[ale] How much wattage in my server?

[Sean Kilpatrick]

On Wednesday 12 February 2003 08:17 pm, Robert L. Harris wrote:
>   16x 120Gig Maxtor Hard drives (yes, 16 drives)
>   Dual Nic (100bT and 100bT)
>   ATI VGA card
>   3 Case Mount Fans...
>
> I've never had to calculate the wattage needed for a power supply
> before.

I'd guess that the original power supply was not sized to handle
the draw from 16 hard drives. Hard drives use both 5Vdc and 12Vdc
power -- at least both of the older ones I have lying around do and
I don't think that has changed.  An older Western Digital HD with
four platters draws .66A at 5 volts and .24 amps at 12 volts. I 
suspect that newer/ faster hard drives draw a bit more power.  If
you're lucky the data will be on the drives. Volts * amps = watts.
So my older drive was drawing about 6 watts. Your 120 gig drives
might easily be drawing 10 watts each or 160 watts just for the
drives.
So how much power supply do you need? Take the calculated draw
for your 16 drives (plus at least 20% for insurance) and add that
to the size of the original (now dead) power supply, along with the
draw of those extra case fans.  Go shopping.

But a recent review (I can't remember where I read it) pointed out
that there is a significant difference between rated and actual
output of power supplies, and there was a high correlation between
cost and quality. So if you calculate you need a 500 watt power
supply, don't waste your money on a cheap one.

Sean


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