Are Data Centers Finally Ready For DC Power?

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?"

Comments

Edison reaching out from beyond the grave

[ravenspear]

I told you bitches I would prevail one day!

Re:Edison reaching out from beyond the grave

[rolfwind]

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

[Wonko the Sane]

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

[Elder Entropist]

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

[Mr Z]

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.

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, 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

[khallow]

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

[Anonymous Coward]

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

[Anonymous Coward]

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

[EETech1]

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

[Relayman]

At 60 Hz, the skin effect is virtually nonexistent.

Re:Edison reaching out from beyond the grave

[Anne Thwacks]

The skin effect is only significant at frequencies WAY above 60Hz, so this is not relevant. AC is used because transformers can convert huge amounts of power from one voltage to another reliably, efficiently and cheaply.

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 :-)

Re:Edison reaching out from beyond the grave

[budgenator]

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 switching power supplies aren't used on DC is because one side of the input rectifier bridge will probably burn out from not having a rest cycle to cool off. Beef up that bridge rectifier and the power supply will not care what the input frequency is. It would be trivial to convert power supplies to 380 VDC.

Re:Edison reaching out from beyond the grave

[afidel]

That's only true with very expensive solid state components that didn't exist when the decision to go AC was made and it also ignores the fact that DC branching is extremely complex so it only works when you are moving power from generation site to large single use site, a wider grid is much harder to do with DC.

Re:Edison reaching out from beyond the grave

[WaffleMonster]

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.

Re:Edison reaching out from beyond the grave

[ssyladin]

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

[aXis100]

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

[lgw]

That "whooshing" sound you hear? Yeah, the guy who modded that post "informative" heard it too.

Re:Edison reaching out from beyond the grave

[Anonymous Coward]

At 60 Hz, the skin effect is virtually nonexistent.

Monster Cable begs to differ!

Re:Edison reaching out from beyond the grave

[ktbaia]

I beg to differ. The Electronic Power Steering in my 1995 NSX decidedly does NOT feel like crap. When EPS systems were first put on production cars (the NSX was the first), it was on sports cars, where good steering feel is very important. See this link for information on how a decent EPS system should work. Just because Toyota can't figure out how to do a decent EPS doesn't mean that it hasn't been done. http://www.nsxprime.com/FAQ/Technical/eps.htm

Re:Edison reaching out from beyond the grave

[Wonko the Sane]

but reliably at 132kV? It aint easy, cheap and certainly neither if you want efficiency.

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.

Re:Edison reaching out from beyond the grave

[JoeMerchant]

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

[bkcallahan]

A/C skin effect applies *based on frequency*; I assure you skin effect at 50/60Hz, even at high voltages, is negligible -- Doesn't matter if it's 420kV or 4.2V. A circuit at 29.350 MHz at low voltages has to worry a LOT more about it than a 50/60Hz line voltage. (And it really starts kicking off at the start of the microwave range, 300MHz, and is exceptionally important by the end of the microwave range 3GHz.) The reason A/C is used is based off of Ohm's law and is based on current and resistance; Jack up the voltage 1,000x and you can reduce the current (and therefore, heat loss) 1,000x.

Re:Edison reaching out from beyond the grave

[PhinMak]

My 2004 Mini S had electric power steering... and Mini Cooper's brand is built on nimble driving, including responsiveness and steering feel.

The one drawback that I have to point out is that the electronic pump is a one of the weaker parts in the car. Anecdotal evidence (my experience plus discussions with dealer service managers and wrench turners) suggests that they fail at least once every 5 years... To add insult to injury, the part ALONE costs $900 at the dealer. Compare to less than $100 for a comprable hydrolic pump in a domestic car. This suggests serious design/material costs or price gouging by the manufacturer.

Re:Edison reaching out from beyond the grave

[Grishnakh]

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.

also needed for houses

[Anonymous Coward]

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

[oh_my_080980980]

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

[LehiNephi]

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

[vlm]

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

[ShavedOrangutan]

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

[Obfuscant]

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.

Re:also needed for houses

[c 0xFF]

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 expensive.

In the end, that conversion has to happen no matter what, whether at the bulb or at a central box somewhere else, so there's always going to be some wasted energy. Hopefully you'll get improved efficiency by centralizing everything.

But, even if the overall efficiency is the same, there's still the benefit of moving the heat to a different location. One major problem with LED bulbs is that they dim and can handle less current as they heat up. Notice the heat sinks they're putting on the really high power LEDs these days. Performing the voltage conversion elsewhere means that this heat is moved elsewhere.

And if you're smart about where "elsewhere" is located, you're also reducing the strain on the air conditioners! Put the conversion in a basement or outside the building, for example.

I wonder how much of the heat produced in a data center is actually produced by the power supplies for each server. 10% to 20% feels about right. Ignoring any other benefits of moving to DC, I would think that the 20% reduction on the air conditioning bill would be justification enough.

Re:also needed for houses

[Obfuscant]

but the 100 other widgets in my house could plug in DC.

That's 100A of 12V. From here, 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.

Re:also needed for houses

[Muad'Dave]

...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.

[Anonymous Coward]

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.

[Shatrat]

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.

[the linux geek]

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.

[Anonymous Coward]

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.

[vlm]

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.

[mjwalshe]

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.

[Anonymous Coward]

2) Lead Acid batteries are hugely more reliable and less expensive than equivalent UPS systems, and provide more holdover time.

Ummm, what do you think UPS systems use? Lead-acid batteries.

You probably mean that 48V DC UPS systems are much simpler than AC UPS systems since you don't have to convert from AC to charge the battery, then discharge the battery & convert to AC to power your equipment.

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

[WaffleMonster]

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.

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

[GumphMaster]

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 running about the ceiling would have been a _very_ lively show.

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

[Wonko the Sane]

The thing is that it doesn't really matter which way you conceptualize it, except for some specific situations like trying to understand how a vacuum tube or CRT works.

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

[petermgreen]

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 devices

The combination of these factors make a 48V DC system expensive.

Google 12VDC proposal better.

[Animats]

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.

[Mr Z]

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.

[vlm]

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.

[hpa]

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.

Re:Google 12VDC proposal better.

[Wonko the Sane]

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?

why 380v?

[wierd_w]

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?

Re:why 380v?

[DerPflanz]

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?

[Urban Garlic]

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?

[RichMan]

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.

You'd need much larger conductors

[bigtrike]

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

Re:You'd need much larger conductors

[nzac]

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:You'd need much larger conductors

[nzac]

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

[vlm]

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 of TN , WI, and a couple other states.

I am told the main thing they teach you in high voltage continuing education class is that for all practical purposes, all accidents are fatal above 500 volts. That's pretty much what I've heard from the grapevine... 120 volt deaths are always two parters, like grayhair's heart couldn't take it or the shock made him fall off the ladder and the broken neck is what killed him, whereas 440 threephase and above its always "condolence cards can be sent to..." except for true miracles. That and they put you thru the ringer about threephase and wye vs delta and figuring out rotation directions without destroying industrial equipment, none of which matters in a data center.

We have 48VDC as one standard...

[mlts]

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...

[Wonko the Sane]

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...

[mkiwi]

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...

[Wonko the Sane]

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:Am I the only one that thinks this is a step ba

[LehiNephi]

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.

Re:And in related news...

[DickBreath]

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

But what about the poor switches???

[Oryn]

Has anyone considered all the arcing and sparking that simple on / off / circuit breakers will have to deal with? At least with AC you have a chance that the switch will be opened or closed at the zero crossing period and that AC makes it harder to draw arcs when breaking a circuit.

I'm not sure its really going to present any more effeciancy. I guess if you use a 3 phase site rectifier then it will save you the cost of 3 phase copper and make the server power supplies cheaper. Not forgetting that you could actually plug an unmodified server directly into 384V DC (so long as the psu is set to 240v).
I guess the days of computers using 60hz as a reference are over :)

Re:But what about the poor switches???

[Wonko the Sane]

Even modern nuclear boats have a big ass 12VDC (in the US) battery for backup power.

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.

Re:Power monitoring

[blair1q]

Hall effect.

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.

DC power distribution is awesome

[wezelboy]

At least 25% power savings. Higher reliability. Lots of copper though.

My GTI's steering is wonderful.

[zerofoo]

My 2008 VW GTI has an electric assist rack, and it is one of the best systems I've ever felt in terms of feedback and heft. I've also driven overboosted hydraulic systems that feel like mush.

Electric assist steering can be done well, and hydraulics can be done poorly. The technology isn't to blame, it's the engineering that matters.

Amps, not volts

[DragonHawk]

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 material. And the arc itself can be dangerous. Temperature of the sun, chunks of hot metal flying around, etc.

Now consider that the battery plant in a typical telco CO is the size of a small one-bedroom apartment. The amount of power in that battery string is truly frightening. The main bus bars are often *several inches thick*.

As one guy put it, "Drop a wrench, learn braille."

Telco power connectors

[DragonHawk]

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.

Arc flash hazard

[DragonHawk]

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.

Re:Plus brushless motors

[LinuxIsGarbage]

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.

Re:DC is more expensive

[gavron]

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 "failure".

Re:Er, but all things are NOT equal

[Wonko the Sane]

You can not do this with DC power. End of story.

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.

Re:Back in the days

[Wonko the Sane]

How did that change?

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.

Re:Er, but all things are NOT equal

[OeLeWaPpErKe]

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.