Are Data Centers Finally Ready For DC 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?"
Edison reaching out from beyond the grave (Score:5, Funny)
I told you bitches I would prevail one day!
Re:Edison reaching out from beyond the grave (Score:5, Informative)
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 (Score:5, Informative)
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:Plus brushless motors (Score:4, Informative)
Computer fan motors are brushless DC. But really they are permanent magnet AC motors with a simple VFD (variable frequency drive) in it. I suspect RC planes are the same.
In the industrial world VFDs are very popular. On anything from a 2HP conveyor to a 1000HP+ piece of equipment. They rectify three phase input to DC, then convert it back to AC at the desired speed. Some are setup so you can have one central rectifier, and multiple inverter sections for your different loads.
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Sorry, while that may have been true at the beginning of the 20th century it certainly isn't true at the beginning of the 21st.
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Try building a circuit to increase the voltage of a DC power source, then you'll understand.
Yes, we know that once you magically have huge voltage DC, there is no more problem. Getting to that point, however, is the problem.
Re:Edison reaching out from beyond the grave (Score:5, Informative)
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Re:Edison reaching out from beyond the grave (Score:5, Informative)
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.
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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
Re:Edison reaching out from beyond the grave (Score:5, Informative)
Re:Edison reaching out from beyond the grave (Score:5, Funny)
At 60 Hz, the skin effect is virtually nonexistent.
Monster Cable begs to differ!
Re:Edison reaching out from beyond the grave (Score:5, Insightful)
Its true you can convert voltages DC to DC using electronics, but reliably at 132kV? It aint easy, cheap and certainly neither if you want efficiency.
(Blow up a 132kV IGBT, then come back and tell me about the damage :-)
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Nothing that involves large amounts of power at 123 kV is cheap.
Even if a solid state substation is initially more expensive to build than a traditional substation that's a sunk cost while the efficiency gains of using DC accrue every day.
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As an aside, car manufacturers are also moving towards higher voltage because that gives them easier access to drive high-power systems like power steering. Currently most power steering is pneumatically driven, which comes with a hefty overhead cost in terms of manufacturing and maintenance. With a high-voltage bus to drive it, the complex machinery simplifies it to an electric motor and some gears.
Re:Edison reaching out from beyond the grave (Score:5, Informative)
Comment removed (Score:4, Interesting)
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Wrong. ALL power brakes in passenger cars and other lightweight vehicles are hydraulic. Most power brakes in heavy vehicles (over-the-road trucks, etc.) are pneumatic.
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The problem with DC back in Edison's day was that you couldn't easily step it up or down.
There's also the problem that, at reasonable transmission voltages, if you shock yourself on 60Hz AC, you're likely to spasm off the terminals within a few cycles, but a DC shock is more likely to cause your muscles to lock you onto the source where you will stay until fried extra crispy, unless helped off by a bystander.
Re:Edison reaching out from beyond the grave (Score:4)
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.
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The typical computer power supply and almost everything else anymore uses a rather efficient switching power supply, it takes the input power, rectifies it, runs it through a transformer by switching the DC on and off at high frequency, then rectifying the output from the transformer to supply the rest of the computer. The power supplies change from 115 VAC to 230 VAC input by a simple switch, the 230 VAC , which has a peak to peak voltage of 325 volts, just a stones throw from 380 VDC. The only reason that
Telco power connectors (Score:4, Informative)
Only very stupid engineers design power connectors that can fit both ways.
The DC power supply connections in telco equipment is generally screw terminals and spade connectors.
Re:Edison reaching out from beyond the grave (Score:5, Funny)
That's why they use 380 volts! One big splice goes to all the 12 volt stuff, then another splice comes off of that splice to do the 5 volt stuff. It is not run through regulators, it just happens automatically due to the superior characteristics of DC power! They also tap into the ground wire at various places to get the -5 and -12. Magic I tell ya!
It sees it's best efficiencies running near 100% utilization through so you want to plan your workloads accordingly, or you risk watching your $#!+ let out it's magic smoke! So all in all it should drive down the price of "the cloud" by forcing competition!
Win, Win!
Re:Edison reaching out from beyond the grave (Score:5, Funny)
That "whooshing" sound you hear? Yeah, the guy who modded that post "informative" heard it too.
Re:Edison reaching out from beyond the grave (Score:5, Insightful)
Try being less of an asshole for a day or two. You might find that people hate you less.
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I would argue that #2 is becoming less relevant too.
Many industrial 3 phase motors are being driven by variable frequency drives for improved control and huge efficiency savings. The first stage of a VFD would be rectifying the 3 phase AC back to a DC bus (same as a UPS) so DC distribution would work fine for that too.
Re:Edison reaching out from beyond the grave (Score:4, Informative)
I told you bitches I would prevail one day!
There seems to be a popular/fundemental misunderstanding of the tesla/edison debate.
DC is MORE effecient on the wire than AC given the same voltage, amperage and wire gauge.
The reason for this is in AC systems eddy currents induced by changing electric fields at 50/60hz cause electrons to migrate away from the core effectivly reducing wire size.
Why AC has been the choice for so long is an engineering problem.
Building rectifiers to convert AC to DC from huge AC generators which produce virtually all of our electricity with the kinds of voltages needed to carry massive quantities of volumes of energy is difficult, unreliable and ineffecient..even today.
Back then it was practically impossible. The choice between Tesla and Edison really boiled down to high vs low voltage. Low voltage transmission required impossible quantities of copper or decentralized generation.
Tesla wanted larger more centralized generation which given what we use for fuel these days is an exceedingly smart move.
also needed for houses (Score:3, Insightful)
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.
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Re:also needed for houses (Score:4, Interesting)
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 (Score:5, Interesting)
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.
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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 ba
Re:also needed for houses (Score:5, Informative)
What bothers me is all the new LED bulbs that have transformers in them (guessing, because they get hot! ... feels like wasted energy)
High power LEDs get hot because you are running good amounts of current through them, not because there is a transformer. Transformers are pretty much useless with the DC current that runs LEDs.
I'd think it would be more efficient to run DC to lighting and certain outlets like those where small devices would sit ...
The problem comes in deciding what voltage to use. 12V means you need rather hefty wires to get the required current for some devices. A 6W LED needs half an amp at 12V. If you use a voltage that makes the current resonable, then you need to convert that voltage to what your device needs, every place you have a device.
Sending 380V means you can use the same or smaller wires than you'd use for 120V systems, but you'll be busy converting that 380V DC to 12V DC or 5V DC or 1.2V DC -- and while DC-DC conversion has gotten a lot better, it is still more complicated than a simple transformer.
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but the 100 other widgets in my house could plug in DC.
That's 100A of 12V. From here [powerstream.com], you'd need at least number 2 or number 1 wire to carry that current. Ballpark figure.
Same reference, you lose 3 volts for every ten feet of 12 gage at that current (one wire for supply, one for return.) Can your 12V device run happily on 9V?
Sure, the TV and PC would still convert AC power,
The costs of running two power systems in a house would swamp any savings you think you'd make by using DC.
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Well, it's not exactly a transformer, but you're essentially correct -- a high-power LED bulb needs to be supplied its forward voltage at a constant current, which means rectifying and bucking the voltage down. There's lots of schemes to do this, some more efficient than others. The current limiting resistor scheme most of us are familiar with is about the most inefficient way, but it's also very inexpensive. LDOs and linear regulators are still very inefficient. Buck converters are better, but very exp
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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.
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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.
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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).
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This is equally true of both AC and DC.
We have these things now called semiconductors. You may have heard of them.
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...newer PoE gear will get you almost 30A per device...
You probably mean 30W, not 30A. I agree that it's a pretty good standard wrt safety. I assumed it was just 48V on the pair with no communication. Boy was I wrong!
Telecom's been doing this for many, many years. (Score:4, Insightful)
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. (Score:5, Informative)
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. (Score:5, Interesting)
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.
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I work with DC power in Telecom and it has 3 huge advantages I can think of off the top of my head:
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.
Short the posts of a car battery, count the number of milliseconds it takes the pliers to be welded to the leads... Then come back here and tell us all about how low voltage is "safe" and requires no qualifications.
Amps, not volts (Score: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.
Voltage only determines if it can overcome the resistance of your skin (and maybe clothing). Beyond that, it doesn't matter. Amperage, on the other hand, determines the power -- the amount of damage the current will cause.
10 milliamps can kill you. But without at least several dozen volts behind it, it won't make it through your body.
But. Put something nice and conductive (like a tool) across a low-voltage circuit and you'll get an arc from the short. You don't need high voltage with that conductive ma
Arc flash hazard (Score:3)
If I touch a 1000 volt wire that is carrying 100 amps and resistance of the return path (including my body) is 1 megaohm then exactly 1 milliamp will flow through my body.
Riiight. I=V/R, not just a good idea, it's the law.
Remember where I talked about shorting a wire with a tool? That's the danger in telco power system. Not you touching the wire -- your body is a lousy conductor, compared to copper. But if you short a bus bar with a screw driver, or something like that, the resulting arc flash will really ruin your day. The arc converts the electrical energy to thermal and kinetic energy, which is perfectly capable of burning your face off.
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Having witnessed the demise of a mere 5kVA UPS in the bottom of an HP server (in a telephone switch building) I can certainly attest to the boom-ness of the large capacitors. It was a great light show that would have been better had it not been the new replacement unit (for the already failed original) that went boom. The noise drew attention from all over the floor. I can also attest to the need for spare underwear on the part of the HP tech :)
I am quite sure that accidentally shorting the DC bus bars r
Re:Telecom's been doing this for many, many years. (Score:4, Insightful)
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Afaict there are a few issues with 48V DC for a dataceventer.
1: it's nonstandard (in the computer industry) so you pay a premium for equipment that runs off it and reduce your choice of equipment.
2: It's lower voltage so for a given level of tolerable loss your cables have to be much bigger
3: It's DC so it's more prone to arcing making all your switches and protective devices more expensive and basically ruling out the use of plug and socket connections for anything other than final connection of individual
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^ 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..
Re:Telecom's been doing this for many, many years. (Score:4, Informative)
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.
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Google 12VDC proposal better. (Score:5, Interesting)
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.
conversion on the motherboard? (Score:2)
Wouldn't you just end up putting a switching power supplies elsewhere and create heat problems, then?
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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. (Score:5, Informative)
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. (Score:5, Funny)
Excellent idea! Hydrogen gas, oxygen gas, chlorine and an ignition source all in the same package. What could possibly go wrong?
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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.
Re:Google 12VDC proposal better. (Score:4, Informative)
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. (Score:4, Interesting)
why 380v? (Score:4, Interesting)
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 (Score:5, Informative)
Lower voltages require larger conductors to carry the same current. Copper isn't that cheap.
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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 (Score:5, Informative)
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.
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*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.]
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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
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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.
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Lower voltages require larger conductors to carry the same current. Copper isn't that cheap.
And you're limited on the high end by state electrician licensing boards who require "high voltage license" instead of regular license somewhere around 440 volts to 600 volts. So however cool you think it might be to design your entire infrastructure around 1024 volt DC, the cost of electricians would be much cheaper if you can keep it under 400 volts.
Obviously there are some states where this doesn't matter, all I can say is I've heard of cutover points of 440 volts, 600 volts, in some weird combination o
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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.
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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? (Score:4, Informative)
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.
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Why 380v? (Score:2)
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? (Score:5, Informative)
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.
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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.
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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 comp
We have 48VDC as one standard... (Score:5, Interesting)
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.
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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... (Score:5, Informative)
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.
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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% a
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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.
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Nah, he will just be proven right, again.
Re:And in related news... (Score:5, Funny)
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Re:Power monitoring (Score:5, Informative)
Hall effect. [yeint.fi]
In the presence of a static magnetic field (as around a conductor carrying a constant current), electrons in the clamp circuit, which also carries a DC current, will be pushed to one side of the clamp conductor, inducing a voltage relative to the other side. Measure the voltage and you know the current in the wire it's clamped around.
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That's only true for large values of "12" that approach 300. It is a very big battery though, and they will reliably handle discharges at over 1 MW.
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FYI those of you who are thinking "Oh but 380VDC could be used in a 240VAC PSU if we take the rectifier out" you are RIGHT except for the fact that these are switching PSUs so... no... it wouldn't work at all.
Back to -48VDC we go.
Try making up new standards all day long. This has been a standard in data centers for over forty years for a reason. And if battery rooms aren't going to be funded by data centers, and expensive PSUs won't be funded by server owners, the warlock tiger blood winner here is "failu
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You can still regulate voltage that way but instead of being 95% efficient your computer's power supply would be about 60%, with a huge increase in power consumption, size and heat generation.
Switching power supplies do create high frequency noise that must be filtered out but that's the price you pay for the increased efficiency.