> Also, much of the power in computers is consumed in cooling and powering
> them. By using 1 power supply for multiple computers, you can save a
> bunch of power.
Power supplies only supply current for what's needed. Although they do
indeed generate quite a bit of heat all the time, regardless of load, an
overrated supply doesn't use more power than a matched supply would under
the same stress.
I can take a 500W power supply and it won't consume *much* more than a 180W
supply would when hooked to the same motherboard. The 500W supply can power
a lot more, but it's not being asked to do so in the above example, so
besides a bit more heat on average, having 2 250W supplies or a single 500W
supply is not a big difference.
> I am working with a friend of mine to do just this. We have 2 HP
> mainframe
> PS's (500W), an older mainframe PS (circa 1980) that I got at a yard sale
> (300W), and several PS's from IBM microchannel servers (~200W each). With
> a fair amount of work :), we hope to have a number of 486/pentiums in a
> cabinet with central cooling. These computers will (if we ever get the
> thing built) be factoring Mersenne numbers in the DecMega range.
Having one power supply per computer, besides the convenience of having it
self contained, is the fact that the fan in a power supply is used not only
to cool the supply itself, but to circulate air throughout the entire case.
This is especially true for ATX spec cases and supplies, but is a general
rule of thumb for all systems.
You mention having central cooling for a cabinet, but I wonder if the added
power that a central cooling unit (a 120V cabinet fan?) is offsetting any
potential power savings by running less supplies total.
Even though most power supplies come in ratings of at least 220W or so, the
average motherboard uses only a fraction. More power savings can be had by
finding less watt hungry hard drives. Laptop drives are 2.5" and generally
consume far less power than your average 3.5" drive. There are adapters
aplenty from electronics shops that let you plug your 2.5" drive into a
normal IDE cable. CD ROM drives and floppies are big power hogs too, but
they're not on all the time anyway, so that's not a problem.
I'd just take a wild guess that the average computer (sans monitor) only
uses about 100W on average, even with Prime95 running (maximum motherboard
power usage: cpu, memory, etc. and hard drive spinning). Average power
consumption is just that. But hard drives for instance will use more power
when spinning up, so you do need to have a bit more "oomph" in your supply
that what the normal running consumption is.
For real fun, you can get power consumption figures for everything in a
computer...add up the maximum values and tack on another 50% or so for a
conservative margin, and that's really all you need.
You could always maximize power transfer from the supply by finding a supply
that isn't grossly overrated, but modern switching supplies, as I mentioned,
don't tend to use much more power than the load is demanding, regardless of
overrating.
> This will (of course) still draw a massive amount of power, but it has the
> decided advantage of all the hardware being free! This is still an
> impractical watt/cycle, but we're doing this for the experience (TM).
As long as you have fun, why not? :-) Of course, then if you have one
supply go out, you lose all your computers. But there's always a tradeoff
between cost and reliability. The servers I work with (even the storage
units) all have N+1 power supplies...but the cost! Whew!
Aaron
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