Power Factor and UPS Batteries

I will use the formula you have posted in your article, UPS Battery Sizing, but I question the use of the Power Factor being in the numerator.  If Power Factor is an expression of an inefficiency in a system, shouldn't the load on the batteries be INCREASED by way of the power factor, and thus the Power Factor would belong in the denominator in order that the batteries be sized to handle the extra load represented by this inneficiency?

asked 7/3/2013
Dwain Seppala3
Dwain Seppala

1 Answer

I would not look at power factor as an expression for efficiency.  What is really happening here, is converting VA into Watts. 

In a d.c. system real power is measure in watts and the concept of VA (volt-amps) does not exist.  Batteries are d.c. and deliver watts. 

In an a.c. system real power is measured in watts, but concept of VA now exists (due to reactive power).  UPS are normally rated in VA (or kVA).  To relate this VA to the battery capacity, it needs to be converted to watts.

If you had the rating of your UPS already in watts, then you would not need to apply the power factor. 

We have note on Power Factor, which will explain this better.

answered 7/4/2013 Steven McFadyen 246
Steven McFadyen

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