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Build Your Own iPod Battery
OmniVector writes "With various complaints about the iPod battery's life, and its mere 10-8 hours of charge many of us are left looking for a way to keep the tunes kicking a little longer. Drew Perry has come up with a novel solution which can only run you a few bucks for an extra 10 hours of battery life out of a box of playing cards and a everyday batteries. Not bad for that long car trip where you just don't have a firewire charger handy."
batteries are a known quantum in the world of travel security. scanners are designed to know what they are and how they're used.
...
contrary to popular belief, batteries do not look like explosive devices.
this diy-playing-card-battery-charger might raise a few eyebrows for its 'concealment' factor, but then, you don't have to use a playing-card box. you could just as easily use something else that actually looks like a plastic case designed for carrying batteries.
this is a clever hack, anyway. the schematics are where the value is - whats the bet it won't be long before you can get these plastic cases in the akihabra back-streets, selling as 'cheap firewire-device rechargers' or whatever
; -- the corruption of government starts with its secrets. a truly free people keep no secrets. --
6 pin Firewire pin assignment (& others)
;)
Need to know which ones are the power pins, right?
Anonymous Joe
Backup battery pack
LotD
I'm assuming he chose this configuration because a 9V will discharge faster at a given current than a AA.
He chose this configuration only because he was trying to be clever and fit it into a playing-card pack.
As to what you're assuming - no. Battery voltage is determined by the chemical type of the battery. Size doesn't matter. So for example, standard alkaline AA, AAA, C, and D batteries all put out 1.5V, but Ni-Cads put out 1.2V. Lead-acid like your car battery is 2V.
Therefore, a 9V battery is just six tiny 1.5V batteries in series. Get some tin snips or whatever, and carefully cut open the outer casing on a 9V and you can see for yourself.
Also, you *can* safely run batteries in parallel. The only gotcha is that you can run into problems if you try to charge the batteries in that configuration when they are not evenly discharged. His picture looks like he isn't using rechargeable batteries, though. Or if you had rechargeables, you could pop the batteries out and charge them individually.
Personally I think it'd be more straightforward to just wire up 8 AAA batteries in series and forget the 9V nonsense. Probably would get longer battery life too. I don't know if they'd fit in a playing-card pack, but they wouldn't be much larger.
To be blunt, this design isn't so bright... Sure, it produces a reasonable voltage, but it's not a good idea to mix different types / sizes of battery in this way. If batteries are mixed in parallel like the PP3 batteries in this circuit, large currents may flow from one of the batteries to the other - it's unlikely both batteries would output exactly the same voltage. If batteries of different sizes are mixed in series, one type may discharge before the other. The discharged cell may potentially be reversed - i.e. current will flow through it backwards. Either of these situations may cause the batteries to vent gas, overheat, or if safeguards fail they may even potentially explode. This is the sort of thing that you may get away with for some of the time, and you may not see any problems immediately - but in the long term you may well burn your house down. This advice comes from experience. If you short a rechargeable battery you can draw extremely high currents (even 10s of amps) and start fires very quickly. I once melted a long piece of plastic insulation very quickly when two contacts touched at the end of a battery lead. The battery got very hot - I burned my fingers trying to disconnect it. Treat batteries with respect. I'd be willing to wager that electronics kills many more people through fire than electrocution.
It's obviously not the work of a professional engineer, but that's what makes it neat. Taking a just barely functional knowledge of what's going on and solving a problem using available tools. I suspect this guy isn't going to be the professional EE you all think he should be for at least 4 more years
Actually, I've seen a lot of EEs do the same thing, with no more understanding than the basic voltage drop analysis. You have to keep in mind that an engineering degree confers exactly the *opposite* thing to the practical knowledge required in the real world. Those people who make good engineers already got their practical knowledge from playing with Lego and hacking their bicycle.
You see, the reason why a D cell is bigger than a C cell is bigger than a AA cell is bigger than a AAA cell despite all putting out ~1.5V is because of current capacity. A modern D cell will put out 1.5V into a 1A load for many (~15) hours, while a modern AAA cell will put out 1.5V into a 1A load for around an hour and ten minutes.
Trivia question: why is there AA, AAA, C and D but no A or B? Answer: The A battery was a big 1.5V lantern battery used to heat the filaments in radios before rectifier tubes were practical to allow the radio to be plugged in to a regular outlet, and the B battery was a 30V, 45V or 90V battery used to provide the plate voltages for the tubes in these radios. The B battery stuck around until the early transistor radios of the late 1950s replaced all the tube portables. You can actually still buy both battery types but generally only through big electronic parts suppliers.
(Quoting Duracell's alkaline battery data sheets, difficult to link directly to the PDF so click on "Technical Bulletin" and scroll to page 9/13, D cell 15Ah (15,000mAh) and AAA cell 1.15Ah (1,150mAh).)
Go to Radio Shack and buy a multimeter. Stick it in current mode, and measure the current consumed by the iPod. Then look up the mAh (milliamp-hour) ratings for the type of battery you wish to use - NiMH, Energizer Lithium, Duracells, whatever. Do not mix battery types (brands, chemistries, etc), ages (new batteries and old batteries should never be put together in series), or sizes (AA, 9V, D-cells, etc.) because you will have some discharge faster than others, sometimes to the point of actually trying to "recharge" the weakest cells off the strongest cells.
Figure out which battery size you need to use based on whatever you consider to be an acceptable battery life for long trips, and use it. Of course, there will be design trade-offs in order to achieve a reasonable size - shorter battery life or bigger and heavier batteries - some compromise will probably have to be reached. If all you care about is battery life, for example, just stick the iPod directly across a car battery.
Get appropriate sized battery holders at Radio Shack or any number of electronic parts places - MCM Electronics, All Electronics, Digikey, Newark, Electrosonic, etc. Connect them in series and build them into a plastic or aluminum box, properly secured and screwed down. Use heat shrink tubing instead of electrical tape for all connections, and use a grommet (those little plastic things where the power cord enters your kettle or toaster or whatever) to prevent the wires getting frayed.
And, most importantly, once you know the current the iPod consumes, multiply that number by two and buy a fuse with that rating. Put it in a holder in the battery box - that way, if the power cord to the iPod gets caught and damaged, or if the iPod fails catastrophically - there won't be a fire.
Fire and Meat. Yummy.