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Can You Power a Phone With a Capacitor? And, can we understand that?

Posted on | June 9, 2013 | No Comments

“There was a recent news item regarding a teenager’s project to use a super capacitor as a quick-charging energy storage device. The primary claim is that this could be used to fully charge a phone in just 30 seconds.”

http://www.nbcnews.com/technology/teens-invention-could-charge-your-phone-20-seconds-1C9977955

nbc_khare

 

 

 

 

 

 

Luckily, Wired put a physicist on the case, and he discusses this in much length.

http://www.wired.com/wiredscience/2013/05/can-you-power-a-phone-with-a-capacitor/
Maybe a bit too complicated for most people.
Here s a simplified version (not precise, just testing whether this is realistic at all):

To charge a mobile phone (battery is typically 1500 mAh at 3.7 V or 5-6 Wh) in 30 secs,
you d need about 600 -700 W for those 30 seconds. Pretty hot.
The energy needed would be about 20,000 J

The energy stored in a capacitor is

W = 0.5 * C * V**2

so that wouldgive

C = 1600 F

Do such capacitors exist?

 

 

 

 

 

 

 
Yes, they are called supercaps, and no, Khare did not develop them.
They have been used in lost of electronics for decades.

They are inside  some of the stuff you use.

You can get them on ebay:
http://www.ebay.com/itm/3000F-2-7V-Supercap-3000-Farad-Super-Ultra-Capacitor-/150642133382

A supercap of 1600 F would be a bit too big for your phone, but
since her work,

https://www.usc.edu/CSSF/History/2013/Projects/S0912.pdf

in fact looks at improving (rather than “inventing”) supercaps,
it s not entirely impossible that you d see something like this, at some point in time.

just not next week.

 

Her report claims

“an energy density of 20.1 Wh/kg, comparable to batteries,
while maintaining a high power density of 20540 W/kg.”

The energy density limit would make her current supercap about 250 grams –
a bit heavy still, but the right way to go and the rest, that’s gradual improvement.

So, not possible – not all bad,  just reported by most media in a wrong way.

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