Guilherme's Blog

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Anker Wireless Charger

Wireless Chargers

Rarely, if ever, I proclaim an invention completely useless. Even unitaskers such as banana slicers serve a purpose and excel at what they’re made to do, so every invention has it’s place. However, one concept escapes that rule: wireless phone chargers.

“But don’t they charge phones?”, you might ask. Well, of course they do, just the same way swapping your car wheels for square ones would get you to work too, but with a lot more rumbling and road surface damage. There is already a widespread, cheaper, more efficient alternative to this kind of charger, so why are they used at all? Is it just a gimmick, or is there really a positive side to them? Short answer: there isn’t. But hey, humans are curious creatures, we need to know the “why”s and “how”s of things, and that’s what I’m going to explore today.

“They can’t be that inefficient”

Of course, at scale a 47% increase in power usage seems irrelevant. One person using a wireless charger would have about as much impact as a grasshopper has on a aircraft carrier. But let’s go for some basic math, shall we? A regular wired phone charger has an efficiency of 63-80%, so we’ll go with 75% efficiency for this calculation.

At a DC power output of 5 W, that would give us about 6.7 W of power draw at the wall. Now, that means that the average wireless charger draws 9.8 W. Not that much more, right? You wouldn’t even notice a 3 Wh increase in your power bill. Unfortunately, we aren’t alone in this world, so we’ll have to take into account the general population. For this experiment, let’s imagine that the average person charges their phone for 2 hours a day, and that 1/4 of all Brazilians decided to switch to wireless charging overnight because “it looked cool”.

That’s an increase of 6.2 Wh in energy consumption per day, per person. This pans out to 328600 kWh, every single day, or 119939 MWh per year. That’s enough to provide for more than 48000 citizens for a year, according to the Brazilian energy research office. Whew, imagine wasting enough energy to provide for a small town because something looks fancy. Worse yet; the efficiency is known to drop heavily when the coils aren’t properly aligned, so I’m being rather generous in these calculations.

Oh, and I forgot to mention: it uses a “bit” of power to poll for devices to charge. That power usage could match the power used to charge a phone, with no work being done at all! However, the Wireless Power Consortium is working on reducing that to a negligible amount, so I’ll stop for now.

“It saves me time”

It may save you the 300 milliseconds it takes to plug in the phone, which is an astounding improvement… if you’re a Formula 1 team and George Russell needs to charge his phone during a pit stop. However, it takes 50 minutes more to charge a phone wirelessly.

Image by Andrew Martonik from AndroidCentral

Plus, you can’t handle the phone with ease while charging. So no, it doesn’t.

“There’s less wear and tear on the charging port”

That is true! There is indeed a reduction in the amount of cycles necessary. Nevertheless, the average lifespan for a modern Micro-USB port is more than 10000 cycles. If you were to plug in your phone 5 times a day, it would take you at minimum 2000 days to “break” it. For convenience, that’s 5 and a half years, way past the average phone replacement cycle in the US: 3.17 years. Just because a statement is true, it doesn’t mean it’s meaningful.

Furthermore, the increase in heat generated by the sheer inefficiency of the system could reach up to 32 degrees Celsius (about 12 degrees warmer than room temp in this test). Of course, this is still within safety margins, but in a tropical country, allied with other circumstances, it could reduce your battery’s lifespan. Not a fair trade, is it?

“It looks cool!”

Belkin iPhone Charging Dock
Belkin iPhone Charging Dock

Fret not, we also got wired charging pods.

“With advancements in technology, they might be able to match wired chargers”

Wireless chargers are near-field devices, which means the fields reduce in size proportionally to the cube of the distances, while power itself is proportional to the square of the field strength. If you were to double the coil distance, power would drop by a factor of 64.

Progress is being made, slowly but surely. However, it’s hard to beat wires in efficiency terms, as they offer very little resistance. Even if we were instantaneously able to use basic field electromagnetics, employing a concept similar to the one used in transformers where cores aid in providing near 99% efficiency, you would still face rectification and power control circuitry. That means you’d be stuck with all the other problems, minus efficiency.

“So you’re saying we should never use wireless power transfer, ever?”

Absolutely not! There are many applications for it that could genuinely improve people’s lives. You could, for example, power a low-power sensor in a sealed environment or utilize it in medical equipment, such as pacemakers. Scientists and engineers are making great strides in wireless power transfer, in order to solve real world problems. However, phone charging is not a life-threatening or limited situation that excuses an immense loss of efficiency.

If you can, avoid using wireless power. Like everything in life, electrical systems have tools that are better suited for a specific situation, and we should be careful not to adhere to the “when you have a hammer, everything looks like a nail” school of thought.


I’m not trying to be a killjoy here. We can all excuse ourselves every once in a while from doing the “most logical thing”, we’re human after all. All I’m asking is that, if you can, please reconsider wireless charging. If you’re willing to indulge in guilty pleasures, go for some cake or go rallying in a beater car, at least those have some purpose.

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