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Given a home made USB charger that simply provides 5 volts across the GND and VCC pins of a USB port, what should the default behavior be of any mobile device (mobile phone, tablet, iphone etc) plugged into that device. ('data +' and 'data -' left unconnected)

Will it...

  1. completely ignore the device (i.e. not charge at all)
  2. attempt to trickle charge very slowly at low current
  3. attempt to charge at a current of no more than 500ma
  4. attempt to charge at a current exceeding 500ma

I have read this but am no wiser.


marked as duplicate by Elliot Alderson, Ale..chenski, JRE, RoyC, pipe May 11 at 11:15

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    \$\begingroup\$ are you really interested in "what should" or are you interested in "what does the majority actually do"? \$\endgroup\$ – Marcus Müller May 4 at 13:52
  • \$\begingroup\$ Answers to either or both would be good! \$\endgroup\$ – ConanTheGerbil May 4 at 15:08
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    \$\begingroup\$ yeah, but what is the purpose of your question? as it is, the answer will be "any of 1-4, depends on your USB device and how the supply behaves under load", so I'm afraid this question would be too broad. What USB-compliant devices should be doing is try to ask for more than 150 mA, and failing to do so, not draw more. Nearly nobody does that. On the other hand, without some smarts that signal fast charging ability to the USB device, very few devices will try to draw a lot of current. Now, this simply sounds like "don't call a 5V voltage supply a "USB charger", because it's not", but I'm \$\endgroup\$ – Marcus Müller May 4 at 15:23
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    \$\begingroup\$ sure there is a story to your question, with a sensibly answerable question hidden beneath! \$\endgroup\$ – Marcus Müller May 4 at 15:23
  • \$\begingroup\$ Try to search for "charger signature", for example: electronics.stackexchange.com/q/130559/117785 and electronics.stackexchange.com/a/271681/117785 and \$\endgroup\$ – Ale..chenski May 4 at 15:50