Max current from USB port?

Discussion in 'DIY PC' started by Piotr Makley, Apr 12, 2004.

  1. Piotr Makley

    Piotr Makley Guest

    What is the maximum current or power which the USB specs say can be
    drawn from a USB port?
     
    Piotr Makley, Apr 12, 2004
    #1
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  2. Piotr Makley

    DCA Guest

    "Piotr Makley" <> wrote in message
    news:94C9D878D1A1A31E75@130.133.1.4...
    | What is the maximum current or power which the USB specs say can be
    | drawn from a USB port?

    500mA I believe
     
    DCA, Apr 13, 2004
    #2
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  3. Piotr Makley

    Regal Guest

    "DCA" <> wrote:

    > "Piotr Makley" <> wrote in message
    > news:94C9D878D1A1A31E75@130.133.1.4...
    >| What is the maximum current or power which the USB specs say
    >| can be drawn from a USB port?
    >
    > 500mA I believe


    ISTR that USB is at 5v so that is about 2.5 Watts.

    Do you know what the figure is for Firewire?
     
    Regal, Apr 13, 2004
    #3
  4. Piotr Makley

    Alex Guest

    "DCA" <> wrote in message
    news:tlNec.16$KC6.12@newsfe1-win...
    > "Piotr Makley" <> wrote in message
    > news:94C9D878D1A1A31E75@130.133.1.4...
    > | What is the maximum current or power which the USB specs say can
    > | be drawn from a USB port?
    >
    > 500mA I believe


    Or 100mA for:

    - a downstream port on a bus-powered hub,
    - a port on a root port hub on a battery-powered system (possibly), or
    - a downstream port on a battery-powered self-powered hub (possibly).

    And, as noted by another poster, this is at 5V, so the maximum power is 2.5W
    (500mA) or 500mW (100mA).

    Alex
     
    Alex, Apr 14, 2004
    #4
  5. Piotr Makley

    Alex Guest

    "Regal" <> wrote in message
    news:94CA76AF9A06D628D1@130.133.1.4...
    > "DCA" <> wrote:
    > > "Piotr Makley" <> wrote in message
    > > news:94C9D878D1A1A31E75@130.133.1.4...
    > >| What is the maximum current or power which the USB specs say
    > >| can be drawn from a USB port?
    > >
    > > 500mA I believe

    >
    > ISTR that USB is at 5v so that is about 2.5 Watts.
    >
    > Do you know what the figure is for Firewire?


    1.25A at 12V; 15W.

    Alex
     
    Alex, Apr 14, 2004
    #5
  6. Piotr Makley

    Piotr Makley Guest

    "Alex" <> wrote:

    >> >| What is the maximum current or power which the USB specs
    >> >| say can be drawn from a USB port?
    >> >
    >> > 500mA I believe

    >>
    >> ISTR that USB is at 5v so that is about 2.5 Watts.
    >>
    >> Do you know what the figure is for Firewire?

    >
    > 1.25A at 12V; 15W.



    So you could power devices needing far more power on Firewire than
    on USB?
     
    Piotr Makley, Apr 14, 2004
    #6
  7. Piotr Makley

    Tim Auton Guest

    "Alex" <> wrote:
    >"DCA" <> wrote in message
    >news:tlNec.16$KC6.12@newsfe1-win...
    >> "Piotr Makley" <> wrote in message
    >> news:94C9D878D1A1A31E75@130.133.1.4...
    >> | What is the maximum current or power which the USB specs say can
    >> | be drawn from a USB port?
    >>
    >> 500mA I believe

    >
    >Or 100mA for:
    >
    >- a downstream port on a bus-powered hub,
    >- a port on a root port hub on a battery-powered system (possibly), or
    >- a downstream port on a battery-powered self-powered hub (possibly).


    - a port which doesn't think it's talking to anything (according to
    the spec anyway, in reality you can often get 500mA or more just by
    hooking up to the power lines).


    Tim
    --
    Love is a travelator.
     
    Tim Auton, Apr 14, 2004
    #7
  8. Piotr Makley

    Alex Guest

    "Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
    news:blush:...
    > "Alex" <> wrote:
    > >"DCA" <> wrote in message
    > >news:tlNec.16$KC6.12@newsfe1-win...
    > >> "Piotr Makley" <> wrote in message
    > >> news:94C9D878D1A1A31E75@130.133.1.4...
    > >> | What is the maximum current or power which the USB specs say can
    > >> | be drawn from a USB port?
    > >>
    > >> 500mA I believe

    > >
    > >Or 100mA for:
    > >
    > >- a downstream port on a bus-powered hub,
    > >- a port on a root port hub on a battery-powered system (possibly), or
    > >- a downstream port on a battery-powered self-powered hub (possibly).

    >
    > - a port which doesn't think it's talking to anything (according to
    > the spec anyway, in reality you can often get 500mA or more just by
    > hooking up to the power lines).


    True, but in normal operation this is a temporary state of relevance only to
    developers of USB devices. And maybe hubs... are they supposed to limit the
    current?

    Alex
     
    Alex, Apr 14, 2004
    #8
  9. Piotr Makley

    kony Guest

    On Wed, 14 Apr 2004 16:03:22 GMT, Piotr Makley <> wrote:

    >"Alex" <> wrote:
    >
    >>> >| What is the maximum current or power which the USB specs
    >>> >| say can be drawn from a USB port?
    >>> >
    >>> > 500mA I believe
    >>>
    >>> ISTR that USB is at 5v so that is about 2.5 Watts.
    >>>
    >>> Do you know what the figure is for Firewire?

    >>
    >> 1.25A at 12V; 15W.

    >
    >
    >So you could power devices needing far more power on Firewire than
    >on USB?


    Not necessarily. Sometimes it supplies NO power whatsoever, like on a
    laptop with only 4 pin, not 6 pins. Other times it may supply less than
    the 1.25A, perhaps only 400mA... don't remember if there's a lower limit
    to how much it "must" supply if it supplies *any* power. It may be best
    to always use an external power source whenever possible.
     
    kony, Apr 14, 2004
    #9
  10. Piotr Makley

    Tim Auton Guest

    "Alex" <> wrote:
    >"Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
    >news:blush:...
    >> "Alex" <> wrote:
    >> >"DCA" <> wrote in message
    >> >news:tlNec.16$KC6.12@newsfe1-win...

    [USB max current]
    >> >> 500mA I believe
    >> >
    >> >Or 100mA for:

    [...]
    >> - a port which doesn't think it's talking to anything (according to
    >> the spec anyway, in reality you can often get 500mA or more just by
    >> hooking up to the power lines).

    >
    >True, but in normal operation this is a temporary state of relevance only to
    >developers of USB devices. And maybe hubs... are they supposed to limit the
    >current?


    It's not totally irrelevant to us consumers though, as there are an
    increasing number of USB-powered phone chargers and the like. AFAIK,
    most don't bother talking to the USB host, they just suck power.

    No idea about hubs.


    Tim
    --
    Love is a travelator.
     
    Tim Auton, Apr 14, 2004
    #10
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