Laptops and power from usb port

Archived from groups: comp.sys.laptops (More info?)

I've been reading reviews on the Compaq NC8000 when I found this article:

http://reviews-zdnet.com.com/HP_Co [...] 4-3121_16-
30583495.html

.... that says the unit doesn't supply USB bus power. How common is that
among laptops... I can't find an answer in google searches. It seems like
it would be a pain to have to lug around power supplies for each peripheral
and might be a big pain. Or maybe usb hubs are powered and it would just be
one extra power supply?

Any input appreciated =)

Archived from groups: comp.sys.laptops (More info?)

Many laptops can & do provide power via USB ports:
o Current capability is limited - typically 500ma
o Some peripherals plug into 2 ports - to distribute power demands
o Current draw limit is by a resettable fuse IIRC - on some by failure

I have connected USB-powered devices to a USB port, and after a
time have found they have cut-out requiring time to "reset". This was
most common with a USB-powered CanoScan Lide 20 - a very cheap
but also surprisingly high quality scanner, lightweight, like a laptop.

Some laptops deliver power via the PS/2 port (if fitted), which can
be used to boost power. However, realise that USB ports in general
are low power output devices - an external powered hub is advised
if you have more than one device, particularly if self-powered.

Power output via the PS/2 ports can be limited too - KVM switches
often do not work with laptops without an add-on powersupply.

So it comes down to...
o Exactly what device you wish to power
o Whether the USB ports provide power, and how much

The CanoScan LIDE 20 supposedly draws 500ma, and the Inspiron
1100 laptop supposedly can supply 500ma. Even so, I could replicate a
power cut-out mid-scan through a run of consecutive scanning operations.

For serious use, a powered hub is A Good Idea just to be safe.
--
Dorothy Bradbury
www.stores.ebay.co.uk/panaflofan for quiet Panaflo fans & other items
www.dorothybradbury.co.uk (free delivery)