Max current from USB port?

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What is the maximum current or power which the USB specs say can be
drawn from a USB port?
 
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"Piotr Makley" <pmakley@mail.com> wrote in message
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| What is the maximum current or power which the USB specs say can be
| drawn from a USB port?

500mA I believe
 

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"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?
 

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"DCA" <MAPSdca860@MAPSntlworld.com> wrote in message
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> "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
 

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"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
 
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"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?
 
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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.
 
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"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.
 

alex

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"Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
news:eek:5pq70lh2lct7aejahh8sjlfg72at6d74o@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
 

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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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