Nice survey of higher end power supplies ...

Jim Lux James.P.Lux at jpl.nasa.gov
Wed Jun 11 00:35:38 EDT 2003


> >
> > http://www17.tomshardware.com/howto/20030609/index.html
>
> it's interesting, but I don't think it's all that useful.
> for instance, how many of you have cluster nodes that need >400W PS's?
> as usual THG seems mainly focused on satisfying the gamer/overclocker
> that he's got Da B35t.
>
> one relevant and interesting factoid was that they claim the PS's
> all operate at about 70% efficiency.  it's a little hard to tell
> how they measured that, but I think it's at peak load.  it would
> be nice to know whether efficiency is better at sane/normal loads.

Probably worse efficiency at light loads. There's a fairly significant
"overhead" power that is consumed at all times, as well as a "proportional
to load" loss.

Also, the power factor is probably much worse at light loads, unless the PS
uses some form of harmonic/PF correction (e.g. it is CE marked, and actually
complies with the mark).  The usual input stage is a rectifier to a
capacitor input filter, which has an input current waveform that is very
"pulse like" at low loads.  High pulse current >> high I^2*R losses

>
> PF .74 on that machine, by the way.  I was kind of surprised,
> since it was a compaq deskpro.  pretty old, though, that's probably why.


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