On Fri, Dec 03, 2010, Joel Jaeggli wrote: > > (OK, so it's not as practical when you have other customers to worry > > about... but it might not be so crazy when you're looking at the > > efficiency numbers for 100,000 small 1u power supplies vs a set > > of much larger ones.) > > Ohm's law is a bitch. 10kamp -48v DC plants are bad enough as far as the > amount of copper required, running 12v for significant distance is comical, > this is the reason small boats airplanes and diesel trucks adopt 24v systems. > There's probably some model where top of rack rectifiers makes sense but > that's really pretty much what a blade server is. When you look at a > motherboard in a server a big chunk of of real-estate is devoted to taking > 12v and switching it down to 1.2-1.8 for distribution to the CPU/memory, a 4 > socket server might have to carry 400amp around in a space of around 300cm^2 > on a layer of the pcb. > > The justification for running 208 or 480 all the way to a cabinet is all > about smaller conductors.
Isn't this one area where Google have already (re-)pioneered recently? Besides, there's a reason why AC won over DC for carrying 0 < x < few hundred (or thousand? Amps) over a reasonable distance. IANA-PowerEngineer, but ISTR the behaviour/efficiency of voltage/current over distance for both AC and DC is well understood. (And no, ISTR it isn't "AC wins." :-) If you're at all serious about discussing this, I bet spending 15 minutes doing some research and then an hour or so crafting some simultaneous equations to solve/graph would be very very eye-opening. Come on guys/girls, you're a bright bunch, post some models and discuss those rather than un-substantiated datapoints! :-) 2c, Adrian
