Date: Wed, 11 Aug 2010 23:58:16 +0200 From: Erik Trulsson <ertr1013@student.uu.se> To: freebsd-questions@FreeBSD.ORG, ryan.coleman@cwis.biz Subject: Re: UPS question Message-ID: <20100811215816.GA81198@owl.midgard.homeip.net> In-Reply-To: <201008112120.o7BLKgxe054400@lurza.secnetix.de> References: <5304A319-0406-4510-B6B2-8FD609239FF9@cwis.biz> <201008112120.o7BLKgxe054400@lurza.secnetix.de>
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On Wed, Aug 11, 2010 at 11:20:42PM +0200, Oliver Fromme wrote: > Ryan Coleman <ryan.coleman@cwis.biz> wrote: > > He thinks that at 500W needed it would give me about 12 minutes on > > a 1400VA. > > That W and VA numbers of the UPS are pretty much irrelevant, > because they tell nothing about the capacity of the battery. > Those numbers only give an upper limit on the power that > the UPS can handle (i.e. you cannot connect devices totalling > 800 W to a 500 W UPS, for example). > > In order to be able to estimate how long the UPS can power > wattage, you need to know the capacity of the battery. > The capacity is usually given in Ah units (Ampere hours). Technically correct, but in practice you can often make a good guess based on the W and VA numbers. When you look at the specifications of various UPSs one will find that a great many of them are specified to be able to provide power for about 5 min when running at max load, and proportionally longer when under lower load. So for an UPS rated 1000W with a load of 500W it will probably be able to power that load for about 10 min. (There are of course UPSs that behave differently, but I believe they are a minority.) -- <Insert your favourite quote here.> Erik Trulsson ertr1013@student.uu.se
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