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

Discussion in 'The Projects Forum' started by Daniel J Clark, May 16, 2016.

  1. Daniel J Clark

    Thread Starter New Member

    May 16, 2016
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    0
    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
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,433
    1,883
    Why do you need a 200Ω resistor?
    What do you think "charging within the USB spec" means?
    BTW, if you actually try to draw 3A @ +5V from a +12V input you will have to dissipate (12-5)*3 = 21 Watts. I think it is going to get awfully hot.
     
  3. Daniel J Clark

    Thread Starter New Member

    May 16, 2016
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    Oh and some more info...

    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. Daniel J Clark

    Thread Starter New Member

    May 16, 2016
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    Ah so I need like a current regulator?

    Re: 200-ohm resistor, because some of the threads I found said this was needed.
     
  5. Daniel J Clark

    Thread Starter New Member

    May 16, 2016
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    Specifically:

    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. hp1729

    Well-Known Member

    Nov 23, 2015
    2,236
    251
    How much current does the device usually draw? Electronic Goldmine often sells a USB plug-in meter that measures USB voltage and current. G21171, about $15.00 US, currently out of stock but it is a big seller and will likely return.
    http://www.goldmine-elec-products.com/prodinfo.asp?

    (edited to add ...)
    Alternate part number to G21171. This one is slightly different but is currently in stock as of 5/16/2016. If history repeats itself they won't stay in stock long.
    .
    G21309, about $10.00.
     
    Last edited: May 16, 2016
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,212
    1,827
    More than likely it's got a tiny switch mode buck regulator in it so the actual efficiency is probably in the 90% + range.
     
  8. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    165
    I could be wrong here but I thought the point of the limiting resistors was to tell the phone how much current the charger was able to supply .. I know apple and samsung vary the resistor based.on the avaible current .. I thought shorted or opened data pins meant the current was limited to 500ma max..
     
  9. Papabravo

    Expert

    Feb 24, 2006
    10,433
    1,883
    The business about chargers was not part of the USB specification 2.0 that I remember. This part is new to me. So is it a requirement of the charger, or is it a requirement of the device to be charged? AFAIK, any given USB port will provide up to 100 mA by default, and up to 500 mA if you can "negotiate" that with the host. Apparently there is additional functionality that has been added in the last decade.
     
  10. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,220
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    Yeah I can't really say cause I am new to usb and only have been reading usb specs for power and charging circuits ..I plan on making a power bank and 12v to 5v car charger..
     
  11. Daniel J Clark

    Thread Starter New Member

    May 16, 2016
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    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.

    And if that doesn't work Dr.killjoy reminded me I have a bunch of car USB chargers, I bet I could just open one up and use its circuit, although it'd need to get some plasti-dip or something to waterproof (just a resistor I can put in adhesive lined heat shrink tubing or marine goop) so would prefer to avoid that.
     
    Last edited: May 17, 2016
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