Technology
HOW TO – Make a portable USB charger

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GoodAtIt writes – “The project name says it all. It is a device that will charge things like Ipods, PDAs, that accepts charge from a USB port. It runs off a 9-V battery, and through the simple circuit, out comes a regulated 5-V perfect for a USB port.”Link.

14 thoughts on “HOW TO – Make a portable USB charger

  1. Doesn’t a USB device have to connect and ask the host permission before taking more than (mumble) mA? My iPod refused to recharge on a Linux system without the USB host driver installed.

  2. I think if the data pins are un-occupied, there wont be a problem. If there is no data being exchanged and only the voltage pins are being used, then it defaults to charge

  3. Ever plug an ipod into an xbox [for a charge]?

    (Mine has a usb thingie – you all know the ease of that)

    “Do not disconnect”

    Needless to say, I did.

  4. from the ipod linux wiki: http://ipodlinux.org/Dock_Connector

    25 and 27, USB D- and USB D+.
    Different kind of behaviour of the iPod if those pins are set to a certain state. To force
    the iPod (useful for the iPod 5G) to charge in any case, when ‘USB Power 5 VDC’ (pin 23)
    is fed, 25 must be connected to 5V through a 10kOhm resistor, and 27 must be connected to
    the Ground (for example: pin 1) with a 10kOhm resistor. 10kOhm resistor has been determined
    experimentally.

    The pin numbers reference the ipod docking port connector you can get from sparkfun for $3 USD.

  5. Why do people use 9V batteries for this? You’re burrning off 44% of the battery’s power as heat before you even consider the inefficiency of charging a battery from a battery.

    Why not use a 6V battery pack (4xAA) with a low dropout regulator.

    AA’s have about 5 times the capacity in mAh and a set of 4 is half the price of a AA (I buy my batteries at costco). So you end up with 10 times as many charges for the same price in batteries.

  6. Unlike alkaline AA’s, NiMH AA batteries are labeled for 1.2 V output. A set of four would then give 4.8 V.

    I assume a battery will lose some output strength as it drains, and there seems to be no real concern over this, so can four AA NiMH be used directly? Is 4.8V close enough?

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