USB power charging station

Discussion in 'The Projects Forum' started by bert123, Nov 15, 2010.

  1. bert123

    Thread Starter New Member

    Nov 15, 2010
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    Hi guise,
    Building a USB charging station. Will be using ExpressPCB/ EXpress SCH.
    How would I get started on this? What are the names of the components I need to put in the schematics? I know I'll need USB inputs and the a/c power source to name a few...
    I'm starting this from scratch with little electrical engineering experience. Thanks!
     
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    You can buy USB chargers for almost nothing.
     
  3. bert123

    Thread Starter New Member

    Nov 15, 2010
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    great, but this is for the hands on expereince!
    I need a hub that can charge 20 USB devices.
     
  4. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Who has 20 USB devices that need charging?
    1 Phone
    2 MP3 player

    What else?
     
  5. bert123

    Thread Starter New Member

    Nov 15, 2010
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    It's for charging 100 mp3 players...but either way...I want some hands on EE experience. This should be fun...
     
  6. bert123

    Thread Starter New Member

    Nov 15, 2010
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    It's a simple project for myself..I'm just fishing for some good guidance.
     
  7. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    A typical USB port is 5V @ 100mA to 500mA
    A 500mA PTC fuse on each USB's +5v rail should keep bad things to a minimum. A switch mode 5v wall wart would work but you'll need at least 2A for 20 devices.
    Some USB devices may not charge on such a simple charger (iPhone iPad come to mind)
    Build a single port prototype and see if it works.
     
  8. bert123

    Thread Starter New Member

    Nov 15, 2010
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    Thanks for replying. The particular device I have in mind runs at 250mA max. So then i should need about 5A. We shouldn't worry about different devices being charged on this hub, it is being specifically built for a specific device.
    Can you please define wall wart?
     
  9. blueroomelectronics

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    Jul 22, 2007
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  10. bert123

    Thread Starter New Member

    Nov 15, 2010
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    Excellent, thank you. Where would be a good place to start for designing the schematic? I'm unfamiliar with the ExpressSCH program and the component names.
    I'm guessing that a USB would be a 4 pin connector component? And what would be the name for the power component?
    It would seem I would have to design a circuit that is parallel.
     
  11. wayneh

    Expert

    Sep 9, 2010
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    You can find online the pinouts for the various USB connectors. If all you need is power (nothing on the data pins), this will be two of the 4 pins, and that'll be all you need to worry about. On the standard female USB port on a computer, the two pins on opposite ends provide 5v to whatever is plugged in. Current is limited to 100mA without an active negotiation, although I've heard this may be weakly implemented. Meaning more current might be available without a handshake Anyway, a regulated 5v DC supply (for instance a 7805 IC regulator) can be used to act as a USB power supply. Just put the right voltage onto the right pins, and you're good.

    Many iPods require a pull-up and a pull-down resistor on the two data pins in order to initiate charging.
     
  12. bert123

    Thread Starter New Member

    Nov 15, 2010
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    Thank you for replying.
    So for designing the schematic in ExpressSCH, will I need any capacitors for this kind of board? If so, how do I determine how many capacitors I will need?
     
  13. wayneh

    Expert

    Sep 9, 2010
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    No one can answer this without more detail on your supply and approximate design. The datasheets for the linear regulators such as the 7805 recommend a small cap on both the input and the output. You don't need big filtering caps, especially for battery charging, since the battery itself is a giant capacitor.
     
  14. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Don't use a linear regulator, it's wasteful for that kind of current. Use the type of supply I posted earlier. Also don't forget the PTC fuses.
     
  15. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If you use the 5A @5V regulated wall wart to start with, it would be a matter of making a +V bus and GND bus, and connecting all of the ports to that bus, with each port having a 500mA PTC fuse inline, as well as a 0.1uF and possibly a 10uF capacitors across the lines for each port to prevent a bad device from messing up the rest of the charging ports from too much current or by noise on the power bus. It'd be best done with a dual sided board, one side ground, other side power and individual lines with fuses and caps for each port.
     
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