Hi Arjen, I understand your technical points, but I think you are overkilling this user with information. He asked a simple question about what UPS he should buy. For reference, here is his original question:
Clay Barnes wrote: > I am running a home box (600watt total load, may expand to 800-900) and > I need a UPS that can sustain power to that for at least 20 min, but > I want as much time as I can get. > > Does anyone on the list have a similar setup with a UPS that was easy to > set up with NUT? > > Generally speaking, what mfrs. and models are very well supported? > Which should I avoid at all costs? > > I know this seems like something that would be in the archives, but my > searches thus far have been fruitless. Many PC's nowadays ship with power supplies rated 3A or similar (for example, I have such a PC). This is of course overengineered, as no PC will actually draw this much power, but I guess consumers are happy with the idea that they could put, I don't know, ten motherboards into their computer without changing the power supply. The downside is that a UPS's nominal output power should ideally match the nominal power supply of the PC, regardless whether that power is actually utilized. So when I got my PC, I multiplied 3A by 120V to obtain 360VA. To this, I added some more VA for the monitor and other miscellaneous stuff. As a consumer, I didn't know much about the difference between Watts and VA, so I may have easily confused one with the other. Fortunately, this didn't matter since my power supply was rated in Amps anyway, so when I multiplied that by 120 Volts I got the correct answer. Perhaps Clay did a similar calculation. (In which case he would, indeed, be speaking of maximum, not average, load). So to answer his question: pretty much any store-bought UPS will do in your situation. My personal advice: avoid Belkin; their hardware and software is crap. Look at the compatibility list at http://www.networkupstools.org/compat/, and get a UPS that is listed there, if possible. On the box, it is usually written (in big letters) how much runtime you can expect at a given load, so just buy one that says you get at least 20 minutes for some reasonable load. -- Peter Arjen de Korte wrote: > > Peter Selinger wrote: > > >>>> I am running a home box (600watt total load, may expand to 800-900) and > >>>> I need a UPS that can sustain power to that for at least 20 min, but > >>>> I want as much time as I can get. > >>> Is that rated load, or actual load? That seems like an awful lot of > > 600 watt (or 600VA) does not strike me as an unduely large load rating > > for a UPS. > > Please don't mix up VA and Watt ratings, they are very different things. > > > My smallest UPS has 800 VA. > > This is irrelevant when it comes to runtime. You can have an 800 VA UPS > with a Watt rating of just 10 Watts and a runtime of 1 second for > instance. Not very useful, but it is possible. The VA rating of a UPS > says nothing about the runtime. > > > What did you have in mind Arjen? > > As a summary from my previous post, you should consider both peak load > and average load when selecting a UPS. Just considering peak load, will > mean that you will select a way too big UPS if the average load is much > smaller, which is usually the case for computers. I have yet to see a > home computer system that draws more than about 50% of the full load on > average (and usually this figure is even lower). > > > Also, 20 minutes runtime is not too much to ask. > > Probably not, but at a load of 900W, conversion efficiency of 80% and > lifetime derating (due to aging of the battery) to 80%, this will > require a 1400 Wh of battery capacity (which is about 120Ah @ 12V, which > is a very large battery). You won't see many consumer grade UPSes with > that amount of battery storage installed (if there are any). Therefor my > question, if this is rated or actual (or better put, average) load? > > > It's true that the system can shut down faster than that, but a human might > > appreciate a chance to save his work. > > Of course. I'm not questioning the legitimacy of the need for a 20 min > runtime, it's the amount of power drawn that looks excessive. > > Regards, Arjen > _______________________________________________ Nut-upsuser mailing list [email protected] http://lists.alioth.debian.org/mailman/listinfo/nut-upsuser
