Will Dyson on 9 Jun 2009 15:46:09 -0700 |
On Mon, Jun 8, 2009 at 11:58 PM, Paul L. Snyder<plsnyder@drexel.edu> wrote: > Just tripped the circuit breaker...the second time this summer that the > combined load of the printer and the A/C have pushed it over the edge. <snip> > Any suggestions for a where to start when shopping for a UPS? Aside from the basic considerations of inverter power (the VA rating) and battery capacity, there are a few qualitative differences between UPS models. One difference is if the UPS is a "standby" or "online interactive" type. This refers to how the inverter is hooked to the output. In the standby type, the mains waveform is normally passed directly to the output (well, hopefully through the surge suppressor circuit). The UPS monitors the mains waveform and switches the output over to batteries + inverter if things go outside its "normal" parameters. This switchover takes a few milliseconds, in which the output is not powered. In the online interactive type, the inverter is always wired into the output, and can be used to supplement the mains power in a brown-out or reduce an over-voltage. Because this uses less energy from the battery than fully powering the output, this type can have much tighter tolerances for when to kick in. It also means that there is much less of a gap when going to battery power. While the online interactive type is nice for expensive and delicate equipment, it is mostly wasted on a computer's PSU. The PSU has its own internal capacitors that can ride out the standby's switch to battery power. It also tolerates under and over-voltage pretty darn well. The other thing that more expensive UPSs have is a serial port interface that allows you to read and set values in the UPS's firmware. Things like the threshold voltages for going to battery, current battery charge, power draw history, you name it. This is generally termed a "Smart UPS", although some units without this label have a serial port with some basic functions. Oh, and replaceable batteries. Lead-acid gel cells have a finite lifetime, and the charging circuits in most UPSs are not very gentle. This is generally a feature of all but the smallest UPSs. Ones without it are really thow-away units. Of these three items, I think replaceable batteries is the only thing worth spending extra cash on. I like the Trip-Lite brand of UPSs, but I've owned a number of APC units as well. -- Will Dyson ___________________________________________________________________________ Philadelphia Linux Users Group -- http://www.phillylinux.org Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce General Discussion -- http://lists.phillylinux.org/mailman/listinfo/plug
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