Terry allow me to disagree. I understand the UPS manufacturers rating game, I have played it myself, but it is not misleading in fact, it is not even a little cheating as you imply: if the 15 kW UPS you mention has to spit out 15 kW, it _will do it_ of course, and if it's load has a power factor of 0.75 as is quite common, the rms current will _actually be 167 A_ (15000/(120*0.75)), so it will _really_ be outputting 167*120=20 kVA. And the wires will heat up as if the 167A were real, which they are.
The UPS rating only misleads the dudes who think that Pavg=Urms*Irms, and those deserve to be misled anyway ;) Controversy solved? Michel P.S. As for the UPS's IGBTs or Mosfets, they often paradoxically prefer this kind of load (rectifier+filter, PF=0.6 to 0.8) to a purely resistive load drawing the same kW. Mine did in any case, as such loads only drew current when they were saturated :) ----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[email protected]> Sent: Wednesday, June 07, 2006 5:28 PM Subject: Re: Battery shapes > > > -----Original Message----- > From: Michel Jullian > > I don't understand why it is absolutely impossible, is the load's power > factor > unity i.e. is it purely resistive? If the load's power factor is equal > to 0.8 > which is typical of computer power supplies, the dudes are right I am > afraid. > > <><><><><><> > > The UPS IGBT switches are not designed for a sustained 167 A output. > > It's a game the manufacturer's play. Almost everyone makes a 15 kW UPS > which they *used* to call a 17 kVA (nominal) UPS assuming a 0.9 PF. > Then one day another manufacturer advertized the same UPS as a 20 kVA > (nominal) and in small print at the bottom he stated that he assumed > 0.8 PF. > > Careful of any spec which says "nominal", BTW. :-) > > Terry > ___________________________________________________ > Try the New Netscape Mail Today! > Virtually Spam-Free | More Storage | Import Your Contact List > http://mail.netscape.com >
