At 16:06 12-06-98 -0700, you wrote:

>IN GENERAL.... a SCSI drive will draw around 1 1/2 to 2 amps
>while running but they have a peak (the initial uuummph to get
>the spindle motor and platters spinning) of about 4-5 amps.
>
>...as a matter of caution, I always try to mate a hard drive
>with a floppy or CD if I need to split a cable.


One time I used the same wire (with a "Y" adapter) for a hard drive
(5.25" full height SCSI) and a tape drive. I had intermittent
problems (blue screen errors) when doing backups from that drive to
tape. (No problems with either of the other three drives to tape.)
The problems went away when I used seperate power wires for the
hard drive and tape drive.

That full height SCSI drive (ST-43400N) I mentioned draws up to 3.98
amps at 12 V while starting, 1.9 amps once it has spunup. It also uses
3.4/1.2 amps at 5 V. That's 28-33 watts once running. (Numbers are
from Seagate's website.) But it could require 65 watts at spinup!
Good thing I have a 300 watt power supply in my external SCSI box,
since I have four of these drives. (That tape drive has been moved.)

On the other hand, I have a more recent 1/2 height 3.5" SCSI drive
(ST-15230N) in my computer case. It draws only 2.4 amps at startup
(.54 amps while idle) and .6/.36 amps at 5 V. That's "only" 33 watts
at spinup, 9-11 watts while running.

You can use P=IV (power equals current times voltage) for DC (direct
current) calculations. Include both the 5 and 12 volt currents.

Recent 1/3 height 3.5" drives require less power.

Regards,
Bill