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Dumb USB Charger - Just 5v DC & 200 ohm resistor on +?

Discussion in 'General Electronics Discussion' started by Daniel Clark, May 16, 2016.

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  1. Daniel Clark

    Daniel Clark

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    0
    May 16, 2016
    Sorry for such a basic question but I've searched for like half an hour and haven't found anything that looked 100% definitive.

    I have a 12v DC power source, and then a voltage converter to 5v DC from eBay with these specs:
    • Non-isolated
    • Input voltage range: DC 8~23v
    • Output voltage: DC 5V
    • Output current: Max. 3A
    • With overload/over-current protection
    • With over/low voltage protection
    • Stable performance.
    To charge do I need to do anything other than place a 200-ohm resistor between the 5v DC positive lead and the 5v positive wire of the USB cable?

    Is there a way to test that the supply is charging within the USB spec (without an oscilloscope or other higher end stuff) before deployment?

    Thanks for any help,
    -Danny
     
    Last edited: May 16, 2016
  2. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Welcome to EP Daniel.
    What USB standard are you talking about?
    There are a few already, and they are evolving and changing in many ways.
    What are you going to use the USB for?
    Look here for details
     
  3. Daniel Clark

    Daniel Clark

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    0
    May 16, 2016
    It's charging a little basically old-school pocket organizer device called a Ben Nanonote.

    The Nanonote uses a Seaward Electronics SE9016 Standalone Linear Lithium Battery Charger Integrated Circuit. (their page) (datasheet).

    It has a USB 2.0 Mini port.
     
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    As long as the device was designed to charge from a USB port, there should be no resistor. Where did you get the idea there should be?

    Bob
     
  5. Daniel Clark

    Daniel Clark

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    0
    May 16, 2016
    Several threads I found. Just google "usb charger 200 ohm resistor" - this is from one thread post:

    Many cheap/generic USB chargers have not done this, and the detection of a short (up to 200ohm) between D+ to D- tells the phone "this is a charging device, so you can take full current" rather than the phone trickle charging only from the charger (in my case... and the phone battery runs down faster than it takes from the charger without that short). See the USB wiki, particularly the charging section: http://en.wikipedia.org/wiki/Universal_Serial_Bus#Power
     
  6. Daniel Clark

    Daniel Clark

    8
    0
    May 16, 2016
    Although actually, this device will just be plugged in all the time, so I guess I don't actually need the 200-ohm resistor - yay less parts to waterproof (will be buried underground) :)
     
  7. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    These are not the same thing. The 200Ω resistor referred to in the second post is between the two data lines of the USB connector, not between the + power and the connector. And even then, this is not the way charging current is usually signalled, More often the device looks for certain voltage on the D+ and D- lines and you need 4 resistors to set it up, and their values depend on what device you are trying to charge.

    Bob
     
  8. Daniel Clark

    Daniel Clark

    8
    0
    May 16, 2016
    So so far it sounds like it is safe to just try 5v on the P(ower)+ and P(ower)- lines, and then if the device doesn't charge try the 200-ohm resistor shorting the D(ata)+ and D(ata)- lines, and if that doesn't work look into the 4-resistor thing.
     
  9. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    It will charge with nothing on the data lines. This is what happens when you plug it into the USB port on a computer. But it will pull a max of 500mA. I charge my iPhone from my computer USB port instead of the 2A charger they provide, just because it is handy.

    Bob
     
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