Off-Topic: question about usb-hub power

[Mehmet Erol Sanliturk]

On Thu, Jul 21, 2011 at 9:50 AM, Uffe Jakobsen <uffe at uffe.org> wrote:

>
>
> 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
>
>
>




>From the Wikipedia page

http://en.wikipedia.org/wiki/USB_hub :

"However, there are many non-compliant hubs on the market which announce
themselves to the host as self-powered despite really being bus-powered ."


It seems that the above unit is NOT using the power supply .


One way to learn a suitable model is that one of the subscribers of this
list knowing that will answer over time .

Personally I do not know . <-------- Forget this , please :


I have a


Targus 7-port Hub
USB 2.0 Desktop Hub with a AC Adapter
Barcode : 5 024442 863608
( ACH82EU )


Targus Europe Ltd.

http://www.targus.com/uk/

In that site , search


Targus 7-Port USB Desktop Hub



My unit is different than the above as model number . Therefore I can not
say that they are exactly equivalent , but my expectation is that they will
be similar with respect to power delivery to pins .

I have measured voltage across pins 1 and 4  just only it is connected to AC
power line ( without any connection to any computer , even USB connection
cable is not plugged ) .


It is giving 5.00 volts between these two pins . I checked by reverse
measuring ( to see effect of sign ) . It is giving either 5.00 or -5.00
volts when measuring pins are reversed .

It is very likely that you will be able to find that model .


Unfortunately , within product definition documents , mostly there is no any
clue about your question .


Another very simple test may to use a USB light .
In computer shops it is very likely that it is possible to find "open" units
for inspection by customers .

Attach a USB light such as

http://www.amazon.com/Portable-Flexible-Light-Laptops-Notebooks/dp/B002WI8GG8/ref=sr_1_1?ie=UTF8&qid=1311265897&sr=8-1

If it gives light , means that pins are receiving power directly from AC
power supply .


My knowledge is so much .


Thank you very much .


Mehmet Erol Sanliturk