. Any other phone (even some Android phones) can simply be placed on the MagSafe connector, but it will not lock into place.

    Plus, how one Seoul-based design studio is adding their minimalist style to the mix.

    Published on January 13, 2018

    Wireless charging has been around for years, but do you actually know how it works? Brands are only just beginning to reimagine how we can seamlessly integrate our smartphones with our smart homes, as well as charge our beloved devices with total ease. Among those pioneering tech-friendly side tables and chic charging office accessories is designstudio PESI, a Seoul-based studio that’s focused on reinterpreting everyday objects through a material-focused, minimalist lens.

    “We wanted to design charging devices that provide a charging environment that can be naturally mixed with the living space,” Byounghwi Jeon, designstudio PESI co-founder and designer, tells Domino.

    In collaboration with Samsung Creative Square, the studio recently debuted a collection of wireless-charging products (dubbed “Blend Into Space”) that give regular household objects—from a streamlined speaker to a table mirror—new purpose. While currently not for sale, their products offer a sneak peek into the future of wireless-charging furniture and its stylish potential (however, if you’re looking to buy right now, there are a few brands to choose from; see below).

    Ahead, we run through the basics of wireless charging technology and offer a glimpse of the decor brands and designers who are doing it best.

    How Wireless Charging (Essentially) Works

    Assuming you’ve popped into a Starbucks sometime in the past four years, then you’ve probably noticed that a number of their stores have installed charging pads on the tables and countertops. If you’ve ever sat your phone down and wondered why your iPhone isn’t charging (or just straight up how the power mats work), you’re not alone.

    In simple terms, wireless charging is based on the principle of magnetic resonance. An electrical current is created between two objects—one with a transmitting coil (the charging pad) and one with a receiving coil (your wireless-enabled phone)—that together create an electromagnetic field that enables a power transfer.

    Wireless Charging Is…Chic

    Can you envision the day when every surface in your home will double as a charger for your phone? Designstudio PESI can—and they’re not willing to skimp on style to get there, either. Their “Blend Into Space” collection encompasses two individual lines that both reinterpret the experience of using and charging mobile products through the spaces and objects we encounter each day in our homes.

    “Wireless charging is a calm technology, because it doesn’t need any other interaction except putting the device on the charger” says Jeon. “We wanted to offer an environment in one perfect form of furniture to match the nature of ‘natural’ technology.”

    Focused on the everyday items that often grace our tables, “On the Surface” fuses bedside accessories and catch-all containers with a flat charging landing pad. The exclusively white collection even features a flower vase-turned-charging station; a seemingly poetic ode to nature and machine’s promising future. “Composition,” on the other hand, dares to play with color—but strictly in tray form. Fit for dining, working, or displaying treasured objects, these tech-approved surfaces also double as a worthy home for your phone.

    How Do I Know If My Device Is Compatible?

    “Wireless charging products are compatible with any products that have a coil-type battery (mobile-phone, smart watch, speaker, etc.),” explains Jeon. When it comes to wireless charging standards, tech companies rely on two major charging brands: Qi and AirFuel. According to Field Guide, Qi has become the dominant wireless charging standard and is supported by most phones, including the latest phones from Apple, Samsung, and LG.

    However, some phones like the Galaxy S8 can work with both Qi and its contender, AirFuel (formerly known as Powermat). While a number of devices are supported by AirFuel, the iPhone 8, iPhone 8 Plus, and X, for example, are only compatible with Qi-enabled wireless charging stations.

    Unsure about whether your device can charge wirelessly? You can see a full list of Qi-certified devices here and AirFuel-enabled products here. In the case of Starbucks, their charging stations are currently only compatible with AirFuel-supported phones. So, at least for now, you can’t sip on your macchiato while charging up your iPhone.

    If you’re holding onto an older iPhone or any other device that doesn’t have a coil built in, you can still get in on the wireless action, too. Plenty of brands (including Ikea) make adapters, covers, and charging stations that will enable your phone to charge wirelessly.

    Where to Buy Wireless-Charging Furniture Now

    Feeling inspired to savvy-up your space? While designstudio PESI’s streamlined solutions have yet to hit production, there are a number of companies that are currently selling built-in wireless charging home goods and furniture. For starters, Ikea has been offering Qi-enabled wireless charging products for a number of years now, namely in the form of desk lamps and night stands. In addition to furniture, the Swedish retailer also sells charging pads that can be tucked away or displayed just about anywhere in the home.

    Curvilux has created a smart side table that totally goes above and beyond. The bedside essential will not only charge up to three devices at one time, but it also features a motion-activated night light and a password-safe drawer that can be controlled from your phone. FoneSalesman also sells a simply-designed wireless charging side table made by FurniQi that only takes minutes to assemble.

    With fresh, tech-savvy designs on the horizon, the future of interiors is shaping out to be as polished as it is practical.

    See more design trends we’re excited about:

    Get all the news you never knew you needed when you sign up here.

    Say Goodbye to Wires

    How does wireless charging work

    Can you imagine that you are taking a self-driving travelling with good mood and suddenly realized that you forgot to bring the charging line and the power bank? It’s absolutely a tragedy.

    Some people would not worry about that because their cars are equipped with wireless charging pads. These wireless charging pads may located in hidden storage bin behind the infotainment screen, near the gear shifter, in the back seat, on the top of or inside the armrest. It’s so convenient that people have no need to keep so much things such as power bank, data lines, chargers in the car. But these cars are obviously more expensive than ordinary cars.

    How does wireless charging work

    What if I told you that you can equip your car with wireless charger with no more than 20$.

    How does wireless charging work

    The Physics of Wireless Charging

    Let’s talk about wireless charging and how it works first.

    How does wireless charging work

    Actually, the physics of wireless charging is not difficult. Wireless chargers use magnetic induction to transmit energy. As the picture shows, wireless charging uses the two electromagnetic coils to create a magnetic field between two devices. The wireless charger has a transmitter coil, and your phone has a receiver coil. When you put your phone on the charger, the current moves through the wire in the wireless charger, creating a magnetic field. Then, the magnetic field creates a current in the coil inside the phone which is used to charge the battery.

    And now, think about put the wireless charger together with a car phone mount, and that’s Lamicall wireless charging air car phone holder – Collapsar.

    Welcome to our Wireless Charging Guide. Below you will discover the wonders of wireless charging; let’s get started!

    Page last updated: May 20th, 2020

    What is Qi?

    How does wireless charging workWireless charging is a technology that allows charging over (very) short distances without cables.

    The advantage of wireless charging is that it’s quicker and easier, as you don’t have to plug and unplug each time – you just place your device on top of your wireless charging pad . It also looks neater.

    There are various competing standards for wireless charging. The most popular is Qi (pronounced ‘chee’), which has been supported by all of the major companies. Apple have included wireless charging on their latest iPhone models, and Samsung have done that for years; they’ve also made a wide range of Samsung wireless chargers that work with all phones with Qi wireless charging built in. More recently, OnePlus, Motorola and Huawei have all included wireless charging in their handsets.

    Compatible devices?

    A few phones have wireless charging built right in. See them here.

    Other phones need a replacement rear cover or case. These are built to fit specific phones, so make sure you choose the right one. To make it easier, we’ve linked to appropriate cases and rear covers.

    If a wireless charging cover isn’t available for your phone, you can use a universal adapter instead, allowing even much older devices to support wireless charging.

    Phones and tablets with built-in Qi wireless charging

    If your phone is among one of the devices that appear here, you just need to buy a wireless charger . Note that you don’t need to get a wireless charger made by the same company as your phone, e.g. Samsung wireless chargers work just fine with the iPhone X.

    • Apple iPhone: 12 Pro Max, 12 Pro, 12, 12 mini, SE 2020, 11 Pro Max, 11 Pro, 11, XS Max XS, XR, 8, 8 Plus,
    • Samsung Galaxy: Z Fold 2 5G, Z Flip 5G, Note 20 Ultra, Note 20, S20 FE, S20 Ultra, S20 Plus, S20, Z Flip, Note 10 Plus 5G, Note 10 Plus, Note 10, S10 5G, S10 Plus, S10, S10e, Note 9, S9, S9+, Note 8, S8, S8+, S7, S7 Edge (Plus more devices)
    • Sony: Xperia 1 II, Xperia 10 II, Xperia XZ3, Xperia XZ2 Premium, Xperia XZ2 (Plus more devices)
    • LG: Velvet, G8 ThinQ, G7 ThinQ, V30, G6 (US version only), G4 (optional), G3 (optional) (Plus more devices)
    • OnePlus: 8 Pro
    • Nokia: 9.3 PureView, 9 PureView, 8 Sirocco
    • Huawei: P40 Pro+, P40 Pro, Mate 30 Pro, P30 Pro, Mate 20 Pro
    • Motorola: Edge+, X Force, Droid Turbo 2, Moto Maxx
    • Microsoft Lumia: 1520, 1020, 930, 929, 928, 920
    • Google: Pixel 4 XL, Pixel 4, Pixel 3 XL, Pixel 3
    • Nexus: Nexus 6, Nexus 5
    • BlackBerry: Priv (Plus more devices)

    How does wireless charging work

    Do I need an adapter?

    If your phone appears here, you need the accessory linked and a wireless charging pad.

    • Apple: iPhone 7, iPhone 7 Plus, iPhone SE, iPhone 6S, iPhone 6S Plus, iPhone 5S
    • Samsung: Galaxy A71, Galaxy A51, Galaxy A41, Galaxy A31, Galaxy A21, Galaxy A01, Galaxy A90 5G, Galaxy A80, Galaxy A70s, Galaxy A70, Galaxy A60, Galaxy A50s, Galaxy A50, Galaxy A40, Galaxy A30s, Galaxy A30, Galaxy A20s, Galaxy A20e, Galaxy A20, Galaxy A10e, Galaxy A10, Galaxy A8 2018, Galaxy M40 Galaxy M30s, Galaxy M30, Galaxy M20, Galaxy M10, Galaxy S5, Galaxy S4, Galaxy S3, Galaxy Note 3, Galaxy Note 2
    • Huawei: P40, P40 Lite, P30 Lite, P30,P20 Pro,P20,P20 Lite
    • Nokia: 7.2, 7 Plus, 6.2, 6.1 Plus, 8.1, 7.1, 6, 2.2
    • LG: Stylo 5
    • OnePlus: 8, 7T Pro, 7T, 7, 6T, 6, 5, 3T, 3, 2, 1
    • Sony: Xperia 5 II, Xperia 5, Xperia 1, Xperia Z5, Xperia 10 Plus, Xperia XZ3, Xperia 10, Xperia X Performance, Xperia X Compact, Xperia XZ Premium, Xperia Z3, Xperia Z2, Xperia Z
    • Google: Pixel 2 XL, Pixel 2, Pixel XL, Pixel
    • Microsoft: Lumia 930, Lumia 925, Lumia 830

    How does wireless charging work

    Universal wireless charging adapters

    If your phone isn’t listed above, then you’ll need a universal adapter and a wireless charger. You can get these for phones with Micro USB ports (e.g. Android) and Lightning ports (e.g. iPhone).

    You have a choice of an internal adapter, which slides into the back of a case, and an external adapter, which hangs outside. In most cases, we recommend internal adapters.

    Internal adapter External adapter
    Micro USB (Android) Ultra-Thin aircharge
    Lightning (iPhone) Lightning Adapter aircharge
    USB C (Android) Ultra-Thin N/A

    How does wireless charging work

    Wireless chargers

    Once you’ve determined your phone has wireless charging built in or you’ve added it with an accessory, you just need a wireless charger.

    There are plenty of Qi wireless chargers available, in different sizes, shapes and colours. You can get Qi chargers for your desk, for your car, or even portable Qi battery packs. One of our favourites is the Slim 10W Fast Wireless Charging Pad from Olixar, thanks to it’s sleek modern styling and super fast charging speeds, or see all of our Qi wireless chargers here .

    How does wireless charging work


    Our video team has made some excellent videos explaining wireless charging. Take a look at one of the videos linked below!

    How does wireless charging work


    Have any questions about wireless charging? Leave them in the comments below, and we’ll get back to you with the answers you seek.

    Qi-certified wireless charging devices are now commonplace in the consumer market. But how exactly does Qi achieve wireless power transfer at the circuit level?

    Qi is a wireless power transfer standard developed by the Wireless Power Consortium that specifies an interoperable solution for inductive charging over distances of up to 4 cm. The Qi standard specifies several key features such as operating frequency, coil configuration, minimum system efficiency, power control methods, and communications protocols.

    Recently, STMicroelectronics announced a Qi-compliant 50 W wireless charging IC, the STWLC88, that targets applications such as smartphones, tablets, and laptops. The company claims the new device enables safe wireless power delivery nearly as quickly and efficiently as a wired charging solution.

    How does wireless charging work

    ST says the STWLC88 is the “world’s fastest Qi wireless charging IC.” Image used courtesy of STMicroelectronics

    For safe wireless power delivery, careful attention should be paid to several design challenges such as efficiency, reliable communication, foreign object detection (FOD), thermal considerations, and over-voltage/over-current protection. In this article, we’ll take a look at a few basic concepts of the Qi standard.

    Block Diagram of a Qi-Compliant Charger

    The block diagram of an inductively-coupled wireless power delivery system is shown below:

    Functional diagram of a typical wireless power transfer. Image used courtesy of Texas Instruments

    The AC voltage applied to the primary coil is transferred to the secondary through magnetic coupling. With the Qi standard, the transmitter and receiver coils should be relatively well-aligned to have efficient power delivery. The magnetic coupling between the coils is also used to send the communication packets from the receiver to the transmitter.

    Before power delivery can be performed, several different phases should be completed. Below, we’ll briefly review different steps of the Qi-compliant charging algorithm.

    Analog Ping

    During standby mode, the transmitter is in the idle state and no appreciable power is output. The transmitter uses “analog pings” to detect the presence of any potential power receiver. Analog pinging is achieved by applying periodic test pulses to the primary coil.

    Without a power receiver (and passive metal objects such as coins, keys, etc.), the voltage across the primary coil will be much larger. For example, bringing a power receiver close to the transmitter might reduce the voltage across the primary from 60 Vp-p to 30 Vp-p. This is due to the loading effect that a metal object can have on the primary coil.

    Hence, the voltage that appears across the primary during analog pinging can be used to detect the presence of a potential power receiver. Note that some Qi-compliant power transmitters do not use analog pings and rely only on digital pings to detect a power receiver.

    Digital Ping

    After the transmitter detects a potential power receiver in proximity, it uses “digital pings” to communicate with the receiver. Digital pings are longer pulses compared to analog pings and have sufficient energy to activate the power receiver (if one is present).

    Upon being powered by the digital ping signal, the receiver should send signal strength packets back to the transmitter. A valid signal strength packet lets the transmitter distinguish a valid power receiver from a passive metal object or a non-compliant receiver.

    How does wireless charging work

    Analog and digital pings at startup. Image used courtesy of Texas Instruments

    With a valid signal strength packet, the transmitter will maintain power to the coil and proceed to the next phase: the identification and configuration phase.

    Identification and Power Transfer Phases

    In the identification and configuration phase, the power receiver sends the transmitter data packets that contain information about the Qi version of the receiver, the maximum required output power, and other configuration information.

    After the identification phase, the power transfer phase begins. In this phase, the receiver measures the power it receives and sends this information back to the transmitter so that the transmitted power level can be adjusted depending on the receiver requirements. This information also helps the transmitter detect any foreign metal object that steals the power.

    Foreign (metal) object detection (FOD) is achieved by comparing the transmitted power with the received power reported by the power receiver. A large difference between the transmitted and received power levels can be an indication of a metal object in close proximity to the transmitter.

    Transmitting a large amount of power to a metal object can increase its temperature and cause hazardous situations. That’s why the transmitter will stop supplying power if a foreign metal object is present.

    How Does the Transmitter Adjust the Power level?

    A typical power transfer function from the LC circuit of the transmitter to the rectifier output of the receiver is shown below.

    How does wireless charging work

    Graph of a Tx-Rx transfer curve. Image used courtesy of Richtek

    In this example, the operating frequency of the transmitter is on the right side of the resonance frequency of the LC circuit. As such, we can reduce the transmitted power level by increasing the frequency of the power signal that is applied to the transmitter coil. The amplitude of the AC signal is another parameter that the system can tweak to adjust the transmitted power.

    How Does the Receiver Communicate With the Transmitter?

    The magnetic coupling is used for both power delivery and communication purposes. Interestingly, this can be achieved by changing the receiver side load. This RX coil modulation will reflect back to the TX side and allow us to send data packets from the receiver to the transmitter. Capacitive modulation of the RX coil is illustrated below.

    The architecture of a 5 W wireless power transfer. Image used courtesy of Texas Instruments

    With the Qi standard, both capacitive and resistive modulations of the RX coil are supported.

    Do you have hands-on design experience with Qi wireless charging technology? What benefits and challenges have you faced with it? Share your thoughts in the comments below.

    How does wireless charging work



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