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Has anyone actually measured the maximum amount of power that can be drawn from a smartphone's (say Samsung S4) USB OTG in host mode?

I've read people suggest 100mA but can't find if anyone has actually tested it. I have seen it work with a keyboard, mouse and both keyboard & mouse but these are only around 50mA.

If I need say 1W for 2 minutes, is there any way to make it possible (without the use of additional batteries)?

as_yu_like_it
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    If you can store energy you can power a boiler... It would take some time. Just explain what you have in your mind so that we can help you. – Vladimir Cravero May 05 '14 at 07:52
  • Hi Vladimir, thanks. I meant no batteries. But other components say capacitor is ok. – as_yu_like_it May 05 '14 at 12:26
  • Well 1W for two minutes is 120J, at 5Vdc that's 6000F. You will need to go up in voltage, and then back down. – Vladimir Cravero May 05 '14 at 12:38
  • That's a massive capacitor! Is there any other options (that's smaller & low cost)? – as_yu_like_it May 05 '14 at 12:44
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    Yes, step up voltage, charge a smaller cap, step it back down. But that's not trivial nor small... please tell us exactly what you're trying to accomplish. – Vladimir Cravero May 05 '14 at 12:46
  • I made an error that's 9.6F, quite big anyway. – Vladimir Cravero May 05 '14 at 13:34
  • I am trying to use a smartphone as power source to a uvc lamp. Something small and compact for travel but need more power for the lamp. – as_yu_like_it May 05 '14 at 14:16
  • It's not solving your question as you asked it, but since you're willing to power this from USB, maybe consider looking into USB battery packs. They're essentially lithium polymer batteries with a support circuit to charge off USB and output USB. They're pretty cheap, and have a much higher capacity than most smartphones. Checking the one in my pocket, we're sitting at 5000mAh with 5V, 1.5A maximum ratings. – Jason_L_Bens May 16 '14 at 02:09
  • Hi Phox, thanks for the comment. That's a good suggestion. Could be a fall back/stop gap option. Much appreciated. :) – as_yu_like_it May 17 '14 at 08:56

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