The problem is that iPhone's do not send a signal to the wireless charger so the charger does not know when the iPhone is fully charged, so it keeps charging anyway. When using a cable it knows when it's at 100% and stops.
I think there’s a basic misunderstanding here of the way that electricity works. In simplest terms, regardless of a wired or wireless connection, electrical current is
pulled by the device not pushed or ”forced” into it. This is why the term “draw” is referred to when measuring current or amperage (e.g. a device is said to be “drawing current” from a power source).
The amount of current drawn is entirely under the control of the iPhone, and it doesn’t require any kind of special communication with the charger beyond the basic principles of electricity — it simply starts consuming less power. This actually happens at around 80%, when the charging rate slows down, and once the iPhone reaches 100%, it should drop to nearly zero, although the iPhone should continue to draw a small amount of current from the charger in order to avoid using the battery. From the iPhone’s perspective, this works the same whether it’s a wired or a wireless charger, as it’s just physics.
Where Qi chargers differ is that the power
output of the charger is controlled by a data communication (“handshake”) between the iPhone and the charging pad itself. So unlike a wired charger, a Qi wireless charger doesn’t know how much power to send until the connected device tells it, and similarly doesn’t know when to stop sending power as it has no reliable way of actually measuring the draw from the attached device due to the vagaries of the inductive connection.
However, even IF the Qi charger gets this wrong — either by supplying too much current or continuing to provide full charging current after the iPhone battery is topped up — this doesn’t mean that your iPhone will be in danger of overcharging the battery, but it might be at risk of overheating. Again, basic thermodynamics says you can’t “force” power into a device that doesn’t want it. Instead, what happens is that the power being sent out by the Qi charging pad that’s no longer being consumed by the iPhone is dissipated as heat, which of course can still be a bad thing for your iPhone, but in a totally different way. In fact, if you find your iPhone getting excessively hot when wirelessly charging, this is probably the reason why, and it’s almost certainly the fault of the a cheap or poorly designed charger, and not anything wrong with your iPhone.
This is also why “foreign object detection” is so important in the Qi charging standard. If a charging pad was always sending out power, a metallic object placed on top of the charging pad would absorb the energy sent out by the pad, turning it into heat, which could be extremely dangerous depending on the type of foreign object placed on the charging pad.
www.bestbuy.com
