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Would commodity usb cables and ports survive an over-standard voltage and current?

  1. Apr 21, 2012 #1
    would commodity usb cables and ports survive an over-standard voltage and current??

    suppose we want to make an adapter to power a gadget that require more voltage and power than what is allowed by the USB standard. But, suppose we try to use off-the-shelf USB cable in the above-standard demanding gadget and a USB port where that cable would plug in in the adapter. (For safety purposes maybe we would find a cheap way to slightly alter the "hyper usb plug" and "hyper usb port" so that they would mechanically refuse to interoperate with regular ones, but this is off topic for this question).

    Well, so would the usb cable and port survive usage at higher voltage and current? If we did empirical tests on cables and ports from various manufacturers at let's say 8V and 0.7A, should we expect to find at least some that would work fine, or are they explicitly limited according to the standard and so would melt or something like that?
     
  2. jcsd
  3. Apr 21, 2012 #2
    Re: would commodity usb cables and ports survive an over-standard voltage and current

    I just happen to have hacked up a USB cable and the wires look to be around .015" diameter conductor with about .010" of insulation.

    According to this nice wire table:
    http://www.powerstream.com/Wire_Size.htm
    #24 is .020" and good for .5A in power transmission mode, which matches the USB spec so maybe it's #24. By pushing your luck and calling it "chassis wiring" you could get up to 3.5A...

    Then I found a "spec" for telephone wiring, which is maybe sorta like the USB wire:
    http://www.spsx.com/uploadedFiles/Communications_Cable/Docs/PDF/Tech-Guidelines/TG31-Telephone-WireCable.pdf [Broken]
    This indicates that 300v between adjacent conductors is the most one can hope.

    So you are probably well within your rights to ask for 8v and .7A out of most any cable...YMMV when taking advice from the internet however...
     
    Last edited by a moderator: May 5, 2017
  4. Apr 21, 2012 #3
    Re: would commodity usb cables and ports survive an over-standard voltage and current

    I'm pretty sure USB cables can tolerate much higher voltages and current than the nominal 500 mA for USB 2.0 and 900 mA for USB 3.0. To reach the breakdown voltage of the dielectric used in the cable you would probably have to apply more than 200 V...

    However the ports are much less tolerant. Applying a voltage of more than the nominal 5.25 V to a USB port may damage it permanently. But drawing an excessive current out the port is generally not a problem. I've not tested it, but I heared that USB ports are designed to simply shutdown when their power pins are shorted. Once the computer is rebooted everything comes back to normal.
     
  5. Apr 21, 2012 #4
    Re: would commodity usb cables and ports survive an over-standard voltage and current

    schip666!, thanks for the interesting info.

    LotusEffect, yeah, I understand that demanding more power out of an adapter that doesn't feel like giving it (like usb port in laptop) is not a good idea. But my question was predicated on having my own custom adapter that happens to use USB components because they are nice, off-the-shelf available components. So based on what schip666! says, sounds like it's doable.
     
  6. Apr 22, 2012 #5
    Re: would commodity usb cables and ports survive an over-standard voltage and current

    The cables generally would do fine; it's the IC electronics they are connected to that will have the problem.
     
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