Power rating on Laptop USB ports

Are all USB 2.0 ports on Laptops rated at 500ma?

I have several Freecom USB 2 drives that require a 500ma port - so they will
run without need of a power supply


thanks

Clive

Clive wrote:
> Are all USB 2.0 ports on Laptops rated at 500ma?

The USB spec says a root hub should supply 500mA. Empirically, many
portable machines do not supply this much.

Also, a 2.5" hard disk requires more than 500mA peak current to start
up. So bus-powered HDDs are almost always relying on being able to
squeak a brief pulse of 1.5 A or more out of the port before it shuts
down.

Clive wrote:
> Are all USB 2.0 ports on Laptops rated at 500ma?
>
> I have several Freecom USB 2 drives that require a 500ma port - so they will
> run without need of a power supply

The USB spec is 500mA, but in reality, the over-current trip limit is
usually set to 1000mA.

On Wed, 26 Jul 2006 20:23:25 -0700, SMS <> wrote:

>Clive wrote:
>> Are all USB 2.0 ports on Laptops rated at 500ma?
>>
>> I have several Freecom USB 2 drives that require a 500ma port - so they will
>> run without need of a power supply
>
>The USB spec is 500mA, but in reality, the over-current trip limit is
>usually set to 1000mA.

I'd believe that for desktop machines, but most laptops I've checked would crap
out at or before the spec 500mA.

budgie wrote:
> On Wed, 26 Jul 2006 20:23:25 -0700, SMS <>
> wrote:
>
>> Clive wrote:
>>> Are all USB 2.0 ports on Laptops rated at 500ma?
>>>
>>> I have several Freecom USB 2 drives that require a 500ma port - so
>>> they will run without need of a power supply
>>
>> The USB spec is 500mA, but in reality, the over-current trip limit is
>> usually set to 1000mA.
>
> I'd believe that for desktop machines, but most laptops I've checked
> would crap out at or before the spec 500mA.

This is one of the reasons that I use externally powered USB hubs to feed my
USB powered external hard drives when ever possible. They are cheap and
easy to replace should they crap out from an "overload".

<> wrote in message
news: oups.com...
>
> Clive wrote:
>> Are all USB 2.0 ports on Laptops rated at 500ma?
>
> The USB spec says a root hub should supply 500mA. Empirically, many
> portable machines do not supply this much.
>

Almost.

Paragraph 7.2.1 of the USB2 specification states that root ports *must*
supply 500 mA.

> Also, a 2.5" hard disk requires more than 500mA peak current to start
> up. So bus-powered HDDs are almost always relying on being able to
> squeak a brief pulse of 1.5 A or more out of the port before it shuts
> down.
>

If they are incapable of supplying 500 mA, then they are not compliant and
cannot claim to be USB2 (or USB1) compliant.

Para 7.2.4.1 requires a port to provide transient current suppression.
Transient currents must be available, but are only required to feed load
capacitances (which are limited). Further, any transient that causes Vbus
to depress by more than 330mV, must be signalled back to the host and the
device de-enumerated. A message about a current surge pops up. It is not
unkown for ports to be damaged by large surges (It shouldn't be a fuse
because these are not allowed (Para 7.2.1.2.1)).

"SMS" <> wrote in message
news:44c831b5$0$96210$...
> Clive wrote:
>> Are all USB 2.0 ports on Laptops rated at 500ma?
>>
>> I have several Freecom USB 2 drives that require a 500ma port - so they
>> will run without need of a power supply
>
> The USB spec is 500mA, but in reality, the over-current trip limit is
> usually set to 1000mA.

The upper limit is not explicitly specified other than an absolute limit of
5A for all the ports on a hub.

"budgie" <> wrote in message
news:...
> On Wed, 26 Jul 2006 20:23:25 -0700, SMS <> wrote:
>
>>Clive wrote:
>>> Are all USB 2.0 ports on Laptops rated at 500ma?
>>>
>>> I have several Freecom USB 2 drives that require a 500ma port - so they
>>> will
>>> run without need of a power supply
>>
>>The USB spec is 500mA, but in reality, the over-current trip limit is
>>usually set to 1000mA.
>
> I'd believe that for desktop machines, but most laptops I've checked would
> crap
> out at or before the spec 500mA.

Any laptop that cannot supply 500mA through its USB ports cannot claim to be
USB2 (or USB1) compliant (Para 7.2.1).

"GlowingBlueMist" <> wrote in message
news:44c85ce0$0$94252$ anews.com...
> budgie wrote:
>> On Wed, 26 Jul 2006 20:23:25 -0700, SMS <>
>> wrote:
>>
>>> Clive wrote:
>>>> Are all USB 2.0 ports on Laptops rated at 500ma?
>>>>
>>>> I have several Freecom USB 2 drives that require a 500ma port - so
>>>> they will run without need of a power supply
>>>
>>> The USB spec is 500mA, but in reality, the over-current trip limit is
>>> usually set to 1000mA.
>>
>> I'd believe that for desktop machines, but most laptops I've checked
>> would crap out at or before the spec 500mA.
>
> This is one of the reasons that I use externally powered USB hubs to feed
> my USB powered external hard drives when ever possible. They are cheap
> and easy to replace should they crap out from an "overload".

A wise precaution. Tne USB2 spec. requires the overload current limit to be
self resetting. However, anecdotal evidence suggests that ports sometimes
suffer failure following a current overload.

On Thu, 27 Jul 2006 08:14:45 +0100, "M.I.5¾" <_SPAM.co.uk>
wrote:

>
>"budgie" <> wrote in message
>news:.. .
>> On Wed, 26 Jul 2006 20:23:25 -0700, SMS <> wrote:
>>
>>>Clive wrote:
>>>> Are all USB 2.0 ports on Laptops rated at 500ma?
>>>>
>>>> I have several Freecom USB 2 drives that require a 500ma port - so they
>>>> will
>>>> run without need of a power supply
>>>
>>>The USB spec is 500mA, but in reality, the over-current trip limit is
>>>usually set to 1000mA.
>>
>> I'd believe that for desktop machines, but most laptops I've checked would
>> crap
>> out at or before the spec 500mA.
>
>Any laptop that cannot supply 500mA through its USB ports cannot claim to be
>USB2 (or USB1) compliant (Para 7.2.1).

They can *claim* compliance without actually being compliant. It's called
marketing, and has litlle to do with truth or fact.