On 10/1/07, Karl Larsen <k5di@xxxxxxxxxx> wrote: > Kam Leo wrote: > > 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. > > > > > The 12 volts can not be moved as 12 volts DC very far. The length of > a car is about it. So Google must have a lot of racks in close proximity. > It's probably more like one AC/DC converter per rack. Similar to a blade system where there is one power supply sending regulated power to blades which plug into the main chassis.
