More than somewhat off topic, but what the heck. First off, the "joules" rating of your UPS probably refers to its built in TVSS's ability to absorb surge energy.
That strongly suggests that you have a small office or home device. These usually cost in the low to mid 2-figures to the low 3-figures. They're meant to keep your desktop computer and monitor going long enough to save your work and shut down in an orderly manner, not to keep on working. The battery in these is tiny, usually good for no more than 50-80 watt-hours at full load. There's no point to connecting bigger batteries to them because their inverters aren't suited to continuous use. They will overheat and (if you're lucky) shut down. Also it's worth noting that the waveform from these cheap inverters is usually pretty hideous. A larger commercial UPS will typically be a cabinet a few feet square that sits on the floor. I worked in a place dependent on electronics that used these as temporary sources until the building genset could start and stabilize, and the automatic transfer switch change over to the genset. These larger UPSes are much more robust and can work continuously, but they're still limited by their battery capacity. They also aren't cheap. They cost in the upper 3 figures to well into the thousands. Sometimes you can find used ones cheaply on Ebay and fix them up, though. I'm not an expert on this, but here's another thought for you. I set up a standby power system here many years ago, to keep our refrigerator, freezer, and water pump working, and to provide power to a blower on our fireplace insert, in case of power cuts. My original idea was to measure the loads, calculate the duty cycle for each load, and size a battery to run the loads for 24 hours. I don't recall the result but I decided that it was more (in cost and size) than I wanted to get into, so I settled for eight group 24 gel batteries in series-parallel for 24 volts at around 3.6 kWh. I bought a used boat anchor - I mean a Trace 24 volt 2.5kW inverter, which to my surprise turned out to be just barely able to start the water pump. I moved the circuits to be protected to a Square D transfer subpanel. This is a nifty and relatively affordable gadget with 2 main breakers and a handful of branch circuit breakers (mine has 4). There's a clever mechanical rocker between the main breakers so that only one of them can be on at a time. One main breaker is connected to the mains (actually to a subfeed from the main panel), and the other is tied to my inverter through a power inlet (male panel mount receptacle). This setup served me well a few times, but over the years I've let the battery decline. I doubt that I could get more than an hour or so out of it now. But I don't really worry about it because I've realized that (1) we don't have as many power cuts as I expected; and (2) they usually only last a few hours. Others may have better suggestions for you. Good luck! David Roden, EVDL moderator & general lackey To reach me, don't reply to this message; I won't get it. Use my offlist address here : http://evdl.org/help/index.html#supt = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Some people, when confronted with a computer programming problem, think "I know, I'll use regular expressions." Now they have two problems. -- Jamie Zawinski = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ Address messages to [email protected] No other addresses in TO and CC fields UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/ LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
