Instant Cell Phone Charger

[electronupdate]

My smart phone runs down it's battery so quickly I often find it flat at the most inconvenient times... most recently while travelling and switching between planes. Frustrating as there were lots of power outlets where I could snag more than enough energy to run/recharge the phone if I could scoop it up in the few short minutes I had... however batteries are just not designed to charge in a few seconds.

The obvious solution would be to try to use a super capacitor as a short term storage.  A short video on the simple circuit and how it performs at the following youtube address:

Video here:

Now, nothing to stunning going on here.... those who track battery and capacitor technology are well aware that as good as super-capacitors have become, battery technology still far outpaces them in terms of energy stored per volume. 

[dfmischler]

I had to get my wife a mophie for her iPhone 5.  It has a micro-USB jack, and a little switch that she can flip when the phone is dead to charge it on the spot.

[sorin]

For your application is better to use LiFePO battery and not a supercap
 

[peter.mitchell]

For your application is better to use LiFePO battery and not a supercap

Why do you say this?
If he could source more current into the supercap to charge it would be far more effective, making it more "instant", whereas with LiFePO4 I'd strongly recommend not charging them beyond 1C, so he can't charge them any faster anyway, the only difference is the boost converter will work from all the charge in the energy storage, and wouldn't "miss" the last "bottom" volt or so.

[amyk]

The title is somewhat sensationalist...

Aside from that, any regulations on bringing supercaps aboard planes?

[sorin]

s

Why do you say this?
If he could source more current into the supercap to charge it would be far more effective, making it more "instant", whereas with LiFePO4 I'd strongly recommend not charging them beyond 1C, so he can't charge them any faster anyway, the only difference is the boost converter will work from all the charge in the energy storage, and wouldn't "miss" the last "bottom" volt or so.

sure if you take with you at Airport, a50A ATX power supplyThe supercap are better, but ...
with 2x APR18650 You can charge with more than 10A witch is 3.7*10=37W so you need a 37W power supply which is biiiiig in dimension and impractical

[Psi]

I do love solutions that involve supercaps

Maybe it would be better to use a relay instead of the blocking diode.
Have it energize when mains voltage is present and switch the DC output onto the cap.
This way you get zero voltage drop and it will still isolate the caps when the device is unplugged.

You might get better results with a few more smaller supercaps in series.
Just because of the higher output voltage and the boost reg dropout voltage being a smaller percentage of the total cap capacity.

Better design a professional looking case into the final version before it gets anywhere near a US airport   They love to panic at stuff that's unusual.

[Psi]

Another idea, (which would make charging easier), is to have 4 banks of tiny supercaps that add up to 25V or so.
Then have a system which switches the 4 banks between series and parallel (maybe relays, or just a fancy multipole switch that's rated for 120V)
Quickly charging up a 100V cap bank from 120V is much easier to deal with.

Then, when the device is unplugged from the wall, the relays switch the 4 banks into parallel mode (or you throw the switch) and a sepic converter produces 5V from the 25V all the way down to 2V or so.

Of course it's all about the tradeoffs.
- Lots of little caps is going to be less efficient capacity wise compared to one big cap but you can fit more in due to the much simpler AC charging system.
- The higher voltage should boost the overall efficiency