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midrange.com
Hmmm... I'm wondering if the "wall warts" were required because of one of
the following:
1. Interference issues of having power and data running on the same USB
cable.
2. The external device either exceeded the 100ma spec or used enough power
that the manufacturer didn't want to overtax the PC power supply with their
external device (think either old PC's or notebooks).
3. They didn't think they could depend on the quality of power from the
USB cable. USB was a bit flaky when it was first introduced.
4. The cost to handle devices exceeding the 100ma spec far exceeded the
cost of using an external power supply.
I know that I've heard of external power supplies being used instead of
internal ones because if it were internal then the whole device would have
to conform to FCC or UL standards, or something to that effect. When the
power supply is external then only the power supply has to conform.
About 5 years ago I bought a USB drive cage that I really liked. It took a
standard PC power cable and had an internal power supply to transform the
120 volts AC to 12 volts DC. It was real handy to take places. A year
later I bought another one and they had changed the design to use an
external power supply which was a bit more cumbersome. That one stayed
parked and hasn't really been moved since. That was the last one of those
that I bought. A USB-powered one would be even better.
Dave Parnin
--
Nishikawa Standard Company
Topeka, IN 46571
daparnin@xxxxxxxxxxxxxx
Booth Martin
<booth@xxxxxxxxxx To: PC Technical
Discussion for iSeries Users
om> <pctech@xxxxxxxxxxxx>
Sent by: cc:
pctech-bounces@mi Subject: Re: [PCTECH] USB
power?
drange.com
12/29/2005 12:16
AM
Please respond to
PC Technical
Discussion for
iSeries Users
Here is a link that discusses the choices of power:
http://tinyurl.com/9arab
David Gibbs wrote:
> Folks:
>
> Anyone know why some external USB hard drive chassis need external power
> and some don't?
>
> A few months ago I bought a USB 2 drive chassis for a 2.5" laptop drive.
> I was quite disappointed when I found out it required either two USB
> connections or a power brick (larger than the drive itself). I returned
it.
>
> The other day I found a similar drive chassis that didn't have a power
> plug. It took it's power directly from the USB bus. I picked it up
> ($25 at compusa) and it works fine.
>
> So my question is ... why did the first one require extra power and the
> second one doesn't? They were both driving the same hard drive.
>
> Thanks!
>
> david
>
>
>
--
-----------------------------------
Booth Martin
http://martinvt.com
-----------------------------------
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