Why Are Wireless Chargers So Slow? – Review Geek


A woman placing her phone on a wireless charger.
Vera Petrunina/Shutterstock

Over the last 5 years, wireless charging speeds have leaped from around 5 watts to 10 or 15 watts in a handful of phones. That ain’t too shabby, but with new flagships like the Galaxy S20 and the Huawei Mate X sporting 45- and 55-watt wired charging speeds, wireless charging still feels slow.

Why are wireless chargers still so far behind the curve? Well, as it turns out, it’s difficult to make wireless chargers powerful without making them unsafe.

First, Let’s Review How Wireless Charging Works

Wireless chargers send power to your phone through magnetic induction and magnetic resonance. Or, in layman’s terms, wireless chargers pull electricity from your outlet, run it around a coil, and generate a magnetic field. This magnetic field interacts with a coil in your phone to generate an electrical current, which your phone uses to charge its battery.

Simple, right? Let’s go a little deeper. Faraday’s Law of Induction states that an electric field will always generate a magnetic field and vice-versa. This means that all electronics, including lightbulbs, emit a magnetic field. Sadly, a lightbulb can’t charge your phone, as your phone is built to only work with magnetic fields of a specified rate and intensity.

This specified rate and intensity are usually described as a “standard.” Modern phones are made to support a variety of different standards, like the Qi wireless charging standard. Each wireless charging standard supports different charging speeds, which is why Samsung phones with specialized coils can take advantage of 15-watt wireless charging, while other devices are capped at lower speeds.

Alright, now that we know way too much about wireless charging and magnetic fields, we can finally approach the big question: why are wireless chargers still so slow?

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Wireless Chargers Could Be Faster, But They’d Fry Your Phone

A man pressing two steaming hot phones against his face.
lassedesignen/Shutterstock

Let’s get right to the heart of things. Wireless chargers could charge your phone a lot faster than they do right now. But today’s wireless charging hardware isn’t efficient enough to safely charge your phone at high speeds. Like the wasteful filament lightbulbs of yesteryear, wireless chargers produce too much heat.

You’ve probably experienced this in person. Even with the refined low-wattage Qi standard, phones heat up while charging wirelessly. And,as we all know, excess heat can damage hardware and lead to dead, swollen, or exploding batteries. Amping up the power of our inefficient wireless chargers just wouldn’t be safe.

Okay, but how far are we from a safe powerful wireless charger? If Samsung’s new 15-watt wireless technology is any indication, we’re crawling in that direction right now. Still, according to a paper published by Digi-Key, wireless chargers waste between 20% to 70% of the power that they use. Maybe Samsung found a way to make its tech more efficient than the competition, but they’re gonna have to push even further if they want to reach half the wired charging speeds of their newest devices.

Even with more efficient wireless chargers, manufacturers still face a few limitations. One immediate example is precision. You may have noticed that some wireless chargers will refuse to work when pieces of metal, such as keys or pocket change, are too close to the charging surface. This is actually a safety measure, as intense magnetic fields can heat up metal objects. As wireless chargers get more powerful, manufacturers will need to develop better foreign object detection algorithms or limit the operating distance of their fast-charging mats.

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In short, wireless chargers won’t get faster until engineers and manufacturers find a way to make them energy efficient and precise. This may mean abandoning the Qi standard, or adopting new hardware that makes better use of what we have now.

We should also acknowledge that charging distance may be a more immediate concern than charging speed. If a phone could charge within 10 feet of a wireless charger, for example, then it wouldn’t really matter how fast it gets to 100%. Hopefully, manufacturers find a way to increase the speed and range of wireless chargers. But in the meantime, we suggest keeping an actual cable around the house.





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