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Spec for Wireless Charging to Be Set Within 6 Months

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Replying to:  Efficiency by BegToDiffer   Jan 11, 2010, 8:40 PM

Re: A little physics lesson

by CellStudent    Jan 12, 2010, 1:32 AM

As "cool" as charging mats are conceptually, they are a ridiculous source of power waste. These things are terrible.

A little science: everyone knows that electricity and magnetism are almost the same thing, and it's fairly easy (thought ridiculously inefficient) to turn magnetism into electricity and the reverse process, but every time this transformation occurs, a tremendous amount of energy is lost.

To charge a small electric device out of a wall socket with a regular charger, the electricity travels through a circuit board that changes the current from AC into DC and then uses some extra resistance to step down the voltage from 120V down to about 10V (my BlackBerry charges at 5V, my electric razor at 12V), while this is pretty efficient compared to coil transformers, you'll still notice your chargers get warm if left plugged in too long, that's all wasted energy.

It gets quite a bit more ridiculous with this charging mat technology. The electricity going into the pad is run through an electric coil, which generates and alternating magnetic field that shifts polarity top-to-bottom 60 times per second. This magnetic field reacts with another coil in the remote unit, creating an AC electric current in the handset. This AC current then has to be run through a circuit board or diode array (inside the device, taking up valuable space that could be used for other electronics) which turns the power into a DC current to charge the battery!

A nice novelty act, but about as UN-green a method of power transfer as I can possibly thing of. It also requires the AC/DC power converter to be located INSIDE the handheld rather then sticking out of the wall socket at the business end of the plug.

A wall socket charge experiences 2 (relatively efficient) power conversion steps before being deposited in the device battery.

A "wireless" power transfer system experiences FOUR power transmutations before being deposited in a battery, two of those conversions are ridiculously wasteful electromagnetic conversions rather then circuit board converters, AND it requires a significant portion of the power converting hardware to be carried around in your pocket all day, every day because the voltage rectifier has to be built and stored INSIDE THE HANDSET.


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