From: Mark F on
I'm looking for a USB cable that supplies power "downstream"
and doesn't send power upstream.

I have seen many powered hubs that supply downstream and don't
specify if they are isolated from the upstream power or in parallel
to it.

I need a cable with power since I can't get support for many
devices if I connect through a hub; I don't want to draw
power from upstream since I have already had 6 motherboard ports
on several machines stop working and I want to eliminate high
current load as a possible cause of the problem.
From: Rod Speed on
Mark F wrote:

> I'm looking for a USB cable that supplies power
> "downstream" and doesn't send power upstream.

> I have seen many powered hubs that supply downstream and don't
> specify if they are isolated from the upstream power or in parallel to it.

It isnt practical to parallel, so you can be confident they dont do that.

> I need a cable with power since I can't get support for many
> devices if I connect through a hub; I don't want to draw power
> from upstream since I have already had 6 motherboard ports
> on several machines stop working and I want to eliminate high
> current load as a possible cause of the problem.

Any decent powered hub will work fine.


From: Arno on
Mark F <mark53916(a)gmail.com> wrote:
> I'm looking for a USB cable that supplies power "downstream"
> and doesn't send power upstream.

> I have seen many powered hubs that supply downstream and don't
> specify if they are isolated from the upstream power or in parallel
> to it.

The external power supply in a hib is allways arranged so that
if connected, it is insulated in upstream direction. If it
was not, a) it would probably not work well and b) it could
well damage the USB port the hub is connected to.

Don't worry about this.

> I need a cable with power since I can't get support for many
> devices if I connect through a hub; I don't want to draw
> power from upstream since I have already had 6 motherboard ports
> on several machines stop working and I want to eliminate high
> current load as a possible cause of the problem.

Well, you do not get this in cable form as basically nobody needs
it. You can roll one yourself by cutting the 5V line and
attaching a regulated (!) 5V PSU on the device side.

However if your device kills ports, then you are doing something
seriously wrong. Maybe look into that?

Arno

--
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name
GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F
----
Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans





From: Mark F on
On 28 Apr 2010 13:05:37 GMT, Arno <me(a)privacy.net> wrote:

> Mark F <mark53916(a)gmail.com> wrote:
> > I'm looking for a USB cable that supplies power "downstream"
> > and doesn't send power upstream.
>
> > I have seen many powered hubs that supply downstream and don't
> > specify if they are isolated from the upstream power or in parallel
> > to it.
>
> The external power supply in a hib is allways arranged so that
> if connected, it is insulated in upstream direction. If it
> was not, a) it would probably not work well and b) it could
> well damage the USB port the hub is connected to.
Cannot use a hub. (I don't know what thing about hubs might
make things go wrong, but whenever a device that had been
working with a hub stops working and I have to call support, the
first thing I am told to do is remove the hub and connect directly
to a USB port. [There may be things that don't work with hubs
for actual protocol reasons or that would require driver changes
to work with a hub, but even when I have used the device through
the hub in the past I am told I have to remove the hub before I can
get support.])
>
> Don't worry about this.
>
> > I need a cable with power since I can't get support for many
> > devices if I connect through a hub; I don't want to draw
> > power from upstream since I have already had 6 motherboard ports
> > on several machines stop working and I want to eliminate high
> > current load as a possible cause of the problem.
>
> Well, you do not get this in cable form as basically nobody needs
> it. You can roll one yourself by cutting the 5V line and
> attaching a regulated (!) 5V PSU on the device side.
>
> However if your device kills ports, then you are doing something
> seriously wrong. Maybe look into that?
>
> Arno
From: Arno on
Mark F <mark53916(a)gmail.com> wrote:
> On 28 Apr 2010 13:05:37 GMT, Arno <me(a)privacy.net> wrote:

>> Mark F <mark53916(a)gmail.com> wrote:
>> > I'm looking for a USB cable that supplies power "downstream"
>> > and doesn't send power upstream.
>>
>> > I have seen many powered hubs that supply downstream and don't
>> > specify if they are isolated from the upstream power or in parallel
>> > to it.
>>
>> The external power supply in a hib is allways arranged so that
>> if connected, it is insulated in upstream direction. If it
>> was not, a) it would probably not work well and b) it could
>> well damage the USB port the hub is connected to.
> Cannot use a hub. (I don't know what thing about hubs might
> make things go wrong, but whenever a device that had been
> working with a hub stops working and I have to call support, the
> first thing I am told to do is remove the hub and connect directly
> to a USB port. [There may be things that don't work with hubs
> for actual protocol reasons or that would require driver changes
> to work with a hub, but even when I have used the device through
> the hub in the past I am told I have to remove the hub before I can
> get support.])

I think this is several issues. First, there are substandard
hubs out there with bad signal quality and protocol errors.
Second is that the MS USB stack is pretty brittle compared to
the alternatives. Combinations that fail for Windows only
give the occasional error log entry under Linux. (Nothing
new here, monopolies are always bad for quality...)

Arno

--
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name
GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F
----
Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans