Episode suggestion: Efficiency of wireless charging

[Highcooley]

Hey Dave

As it seems, wireless charging is suddenly all over the place. Generally a very convenient way to get rid of the hundreds of chargers, the cable salad and the anoying propriatry connectors. But what about the over all efficiency of such systems? As far as my understanding of physics and electronics goes, the efficiency of a transformer drastically reduces the bigger the gap between the two spools is, no matter what exotic waveform is used to transform the power. But see how TI tries to convince developers with their bogus calculations: http://www.wirelesspowerconsortium.com/technology/why-not-a-wire-the-case-for-wireless-power.html

Especially compare slide 7 to 8. They claim that their system has a bigger over all efficiency than a wired charger assuming that their AC/DC "adapter" already has an 80% efficiency to begin with. They relativise to the end of the presentation but still assume a higher developed charging system in their next gen controller which should be more efficient than a regular charger. Smells like BS to me.

Of course, the topic is a bit more complex than that. Less copper used, maybe less different chargers (if the industry will agree upon a common standard which seldom happened in the past), more efficient if the primary side detects when no device is in range and shuts down, but more electronics for the transmission and the detection is needed.

Are we going a huge step back in terms of energy efficiency if we widely introduce this technology to humanity? Might be an interesting topic for a white board session. What do you think?

Cheers,
Andy

[max666]

Just last week I saw a wireless charging pad at Ikea http://www.ikea.com/us/en/catalog/products/80289790/.
I too am curious about the efficiency of these things. What if the case of the phone is out of aluminium? What if the charging pad is placed on a metal surface? Or is wireless heating a feature not a bug?

Now to be fair, just because the gap between two coils is big doesn't necessarily mean the efficiency is low, it just means the coupling is low. With resonance and very high quality factor (Q factor) for the resonators I could still achieve high efficiency. But as far as I understand it, every conductive object in the vicinity of the coils will necessarily reduce the Q factor and thereby drastically reduce efficiency.
But to the point, a wire will always be more efficient at transferring power than two magnetically coupled coils. And arguments like "If the wireless charger supports direct charging ..." are moot, because the same applies to what if wired chargers support direct charging.
I will give them the convince and connector fatigue argument though.