On Tue, 30 Nov 2010, Jack Coats wrote: > Back 'in the day', I remember Sun selling servers being available with 48VDC > power supplies > especially for the telcom industry. > > Most CO's (central office exchanges) had to provide at least 8 hours of > service even with power > grid not available, so to do this they really ran off of large banks of > batteries... 48V DC was the > preferred. And it was used for all the switching and related equipment at > the CO. They charged > the battery bank from commercial power, and normally have generators for > when the commercial > power fails, but still everything ran off of 48VDC. If you needed AC, you > had to run an inverter, > but again, it had to take in 48VDC. > > Why 48VDC? I am sure it is in the history books for the Bell System and > Western Electric somewhere. > If someone knows the original reason, I would be interested. > > In any case, legacy 48VDC system are there, and some vendors take advantage > of it, since telcom > is a pretty big market and the infrastructure for distributing the power is > already well developed. > > If they need some other voltages, they invert it and use appropriate > switching power supplies to get > the desired voltage.
more precisely, it's -48v from ground that's used in telco environments. there's a lot of value for those companies to be able to just wire stuff in to the battery banks rather than having to run separate power. David Lang _______________________________________________ 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/
