I am planning to buy a lightweight (<5lb) laptop to run an external
sound processor/analyzer by USB and have heard that some units that
are capable of supplying less (or more) power than others. Are there
any that are significantly low (or high) in this regard? I will be
running from AC most of the time.

(Currently considering the Fujitsu S6240.)

Kal

On Mon, 07 Nov 2005 13:39:10 -0500, Kalman Rubinson <kr4@nyu.edu>
wrote:

I don't have any experience with the "ultra-portable" systems but from
my experiences with notebooks, Dell seems to be at the low end for
providing decent power out the USB ports, and IBM/Lenovo seems to be
at the higher end. I have only seen one [relatively] recent Gateway
and it was near the Dell's in USB power. In my testing, AC or
battery had little impact on the USB port power.

The spec for the port is 500ma (one-half amp) which give you 2.5 watts
at 5 volts. Most USB ports monitor power consumption and won't allow
more, but in a few instances the USB power is tied to the motherboard 5
volt bus with no specific limits. But I can't tell you specifically
about any given laptop model.


Kalman Rubinson wrote:

Kalman Rubinson wrote:
I have two USB devices whose power requirements sometimes exceed 500ma.
Each of these devices came with a USB cable that splits into two
connectors at the computer end. That is, one of the connectors is a
normal USB plug, and the other is a USB plug whose function is only to
obtain additional power from another USB port. I'd assume that there
are no electrical reasons that these cables cannot be used with ANY
device. If such is the case then you need not use power supply as a
criterion in your laptop selection. Rather, you'd need to think of how
how many USB ports are available.

To answer your question a bit more directly, my Packard Bell Easynote
M5 (year 2003), which I believe to be identical to one particular NEC
Versa machine (M300 or M400, can't recall), is able to satisfy the
1100ma requirement of my capture (hardware encoder) device even from
one USB port. Of course, this doesn't tell us anything about other
models from this manufacturer.

"Barry Watzman" <WatzmanNOSPAM@neo.rr.com> wrote in message
news:436FF6E4.2020501@neo.rr.com...
No it isn't - at least not quite.

The spec requires a guaranteed minimum current availability of 100 mA from
any port. Any extra current requirement is entirely by negotiation with the
host, but is not guaranteed to be available. Bus powered hubs, for example,
will never grant more than 100 mA per port.

The USB 5 volt line is invariably fused, but this is more to protect against
port failure rather than short circuits.

Thanks for the responses. Seeing that there is no available specific
info on which laptop does what, I went ahead and ordered the Fujitsu.
FWIW, despite what was in another post, my old Dell C800 handled the
external USB devices just fine. So, I am hoping that the Fujitsu will
do as well. If not, I'll have to get the external PS for the analysis
box.

Kal