The Qi charging standard has come a long way since it was first specified. What started as a very slow and very wasteful technology to recharge low-power devices (like the battery in your phone) has expanded to include things that need more power like a laptop and the Wireless Power Consortium has even demonstrated the tech powering kitchen appliances at 1kW. But for most of us, the biggest advance has been the introduction of wireless fast charging.
Any Qi-enabled phone will charge on any Qi pad, even if Fast Charge isn't available.
Qi (pronounced Chee and roughly translated to "spiritual energy") is a charging standard. The Wireless Power Consortium — imagine a group of electrical engineers that really love chargers working with the smart people who make things that need to be charged — developed the specification in 2009. The first version supported wireless power transfer up to 4.999 watts, and it works by using two coils that send a signal across the gap when they get close to each other, then magnetic induction produces electricity on the receiver side. As long as your phone and the coil have the necessary computer logic it works using very basic principles of electricity. In the early days, you had to waste a lot of power creating an oscillating magnetic field in the base (transmitter) that was strong enough to induce the same oscillation and field in the receiver in order to charge your phone. And even then it charged very slowly. It was more of a convenience thing than an efficiency thing.
The folks at the WPC have kept expanding and developing the standard and besides additions like a medium-power mode that can provide up to 120 watts, they have been working on three specific ways to make it better: a longer range (it's up to 40mm now), higher output done safely, and less wasted power in the form of heat.
In June 2015, the WPC released the current public version of the standard that increased the power transfer to 15 watts without any increase in the amount of wasted electricity as heat. That means the power created by the receiver coil (the one inside your phone) has increased by 300% and charging is faster, without either coil getting any hotter. There is a newer standard published as of March 2018 but so far it's only available to members of the WPC. It's expected to have increased the range (which translates into charging more easily through a case), the power and the efficiency. We'll know once WPC members are finished with it and it becomes available to the public.
Using a charger and a phone with the "Fast Charge" label you can charge a typical phone to about 50% in 30 minutes, or charge fully in 90 minutes. While not as fast as a wired quick charge solution, this is a lot faster than it used to be. But not all phones are typical. Vendors are allowed to maned the Qi standard with their own technology as long as they still follow the original and any Qi-compatible device will charge with any Qi-enabled transmitter. Samsung adds some of their own tech to phones like the Galaxy S9 and bases like Samsung's Wireless Fast Charger to charge wirelessly even faster. While the small amount of extra charge you can get in the same time period may not seem like much, every minute counts when you're waiting for your phone to charge.
The smart parts
Whether you're wirelessly charging fast or slow, the tech inside has to monitor the transfer rate, the temperature, and the amount of charge the battery has. From a "cold" state, it takes about a fair amount of time for things to reach a temperature or charge state where they need to be scaled back but it will make it there eventually. Reducing the amount of electricity provided (the base modifies the frequency and wavelength of the magnetic field created by its coil) is done to protect the battery and electronics inside your phone from getting too hot. At this point, the power generated is dropped until the battery is full, then it shuts down. Your phone monitors itself and sends the signals to the base that indicate when things need to change.
A lot of engineer speech is involved here, because of the subject matter. Essentially, your phone and your charger carry on a little electronic conversation.
- Phone: I need some power!
- Base: OK, I'll start my end. Make sure you stay close enough so the way my coil hums makes your coil hum, too. If I see your coil stop humming I'll turn everything off.
- Phone: Gotcha. Staying close.
- Base: I see that you are using the latest Qi standard, so I'll go full speed ahead until you give the word.
- Phone: OK, I'm getting warm, so scale things back a little.
- Base: OK. Lowering the frequency and pitch of my coil's hum so things don't get any hotter. Let me know when we're done.
- Phone: My battery is full. You can stop now.
This is how Qi charging has always worked, even though now things are faster. The only differences are changes to the resonant circuits in both the phone and the base that allow the coils to oscillate at a higher frequency with less damping (resistance) and less radiated energy (wasted energy in the form of heat) production. The current generated is higher while the resistance and heat produced are lower than previous versions, so more juice can flow from the coil in your phone to the battery without things getting too hot too fast. These changes were part of an update to the Qi standard, and everyone who is part of the WPC — Belkin, HTC, Lexus, Motorola, Samsung, Verizon and the rest of the 230+ members — can use the design to build chargers and devices that need charged and be sure everything is compatible.
Qi Fast Charge can generate up to 300% more current than the original specification.
The Qi specification is generally followed to the letter by everyone involved. It's also freely available to anyone after a short term of WPC members-only access so everyone can use it — even a startup who might not have an extra $20,000 for the annual fee. Thankfully, you don't have to worry about the things you buy not meeting the full specifications. It just works. And now it works even faster as long as both parts (your phone and your charging base) follow the standards for fast -charging.
For us as consumers, there isn't a lot to think about. If our phone is Qi Fast Charge compatible and we use a charging base that's also Qi Fast Charge ready, our phone will charge faster. The system is designed to slow down before things get too hot and shut itself off completely once the battery is full — we don't need to intervene at any level. Qi is also backwards compatible so all your devices that use it will charge with any charging base, even if Fast Charge isn't available. The one thing we should do is to use the proper wall plug to make sure the right amount of current is available to the charging base and it doesn't overheat or charge too slowly.
If you like the convenience of wireless charging, make sure the next charging base you buy is Fast Charge ready!
Updated March 2018: Added information about the latest Qi standard and the Galaxy S9.
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