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Thread: DIY external battery USB charger

  1. #1
    Join Date
    Jul 2012

    Default DIY external battery USB charger

    Hi, I'm trying to do a small diy project but I have very minimal to no knowledge in electric circuitry.

    I'm basically trying to make an external battery pack for my phone. My phone's battery is rated at 3.7v and I plan to use the same type of battery for my external pack. The basic idea is that my external battery would be rechargeable via USB from one end of the pack. The other end would be the cable that connects to my phone. The pack would be able to charge the phone when the external battery has a charge and is not connected to a power source as well as being able to charge the phone even with a depleted battery when the pack is connected to a USB power source.

    If any of you are familiar with electronic cigarette passthroughs, it's basically the same idea. Or basically a USB charging cable with a rechargeable battery stuck in the middle. It would function like a normal USB charging cable when attached to a power source and an external battery pack when not.

    Is it as simple as connecting the USB wires to some sort of current regulator which converts the 5V current to the needed 3.7V, have that regulator connected to the battery and connect the phone's wires to the battery as well. Logically, it seems like everything should be connected in this sort of fashion. Current from a USB source would travel into the regulator, then travel into the battery then travel back out through the other cable to charge the phone. When not connected to a power source, current from the battery would travel to the phone. But since I have no knowledge in this field, I'm certain I'm missing something.

    I'm also wondering if it would be possible to print this sort of current regulator on a flexible circuit board. I would like this device to be as thin and small as possible.

    Any input and advice as to how to go about building this would be greatly appreciated.
    Thank You.

  2. #2
    Retired Administrator Norm's Avatar
    Join Date
    Jun 2006

    Default Re: DIY external battery USB charger

    This thread maybe of interest : Really cheap true cc/cv usb charging board .


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