It's nighttime in Barcelona, you can't find your hotel and your phone battery is dead. Double-A batteries won't go in a phone so you're screwed, unless you've read the following advice. If a phone sports a removable battery then you can carry a charged spare, and there are numerous pocket chargers on the market, but they all …
Plenty of "rechargeable battery chargers" around (i.e. a largish rechargable battery with a power out socket and normally a selection of "ends" to put on the cable ... though nowadays micro-usb may be all you need ... unless you have an iThingy). And, didn't one of "The Apprentice" teams last year try flogging emergency mobile chargers at a train station last year in one of the "sell cheap tat" tasks?
On a slightly different note...
... I'm thinking of developing a battery powered liquid holders.
I'm going to name them AA cups.
Re: On a slightly different note...
Before the pedants notice, apologies for the mistaken pluralisation there.
"Modern aa rechargeables are 1.2v out of the charger"
Except that is completely untrue - I just tested 3 different brands I use and they were 1.35v, 1.33v and 1.29v.
I never said the NiMH rechargeables were 1.6v but standard Duracell alkaline cells can be - did you actually measure the actual voltage you were getting?
"...did you actually measure the actual voltage you were getting?..."
Yes, 1.2v on the dot, generic NiMH cells. I also just tested some Duracell NiMH cells too, also 1.2v.
1.2v is the typical 'nominal' voltage of a NiMH rechargeable - the actual open circuit voltage will vary depending on the actual chemistry used etc. For the same reason what most people regard as a 12v (lead acid) battery is usually around 12.6-12.8v when fully charged (technically nearer 13v than 12v).
As someone said Dimension Engineering make some nice components that are basically ready to use - but they are not especially cheap / so readily available in an 'emergency'. The other problem is the standard 'Anyvolt' (which can handle voltages above or below the desired output) only handles 500ma input or output - so if your input was below 5v you would get 5v but not 500ma output. If your input was above 5v you could use one of their cheaper step-down regulators (they do one that handles something like 3a).
They do a more powerful Anyvolt but it's more like £45-50 last time I looked which is excessive for an 'emergency' charger.
Realistically in an "emergency" can you really plan on being able to get any 5v regulator - more likely you would be best to just use 4 AA rechargeables or 3-4 AA alkaline batteries in series - under load the voltage is likely to be close to 5v or your device may not be that picky if the voltage is a bit low.
More than meets the eye.
The Rolson gadget isn't 'just' a battery holder though, it's got a spanky little boost converter built into the translucent bit at the top, how else do you get 5 volts from a 1.5v cell?
Makes a lovely little power supply for microcontrollers too :)
You can also pick up exactly the same gadget, branded with some weird name, at petrol stations in the UK for £2.99 at the moment (Esso I think)
7805 aren't a good solution...
...because they are linear regs which dump the excess energy as heat and are therefore inefficient - the last thing you want when trying to get as much joice as you can from a couple of AAs. What you really need is a buck-boost converter, there are instructions for how to build your own on that page, or you can buy a kit from https://www.adafruit.com/products/14
Note that charging Fruit-themed devices is *not* straightforward, see http://www.ladyada.net/make/mintyboost/icharge.html for the gory details.
A much better solution-in-advance, a Brookstone external battery:
Or check out Casemate's offerings: a case with included battery:
Casemate also make phone 'holsters' which charge the phone whenever it is 'holstered'.
Or use the non-techy solution..
The alternative being, hop in a cab and tell the cabbie the name of your hotel. Fifteen minutes later you're there; rather than faffing about finding electronics to kludgily charge your phone!
Alkalines not as ubiquitous as you think
I used to think alkaline AAs could be got anywhere and bought gadgets for travel accordingly equipped. Disappointingly I found this to be far from the case in much of Asia and Africa and some parts of South America. AAs can be found absolutely everywhere, just not alkaline ones. You can very often find "Duracells" in ordinary shops but they are nearly always fakes: very cheap zinc carbons dressed in black and gold labels.
In these sorts of towns, for real alkaline AAs you need to go find a proper camera shop where you pay though the nose, sometimes the equivalent of $8 for a pair of off-brand ones.
Fortunately, AC mains is found pretty much everywhere (as is cellphone reception these days). Even in remote Indian villages and far flung islands in the South China sea, someone will be running a generator. Of course it won't be an uninterrupted supply, but always more convenient than dry cells. I learned my lesson: rechargeables are the only realistic way to go.
I'll carry on using my Samsung GTE-1170 Non Smart phone.
I last charged it on the 10th and it's still got about another 5 days before it runs out.
Plenty of time to find a plug socket :)
As yet however I've not managed to get a single fart app running on it.
"The Rolson gadget isn't 'just' a battery holder though, it's got a spanky little boost converter built into the translucent bit at the top, how else do you get 5 volts from a 1.5v cell?"
The reality is those 1 x AA gadgets and alkaline cells are pretty cr@p - to get 5v and 500ma from a 1.5v battery means pulling more than 1.5 amps (a lot for most alkaline AA cells). At 1.5 amps the voltage will sag quite a lot so you are probably pulling more than 2 amps. As the voltage drops (as the cell depletes) the current draw will increase - so you will often get very little actual capacity out of the cell and into your phone.
Using a lithium (primary) AA cell would be better (as would using a rechargeable NiMH cell) - but still not great.
"Yes, 1.2v on the dot, generic NiMH cells. I also just tested some Duracell NiMH cells too, also 1.2v."
Checked with 2 different multimeters - the Sanyo Eneloop was 1.35v, a Duracell rechargeable was 1.33v and another NiMH cell was 1.29v. None were 'hot off the charger' - they were fully charged in the last few days.
Also NiMH charge at around 1.4-1.6v anyway - so hot off the charger they are unlikely to be 1.2v.
Stick with my desires slim battery which can be put in the case with the phone.
Got a wallet style case not much thicker than the phone which the spare battery fits perfect in.
The product is not listed on the yank flavor amazon site, I am heartbroken.
I just always carry a wall charger around with me. If it's 2am you're bound to find a place that'll let you charge up for 10mins as long as they can serve you *something*, a pub, a kebab shop, anything.
What a waste of batteries
If your phone is important to you, you select one that allows you to carry a spare battery, or alternatively you carry a mains charger. If you're away on business and don't keep your phone topped up, you're an idiot.
No need to waste expensive and polluting batteries on keeping your handheld twit machine topped up. Simply select an appropriate phone (that lasts a couple of days) and put it on charge from time to time.
"Pair of double-As give you a cheap, quick charge"
But they won't get you featured in Zoo or Nuts...
Not trying to be a bit finicky about your DIY design but, using a regulator to drop the voltage down from a 9 volt can lead to a fe problems with charging a phone, firstly if the regultator goes faulty then it will send the full 9 volts to the phone, also no smoothing capacitor is fitted on your design so it will quite a dirty regulated supply.
"It comes with a selection of connectors and will charge an iPhone too (iPhones need a special circuit to confirm it's a proper connector; it's not complicated but we didn't have one to test)."
In other words nobody dared plug it into their iphone incase it fried it lol
1- If the Regulator goes faulty then they almost always fail open-circuit.
2- Most phones can survive 9v for a little while.
3- Smoothing capacitor not needed as there is nothing to smooth. They are only needed if you start off with an AC power supply.
However, the best method is to rub your smartphone against your nipples and crotch whilst making groaning noises. It won't charge your phone and definitely won't help find your hotel, but that nice man with Guardia-Civil on his jacket will almost certainly put you up for the night in one of his nice cells. <LOL>