From owner-freebsd-questions@FreeBSD.ORG Wed Aug 11 21:59:01 2010 Return-Path: Delivered-To: freebsd-questions@FreeBSD.ORG Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 3A421106566B for ; Wed, 11 Aug 2010 21:59:01 +0000 (UTC) (envelope-from erikt@midgard.homeip.net) Received: from ch-smtp01.sth.basefarm.net (ch-smtp01.sth.basefarm.net [80.76.149.212]) by mx1.freebsd.org (Postfix) with ESMTP id E8DAC8FC0C for ; Wed, 11 Aug 2010 21:58:59 +0000 (UTC) Received: from c83-255-61-120.bredband.comhem.se ([83.255.61.120]:61535 helo=falcon.midgard.homeip.net) by ch-smtp01.sth.basefarm.net with esmtp (Exim 4.71) (envelope-from ) id 1OjJJS-0000Ku-3Z for freebsd-questions@FreeBSD.ORG; Wed, 11 Aug 2010 23:58:20 +0200 Received: (qmail 12020 invoked from network); 11 Aug 2010 23:58:16 +0200 Received: from owl.midgard.homeip.net (10.1.5.7) by falcon.midgard.homeip.net with ESMTP; 11 Aug 2010 23:58:16 +0200 Received: (qmail 81228 invoked by uid 1001); 11 Aug 2010 23:58:16 +0200 Date: Wed, 11 Aug 2010 23:58:16 +0200 From: Erik Trulsson To: freebsd-questions@FreeBSD.ORG, ryan.coleman@cwis.biz Message-ID: <20100811215816.GA81198@owl.midgard.homeip.net> References: <5304A319-0406-4510-B6B2-8FD609239FF9@cwis.biz> <201008112120.o7BLKgxe054400@lurza.secnetix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201008112120.o7BLKgxe054400@lurza.secnetix.de> User-Agent: Mutt/1.5.20 (2009-06-14) X-Originating-IP: 83.255.61.120 X-Scan-Result: No virus found in message 1OjJJS-0000Ku-3Z. X-Scan-Signature: ch-smtp01.sth.basefarm.net 1OjJJS-0000Ku-3Z 0528b4dd7a40f95cc844b4f16ed2c968 Cc: Subject: Re: UPS question X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 11 Aug 2010 21:59:01 -0000 On Wed, Aug 11, 2010 at 11:20:42PM +0200, Oliver Fromme wrote: > Ryan Coleman 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.) -- Erik Trulsson ertr1013@student.uu.se