The Charge of the Speed Brigade

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It's a reflection of how much of a sore spot the smartphone battery is,  that young Eesha Khare's science exhibit triggered so much excitement in the media.


The 18-year-old Indian-American high school student from California won $50,000 in Intel's International Science and Engineering Fair (ISEF), ahead of 1,600 finalists from 70 countries.

She made an energy storage device that could be charged in 20 to 30 seconds. Such a device could, someday, replace a mobile-phone battery.

Media went into hyperbole - "Your charging woes are over. Soon, you will be able to charge your phone in 20 seconds." Which got people very excited. I got questions on mail and Twitter about when this "fast charger" would be available and how much it would cost.


I had to disappoint them. This wasn't a charger. It was a preview of a future technology, which could replace the phone battery as we know it with a "supercapacitor". A capacitor stores charge in an electric field, unlike a battery, which uses a chemical reaction to store and discharge electricity.

With supporting circuits and a special charger, this could mean future phones - perhaps by 2020 - that charge real fast, in ten minutes, or even five.

Why not 20 seconds? Well, that's not impossible, but would face some


challenges for a small, portable charger and a compact phone. For the laws of

physics are unlikely to change in our lifetime.

A standard smartphone with a 2,000 mAH battery takes 4 hours to "fastcharge". Someday soon, in perhaps two years, such phones will charge up in one


hour. It will then need over 2,000 mA, or 2 A (amperes) for one hour at 5 volts.

If someday, this battery were replaced by a capacitor with the same

capacity, then to fast-charge it in one minute would need some heavy current:


120 amperes at 5 volts. To charge it in 30 seconds would need 240 amperes.

That would need some heavy electronics (and thick wires).

heavy electronics would remain--for switching, voltage conversion


and power delivery.

From the 220V mains this would draw less than 5A, but thetypically charges and discharges quickly - to deliver power to the

mobile consistently over a day or two from a single charge.


instantly and then discharging over the next hour or so to charge

up the battery through a fast-charge circuit. That would increase

bulk and complexity in the phone.

less than five years - would be a capacitor-based charging base or

"juicer-pack". Plug it in for five minutes, and it gets charged up. Walk off with it

and stick your phone in, and it charges your phone up while you're on the go.

There are other challenges with this, such as in-aircraft use (the heavy currents

involved can cause sparking), but such products are feasible.

Till then, what we have is fast-charge technologies, such as Qualcomm's

Quick Charge, which reduces charge time down to about 3 hours. QuickCharge

2.0 will bring that down to 2 hours, in 2014 devices. Quick Charge is already in

place in, among others, Samsung's Galaxy III, LG's Nexus 4, Nokia's Lumia 820

and 920 and HTC's Droid DNA (but not in the HTC One).

Then there are other challenges of using a capacitor - which

One answer could be to use the capacitor as a buffer, charging

The more likely solution, which I predict we will see earlier - in


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