Re: power supply with a large number of connectors?
From: Floyd L. Davidson (floyd_at_barrow.com)
Date: 01/29/05
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Date: Sat, 29 Jan 2005 11:55:21 -0900
"/dev/null" <dev.null@BeginThread.com> wrote:
>I'm trying to figure out the largest number of hard drives I can safely use
>off of one power supply. The largest power supply wattage I see available
>is 500, and those come with 6 hard-drive type connectors. I know I can use
>splitters to increase the number of connectors I can use, but I don't know
>what the max limit on that is.
>
>What's the max number of splitters I should use to support hard drives on a
>standard single-CPU ATX-style board? I plan on buying extra IO controller
>cards to support the extra drives.
It all depends...
Off hand, if the board has only one CPU and you are going to do
this with just one "extra IO controller" (assuming you mean an
IDE controller), the most you will have are 8 drives, and the
maximum power requirements can be approximated from that.
First, different CPU's have different power requirements, and
power supplies are advertized by total power, but do have
specified maximum power levels for each bus. Hence one 250-300
watt supply might well power what you have, and another one
won't. With one CPU, and a max of 8 typical disks, probably any
400-600 watt supply will handle it easily. (Hence, go for a big
one and don't worry about it, or sit down and figure it out down
to the last amp on each bus if you want to use a smaller supply.)
To give you some ballpark figures, a check of half a dozen old
hard disks of different types that are laying around here at the
moment (IBM, Maxtor, Western Digital and Quantum, both SCSI and
IDE, that ranged from 18Gb to 40Gb) found current requirements
from .6 to .8 Amps on the 5 volt bus and from .9 to 1.1 Amps on
the 12 volt bus. So 8 drives, if they all happened to draw that
particular maximum, would be 32 watts from the 5v bus and 106
watts from 12v bus, for a total of 138 watts, or about 28% of
the total power available from the 500W supply mentioned.
With 300-350 Watt supplies and typical motherboards/CPUs/video
cards/etc, it should be easy to find one that can handle it, but
I would certainly check the exact specs to be positive. At
400-600W, just go buy it and don't worry.
As for splitters... I'd get a supply with *lots* of connectors,
and would not put more than one splitter on a connector, if at
all possible. And, especially if you go with more than one
(branching out from single connector to make 4, for example), I
would look for the highest quality you can find. Heavier gauge
wires, and quality connectors. In fact, if you can find a 4 way
splitter, use that to reduce the number of connectors. (Or make
one.) I'm leary of putting 4-5 Amps through one of those
connectors though, and would try to avoid it. (I have no idea
what they are rated at, but...)
As others have mentioned, with a lot of drives you have a lot of
heat. That 138 watts or so will almost all be turned into heat.
You know how hot a 100 Watt incandescent light bulb gets..., and
this is nearly half again as much heat as that. If you don't
give some really serious thought to air flow and cooling, you'll
cook everything! For example, I have one machine here with 4
drives and another with 5. The only way I'll do that is in a
case that allows an air space between each drive. I simply do
*not ever* stack anything immediately on top of a hard disk. I
want a significant air space, and I want air flowing through
that space.
-- Floyd L. Davidson <http://web.newsguy.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@barrow.com
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