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DC Power Poised To Bring Savings To Datacenters

timothy posted more than 5 years ago | from the anthropomorphism-loves-you dept.

Power 287

snydeq writes "InfoWorld's Logan Harbaugh follows up his '10 IT Power-Saving Myths Debunked' to argue in favor of using DC power in the datacenter. The practice — viewed as a somewhat crackpot means for reducing wasteful conversions in the datacenter just a few short years ago — has gained traction to the point where server vendors such as HP, IBM, and Sun are making DC power supplies available in their server wares. Meanwhile, Panduit and other companies are working to bring down another barrier for DC to the datacenter: a standardized 400-VDC connector and cabling solution. And with GE working to list 600-VDC circuit breakers with the Underwriters Labs, DC's promise of reduced conversion waste could soon be commonly realized."

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287 comments

The arguments of olde (5, Funny)

cosm (1072588) | more than 5 years ago | (#26453981)

Tesla smiles in his grave as Franklin catches on fire from Nikolai's coil-arcs-of-doom.

The arguments of olde - don't carry much weight (5, Interesting)

trolltalk.com (1108067) | more than 5 years ago | (#26454407)

Alternate view: http://cim.pennnet.com/display_article/347089/27/ARTCL/none/none/1/A-powerful-debate:-AC-vs-DC-distribution/ [pennnet.com]

Or, to summarize - if you take a high-efficiency AC system and convert it to 480 volts, downstep to only 240 volts (and all todays' boxes can run either 110 or 220-240), you can get to within 1% of the DC system.

Add to that the savings in materials (1.5" copper wiring? Booster cables for diesels aren't anywhere near that thickness) and there's no real reason to change.

In fact, the biggest saving would probably be if we went from 120v to 240v for everything. One less down-conversion, etc.

Re:The arguments of olde - don't carry much weight (4, Interesting)

wsanders (114993) | more than 5 years ago | (#26454563)

You can achieve substantial savings just by wiring your datacenter for 240V only (in the US). The rest of the world knows this already, but every time I suggest this in the US, people look at me like I have monkeys flying out my nose. Half as many amps == half as many power strips, half as many UPS devices, half as much wire, etc. With the exception of cheap-ass wall wart powered devices, I have not encountered any equipment that was not 240V compatible in the US in years.

Re:The arguments of olde - don't carry much weight (2, Informative)

aaarrrgggh (9205) | more than 5 years ago | (#26454781)

It isn't half as many amps, it is only a 15% reduction since 208V is used in the US for data centers. The benefit (albeit at the expense of fault current) is eliminating one AC:AC transition in the process. The same could be said for getting equipment to operate at 277VAC similar to lighting in the US.

Re:The arguments of olde - don't carry much weight (1)

GagliardiMan (974622) | more than 5 years ago | (#26455093)

Would this be practical for home use? I believe most computers and home appliances will run off 240V.

Re:The arguments of olde - don't carry much weight (0)

Anonymous Coward | more than 5 years ago | (#26455151)

You have monkeys flying out of your nose.

If I have 20 servers, I'm going to need 20 outlets on my power strips.

Re:The arguments of olde - don't carry much weight (4, Informative)

aaarrrgggh (9205) | more than 5 years ago | (#26454769)

The concept is actually to go with a European 240/415V system rather than ever using US voltages of 480/277 and 120/208V; you step down from medium voltage directly to the 400V. "Best practices" would be to have an offline or line-interactive UPS.

The biggest gain is actually in the power supplies and not the electrical distribution system. I'm a fan of 600VDC in the data center from an engineering perspective, but there are huge safety issues that need to be resolved to make it viable. (DC arcs don't self extinguish as there is never a zero crossing.)

When discussions were first being done five years or so ago, my theory was that for it to be practical you would need a 3N design rather than today's 2N system, as all work would need to be done on cold busses and you still had to maintain 2N redundancy.

Re:The arguments of olde - don't carry much weight (0)

Rei (128717) | more than 5 years ago | (#26454839)

Add to that the savings in materials (1.5" copper wiring? Booster cables for diesels aren't anywhere near that thickness) and there's no real reason to change.

At least when it comes to HVDC power transmission, I've seen it reported that they can put *more* power over lines of a given thickness than they'd be able to with AC, *and* it takes less wires. The justification for the more power aspect is that the voltage is limited by arc-over, and in DC it's constant, at near max, while in AC it fluctuates up and down, averaging significantly below its max. Also, there's no skin effect. Concerning wires in HVDC: with ground return, you only need one wire, and without ground return, you need two. I saw one interesting scheme for retrofitting existing AC lines involving having two positive and one negative, or vice versa, with the matching ones each running at under their rated current and the non-matching one running over its rated current, but rotating which line is which every few minutes to prevent overheating.

Now, what goes on in HVDC is not necessarily applicable here, of course, since that involves extreme voltages and distances...

Re:The arguments of olde (5, Interesting)

Smidge204 (605297) | more than 5 years ago | (#26454439)

Ere... not sure why "Insightful" since Tesla was the one who invented the AC polyphase distribution system, and would probably not approve of using Edison's (not Franklin's?) DC distribution method.

That said, AC power made a lot more sense before the event of solid state power electronics. You can't reasonably convert DC to DC efficiently without using an AC phase via transformer, which was a major hurdle in using DC power. High frequency power supplies can do the job just fine, though.
=Smidge=

GNAA poised to bring FP to slashdot (-1, Offtopic)

Anonymous Coward | more than 5 years ago | (#26453985)

eat my asshole.

Re:GNAA poised to bring FP to slashdot (-1, Offtopic)

Anonymous Coward | more than 5 years ago | (#26454097)

I would have eaten your asshole, but I don't do that for non-FPers. I ain't no slut, y'hear?

GE working with DC. (5, Funny)

jellomizer (103300) | more than 5 years ago | (#26454003)

Who would have thought the GE would be a big supporter of DC.

Re:GE working with DC. (-1, Flamebait)

Anonymous Coward | more than 5 years ago | (#26454083)

Yeah, but I'm stickin' with Marvel.

only because (4, Informative)

ArchieBunker (132337) | more than 5 years ago | (#26454107)

Switching power supplies have gotten much more efficient in the past few years. Now it makes sense for a standard DC bus to run everything. The telecoms have been doing this for ages.

Re:only because (3, Insightful)

Anonymous Coward | more than 5 years ago | (#26454687)

Telcos have been doing it at -48VDC for ages. I'm not so sure -400VDC is a good thing. DC voltage doesn't let go, if you grab a wire by accident you'll be toast

-48VDC is safe, -400VDC is scary

Re:GE working with DC. (5, Informative)

bughunter (10093) | more than 5 years ago | (#26454175)

GE is what became of the Edison General Electric Company [wikipedia.org], the losing proponent of DC Municipal Power a century ago.

Re:GE working with DC. (3, Insightful)

afidel (530433) | more than 5 years ago | (#26454897)

I saw some cool DC gear a couple weeks ago at the Henry Ford Museum, the original DC power plant from NY and a huge 4MW DC generator which was one of nine installed at the Highland Park Ford plant in 1913.

As far as using DC in the datacenter, my calculations show it just doesn't pay, one or two percent more efficient power use does not justify the large premium DC parts demand today. Part of this is economies of scale and part is market segmentation, DC has historically been used for carrier grade equipment which equipment manufacturers have been able to demand a premium for.

Re:GE working with DC. (0)

Anonymous Coward | more than 5 years ago | (#26454731)

DC in certain datacenters MAY be an advantage. The fact that HP, GE, and whoever is making things that make DC in the datacenter easier does not change the factors to determine IF it is a logical choice for you. It just means they are selling what they think people will buy.

 

Battle of the Currents (5, Funny)

Wonko the Sane (25252) | more than 5 years ago | (#26454019)

I felt a great disturbance in the Force, as if millions of Tesla fanboys suddenly cried out in terror and were suddenly silenced. I fear something terrible has happened.

terrible indeed (1)

unity100 (970058) | more than 5 years ago | (#26454505)

as in all those datacenters saving power through dc, actually receiving the electricity from the national distributing network through ac ?

Re:terrible indeed (2, Interesting)

peragrin (659227) | more than 5 years ago | (#26454891)

Yes,
AC has better voltage drop and in most cases voltage conversions.
DC is more effecient in closed loops.

So you want distance ac is king. However your car will never be AC. DC is far safer in such situations.

I have always been under the thought. Electric companies should deliver AC to the home. Where it gets converted to DC.

Re:terrible indeed (1)

Rei (128717) | more than 5 years ago | (#26454963)

If we switch over to HVDC for long-distance power transmission, they may well not be.

Re:Battle of the Currents (0)

Anonymous Coward | more than 5 years ago | (#26454981)

Thanks, Suddenly Susan.

600VDC is not chicken soup for the soul (4, Insightful)

fred fleenblat (463628) | more than 5 years ago | (#26454021)

Suggestion for the DC power supply designers: have a heart and build GFCI into the spec.

Re:600VDC is not chicken soup for the soul (1)

rabtech (223758) | more than 5 years ago | (#26454771)

While this is a good idea in the sense that no one likes being electrocuted, the risk of DC shock is more about burns than anything else, since there isn't any alternating current to cause fibrillation of the heart.

The idea of GFCI is to detect the current imbalance (magnetically) within a short enough time frame that the AC jolt doesn't cause a disruption of your heart rhythms.

Re:600VDC is not chicken soup for the soul (1)

aaarrrgggh (9205) | more than 5 years ago | (#26454865)

Even GFCI isn't enough; you have to also have active arc-fault detection, and you need all this fault detection throughout the entire system. It isn't as easy as stringing together 480 D-Size batteries...

Why wasn't this tagged 'edison v. tesla'? (1, Informative)

Smidge207 (1278042) | more than 5 years ago | (#26454027)

One of the important factors that was overlooked other than the inefficiency of DC over large distances is the risk of electric shock. DC is unforgiving and anyone who receives a shock at the higher voltage levels will have very little to no chance of survival as DC current polarizes the blood and there is no way to reverse that effect in time to save that person.

See the following for a basic description of what this is about.

http://www.cdc.gov/eLCOSH/docs/d0500/d000543/section2.html [cdc.gov]

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/shock.html [gsu.edu]

The difference between direct and alternating voltages and currents is that one swings negative to positive thereby reversing the polarity of the potential while with dc everything is a constant supply and thus more harmful.

=Smidge=

Re:Why wasn't this tagged 'edison v. tesla'? (3, Funny)

Wonko the Sane (25252) | more than 5 years ago | (#26454217)

One of the important factors that was overlooked other than the inefficiency of DC over large distances is the risk of electric shock. DC is unforgiving and anyone who receives a shock at the higher voltage levels will have very little to no chance of survival as DC current polarizes the blood and there is no way to reverse that effect in time to save that person.

Assuming that you don't modulate the phase variance of the deflector dish, of course.

Re:Why wasn't this tagged 'edison v. tesla'? (1)

Shakrai (717556) | more than 5 years ago | (#26454301)

DC current polarizes the blood and there is no way to reverse that effect in time to save that person

Huh???

Re:Why wasn't this tagged 'edison v. tesla'? (1)

Shikaku (1129753) | more than 5 years ago | (#26454399)

In other words, you have a much higher chance of dying from a DC electric shock than compared to an AC shock.

Re:Why wasn't this tagged 'edison v. tesla'? (2, Interesting)

Wonko the Sane (25252) | more than 5 years ago | (#26454723)

In other words, you have a much higher chance of dying from a DC electric shock than compared to an AC shock.

Maybe, but it it has nothing to do with "blood polarization". There is more than one way to measure AC: peak, or RMS

1 amp DC carries more energy than 1 amp AC (peak) and thus is more harmful.

1 amp DC is exactly equivalent to 1 amp AC (RMS) in terms of energy and harm*.

*One possible exception is if the AC is very high frequency and the load is not purely resistive. Then you get wacky tesla coil effects.

Re:Why wasn't this tagged 'edison v. tesla'? (1)

Shakrai (717556) | more than 5 years ago | (#26455027)

One possible exception is if the AC is very high frequency and the load is not purely resistive

I'm guessing that a human being is a purely resistive load? ;)

Re:Why wasn't this tagged 'edison v. tesla'? (1)

Chris Mattern (191822) | more than 5 years ago | (#26454531)

Apparently you can't reverse the polarity of the blood flow if you don't have a sonic screwdriver.

Re:Why wasn't this tagged 'edison v. tesla'? (1)

Yvan256 (722131) | more than 5 years ago | (#26454685)

If I hit my screwdriver on the wall, it makes a sound, doesn't it?

Re:Why wasn't this tagged 'edison v. tesla'? (3, Informative)

clonan (64380) | more than 5 years ago | (#26454635)

I call not true!

The body is exceptionally good at accomidating a stable force acting on the system. What causes most electricution deaths are the sudden change in voltages throwing the heart out of rhythm or scrambling the brain log enough for the person to die.

The actual physical damage of electricution is usually very minor (first or second degree burns through the path of the current). The alternating nature of AC makes it much more likley to mess up the heart and brain. 120 chances a second. DC only has one chance.

Now DC will cause greater BURNS because the constant voltage at the same power can generate more heat, but the burns are not what kill you.

Neither article you cited mentioned DC vs AC. Almost every mention of current related it to HOUSEHOLD current which suggests AC.

Finally, the blood cannot be "charged." It is a fluid with some conducting ability since it is full of various ions. Any charge it does accumulate would almost immediatly ground out to the rest of the body and from there to the earth.

If you want to make dramatic claims please provide plenty of citations

Re:Why wasn't this tagged 'edison v. tesla'? (4, Insightful)

bradgoodman (964302) | more than 5 years ago | (#26454653)

I was so bemused by the explanation of the "polarization of the blood" - that I had to read the links you provided.

However, in these links there was no reference to this at all.

I don't think there is any truth to this.

Re:Why wasn't this tagged 'edison v. tesla'? (1, Informative)

Anonymous Coward | more than 5 years ago | (#26454677)

OH look, a TROLL!!

Whoever modded this informative is an IDIOT.

In reality:

"Low frequency (50-60 Hz) alternating currents can be more dangerous than similar levels of DC since the alternating fluctuations can cause the heart to lose coordination, inducing ventricular fibrillation, which then rapidly leads to death within six to eight minutes from anoxia of the brain and medulla.[9] However, any practical distribution system will use voltage levels quite sufficient for a dangerous amount of current to flow, whether it uses alternating or direct current. Since the precautions against electrocution are similar, ultimately, the advantages of AC power transmission outweighed this theoretical risk, and it was eventually adopted as the standard worldwide."

Here is a whole thread about the subject:

http://cr4.globalspec.com/thread/3212/Which-is-More-Dangerous-AC-or-DC [globalspec.com]

Re:Why wasn't this tagged 'edison v. tesla'? (2, Funny)

Valdrax (32670) | more than 5 years ago | (#26454779)

Re: Title

Why don't you do it yourself? It's not like there's anything stopping you.

PARENT IS A TROLL - MOD DOWN (0)

Anonymous Coward | more than 5 years ago | (#26454957)

Parent is a troll, stop modding him informative you idtios.

-Tesla

And Nikola Tesla.... (0, Redundant)

kcbanner (929309) | more than 5 years ago | (#26454045)

rolls over in his grave.

Re:And Nikola Tesla.... (5, Funny)

Farmer Tim (530755) | more than 5 years ago | (#26454123)

rolls over in his grave.

If that's because of DC, does it mean he's fitted with a brushless commutator?

Re:And Nikola Tesla.... (1, Funny)

gblackwo (1087063) | more than 5 years ago | (#26454149)

The same joke occurred to me, but I felt it was a little to lame to post.

Re:And Nikola Tesla.... (-1, Flamebait)

Anonymous Coward | more than 5 years ago | (#26454473)

I felt it was a little to lame to post.

Too, you dopey cunt.

Re:And Nikola Tesla.... (2, Funny)

Devil's BSD (562630) | more than 5 years ago | (#26454143)

Well, if you put a magnet on him and wound wire around the coffin that could be a clean source of electricity...

What about a _home_ standard for DC power? (5, Insightful)

mrchaotica (681592) | more than 5 years ago | (#26454063)

I don't run a datacenter, but I sure would like to get rid of the power bricks that all small electronic appliances seem to come with these days!

Re:What about a _home_ standard for DC power? (2, Interesting)

ryanleary (805532) | more than 5 years ago | (#26454221)

Well, particularly for those small devices it would seem that they would still require stepdown circuitry--likely a transformer. It just won't require rectification and smoothing.

Re:What about a _home_ standard for DC power? (0)

Anonymous Coward | more than 5 years ago | (#26454415)

...likely NOT a transformer, since those work for AC, not DC.

Re:What about a _home_ standard for DC power? (1)

petermgreen (876956) | more than 5 years ago | (#26454543)

I would guess a transformer based SMPSU (since you would probablly want isolation between input and output)

Re:What about a _home_ standard for DC power? (3, Interesting)

bughunter (10093) | more than 5 years ago | (#26454279)

Agreed. My PC and media installations are plagued by a plethora of these heat-generating devices, as I add on printers, ethernet devices, networked disks, extra storage, converters, encoders, decoders, and the like. I had to learn to include plans for a well-ventilated place for these things.

Also, it's an inherently good idea for power savings. Power supply efficiency can go way up when both a) total power goes up and b) the supply can be designed for a constant load (which would be the case for a large data center, for sure).

Re:What about a _home_ standard for DC power? (3, Interesting)

WorthlessProgrammer (895488) | more than 5 years ago | (#26454659)

I don't run a datacenter, but I sure would like to get rid of the power bricks that all small electronic appliances seem to come with these days!

probably because these 'wall-warts' are linear converters - seldom better than 40% eff.

As more stuff conforms to the ENERGY INDEPENDENCE AND SECURITY ACT OF 2007, these will become much less of an issue.

Re:What about a _home_ standard for DC power? (2, Insightful)

Doctor Faustus (127273) | more than 5 years ago | (#26454753)

I don't run a datacenter, but I sure would like to get rid of the power bricks that all small electronic appliances seem to come with these days!
We (EPA?) should start with standardizing 12 volt DC connectors to let a PC run directly off of a UPS without going through the DC->AC->DC pass.

This is snake oil (4, Informative)

jmorris42 (1458) | more than 5 years ago | (#26454775)

> I don't run a datacenter, but I sure would like to get rid of the power bricks...

DC vs AC wouldn't help you rid yourself of power bricks. No more than it can help a datacenter get rid of power supplies in each server. Telco equipment runs on 48 volts not to save electricity but because of the way telephone exchanges are built. Telephones don't go down, period. So how do they accomplish this miracle? Huge battery banks. Back in the day a DC-AC conversion system large enough to run a whole switch plus drive every telephone would have been all but impossible. So they just ran everything directly from the batteries and used the mains to charge the batteries.

This DC in the datacenter thing is just a green craze that will pass. It is pure unadulterated snake oil. Go reread the summary. They ain't even doing the smart thing and adopting the telco 48V standard. Does anything in a server run on 48V? No. Does anything in a server run on the 400V they are proposing? No. So a DC-DC conversion will be needed, i.e. a switch mode power supply. Guess what is in a current server? A switch mode power supply. Current PC power supplies are available with efficiencies over 90% without buying too far off the mainstream. I seriously doubt these DC powered supplies will be much better and in the end that is the ONLY number that matters. Except these DC installations have to factor in the power loss from the big AC-DC conversion and worry about redundency, backup power, etc.

The world needs love (-1, Troll)

Anonymous Coward | more than 5 years ago | (#26454073)

I know this is off-topic but please forgive that. I urge you to give someone a warm embrace and tell them that you love them, and mean it. There is not enough of this in the world today.

In the good old days (3, Informative)

oldzoot (60984) | more than 5 years ago | (#26454081)

In the 80's we built custom interfaces for large computers using wire-wrap Standard Logic Inc. wiring modules. The planes of wiring were assembled into rackmount chassis which were fed DC power via a vertical bus-bar system in the rack. The busbars were about .5 X 1 inch solid copper, insulated by shrink tubing with holes cut for the threaded holes in the busbar. The power supplies were rackmount 100 or 200 A Lambda supplies providing either 5 volts or 12 Volts. It was occasionally a pain to be called into the computer center in the middle of the night to replace one of those heavy power supplies - at least they were at the bottom of the rack.

OZ

Re:In the good old days (1)

Muad'Dave (255648) | more than 5 years ago | (#26454877)

You didn't work for Concurrent Computer, did you? I remember the same sort of beastly power supplies - I still have a couple of them. The rumor (possibly fact) was that Concurrent (which was Perkin Elmer Data Systems) had some of the first patents on switching supplies.

Those were the days - a 32 bit Floating Point Unit made out of _discrete_ 74xx series chips, mainly 74181's. It took a full 17" x 17" board. Youch! Their flagship system, a 3280 [cbronline.com] clocked a whole 6 MIPS for a uniprocessor system. I think at one point they actually burned the whole 3280 system that used to take up at least one full 6 foot cabinet into a single FPGA. That's progress!

Re:In the good old days (1)

kiehlster (844523) | more than 5 years ago | (#26454947)

Yes, in the good ol' days we had DC power transmission lines, but the last ones were decommissioned last year [boingboing.net]. So sad. And we just learned the benefits now.

WTF? (5, Funny)

Shadow Wrought (586631) | more than 5 years ago | (#26454115)

I thought the power in D.C. caused waste and ineffeciency.

Re:WTF? (5, Informative)

ivan256 (17499) | more than 5 years ago | (#26454157)

The article can basically be summed up as follows:

Though there are more transmission losses with DC than with AC, if your DC->AC conversion can be done with an outdoor-rated supply, you save more in cooling by doing the conversion outdoors than you'd lose in transmission losses.

Re:WTF? (2, Insightful)

amorsen (7485) | more than 5 years ago | (#26454275)

Though there are more transmission losses with DC than with AC

There aren't, at the same voltage. In fact AC loses slightly more at a given voltage, up to a lot more for really long wires.

Re:WTF? (4, Informative)

girlintraining (1395911) | more than 5 years ago | (#26455123)

In fact AC loses slightly more at a given voltage, up to a lot more for really long wires.

Whiskey. Tango. Foxtrot. Line losses are based on current not voltage. And with AC you can convert current and voltage with a transformer with a very high Q. That's why AC (Tesla) beat DC (Edison) at the turn of the century for power distribution. Also, direct current generates more heat than alternating current. -_-

Re:WTF? (4, Informative)

rabtech (223758) | more than 5 years ago | (#26454719)

DC power lost the "current wars" because we didn't have solid state transformers capable of doing voltage step up/down like we did with AC back in the day (simple wound transformers).

These days even the cost of really high power DC transformers (>500,000 volts) is offset by more efficient transmission and a number of notable long-distance power lines are actually DC for that reason (lower losses offset cost of transformers).

By stepping up the voltage, such as to 48v, you can significantly lower the losses, shrink required conductor sizes, make the circuit breakers cheaper, and still derive the same benefits (48v->12v->5v->3.3v DC transformers are actually fairly cheap, unlike their high-power cousins).

Why do you think some car makers are switching to 48v DC on-board power and 48v batteries? You can greatly increase efficiency and lower weight since so many devices are electrical on modern cars.

Old hat in the telco world (5, Interesting)

Anonymous Coward | more than 5 years ago | (#26454121)

Telco gear tends to be 48VDC all over the place. It just works. Speaking as a guy working at a telco in the IT department, I'm hugely in favor of moving to 48VDC servers.

Re:Old hat in the telco world (1)

denis-The-menace (471988) | more than 5 years ago | (#26454443)

I'm not a telco guy but I am aware of the 48VDC standard.

Why didn't they just do the same for servers in a datacenter?

Re:Old hat in the telco world (1)

fuzzyfuzzyfungus (1223518) | more than 5 years ago | (#26454765)

They seem to be heading in that direction; but I assume that it has something to do with the fact that most servers have an evolutionary heritage that goes back to normal x86 boxes plugging into generic wall current. Sure, today's servers are specialized a bit, but their design very much takes advantage of the extraordinary economies of scale to be had in sharing components with normal computers. Not until there is a critical mass of very large datacenter installations(which it seems like their is, because we are, after all, reading this article) does switching to some other power source make sense.

Re:Old hat in the telco world (1)

Pontiac (135778) | more than 5 years ago | (#26455183)

HP tried with their first Blade servers.
They came with a 48v power supply that mounted in the bottom of the rack that could power a whole rack full of blade chassis or you could wire it to your telco PS.

The 2nd generation moved to AC power, funny that they are thinking of going back again.

Re:Old hat in the telco world (1)

WorthlessProgrammer (895488) | more than 5 years ago | (#26454749)

Telco gear tends to be 48VDC all over the place. It just works. Speaking as a guy working at a telco in the IT department, I'm hugely in favor of moving to 48VDC servers.

It "just works" because you have a huge battery 'stack' somewhere - very filthy and dangerous lead-acid stuff.

Also, a TNV power distribution system is not necessarily any more safe than AC mains power at overvoltage cat I or II.

Why not 12V, 6v or 3.3v, etc? (3, Interesting)

olddotter (638430) | more than 5 years ago | (#26454227)

I'm not an EE. But back during the dotboom I thought it would make sense to have a big ups in the data center that output voltages that mother boards expected as input. I almost thought of rigging my own experiment using laptops as servers and feeding them all 12vdc directly from the UPS battery pack.

Ok rip it apart guys, why is wrong with that plan?

Re:Why not 12V, 6v or 3.3v, etc? (0)

Anonymous Coward | more than 5 years ago | (#26454303)

The enormous cables you'd have to run everywhere?

Re:Why not 12V, 6v or 3.3v, etc? (5, Informative)

autocracy (192714) | more than 5 years ago | (#26454413)

Power loss over distance. 12 volts loses four times as much energy in one foot of travel as 24 volt transmission does. Telecom gear, for example, runs on 48 volt DC. For the few feet of travel in your laptop, 12 volts is fine. Crossing a room at 12 volts, you'd get too much voltage drop.

See http://en.wikipedia.org/wiki/Electric_power_transmission#Bulk_power_transmission [wikipedia.org]

Transmission efficiency is improved by increasing the voltage using a step-up transformer, which reduces the current in the conductors, while keeping the power transmitted nearly equal to the power input. The reduced current flowing through the conductor reduces the losses in the conductor and since, according to Joule's Law, the losses are proportional to the square of the current, halving the current makes the transmission loss one quarter the original value.

Re:Why not 12V, 6v or 3.3v, etc? (1)

rabtech (223758) | more than 5 years ago | (#26454613)

Because the power delivered is roughly voltage * current (amps), by bumping the voltage you can lower the current and carry the same effective power across smaller wires, which is a huge cost savings given the cost of copper, circuit breakers, etc.

*Yes, I know this is a very rough description and I haven't posted the proper mathematical formulas.

Re:Why not 12V, 6v or 3.3v, etc? (1)

Gat0r30y (957941) | more than 5 years ago | (#26454895)

Single point of failure. At least last time I proposed a this idea on slashdot the prevailing mods seemed to think this was the case.
On a related note, what do you have at your desk that actually requires more than 12V? If we are able to make this switch in a data center, why not in an office? If we got LED lighting (obviously florescent lighting requires higher voltages, but who's really gonna miss florescent light anyway) I can't think of anything on my desk that actually runs on AC, rather than converting it to 12V, 5V and or 3.3. CRT's would have to go, but they have already been replaced with LCD's for the most part anyway. Thoughts?

48VDC pros/cons (IMHO) (5, Interesting)

mlts (1038732) | more than 5 years ago | (#26454229)

Pros:

No power supply needed for each machine. This removes a major point of failure. Instead, one would need to just step down voltages to the 5 and 12 volt rails. This also helps with cooling because the room AC/DC converter can be cooled with a dedicated system, either liquid, or part of the HVAC system.

Cons:

48 VDC needs a dedicated connector with a high plug/unplug cycle rating that people know is 48 volts and 48 volts only. It sucks when you have to manually wire it up, because this takes time and there is always the risk of getting zapped if you don't throw the right circuit breaker (or pull the right fuse) on a telco rack where 48V is in use.

Because there is only one 48VDC power supply for a room, it has to be held up to a lot more rigorous standards than average mains current. It has to not just provide 48VDC, but provide it under extremely heavy load without the voltage dropping by much.

Maybe 48 volts would be a new computer standard. The key is not having to wire it up manually like some stereo speakers, but giving it a dedicated, foolproof, power connector that Joe Twelvepack who is slurping down his seventh can of Bud Light can easily and reliably plug and unplug while staggering around in the back of the server room until his shift ends.

Re:48VDC pros/cons (IMHO) (4, Insightful)

PPH (736903) | more than 5 years ago | (#26454499)

Another pro:

A UPS would consist of nothing more than a battery charger and 48V battery.

Re:48VDC pros/cons (IMHO) (5, Interesting)

harmic (856749) | more than 5 years ago | (#26454837)

As someone else here has already noted - 48VDC power supply distribution has been standard in Telco exchanges since.... forever as far as I know. When I first started working in Telecoms (early 90's) the exchange would have a separate power room with rectifiers and huge battery banks. The resulting 48VDC was distributed through the equipment room using large busbars. In latter years this approach has mostly been replaced with smaller power supplies installed in each suite of racks, but the principle is still the same. It has always seemed somewhat ridiculous to me that one powers one's server by passing 240 or 110 VAC into a UPS, convert it to DC, charge a battery with it, invert it back up to 110/240, feed it into the server, which then converts it back to DC.

Re:48VDC pros/cons (IMHO) (1)

morgan_greywolf (835522) | more than 5 years ago | (#26454519)

The key is not having to wire it up manually like some stereo speakers, but giving it a dedicated, foolproof, power connector that Joe Twelvepack who is slurping down his seventh can of Bud Light can easily and reliably plug and unplug while staggering around in the back of the server room until his shift ends.

Don't blade servers kind of solve this problem already? The bus box already supplies a DC current to each of the blades, right?

Cancer-Fighting Beer (0, Offtopic)

troll8901 (1397145) | more than 5 years ago | (#26454617)

From your post:

... that Joe Twelvepack who is slurping down his seventh can of Bud Light can ...

From another TFS [slashdot.org]:

... helping Joe Six Pack fight aging and cancer with every swill of beer ...

There's a correlation somewhere here, but I can't figure it out.

Re:48VDC pros/cons (IMHO) (2, Interesting)

MBCook (132727) | more than 5 years ago | (#26454641)

The whole 48v DC thing sounds good to me (I don't run a data center though, or anything like it).

That said the article discusses (and I've seen it said elsewhere) the large copper bars used for wires in this kind of setup, and how they will lose more power between the wall and the rack than AC.

I can see the appeal of going TOTALLY 48v, but why not run AC to the racks, and just have a large converter for every 2 or three that provides the full DC power and backup for those three racks? You're still avoiding inefficiency in having 20+ individual power supplier per rack. And you avoid a voltage conversion (instead of thousands->hundreds->110v->whatever DC you need you'd have thousands->hundreds to top of rack->whatever DC is output). That would save some juice.

Plus the per-rack theory would make it really easy to convert equipment a few racks at a time without having to move a whole large chunk of a data center.

PS: I assume people would still use dual (or more) redundant PSUs on the individual boxes, even though they wouldn't be dealing with nearly as much heat since they don't have to do the whole AC->DC thing.

Re:48VDC pros/cons (IMHO) (1)

rabtech (223758) | more than 5 years ago | (#26454655)

Because there is only one 48VDC power supply for a room, it has to be held up to a lot more rigorous standards than average mains current. It has to not just provide 48VDC, but provide it under extremely heavy load without the voltage dropping by much.

No, you can have multiple DC supplies dumping power onto a common supply rail with just a few extra electronics and protection devices. You don't have sync issues like with AC power where everything needs to be exactly in-phase.

Furthermore these devices can be placed in the basement, on the roof, etc in locations that aren't necessarily required to be held at some constant cool temperature, as they can function in a much wider range without noticeable loss of service life.

Re:48VDC pros/cons (IMHO) (2, Interesting)

Cobralisk (666114) | more than 5 years ago | (#26454699)

A. You won't get zapped from 48VDC. If you are extremely sweaty you might feel a slight tingle, but nothing to get excited about.

2. Just wire up some big batteries in parallel and you don't have to worry about voltage drop under load. As long as the rectifiers can keep with the current needed to float the batteries at 48V (really more like 52V in practice) you're fine. As stated by an earlier poster, this is proven technology in use by telcos for a very long time.

D. This whole article is about datacenters. I hope Joe Twelvepack hasn't just slurpped down 7 Bud Lights and wandered in to wire up some servers, but if he has I doubt a dedicated power connector is gonna keep him from fouling something up. There already exist standard 48VDC connectors. They're called lugs. Just remember, the positive terminal goes to ground. Actually I have seen modular plugs for this purpose, but any tech worthy of working near such equipment should be able to terminate a color-coded cable easily enough.

Re:48VDC pros/cons (IMHO) (0)

Anonymous Coward | more than 5 years ago | (#26455205)

Even a colour blind electrical worker?

Seriously though, I'm all for 48v. Let's just standardize on a connecter. Make it easy

- One round hole and one square hole.
- Ground pin (square) slightly longer so it makes contact first
- this should also close a "connected to mains" circuit in the 48DC to 12/4/3.3/1.5 down conversions.

If you want to improve upon it, Plugging in a 48DC battery should have the same connector. So each DC-DC power supply should have two connectors, one intended for use with the 48V mains, and one intended for use with a 48V UPS/Battery or can be connected to a secondary 48V system for failover.

So in an ideal configuration you get
a) 48V rail to the rack from mains
b) 48V rail to the rack from UPS/Diesel generator/etc

If the mains cuts out, there is no sudden power loss from the switch to the UPS/generators.

Re:48VDC pros/cons (IMHO) (0)

Anonymous Coward | more than 5 years ago | (#26454789)

you don't get zapped by 48V, unless you try to taste it.

Re:48VDC pros/cons (IMHO) (1)

pz (113803) | more than 5 years ago | (#26455101)

Pros:

No power supply needed for each machine. This removes a major point of failure. Instead, one would need to just step down voltages to the 5 and 12 volt rails.

Um, no. Stepping down a higher voltage to a lower voltage, say 48VDC to 5VDC and 12VDC from your example, would still require a power supply. That, precisely, is what a power supply does: voltage conversion. What you're talking about is a DC/DC power supply, rather than the traditional AC/DC ones. But, when it comes down to it, all of the modern computer power supplies are switching supplies that take AC, put it through a bridge rectifier, filter it a little, and then follow that with a DC/DC converter.

By providing 48VDC instead of 120VAC to the input to a power supply, you're eliminating the bridge rectifier (with typically less than 1% losses) and the filtering capacitor (with even lower losses, in a decent design at least). That's it.

Now, converting the noisy, ripply 170VDC that results from rectifying 120VAC to a low voltage is a harder task than converting relatively clean 48VDC to the same low voltage, and starting out with a input voltage that's almost the same as the output voltage means lower current losses, especially in a switching supply. But -- and this is a huge issue -- high current DC connectors are extremely difficult to design because of the inherent electromigration/electrolysis you get with DC current that is just not present at all with AC current. Where are said connectors? At the input to the power supply.

 

Because there is only one 48VDC power supply for a room, it has to be held up to a lot more rigorous standards than average mains current. It has to not just provide 48VDC, but provide it under extremely heavy load without the voltage dropping by much.

Any decent power supply works over a large range of input voltages. Designing for a precise input range (say, 48 to 48.5VDC) is shortsighted. Ever notice that the laptop power supply you have is rated for 100-240VAC? So are many (not all, but many) desktop power supplies. While the hypothetical room's 48V needs to be pretty good, it does not have to be held to any higher standards as you suggest. The circumstances where it would need to be held to higher standards would be if the delivered voltage were to be used directly without any local regulation / re-provisioning. And that would be just plain poor engineering.

Edison vs Tesla (4, Insightful)

swell (195815) | more than 5 years ago | (#26454347)

One can't help but reflect upon these two and their stubborn support of DC and AC respectively. Edison created a circus atmosphere demonstrating the dangers of AC. He electrocuted dogs & other animals and even participated in the design of the electric chair to prove his point.

Edison's financial ambition was part of the problem, and his inability to understand AC, but mostly it seems to have been an emotional attachment to DC.

Let's hope that in our time emotion and personal gain have no part in such decisions.

Already on board (5, Funny)

Waffle Iron (339739) | more than 5 years ago | (#26454437)

a standardized 400-VDC connector and cabling solution

I set this kind of system up myself and it works great, assuming you need a lot of cores. I strung together 296 Intel Core 2 Duo chips in series accross the 400VDC supply, so each one gets the specified 1.35 volts. If I want to overclock, I just take a set of alligator clips and shunt across a few dozen of the chips, and it boosts the voltage to the remaining CPUs.

The only problem is that with so many chips, I get occasional failures, just like I do with my old Christmas lights. Then I have to try shunting around each of the CPUs by trial and error until I isolate the burnt out one before I can get my cluster running again. Oh yeah, I also have to be really careful to keep any peripherals I plug in away from each other and/or grounded objects.

A reasonable idea (0)

Anonymous Coward | more than 5 years ago | (#26454455)

The only issue I really see with this would be a safety issue. 110VAC and 220VAC aren't particularly safe (anything over 50V AC or DC isn't safe to touch), but 600VDC is very scary to be working around. Aside from that I have no problems with the logic in TFA, besides a few minor errors: stepping down 16kVAC to 440VAC to 220VAC to 110VAC should only incur a total loss of less than 2% (more likely less than 1%) since transformers are typically efficient in the 99% and higher range.

Already seen on UPS units (3, Informative)

jockeys (753885) | more than 5 years ago | (#26454493)

Just a side note, this has already been growing in the field of UPS units for at least 5 years, and it's not terribly hard to find UPS units and PSU units with DC connectors.

(Since to use a UPS without DC means converting battery's DC, sending it to the PSU in AC where it's converted back again.)

Rocking news (0)

Anonymous Coward | more than 5 years ago | (#26454603)

It's great news when a brain-shake idea that started off as a fly in the wall is able to stand up and be back in business with a flick of a switch. When dealing with such high voltage and when dealing with rising power costs from power companies who got you by the balls, ideas like this shake your foundation. It's time to show business you ain't got hold on me. It isn't important who made who. Let's make it. The IT budget must get back in black.

And I say it with a stiff upper lip.

P.S.: AC/DC fans, I salute you.
P.S.2: cowardly posted to protect the guilty.

IIRC there was a UPS study on DC power recently (3, Interesting)

petermgreen (876956) | more than 5 years ago | (#26454873)

That concluded that using the european system of 230/400 3 phase AC for distribution splitting out to 230V single phase AC near the point of use was almost as efficiant as a 400V DC system and far cheaper and easier to deploy. Your servers existing power supplies can almost certinaly handle 230V without any problems (changing a switch may be required on crappier models)

BTW in many cases there are often huge savings to be made without changing your infrastructure just by using better PSUs, cheapasss PSUs are both inefficiant and unreliable.

Commercial DC Data Center solutions (3, Informative)

miller60 (554835) | more than 5 years ago | (#26454975)

There are a number of companies providing commercial DC solutions for data centers. Validus DC Power [datacenterknowledge.com] is providing products for DC power distribution, while Power Loft [datacenterknowledge.com] is building a brand new data center optimized for DC power.
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