Reverse wireless charging
How your iPhone could one day charge your AirPods without wires
YOU WILL LEARN
How wireless charging can be reversed to top up the charge in accessories such as Apple’s MagSafe Battery Pack
Key fact
The speed of wireless charging will depend on the power that your charging pad delivers and the receiver in your phone can handle. For example, the iPhone 11 charges at 7.5W on Apple-approved Qi charging pads and 5W on others; the iPhone 12 charges at 15W on MagSafe (12W for the iPhone 12 mini) and 7.5W on standard Qi pads.
With the launch of the new iPhone 13 at Apple’s September event, we were hoping to see one much-wanted feature: reverse wireless charging. Unfortunately, while the technology has apparently been found in the iPhone 12 (according to the US Federal Communications Commission) and can be used to reverse charge Apple’s MagSafe Battery Pack, it hasn’t been made more widely available. So what is it and how does it work?
How wireless charging works
Wireless charging isn’t exactly new: it was first demonstrated over 100 years ago by Nikola Tesla, and if you have an electric toothbrush you’ve probably got a wireless charger in the bathroom. The technology hasn’t really changed much over the decades. It’s just got more efficient. When we talk about wireless charging in a phone or tablet context, we’re talking about using electromagnetism: it’s possible to transmit electricity via radio frequencies, but it isn’t powerful or practical enough for everyday use.
Electromagnetic charging consists of a transmitter and one or more receivers. The transmitter, which is your wireless charging pad or puck, creates an oscillating magnetic field. When they’re close enough, that magnetic field induces a current in the coiled wire loops inside the receivers. That current can then be used to recharge the battery or even power small electronic devices.
The amount of power you can transmit is largely based on the size of your coils and the strength of the magnetic field. Because there isn’t a great deal of room inside your iPhone or Apple Watch, which also charges wirelessly, the copper coil needs to be very small. That’s why you have to sit your iPhone on top of your wireless charger instead of near it, and it’s why
What you lose in charging speed you gain in convenience and reduced cable clutter
Apple uses magnets to clamp your wireless charger to the sweet spot on your iPhone 12, 13 or Apple Watch. But if you increase the size of everything, you can increase the charging distance, so for example you can create a charging pad for electric cars that sits underneath the car and recharges the battery without having to be clamped to it.
The big downside to wireless charging is that it’s slower than wired: Apple’s MagSafe charges at roughly half the speed of a wired 20W charger, and earlier wireless charging options are slower still. The iPhone 11 can’t charge wirelessly at more than 7.5W. But what you lose in charging speed you gain in convenience and reduced cable clutter.
Reverse wireless charging, as the name suggests, transmits power in the opposite direction – so you might use your iPhone to charge your AirPods or Apple Watch. And to do that, you need to take standard wireless charging and do a Missy Elliott on it: put your thang down, flip it and reverse it.
Works both ways
Reverse wireless charging has been popping up in a lot of Android phones. Huawei was one of the first firms to offer the technology in its Mate 20 Pro, and Samsung calls it PowerShare in its Galaxy S20 series phones.
With reverse wireless charging, the induction coil in the phone or tablet is reversible – so in addition to receiving a current from a magnetic field, it can also generate a magnetic field for another device to receive. It’s much lower power than the normal wireless charging – most of the current phones with reverse wireless charging max out at 4.5W – but that’s still enough to quickly top up the charge in your earbuds or smartwatch.
Multiple choice
Because this is a technology, there are of course multiple competing standards. The most commonly supported wireless charging standard is Qi (pronounced ‘chee’), which Apple has supported since the iPhone 8.
Qi is also the standard used by many public wireless chargers, such as the chargers you’ll find in fast food restaurants.
The Qi standard is created, controlled and certified by the Wireless Power Consortium, WPC for short, which has more than 600 tech firms as members. In addition to Apple, Qi is the preferred tech of third-party accessory firms such as Belkin and Mophie.
The key benefit of Qi is its widespread compatibility: if a charger is Qi-compatible it doesn’t matter who made the device you’re charging, so you can charge your iPhone on the same pad as an Android phone and vice-versa. There’s also a huge choice, so if you don’t fancy Apple’s MagSafe (or you have a pre-iPhone 12 iPhone, which doesn’t have MagSafe) there’s a ton of alternatives, often at much lower prices too.
Carrie Marshall