Thank you Eric. This was the explanation I was looking for. The UPS is saving me money when drawing 181 Volt-Amps, yet the electric meter is only recording and charging me for 31 Watts. I wonder if APC did this on purpose. I don't know how much current is actually being fed to the batteries; they've been in there for a couple of months and should be fully charged by now, so it should just be trickling them (eight 12V 7A SLA cells in series/parallel for 48V).
Bob M. ====== --- On Tue, 9/16/08, Eric Lemmon <[EMAIL PROTECTED]> wrote: > From: Eric Lemmon <[EMAIL PROTECTED]> > Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) > To: [email protected] > Date: Tuesday, September 16, 2008, 9:21 PM > Albert, > > You are forgiven, because you pose an important question! > > The spinning aluminum disk in the kilowatthour meter found > on most > residential service-entrance panels measures true power in > kilowatts versus > time, which equals energy. Thus, your electric utility > charges you for the > true power you use, not for volts times amperes- known as > reactive power. > Although the utility must provide the capability to supply > all of the > amperes you need, some of those amperes are "given > back" to the utility due > to a lower than unity power factor. That is why many > utility companies > charge a "kVAR Penalty" to certain industrial > power users whose volt-ampere > demands far exceed their watt demands, meaning that the > power factor is low. > Industrial power users strive to keep their power factors > at 0.95 or above, > to avoid some really painful penalties! The power factor, > or PF, is simply > watts divided by volts time amperes. > > The issue of power factor is why large Diesel generator > sets have ratings > such as 1000 kW/1250 kVAR. In simple terms, any AC > generator requires > torque (engine horsepower) to meet true power demands, and > excitation (field > flux intensity) to meet reactive power demands. When the > generator load is > reactive, that is, it has a power factor less than unity, > the generator must > not only have the horsepower to supply the energy in watts, > but it must have > excess capacity to handle the additional current required > by motors and > other low-power-factor loads. In a nutshell, that is why a > 1000 watt > generator may be unable to keep running a refrigerator that > uses only 900 > watts; the fridge may require 1200 VA to operate because it > has a low power > factor, and the small generator has no ability to handle > such loads. > Because of its relatively small amount of spinning mass, > such a small > generator probably could not even handle the > refrigerator's starting > current- which is about 5 to 6 times its running current. > > 73, Eric Lemmon WB6FLY > > > > -----Original Message----- > From: [email protected] > [mailto:[EMAIL PROTECTED] On Behalf Of > Albert > Sent: Tuesday, September 16, 2008 2:13 PM > To: [email protected] > Subject: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging > Power) > > Hopefully, you will forgive me for hijacking the post, but > this brings up a > question I have had for a long time. What on earth is a > "volt-amp"? > My logic would state that is is the same as a watt, which > is volts x amps, > as you probably well know. So what on earth is it? > > Confused..... > > Albert
