Charles Craft wrote:
> http://www.hp.com/racksolutions/prodinfo/power_access/ups_ux.html

> PowerTrust II-LR 2.0kVa(1.4kW) UPS 120V

> Anyone have a clue on the dual labeling of UPS power capacity?

> When dealing with AC is power (W) not equal to I x V but rather I X V(RMS)?

Presumably those would be the same, since AC voltage is usually
specified as RMS.  The issue with VA versus W in AC circuits is "power
factor" -- the phase difference between the current and voltage
waveforms.  Just because RMS voltage is 120V and RMS current is 1A
doesn't mean you are drawing 120W -- you could be using no power at
all!  It is entirely possible to have a VA figure that is much
higher than the actual power draw if the load is significantly
reactive (and most switching power supplies are).  Your UPS appears to
be specced for a power factor of 0.7.

> PC power supplies are rated in watts but should it really be the volt x amp total used when calculating UPS load?

Depends on the situation and the specifics of the power supply design.
I could envision situations where either VA or W could be the
appropriate metric to use, or where neither would really be
sufficient.  In this case, whichever is higher is probably the number
to use.  They are basically saying that you can draw up to 1.4kW with
a power factor as low as .7, but no more than 2kVA if the power factor
is lower, and no more than 1.4kW if it is higher.  Whew.

--

Mike Poulton
mpoulton@mtptech.com
MTP Technologies
KC0LLX

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