[nSLUG] Low Power system

Ian Campbell ian at slu.ms
Mon Aug 25 13:36:36 ADT 2008


On Mon, Aug 25, 2008 at 01:08:40PM -0300, Daniel Morrison wrote:
> 
> 39.8 W with the system running under 100% load, and powering a hard
> drive and a CD/DVD, using an efficient (large) power supply.  (As I
> understand it, a large power supply running at 20% capacity is much
> more efficient than a small power supply running at 80% capacity, even
> when they output the same power).
> 
> So I'd say: 40 W or less.

Stephen said what I'm trying to say far better than I'm about to, but
research into the specific parts you're looking for is better than
anecdotal evidence. Stuff we knew a couple years ago doesn't always
apply today.

What's most important is the efficiency curves. Most PSUs
(older/current ones not covered by 80plus) are quite inefficient at
the low end of output, and relatively inefficient at the high end,
with a sweet spot somewhere in the middle. I'm not an EE, not sure why
that is... anyone?

What I've seen people do in the past was try to estimate how much
power their setup would draw, and then pick a PSU such that their draw
fell somewhere in/around the sweet spot.

That said, there's no reason a low-power PSU can't be efficient,
example: http://www.silentpcreview.com/article601-page3.html

In this case it looks like the sweet spot is at ~60W output. Not that
it really matters, it's ~85% efficient for most of its range.

Shrug. Just nitpicking.
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