I think you haven't seen the price of copper distribution wire and installation lately. That 48v dc wire is *much* bigger than 208v wire. If you've ever seen a dc only telco datacenter you've probably seen some monster copper alloy distribution busses. There is a lot of loss in low voltage distribution. The current preferred distribution by google and others is distributing 480v ac direct to the computer, often without any ups or with small battery pack direct attached to each machine and a single 480v to 12v conversion. 48v distribution is very expensive. People who are doing this these days tend to try high voltage to the floor to lower the insane copper costs. High voltage dc distribution is in theory more efficient, but because there aren't that many vendors, the benefits are currently speculative and payback is uncertain. On Feb 28, 2012 10:07 AM, "Edward Ned Harvey" <[email protected]> wrote:
> > From: [email protected] [mailto:[email protected]] > > On Behalf Of Doug Hughes > > > > > I continue to wonder why more data centers don't use -48V DC > > distribution. > > > > > Because it would hugely expensive in terms of copper. to deliver 200W at > > -48V DC requires copper capable of carrying 4A. To do so at 208V > > requires a cable capable of 1A > > Which is more expensive? > You run AC to your UPS, convert it to DC, convert it back to AC, deliver it > to your systems, and convert it to DC again... > Or > You run AC to your big UPS, and deliver 48V DC to all your systems using 4A > wire. > > By using your 4A wire, you're able to eliminate the D2A, and all the A2D's > in all the systems. I think the wire is cheaper, at least in theory. The > real question is ... How popular is it? If it's insufficiently popular, > then the prices will be unnecessarily high. And that's all there is to it. > If only the DC standards were more widely adopted, this would be a very > clearly beneficial winner. Not so much in terms of energy savings > (assuming > you were going to use well-designed D2A's and A2D's, you only have a few > percent energy loss in the power conversions) Mostly the benefit is in > terms > of hardware. Not needing to buy all those computer power supplies. > > As-is today, only some of the largest server facilities are deploying DC > power to their systems. Because they're the only ones who have a scale > large enough to make it worthwhile. > >
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