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Was Thomas Edison Right about DC Power?

CowboyNeal posted more than 8 years ago | from the menlo-park-mysteries dept.


Declan McCullagh writes "Everyone knows the alternating vs. direct current wars ended with Thomas Edison and Nikola Tesla. But now DC power is being seriously considered for data centers. DC advocates say that plugging servers into AC power is inefficient, and switching to DC cuts down on waste heat and component failure. The University of Florida has even bought 200 DC servers."

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Sensationalist, but effectively correct (4, Interesting)

AKAImBatman (238306) | more than 8 years ago | (#14839936)

Was Thomas Edison Right about DC Power?

Oh, well, nothing sensationalist about that headline. (*rolls eyes*)

DC advocates say that plugging servers into AC power is inefficient, and switching to DC cuts down on waste heat and component failure.

In this case they're right. With that much hardware that close together, it's easier to treat the entire room as a single device. As the article suggests, this cuts down on waste heat produced by inefficiencies in AC->DC conversion. In fact, it significantly cuts down on the amount of equipment needed in the entire room. The concept can be taken as far as to cutting down to a single power supply per rack.

The amusing part about this is that the resulting racks might look a lot like Big Iron servers with pluggable motherboards. :-)

How Tesla can still make electricity (5, Funny)

Dukeofshadows (607689) | more than 8 years ago | (#14840125)

Wrap the casket in copper, replace the headstone with a magnet, and expose corpse to this article. As Tesla turns in grave, free power.

Westinghouse (0)

Anonymous Coward | more than 8 years ago | (#14839944)

I thought it was Westinghouse for AC.

Re:Westinghouse (1)

clymere (605769) | more than 8 years ago | (#14839968)

they bought it from tesla.

Re:Westinghouse (2, Interesting)

PabloJones (456560) | more than 8 years ago | (#14839969)

Tesla developed AC, and sold the patents to Westinghouse.

That settles it. (0, Flamebait)

SinGunner (911891) | more than 8 years ago | (#14839945)

If UF is doing it, it must be right, a-hyuck! GO GATORS!

(No, I'm not proud of having graduated from FSU, but I am proud of having not graduated from UF)

Re:That settles it. (1)

Pres. Ronald Reagan (659566) | more than 8 years ago | (#14839953)

Are you proud of having been rejected from UF, too?

Re:That settles it. (0, Troll)

SinGunner (911891) | more than 8 years ago | (#14840058)

Are you proud of having been rejected from UF, too?

That was weak. Seriously, were you even trying? I may have been taking a pot shot, but taking that big of a stretch, you had the gun turned 180 degrees.

For future reference, recursive insults are best left to the professionals. Expanding your horizons can be good, but in this case, you gotta stick with what you know, even if it is fart jokes and calling people gay.

Re:That settles it. (1)

HunterAmor (903799) | more than 8 years ago | (#14840068)

ha, judging from the quality of that post, you must have been an english major at FSU

Re:That settles it. (0, Offtopic)

Pres. Ronald Reagan (659566) | more than 8 years ago | (#14840091)

No, seriously. The fact that you were too dumb to attend the state's flagship university... Are you proud of that?

Re:That settles it. (-1, Offtopic)

Anonymous Coward | more than 8 years ago | (#14839999)

FSU = Florida State School for Women, where the Women are Women and the Men are Too!

GO GATORS (UF 81 BSEE, Linux user since 0.99pl13)

New Power System (5, Funny)

9mm Censor (705379) | more than 8 years ago | (#14839946)

I heard of this new power system. Seems like a mix of AC and DC, to create the ultimate power form. AC *lightningbolt* DC was the name, and with a lightning bolt in the name, it has to strike you like thunder.

Re:New Power System (2, Funny)

hpa (7948) | more than 8 years ago | (#14839980)

AC/DA (1)

Macgrrl (762836) | more than 8 years ago | (#14840051)

Am I ever going to see your face again? No way, get.... oh, it's the radio version...

no, dude, that's a band. (1)

swschrad (312009) | more than 8 years ago | (#14840123)

rock on.

AC`,DC (1)

BorgCopyeditor (590345) | more than 8 years ago | (#14840132)

"Swinging both ways" effectively gives you twice the power by increasing by a factor of 2 your opportunities for coupling. :-o

Number one with a bullet, I'm a power pack! (2, Funny)

mudshark (19714) | more than 8 years ago | (#14840174)

Back in black!
Yes, I'm back in black!

[tap tap]

Hey, who turned off the microphone?

Was Edison right? (1)

Fulcrum of Evil (560260) | more than 8 years ago | (#14839947)

No, he was having a pissing match with Tesla.

Re:Was Edison right? (2, Insightful)

AndroidCat (229562) | more than 8 years ago | (#14840012)

It was a proprietary patent pissing match too. Edison went with the system that he controlled the patents on, and didn't really care about the technical merits of each system.

Just think, if he'd settled with Tesla back then, today they could be sending people to be killed on the Edison Chair.

Re:Was Edison right? (1)

Sabaki (531686) | more than 8 years ago | (#14840023)

Never argue with a man that has a death ray [] .

Re:Was Edison right? (0)

Smallpond (221300) | more than 8 years ago | (#14840136)

My advice. Never piss on the third rail.

Antistropic Magnetic Fields (0)

JoeShmoe950 (605274) | more than 8 years ago | (#14839948)

Although Alternating current has provided easier long range transfer of power, it does seem to be causing problems with machines. A recent study conducted by Maxtor (sorry, I lost the link, probably on google), found that AC power generates weak antistropic fields. Although this is normally not a problem, as the power supply converts the flow to DC, a poorly shielded power supply can leak the antistropic magnetic field, sometimes corrupting data on the harddrive. Although not usually a problem, this can be dangerous around production machines, so either switch to dc, or check your power supplies carefully. Usually, it is not a problem of a poorly built power supply, but simply one who's shielding fails over time.

Re:Antistropic Magnetic Fields (2, Insightful)

imsabbel (611519) | more than 8 years ago | (#14839979)

"Anisotropic Magnetic Field" has to be the worst offense in terms of technobabble i have seen recently.
Newsflash: there are no magnetic monopoles, so EVERY magnetic field is anisotropic...

Re:Antistropic Magnetic Fields (0)

Anonymous Coward | more than 8 years ago | (#14840158)

That's why I always wear my antistropic copper bracelet when handling hard drives. It channels my negative chi ions away from the sensitive magnetic recording surfaces, as well as energising my unactualised psychic potential.

I find that really supportive, when I'm birthing perl scripts.

Re:Antistropic Magnetic Fields (2, Insightful)

demonbug (309515) | more than 8 years ago | (#14840026)

First, that would be anisotropic.
It doesn't seem too surprising that AC power would produce an anisotropic field since the current keeps switching, so the magnetic field should be switching direction also. I suppose this would make the magnetic field from a DC current isotropic (invariant with direction, or I suppose in this context constant orientation), but I don't really see why either would be an issue (since you referred to Maxtor, I assume the issue was something that had to do with hard drives). Although if you have a weak, constantly switching magnetic field it might demagnetize (randomize) low-coercivity magnetic grains (domains, whatever - I work with sediment, dammit!), but unless it is a pretty strong field it shouldn't bother the relatively hard (magnetically) magnetic media in use.
I'm too lazy to actually look up what you are referring to, though, so whatever.

Old news, for Verizon WA (3, Informative)

Anonymous Coward | more than 8 years ago | (#14839954)

In Washington State, Verizon (Was once GTE) runs almost all DC powered servers and Telco equipment in their Data Centers. Many of the IBM server my company buys support DC power.

Phone companies are all DC powered (4, Informative)

isdnip (49656) | more than 8 years ago | (#14840118)

Actually, that's the norm across the phone industry. Everything, and I mean everything, runs on -48V DC. Okay, not the fluorescent lights....

This goes back to the telephone talk battery, which is -48 V DC. That powered the phones via old cord switchboards, and was the voltage of electromechanical (stepper, and later crossbar) switches, which basically used relays. Electronic gear was then designed to run on the same power plant. A telephone building has a big bank of batteries, powered by multiple "rectifiers" (DC supplies) which, btw, are normally engineered to not run over 40% of load. (That way they can still run the systems and recharge the batteries when one of them is kaput.)

If you then put anything else into one of their buildings, the Network Equipment Building Standards (NEBS), which are Telcordia documents that practically carry the force of law, dictate that equipment be DC powered. Among other things -- NEBS gear has to meet the brick schytthaus test. (Sun Netras and many Cisco routers meet NEBS. Your basic rack server doesn't. And aluminum racks are STRICTLY forbidden; it has to be steel.)

So because of the talk voltage on analog phones, lots of computing equipment is engineered for -48 V DC power. Sort of like the legend (I know, that one is not really true) about the railroad track gauge being based on Roman chariots. But in this case it's surprisingly effective.

Copper bus bars?? (1)

TechSnack (957035) | more than 8 years ago | (#14839955)

TFA says
The current travels through massive copper bus bars that are bolted together, but joints must be inspected regularly. Loose joints are a big problem.
I am no electrical techie... but why 'bars' of copper? Cannot DC be safely and efficiently transmitted with thicker 'wires' as opposed to 'bolting' bars together? Hmm.. time to catch up on Electrical Engg stuff...

Re:Copper bus bars?? (1)

BigSlowTarget (325940) | more than 8 years ago | (#14840083)

Yes - that comment is weird. The only real reason for massive wires is high amperage. That implies that the AC/DC and voltage conversion is all done at one point and the power is sent around at five or twelve volts. If that's the case you need the big wiring to handle the amperage.

The other issue is big wires mean big circuit breakers and that implies if you hook up the wrong size wire between the wrong two points you rediscover arc welding. Ouch
If the wire is a coil and you do it just right you might make yourself a happytime junior camper EMP device. In your datacenter.....

This is part of the reason we have standard voltages fed to all sorts of appliances.

Re:Copper bus bars?? (1)

wed128 (722152) | more than 8 years ago | (#14840100)

The wider the conductor, the less resistance. If copper wire gets wide enough, it becomes a bar.

Re:Copper bus bars?? (1)

scat-cat (606809) | more than 8 years ago | (#14840113)

Copper bars are just thicker wires. Current flowing through a conductor generates heat due to the inherent resistance of the material. The larger the conductor, the less the resistance, thus less heat. Copper bars are a very common method of conducting DC. You get lower heat, and what heat is generated radiates away quite easily. Plus, you can tap into the line anyplace you can drill and tap a hole.

Re:Copper bus bars?? (1)

StikyPad (445176) | more than 8 years ago | (#14840146)

Better conductivity and heat dissipation. Double the cross section of a conductor and you halve its resistance. Wires are not the most efficient conductors, just the most convenient for many applications.

Belly up to the bus bar (1)

Tau Zero (75868) | more than 8 years ago | (#14840176)

They use bus bars because the voltages are low and the currents are high.

Of course, this just vindicates Tesla. Shipping low-voltage DC around a facility, whether ancient telephone switching center or modern server farm, is a lossy affair without big, fat wires to keep the voltage drops down (losses rise as the SQUARE of current; P = I^2 R). Centralizing the AC-DC conversion a few yards away where heat can be handled better is sensible (just making power supplies which can be cooled with ambient air would save a lot on A/C), but moving it even a fraction of a mile makes no sense without superconductors.

fucking gay (-1, Flamebait)

Anonymous Coward | more than 8 years ago | (#14839959)

this is stupid and i hate niggers

Uhh... (-1)

Inside_Joke (246574) | more than 8 years ago | (#14839963)

Tesla promoted DC. Edison (backed by Westinghouse) pushed for AC.

Re:Uhh... (1)

Burdell (228580) | more than 8 years ago | (#14839994)

Bzzt. Tesla held the patent on AC and licensed it to Westinghouse (and eventually abandoned the patent to help AC by reducing costs). Tesla worked for Westinghouse. Edison promoted DC and founded his own power company, Edison Electric (now part of ConEd).

-1 False (1)

Yjerkle (610052) | more than 8 years ago | (#14840003)

This is simply not true.

Re:Uhh... (1)

hunterx11 (778171) | more than 8 years ago | (#14840005)


Re:Uhh... (1)

PabloJones (456560) | more than 8 years ago | (#14840008)

You've got it completely backwards. Edison promoted DC, while Tesla was backed by Westinghouse.

Re:Uhh... (1, Funny)

Morky (577776) | more than 8 years ago | (#14840016)

Uhh.. is a fucking arrogant subject line and even worse when you're fucking wrong.

Re:Uhh... (0)

Anonymous Coward | more than 8 years ago | (#14840019)

Err, reverse that. Edison thought AC power was much too dangerous. Tesla didn't care.

Re:Uhh... (1)

AndroidCat (229562) | more than 8 years ago | (#14840078)

Two wrong posts don't make a right. Edison only said AC was dangerous because he wanted to spread FUD with the public that rivil AC was inherently more dangerous than DC. He even tried to turn Westinghouse into a word meaning "to be electrocuted" and pushed for the first use of an alternating current electric chair.

Re:Uhh... (1)

indianajones428 (644219) | more than 8 years ago | (#14840022)

Sure, Edison pushed for electric chairs. He lobbied for the criminal system to use the AC current, knowing that people wouldn't want the same type of power running through their homes. In fact, Edison tried to get people to say that criminals got "Westinghoused," not "electrocuted."

Re:Uhh... (2, Informative)

jdaomteys (825374) | more than 8 years ago | (#14840039)

Nope, sorry. Please play again. [] Tesla and Westinghouse patented all of the AC equipment. Edison wanted to sell his stuff. He even went as far as designing electric chairs with AC to prove it was "more deadly."

Re:Uhh... (1)

cpt kangarooski (3773) | more than 8 years ago | (#14840163)

Tesla promoted DC. Edison (backed by Westinghouse) pushed for AC.

That's the most subtle Soviet Russia joke I've seen yet. I tip my hat to you.

They were both right...and wrong... (5, Insightful)

davmoo (63521) | more than 8 years ago | (#14839966)

Tesla and Edison were both right...and wrong. Like many Slashdotters do when debating which operating system is best for any given job, Tesla and Edison wanted to apply one power system to every job. Its like having a toolbox with only a screwdriver in it. Ever try to drive a nail with a screwdriver?

For moving power over long distances, AC is king. But for short distances with most modern electronics, DC would win. The first thing a desktop system or server does with AC is converts it to DC. So if you have a number of machines all in the same room, why not do the conversion in one spot, and eliminate the redundancy in every machine.

Would it benefit the average user with one or two machines? Not at all. But for a major center with many machines in the same room, I can see quite a bit of benefit with going with DC.

Re:They were both right...and wrong... (4, Funny)

daniel_mcl (77919) | more than 8 years ago | (#14840021)

"Ever try to drive a nail with a screwdriver?"

Nope, but I've put in screws with a hammer, even when I had a screwdriver on hand.

Re:They were both right...and wrong... (1)

Chanc_Gorkon (94133) | more than 8 years ago | (#14840029)

Yes, but I would still have more then ONE invertor. Redudancy in a data center is something you WANT. Redundant PDU's attached to two different substations as well as a generator backup.

Re:They were both right...and wrong... (4, Informative)

Phanatic1a (413374) | more than 8 years ago | (#14840035)

For moving power over long distances, AC is king.

Nope. For the longest-distance transmission lines, you see DC being used. There comes a point when the capacitive losses you get from using AC encourage you to switch to DC, and for lines of several hundred miles, you start seeing DC transmission lines.

Re:They were both right...and wrong... (3, Informative)

hpa (7948) | more than 8 years ago | (#14840080)

In addition to capacitive losses, there is also the fact that you have to dimension your transmission lines to handle up to Vp (peak), not just Vrms which is what controls the amount of power that actually travels through your system. In effect, by going to DC, you can run the whole system at 1.4 times the voltage, and run more power through the same wires with no additional losses (other than conversion.)

Re:They were both right...and wrong... (1)

Stevyn (691306) | more than 8 years ago | (#14840052)

The big problem is also the length of the transmission cable. A few feet of wire carrying 12 and 5 volts in your PC won't be too wastefull. But that wire is suddenly say 100 feet long than it can start to waste electricity as heat. Say at 12 volts your powering a component that needs 2 amps. And the long wire now acts say as a 1 ohm resistor. So using V=iR, the voltage drop becomes significant and your power supply now needs to account for it. But yes, you are right in that a few machines next to each other don't need such a long cable and it would be a good idea.

It's true only in a pretty restricted sense (2, Informative)

hpa (7948) | more than 8 years ago | (#14839971)

It's true that DC-DC power converters are more efficient than AC-DC converters, only if you consider than the typical DC-DC converter has a much lower voltage ratio than the typical AC-DC converter. DC power distribution is usually done in the 12-48 V range, depending on application, whereas AC is 100-240 V. It's also only a win in if you don't end up losing that power in the wiring.

How come there is no real difference? Because both modern AC and modern DC supplies start out by converting the power to high frequency AC (on the order of several kHz), and operate on that. That's what you actually want as input, if anything.

The article states:

By distributing redundant direct current power to each server--and replacing the standard AC power supply with a far more reliable and efficient DC power supply...server reliability is increased by as much as 27 percent, and monthly power costs are reduced by up to 30 percent.

In other words, the DC supplies they use are more efficient than standard AC supplies, which are the cheap crap and notoriously inefficient.

Re:It's true only in a pretty restricted sense (1)

m85476585 (884822) | more than 8 years ago | (#14840037)

"How come there is no real difference? Because both modern AC and modern DC supplies start out by converting the power to high frequency AC (on the order of several kHz), and operate on that. That's what you actually want as input, if anything." Isn't it DC with pulse width modulation? Basically they take AC, filter it to make DC, switch it on and off quickly, then filter that to get the average voltage. "In other words, the DC supplies they use are more efficient than standard AC supplies, which are the cheap crap and notoriously inefficient." The power supplies in servers/data centers are not very cheap, and they are probably not too bad for efficiency.

Re:It's true only in a pretty restricted sense (1)

hpa (7948) | more than 8 years ago | (#14840060)

Most of them aren't optimized for efficiency; if they're more expensive it's because they are hotswappable, high reliability, or just because they can take your money.

"DC with pulse with modulation" -- sounds like an alternating current to me. Yes, it's typically a very messed up square wave (due to all kinds of filtering) rather than a sinusoid pure sinusoid, but spectrally, it's just noisy AC.

Re:It's true only in a pretty restricted sense (1)

m85476585 (884822) | more than 8 years ago | (#14840144)

I could be wrong, but I always thought it had to be positive and negative. I do agree that square waves can be AC.

Re:It's true only in a pretty restricted sense (0)

Chanc_Gorkon (94133) | more than 8 years ago | (#14840044)

There's no REAL DC-DC convertors. All you have to do to "convert" one DC level to another is measure or caculate or find out the total resistance of the load and do a simple OHM's Law calculation to figure out the resistor you would need to insert....but there's no "conversion" needed....DC is DC!

Re:It's true only in a pretty restricted sense (2, Informative)

atrus (73476) | more than 8 years ago | (#14840088)

What you just described is a voltage divider circuit. And its terribly inefficient for transferring power, since you're burning all of the extra energy up in the resistors.

DC->DC converters are basicly AC power supplies. They pulse the DC current up to several hundred kHz, using an inductor, and convert it down/up on the other side. They're very efficient, although somewhat costly.

Re:It's true only in a pretty restricted sense (0)

Anonymous Coward | more than 8 years ago | (#14840130)

That's fine if you want to go down in voltage, but if you want to take the voltage up you'd need to use transformers, with some type of AC.

Re:It's true only in a pretty restricted sense (1)

wed128 (722152) | more than 8 years ago | (#14840134)

You don't even need to measure the resistance of the load. You could just use an active load to sinc voltage dynamically.

Re:It's true only in a pretty restricted sense (0)

Anonymous Coward | more than 8 years ago | (#14840156)

So the only argument for using AC is no longer valid these days?
(I'm assuming the only reason AC was adopted was because you could transform it to whatever voltage required with some coils)

DC - better for carry power long distances, not as dangerous, no issues with interference, induction or impedence.

low frequency AC - Legacy choice of all our infrastructure and appliances.

high frequency AC - Wouldn't running this over cables cause interference as well as suffer loss to induction and impedence?

Is there an advantage to AC I'm missing?

Re:It's true only in a pretty restricted sense (1)

goodie3shoes (573521) | more than 8 years ago | (#14840159)

Ahem. Well, it's not true that AC to DC conversion is inherently more or less efficient than DC to DC conversion. Any power conversion has power loss, but it can be as efficient as you like, depending on how much money you want to spend and what component size you can tolerate. Likewise reliability - no inherent advantage one way or the other, but I must say that the standard method of converting AC to DC, with rectifiers and capacitors, is an order or magnitude more reliable than the common method of changing one DC voltage to another with switching regulators.

in certain applications... (1)

Doppler00 (534739) | more than 8 years ago | (#14839972)

Yes this is good in certain applications. I could imagine places like homes and server rooms having this. The conversion from 120V AC to DC at every device is pretty ineffecient. Having one large AC->DC converter would probably be much better. For one, you could locate the device outside. A majority of the heat generated by servers is from the power supplies. However, you would still need DC->DC converters which waste heat too, although I don't think it's that much.

For home use, just imagine getting rid of all those ugly AC power adapters for everything! You could have much smaller DC plugs and fit 20 ports on one outlet.

For industrial settings, you still need AC. It's just the best way to distribute power to things like motors and high power AC systems (120, 208, 240, 480V, etc...)

No, Thomas Edison was wrong (1)

VegeBrain (135543) | more than 8 years ago | (#14839976)

It's simply not possible to make a DC power transformer because only alternating current provides the changing magnetic field that makes them work. Power transformers are required for stepping up the voltage before transmitting the power over long distances in order to reduce the power losses.

Re:No, Thomas Edison was wrong (1)

hpa (7948) | more than 8 years ago | (#14840002)

It's simply not possible to make a DC power transformer because only alternating current provides the changing magnetic field that makes them work. Power transformers are required for stepping up the voltage before transmitting the power over long distances in order to reduce the power losses.

DC-DC converters work by chopping the input power into high frequency AC, which require smaller magnetics than typical line frequencies, which were selected for the benefit of early rotating machinery. If you don't care about isolation, you can also get away with less than a full transformer core, or even substitute capacitors and switches.

Tesla strikes back with wireless power! (1)

Baldrson (78598) | more than 8 years ago | (#14839985)

So Edison wants to rise from the grave and defeat his nemisis, Tesla, eh? Now all Tesla has to do is rise up and strike back with his wireless power transmission system at GHz frequencies. Not only would this eliminate the per system power supplies but also the wiring and the master clock!

I'm pretty sure I'm just joking about that idea...

Eh? (1)

GoMMiX (748510) | more than 8 years ago | (#14839986)

Computers already use DC power?

Is this not the entire point of the PS? To convert AC to DC?

So basically all these new DC computers would be is a computer that relies on yet another source to convert AC to DC then still requires some sort of internal component to convert THAT DC to the correct voltage for the various devices within the computer itself?

Re:Eh? (1)

m85476585 (884822) | more than 8 years ago | (#14840069)

But think of laptops. They have external AC-DC supplies for heat, weight, and size reasons. The internal supplies can be tiny. And if this is in a data center, it wouldn't be too hard to make a central psu output all the voltages required.

Re:Eh? (1)

GoMMiX (748510) | more than 8 years ago | (#14840085)

I see, I misunderstood the intent of the article. It doesn't do a lot of good to RTFA if you don't get it! Heh.

Re:Eh? (0)

Anonymous Coward | more than 8 years ago | (#14840127)

I didn't read it either!

Re:Eh? (1)

jonnythan (79727) | more than 8 years ago | (#14840086)


It will make the servers smaller, save space by consolidating power supplies into one unit, save lots of power by having one large power supply that's more efficient than small ones, and make it way easier to remove waste heat by concentrating most of it into one big unit.

Wow (1)

Eightyford (893696) | more than 8 years ago | (#14840009)

What a stupid headline. Sure he was right about DC power, but he was wrong about AC power and that still has nothing to do with the article.

Thomas Edison was wrong. Period. Full stop. (0)

Anonymous Coward | more than 8 years ago | (#14840010)

If DC was so great it would've succeeded in the 19th century. The argument ended around that time, too.


Perfect (4, Funny)

HangingChad (677530) | more than 8 years ago | (#14840014)

Let's see, how do we get a functioning data center to not just replace their computers, but their whole infrastructure? Replace AC with DC!


A boon for the elephants (1)

Potato Battery (872080) | more than 8 years ago | (#14840041)

All the elephants [] in the University of Florida server room are probably breathing a sigh of relief over this one.

Old news (1)

pcguru19 (33878) | more than 8 years ago | (#14840046)

Telco cabinets are DC and have been for some time.

The HP Blade chasis has an AC to DC PDU outside the chasis.

One thing to remember about DC VS AC cabling. DC requires thicker gaugue cable to push the same wattage. If you think the back of your server cabinet looks cluttered now, wait.

this is news? (4, Informative)

iggymanz (596061) | more than 8 years ago | (#14840048)

for crap's sake, dc powered servers are nothing new, many have config option of "-48VDC standard telco" supply.

Phone company example (1)

michael_cain (66650) | more than 8 years ago | (#14840049)

Is it worth pointing out that the phone company, whose switches and local distribution network all required DC to drive the (first) electromechanical components and (then) electronic ones, never made the switch? Commercial power was (and still is, AFAIK, although I've been out of that business for years) used to charge massive banks of 48V batteries that actually power the central office equipment. Once they made the decision to have UPS on that scale, AC/DC/AC conversions were expensive and hence minimized. Modern conversions are much more efficient than they were in the old days; but unless they're cheaper than the electricity, at some point it makes sense to convert once then distribute DC.

Everything Old is New Again (1)

twalton (71489) | more than 8 years ago | (#14840061)

Stodgy old telcos figured this out years ago - the bulk of the switching center equipment runs on 48 VDC. This also makes power backup simple - lead-acid cells in big batteries...

Solar (1)

merphant (672048) | more than 8 years ago | (#14840064)

This works especially well when combined with solar panels, since they output DC anyway; why waste energy converting to AC and then back again? Especially since the power is generated on-site so it doesn't have to deal with the resitive loss of travel down miles of power lines, although I realize there can be a lot of wiring inside the building too. Seems like if you're running a large facility with big machines that are contantly running, it makes sense to have some DC infrastructure. The supermarket down the street has about a megawatt of PV on the roof, and uses all DC refrigerators and air conditioning.

Edison was wrong (1)

penguin-collective (932038) | more than 8 years ago | (#14840065)

DC power is not very good for distributing power over anything other than short distances, in particular given how trivial AC-to-DC conversion is using modern solid state power supplies. Once you reach the end user, then DC starts making more sense.

No (2, Informative)

dbIII (701233) | more than 8 years ago | (#14840070)

Short answer no. Long answer - sometimes. DC is somethimes useful right in front of you, but it's hard to get it there.

I've seen houses wired with 12V DC from mini hydro and solar - but in those cases it was a long way to the nearest transmission wire and would cost a fortune to get mains power onto the site.

Telcos have run on DC for decades (1)

billstewart (78916) | more than 8 years ago | (#14840071)

Telco switches normally ran on 48V DC back in the electromechanical days, and standard telco offices have rooms full of big honkin' batteries to act as a UPS for the building. And yes, power gets distributed on fat copper busses that you don't want to drop wrenches on. As electronic switching systems replaced the old mechanical ones, the capacity increased rapidly while the floor space for electronics decreased, but there's been enough opportunity to fill it back up again.

To Westinghouse (2, Informative)

jheath314 (916607) | more than 8 years ago | (#14840075)

Perhaps we'll see the AC group hitting back with demonstrations of how dangerous these DC powersupplies are to the hamsters and other wildlife native to big server rooms.

Incidentally, that's how the electric chair came about:

[Edison]AC is dangerous! Just watch what happens to these various animals when I close this circuit!
Edison electrocutes some horses
[US_Gov]Ooooo... I'll bet that works on people too!
US_Gov introduces new grisly method of executions, while disregarding the main point of Edison's demonstrations.

The story has a good post script too... some reporters came to Edison to get his take the new, modern form of executions. When asked what name he would give to the method, Edison, in an attempt to forever link his competitor's name with electricity's most grusome application, offered "to Westinghouse someone."

DC for a building is good, but (1)

RustNeverSleeps (846857) | more than 8 years ago | (#14840077)

The long distance power distribution network relies on AC power, for reasons that I assume many/most slashdotters are aware of (high voltage to minimize voltage drop across lines, with transformers at the ends). That said, I've long thought it would be really nice to have a big DC power supply with a DC power distribution system in buildings. Just think about getting rid of all the wall warts and power supplies that we currently have to deal with and instead just having regular straight cables to plug DC-powered electronics in to the wall. I believe it would also greatly reduce wasted electricity that people complain about now. I know that many wall warts and other power supplies just waste electricity all day when they're plugged in but not being used. With a well designed large central DC power supply for the whole building, efficiency could be greatly improved. Of course, there are still definite applications where AC is useful. Big appliances with motors (washers, driers, vacuums, etc) are much better suited to running on AC.

Of course Edison was right. (0)

Anonymous Coward | more than 8 years ago | (#14840082)

He also raised turkeys. That was on his turkey farm.

-48v Power (1)

kjs3 (601225) | more than 8 years ago | (#14840096)

Not that there's a reason the telco world has been running it's stuff on -48v power for, what, forever? Try to make that work well across town, though.

Misinformation in article (4, Informative)

gvc (167165) | more than 8 years ago | (#14840102)

For physics reasons, it's easier to transmit AC over long distances; DC requires thick copper cables or bars, instead of comparatively lightweight wires. But DC becomes a more serious possibility for power once AC reaches a building.
What a load of crap. Low voltage (high current) requires thick wires - it has nothing to do with AC/DC. AC is horrible for long-distance transmission; up north megavolt DC is popular. AC is useful because it is easy to transform - you can step the voltage up or down with turn-of-the-previous-century technology and hence transmit at a higher voltage than you'd like to use.

That said, if space and cooling are an issue it might well make engineering sense to get the transformers, capacitors, and rectifiers out of the computer boxes. Big 5v/12v power busses wouldn't even need to be insulated. So while the reporter badly mangled the story, the engineering sounds reasonable to me.

Telcos have been on DC for years (2, Interesting)

buttfuckinpimpnugget (662332) | more than 8 years ago | (#14840107)

Where I work (Small regional wireless co) 80% of our equipment is DC. Granted that most of that power is for the telco switches a great deal are sun and other servers. The advantage for dc is only having to convert power once. We have a power plant (inverters,rectifiers and a huge battery bank) that takes up an entire room. To keep the battery bank charged requires converting from AC->DC. If the power goes out the batteries take over, end of story. If we were all AC in the switch room we would have to do another conversion from the DC in the batteries back to AC meaning more equipment, losses from the conversion and so less efficiency and more points of failure.

Yes he was? (1)

Scrameustache (459504) | more than 8 years ago | (#14840108)

Therefore, if you live farther away than, what was it? 20 miles? TURN OFF ALL YOUR POWER! DC current can't go that far.

However, if you enjoy distributed power, no, no he certainly was not.

Not over! (1)

fm6 (162816) | more than 8 years ago | (#14840119)

Everyone knows the alternating vs. direct current wars ended with Thomas Edison and Nikola Tesla.
Thanks to my fellow trivia dweebs at Wikipedia, I found out that Consolidated Edison still sells DC power. Not a big profit center, though.

DC vs AC in data center is about efficiency/heat (2, Informative)

sflory (2747) | more than 8 years ago | (#14840120)

The reason you want to use DC is that a computer's power supply converts AC into DC. The power supply of most computers isn't that efficient at it. This basically converts some of your electricity into heat. (Heat in a 1U server in a big rack of 1 U is really bad.) In theory the data center's big AC to DC converter is more efficient and better cooled. Thus you save money in power bills, air conditioning, and rack space (less heat, and power draw means more servers per rack). Plus in theory your servers should last longer as the power supply is one of the more likely points of failure.

Re:DC vs AC in data center is about efficiency/hea (1)

Shadyman (939863) | more than 8 years ago | (#14840152)

That's true, but DC doesn't travel well, but I'm not sure on the figures. Either way, it loses more than AC, hence why wall power is AC, but I can't see there being much loss from one end of a data center to the other, the losses come from miles of cabling. So.. bring on the DC!

Here is the Answer (1)

layer3switch (783864) | more than 8 years ago | (#14840124)

"I'm sick to death of people saying we've made 11 albums that sounds exactly the same, Infact, we've made 12 albums that sound exactly the same"
-Angus Young "AC/DC"

If you don't get this post, I deserve -Troll, -Offtopic and -Flambait karma from each and every one of you.

Quiet period for Rackable (1)

eltoyoboyo (750015) | more than 8 years ago | (#14840137)

Rackable declined to comment for this story because it is in a stock exchange quiet period, after announcing a plan to sell 3.3 million shares in a secondary offering to raise new financing.

So then... Slashdot exposure during the quiet period is all OK then right? Shankland watches this particular market segment pretty closely. I wonder if he has any options? *cough* *just a theory* *cough*

IBM has had DC power in the mainframes for years (1)

DaKrzyGuy (25850) | more than 8 years ago | (#14840149)

IBM Has had DC Power in their mainframes for years. The latest ones convert redundant 3-phase power to 480v DC for distribution between the frames. All the details you want can be found here []

My favorite use for DC (0)

Anonymous Coward | more than 8 years ago | (#14840154)

DC is way better than AC for very long transmission lines. For lines longer than 1000 miles, AC results in very unfavorable reactances and even radiation resistance. So, if you want to build a power line across the top of Siberia, you should use DC.

As for distribution within an equipment rack, you're going to use on-board regulation anyway. Thus there's no particular advantage for AC. Switching regulators are now easy and cheap so you can get all the different DC voltages from a single source.

Thomas Edison was STILL wrong (1)

GenKreton (884088) | more than 8 years ago | (#14840157)

Anyone how has any understand of electricity knows it is much easier and more efficient to transfer large amounts of electricity over large wires with huge potential volt differences on AC than to use DC current. Much less line loss and greater distances. Whether DC is better in a specific application is an entirely different consideration than if Tesla or Edison was more right about our power grids. If Edison won we would have generators every two blocks...

This FP fory GNAA (-1, Redundant)

Anonymous Coward | more than 8 years ago | (#14840160)

About half of the channel, you might For successful good to write you Blue, rubber but now they're session and join in Are just way over and coders big deal. Death Politics openly. declined in market the numbers. The I ev3r did. It turned over to yet '*BSD Sux0rs'. This troubles of those just yet, but I'm that should be demise. You don't be any fucking And building is 40,000 workstations best. Individuals as one of the FUCKING USELESS

No outlets in the future (1)

ant-1 (120272) | more than 8 years ago | (#14840170)

The future, as I (and a lot of others) envision it, will be essentially DC-based. Some day they will standardize battery form factor, and I'm talking about things like our curent ion/Lith batteries here, and you will basically only have that for each of your appliances. Shapes will range from watch battery to big "cellpacks". This will be the so needed end of wires. We will have only one outlet to recharge them all in the whole house, or even dispose of them if they last a very long time.

Of course, this will require a revolution in batteries technology, but I'm sure deep down in the googleplex some mad PhDist with an ugly assistant is already working on it.

So, yes Edison was right, but he may have been slightly optimistic about the pace of change.
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