# How efficient is wireless electricity compared to wired electricity?

I am looking for data showing practical data/information on the efficiency of wireless (induction) transfer of electricity vs. wired transfer. There is some information out there but the source makes me hesitate at taking this at face value.

Assuming standard US mains power (120 V AC), charging an iPhone 5S battery (3.8 V 5.92 W·h (1560 mA·h)) from 0% to 100%, how many Watt-hours would be consumed from a standard wired connection vs. a non-standard wired connection?

If we take the presentation linked above at face value, and we work backwards, we would get:

Wired (best case): 5.92 / 85% / 90% / 90% / 95% = 9.05 Watt-hours (65.4% efficiency)
Wired (worst case): 5.92 / 85% / 80% / 80% / 95% = 11.46 Watt-hours (51.6% efficiency)
Wireless (best case): 5.92 / 85% / 89% / 89% / 95% / 80% = 11.57 (51.1% efficiency)
Wireless (worst case): 5.92 / 85% / 89% / 89% / 95% / 60% = 15.32 (38.3% efficiency)

Yet the conclusion of the presentation is:

The improvement over the standard charger seems to be based on the assumption that the efficiency of the device will improve if the charger is integrated in to the wireless receiver.

At the end of the day, what is the actual efficiency of a wired charger vs. a wireless charger? Can the wireless charger actually be an improvement in efficiency over a wired charger for things like charging an iPhone, or is it strictly a convenience-based change?

• @geometrikal, thanks for the heads up. I've edited it out. Any chance you have insight on to the actual comparative efficiencies?
– jmac
Commented May 26, 2014 at 5:42
• I think it will depend mainly on the distance between coils. For example, an AC transformer performs a wireless transfer of energy at very high efficiency. Maybe the academic literature has some more information? Commented May 26, 2014 at 6:30
• @geometrikal Non galvanic and wireless have the same meaning? Commented May 26, 2014 at 7:20
• @GRTech I'm taking 'wireless' to mean inductive transfer of energy also known as wireless charging. Some inductive chargers also use a metal core. electronics.stackexchange.com/questions/13334/… Commented May 26, 2014 at 8:39

I'm not ecstatic about the following picture shown in the TI document: -

I've drawn a big red square rectangle on the top diagram and it seems TI are saying the efficiency is between two limits: -

Minimum = 0.95 x 0.80 x 0.80 = 60.80% Maximum = 0.95 x 0.90 x 0.90 = 76.95%

For the wireless diagram they are saying its efficiency is 60% to the equivalent "wired" point but they are neglecting the lower limit so this has a biased feel about it. The lower limit would be: -

Minimum = 0.60 x 0.95 x 0.89 x 0.89 = 45.15%

Read the small print. They say they are using 80% adapter efficiency yet surely a plastic box that plugs into the AC that produces 5V cannot be assumed to have a significantly worse efficiency to a plastic box that produces 19V.

• Do you think those numbers (76.95% vs. 45.15%) are an accurate representation of the different efficiencies of both systems?
– jmac
Commented May 26, 2014 at 10:13
• 76.95% is TI's estimation of the wired maximum efficiency and 45.15% is (by reading between the lines) TI's estimation of the wireless minimum efficiency from that diagram. If you take the spread of both number ranges you'd have to conclude that wireless looked like being, on average, worse than wired. Commented May 26, 2014 at 11:02