IPhone wireless charging: the trap of 7.5W chargers

IPhone 8, iPhone 8 Plus, iPhone X, iPhone XS, iPhone XR, and iPhone 11 can be charged with one of the (very) many Qi-certified induction chargers available on the Marlet. Only two chargers, according to Apple, can charge them at 7.5W: Mophie’s “wireless charging base” and Belkin’s Boost Up induction charger . Several manufacturers, however, claim that their own chargers are quite capable of this. Is it true ? To find out, we took out our phones and our “consumers”, and tested half a dozen chargers.

Before detailing our conclusions, let us quickly recall the operation of induction charging. Apple has chosen the Qi standard (pronounced “chi”), certified by the Wireless Power Consortium , which uses inductive resonance coupling. Strictly speaking, this is not wireless charging, as meters of cable are still required. The charger must be connected to the mains, and has – like the receiver – a flat coil in the shape of a rectangle with rounded corners, formed of a dozen turns of copper wire .

The charger periodically emits a signal: if it receives a response, it means that a Qi-compatible device is correctly installed, that is to say that its coil is aligned with that of the charger. Early manufacturers used grooves or magnets to ensure alignment, but now prefer to multiply coils for easier positioning. Apple pushes this strategy to its climax with the AirPower , the advancements of which should be incorporated into future revisions of the Qi standard.

The charger coil generates an oscillating magnetic field, which induces an alternating electric current in the telephone coil, according to the phenomenon described by Faraday’s law . The Qi standard ensures that this magnetic induction charge can operate up to four centimeters. In fact, it requires that the phone be glued to the charger, and the efficiency decreases enormously with distance. An iPhone encased in a large case charges up to 20% slower than a “naked” iPhone, according to our measurements.

The Qi standard has long been confined to “low power” 5 W charging, but now defines steps up to 15 W, and even beyond for other applications. The 9 or 15 W load requires complex circuits and coil arrangements, difficult to fit into ever thinner phones, and posing serious heat dissipation problems. While waiting (perhaps) to find a solution, Apple has chosen to operate at 7.5 W.

To check the operation of the induction chargers, we used an iPhone 8 Plus, discharged to 65% before each test. A series of measurements was carried out under iOS 11.3, a second under iOS 11.4, both under controlled conditions. We first recorded the power delivered on the socket side, using a calibrated professional consumption meter, then the power received on the device, with an application recording the charging voltage and according to the battery capacity.

We thus measured six chargers:

  • the Belkin Boost Up induction charger, with its supplied detachable charger, officially charging at 7.5 W ( $54.95 );
  • the Mophie wireless charging base, with its captive charger, officially charging at 7.5 W ( $ 54.95 );
  • the Belkin Boost Up Stand induction charger, with its supplied detachable charger, supposed to charge at 7.5 W ($74.99 );
  • the Anker PowerWave 7.5 Stand charger, with its supplied USB charger, supposed to charge at 7.5 W ( $45.99);
  • the Choetech “panda” charger, with its supplied USB charger, then another charger, supposed to charge at 7.5 W ( $ 15.99 );
  • the Aukey “three coil” charger, with a 12 W Apple charger, announced at 5 W ($ 19.99 );
  • a noname charger , with its supplied USB charger, advertised at 5W (bought in an electronic bazaar store).

The results are clear … and no surprise. Belkin’s Boost Up Charger and Mophie Wireless Charging Base do charge well at 7.5W, as Apple says. The Belkin Boost Up Stand charger also charges at 7.5 W. All others, even those that the manufacturer claims can charge at 7.5 W, charge at 5 W. Before going into this general conclusion, let’s remember that the charging power depends less on the charger than on the phone, which decides the conditions and regulates the electric flow.

The iPhone calculates the power received at an instant t , and sends back to the charger a positive value if it wants to adjust the power upwards, or a negative value if it wants to adjust it downwards. The charger adapts its magnetic field accordingly, and the two devices communicate throughout the charge, the course of which is very similar to that of a wired charge (it ends with a trickle charge in spurts, then the charger is ” put on standby ”by phone).

The measured power is therefore a subtle combination between the charger’s capacities and the iPhone’s demands, which may vary depending on the software and the conditions, in particular thermal. We can notice :

  • that the Mophie charger , on which it is more difficult to position the phone correctly. Belkin’s charger delivers 7.5W stably and consistently, while the charge is choppier on Mophie’s charger, and therefore slightly slower.
  • that the Belkin Boost Up Stand charger is perhaps the most suitable for “mixed” couples, that is, those where one person’s iPhone is next to another’s Android phone. At 7.5W for the iPhone, and even 9W for the latest generation Samsung Galaxy, it will charge as quickly as possible inductively.
  • that the PowerWave charger does not charge the iPhone at 7.5W , despite Anker’s claims. This charger uses Qualcomm’s Quick Charge 3.0 technology: you must absolutely use the charger provided to use it, and of course have a compatible phone, which is not the case with the iPhone. It does not charge much faster than a 5 W charger therefore, but in a very stable manner, no doubt thanks to its fan, which provides good cooling at the cost of an unpleasant high-pitched whistle.
  • that the Choetech charger does not charge at 7.5 W either, especially since it is not supplied with the Quick Charge 3.0 mains unit which would allow it. Even when connected to a Quick Charge 3.0 mains unit, in this case that of the Anker PowerWave charger, it charges at only 5 W… and again! Hot, unstable, it charges slower than other chargers clearly advertised at 5W.
  • that the Aukey charger works as expected, at 5W , slowly but surely. It is an ideal charger for the bedside table (provided you cover its diodes with a few layers of adhesive tape): it is not a war lightning, but it heats little, and therefore ensures a peaceful recharging of the battery .
  • that noname chargers do the trick in the event of a hard blow … but only in case of a hard blow. The copy we bought struggles to maintain the iPhone, doesn’t always recognize it, and charges it incredibly slowly.
  • that the course of charging may change with software: iOS 11.2 had “enabled” charging at 7.5W, iOS 11.4 seems slightly more conservative than iOS 11.3, perhaps to limit the risk of overheating now that the summer is coming.

In short: for the moment, only chargers from partners certified by Apple guarantee you a recharge at 7.5 W. This does not mean that you absolutely have to buy a Belkin or Mophie charger from Apple. The Boost Up Stand charger , or the Aukey and Anker chargers , retain the advantage of their very practical “docking station” presentation. It is not a question of advising you one charger over another, but of allowing you to make an informed choice.

Unless you stick to “official” chargers, be satisfied with a 5W charger for long-term charging, the batteries like nothing better than slow and quiet charges. Buy even two: the first on the bedside table, the second on the desk, you will never run out of battery again. And if you really need a quick charge of your iPhone, keep an iPad power supply handy, nothing is faster… than a good old cable.