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

An iPhone 8 with a wireless charger, as shown during Apple’s announcement.

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

The Galaxy Note 8 and Samsung’s wireless charger.

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 Amazon.com 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.

Chris Hoffman is a technology writer and all-around computer geek. He's as at home using the Linux terminal as he is digging into the Windows registry. Connect with him on Google+.