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DC Power Saves 15% Energy and Cost @ Data Center 371

Posted by CmdrTaco
from the juice-is-loose dept.
Krishna Dagli writes "Engineers at the Lawrence Berkeley National Laboratory and about 20 technology vendors this month will wrap up a demonstration that they said shows DC power distribution in the data center can save up to 15 percent or more on energy consumption and cost. The proof-of-concept program, set up at Sun Microsystems' Newark, Calif., facility, offered a side-by-side comparison of a traditional AC power system and a 380-volt DC distribution system, running on both Intel-based servers and Sun systems."
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DC Power Saves 15% Energy and Cost @ Data Center

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  • Safety (Score:5, Insightful)

    by TimeTrav (460837) on Wednesday August 09, 2006 @09:57AM (#15873282)
    I, for one, would not be comfortable working around high power DC. Call me paranoid, but I rather enjoy my heart beating with its current interval. You can take all the precautions you want, but accidents do happen.
    • Re:Safety (Score:4, Insightful)

      by andrewman327 (635952) on Wednesday August 09, 2006 @10:08AM (#15873379) Homepage Journal
      A 220 volt AC wall outlet will also kill you. Honestly, how many electrical accidents injure or kill IT workers every year? Not very many.
      • Re:Safety (Score:5, Funny)

        by drgonzo59 (747139) on Wednesday August 09, 2006 @10:13AM (#15873415)
        But we wouldn't know...As soon as one dies he gets shredded and a replacement takes his place. Thousands of IT workers die everyday and most people don't even know it.
      • Re:Safety (Score:4, Funny)

        by cswiger2005 (905744) <cswiger@mac.com> on Wednesday August 09, 2006 @10:26AM (#15873514) Homepage
        220VAC can be fatal if you manage to ground yourself in a fashion that causes the current to pass through your chest, but it's uncommon and good practice working with live circuits means you try to avoid the situation. In particular, people working on the innards of CRT tubes are advised to keep one hand in their pocket when near the flyback transformer and HVAC power circuitry driving the vacuum tube to avoid a short from one hand -> chest -> other hand.

        Getting one hand shocked at 220VAC is not pleasant, but it's not especially painful either...
        • Proper PPE (Personal Protective Equipment) should prevent these shocks altogether. If you shut off the power and carefully handle capacitators using thick rubber electrical gloves, you should not be shocked. I'm too lazy/busy to research it now, but I am sure that OSHA has stricter recomendations than "Don't ground through your chest."


          The electrical current that powers your heart is not really all that powerful and can be messed up pretty easily if the amps and volts are high enough.

          • Re:Safety (Score:5, Insightful)

            by cswiger2005 (905744) <cswiger@mac.com> on Wednesday August 09, 2006 @11:16AM (#15874000) Homepage
            Obviously, you don't work on live circuits if you have a choice of working with them off instead, but good habits mean you treat even dead circuits as if they were live until fully isolated & disconnected, just as you should treat a gun as being loaded until you've confirmed that it is not.

            Well-designed power supplies often have a bleeder resistor across the primary filter caps to drain them of juice, but note that the vaccuum tube in a CRT makes an excellent capacitor as well (it's being charged to 20 kilovolts or more), and it's dangerous to try to dead-short it to drain the residual current. 120VAC current shock can be fatal but that is very uncommon; however, the voltages inside a CRT are probably the most dangerous level of current most people have around in their homes or work environments.
        • Re:Safety (Score:3, Funny)

          by neonfrog (442362)
          ...CRT('s)...HVAC power circuitry...

          Your monitor has its own AIR CONDITIONER? Awesome....
      • The first electric chair was AC... although this wasn't because DC is a kitty-cat -- Edison and Co wanted to push DC, so they decided to try and make Westinghouse's AC current look dangerous. They held public demonstrations where they electrocuted animals (including an elephant).

        Also, I read somewhere on the internet that Edison got his kicks off hooking car batteries to his nipples.
    • Re:Safety (Score:5, Informative)

      by Engineering_bully (900092) on Wednesday August 09, 2006 @10:09AM (#15873392)
      You probably don't realize that most of the lighting and mechanical systems in your data center are already 277/480 VAC. That is the standard power configuration for a new commercial building (cuts down on conductor sizes). There is a dedicated transformer to create 120 VAC for all the plug loads.

      In a properly designed DC system, your no more/less safe than your already are.

      (Sorry for the repost - I finally remembered my login)

      • Re:Safety (Score:4, Informative)

        by cswiger2005 (905744) <cswiger@mac.com> on Wednesday August 09, 2006 @10:33AM (#15873568) Homepage
        277/480VAC power distribution involves 3-phases of current which are 120 degrees out of sync with each other and a forth wire for neutral. In order to get 120VAC, you just need to connect between one of the phases and neutral; you don't need a step-down transformer. The wikipedia article here has a decent discussion:

        http://en.wikipedia.org/wiki/Three-phase_power [wikipedia.org]
        • Re:Safety (Score:2, Interesting)

          In the 277/480 VAC system the phase to neutral (and typically ground) voltage is 277 VAC. The difference phase angle makes the phase to phase voltage 480 VAC (not 277*3 = 831 VAC).

          In the 120/208 VAC system the phase to neutral voltage is 120 VAC - so your right. To get 120 VAC for a wall outlet you take one phase of the three phase system. You still need a transformer to get from 277/480 to 120/208.

          • Re:Safety (Score:3, Informative)

            by cswiger2005 (905744)
            Yeah, you're right that you'd need a transformer to go from 277/480 to 120/208.

            On a good day, there is minimal voltage difference between neutral (or common) and ground, but if the site has a poor or floating building ground, you can see some pretty severe voltage swings. Also, if the load on the three phases isn't reasonably well-balanced, that'll nudge neutral away from ground and you'll get current leaking to ground which is wasteful and even dangerous at higher amperages.

            I've even seen old wiring in me
        • Re:Safety (Score:3, Informative)

          by mrball_cb (463566)

          277/480VAC power distribution involves 3-phases of current which are 120 degrees out of sync with each other and a forth wire for neutral. In order to get 120VAC, you just need to connect between one of the phases and neutral; you don't need a step-down transformer.

          Ummm....No.

          1) 480 3 phase can be 3 wire or 4 wire. 3 wire is called Delta (floating ground or one of the legs can be tied to ground). 4 wire is called Y (typically the 4th wire is the "center" of the Y and is grounded.
          2) You get 277 VAC referen

      • by Phreakiture (547094) on Wednesday August 09, 2006 @11:06AM (#15873895) Homepage

        Speaking of conductor sizes, the article said this:

        A DC system also would mean having to bring in larger cables than now exist with AC power.

        I challenge this notion. Conductor size is not related to whether the power is AC or DC or what frequency of AC it might be; it is related to current.

        Larger cables are needed when more current is passed. Traditionally, you need larger cables for DC, because traditionally, DC power systems were lower voltages (12, 24, 48) than AC systems, and these lower voltages required larger currents for same power (e.g. 100W= 830mA at 120V, but 8.3A at 12V). Running at 380V, however, you get to lower the current (excluding the reduced current caused by the 15% power savings) versus a 120V system.

        Expanding on that, the reduced conductor size is proportional to the square of the reduced current. Simply by going from 120V to 380V (a factor of 3.17), you change the current flow downward by a factor of .32. This means you can change the cable cross-section area to by a factor of .1; you reduce the cable to one-tenth its original size; one tenth the copper.

        • I challenge this notion. Conductor size is not related to whether the power is AC or DC or what frequency of AC it might be; it is related to current.

          Not really correct: as the frequency increases, the current tends to flow in the outer regions ('skin') of the conductors, known as the skin effect [wikipedia.org]. Because the core of the conductor is not used, the effective area is reduced and therefore the resistance increased. For this reason hollow or flat conductors are used for high frequency applications.

    • This myth goes all the way back to 1877 when Edison & Westinghouse were electrocuting elephants to show wheter AC or DC was "safer".

      State-sponsored electrocutions used AC ...

    • Re:Safety (Score:4, Interesting)

      by gurps_npc (621217) on Wednesday August 09, 2006 @10:33AM (#15873572) Homepage
      You have your facts backwards. Human beings are far more sucpetible to Alternating current than to Direct Current. One of the reasons Edison prefereed using Direct Current was that if everything else is the same, house hold Alternating Current will kill you, while the same amount of electricity transformed to Direct Current will not.
    • True, accidents happen, but when have you ever been shocked in your current AC data center? If you haven't, than DC should be just as safe... unless you're actually doing the wiring.
  • by krell (896769) on Wednesday August 09, 2006 @09:58AM (#15873286) Journal
    Read Stephen King's "Tommyknockers". You can do a lot of things if you go DC-only!
  • by Firethorn (177587) on Wednesday August 09, 2006 @10:01AM (#15873314) Homepage Journal
    Well, the fact that they're boosting power to 380 volts, three times that of traditional AC, will tend to reduce resistance losses for any given power cable. Power companies tend to up the voltage on their longer runs for the same reason. The same number of watts, run over a given length of wire at a higher voltage will loose less to resistance. In addition, DC to DC power converters have become far more efficient than they used to be.

    When they used to talk about DC power systems be less efficient, you have to remember that most of them were talking about 12-48 volt systems.

    From the article:
    A DC system also would mean having to bring in larger cables than now exist with AC power.
    Not according to my electronics class, if they're really going to be running at 380 volts. They'll need more insulation instead. I'd also want to be real careful around those wires. DC will kill you much quicker than AC of the same voltage/amperage. Then again, you don't have to worry about shorting yourself to ground with DC.
    DC power is more of a niche idea that could help high-end users with large data centers, but will have less use to many other businesses, according to critics.
    For now.
    • Deadly DC? (Score:5, Informative)

      by drgonzo59 (747139) on Wednesday August 09, 2006 @10:08AM (#15873381)
      DC will kill you much quicker than AC of the same voltage/amperage. .
      I always thought the opposite was true. Here is a wiki quote that also supports that:
      Low frequency (50 - 60 Hz) AC currents can be more dangerous than similar levels of DC current since the alternating fluctuations can cause the heart to lose coordination, inducing ventricular fibrillation,...
      Taken from http://en.wikipedia.org/wiki/War_of_Currents/ [wikipedia.org]
    • > Then again, you don't have to worry about shorting yourself to ground with DC.

      That statement makes no sense at all.
    • What are you smoking and where can I get some? 380 volts is not power, it is voltage. Also, just by increasing teh voltage without decreasing the current (as you imply) will not reduce resistive losses. If you up the voltage alone without maintaining constant power, you increase the current thereby increasing losses. AC was implemented so that an efficient and effective conversion (transformers) could be implemented. Regarding 12-48 Volt DC systems, they did propose higher DC voltages for transmission (like
      • I am not sure I completely understand the parents description or your rebuttal of power loss over long lines but... Transmitting power over a wire at higher voltage does lower the power loss overall. Power line loss is referred to as "I^2(R)" or I squared R loss. Power = Current^2 x Resistance. Power used by the transmission line will go down if current goes down. How do you get current to go down? Raise the voltage (P=IE). Therefore, increase voltage on the line and the resistive loses on that line
    • by OzPeter (195038) on Wednesday August 09, 2006 @10:20AM (#15873469)
      Depending on where you are in the world 3 phase AC is 415V or 480V, and in industry we have no problem handling that. 380 VDC doesn't seem much of an issue to me with regards to insulation safety etc and I have dealt with control panels that have operator controls running at 240VDC (and grabbed them accidently and lived to tell the story) Though now days operator controls are being specced as 24VDC.

      But as for DC killing you quicker, I would disagree that its the type of system that kills you, it will depend on the type of damage that the shock causes. You can use a 9VDC battery to kill yourself if you apply it in a manner that a small current (mA level) flows to your heart and I would guess that the same level of AC current would also do the trick. On the other hand if you pass a large current through your body that causes physical damage (major burns etc) then it won't matter if its AC or DC if the so much of the body is destroyed as you will die eventually.

      As for not worrying about grounding yourself with DC .. Bzzt .. Nope. grounding yourself is always an issue with ground referenced power systems. And I would never rely on any power system being perfectly isolated from ground. That sort of misguided thinking leads to nasty surprises.
    • Yes, they will save on resistance losses by about 1/3. (120/380)

      The savings will be somewhat in components and somewhat in power. After your UPS system (in which AC power is converted to DC for battery storage) there will be no need for the DC/AC conversion and then AC/DC in the silver box. This deletes one conversion stage, in theory (in theory communism works, in theory...)

      AC supply -> UPS AC/DC -> battery storage -> bus converter -> several servers

      rather than

      AC supply -> UPS AC/DC ->
    • Would they need much more? Even if they did the would need less shielding since the DC wouldn't be emitting any 60hz "hum".
      My question is do any systems still use 60hz as a time reference? Back in the old days a lot of internal clocks used the 60hz signal as a time reference since it was very stable over time, and it was cheap :).
      High voltage DC would eliminate the need for the big buss bars that they used in low voltage systems.
      I would take a look at some of the Navy research in the DC power area. All US d
  • switching costs? (Score:3, Informative)

    by bigpat (158134) on Wednesday August 09, 2006 @10:01AM (#15873319)
    15% seems compeling for DC power in new construction, but obviously this begs the question of switching costs. But 15% was just for the electricity used to power the servers, the article assumes as would I that there would be additional savings due to reduced cooling needs... that extra 15% electricity would have generated about that much heat. I'd like to see a breakdown of switching costs.
    • Re:switching costs? (Score:3, Informative)

      by ranton (36917)
      What the article didnt mention is what it would take to switch to DC power. You would need to replace all PDUs, UPSs and AC power cables. You would also need to convert each system on each rack.

      Most AC power is 80% efficient, which is where the 15% gain is coming from (and remember, it is UP TO 15%, not 15% all of the time). But AC power supplies are becoming more efficient, with IBM claiming its BladeCenter power supplies are 90% efficient. That means that DC will probably only give a 5%-7% gain in eff
  • by RotateLeftByte (797477) on Wednesday August 09, 2006 @10:04AM (#15873345)
    Telephone Companies had known this for years. This is why you can get 48vDC versions of most systems.
    In a telephon e exchange 48v DC is the norm.
    They have huge batteries and standy generators to keep the phone syste, running.
     
    • re 48V in telco buildings

      Yeh some where (I may have lent them out) i have a pair of 1948 GPO handbooks for technicians. Which describes the technology?

      Including how to build your lead acid batteries on site (48 hours on battery power was required) and the technical details for the pneumatic tubes used in manual exchanges to send tickets up to the trunk floor

      I have also hear some old timers war stores one i liked was about the guy who when painting in an exchange put a paint can on top of the main bu

    • 48VDC is used by the Telcos for a multitude of reasons, efficiencey isn't one of them.

      They use DC because the systems originally ran completely off batteries. The battteries were charged fomr battery chargers on the power line. One of the reasons they did that was so the phones would keep working during a power outage. The original UPS.

      Another reason for DC is that the early carbon element microphones required current running through them to work. You can make one work on AC, by the AC hum is then the pred
    • Instead of using a 380-volt DC distribution system, why not use the telephone standard: 48V? Then you could use the same 48V connectors (STD equipment, lower cost) to plug into converters that would be in the same form factor as regular AC power supplies. Then, if you really what to save money, have solar panels (or other means of power generation) to charge batteries that would feed the 48V system. Built-in UPS!
      Hum, I might be too idealist, here...
  • Edison (Score:3, Insightful)

    by Rob Kaper (5960) on Wednesday August 09, 2006 @10:05AM (#15873350) Homepage
    Good to see some more DC in use. Tesla was right about AC for many applications but DC has its merits and any useful application of DC is a credit to Edison's scientific achievements.
    • Re:Edison (Score:5, Insightful)

      by John Hasler (414242) on Wednesday August 09, 2006 @10:19AM (#15873461) Homepage
      > Tesla was right about AC for many applications but DC has its merits and any useful
      > application of DC is a credit to Edison's scientific achievements.

      For 19th and early twentieth century technology Tesla and Westinghouse were entirely right. They had no practical method of changing voltage.

      BTW you don't want to look too closely at Edison's scientific achievements. You might find that there is less there than meets the eye.
    • Re:Edison (Score:5, Insightful)

      by Svartalf (2997) on Wednesday August 09, 2006 @10:26AM (#15873521) Homepage
      Edison didn't have all that many scientific acheivements.

      The record player was really the only truely unique thing he did. Everything else was a duplication of someone else's efforts where he succeeded and the others failed- or was something one of his employees came up with. Did you know that he'd "Westinghouse" a cat "to show the dangers of AC power" during the time where he was trying to compete with AC power versus his DC system (From which ConEd initially came from...)? This would entail hooking up a grid of alternating plates with some small amount of insulating gap to an AC power connection, place them inside a cage that one's keeping a cat and then plug it in. Edison's NOT someone to be holding up as an example of scientific achievement- unless you want to hold Mengele up as well. Sure, we got a lot further in medical science because of that "Doctor", but how he got his information, I'd rather he didn't do what he did- and it's not a good example of a scientific achievement.

      DC and AC both have their place. DC is good for short-haul power distribution, but if you short out the lines you'll destroy the entire power run. AC doesn't do that anywhere near as bad- which is why electric power is distributed as AC- it doesn't have the same safety issues and it can be transmitted long distances without major losses as it's being transmitted down the wire, not conducted.
      • DC and AC both have their place. DC is good for short-haul power distribution, but if you short out the lines you'll destroy the entire power run. AC doesn't do that anywhere near as bad- which is why electric power is distributed as AC- it doesn't have the same safety issues and it can be transmitted long distances without major losses as it's being transmitted down the wire, not conducted.

        AC can be transmited long distances without as much loss because it's easy to use a transformer to step it up to 30KV

      • Edison also "Westinghoused" Topsy the Elephant, but he was against capital punishment, even though several of his employees went on to invent the electric chair. I guess he had no problem with cats and elephants ;)

        Edison didn't have a lot of inventions, but Edison mainly improved existing inventions like the light bulb and got boatloads of patents on that sort of thing. The money he made on these patents probably funded most of the research, so it wasn't without merit.

        Your final point is something I was g

      • it doesn't have the same safety issues and it can be transmitted long distances without major losses as it's being transmitted down the wire, not conducted.

        Actually DC can also be transmitted long distances as well. It's high voltage that allows long distance power distribution, not something special about AC. The reason why we use AC for power distribution and not DC is that AC can be easily stepped up or stepped down to different voltages using simple technology. It's only recently become possible to d
    • Tesla was right about AC for many applications but DC has its merits and any useful application of DC is a credit to Edison's scientific achievements.

      Edison died in 1931.
      Tesla died in 1943.
      The Bell Labs transistor was successfully built in 1947.

      Neither Edison nor Tesla had the fair knowledge of the proliferation of transistors 60-70 years posthumous. I don't know about you but practically every on-grid device in my apartment is DC based. TV, computer, clocks, cordless phones, DVD player, etc. The only th

  • by jc42 (318812) on Wednesday August 09, 2006 @10:07AM (#15873375) Homepage Journal
    ... those claims of saving "up to 15 percent or more".

    That pretty much covers the entire range of possibilities.

    I often wonder why they didn't say something like "up to 50 percent or more" or "up to 99 percent or more". Those would be every bit as meaningful.

  • by Flying pig (925874) on Wednesday August 09, 2006 @10:08AM (#15873385)
    DC buses have been used in military and industrial equipment since DC/DC converters were invented. (In fact, other former Cambridge undergraduates may remember the old 200V DC bus in the Cavendish labs, exposed contacts to the motors and all. Nostalgia...)

    You can also store DC whereas you cannot store AC, meaning UPS always need an AC-DC followed by a DC-AC stage. Since we have had large FET power transistors it has been possible to make DC/DC conversion very efficient - especially since, if you were beginning again, you would not choose 50 or 60 Hz for best efficiency.

    In fact, already the PC is using a DC bus to power small peripherals (USB) and it works surprisingly well.

    I may be wrong about this, but it was Edison who accused DC power of being more dangerous ("Westinghoused") only to have AC adopted for the pleasant US custom of humanely frying criminals.

    • by sjs132 (631745)
      I may be wrong about this, but it was Edison who accused DC power of being more dangerous ("Westinghoused") only to have AC adopted for the pleasant US custom of humanely frying criminals. From: http://www.ieee-virtual-museum.org/collection/even t.php?id=3456872&lid=1 [ieee-virtual-museum.org] Edison was less than thrilled with the emergence of Westinghouse's technology, which threatened his own dominance in a field he virtually created. He also had genuine concerns about the safety of AC. The two men engaged in a public re
    • by Anonymous Coward
      I'm afraid you are. Edison was the promoter of DC power and coined the term "Westinghoused" for electrocution. He used to go round electrocuting dogs and in one case an elephant to 'prove' how dangererous AC power was.
  • The article didn't really describe technically what they did. Can someone explain to me how moving to DC helps? AFAIK:
    - This eliminates the need for a AC->DC rectifier in each component
    - But they still need to have the transformers to step down the voltage
    - DC requires twice as many wires

    Is the elimination of the rectifier a significant efficiency increase? Or is the real benefit in the move to a higher voltage? But doesn't that just mean they need bigger transformers to step down to the 12V they rea
    • But doesn't that just mean they need bigger transformers to step down to the 12V they really need?

      Ummm... Transformers don't work with direct current.
    • Switching power supplies in computers usually rectify the incoming AC to create a high-voltage DC supply (1.4 or 2.8 times the AC line voltage). This is then chopped at a high frequency before passing through a transformer to both isolate the power and drop the voltage. It's also possible to simply chop (no transformer) if you don't need isolation.

      It may be that they distribute the DC supply which would be used in the PSUs anyway. Therefore the PSU is slightly less complex. Or they could replace the PSU wi
    • by Phreakiture (547094) on Wednesday August 09, 2006 @11:23AM (#15874063) Homepage

      - But they still need to have the transformers to step down the voltage

      This is done with a pulse-width modulator. An AC-DC power supply already has one of these running from 380VDC anyway. The 380VDC in that case is derived from a type of rectifier called a voltage doubler (in the case of 120V sources) or a full-wave rectifier (in the case of 240V sources). The excess voltage then comes from the fact that we are getting peak, rather than RMS, voltage from the AC to the DC side.

      The savings is in that the rectifiers are all consolidated. The pulse-width modulators can have an efficiency as high as 95% easily, whereas a whole switching PS can be as bad as 50% efficient.

      The savings are in the economies of scale for the rectifier. A similar savings could be realised in the pulse-width modulator, too, but would be quickly wiped out by the increase in losses by making long wire runs at low voltages (5V and 12V).

      - DC requires twice as many wires

      Nope. Still two to complete a circuit, just like AC.

  • dc / dc converter (Score:5, Interesting)

    by wwwillem (253720) on Wednesday August 09, 2006 @10:13AM (#15873413) Homepage
    Would be interesting to know what the efficiency is of a 380 -> 12/5 DC-DC converter, compared to a traditional 110 AC -> 12/5 DC converter. This is of course only just a part of the total picture, but in the past this has often been mentioned as the reason for _not_ going DC. Maybe with modern switching power supplies, that problem has disappeared.
  • by miller60 (554835) on Wednesday August 09, 2006 @10:13AM (#15873416) Homepage
    This issue has a been a hot topic [datacenterknowledge.com] at conferences for data center professionals, with a lot of debate about timetables. Several facility designers are advocating DC distribution as the solution to the current power/cooling challenges. Corporate data center managers like the cost savings projections, but want to see it work in someone else's facility before they put their neck on the line and pitch a DC conversion to their bosses. That's the real value of the Livermore project discussed in TFA - it provides a working model.

    Right now the cost of power is remaking the landscape of the data center industry. Yesterday there was another announcement of a huge data center in central Washington State [datacenterknowledge.com]. Sabey will invest $100 million in a facility right up the street from where Microsoft and Yahoo have data centers under construction. It's all about cheap hydro power. Both Microsoft and Yahoo have contracted for more than 40 megawatts of power [nwsource.com] from the local utility. That's why DC is one of the solutions that will begin to get serious consideration.
  • by wowbagger (69688) on Wednesday August 09, 2006 @10:23AM (#15873495) Homepage Journal
    The assertion that DC requires larget cables is WRONG.

    From the article:
    The proof-of-concept program, set up at Sun Microsystems' Newark, Calif., facility, offered a side-by-side comparison of a traditional AC power system and a 380-volt DC distribution system, running on both Intel-based servers and Sun systems.
    (emphasis mine)
    A DC system also would mean having to bring in larger cables than now exist with AC power.


    The power lost in the cables varies as the resistance of the cable and the current in the cable.

    The power delivered to the equipment varies as the current in the cable and the voltage on the cable.

    A 380 volt DC system can deliver as much power per unit current in the cables as a 380 volt AC system (assuming a near-unity power factor).

    Ergo, the size of the cables for a 380VDC system will be the same as the size of cables for a 380VAC system.

    So, if the comparison is against a 240VAC system, then a 380VDC system will have SMALLER cables, not larger. Only if the system being compared against is a 440VAC system will the cables be larger.

    Also - a 380VRMS AC system will have a peak voltage of about 540 volts (two significant digits in, two significant digits out), and thus will require MORE insulation than a 380VDC system.

    Also - the first things a switching power supply does is rectify the AC into DC and dump it into a capacitor (and usually do power factor correction): so a power supply designed to run from DC needs neither the power factor correction nor the big capacitor (a smaller cap will still be needed, but not one that can carry the system through the bulk of the AC cycle when the voltage is below peak). This makes the power supply simpler, and removes switching losses from the rectifier (granted, a modern synchronous rectifier based on IGBJTs will have a very low loss - but it still is a loss.)

    Also - creating a backup for 380VDC is pretty easy - you use a battery bank floated at the 380VDC level. No need to "switch" from mains power to battery - you are ALWAYS running on battery, and the mains power is just charging the battery. This is how the phone company does it - the central office has a bank of batteries providing 48VDC, which is float charged from the mains. Lose mains power, and the system doesn't even blink.

    (Yes, you need to have fusing to prevent those batteries from going nuclear if shorted, but that is a much simpler problem to solve than the issues of switching to backup power for an AC system.).

    Yes, you have to design the equipment to run off the 380VDC - so you need different power supply front ends: most power supplies are split into 2 parts - the front end that takes mains power and makes about 300VDC on a cap, and the back end that makes the lower voltages from that - so the back end of the power supply does not need to be redesigned. Moreover, most power supplies use an off-the-shelf front end module, and any "magic" is in the back end - so this is NOT a major issue.
  • Traditional 110V cables will draw 3.5 times the current 380V does. That means 110 will produce more heat along the wire. Also using DC will cause you to not have to rectify the AC when it enters the powersupply of the device you are powering.

    That being said, you have to GET to 380V. My guess is they are simply rectifying 440VAC to DC.

    Seems like a cleaver, efficient idea.
     
  • residential DC (Score:3, Interesting)

    by tmbailey123 (230145) on Wednesday August 09, 2006 @10:34AM (#15873583)
    I wonder if you would see the same 15% power saving if a home was outfitted for DC use ? When you think about it most electronic devices in the home have power supplies embedded which are nothing more than AC-DC coverters, which in and of themselves waste energy.

    A DC power home would lend itself more readily to home based power generation. I believe most solar panels and windmill generate DC power which then has to be converted back to AC before it can be put on a powerline or used with conventional home appliances. With the new high efficiecy LED DC lights available the AC light bulb (a hundred year old device) is a real power hog and also generates enomrmous amounts of heat.

    100 yrs ago when they were first bring electrical power to the masses perhaps AC was the right answer, but I believe our needs and priorities have changed in the past 100 yrs and perhaps the way we generate, distribute and use electricity is due for a new analysis.
  • by viking2000 (954894) on Wednesday August 09, 2006 @10:50AM (#15873735)
    1. DC/DC conversion is cheaper and simpler bacause with a 60Hz AC signal, you have *no* power during the zero crossing. The PS has to store the energy in a capacitor or a coil to deliver during the 120 "outages" a second. A DC/DC converter operates at hundreds of kHz, so components are much smaller, and since the conversion uses square waves, it does not have the "outages" a sine function has on the input.

    2. A lot of AC/DC switching power supplies is a constant power load on the grid. It tends to draw more Amps as the Voltage decreases, producing a lot of harmonics in the mains power line, and a worse power factor than regular "resistive" equipment. Therefore the mains must be overdesigned to support this kind of load.

    2. 220V AC means 220V *RMS*; 110V is just one of the wires tied to ground. The peak-peak is around 311V. Not that different from 380V
  • by bobmorning (316459) on Wednesday August 09, 2006 @10:53AM (#15873769)
    The math works but I bet the regulatory and life safety issues will be huge. When you start introducing those voltages at the rack level you will have to address issues of Arcing, safety lock-outs, and flash-over protection.

    I bet your local electrical inspector will have issues with this. Moving industrial voltages into the data center can be done, but there will be infrastructure cost that previously didn't need to be budgeted for.

    How many data centers have you been in where there is a wooden cane located nearby? For those who don't know, the cane is there to assist in removing the hapless soul who is getting electrocuted without endangering the rescuer.

    I worked in a power distribution facility and we had them located along with huge rubber gloves in emergency stations located next to any switchgear.

  • Most computer equipment is still powered by 110VAC while mearly all of it is not only capable of running on 220VAC it runs more efficiently .

    At my last job we were expanding our data center and put in a small handful of 220V circuits, by hooking up our biggest servers to 220 we were able to increase our UPS runtime by almost 10% and reduce our HVAC duty cycle by a bit in the process.

    BITD when I went through Compaq ASE training the instructor mentioned that some server configurations (maxed out drive bay

  • This reminds me of a recent discussion I overheard here at work, yesterday. Some vendors were talking about an experiment they had heard of, where an entire office building was converted from fluorescent lighting over to LED lights. They claimed that the long-term cost was higher for LEDs due to an unexpected increase in heating costs, since the ballasts from the fluorescents had been helping to heat the building in the winter.

    Here in Wisconsin, the heat "wasted" by computer systems isn't a complete l

  • by ivan256 (17499) on Wednesday August 09, 2006 @11:08AM (#15873929)
    I see their results, but I come to a different conclusion.

    My headline would read "DC Power Results in 15% Increase in Equipment in Data Centers"
  • Goodnight Tesla (Score:3, Interesting)

    by Doc Ruby (173196) on Wednesday August 09, 2006 @11:20AM (#15874031) Homepage Journal
    Don't hydrogen fuelcells generate DC? I can't wait to hook my home gaspipe to more than just my stove, and suck in the MWs direct to my devices. Without all those AC adapters left over from the 20th Century cluttering my home, getting hot, drawing power when "off", getting lost and mixed up...

    Maybe we can use the old AC network as a 3rd broadband line, after telco and cableco.
  • by YesIAmAScript (886271) on Wednesday August 09, 2006 @11:53AM (#15874342)
    To get AC, you spin a coil in a magnetic field.

    To get DC you, um, spin a coil in a magnetic field, then rectify it, then put a huge capacitor on there to flatten out the humps.

    There's just no good method for generating DC. And even if there were, electric companies aren't going to run two new phases (DC+ and DC-) to get it to you from the source.

    Instead, the power is going to come to near you as 3-phase, then be rectified. There is a loss in that rectification, but sadly, you can't eliminate it, just change where it happens. Moving it to the other side of your power meter will have an advantage since you theoretically wouldn't have to pay for the losses, although the electric companies would surely change their rates to recoup this lost money. But note that even if they don't change their rates, you haven't saved any energy, just not paid for as much.

    So my guess is this experiment bought into this fallacy, that they measured their power usage at DC levels, found it was lower and reported that as a win, when without a source of DC power that doesn't involve rectification it really isn't.

    I'm sure they save some electricity due to the increased voltage. That reduces current, which decreases power lost. This is the same reason electric companies use high voltages for power transmission.

    The article seems to imply that power supplies convert 120VAC to 381VDC internally. This just isn't true. They never raise the voltage, and 120VAC peaks at 175V or something like that. Even 240V input would peak at 350V. So I don't get this. I think they just messed up a few numbers and really in the experiment connected rectified 240V (UK 240V, which is one phase double high, not the US one 120V phase over another) directly into the power supplies after the point where the rectifier would normally be.

    From what I can tell, going to DC just would save you the cost of lots of little rectifiers in favor of the cost of one big one. To be honest, since the small rectifiers come in commodity ATX power supplies, you're paying almost nothing for them anyway. So I don't see that it's all that valueable to consolidate them.

    I would recommend that if we wanted to save the most power on servers, we should just go to 3-phase 440V AC power supplies. A new connector would have to be designed, as the current 440V 3-phase connector would barely fit on the back of a tower, and wouldn't fit on a 1U server. This would save the most possible in losses without having to buy external rectifiers or force the electric companies to install one on site (and charge you back in increased rates).
    • by Anonymous Coward
      It's really easy to create DC. Just take a DC motor and spin the axle.

      A datacenter takes 3-phase 440VAC in, which goes directly into the backup power system. This converts the the AC into DC to be fed into the batteries, then the batteries are fed into a DC-AC converter to put out 60Hz sine wave AC. The AC from that converter then gets distributed to each computer. Each computer in turn takes that AC and converts it into 12/5/3.3VDC. Unfortunately all those AC-DC converters sitting in each computer are unne
    • 380 V DC is the battery voltage on a PowerWare UPS... they have simply removed the DC2AC converter and operates on battery voltage... and most of the loss is from the DC2AC converter.
      A switching mode PSU needs DC so AC from the wall goes first to a rectifier and then to at HF generator (100KHz or more), then to a relativly small transformer (HF = small loss = high efficiency on a transformer), then again to a rectifier and then to some voltage regulators (+12V, -12V, +5V, -5V, +3.3V).
      It is littlt oversimpl
  • by AWhistler (597388) on Wednesday August 09, 2006 @08:58PM (#15877842)
    Telecom companies have been using DC distribution systems for DECADES because they don't have to lose energy converting back and forth between AC and DC. It's about time the computer industry is catching on.

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