On Wednesday, July 06, 2011 12:24:12 PM John R Pierce wrote:
> 500 watts at 12VDC is 41 amps. that requires some hefty wiring, and if
> you have to run it any distances, either the wire is ridiculously heavy
> (and expensive) or you suffer from voltage drop under load.
While not CentOS-specific, this *is* in my area of expertise. We have 540Ah of -48VDC driven by a pair of Lorain Flotrol 200A rectifiers for our telco equipment (including the Cisco 12008 and OSR7609 routers). Our solar sites are mostly 24VDC with, again, 540Ah minimum at each site, with a few 12VDC systems with 75 to 300Ah at each site. I've run enough 4/0 and larger flex cables, that's for sure..... for 41 amps, up to 25 feet or so, relatively small 8AWG is sufficient. That's smaller gauge than the 6AWG and 4AWG I ran for the 12008 and 7609, respectively, for -48VDC power. (I say relatively small; the largest conductor size we have here is 6kA rated busbar, so even 2AWG or 2/0 AWG is relatively small......:-) )
I've seen much larger, specifically in the Brookhaven 5ESS in Atlanta. I remember seeing one branch circuit idling at ~2.5kA. Hmmm, speaking of 5ESS, I wonder what the chance of a CentOS for a 3B15 or 3B20 would be? :-) (No, Russ, before you ask: I don't still have the 3B15's that used to be here.....)
For a reference on DC power design, useful if you need to support CentOS servers with DC supplies in a telco environment, please see "DC Power System Design for Telecommunications" by Whitham D. Reeve for the 'canonical' reference work. Everything you need, including current limit and overcurrent protection, low-voltage cutouts, distribution design, voltage drop and wire sizing calculations, and ampacity tables for DC (NEC includes AC ampacity tables, but not DC).
And I have a few CentOS boxes running on DC power. And, of course, having powertop running on CentOS, and having some low-power modes, helps tremendously.
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