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DIY micro-usb phone charger with high current - not working?

Discussion in 'General Electronics Discussion' started by moeburn, Sep 17, 2012.

  1. moeburn

    moeburn

    41
    0
    Jun 25, 2012
    So I noticed that all my different micro-usb wall-wart chargers are all 5v, but they all have different current ratings. My charger rated at 5v/1.2A (theoretically) charges my phone twice as fast as my 5v/600mA charger.

    So I decided to do away with them all and make my own super-charger out of a large 5v/2A wall wart and a spare micro-usb cable I had kicking around. I just soldered the v+ and gnd of the wall wart to the red and black wires in the usb cable. Then I plugged the wall-wart in, got some very needle-pointed leads for my voltmeter, and checked the voltage between pins 1 and 5 (v+ and GND) on the micro-usb plug, and sure enough, it read +5.1v. I tested another charger I had lying around, and it also read +5.1v. My computer's USB port read +4.8v. These are all unloaded measurements on a $10 DMM, but they're accurate enough to know that my DIY charger is outputting a voltage within the appropriate range.

    So when I plug it into my phone to charge it, nothing happens. My phone is not charging. Unfortunately I don't have any other micro-usb devices to test it on. I thought maybe there is some proprietary internal circuitry in my phone's charger that is different from a normal micro-usb cable, but my phone is compatible with EVERY micro-usb charger that I own, except for the one I just made myself.

    Anyone have any experience with micro-usb that would be willing to shed some light on this would be greatly appreciated!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,214
    2,695
    Jan 21, 2010
    Your phone may require some "magic" connections in order to tell it to (a) charge, and (b) how fast to charge.

    But most importantly, the phone will only charge at the rate at which it wants to charge. Notwithstanding the fact that the charger may specify (via the before-mentioned "magic") the current it can supply, there will be some maximum that the phone can charge at. If the phone is incapable of using a higher current, it just is.
     
  3. moeburn

    moeburn

    41
    0
    Jun 25, 2012
    Thanks for your help!

    I thought of that, but I figured that since it seemed to work with even the cheapest dollar store ac-to-microUSB chargers, that it shouldn't be expecting any proprietary circuitry from the charger. But maybe all micro-USB chargers are a little more complicated than simply wiring VCC to VCC and GND to GND?

    Well yeah I know there's some maximum current that the phone will draw no matter how much my charger can supply, but that maximum appears to be higher than any chargers I currently own, so I figured I'd try to make one out of a 2A wall wart.
     
    Last edited: Sep 18, 2012
  4. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    You need to know the value of resistor connected between pin2 and pin3 of your working charger. Then install same value in your "charger". You can experiment changing value of resistor to increase charging current.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,214
    2,695
    Jan 21, 2010
    if you know the make and model of your phone, you can google for information.
     
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