Off-Topic: question about usb-hub power

[Uffe Jakobsen]

On 2011-07-21 14:55, Mehmet Erol Sanliturk wrote:
>
>
> On Thu, Jul 21, 2011 at 7:12 AM, Uffe Jakobsen <uffe at uffe.org
> <mailto:uffe at uffe.org>> wrote:
>
>     Apologies if this is a kind of off-topic for this list - since it
>     does not have anything to do with FreeBSD.
>
>     The external USB-hubs (v2.0) that I've come across comes in two
>     categories:
>
>     Some are willing to deliver power (500mA pr. connector) even if the
>     hub isn't connected to a computer - and some that doesn't do this -
>     the hubs that I have purchased from Dlink falls into the last category.
>
>     I looking for an USB hub that is willing to deliver power without it
>     beeing connected to a computer in order to drive some external units
>     - no it is not a mobile-phone ;-)
>
>     Could anyone give me a hint what specs to look for ? - before I
>     actually buy another hub - the Dlink ones were not a success...
>

>
> I do not know whether the above answer is correct for you or not .
>

Hi Mehmet,

Thanks for your answer - it has revealed that my initial inquiry was 
quite inaccurate - my apologies for that.

I'll try to fill out the gaps.

The product I'm referring to is a Dlink DUB-H7 
(http://www.dlink.com/products/?pid=149). A standard USB 2.0 hub with 7 
ports that can be powered from an external power supply.

I do know how to determine if there is power on an usb connector (pins 
1+4) - also I know the math involved in making sure that the hub is not 
overloaded - but that it not really the issue here.

This usb-hub will (apparently like so many other usb-hubs) only apply 
power to its connectors if it is connected to a computer (that is 
running) - and that applies even if the external power supply is 
connected to the usb-hub.

Let me give you an example:
You want to charge your mobile phone but you haven't brought the charger 
itself. You've only got the micro-usb cable for the mobile phone and the 
above mentioned Dlink hub - also you've got no computer at hand.
Now connecting the mobile phone to the usb-hub while the usb-hub is 
connected to the external power supply will not make the mobile phone 
start charging. This will only happen once you connect the "uplink" usb 
cable from the usb-hub and to a computer and boot it up.

Let me add here that this has nothing to do with the complexity and 
internal logic of the mobile phone mobile phone and its software - it 
could be any other device that can drain its power from an usb cable.

I've previously owned an usb hub that would deliver power without beeing 
connected to a running computer - but unfortunately that was lost during 
relocation - and I do not remember the model/brand.

Now I realize that this functionality is a part of the usb standard - 
and that leads to my original question:

It there anyway to determine this habit without unpacking and testing 
every the usb-hub ?

Kind regards Uffe