RE: Re: OT USB Scanner stops working after a few scans

["Keith Doxey" <ukha@xxxxxxx>]

Might just be a case of poor translation.

I once bought a car Cassette Player and it had a note which read.....

"Take care to use only the supplied screws. If used longer screws
there may
take place such trouble that the inner mechanism will be damaged"

USB probably uses "Positec" devices for current limiting. These
are "self
resetting fuses". When an overload occurs they get hot. When they get
hot,
their resistance increases greatly thereby limiting the current through the
positec. Because the positec now has significant resistance, the low level
of current flowing continues to heat the positec theby keeping the current
at a very low level. When you either switch off the power or unplug the
devices powered by it, the positec cools down and normal operation is
restored.

Its possible that the combined load of the devices is near the trip limit
so
it gradually heats which is why its OK for a few scans before tripping.

Using a POWERED hub with its own PSU may hels as this would be able to
supple the USB maximum from EACH port.

Keith

> -----Original Message-----
> From: Phil Harris [mailto:phillip.harris1@xxxxxxx]
> Sent: 21 September 2001 21:22
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] Re: OT USB Scanner stops working after a few
scans
>
>
>
> Yeah but this seems to be implying that the PSU will work in a wall
socket
> but not in an extension stripblock...
>
> Phil
>
> > -----Original Message-----
> > From: Keith Doxey [mailto:ukha@xxxxxxx]
> > Sent: 21 September 2001 20:44
> > To: ukha_d@xxxxxxx
> > Subject: RE: [ukha_d] Re: OT USB Scanner stops working after a
few scans
> >
> >
> > USB has current limiting to prevent damage to the host PC.
> >
> > If you are just plugging one device in it will be fine but
> > multiple devices
> > could overload the supply. A reboot clears it because the
> overload clears
> > for long enough to reset the trip.
> >
> > Best to use its own PSU if possible
> >
> > Keith
> >
> > > -----Original Message-----
> > > From: paul.murgatroyd@xxxxxxx
> > > [mailto:paul.murgatroyd@xxxxxxx]
> > > Sent: 21 September 2001 13:39
> > > To: ukha_d@xxxxxxx
> > > Subject: [ukha_d] Re: OT USB Scanner stops working after a
few scans
> > >
> > >
> > > No Phil,
> > >
> > > I kid you not..
> > >
> > > >From http://www.umax.co.uk/support/faqs/usb.htm
> > >
> > > USB - Problems Caused by Low Power
> > > Problems of "scanner not found" or quit/crash
during scans can be
> > > caused by an excessive power load on the USB ports - make
sure that
> > > all USB devices with external power supplies are switched ON
(to
> > > prevent them drawing power from the bus). If some devices
are self-
> > > powered (ie no external power supply) you may need a
"powered USB
> > > hub". In some cases the problems are caused by a tiny
power drain
> > > which can be fixed by plugging the scanner's external power
supply
> > > directly in to a wall socket.
> > >
> > >
> > >
> > > --- In ukha_d@y..., "Phil Harris"
<phillip.harris1@v...> wrote:
> > > >
> > > > > 1. Make sure that the scanner is plugged in to its
own power
> > > source,
> > > > > if possible try directly plugging it into the
mains, according
> > > the
> > > > > UMAX website, the power loss between the plug and
the four gang
> > > block
> > > > > can be enough to do it.
> > > >
> > > > This *HAS* to be a wind up by UMAX?
> > > >
> > > > Phil
> > >
> > >
> > >
> > > For more information: http://www.automatedhome.co.uk
> > > Post message: ukha_d@xxxxxxx
> > > Subscribe:  ukha_d-subscribe@xxxxxxx
> > > Unsubscribe:  ukha_d-unsubscribe@xxxxxxx
> > > List owner:  ukha_d-owner@xxxxxxx
> > >
> > > Your use of Yahoo! Groups is subject to
> > http://docs.yahoo.com/info/terms/
> > >
> > >
> > >
> >
> >
> >
> > For more information: http://www.automatedhome.co.uk
> > Post message: ukha_d@xxxxxxx
> > Subscribe:  ukha_d-subscribe@xxxxxxx
> > Unsubscribe:  ukha_d-unsubscribe@xxxxxxx
> > List owner:  ukha_d-owner@xxxxxxx
> >
> > Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
> >
> >
>
>
>
> For more information: http://www.automatedhome.co.uk
> Post message: ukha_d@xxxxxxx
> Subscribe:  ukha_d-subscribe@xxxxxxx
> Unsubscribe:  ukha_d-unsubscribe@xxxxxxx
> List owner:  ukha_d-owner@xxxxxxx
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>