How Wireless Charging Works and Why It’s Terrible

Wireless charging is pretty convenient, as long as the transmitter and receiver speak the same protocol. Just put the device you want to charge on the wireless charger without worrying about plugging in a cable. Yet as it turns out, the disadvantages of wireless charging may be more severe than you think, at least according to tests by iFixIt’s [Shahram Mokhtari] and colleagues. In the article the basics of wireless charging are covered, as well as why wireless charging wastes a lot more power even when not charging, and why it may damage your device’s battery faster than wired charging.

The inefficiency comes mostly from the extra steps needed to create the alternating current (AC) with wireless coupling between the coils, and the conversion back to DC. Yet it is compounded by the issue of misaligned coils, which further introduce inefficiencies. Though various protocols seek to fix this (Qi2 and Apple’s MagSafe) using alignment magnets, these manage to lose 59% of the power drawn from the mains due to these inefficiencies. Wireless chargers also are forced to stay active, polling for a new device to charge, which keeps a MagSafe charger sucking up 0.2 W in standby.

If the losses from wired charging for a year come down to leaving a 10 W LED lamp on for eight hours total, wireless charging with MagSafe or Qi2 has you leaving that lamp on for 24 days straight. Since your phone is not a lamp, this means that much of this wasted power is dissipated as heat, both on the transmitting and receiving end. With the wireless receiving coil being placed practically on top of the battery in smartphones, this means that you are bumping the battery temperature up by about 8°C in the best scenario (fully aligned MagSafe/Qi2) over wired charging, and a sustained 40+°C in the case of a misaligned Qi charger, or the worst of all: the Tesla Charging Platform with its many overlapping coils.

Thus if plugging in a cable to connect a device is that much of a hassle, be sure to at the very least get a wireless charging solution that doesn’t simultaneously bump up your power bill and shorten the lifespan of the device’s battery.

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