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I'm currently in the middle of a process to specify and design a new server environment for graphics and video rendering.

We know we want to use blades, and we're pretty sure of our vendor decisions.

We've got one massive problem, and that's power.
At the moment, we're looking at getting more 3 phase power into the building. One idea that I've heard of, is using 48v DC to power the servers and networking equipment.

Questions are these:

  1. What are the advantages of using 48V DC over 230VAC or 415VAC 3phase. (We're in the UK.)
  2. Do all of the decent (Dell, HP, IBM, Cisco)/most servers and network vendors support 48V DC power supplies?
  3. Can we expect this to be more expensive in hardware costs?
  4. Will this actually be more power efficient than using single/threephase, if all a PSU is gonna do is downcovert to +/- 12v/5v/3.3v.
  5. Can we expect lower cooling demands because of lower amount of powerloss in downconversion from 230v.
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1  
hightech.lbl.gov/documents/data_centers/DCDemoFinalReport.pdf I found this. Quite interesting. –  Tom O'Connor Dec 15 '11 at 18:05

2 Answers 2

up vote 7 down vote accepted

What are the advantages of using 48V DC over 230VAC or 415VAC 3phase

Efficienty and heat.

  • There is no AC/DC transformation in the server. Yes, you have one large converter, but it is not in your rack - so you produce less heat in the rack.
  • Efficiency. Large converters ?= more efficient. This gets really nice when you talk UPC - battery power is DC anyway, so it gets converted to AC then back to DC.

Do all/most servers and network vendors support 48V DC power supplies?

No.

Can we expect this to be more expensive in hardware costs?

Yes.

Will this actually be more power efficient than using single/threephase

Yes.

Can we expect lower cooling demands because of lower amount of powerloss in downconversion from 230v.

Yes, a little. But you also move heating out of the server rack, and it may be cheaper to cool the central AC/DC converter - depends on your building.

We know we want to use blades, and we're pretty sure of our vendor decisions.

Ok, so waht the hell are you doing here? If you arelady have a vendor choosen, ASK HIM. IF they provide DC (if not - all talks here are not relevant for you) they will have the paperwork answering all your points.

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Last I checked most of the "big" vendors have DC power supplies for their gear (Cisco definitely does for all their datacenter/carrier class gear, as does Juniper. IBM's BladeCenters do, and I believe HP & Dell as well) –  voretaq7 Dec 15 '11 at 17:32
    
Yes, but he is not asking "most of the big" but "most all/most". I for example msotly use SuperMicro and Tyan and both do not. Many smaller ones do not either, so in absolute terms (numbers of vendors) all / most do NOT. He does not ask for the largest / tier 1. So, the answer is "no", and yo ubasically tell him that he does not know how to formulate his question, which I agree with. –  TomTom Dec 15 '11 at 17:35
    
There is nothing that makes larger power supplies inherently more efficient. As long as your server has a good power supply, you won't gain any efficiency switching to a bulk 48v supply, and then since you still have to have a PSU to convert from 48v to 12, 5, and 3.3v, you likely will still end up with about the same losses to heat in the rack. You will also have to use heavier cables ( more copper ) to carry the 48v from the central supply to the cabinets and incur more losses on those cables than you would with 120/240vac. –  psusi Feb 13 '12 at 18:23
    
@psusi - no. DC/DC conversion is extremely efficient. SO efficient the whole rating for power supplies is not depending on it at all. AC/DC is the problem. This is a cost and growth thing. One large PSU is more efficient to build for good money than tons of smaller ones. And you can build it larger, you do not have for example to fit it into a 1u rack –  TomTom Jun 12 '12 at 6:24
    
@TomTom, economies of scale. Mass produced bog standard commodity power supplies are cheaper than one massive custom job. Cheaper still when you add in the cost of a bunch of smaller custom dc/dc supplies, and the copper for those heavy gauge low voltage cables isn't cheap either. How do you define "extremely efficient"? You're still talking a few percent loss that you wouldn't have if you didn't do double conversion. –  psusi Jun 12 '12 at 14:01

I work for Dell. 48VDC is actually pretty rare in Europe outside of Telcos & offers no real advantages over decent 230/400VAC. The lower voltage will mean bigger cables by a factor of around 5 & if you're running blades you'll already have an issue with gettinga the cabling terminated anyway. As for efficiency, then you'l have had to transform the 400VAC down to 48VAC then to DC so the efficiency gains are small. The standard technique these days is to run 400VAC PDUs & then run local whips at 230VAC to each blade PSU. This also enables more even phase loading than running lots of 230VAC feeds. Phase mixing within the chassis (at least with Dell, I don't know for other suppliers) isn't an issue.

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