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Max current from USB port?

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

What is the maximum current or power which the USB specs say can be
drawn from a USB port?
10 answers Last reply
More about current port
  1. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "Piotr Makley" <pmakley@mail.com> 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
  2. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "DCA" <MAPSdca860@MAPSntlworld.com> wrote:

    > "Piotr Makley" <pmakley@mail.com> 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?
  3. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "DCA" <MAPSdca860@MAPSntlworld.com> wrote in message
    news:tlNec.16$KC6.12@newsfe1-win...
    > "Piotr Makley" <pmakley@mail.com> 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
  4. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "Regal" <stua_NOTTHISBITsmith@yahoo.co.uk> wrote in message
    news:94CA76AF9A06D628D1@130.133.1.4...
    > "DCA" <MAPSdca860@MAPSntlworld.com> wrote:
    > > "Piotr Makley" <pmakley@mail.com> 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
  5. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "Alex" <me@privacy.net> 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?
  6. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    On Wed, 14 Apr 2004 16:03:22 GMT, Piotr Makley <pmakley@mail.com> wrote:

    >"Alex" <me@privacy.net> 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.
  7. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "Alex" <me@privacy.net> wrote:
    >"DCA" <MAPSdca860@MAPSntlworld.com> wrote in message
    >news:tlNec.16$KC6.12@newsfe1-win...
    >> "Piotr Makley" <pmakley@mail.com> 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.
  8. Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

    "Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
    news:o5pq70lh2lct7aejahh8sjlfg72at6d74o@4ax.com...
    > "Alex" <me@privacy.net> wrote:
    > >"DCA" <MAPSdca860@MAPSntlworld.com> wrote in message
    > >news:tlNec.16$KC6.12@newsfe1-win...
    > >> "Piotr Makley" <pmakley@mail.com> 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
  9. I found some USB powered Wi-Fi for long range use 1 amp for its current ratings. I was wondering if it would burn my motherboard due to its over current flow. since think USB voltage rating is 5 Volts.
    hence the power required will be 5 Watts. Can a laptop motherboard handle this huge amount of power, outside its h/w?
    I know the lower limit has no value, what is important is what power or current it sucks form the 5 Volts USB.
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