From owner-freebsd-questions@FreeBSD.ORG Wed Aug 11 16:44:43 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 64582106564A for ; Wed, 11 Aug 2010 16:44:43 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from asmtpout027.mac.com (asmtpout027.mac.com [17.148.16.102]) by mx1.freebsd.org (Postfix) with ESMTP id 4B6238FC0C for ; Wed, 11 Aug 2010 16:44:43 +0000 (UTC) MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; charset=us-ascii Received: from cswiger1.apple.com ([17.209.4.71]) by asmtp027.mac.com (Sun Java(tm) System Messaging Server 6.3-8.01 (built Dec 16 2008; 32bit)) with ESMTPSA id <0L6Z007ULYIAL350@asmtp027.mac.com> for freebsd-questions@freebsd.org; Wed, 11 Aug 2010 09:44:35 -0700 (PDT) X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 ipscore=0 phishscore=0 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx engine=6.0.2-1004200000 definitions=main-1008110129 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.0.10011,1.0.148,0.0.0000 definitions=2010-08-11_07:2010-08-11, 2010-08-11, 1970-01-01 signatures=0 From: Chuck Swiger In-reply-to: Date: Wed, 11 Aug 2010 09:44:34 -0700 Message-id: <3135A83C-6FD9-4C3B-958F-11EE85221061@mac.com> References: To: Ryan Coleman X-Mailer: Apple Mail (2.1081) Cc: User Questions 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 16:44:43 -0000 Hi, Ryan-- On Aug 11, 2010, at 8:51 AM, Ryan Coleman wrote: > Total: 495W > > According to a calculator if I enter all that information: > http://www.csgnetwork.com/upssizecalc.html > It says that it will use 693VA. That sounds reasonable. The better PSUs have "80 Plus" certification for efficiency, and that's better than the typical wall warts used for modems and switches and the like commonly manage. (The efficiency they're assuming is a bit over 70%; using 80% would be around 600VA.) > Enter that into http://www.csgnetwork.com/batterylifecalc.html > It requires Amps... 495W / 120 voltage = 4.125 amps... doesn't seem right but... > 192 hours... that's not right, right? Assume for discussion their number was right. In order to get 495W of output load, the UPS needs to provide 693 volt-amps of juice to your equipment. After the inverter and 10:1 stepup transformer used to convert 12VDC or whatever the UPS batteries are charged to up to 120VAC, the current needed would be 5.77 amps. However, the 12VDC battery source itself would be getting a draw of 57 amps (ideally; again, the inverter+transformer themselves might only rate about 90% efficiency for very good quality UPS, so would be drawing more like 60 or 65 amps). A standard APC/Tripplite/whatever 700VA UPS tend so have a lead-acid battery reasonably similar to a car battery, and typically will have around 100 amp-hours of charge; they'd probably give you 90 minutes of backup time. But you can look up the detailed specs of specific models and work from their amp-hour (or watt-hour) ratings-- actually, I think I'm guestimating more from what a 1200VA unit might provide, and a 700VA model is probably going to provide more like 40-60 minutes of power... Regards, -- -Chuck