On 11/17/2010 3:13 PM, Brad Knowles wrote: > On Nov 17, 2010, at 11:30 AM, Daniel Clark wrote: > >> Thanks - at least one useful thing I've gotten from this thread is >> that whatever I end up doing, it would seem to make sense to have >> smaller COTS "front end" UPS units, connected to whatever backend (be >> it COTS or DIY), and have separate "front end" units for servers and >> HVAC. > One thing you don't want to do is to connect a UPS to another UPS. They do > *NOT* like to be chained like that. I've worked at several places where they > absolutely forbade any kind of in-rack UPS for equipment because there was a > UPS system for the whole room, and they didn't want to risk frying everything > in the room because of a single stupid in-rack UPS. > This used to be good solid advice, but is a bit dated (borderline obsolete) these days. *) it's perfectly fine to do this if the second UPS is much smaller than the first (say 10:1) *) this is wisdom from when UPS's often delivered square wave output inside of sinusoidal. If you have good behaving UPS's, then it's reasonable to do this where the upstream might only be twice as big as the downstream.
Many of the rules still present are based upon old manufacturing technology, and the UPS's really don't care as long as they both generate real waveforms. There are still many considerations, though. http://nam-en.apc.com/app/answers/detail/a_id/397/~/daisy-chaining-ups _______________________________________________ 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/
