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DC Power Saves 15% Energy and Cost @ Data Center

CmdrTaco posted more than 7 years ago | from the juice-is-loose dept.

371

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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Safety (5, Insightful)

TimeTrav (460837) | more than 7 years ago | (#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.

Here, here! (1)

fodder69 (701416) | more than 7 years ago | (#15873321)

I definetely see advantages to go DC for server farms and such as there is always a lot of loss (heat) involved in all the AC->DC conversions, but dang, I sure as heck would not want to work around 380 volts DC.

Re:Here, here! (2, Interesting)

cswiger2005 (905744) | more than 7 years ago | (#15873464)

Agreed-- that level of DC voltage is actively dangerous, and I wonder why they are running that high a voltage when most of the equipment in the racks is gonna want +5VDC & +12VDC rails. Perhaps they are using it to power big DC motors in fans and AC/cooling/dehumidifying equipment, but it would seem to make more sense to feed those with 3-phase AC and use a more sensible VDC delivery at, say, 48V, which is a telco standard...

Re:Here, here! (2, Informative)

Anonymous Coward | more than 7 years ago | (#15873539)

They use 380 volts instead of 48, because they can send almost 8 times the power through the same size wire.

Re:Here, here! (2, Informative)

Dun Malg (230075) | more than 7 years ago | (#15873808)

but it would seem to make more sense to feed those with 3-phase AC and use a more sensible VDC delivery at, say, 48V, which is a telco standard
Except that the only reason you see 48vdc for telephone over those tiny 22ga wires is that there's no load. As soon as you go off hook the voltage drops to around 10vdc. This works because telephone circuits don't actually do much work-- they mostly just transmit analog data. The size of the copper you'd need to feed an actual load at 48vdc is prohibitive, particularly now with the price of copper going through the roof.

Re:Here, here! (5, Informative)

saider (177166) | more than 7 years ago | (#15873826)

Copper losses are created by current and are described by the equation I^2 * R. So as you double your current, you quadruple your power losses.

Conversely, if you halve your current by boosting the voltage, you can reduce your transmission losses by 75%. Thats a pretty good reason to go with higher voltage. And since this is in the datacenter, you can train your people not to pee on the red wire.

Let Go (2, Informative)

ajnsue (773317) | more than 7 years ago | (#15873831)

From the Merck Medical Manual "...The effects of AC on the body depend largely on the frequency. Low-frequency currents of 50 to 60 Hz (cycles/sec), which are commonly used, are usually more dangerous than high-frequency currents and are 3 to 5 times more dangerous than DC of the same voltage and amperage. DC tends to cause a convulsive contraction, often forcing the victim away from the current's source. AC at 60 Hz (household current) produces muscle tetany, often freezing the hand to the current's source; prolonged exposure may result, with severe burns if the voltage is high...."

Re:Safety (1)

Lucky_Norseman (682487) | more than 7 years ago | (#15873333)

I was taught that AC is more dangerous to the heart than DC. The pulses in AC interfere with the normal heartbeat frequencies and may cause cardiac arrest.

If this is outdated or errouneous please enlighten me.

Re:Safety (1)

John Hasler (414242) | more than 7 years ago | (#15873408)

AC is very slightly more disruptive of the heart than is AC, but at 380V it makes no difference. Touch that rail and you're toast.

Re:Safety (5, Informative)

peragrin (659227) | more than 7 years ago | (#15873721)

So you also failed electrical theory, as well.

DC is harmless unless it has a path to carry it. You can grab a 380 volt DC line and not feel a thing. now if you then touch a grounded object, or the return path you are dead. But you have to make the connection. AC is lethal at 220v. As others posted it does have the advantage of forcing the mucsles to spasm so you can let go of the wire, But still zaps you every time you touch the cable.

Go look up the history of Edison vs Westinghouse. Edison wanted DC power all around because it is inherently safer. a Broken AC wire can zap you, were as a broken DC wire can be touched with bare hands.

Re:Safety (2, Interesting)

MindStalker (22827) | more than 7 years ago | (#15873419)

Yea DC is a strange beast, a small jolt or small voltage of DC is safer. The dangerous part of DC is
It constricts all your muscles which stops your heart and your ability to move until the power is removed. If you happen to grab a DC power line this is especially dangerous, as an AC line with throw you off while a DC line will cause you to simply grab harder and you can't let go.

Fun hu?

Re:Safety (2, Funny)

DoofusOfDeath (636671) | more than 7 years ago | (#15873600)

"Fun hu?" ???

You claim to know the "Fun Hu" technique? Teach it to me immediately, or I will kill your master just as I killed his other students.!

Re:Safety (2, Informative)

smooth wombat (796938) | more than 7 years ago | (#15873878)

as an AC line with throw you off while a DC line will cause you to simply grab harder and you can't let go.


Which is why my sister-in-law once told me to use the back on ones hand if you aren't sure if a line is still live or dead. Your hand will contract around nothing thus giving you a slightly better chance of survival.

Re:Safety (-1, Redundant)

Anonymous Coward | more than 7 years ago | (#15873341)

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.



Re:Safety (3, Insightful)

andrewman327 (635952) | more than 7 years ago | (#15873379)

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.

Static Discharge (0)

Anonymous Coward | more than 7 years ago | (#15873398)

That stuff really hurts!

Re:Safety (4, Funny)

drgonzo59 (747139) | more than 7 years ago | (#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 (4, Funny)

andrewman327 (635952) | more than 7 years ago | (#15873531)

Quiet you, and back to the data mines!

Re:Safety (3, Funny)

cswiger2005 (905744) | more than 7 years ago | (#15873514)

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...

Re:Safety (1)

andrewman327 (635952) | more than 7 years ago | (#15873712)

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 (1)

gnud (934243) | more than 7 years ago | (#15873658)

Well, if you really want to, I guess it could kill you. But when I tasted some blue juice from the cable to my parents vcr, it hurt like hell, but passed in 10 minutes.

Re:Safety (1)

MrSquirrel (976630) | more than 7 years ago | (#15873702)

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 (1)

fjf33 (890896) | more than 7 years ago | (#15873803)

A lot of the world outside the US uses 220V 60Hz AC power at the outlets. I actually stuck my finger in one when I was much younger. I am not typing this from the neatherworld so I guess it is not 'that' dangerous. Of course this is anecdotal evidence which proves nothing. Then again there is also the 'intelligent' fuses that do detect a short and quickly disconnect power. I am not sure they would work with DC but hey.

Re:Safety (5, Informative)

Engineering_bully (900092) | more than 7 years ago | (#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 (3, Informative)

cswiger2005 (905744) | more than 7 years ago | (#15873568)

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 (2, Interesting)

Engineering_bully (900092) | more than 7 years ago | (#15873672)

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 (2, Informative)

cswiger2005 (905744) | more than 7 years ago | (#15873893)

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 metal conduit where abrasion somewhere had tied the conduit and ground wires to hot...I managed to arc-weld about half the end of my screwdriver to the recepticle finding that out, and the worthless breaker at the site didn't even trip.

Nice shower of electrical sparks and molten bits of the other half of the screwdriver tip, though...

Speaking of conductor sizes.... (4, Informative)

Phreakiture (547094) | more than 7 years ago | (#15873895)

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.

Re:Safety (0)

Anonymous Coward | more than 7 years ago | (#15873435)

For cardio effects AC is worse than DC. The voltage isn't the big deal either until you get up something that can arc through air. The right question is "How much current can that puppy source?" I've worked with supplies that could source up to 300A of DC current -- be very careful around those; if you short a wedding band across the terminals it will blow the finger off. The old old IBM mainframes could do that, the old FastBus spec from particle physics could do it too.

Re:Safety (1)

gtoomey (528943) | more than 7 years ago | (#15873450)

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 (3, Interesting)

gurps_npc (621217) | more than 7 years ago | (#15873572)

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.

Re:Safety (1)

computerchimp (994187) | more than 7 years ago | (#15873629)

Stop the disinformation!!! Please mod the parent out of existance, it is just another example of ignorance coming out of people dying to make the first post (or just plain human ignorance). DC power is not more dangerous than AC power. AC power will screw with a persons heartbeat and make them deader and lower voltages/amps. DC just makes people cripy. Even the 60 V AC coming from a phone ringing will kill a service guy dead. DC at the same power usually just screws a person up (please dont try it). Wikipedia and Google may help all the amateurs or those interested. Computerchimp

Re:Safety (1)

plague3106 (71849) | more than 7 years ago | (#15873631)

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.

Bye bye Tesla (3, Funny)

krell (896769) | more than 7 years ago | (#15873286)

Read Stephen King's "Tommyknockers". You can do a lot of things if you go DC-only!

Safety (-1, Redundant)

DarkShadeChaos (954173) | more than 7 years ago | (#15873301)

If it can't electrocute someone, then it's not good enough for me :)

First twofo (-1, Offtopic)

Anonymous Coward | more than 7 years ago | (#15873312)

dchub://hub.twofo.co.uk:4144

Zeus sucks cock

DC power can be a good thing... (2, Informative)

Firethorn (177587) | more than 7 years ago | (#15873314)

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.

Re:DC power can be a good thing... (1, Insightful)

Anonymous Coward | more than 7 years ago | (#15873346)

> 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.

I think you had better take that electronics class again...

Deadly DC? (4, Informative)

drgonzo59 (747139) | more than 7 years ago | (#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]

Re:DC power can be a good thing... (1)

John Hasler (414242) | more than 7 years ago | (#15873429)

> Then again, you don't have to worry about shorting yourself to ground with DC.

That statement makes no sense at all.

Re:DC power can be a good thing... (2, Informative)

thebes (663586) | more than 7 years ago | (#15873447)

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 when they did the demo of frying the pig). 380 volts does not require significantly more insulation. Consider that regular multimeter cables can handle 500+ volts DC. I'm not even going to talk about your stupid statement about shorting yourself to gound.

Re:DC power can be a good thing... (0)

Anonymous Coward | more than 7 years ago | (#15873499)

You appear to have missed the gp saying The same number of watts. It's quite obvious that the power required by the servers will be more or less constant, so an increase in Voltage will proportionally reduce the current drawn.

Re:DC power can be a good thing... (1)

thebes (663586) | more than 7 years ago | (#15873608)

Using "same number of watts" to say constant power doesn't instill confidence in anything the gp says.

Re:DC power can be a good thing... (1)

nolife (233813) | more than 7 years ago | (#15873665)

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 will go down.

P=IE and E=IR therefore, P=I^2(R)

I have no idea about the other stuff he was talking about.

Industroal systems do this all the time (3, Informative)

OzPeter (195038) | more than 7 years ago | (#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.

Re:DC power can be a good thing... (2, Informative)

jimmyswimmy (749153) | more than 7 years ago | (#15873547)

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 -> battery storage -> DC/AC -> rack AC/DC -> several servers

But you'd still need an intermediate bus converter at the server rack to drop from 380 to 12/5/3.3/-5. This could be a nice opportunity for an APC or someone like them.

Also there are efficiency savings. If you optimistically quote 95% efficiency for each conversion in the existing topology, the overall efficiency from supply to server is (0.95)(0.95)(0.95)(0.95) = 81%. For the DC-only system, it would be (0.95)^2 perhaps, or 90%. These are certainly optimistic numbers but are useful for scale. For a 300W system the difference is 27W. For 1000 300W systems, it's 27000W, at .08/kWh it's 2$/hour or $19k/year.

Am I assuming too small a server farm? This doesn't really seem worth it.

As far as safety goes, 380VDC and 380VAC are both gonna hurt you. Remember that the AC voltage is spec'd as RMS, so they're basically equivalent in power delivery, which means they should kill you equally fast. My recollection is that DC voltage will cause your muscles to tense, so if you grab an energized part you cannot let go, which is a pretty scary idea. On the other hand, it ought to cause less interference (no more 60Hz).

On wire thickness... no more skin effect, at least.

Re:DC power can be a good thing... (1)

joib (70841) | more than 7 years ago | (#15873866)


Yes, they will save on resistance losses by about 1/3. (120/380)


(1/3)**2 = 1/9 actually.

Re:DC power can be a good thing... (1)

LWATCDR (28044) | more than 7 years ago | (#15873883)

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 diesel electric subs used DC motors. The US navy built two turbo-electric subs that I know used DC power. The larger one failed but that is still okay since that means we could learn from it's problems.
The Navy should have a large amount of information on high power DC systems and safety procedures.

switching costs? (2, Informative)

bigpat (158134) | more than 7 years ago | (#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? (2, Informative)

ranton (36917) | more than 7 years ago | (#15873756)

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 efficiency.

A typical high density blade rack could use 24 killowatts of power. That would then require about 78k BTUs of cooling, which would take about 8 killowatts of power. That is 32 kWatts of power per rack, or about $2.56 an hour at $0.08 a killowatt. A saving of 7.5% on average would mean about $0.19 an hour, or $4.56 a day/$1664 a year.

The PDU/UPS for that single rack is going to be thousands of dollars. And if the blade rack has 80 blades, even a $50 per blade (probably very low) switch would be an extra $4000. The entire switch is probably going to be close to $10,000. That would take 6 years to recoup the initial cost.

I do not know what the lifespan of a server rack is, so maybe a six year turnaround would be good enough. I have dealth with enough banks and loan officers to know that American companies rarely look ahead that long for a ROI. Three years would be a little more like it. But maybe my calculations are far off, I have never worked with more than a couple of server racks before so I am not familiar with how the costs will scale for large datacenters.
--

The Telcos have known this for years (4, Insightful)

RotateLeftByte (797477) | more than 7 years ago | (#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:The Telcos have known this for years (0)

Anonymous Coward | more than 7 years ago | (#15873445)

Too few people know this. You can really hurt yourself when someone calls just as you touch the wire.

Re:The Telcos have known this for years (1)

losec (642631) | more than 7 years ago | (#15873730)

thats because you receive 90V that is powering the bell.

Re:The Telcos have known this for years (3, Interesting)

hauntingthunder (985246) | more than 7 years ago | (#15873509)

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 bussbars - which then shorted - an explosive way of painting a room.

I once had to help install some sun servers in an exchange (CAPITAL) and walking around - the building most of the old stuff had been taken out - was quite eerie lots of clicking and odd buzzes.

CAPITAL is/was one of the main exchanges in the uk its actually in Edinburgh not London Rgds M

Re:The Telcos have known this for years (1)

xs650 (741277) | more than 7 years ago | (#15873671)

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 predominant sound coming out of the other an of the line.

BTW, it's a good idea to alway have at least one simple phone in your house that doen't require AC power to work

Edison (2, Insightful)

Rob Kaper (5960) | more than 7 years ago | (#15873350)

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 (4, Insightful)

John Hasler (414242) | more than 7 years ago | (#15873461)

> 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 sucks, Tesla rules!! (0)

Anonymous Coward | more than 7 years ago | (#15873553)

Hell yeah, son. Tesla was on top of his game, he made Edison look like a child at the science fair. Edison spent a lot of time trying to publicly discredit Tesla, while Tesla was busy being an electical bad ass.

 

Re:Edison (1, Funny)

Rocketship Underpant (804162) | more than 7 years ago | (#15873811)

I don't know, I heard about a pretty cool chair he invented!

Re:Edison (4, Insightful)

Svartalf (2997) | more than 7 years ago | (#15873521)

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.

Re:Edison (1)

JesseL (107722) | more than 7 years ago | (#15873797)

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 or so. For a given amount of power (E*I) if you operate at a higher voltage (E) you will use a correspondingly smaller current (I). Smaller current means smaller resistive losses (I*R).

It's just not nearly so easy to step-up or down DC.

Re:Edison (1)

Creepy (93888) | more than 7 years ago | (#15873875)

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 gonna say - AC was chosen mainly because it handles long run distribution of power, although the fact that DC doesn't step-down or step-up as easily also contributed (most DC power grids used multiple lines for varying voltages). Edison wanted lots of small neighborhood-level power generators since DC has a noticable drop in power in as little as a mile.

    The point of using localized DC is to have one large, efficient transformer rather than hundreds of smaller and less efficient transformers.

Re:Edison (1)

Vellmont (569020) | more than 7 years ago | (#15873906)


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 do the same thing with DC using semi-conductors. DC is actually being used for some long-distance power distribution now because it doesn't have to be synchronized with the other side (as well as other reasons). This gives some kind of advantage in preventing failures between parts of the power grid.

Re:Edison (1)

MasterC (70492) | more than 7 years ago | (#15873700)

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 things not are large appliances or those motor-based: stove, refridgerator, water heater, washer (clothes & dishes), clothes dryer, furnace fan, etc.

However and generally speaking, the DC devices are "always on" while the AC ones are "as needed". So, the inefficiences of multiple AC->DC conversions is always there and their transformers will always have some loss even with zero output power.

I highly suspect having a 12VDC or 24VDC bus in your house would also be advantageous for getting rid of the multitude of wall warts [wikipedia.org] . It would rid the need of an AC->DC PSU in your computer (a DC->DC PSU will still be needed of course) to boot.

Re:Edison (0)

Anonymous Coward | more than 7 years ago | (#15873792)

AC has advantages in electricity generation (the generators are much simpler) and it allows to increase the voltage easily. The latter effect is the most important for energy transportation. I think the rule of thumb is: 20kV on one side of the wire, 20 km of wire => 0V on the other side. So to transport efficiently you need to get to much higher voltages (400kV range, normally). Of course, once you have the high voltage it would actually be more efficient to transport DC - in some cases that's already used, but at even higher voltages than 400kV.

I've always liked ... (5, Insightful)

jc42 (318812) | more than 7 years ago | (#15873375)

... 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.

Re:I've always liked ... (1)

Engineering_bully (900092) | more than 7 years ago | (#15873417)

In the 380 VDC system there will only be one transformer/rectifier (277/480 VAC to 380 VDC). Assume that it has an efficency around 90% (typical). In your normal data center you would go from 277/480 VAC to 120/208 VAC with a transformer (90%), then to 5/12/24 VDC with another smaller transformer (most likely 80-85% efficent due to the small size).

15% seems right on to me.

- EB

Re:I've always liked ... (1)

Random Destruction (866027) | more than 7 years ago | (#15873486)

woosh.
His point was the phrase "up to x or more" is meaningless. It provides no information.

Re:I've always liked ... (1)

ggeens (53767) | more than 7 years ago | (#15873529)

What about the conversion from 380 VDC to 5-24 V? How efficient would that be?

Re:I've always liked ... (1)

Anonymous Coward | more than 7 years ago | (#15873731)

Actually, a saving of "up to 15 percent or more" covers the entire range except that 15 percent is specifically excluded.

What's new about this? (5, Informative)

Flying pig (925874) | more than 7 years ago | (#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.

Re:What's new about this? (2, Informative)

sjs132 (631745) | more than 7 years ago | (#15873462)

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 relations battle to determine which system would become the dominant technology. I think you meant to say that "Edison who accused AC power of being more dangerous", but hey whats a letter or two among fiends? ;) http://www.answers.com/topic/fiend [answers.com]

Re:What's new about this? (2, Informative)

Anonymous Coward | more than 7 years ago | (#15873517)

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.

Re:What's new about this? (0)

Anonymous Coward | more than 7 years ago | (#15873624)

DC buses have been used in military and industrial equipment since DC/DC converters were invented.

What are you converting with a DC/DC converter?

Telcos already use -48 DC (0)

Anonymous Coward | more than 7 years ago | (#15873396)

The only reason they save power here is because they increased the voltage, not because it's AC instead of DC. This allows them to reduce power line losses for really high draw equipment. Telcos already use -48v for all of their equipment which I think it simply too low for many modern switches. Some Lucent ATM switches draw over 3000 watts which is over 60 amps at -48 volts.

Old time rivals at it again... (1)

sjs132 (631745) | more than 7 years ago | (#15873399)

When asked his opinion, the ghost of Thomas Edison was Straight
forward and Direct about the conversion of the IT Closet to DC.

While it has been rumored that Mr. Nikola Tesla is spinning in
his grave and refuses to give a comment

http://www.ieee-virtual-museum.org/collection/even t.php?id=3456872&lid=1 [ieee-virtual-museum.org]

Re:Old time rivals at it again... (4, Funny)

Dachannien (617929) | more than 7 years ago | (#15873482)

While it has been rumored that Mr. Nikola Tesla is spinning in his grave

At 60 revolutions per second.

Re:Old time rivals at it again... (1)

Kadin2048 (468275) | more than 7 years ago | (#15873754)

Really, I think Tesla would be much higher-frequency [pbs.org] than that.

Re:Old time rivals at it again... (1)

novus ordo (843883) | more than 7 years ago | (#15873777)

Actually he was cremated.

How does this help? (1)

MobyDisk (75490) | more than 7 years ago | (#15873409)

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 really need? Or are they using equipment that runs on higher voltages anyway?

Errr... So many misconceptions (1)

technoextreme (885694) | more than 7 years ago | (#15873455)

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.

Re:How does this help? (1)

artg (24127) | more than 7 years ago | (#15873588)

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 with a chop-only design (no transformer) and supply isolated DC to the whole network. This would remove a lot of transformers, but create problems with ground-voltage drops which would require careful design of the distribution network.

Re:How does this help? (0)

Anonymous Coward | more than 7 years ago | (#15873822)

How many wires does your DC system have? I have a hot and a neutral. My AC system also has a hot and a neutral. By my count that's 2 in each, but maybe I'm missing something.

dc / dc converter (4, Interesting)

wwwillem (253720) | more than 7 years ago | (#15873413)

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.

Re:dc / dc converter (1)

jimmyswimmy (749153) | more than 7 years ago | (#15873596)

I can't speak from experience with this exact situation, but hey, this is Slashdot, so my mom could write here and say that she knew the answer, so I'll just plod on.

The typical 120VAC silver box converter is basically a forward converter, which means that you could almost call it a DC-AC-DC converter (but that's not what they're called, they're DC-DC converters). These are similar to the flyback converters that make your TV whine and display pretty pictures.

The core (ha, ha) of these converters is a transformer. By going from 120VAC to 380VAC, you're talking about a bigger transformer, with, actually, less wire (fewer turns) but slightly more insulation. That's about it. So the efficiency "should" be pretty comparable to the existing systems. Except since it's new they'll charge a lot more for 'em.

Working Models and Cost Issues (3, Interesting)

miller60 (554835) | more than 7 years ago | (#15873416)

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.

Re:Working Models and Cost Issues (1)

hcdejong (561314) | more than 7 years ago | (#15873799)

Right now the cost of power is remaking the landscape of the data center industry.

What's next? Outsourcing to Canada to profit from lower ambient temperatures (=less cooling required)?

Changing the UPS could get the same. (0)

Anonymous Coward | more than 7 years ago | (#15873436)

The article talked about multiple changes back and forth between AC and DC. That makes it sound to me like the power is always running from the batteries through an inverter. So the power comes through the inverter all the time. The solution is to take the power from the mains almost all the time. The losses in the rectifier and the inverter go away. When there's a power failure the inverter comes on line. That can happen smoothly enough that the load (ie. all the computer equipment) never notices the difference.

So, you might have to buy new inverters but you wouldn't have to rewire the data center. Usually, rewiring costs way more than equipment. A clever power management module could even obviate the need to buy new inverters. There are ways that the data center could actually save money on electricity and they don't involve dc distribution.

"Larger power cables" - WRONG (4, Informative)

wowbagger (69688) | more than 7 years ago | (#15873495)

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.

I see the reason, sort of. (1)

fatboy (6851) | more than 7 years ago | (#15873548)

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 (3, Interesting)

tmbailey123 (230145) | more than 7 years ago | (#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.

Re:residential DC (0)

Anonymous Coward | more than 7 years ago | (#15873715)

DC Transmission and Distribution are out of the question, the losses on the lines would be too high.

This is really a question of how and where you convert your utilities 60Hz AC power from whatever the line voltage is to what your machines use.

I imagine the larger the transformer, the higher efficiency can be obtained.

However, as you run your dc power longer lengths, you lose this advantage.

For a data center, there may be a situation where you can have a high efficiency transformer directly powering all of your units which now have dc/dc transformers in them instead of ac to dc. Interesting results for a facility like that.

AC conversion vs DC conversion and voltage FACTS (3, Interesting)

viking2000 (954894) | more than 7 years ago | (#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

Nikola Tesla does not approve! (1)

Bushido Hacks (788211) | more than 7 years ago | (#15873741)

"His [Thomas Alva Edison] method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90 per cent of the labor. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense." --Nikola Tesla stating that DC current (which Edison prefered) was ineffencet to AC current (which Tesla prefered). (Source wikipedia [wikipedia.org] )

Higher volts in data center (5, Interesting)

bobmorning (316459) | more than 7 years ago | (#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.

What about 220VAC as an easier, partial solution? (1)

raitchison (734047) | more than 7 years ago | (#15873781)

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 bays) you only had N+1 redundant power supplies if you powered the server with 220VAC. IIRC this server had three power supplies and two were enough to keep the server running in most configurations, but with the maximum load they could only keep up if you fed them 220.

Sun launches new ad campaign... (0)

Anonymous Coward | more than 7 years ago | (#15873845)

A 15 minute call could save you 15% or more on your power costs

In Wisconsin, we NEED the HEAT (1)

rdmiller3 (29465) | more than 7 years ago | (#15873865)

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 loss during cold weather (which is the larger portion of the year). Yes, it's more expensive than using the heating system, but it may not be enough of a difference to justify the expense of non-standard equipment.

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