Date: Thu, 21 Jul 2011 08:55:42 -0400 From: Mehmet Erol Sanliturk <m.e.sanliturk@gmail.com> To: Uffe Jakobsen <uffe@uffe.org> Cc: freebsd-usb@freebsd.org Subject: Re: Off-Topic: question about usb-hub power Message-ID: <CAOgwaMt9pKNujjiUHhoutBHstLKqCuo=xqNUV24hzyC6t8s1hg@mail.gmail.com> In-Reply-To: <4E280986.8020701@uffe.org> References: <4E280986.8020701@uffe.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, Jul 21, 2011 at 7:12 AM, Uffe Jakobsen <uffe@uffe.org> wrote: > > > Hi, > > 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... > > Thanks in advance. > > Kind regards Uffe Jakobsen > > > For me . it is difficult to understand your question . Any links to actual products in such questions may clarify the subject matter very much . In market , there are mainly two kinds of USB hubs : - without power supply , mostly up to four ports or less : Example : http://www.amazon.com/Connectland-CL-U2MNHUB-4B-Ports-V2-0-Black/dp/B0028Y4F4S/ref=sr_1_3?ie=UTF8&qid=1311251176&sr=8-3 - with power supply , mostly with more than four ports : Example : http://www.amazon.com/Black-Ports-Speed-Power-Adapter/dp/B00475WJEY/ref=sr_1_9?ie=UTF8&qid=1311250656&sr=8-9 If you need power in ports even it is NOT connected to a computer or there is no power from the computer ( it is switched off ) , you need at least a power supply powered USB hub . Also , the following page contains explanations about power in USB hubs : http://en.wikipedia.org/wiki/USB_hub http://en.wikipedia.org/wiki/Category:USB http://en.wikipedia.org/wiki/USB To understand whether a hub is delivering power to ports when it is not connected to the computer or the computer is switched of , you may measure voltages in its port pins ( 1 and 4 ) by powering the hub by its power supply only : If there is NO voltage , the power supply is bogus ( or eye painting ) . If there is sufficient voltage it means that the hub is powering its ports itself without getting power from the computer port . Power level of power supply should be sufficiently powerful to supply 500 mA to each port , means ( Total power rating ) = ( Number of Ports ) x 500 mA . ( This may require to buy another power supply for the hub if its power supply is not sufficiently powerful ) . OR , It is necessary to consciously NOT to exceed the total power of the power supply by attaching less number of devices to ports : ( Power rating of power supply of hub ) / 500 mA = ( Number of devices attachable to Ports ) ( which is NOT a good selection because if this point is forgotten it is possible to easily exceed the capacity of the power supply means destroy of your hub or malfunctioning of data transmission , if I am correct ... ) . I do not know whether the above answer is correct for you or not . Thank you very much . Mehmet Erol Sanliturk
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAOgwaMt9pKNujjiUHhoutBHstLKqCuo=xqNUV24hzyC6t8s1hg>