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Are Data Centers Finally Ready For DC Power?

samzenpus posted more than 2 years ago | from the edison-wins-again dept.

Power 462

1sockchuck writes "It's been five years since a landmark study outlined the potential benefits of DC power distribution in data centers. But adoption of DC in data centers remains limited, even as the industry aggressively pursues a wide array of other energy savings strategies. Advocates of DC distribution are hoping a new study will jump start the conversation about DC distribution, which can save energy by eliminating several wasteful AC-to-DC conversions within a data center. Meanwhile, an industry association for DC power adoption, the EMerge Alliance, has formed a new technical standards committee for data centers, and is advancing a 380-volt DC power standard. Will DC distribution ever gain momentum in data centers?"

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Edison reaching out from beyond the grave (5, Funny)

ravenspear (756059) | more than 2 years ago | (#38219358)

I told you bitches I would prevail one day!

Re:Edison reaching out from beyond the grave (4, Informative)

rolfwind (528248) | more than 2 years ago | (#38219476)

Not really. AC was the answer to how to transport electricity long distances.

Currently, it is still converted to DC in a huge amount of devices, in the computer at the PSU. Few devices use AC iirc, something like a fan/ceiling fan probably has an AC motor because a DC motor would slice your finger off if you decided to play with the blades. So, the question then just remains how to optimize the point of conversion. It's rather like the electric car-fossil-fuel-electric-plant/gasoline car debate: have a bunch of small inefficient combustion engines or a large efficient one but deal with transport losses (along with a bunch of other issues).

In this case, just where along the line do you convert the AC to DC. Since DC can't really travel far at all without significant losses, I guess that would be at the rack level?

Re:Edison reaching out from beyond the grave (5, Informative)

Wonko the Sane (25252) | more than 2 years ago | (#38219578)

AC was the answer to how to transport electricity long distances

AC was used because using transformers to convert between voltage levels was more efficient than motor-generators and solid state electronics hadn't been invented yet. All other things being equal, DC is always more efficient than AC for long distance transmission.

Re:Edison reaching out from beyond the grave (-1, Flamebait)

Anonymous Coward | more than 2 years ago | (#38219704)

In this case, just where along the line do you convert the AC to DC. Since DC can't really travel far at all without significant losses, I guess that would be at the rack level?

Wow, talk about ignorance!!!

AC is better over DC in only 2 major applications.

  1. power conversion!! - you know, transformers??
  2. motors - AC, high power motors. You know, 3 phase power ones, not the single-phase power you get at your residence.

DC transmission is more efficient than AC! Why do you think long haul lines are preferred to be DC? Never mind, you have no clue.

http://en.wikipedia.org/wiki/Nelson_River_Bipole [wikipedia.org]

Re:Edison reaching out from beyond the grave (5, Insightful)

Anonymous Coward | more than 2 years ago | (#38219906)

Way to take a completely normal, productive conversation and shit all over it.

Try being less of an asshole for a day or two. You might find that people hate you less.

Re:Edison reaching out from beyond the grave (5, Informative)

Elder Entropist (788485) | more than 2 years ago | (#38219718)

Very high voltage was the answer to how to transport electricity long distances. AC was the answer to how to convert that high voltage to safer/useful low voltages cheaply. Very high voltage DC can lose less power over distance than AC. On smaller/cheaper wires too due to the AC skin effect.

Re:Edison reaching out from beyond the grave (5, Informative)

Mr Z (6791) | more than 2 years ago | (#38219738)

The problem with DC back in Edison's day was that you couldn't easily step it up or down. DC doesn't have higher losses than AC at the same voltage. In fact, DC radiates less energy away than AC does, and is therefore more efficient [wikimedia.org] .

Ohmic losses all come down to I^2 * R. R is the resistance of the cable, and I is current. To deliver a given amount of power, you have to have a certain V*I. To reduce Ohmic losses, then, you have to reduce the amount of current, which means going up in voltage.

Incidentally, that's also what's driving automobile manufacturers toward 48v instead of 12v [automotive-eetimes.com] , since it would cut the current from the battery by a factor of 4, thereby reducing the amount of loss in the wiring by a factor of 16. That means you can use smaller wires to deliver the same amount of power, safely.

Re:Edison reaching out from beyond the grave (2, Interesting)

Anonymous Coward | more than 2 years ago | (#38219938)

It's not only the radiation that makes AC less efficent. It is also how you can build conductors.

If you built just a simple very long cylinder out of copper, it is the perfect conductor for DC. For AC only the border is used, as the electric field presses electrons there. So with AC you have to use complex cables working around this, while with DC you get better behaviour with a simpler and less expensive design.

You won't get that for small voltages. But for the big power lines going long distances, this is significant. (And the reason why newer lines are DC nowadays, in the rare cases where there are newer lines).

Re:Edison reaching out from beyond the grave (3)

khallow (566160) | more than 2 years ago | (#38219754)

Since DC can't really travel far at all without significant losses, I guess that would be at the rack level?

Transmission losses are actually less than for AC. They don't lose energy to inductance with nearby conducting loops and impedance losses are about the same as for a three phase line with same RMS voltage. The real problems are conversion to and from AC, and the fact that DC operates at a much lower voltage (low voltage results in high losses, whether AC or DC) when in actual servers.

The idea behind DC powered centers is that the AC to DC conversion is done in one place, away from the servers so that a) the heating load of the center is lower, and b) it can be done in one place with a relatively efficient converter rather than in a thousand places with less efficient designs. The accompanying baggage as I gather is that you're either running a lot of power-losing low voltage lines or doing some sort of power-losing DC voltage step down inside the center.

Re:Edison reaching out from beyond the grave (0)

Anonymous Coward | more than 2 years ago | (#38220036)

a DC motor would slice your finger off if you decided to play with the blades.

Really? Why? I've accidentally stopped computer fans without losing fingers several times, and they run on DC.

Re:Edison reaching out from beyond the grave (0)

Anonymous Coward | more than 2 years ago | (#38219762)

Edison was a hack. Most of "his" good ideas were from Tesla, without attribution.

However, like in most things, both Westinghouse and Edison/Tesla were correct. DC makes more sense for short distances, but AC makes more sense for longer distances. Local DC power makes more sense in a datacenter than pretty much anywhere else. I wouldn't be surprised that most other 'industrial' processes already utilize in-house AC/DC conversion. IT is just behind due to the depth of the problem of moving over to DC - there is a huge supply chain which needs to change, first, and then you've got a LOT of old AC equipment you've got to phase out.

Re:Edison reaching out from beyond the grave (0)

Anonymous Coward | more than 2 years ago | (#38219992)

Tesla replying "Yep if you need to move electricity 100 feet across an indoor facility you are the best but I move it across miles and counties and countries"....bitches indeed ;P

also needed for houses (3, Insightful)

Anonymous Coward | more than 2 years ago | (#38219368)

How many little wall-warts does the average house have? Tens? We need low voltage DC in our houses, and standardize all the little widgets on one of (say) two voltages. Each outlet could supply them in a dedicated connector alongside the current AC.

Re:also needed for houses (2, Insightful)

oh_my_080980980 (773867) | more than 2 years ago | (#38219386)

You've apparently never ran electrical wire in the home nor understand why that would be a completely insane idea.

Re:also needed for houses (0)

Anonymous Coward | more than 2 years ago | (#38219560)

If we're talking about 5V/1A USB or whatever it really wouldn't be that big of a deal, if we're talking about the 1000W you use to power your gaming rig, yeah, it's stupid.

Re:also needed for houses (3, Interesting)

LehiNephi (695428) | more than 2 years ago | (#38219602)

I do/have done both (run electrical and understand the implications), and GP has a point. When I think of the things in our house that *must* run on AC, it's only our fridge, freezer, and HVAC. Everything else in the house either converts it to DC or could run quite happily on DC. For certain you'd want to have a different kind of plug for DC devices, but even that would give us an opportunity to 1) standardize on one global plug standard, at least for DC, and 2) allow us to design a small, rugged, safe type of plug.

Or is there some implication that I'm missing, and that you decided not to point out, in favor of flaming GP?

Re:also needed for houses (4, Interesting)

vlm (69642) | more than 2 years ago | (#38219724)

For certain you'd want to have a different kind of plug for DC devices, but even that would give us an opportunity to 1) standardize on one global plug standard, at least for DC, and 2) allow us to design a small, rugged, safe type of plug.

Aka the famous (in some circles) Anderson Power Pole. Go ask a ham radio guy.

The thing I love about in house DC distribution, which I have in my house, is it forces at least a token effect at "green power reduction". Suddenly given the choice of a 12 volt 6 watt LED fed by $2 of small gauge wire vs something resembling welding cable wire to run a 200 watt halogen, you make the ecologically correct choice.

I used to use cast off surplus 200 watt desktops for my mythtv frontends. Unholy pain to run on 12 V. Now I use 5 watt Zotac boxes. Good for everyone in every way.

Re:also needed for houses (1)

nschubach (922175) | more than 2 years ago | (#38219808)

What bothers me is all the new LED bulbs that have transformers in them (guessing, because they get hot! ... feels like wasted energy) to power the LED bulbs when you could have just run a 12VDC line and powered them all on a central transformer like garden lights. I'd think it would be more efficient to run DC to lighting and certain outlets like those where small devices would sit (with standard plugs as you mention) and keep 112-120VAC for things like the appliances.

You could also centralize a backup battery (easily) to keep your lights on if the power suddenly surges.

Re:also needed for houses (1)

David_Hart (1184661) | more than 2 years ago | (#38219872)

All AC appliances and DC power adapters use a standard voltage of 110v in US/Canada/etc., 220v in other parts of the world (UK/etc.). To implement DC in the house, you would either have to standardize on a specific DC voltage or create a smart power standard (i.e. similar to POE for network gear). Today, most devices that require AC/DC adapters, convert to different DC voltages. That being said, most mobile devices have been standardized to the USB standard of 5V.

Re:also needed for houses (1)

nschubach (922175) | more than 2 years ago | (#38219980)

There are a lot of different voltages for DC transformers, but taking a look around my house this past year I spotted mostly 12VDC. I had one 20VDC (Laptop) but the rest were 12. In the past, I've seen 6 and 9 volt transformers, but I rarely see these anymore.

Re:also needed for houses (1)

amorsen (7485) | more than 2 years ago | (#38219968)

When I think of the things in our house that *must* run on AC, it's only our fridge, freezer, and HVAC

If your fridge, freezer, and HVAC are halfway decent, they convert to variable-frequency AC. Fixed-frequency AC motors are inefficient unless the load is constant (and load isn't constant in those applications).

Re:also needed for houses (1)

stanlyb (1839382) | more than 2 years ago | (#38219608)

And dangerous. And not practical. And expensive too.

Re:also needed for houses (1)

suutar (1860506) | more than 2 years ago | (#38219712)

expensive yes, practical maybe not. I don't see offhand how it's more dangerous than having AC all over, but I'm not an EE. Would you care to explain?

Re:also needed for houses (1)

snowraver1 (1052510) | more than 2 years ago | (#38219932)

The Alternating Current allows your muscles to have a chance to let go when you grab on to the wire, while DC will freeze your muscles up. That is one theory anyways... I have never personally been shocked good enough with DC to confirm this.

Re:also needed for houses (2)

ShavedOrangutan (1930630) | more than 2 years ago | (#38220116)

It's a lot harder to let go if you grab a hot DC wire. And I'm guessing, but I'll bet a DC shock to the heart would be worse than AC.

Re:also needed for houses (1)

sjames (1099) | more than 2 years ago | (#38220184)

I've heard it said many times that when you accidentally contact the wires, DC tends to seize up your muscles so that you freeze in place and cook while AC tends to throw you off. I have no idea if that's actually true or not but I can see how it might be.

Re:also needed for houses (0)

Anonymous Coward | more than 2 years ago | (#38219618)

the issue isn't running the electrical wire in the home, the issue is distribution over long distances. You can't distribute DC at low voltages due to massive resistive losses, and DC doesn't play well with voltage changes. Once in the home, there's no problem running DC per say, but that being said, you'd probably still want to distribute in the home at 100+ volts, which means that all the problems of changing voltages around would in macro would still hold for household size.

And for those who don't know what I'm talking about, math Vloss = I*R where I is the number of amps being pulled and R is the resistance of wire. I is determined by I=P/V where V is the line voltage, R is determined by the width of the wire and the length, there's an equation that I can't remember off the top of my head and can't be bothered to look up. But basically, the narrower the wire, the higher the resistance. The longer the wire, the higher the resistance.

Re:also needed for houses (1)

Wonko the Sane (25252) | more than 2 years ago | (#38219734)

You can't distribute DC at low voltages due to massive resistive losses

This is equally true of both AC and DC.

DC doesn't play well with voltage changes

We have these things now called semiconductors. You may have heard of them.

Re:also needed for houses (1)

PimpDawg (852099) | more than 2 years ago | (#38220056)

I have a 7805 voltage regulator next to me right now that does a fine job of stepping 12V into 5V at up to 1A without a heat sink. And that was a very cheap component. I imagine that one can do a lot more with more money or volume.

Re:also needed for houses (1)

AK Marc (707885) | more than 2 years ago | (#38219884)

Then can you explain why running 12VDC along-side 120VAC (assuming they are sufficiently separated/shielded to not induce 120VAC on the DC line) is a "completely insane idea." Just saying "if you knew what you were talking about, you'd know why it's a bad idea, but I'm too stupid to explain why, I can just mock" isn't very useful

Re:also needed for houses (1)

Wonko the Sane (25252) | more than 2 years ago | (#38219934)

It's a matter of how many watts you expect to supply and how large the wires must be to supply that power at 12 volts while maintaining the voltage at the outlets within an acceptable range.

Re:also needed for houses (0)

Anonymous Coward | more than 2 years ago | (#38220048)

"You've apparently never ran electrical wire in the home nor understand why that would be a completely insane idea."

Actually, if you stop and think instead of flaming for a sec, the post you reply to isn't a bad idea. It would centralize the AC->DC conversion in a single more efficient place, and it would allow all those little devices to be cheaper and less of a pain in the butt since they wouldn't all have to include their own transformer. Sure, low voltage power distribution is inefficient over long distances, but for the small ranges inside a house it wouldn't be a problem to have 12VDC everywhere.

Telecom's been doing this for many, many years. (4, Insightful)

Anonymous Coward | more than 2 years ago | (#38219392)

DC power is the standard in the telecom industry.

I design systems based around HP's BladeSystem, and the DC power modules just drop in and go. It's very easy, works great, and most of all, my telecom customers love them.

Re:Telecom's been doing this for many, many years. (5, Informative)

Shatrat (855151) | more than 2 years ago | (#38219510)

I work with DC power in Telecom and it has 3 huge advantages I can think of off the top of my head:

1) You centralize your rectification. Instead of having hundreds of power supplies running at 80% efficiency, you can have a large rectifier system running at up to 96%.
2) Lead Acid batteries are hugely more reliable and less expensive than equivalent UPS systems, and provide more holdover time. They're still expensive and finicky, but many times less so than a UPS.
3) Any old technician with a brain in their head can run DC power feeds to equipment relatively safely due to the low voltages involved. AC power work of any kind should have a qualified electrician involved.

Re:Telecom's been doing this for many, many years. (5, Interesting)

vlm (69642) | more than 2 years ago | (#38219830)

4) Done right with a positive ground system, leads to less corrosion problems with outside plant. Admittedly "inside" the data center, if you're got corrosion, you're doin it wrong.

5) Less AC hum. We had some microwave site to site short hop gear back in ye olde NTSC days that could only be run off battery without 60 hz interference bars on the screen. Not technologically relevant anymore, but the point remains that DC is always going to be cleaner than AC.

6) Better lightning protection. I'm sure its happened, but I've never heard of losing a telco DC bus. Big conductors, giant batteries across them, lightning is just not an issue anymore at the power level (still need to ground feedlines / waveguide / whatever you've got at home like that)

7) dump most of the power conversion heat in the battery room where its all built to handle high temp and no one visits (other than occasional battery maint). Cheaper cooling in the data center, data center is somewhat more habitable, etc.

Re:Telecom's been doing this for many, many years. (1)

elkto (558121) | more than 2 years ago | (#38219524)

I would Mod you Up, but Slashdot is behaving strangely. The only bizarre part of the 48 volt telecom standard is the positive ground. From an Engineers perspective, no stranger than a negative one though.

Re:Telecom's been doing this for many, many years. (4, Informative)

Anonymous Coward | more than 2 years ago | (#38219682)

The positive ground in telco systems is not bizarre at all: one end of the twisted pair is grounded, and, being at zero volts does not suffer galvanic corrosion. The other end is at -48V and benefits from cathodic protection: it's the anode that generally gets corroded in a galvanic cell.

Re:Telecom's been doing this for many, many years. (3, Insightful)

the linux geek (799780) | more than 2 years ago | (#38219582)

Yeah, I've never quite figured out why telecoms have standardized on 48VDC while everyone else completely ignores its existence. Most midrange servers (HP Integrity and Nonstop, iirc most smaller SPARC Enterprise boxes, some commodity stuff) are available in 48VDC configurations, so it's not like there's a lack of hardware for it.

Re:Telecom's been doing this for many, many years. (2)

mjwalshe (1680392) | more than 2 years ago | (#38219896)

because telcos have much much more stringent requirements for up time - a major switch failure is a once in a lifetime event for most people - we have had 3 failures for amazon in the last 4 months at work.

Re:Telecom's been doing this for many, many years. (1)

the linux geek (799780) | more than 2 years ago | (#38219920)

Oh, certainly. My post was more a question of why everyone else has ignored 48VDC, not why telcos use it.

Re:Telecom's been doing this for many, many years. (0)

Anonymous Coward | more than 2 years ago | (#38219592)

Our Uni did a DC battery protected power install for one half of our network core many years ago.

It's amazing how simple DC is to get right compared with more complex AC UPS systems.

The only issue is complacency as it was "low voltage" (48V) system the current draw was quite high.

If you do DC make sure an appropriately qualified electrician does your cabling etc.

Re:Telecom's been doing this for many, many years. (1)

uncledrax (112438) | more than 2 years ago | (#38219888)

^ This ^
Although we're a ISP grown from a Telecom.. so we have large DC plants at most of our sites anyway, so for us, it's just asking our vendors for DC options... most vendors DO have DC PSU options.. it's more of a pain to adapt to the annoying 21" 2-post telecom racks we have.. :/

And in related news... (0)

Anonymous Coward | more than 2 years ago | (#38219398)

Tesla rolls over in his grave

Re:And in related news... (1)

nurb432 (527695) | more than 2 years ago | (#38219564)

Nah, he will just be proven right, again.

Re:And in related news... (5, Funny)

DickBreath (207180) | more than 2 years ago | (#38219778)

Would an AC current be generated by Tesla spinning in his grave?

Re:And in related news... (1)

Bucky24 (1943328) | more than 2 years ago | (#38219858)

Depends on how you harness the energy I would imagine... Though I'm not very familiar with electrical systems.

Google 12VDC proposal better. (4, Interesting)

Animats (122034) | more than 2 years ago | (#38219406)

There's no particular reason that 380 VDC distribution should help efficiency. You still need about two more levels of switching power supply before power reaches the ICs.

Google's proposal that motherboards should need only 12VDC made more sense. Drives already run on 12VDC, and there's already a level of power conversion near the CPU to get the desired CPU voltage. The USB devices do need +5, but a 12VDC to 5VDC switching converter can handle that. And single-voltage power supplies are more efficient and simpler than multi-voltage ones.

Re:Google 12VDC proposal better. (1)

Anonymous Coward | more than 2 years ago | (#38219462)

This is my biggest complaint with the USB standard. Why the hell not 12v?!

Re:Google 12VDC proposal better. (3, Informative)

vlm (69642) | more than 2 years ago | (#38219984)

The original low speed USB electrical spec was pretty much classical 5 volt NRZI TTL. So insisting on 12 volt supply would mean every USB device would require a 5 volt regulator inside it to talk to the data lines, and the data lines would need protection circuitry on both momma boards and all USB devices because TTL traditionally gets really pissed off when an input voltage rises about its power voltage in case of a short. CMOS gets pissed off too at over voltage. It would just be a bad scene.

Something like RS-485 but really faster would have been "better", but ...

Re:Google 12VDC proposal better. (3, Interesting)

hpa (7948) | more than 2 years ago | (#38220014)

USB is designed to enable inexpensive devices. 5 V is so that when cable losses are counted in, you can use a LDO linear regulator to obtain 3.3 V (Vcc) without excessive losses. 12 V would require a switching regulator.

conversion on the motherboard? (1)

bigtrike (904535) | more than 2 years ago | (#38219478)

Wouldn't you just end up putting a switching power supplies elsewhere and create heat problems, then?

Re:conversion on the motherboard? (1)

compro01 (777531) | more than 2 years ago | (#38220142)

You already do that anyway. Motherboards take most of their power at 12V and regulate it down to what's needed.

A modern CPU can use up to 65-ish watts, but runs at about 1.5V, so you're needing 43.3 amps of current. You're not going to be running that little voltage and that much current down a reasonably sized wire of any useful length.

Videocards do the same thing.

Re:Google 12VDC proposal better. (4, Informative)

Mr Z (6791) | more than 2 years ago | (#38219812)

The current carrying capacity of the wires would need to be about 30 times larger, though, to deliver the same amount of power. That's pretty huge. To go to 12v everywhere, you'd need huge current-carrying wires everywhere (think "as big as your car battery cables or bigger"). To carry 1kW through a 380V line, you only need to handle 2.6A. To carry 1kW through a 12v line, you need to handle 83A. And that's just one beefy server.

Now think of your house wiring. Outside of your major appliances, where do you see runs higher than 15A or maybe 30A? There's a reason high voltage is good.

Re:Google 12VDC proposal better. (0)

Anonymous Coward | more than 2 years ago | (#38219898)

what about salt water filled copper pipes for the conductors?

Re:Google 12VDC proposal better. (5, Funny)

Wonko the Sane (25252) | more than 2 years ago | (#38220018)

what about salt water filled copper pipes for the conductors?

Excellent idea! Hydrogen gas, oxygen gas, chlorine and an ignition source all in the same package. What could possibly go wrong?

Re:Google 12VDC proposal better. (1)

mjwalshe (1680392) | more than 2 years ago | (#38219976)

bollocks do you not understand ohms law - running any thing non trivial on 12v dc is a non starter - any telecom engineer will(and thats on 48V have amusing horror stories about near death (if they where lucky) with big dc systems and that is using 48V

Re:Google 12VDC proposal better. (1)

amorsen (7485) | more than 2 years ago | (#38220046)

There's no particular reason that 380 VDC distribution should help efficiency. You still need about two more levels of switching power supply before power reaches the ICs.

It is easier to step down DC than AC. You don't have to contend with keeping current up during the parts of the wave where AC supplies close to zero power. Instead you just chop at a sufficiently high frequency that your ripple current gets sufficiently low.

Death (0)

Anonymous Coward | more than 2 years ago | (#38219422)

But won't more geeks die due to more harmful shocks, as DC (high voltage/amperage) becomes more common? I thought DC was more likely to burn your nerves when you compare the same AC to DC potential.

why 380v? (3, Interesting)

wierd_w (1375923) | more than 2 years ago | (#38219430)

Wouldn't it make more sense to drive at 12v with an insane amperage behind it, than to drive at 380v and garantee the necessity of a voltage regulator rated for high voltages?

I mean, the whole reason for doing away with ac current was to eliminate the rectifier and regulator circuits, which belch heat into the data center. Using 380v, which no datacenter device that I know of uses natively (well, maybe the innards of a crt, but that's actually much higher than 380v... AND a deadend tech.), seems kinda... well.... unproductive.

Is it because of impedence problems or something?

You'd need much larger conductors (4, Informative)

bigtrike (904535) | more than 2 years ago | (#38219500)

Lower voltages require larger conductors to carry the same current. Copper isn't that cheap.

Re:You'd need much larger conductors (1)

Anonymous Coward | more than 2 years ago | (#38219612)

Lower voltages require higher current to carry the same power. More current requires a larger conductor.

Re:You'd need much larger conductors (1)

wierd_w (1375923) | more than 2 years ago | (#38219630)

Skin effect.. that's right.

But you can get around that with multistranded wire, right? A bundle of 7 small conductors netting the same approximate volume as 1 big conductor has substantially more conduction surface.

Re:You'd need much larger conductors (4, Informative)

nzac (1822298) | more than 2 years ago | (#38219862)

No the skin effect is for (High frequency) AC.

For DC impedance is determined by the material and the cross section area.

It does make the cables easier to bend though.

Re:You'd need much larger conductors (1)

wierd_w (1375923) | more than 2 years ago | (#38220096)

*smacks forehead*

[Note to self: Avoid asking questions about EE, a field you DID NOT take in college, while recovering from a head cold and while under the influence of medication. Seriously, you'll thank me later. There is a reason why the bottle says not to operate heavy machinery. Hint: it also applies to high energy electronic devices.]

Re:You'd need much larger conductors (-1)

Anonymous Coward | more than 2 years ago | (#38219886)

Excuse me? Skin effect does not apply to DC.

Re:You'd need much larger conductors (-1)

Anonymous Coward | more than 2 years ago | (#38219926)

Skin effect.. that's right.

But you can get around that with multistranded wire, right? A bundle of 7 small conductors netting the same approximate volume as 1 big conductor has substantially more conduction surface.

The "skin effect" only comes into play with AC.

Re:You'd need much larger conductors (1)

pclminion (145572) | more than 2 years ago | (#38220050)

It's not skin effect, it's the fact that P = VI. If the machine draws 500 watts at 12 volts, the current in the conductor must be 42 amps. The power dissipated in the conductor is I^2*R. Suppose you're willing to dissipate 10 watts in the conductor. That means 10 watt = (42 amp)^2*R, which implies the conductor resistance must be 0.005 ohms.

Suppose that instead you supply the power at 380 volts. The current is now only 1.3 amps. 10 watt = (1.3 amp)^2*R, which means a conductor resistance of 6 ohms, which is over *1000 times* greater than at 12 volts. What this means is you don't need a huge freakin' wire.

Re:You'd need much larger conductors (0)

Anonymous Coward | more than 2 years ago | (#38219646)

Yup. If you need to provide 200 watts, at 380V you can do it with only about .5 amps, easily carried on 26- or 28-gauge wire. But at 12V, you'd need to allow for 16 amps, for which you need 12-gauge or larger.

Re:You'd need much larger conductors (2)

nzac (1822298) | more than 2 years ago | (#38219810)

Lower voltages require larger conductors to carry the same power, (due to I^2*R losses). Copper isn't that cheap.

FTFY

Losses in a wire are determined by the current alone.

Re:why 380v? (2)

DerPflanz (525793) | more than 2 years ago | (#38219566)

High current ('insane amperage') needs very thick cabling. Not very cheap or efficient. For transport, high voltage AC is the best choice. That's why transport networks use that.

I didn't do the math on DC transport/distribution in datacenters, but it at first glance it does need high voltage for transport, just to keep the cabling anywhere near affordable. Change to lower voltages when needed.

Re:why 380v? (1)

amorsen (7485) | more than 2 years ago | (#38220076)

For transport, high voltage AC is the best choice.

For transport, high voltage DC is the best choice. No impedance worries, no phase to keep in sync over thousands of km. AC is legacy.

Re:why 380v? (0)

Anonymous Coward | more than 2 years ago | (#38219580)

I hope the backlight in my LCD isn't deadend tech. These things are hard to see without the 700V inverter keeping the light on.

Re:why 380v? (1)

BZWingZero (1119881) | more than 2 years ago | (#38219874)

Sorry to tell you this, but it is. Newer LCDs have LED backlights which don't require that pesky inverter.

Re:why 380v? (3, Informative)

Urban Garlic (447282) | more than 2 years ago | (#38219652)

Basic Ohm's law -- the resistive loss through a DC wire is the voltage drop across the wire, times the current through the wire. But the voltage drop across the wire is proportional to the current, it's just I*R, so the total power dissipated in the wire itself (i.e. not transferred to the load) is I*I*R. So, you want the current going to the load to be as small as possible. But, of course, the load still needs to get all the power it needs, so the operating voltage (which is distinct from the through-the-wire voltage *drop*, of course) needs to be higher if the current is lower.

So, high operating voltages reduce distribution losses.

The same analysis works for AC too, and is the reason that trans-continental transmission wires have such crazy-high voltages. AC has additional losses due to radiation and induction, of course.

Re:why 380v? (0)

Anonymous Coward | more than 2 years ago | (#38219868)

That is basically Google's proposal for a standard in power.

As for why they want a high voltage, it's simple. Low voltage dc is terribly inefficient when traveling even moderate distances. There was one article i remember, the gains you got from having a central more efficient adapter, you lost due to requiring, at minimum, several feet of wires between the adapter and the various server racks.

It might be possible that the efficiency of ac to dc saves you quite a bit as dc to dc (especially when dropping voltage) is relatively simple and easy (more efficient basically).

Basically:
A 120v ac to 380v dc adaptor for sections/all of the datacenter
380 dc to 12v/5v/3.3v dc adaptor for each mb

vs

120v ac to 12v/5v/3.3v dc adaptor for each mb

While the above seems more complex, dc to dc conversion is simple when it's just dropping the voltage meaning you the redundant parts are also the more simpler parts while the more inefficient conversion is centralized to be more efficient. This basically is a system designed to avoid power loss through the distance between the adapter and servers.

Re:why 380v? (0)

mjwalshe (1680392) | more than 2 years ago | (#38219994)

its the Amps that kill - and 12v at insane amps would require very very thick wires

Re:why 380v? (1)

hpa (7948) | more than 2 years ago | (#38220028)

380 V is presumably because it is the phase-to-phase voltage in 220 V 3-phase wiring, so there is plenty of distribution products already rated for that voltage. Why 380 V and not 400 V (230 V 3-phase, which is the modern standard) is a good question; it might have been what they actually intended.

Why 380v? (1)

Hadlock (143607) | more than 2 years ago | (#38219466)

The article says that 380v DC is the sweet spot, but why? Here in the US 440v (3 phase) AC is pretty common, as is 220v AC. I realize there's a world of difference between AC and DC, but that's about all I can think of. 380/4=95 x 4v rails I suppose? Someone with an EE degree or master electrician jump in here and explain this to me please.

Re:Why 380v? (0)

Anonymous Coward | more than 2 years ago | (#38219594)

http://hightech.lbl.gov/dc-powering/faq.html

6. Why have you chosen 380 VDC?

We have chosen 380 VDC because losses are lower than 48 VDC and server power supplies today convert AC to 380 VDC. It would be a simple process to manufacture power supplies to accept 380 VDC.

Re:Why 380v? (5, Informative)

RichMan (8097) | more than 2 years ago | (#38219664)

440 * sin(120) = 381.05 ....

3 phase has 2 ways of looking at the voltages, Y or delta.
The 3 phase delta is 440v when you measure between any pair of the 3 wires. The center point is ground. You don't see that in delta, but you do when measuring it in Y form. The same signals that are 440v when measured as a pair are 3 x 380v when looked at in the Y configuration.

So 3 phase 440v gives you 3x 380v to ground.

As to the 12v/5v/1.5v/ whatever you are going to have to do DC to DC all over the place. Better to have as high a voltage as possible for less current and less losses.

Re:Why 380v? (1)

Mr Z (6791) | more than 2 years ago | (#38219844)

Well, it would allow for about a 10% sag in the AC source, if that was 440v. 90% of 440v is 396v, which gives you some margin for conversion losses.

Re:Why 380v? (0)

Anonymous Coward | more than 2 years ago | (#38219848)

You can just look up HVDC for the reasons why.

Re:Why 380v? (1)

russotto (537200) | more than 2 years ago | (#38219982)

The article says that 380v DC is the sweet spot, but why? Here in the US 440v (3 phase) AC is pretty common, as is 220v AC. I realize there's a world of difference between AC and DC, but that's about all I can think of.

They've probably figured that common power supplies designed for 240VAC can be run off 380VDC by bypassing the rectifier diodes. Doing the math gets you 340V, but maybe they've looked at the actual devices available or in common use.

Re:Why 380v? (1)

vlm (69642) | more than 2 years ago | (#38220088)

The article says that 380v DC is the sweet spot, but why? Here in the US 440v (3 phase) AC is pretty common, as is 220v AC. I realize there's a world of difference between AC and DC, but that's about all I can think of. 380/4=95 x 4v rails I suppose? Someone with an EE degree or master electrician jump in here and explain this to me please.

OK

Look at the input stage of a stereotypical switchmode power supply. in 120 volt mode you see a voltage doubler config. In 220 volt config you see a plain ole straight rectifier. (If you ever wondered why you can run a switcher configured for 220 on 120 with no fireworks, but config for 120 and plug into 220 and it blows up, now you know) Your DC voltage to the input of the switch mode chopper is gonna hover right around......... 380 volts. No point getting overly precise because line voltage and component tolerance is not overly precise, but pretty much you take an off the shelf switcher, rip out the input rectifier and filter, dump in raw 380 VDC and off ye go.

Now the "pretty much" relates to all kinds of fun like inrush current limiting for the chopper may have relied on the resistance of the rectifier and filter, or maybe your chopper controller runs off a tiny little AC transformer.

But to a first approximation, if you're reading this on a desktop PC, you are already using a more or less 380 volt DC power supply, so its pretty easy to bodge anything using 380 VDC.

Am I the only one that thinks this is a step back (-1)

Anonymous Coward | more than 2 years ago | (#38219494)

Oh boy... here we go again with the Edison/Tesla debate. If the plan is to bring a large DC power supply online to feed a datacenter then I do not believe anyone has done the math. Sure it's easier, that's about it. A quad multiphase feed into a distributed commercial UPS is more efficient . What you gained from the AC/DC conversion process you lost over your power distribution cables. This technology is available due to the dumbing down of society. Most power inverters are around 97% efficient and going from ac/dc rectifiers are very efficient. Hmm what happens when you deliver 380 volts DC through 500 feet of 16 gauge wire ? LMAO You loose what you gained from not converting the power. AC is more effecient

Re:Am I the only one that thinks this is a step ba (2)

LehiNephi (695428) | more than 2 years ago | (#38219658)

I think you failed to mention how much current is being pushed down that pair of 16AWG wires. The power loss comes from (current * resistance (of the conductors)), not from the voltage.

We have 48VDC as one standard... (4, Interesting)

mlts (1038732) | more than 2 years ago | (#38219588)

If one has worked in a telco, we already have a standard, and that is 48VDC. This is the domain of the Sun Netras of yore.

If I were to recommend a voltage, why not plain old 12VDC? Yes, the amps have to be high, but we already have a connector for this (beats wiring up things by hand and throwing a breaker), and it is not hard to find off the shelf hardware to support this, be it batteries, power distribution units, inverters/converters, solar panels with MPPT controllers, and so on. We have two large markets (RV/marine) that are dedicated to 12VDC.

Why not just use an established standard? 12VDC works and has a lot of support, or if a higher voltage is needed, then 48VDC.

384VDC just seems to be asking for trouble. It would require yet another separate connector that can't be plugged into 120VAC or 240VAC, generators would have to have an adapter for it. It would require a complete retooling to get to that standard.

Making another voltage level is throwing the baby out with the bathwater. Why not just go with an established DC voltage level?

Take 12VDC. Most generators, from the expensive inverters by Honda or Yamaha can generate that, as well as the construction grade open-framed ones.

Re:We have 48VDC as one standard... (2)

Wonko the Sane (25252) | more than 2 years ago | (#38219698)

why not plain old 12VDC?

Look up the rating of the power supply currently operating your computer then calculate how many amps would be required to deliver that power at 12 volts. Look up the gauge of wire that would be required to supply that much current without melting the insulation. Then multiply by the number of computers in a typical data center.

Re:We have 48VDC as one standard... (1)

Anonymous Coward | more than 2 years ago | (#38219958)

480watts/12V = 40amps

40amps requires a minimum of 12 gauge wire.

That's beefy.

Re:We have 48VDC as one standard... (0)

Anonymous Coward | more than 2 years ago | (#38220002)

You seem to have some lack of basic understanding. Yes, the current will be higher at lower voltage. This does NOT correlate to needing thicker wires, as the wire has to withstand not current but power which is the result of multiplying voltage with current.

If you have half the voltage but twice the power, the loss in the cable will be the same and therefore the cable needs the same rating.

He, this is really basic electric theory. Maybe you want to learn about Ohms law.

Re:We have 48VDC as one standard... (0)

Anonymous Coward | more than 2 years ago | (#38220108)

Of course this needs to read "If you have half the voltage but twice the current".

Re:We have 48VDC as one standard... (4, Informative)

Wonko the Sane (25252) | more than 2 years ago | (#38220128)

Yes, the current will be higher at lower voltage. This does NOT correlate to needing thicker wires, as the wire has to withstand not current but power which is the result of multiplying voltage with current.

You've managed to be right while also being wrong at the same time.

You could use voltage*current to calculate the thermal losses in a conductor but what you've done incorrectly is assume that "voltage" in this equation is the voltage between the conductor and ground.

The correct way to calculate losses in a conductor is current * end-to-end voltage difference

The end-to-end voltage difference is directly proportional to the current so the most efficient way to calculate the losses is current squared times resistance.

Since the surface area of a wire is proportional to the square of the wire diameter and the conductivity required is proportional to the square of the current carried it ends up that wire diameter is directly proportional to the current.

Re:We have 48VDC as one standard... (1)

geekmux (1040042) | more than 2 years ago | (#38219970)

384VDC just seems to be asking for trouble. It would require yet another separate connector that can't be plugged into 120VAC or 240VAC, generators would have to have an adapter for it. It would require a complete retooling to get to that standard....

I'm sorry, but according to the 1%, you've exceeded the allowed threshold for Common Sense with your remarks here. Such atrocities against Greed will not be allowed or tolerated.

Anytime a new standard is being proposed, you can bet there are several people standing behind it poised to make money off it. And based on your suggested necessary changes, they stand to make a lot of money off this new standard.

Who ever said the creation of new standards needed to make sense anymore? We're here to feed the 1% and "create" jobs, which is yet another purpose of new standards. Nobody ever said anything about current standards and interoperability, and you sure as hell aren't going to hear it coming from the guy looking to build and sell 384VDC widgets.

Re:We have 48VDC as one standard... (2)

mkiwi (585287) | more than 2 years ago | (#38220024)

384 VDC is a common voltage used in "Boost" regulators that are universal input. That's probably why that voltage was used. You obviously can't power a microprocessor off of a 384V line (SiC would be necessary to withstand the high voltage). There has to be some sort of switching going on.

I have not RTFA, but what would make sense to me would be to use a boost converter to get 384V, send that 384V all around the building, then convert it down to 12V, 5V, 3.3V, and 1.2V using a few large DC-DC converters. Most enterprise computer power supplies have a PFC boost converter already, so doing all that in one massive stage would save space inside the PSUs and improve efficiency (although the current Boost converters are generally 90%+ efficient).

12VDC and 5VDC would easily cook a modern microprocessor. I guess it's a question of doing the PFC boost for everything at the start, or breaking it up into tiny sections (as is already the case). Safety shouldn't be a big issue, and you need the 384V to supply enough power to all your DC-DC converters. To get the same power with lower voltages you'd need to use expensive superconductors.

Re:We have 48VDC as one standard... (0)

Anonymous Coward | more than 2 years ago | (#38220080)

Why not just use an established standard?

It's not so profitable.

Since time immemorial vendors have been creating incompatible standards to encourage people to buy stuff.

Actually no generator change required (0)

Anonymous Coward | more than 2 years ago | (#38220136)

As mentioned above, a Y configuration on a 440V (delta) 3-phase generator is 381.05V. once rectified, this is almost exactly what you need.

3-phase diesels for this type of thing are incredibly common and in industrial electrician would find setting up this configuration trivial.

As mentioned by many, high amps mean large gauge wire, and copper prices continue to rise.

Safety concerns for regular customers (1)

Anonymous Coward | more than 2 years ago | (#38219622)

I barely trust my first level tech guys to work on DC power let alone customers who have a hard enough time configuring their routers.

We use DC all the time for our telephone gear, core and border routers (so we only have one type of power supply to stock), and other odds and ends. This mentality comes from us being a telephone company as well as an ISP/colocation center. Otherwise we would be all AC I imagine.

So the first concern I have would be safety if one expects customers to be around DC power plants, power distribution panels, and possibly pulling out a -48V wire
from the back of a server because they failed to tighten down the screw enough holding it in. DC, when it shocks you, does not let go!

Ten years? (1)

Anonymous Coward | more than 2 years ago | (#38219648)

Ten years ago I worked for a startup that was making 1U and 2U appliances for streaming video distribution. Back then the hardware guys were saying that DC was the way to go.

Now it's ten years later and who uses DC? I guess I'll believe it when I see it.

What do you mean? (0)

Anonymous Coward | more than 2 years ago | (#38219822)

Where are all the Tesla leg humpers when we need them!!??!?

It's complicated (0)

Anonymous Coward | more than 2 years ago | (#38219866)

It's a complicated subject that is mostly immune to a simple analysis.

The goal is to increase efficiency, by eliminating a few levels of voltage conversion.

One simple plan would be to convert then incoming AC to a medium Dc voltage, a few hundred volts, then distribute that down to the board level, at which you'd have your basic switching converter/regulator to drop it down, in one step, to the 12 and 5 and 1.X volts that the disks, logic, and CPU need.

You can't drop it down any earlier than the board level, as the cost of copper quickly limits that. For instance a 5 volt supply at the rack level would require fire-hose size copper conductors from rack to boards.

Problem is, 300 volts DC is kinda hard to handle. Dc likes to arc and does not like to stop arcing, making 300 VDC switches and circuit breakers very large and complex. Also running 300VDC to the board level increases the cost of wiring, as wires at that voltage have to meet a higher code level. it's a very delicate thing to find the right topology of AC, DC, and voltage levels.

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