The idea of being able to transmit power without wires is nothing new. US physicist and inventor Nikola Tesla came up with the idea over 100 years ago. But it’s never become a commercial reality. Why? Because using wires is cheaper and more efficient. And with power bills skyrocketing on the back of government-backed electricity prices rises around the country, “efficiency” is the name of the game.
Which is why I’m surprised at the growing movement in wireless charging. You may have seen a few of these reviewed in recent times. You’ve probably even seen a few advertised on the web. The claim always seems to be “charge your device without wires”. The problem is it’s a furphy – and on several levels.
If you just look at the “without wires” claim, it doesn’t stack up. Most of the wireless-charging devices available are not much more than power couplers: you have a power brick which attaches to a base plate or mat via – you guessed it – a wire. You then have an inductive coupling device that connects to your phone, camera or whatever by a sleeve or by – yep, you’ve got it – another wire.
If you think of wireless charging as a convenience thing, well, I don’t see it winning here either. Yes, carrying around a small power brick for your phone is a pain but few of us need to charge a phone more than once a day so plugging a power brick into a phone isn’t all that tough a chore. But with these wireless chargers, you have to fit your device into a sleeve or plug it into a coupler device then place it on the charge mat or base. I don’t see how that’s any easier than just plugging in a power brick directly.
But the other thing that’s not spoken of much but something that in these days of high power prices and power usage concerns needs more discussion is the efficiency of wireless charging.
Charging via induction coupling is always going to be less efficient that a direct connection. End of story. Its basic electronics – what you’re creating is essentially a device called an air-core transformer and any transformer will have energy losses. It’s just how they work. Perfect power transfer just isn’t a reality.
And frankly, AC power bricks for phones and the like are now so small and light thanks to SMPS (switch-mode power supply) technology that the hassle of carrying a power brick is not what it used to be.
Work being carried out by the Massachusetts Institute of Technology (MIT) suggests that a resonant-frequency magnetic charge process (not too dissimilar to how a radio tunes into a particular radio station) may get off the ground and offer greater efficiency. But we’re not talking great efficiency levels here. The latest MIT work is showing a power transfer efficiency of just 30% – that means for every watt of power you transmit, you need a bit over three watts to start with. MIT has found a technique whereby the more devices you have the greater the efficiency becomes and they hope to achieve the ideal goal of 100% transfer. But given the idea has been kicking around for more than 100 years, I’m not going to hold my breath.
Aside from the efficiency aspect, the only way wireless charging can work in a practical sense is if we get a universal standard for wireless charging and it’s integrated into all devices. This way, there’ll be no sleeves or connectors required. The induction charging coil is built into the device so that it simply just needs to be placed on a charge base or mat that meets the same standard and does its thing.
However, Japanese technology giant Fujitsu displayed in mid-September prototype technology to show power being transmitted over a distance using magnetic resonance. Fujitsu managed to get 85% efficiency from their demonstration, which leaves everything else so far for dead. But again, that still leaves 15% of the power just wasted. And as Fujitsu admits, getting it right becomes more and more difficult the smaller the device you’re trying to charge. Still, Fujitsu is hopeful that it will get products to market using the technology in 2012. Further down the track, it sees an option for mobile charging of electric vehicles.
We may well get to a point where wireless charging becomes a practical reality. But in the meantime, if it’s going to cost $200-$300 just to replace a power cable, I think I know which I’d choose.