21Oct 2014
My prior posts are begging for today’s post: “Mirror, mirror on the wall, who’s the fastest of them all?”

Yes, you guessed it right, not all mobile smartphones are created, ehem, designed equally. Yes, some are designed in Cupertino, others in Taipei or Tokyo or Seoul, and many somewhere in China, and they all seem to share many common features such as a processor, radio modems and a beautiful screen with lots of pixels….but when it comes to power and charging, the designs vary vastly. It’s because power and battery don’t like to adhere to standards. The temptations for engineers to design and redesign the power path is too great. To their credit, there is not one-size-fits-all when it comes to power and charging. Let me give you an example, changing the charging current from 1A to a mere 2A is plenty reason to wreak havoc on the design. The thermal design will most certainly be different. Some components such as inductors will have to be selected with greater care. Electrical resistance in the path to the battery will probably have to be cut in half! With these tasks, it is normal to expect some smartphone makers to be more bold than others about introducing fast charging. But in all cases, expect to see more introductions in the coming year or two.

Battery charging has an inherent safety limitation built into the software and hardware: the charging voltage of the battery may not exceed 4.35 Volts! This bears a serious consequence: the charging current must be scaled back when the battery begins to approach getting full. I will leave the details to another discussion, but for now, an average consumer will observe this limit as a slower charging once the battery meter on the smartphone begins to exceed somewhere between 60 and 80%. Consequently, the device charges at its fastest rate when it is mostly empty, which is exactly when you also want it to be at its fastest — you find yourself at the airport and your battery is about to die; or you are rushing to a morning event and you realize that you forgot to charge your device overnight!

Consequently, one useful metric of charging speed is the time it takes to go from zero (empty) to 50% (half-full). The fastest charging smartphone on the market today is from a small company out of China called Oppo. Their device is labeled the Find 7 — one can buy it directly from their China store, but beware, its radio bands are not fully compatible with many network bands in the US, especially AT&T and Verizon.

So mirror, mirror on the wall, what device thou shalt recommend after all? If charging times are important to you, you should be able by now to make your own informed decision. If you can’t find a satisfactory product that meets your wish list, let your favorite wireless carrier hear from you, in person at their store, or on your favorite social network.  But one thing is certain, once you get used to fast charging, there is never returning back to regular charging, or should I rather say, slow charging!

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