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Dell XPS 9000 vs SW5548 - Page 4

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Posted by Ron Rosenfeld on February 24, 2010, 5:08 am

On Tue, 23 Feb 2010 15:45:01 -0700, wmbjkREMOVE@citlink.net wrote:

This is definitely an issue with the newest Dell computers.  And has been
traced to a change in the power supply design.

What happened is my wife got a new computer at our "on-grid" house where we
have UPS's on the computers.  Her old Dell and my "home-brew" worked fine
with APCC RS style UPS's.

I was installing the software on her new XPS9000 and had just installed the
monitoring software for the UPS.  When I did the UPS self-test, where it
puts it on battery for a while, the XPS 9000 shut down immediately.  It
rebooted once mains power was restored.  Nothing else on the UPS shut down.

My first thought was that the UPS was not switching over quickly enough,
but if that were the case, the Dell should have rebooted before returning
to mains power.

When I contacted APC about their UPS, they wrote that the Back UPS "outputs
stepped approximation to a sine wave when on battery mode. Stepped
approximation to a sine wave is an ideal for most of the modern Computer
and Computer related equipment. However, if the connected equipment does
not accept stepped approximation to a sine wave, then it will shutdown as
soon as the UPS transfers to battery. My research has found that the Dell
XPS 9000 requires pure sine wave input in order for it to work properly. In
this case, the Back UPS will not support the Dell XPS 9000 as it outputs
stepped approximation to a sine wave on battery mode."

And there's stuff on Dell forums confirming that statement.

So it seems that the only way to know if the newer PSU's will worked with
the SW5548, whose output could also be described as a "stepped
approximation to a sine wave" will be for someone to have tried it and
report that information.

My wife will NOT be moving this computer to our off-grid home (she uses a
different computer up there), so it's not an immediate problem.  But
something we might have to plan for.


Posted by Ron Rosenfeld on February 24, 2010, 4:55 am

The SW5548 doesn't really put out a true sine wave.  It produces a stepped
wave form that look like a staircase that resembles a sine wave.  The
number of steps varies from 34 to 52 steps per cycle, depending on load and
DC voltage.  THD is usually 3-5%.  (This info is from my manual, not the
advertising hype).

Posted by z on February 24, 2010, 6:09 am

In that case it may fail.  Maybe get a new PSU for your dell if it
doesn't work.  Won't hurt to try it though

Posted by Ron Rosenfeld on February 24, 2010, 1:02 pm

Yeah, it may.  I was hoping that there was someone around who had tried
this combination.

Posted by Jim Wilkins on February 24, 2010, 2:35 pm

I haven't tried it, but a little searching shows that the new Dells
implement Power Factor Correction to save the planet from the evil of
incorrect power factors, which add a load on the electric grid that
the power companies can't charge to home users. In simple terms power
factor is the difference between the Wattage and the Volt-Amp ratings
of a UPS.

Apparently they needs a purer sine wave input than stepped inverters
provide, Dell suggests the APC SmartUPS line and will be happy to sell
you one.


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