Mike Bilow wrote:
>
> On Sat, 8 Apr 2000, Edward Schernau wrote:
>
> > Mike Bilow wrote:
> > >
> > > Drives use by far more instantaneous current to spin up then they
> > need to
> > > run in active idle mode. A big, modern IDE drive can consume
> > about 2.0A
> >
> > [Excellent analysis trimmed]
>
> Thanks!
>
> > Nowadays I think the "danger" comes from two sources. First is
> > poor PS quality, and the second is the increased power demands of
> > other components.
>
> This is true, but they stick labels on the supplies. If you can't believe
> the label, you should not be buying from that vendor. (Then again, the
> labels probably also say "No user serviceable parts inside.")
>
> > Cheap PS' will not be able to hold the voltage constant under an
> > instantaneous load. Even the best can't, but its a measure of
> > how "stiff" the PS is if it can maintain a stable +5V line, under
> > sudden load. Dips on this line (and others) can affect the entire
> > system.
>
> This is true, but all 3.5-inch and 5.25-inch drives use the 12V line to
> spin up the motors. As a result, the loading on the 5V line is minimal
> for a drive spin-up, essentially the same or less than for normal
> operation. Virtual nothing in the machine except for hard drive motors
> and head positioners uses the 12V line, so you can as a general rule
> assume that all available 12V rated current is available to you. There
> may be exceptions, as you may have something like a tape drive that does
> an expensive power-on self-test routine, but ordinarily the hard drives
> are the only things eating 12V. (Some CD-ROM drives, especially writers,
> also use 12V. I have an Acer CDRW-8432 which even has a cooling fan!)
>
Just a mention that another problem is underloading the +5V.
This is not an issue in pcs/workstations as motherboards draw most
of the +5V. However, drive requirements for +5V have decreased over
time while +12V loading has increased. Both older power supplies and
cheaper PS depend upon +5V being loaded sufficiently to provide good
regulation of all voltage outputs.
--
Dan Jones, Storage Engineer VA Linux Systems
V:(408)542-5737 F:(408)745-9130 1382 Bordeaux Drive
[EMAIL PROTECTED] Sunnyvale, CA 94089
