[Malvern] PC PSUs

[Steve Cashmore]

Ian Pascoe wrote:
> Hi All
> 
> Why are PC PSUs so highly rated ie 400+ watts?
> 
> I know that the CPU and Graphics card gets rather hot so must take some of
> the power, and of course you have the power for the hard and optical drives,
> but even so this still seems a high wattage compared to what there is inside
> a normal PC these days.
> 
> My only thought on this is that they have to spec up what the power drain
> would be if all PCI slots were used, all USB devices were powered from the
> PC etc etc - am I on the right track here?

You're thinking along the right lines, but PSU ratings should be taken 
with a pinch of salt rather like car top speeds.  I doubt many available 
400W PC PSU could deliver 400W for any useful period of time!  I've run 
lots of industrial embedded PCs trouble-free on properly rated 90W 
industrial PSUs.  Sometimes these same PCs had problems with cheap, 
generic 250W PC PSUs.

Hard disc drives need a much higher startup current than steady state 
which is one reason larger ratings might be needed.  But I have measured 
the power consumption of several typical domestic PCs and found they 
drew around 60W-90W steady state depending on activity and excepting the 
monitor.  Start adding lots of extra drives and fancy ultra high 
performance graphics cards and the requirements do start rising though.