On 10/1/07, Karl Larsen <k5di@xxxxxxxxxx> wrote: > Bob Goodwin wrote: > > Les wrote: > >>> > >> These supplies are switching supplies, not linear. You should check > >> some of the draws, I think you will be surprised about how little some > >> of them draw (admittedly there are various design strengths out there.) > >> > >> In general, a linear supply is about 20-35% efficient, meaning that a > >> 450 watt supply would draw about 90 watts all the time. But these new > >> switchers are about double that or more, meaning that the supply will > >> draw somewhere between 20 and 50 watts. Moreover that draw will > >> basically be independent of the size of the ultimate supply, simply > >> existing to control the switcher itself, and not the drive current. > >> Technology exists in some forms of "buck control" that could boost the > >> on line efficiency further reducing the drain. Power stuff is evolving > >> even faster than much of the other technology, but is less glamorous, so > >> doesn't get as much of the press. > >> > >> Regards, > >> Les H > >> > >> > > Here's some more interesting information on power supplies. Note that > > best efficiency is attained at/near maximum load. So a 500 watt > > supply looks good but may not be what you want when considering power > > consumption and disposing of waste heat. > > > > http://services.google.com/blog_resources/PSU_white_paper.pdf > > > > Bob Goodwin > > > Hi Bob, I am interested in what Google has done but need a lot more > information. They say changing the PS to one making just plus 12 volts > will save energy. I do not see that as a given. In fact it makes me > think they are just passing on the voltage change to the mother-board > makers. I think the idea being the MB makers can make just the other > voltages their board needs. But converting 12 to 1.5 volts with economy > of power is complex and will jack up the MB cost somewhat, and will make > it hotter. > > > > -- > > Karl F. Larsen, AKA K5DI > Linux User > #450462 http://counter.li.org. They're trying to get rid of distributing AC to all the racks and the losses resulting converting from AC to DC for each MB. If the MB design only requires 12 VDC input then it is more efficient to have only one AC to DC converter and buss the DC to all the boxes in a rack. By the way, people have been bussing 24 and 48 VDC in equipment racks for years.
