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Electronics Circuit for charging Nimh batteries through USB?

Discussion in 'Modding' started by quizz_kid, 11 Jun 2013.

  1. quizz_kid

    quizz_kid Squid

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    Hi guys. I going to have two battery driven devices rechargable through USB, and could use some help. I guess I'll need a resistor between battery pack(+) and 5v(usb), but I don't know the calculations for ohm values.

    The first device uses 2xAA. What res value do I need for charging those with 5v? These are 2700mAh AAs

    The other device uses 3xAAA. Res value there? These are 1000mAh AAAs

    Of course it would be nice with a LED intergrated in the circuit somehow, an indication for charging. But this is not a must.

    //quizz
     
  2. Dudey109

    Dudey109 Minimodder

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    Pound land has usb AA/AAA chargers for ... a pound each
    Might be worth tearing one of those apart
     
  3. quizz_kid

    quizz_kid Squid

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    Can't seem to find them there...
     
  4. Dudey109

    Dudey109 Minimodder

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    I bought 1 a while back. It was behind the counter with the Battery's i had to ask for it. Not every store may stock them but ive seen them at a couple near here

    Jake
     
  5. quizz_kid

    quizz_kid Squid

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    OK. I live in Sweden, we don't have that store here. I just checked their web
     
  6. stuartwood89

    stuartwood89 Please... Just call me Stu.

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  7. Dudey109

    Dudey109 Minimodder

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    Ah sorry i didn't read your location assumed you were UK based, bit silly of me! Sorry

    Jake
     
  8. Andersen

    Andersen Brain for hire

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    "Charging Currect: 200MA"

    You'll be waiting five hours with AAA and ten hours for AA to charge. Find a charger that uses a wall-wart that puts out 12V and 1,5-2A. Cut the charger-side cable, dump the wart and add molex connector. If you want to be fancy, add a suitable socket in expansion slot cover where you plug the charger. Also add fast 2A in-line fuse for some short-circuit protection.

    My 50c fleamarket charger is like that and can charge four 2700mAh AAs in about 15 minutes. Yeah its overkill and kills the batteries in couple months but they are pretty cheap and I never have to curse at empty ones.
     
  9. quizz_kid

    quizz_kid Squid

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    Thanks, but the thing is that I need to charge them USB. I don't really care if it's 5-10 hrs. And I dont want to remove the batteries from the devices while charging, that's why I want to build a simple solution myself. Someone told me I could use a 20 ohm resistor for the 3xAAA setup. I'm not sure about the 2xAA though.

    Help is appreciated!
    /Quizz
     
  10. Tealc

    Tealc What's a Dremel?

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    Unless you have a always high current USB port or can find a way to negotiate with the USB controller you'll be stuck with 100mA of current from the USB port.

    You can pick up chargers for 2x AAs from eBay for a small fee and these'll charge around 100mA. Useful for an overnight charge. I haven't taken mine apart because it is heat sealed.

    The circuit inside will probably look something like this.

    http://stufinnis.co.uk/usbcharger.html
     
  11. quizz_kid

    quizz_kid Squid

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    Thanks a lot Tealc. I'm not very used to read schematics, but that one looks simple enough.

    So, is this what I'll need?

    1x 5.6 ohm res
    1x 270 ohm res
    1x bc635 transistor
    1x red LED


    So, does anyone knows how to make a similar circuit for 3xAAZ NiMHs?
     

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