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Max current from USB port?

 
 
Piotr Makley
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      12th Apr 2004
What is the maximum current or power which the USB specs say can be
drawn from a USB port?
 
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DCA
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      13th Apr 2004
"Piotr Makley" <(E-Mail Removed)> 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


 
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Regal
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      13th Apr 2004
"DCA" <(E-Mail Removed)> wrote:

> "Piotr Makley" <(E-Mail Removed)> 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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Alex
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      14th Apr 2004
"DCA" <(E-Mail Removed)> wrote in message
news:tlNec.16$KC6.12@newsfe1-win...
> "Piotr Makley" <(E-Mail Removed)> 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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Alex
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      14th Apr 2004
"Regal" <(E-Mail Removed)> wrote in message
news:94CA76AF9A06D628D1@130.133.1.4...
> "DCA" <(E-Mail Removed)> wrote:
> > "Piotr Makley" <(E-Mail Removed)> 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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Piotr Makley
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      14th Apr 2004
"Alex" <(E-Mail Removed)> 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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Tim Auton
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      14th Apr 2004
"Alex" <(E-Mail Removed)> wrote:
>"DCA" <(E-Mail Removed)> wrote in message
>news:tlNec.16$KC6.12@newsfe1-win...
>> "Piotr Makley" <(E-Mail Removed)> 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.
 
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Alex
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      14th Apr 2004
"Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
news(E-Mail Removed)...
> "Alex" <(E-Mail Removed)> wrote:
> >"DCA" <(E-Mail Removed)> wrote in message
> >news:tlNec.16$KC6.12@newsfe1-win...
> >> "Piotr Makley" <(E-Mail Removed)> 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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kony
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      14th Apr 2004
On Wed, 14 Apr 2004 16:03:22 GMT, Piotr Makley <(E-Mail Removed)> wrote:

>"Alex" <(E-Mail Removed)> 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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Tim Auton
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      14th Apr 2004
"Alex" <(E-Mail Removed)> wrote:
>"Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
>news(E-Mail Removed)...
>> "Alex" <(E-Mail Removed)> wrote:
>> >"DCA" <(E-Mail Removed)> 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.
 
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