If someone puts two phones on a wireless charger, where does the energy to charge the second phone come from?

Question

I understand that the current in the wireless charger causes a current to be induced in the first phone via magnetic fields. However, if I place a second phone on the wireless charger at the same time, what happens? Does the second phone steal some of the energy that would have gone to the first phone? Does it cause the wireless charger to somehow pull in more power from the outlet? Would the first phone now charge at a slower rate compared to before? Or does it merely productively use some of the energy that would have been lost due to heat or something else?

In: 1

Answer 1

It mostly just depends on the charger, and how close the phones are to the charger.

The charger produces an alternating magnetic field. A simple oscillating circuit would produce a quite strong field with nothing to absorb its energy. So, in this simplified case, adding a phone to charge weakens the field. adding another phone weakens it further and the phones charge slower than of just one was present.

But in reality, the charger has a control circuit which decides how much power it puts down. When there’s no phone, it doesn’t put any power down, since it would just be wasting it. When a phone is added, it increases power to cope. When a second phone is added, it could increase even more. I’m not certain that engineers planned for that eventuality, though.

Answer 2

Depends on the charger and the phones. If the whole charger can charge at 20W, and you put two phones capable of charging at 10W each, then they both charge at their maximum.

It’s the same as if you had a two-port 20W USB charger and charged two phones off it it. Add up the phone charging wattages, and if they’re more than the charger then neither will charge at full speed.

Answer 3

So a thing about wireless chargers is the the the charger and device have to closely lined up with each to work so you won’t have two phones drawing energy from the magnetic fields created by the same coils.

All multi device wireless chargers currently have multiple coils, one for each device. And the power delivered will behave just like if you plugged two phones into a multiport wired charged.

The power is split between the two phones with the total power not exceeding the chargers rating.