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Tom O'Connor
Asked: 2011-12-16 09:14:04 +0800 CST

Using 48v for servers

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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.
hardware physical-environment datacenter electrical-power blade-server

2 Answers

  1. Best Answer

    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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  2. 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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