Power capabilities of USB 3.0 vs 2.0?

08
2014-07
  • Naftuli Tzvi Kay

    I'm currently buying some new USB micro cables for my Samsung Galaxy S5. It supports both USB 2.0 micro and USB 3.0 micro connectors.

    Will I see better charging times when using the USB 3.0 cable connected to a wall charger vs. a USB 2.0 cable? I would assume not, but I'm not sure. AFAIK, not too many things draw any more than 2A.

    • Answers
  • tapped-out

    Theoretically, you shouldn't, since wall chargers can supply the same amount of current over a USB 2.0 cable as a USB 3.0 cable.

    However, you might see a difference in difference in charging times due to the electrical properties of the cables. Because the USB 3 spec calls for a higher maximum current than USB 2 (950 mA vs. 500), it stands to reason that USB 3 cables will be better constructed and thus able to conduct higher amounts of current than run-of-the-mill USB 2 cables. See this Reddit thread for more information.


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    USB to power other devices
  • Tester101

    I have a small desk fan that is currently powered by 4 AA bateries, I have measured the voltage output and it is 5.5VDC which got me thinking. Is it safe to modify the fan to run off a USB port on my PC?

    I'm not sure if the fan draws more than 100mA, but it is my understanding that USB will only allow me to draw 100mA by default anyway. Is this correct, or could my fan draw too much power?

    I also read this

    A dedicated charger can supply maximum 1.8 A of current. A portable device can draw up to 1.8 A from a dedicated charger. The dedicated charger shorts the D+ and D- pins together disabling data transfer and will not send or receive any information, allowing very simple, high current chargers to be manufactured. The increased current (faster charging) will occur once the host/hub and devices both support the new charging specification.

    Is this supported by USB 2.0, or will this not be supported until 3.0?

    should I short the data wires in my case or just leave them disconnected?


    • Related Answers
  • hanleyp

    The USB 2.0 specification allows up to 0.5A of current draw from the 5V pin from each port. You can leave the D+ and D- wires unconnected, just connect power and ground.

  • 8088

    You can use a USB Y cable to draw more power. They're commonly used for portable hard drives and DVD burners, requiring more power than can be provided by a single USB port.

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