On Nov 29, 2010, at 3:18 PM, Chris Hoogendyk wrote: > Since they listed item 4 and said, "in most cases," one might assume that the > UPSs they manufacture and sell still provide a step-approximated sine wave > when running on battery power. Looking for details on their web site, the > Smart UPS series claim a pure sine wave on battery, but the Back UPS series > have nothing regarding sine wave, square wave or step-approximated. They > don't say anything. I guess you don't advertise the shortcuts you take on > less expensive hardware.
The BackUPS units and even some of the SmartUPS units do generate step-approximated sine waves -- you have to check the individual descriptions of each unit to see if they advertise it as generating a "pure sine wave" or not. Any unit where they don't advertise generation of a "pure sine wave" means that they use step-approximated sine waves instead. And given the losses that result from converting AC to DC back to AC even in just a single UPS, I definitely would not want to be daisy-chaining multiple UPSes together if I had any choice at all. I read a very interesting paper a while back that said that Google gets around this issue by having a large battery directly attached to the motherboard of each of their computers, and then providing whatever dirty power they have available to the batteries. In other words, basically each computer has a dedicated UPS built-in, and they don't make any attempt to provide any kind of whole-room style of UPS. The battery on each system is big enough to provide a significant amount of runtime, so that they can switch over to generator backup at a relatively leisurely pace, and they have remote power monitors on each system so that when the battery starts losing the ability to keep a charge, that system is marked as "down", and they stop using it. When enough systems in a given container are marked as down, they mark the whole container as down and then replace it wholesale. And they have enough spare containers on hand at each site that they never have to worry about running out. -- Brad Knowles <[email protected]> LinkedIn Profile: <http://tinyurl.com/y8kpxu> _______________________________________________ Tech mailing list [email protected] https://lists.lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
