Apple Iphone Charger efficiency test!

I've bought my electrical meter for quite some time now and have been testing the power consumption of various appliances in my house.

One of my more prominent device is my Apple Iphone charger. It is a rather mysterious gadget because there is very little technical specifications about it other than the fact that it outputs up to 1A @ 5v.

Some did a tear down review of the little charger and concluded that it is actually very well designed compared to a counterfeit charger. But that does it translate to in real world usage? And what can we find out about charging iphones?

Efficiency Test

What I did was to record the power consumption of the charger when charging an iphone with less than 20% capacity. In this test, I assumed that the charger is putting out its maximum wattage indicated on the charger, which is 5w. This is because the iphone is likely to pull as much power as it can from the charger to fill up the battery fast since the battery is almost empty.

 

What we have here is a 6.5w consumption from the wall socket. If 5w was going to my phone, 1.5w was being wasted as heat. So, this charger is 77% efficient. Quite a decent figure here.

For a more accurate test, we can measure the output current from the USB. But that is for another time.

Any parasitic drain when left on?

Apparently, the charger has negligible drain when plugged in and switched on. This is good considering that some of us simply leave these chargers switched on even when we aren't charging anything. I like it when devices are so well designed to be able to achieve this. Saves the hassle of having the need to turn it off and on every time without the guilt of wasting energy.

 Charging with an extra long cable

For some reasons, my parents thought that it was a good idea to buy an extra long wire so that they can bring their phones to their bedside while they charge. Before I tested it, I had the expectation that the power consumption is similar to the first case above or more so as to compensate for the energy loss through such a long wire.

It came as a surprise that power consumption dropped! The iphone was deliberately pulling off less power from the same charger. It has been well established that the iphone is controls its power input quite smartly and it may have sensed that it was not able to receive the full 5w it expects. Hence, lowering down itself to the next lower rate which was 2.5w - computer USB ports give out this much.

 Assuming that it is indeed outputting 2.5w, the whole charger set up efficiency is now 64%, which is a whole 13% weaker!

Is it true that the iphone charges faster when you put it on airplane mode?

Some websites are claiming this, but looking at the power consumption when airplane mode is turned on and my screen switched off, the power consumption dropped. This indicates that the iphone is now pulling less power than before.

This suggests that the iphone dynamically takes in power from the charger to supply itself while the phone is being used. The myth that iphone charges faster in airplane mode implies that the charger is always outputting its maximum power solely to charge the battery and less power will end up going into the battery when more power consuming features/apps are used, lowering the charging speed.

 

However, this it not the case here. The lowering of the power consumption implies that the the charger is more than sufficient to supply the iphone the power it demands. So, no point switching off your phone or putting it on airplane mode hoping that it will charge faster.

I hope this is useful for you iphone users! Oh yes, avoid long wires!