Harddrive power supplies

[Thad P Floryan]

dougm at madnix.UUCP (Doug McIntyre) in <1630 at madnix.UUCP> writes:

	I want to move the hard drive out of my Unix PC to reduce the
	drain on the poor little power supply and have a second one as well.
	How much power can an average hard drive draw? Would a 60W supply
	be enough for a couple drives or do I have to go a little bigger?

and is answered by:

mvadh at cbnews.att.com (andrew.d.hay) in <1990Nov19.134747.26946 at cbnews.att.com>
who writes:

	yes; the most i've seen for any hd is ~36w.  most are *well* under
	this (18w for my 40M hh, *9w* for 80M 3.5").  the 67M 3b1 drives were
	28w.

Ahem.  Sorry for my delayed reply; past 3 days been working 25 hrs/day at the
office, then when I arrive home PORTAL is dead and nada.  In any event ...

As to whether a 60W supply will function CORRECTLY, it depends on the TYPE
of hard drive.

For example, a Maxtor drive (any of XT2190, XT3380, XT4380, XT8760, etc.) is
specified as approx. 27.5W.  But just TRY and get one of those suckers started
using your common, everyday 45W or 60W or even 80W supply; heh heh.  The
startup surge requirements for said drives is so great that those "common"
supplies will NOT work and will only serve to cog the drive (no damage will
occur if you realize what's happening and shut everything down).  What IS
required for such drives are the "special" power supplies manufactured by
companies such as Astec and a few others, which are designed to supply the
humongous amount of startup current for a short time even though the supply
itself may be rated for only, say, 45W.

Believe me, I run Maxtor drives myself on MANY systems, and just two months
ago replaced the DEC RA81 and RA82 floor-standing drives on my VAXes with
in-the-cabinet Maxtor XT8760E drives; what I used for the VAXes were some
surplused, but new, IBM AT chassis, gutted, for their mongo power supplies and
strong cabinets to hold the drives ... this whole combination was able to be
mounted in the VAXes' racks (I'm NOT talking about desktop systems here :-)

If you have the OEM manual for Maxtor drives, you'll note that the drives can
be programmed for startup delays; this means that although, say, an 80W supply
may be able to operate the drives once spinning, it may be inadequate to START
the drives spinning, so a staged turn-on sequence is de rigeur.

"Most" drives available to the consumer don't have the startup "problem"
typified by industrial quality HDs, and the only reason I've rambled on here
is to alert you to the possiblity that the power supply you get "may" not be
adequate for your (unspecified) HD.

For the record, the 3B1 power supply IS able to start and sustain a Maxtor
mounted in the system cabinet; I have NOT tried a 7300 power supply that way
(but that's moot since the mongo Maxtor won't fit in a 7300 cabinet! :-)

Thad Floryan [ thad at cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]