Which UPS?

[Lennart Sorensen]

On Wed, Jun 13, 2012 at 10:19:05AM -0400, James Knott wrote:
> Scott Allen wrote:
> >Who said anything about two stages being more efficient than one? Go
> >back and reread the post you are questioning. I'm saying that two
> >stages is more efficient than three.
> >
> >Note that I was talking about the specific case where the user is
> >limited to a 120VAC source, which is on line, and either a 120VAC
> >output UPS is used, or a 48VDC output UPS is used.
> >
> >My statement, that you quoted and questioned, was for the 48VDC output UPS:
> >-----
> >With a 48VDC output UPS powered by mains AC:
> >  - While on mains (most of the time):
> >UPS needs to convert 120VAC to 48VDC at, let's say, 85% efficiency.
> >The 48VDC PC power supplies above are 70% efficient but let's say we
> >find one that's 85%. UPS 85% and PC 85% is 72.25% overall.
> 
> As I mentioned in another note, the high voltage DC in power
> supplies approaches 170V.  Why should a power supply that runs on AC
> and be more efficient than one that runs on a similar DC voltage?
> What is it about that referenced DC supply that makes it so
> inefficient?  Why should the rectifiers in an AC supply be
> significantly more efficient than a separate rectifier?  Either way,
> you have to convert AC to DC and then back to high frequency AC.
> Something about that DC power supply that was linked to doesn't make
> sense.  In this day & age, why is it so inefficient?
> 
> >UPS needs to convert 120VAC to 48VDC at, let's say, 85% efficiency.
> What is the conversion efficiency of the rectification part of the
> AC supply?  Why should a separate rectifier be significantly
> different
> 
> 
> >Note that I was talking about the specific case where the user is
> >limited to a 120VAC source, which is on line, and either a 120VAC
> >output UPS is used, or a 48VDC output UPS is used.
> 
> An AC output UPS will have an additional stage to convert DC to AC.
> The computer will then have an additional stage to convert that AC
> back to DC.  Even if UPS is not used, why should producing DC in a
> separate box be less efficient than when in the same power supply.

This one seems to be 96% efficient: http://www.mini-box.com/picoPSU-160-XT

A bit small I suppose.

-- 
Len Sorensen
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