Instant Cell Phone Charger - Page 1
Forum section: electronics / projects

author: electronupdate
author_rank: Regular Contributor
timestamp: September 08, 2013, 11:34:31 pm
content: 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.

author: dfmischler
author_rank: Frequent Contributor
timestamp: September 09, 2013, 02:37:57 am
content: I had to get my wife amophiefor 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.

author: sorin
author_rank: Frequent Contributor
timestamp: September 09, 2013, 05:06:50 am
content: For your application is better to use LiFePO battery and not a supercap

author: peter.mitchell
author_rank: Super Contributor
timestamp: September 09, 2013, 06:02:09 am
content: Quote from: sorin on September 09, 2013, 05:06:50 amWhy 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.

author: amyk
author_rank: Super Contributor
timestamp: September 09, 2013, 08:18:16 am
content: The title is somewhat sensationalist...Aside from that, any regulations on bringing supercaps aboard planes?

author: sorin
author_rank: Frequent Contributor
timestamp: September 09, 2013, 08:37:14 am
content: sQuote from: peter.mitchell on September 09, 2013, 06:02:09 amsure 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

author: Psi
author_rank: Super Contributor
timestamp: September 09, 2013, 09:02:51 am
content: I do love solutions that involve supercapsMaybe 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 airportThey love to panic at stuff that's unusual.

author: Psi
author_rank: Super Contributor
timestamp: September 09, 2013, 09:18:50 am
content: 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