DC Power Poised To Bring Savings To Datacenters 287
snydeq writes "InfoWorld's Logan Harbaugh follows up his '10 IT Power-Saving Myths Debunked' to argue in favor of using DC power in the datacenter. The practice — viewed as a somewhat crackpot means for reducing wasteful conversions in the datacenter just a few short years ago — has gained traction to the point where server vendors such as HP, IBM, and Sun are making DC power supplies available in their server wares. Meanwhile, Panduit and other companies are working to bring down another barrier for DC to the datacenter: a standardized 400-VDC connector and cabling solution. And with GE working to list 600-VDC circuit breakers with the Underwriters Labs, DC's promise of reduced conversion waste could soon be commonly realized."
Old hat in the telco world (Score:5, Interesting)
Telco gear tends to be 48VDC all over the place. It just works. Speaking as a guy working at a telco in the IT department, I'm hugely in favor of moving to 48VDC servers.
Re:What about a _home_ standard for DC power? (Score:2, Interesting)
Why not 12V, 6v or 3.3v, etc? (Score:4, Interesting)
I'm not an EE. But back during the dotboom I thought it would make sense to have a big ups in the data center that output voltages that mother boards expected as input. I almost thought of rigging my own experiment using laptops as servers and feeding them all 12vdc directly from the UPS battery pack.
Ok rip it apart guys, why is wrong with that plan?
48VDC pros/cons (IMHO) (Score:5, Interesting)
Pros:
No power supply needed for each machine. This removes a major point of failure. Instead, one would need to just step down voltages to the 5 and 12 volt rails. This also helps with cooling because the room AC/DC converter can be cooled with a dedicated system, either liquid, or part of the HVAC system.
Cons:
48 VDC needs a dedicated connector with a high plug/unplug cycle rating that people know is 48 volts and 48 volts only. It sucks when you have to manually wire it up, because this takes time and there is always the risk of getting zapped if you don't throw the right circuit breaker (or pull the right fuse) on a telco rack where 48V is in use.
Because there is only one 48VDC power supply for a room, it has to be held up to a lot more rigorous standards than average mains current. It has to not just provide 48VDC, but provide it under extremely heavy load without the voltage dropping by much.
Maybe 48 volts would be a new computer standard. The key is not having to wire it up manually like some stereo speakers, but giving it a dedicated, foolproof, power connector that Joe Twelvepack who is slurping down his seventh can of Bud Light can easily and reliably plug and unplug while staggering around in the back of the server room until his shift ends.
Re:What about a _home_ standard for DC power? (Score:3, Interesting)
Agreed. My PC and media installations are plagued by a plethora of these heat-generating devices, as I add on printers, ethernet devices, networked disks, extra storage, converters, encoders, decoders, and the like. I had to learn to include plans for a well-ventilated place for these things.
Also, it's an inherently good idea for power savings. Power supply efficiency can go way up when both a) total power goes up and b) the supply can be designed for a constant load (which would be the case for a large data center, for sure).
The arguments of olde - don't carry much weight (Score:5, Interesting)
Alternate view: http://cim.pennnet.com/display_article/347089/27/ARTCL/none/none/1/A-powerful-debate:-AC-vs-DC-distribution/ [pennnet.com]
Or, to summarize - if you take a high-efficiency AC system and convert it to 480 volts, downstep to only 240 volts (and all todays' boxes can run either 110 or 220-240), you can get to within 1% of the DC system.
Add to that the savings in materials (1.5" copper wiring? Booster cables for diesels aren't anywhere near that thickness) and there's no real reason to change.
In fact, the biggest saving would probably be if we went from 120v to 240v for everything. One less down-conversion, etc.
Re:The arguments of olde (Score:5, Interesting)
Ere... not sure why "Insightful" since Tesla was the one who invented the AC polyphase distribution system, and would probably not approve of using Edison's (not Franklin's?) DC distribution method.
That said, AC power made a lot more sense before the event of solid state power electronics. You can't reasonably convert DC to DC efficiently without using an AC phase via transformer, which was a major hurdle in using DC power. High frequency power supplies can do the job just fine, though.
=Smidge=
Re:The arguments of olde - don't carry much weight (Score:5, Interesting)
You can achieve substantial savings just by wiring your datacenter for 240V only (in the US). The rest of the world knows this already, but every time I suggest this in the US, people look at me like I have monkeys flying out my nose. Half as many amps == half as many power strips, half as many UPS devices, half as much wire, etc. With the exception of cheap-ass wall wart powered devices, I have not encountered any equipment that was not 240V compatible in the US in years.
Re:48VDC pros/cons (IMHO) (Score:3, Interesting)
The whole 48v DC thing sounds good to me (I don't run a data center though, or anything like it).
That said the article discusses (and I've seen it said elsewhere) the large copper bars used for wires in this kind of setup, and how they will lose more power between the wall and the rack than AC.
I can see the appeal of going TOTALLY 48v, but why not run AC to the racks, and just have a large converter for every 2 or three that provides the full DC power and backup for those three racks? You're still avoiding inefficiency in having 20+ individual power supplier per rack. And you avoid a voltage conversion (instead of thousands->hundreds->110v->whatever DC you need you'd have thousands->hundreds to top of rack->whatever DC is output). That would save some juice.
Plus the per-rack theory would make it really easy to convert equipment a few racks at a time without having to move a whole large chunk of a data center.
PS: I assume people would still use dual (or more) redundant PSUs on the individual boxes, even though they wouldn't be dealing with nearly as much heat since they don't have to do the whole AC->DC thing.
Re:What about a _home_ standard for DC power? (Score:3, Interesting)
I don't run a datacenter, but I sure would like to get rid of the power bricks that all small electronic appliances seem to come with these days!
probably because these 'wall-warts' are linear converters - seldom better than 40% eff.
As more stuff conforms to the ENERGY INDEPENDENCE AND SECURITY ACT OF 2007, these will become much less of an issue.
Re:48VDC pros/cons (IMHO) (Score:3, Interesting)
A. You won't get zapped from 48VDC. If you are extremely sweaty you might feel a slight tingle, but nothing to get excited about.
2. Just wire up some big batteries in parallel and you don't have to worry about voltage drop under load. As long as the rectifiers can keep with the current needed to float the batteries at 48V (really more like 52V in practice) you're fine. As stated by an earlier poster, this is proven technology in use by telcos for a very long time.
D. This whole article is about datacenters. I hope Joe Twelvepack hasn't just slurpped down 7 Bud Lights and wandered in to wire up some servers, but if he has I doubt a dedicated power connector is gonna keep him from fouling something up. There already exist standard 48VDC connectors. They're called lugs. Just remember, the positive terminal goes to ground. Actually I have seen modular plugs for this purpose, but any tech worthy of working near such equipment should be able to terminate a color-coded cable easily enough.
Re:Why wasn't this tagged 'edison v. tesla'? (Score:3, Interesting)
Maybe, but it it has nothing to do with "blood polarization". There is more than one way to measure AC: peak, or RMS
1 amp DC carries more energy than 1 amp AC (peak) and thus is more harmful.
1 amp DC is exactly equivalent to 1 amp AC (RMS) in terms of energy and harm*.
*One possible exception is if the AC is very high frequency and the load is not purely resistive. Then you get wacky tesla coil effects.
Re:48VDC pros/cons (IMHO) (Score:5, Interesting)
IIRC there was a UPS study on DC power recently (Score:4, Interesting)
That concluded that using the european system of 230/400 3 phase AC for distribution splitting out to 230V single phase AC near the point of use was almost as efficiant as a 400V DC system and far cheaper and easier to deploy. Your servers existing power supplies can almost certinaly handle 230V without any problems (changing a switch may be required on crappier models)
BTW in many cases there are often huge savings to be made without changing your infrastructure just by using better PSUs, cheapasss PSUs are both inefficiant and unreliable.
Re:terrible indeed (Score:3, Interesting)
Yes,
AC has better voltage drop and in most cases voltage conversions.
DC is more effecient in closed loops.
So you want distance ac is king. However your car will never be AC. DC is far safer in such situations.
I have always been under the thought. Electric companies should deliver AC to the home. Where it gets converted to DC.
440 VAC, to 220 VAC, then to 110 VAC ??? (Score:3, Interesting)
From TFA:
The power starts at the utility pad at 16,000 VAC (volts alternating current), then converted to 440 VAC, to 220 VAC, then to 110 VAC before it reaches the UPSes feeding each server rack.
That's just stupid. I hope it's just a case of a journalist not correctly understanding (which is a common problem). Given the usage of numbers like 220 and 110, instead of the standard 240 and 120, I do suspect it is a journalist giving wrong info. But even many computer people don't know what the standard power voltages are (and have been for decades). Lots of people in the USA still refer (incorrectly) to "two twenty" and "one ten". The standard in Europe is 230 volts.
With so many conversions taking place, there will be a lot of power loss. To begin with, the computers should have been operated directly on the 240 VAC, not 120. That 240 VAC should have been obtained from the utility power directly (though voltages like 7200, 7620, 7970, 12470, 13200, 13800, 14400, 19920, 22860, 23900, 24940, 34500, etc, are more common ... I've never heard of 16000 being used). Since power comes in as three phase, the ideal voltage conversion would have been 240 VAC line-to-neutral, which would give 416 VAC line-to-line. Neutral harmonics issues can be avoided by use of oversized neutrals or multiwire neutral.
Do AC wiring correctly, and the advantages of DC are minimal at best. Where the DC plan can have an advantage is that the conversion to 400 VDC, done on a large scale, can be done more efficiently. If that doesn't happen, then it's just one AC-to-DC conversion vs. another AC-to-DC conversion. When the 400 VDC gets to the computers, you still need a PSU to convert the 400 VDC to the various voltages provided to the components inside the computer box (e.g. 12V, 5V, 3.3V, etc).
AC voltage conversion can be more efficient than 98% when properly designed low impedance transformers are used. That can beat the DC conversions ... even DC-to-DC, in most cases. So you want to do conversion of DC only once or certainly no more than twice.
It has been reported that mainboards can be designed to efficiently convert 12 VDC to the other voltages needed. Google's original proposal was to supply computers with 12 VDC, allowing them to be manufactured without the PSU entirely, and thus in a smaller footprint as well as having the increased efficiency. The 12 VDC would come from a large PSU in the middle of the rack (to limit the length of wire carrying the higher current that is involved with a low voltage). That large PSU would be designed to accept AC at any voltage from 380 to 480, 50 or 60 Hz, and thus be usable just about everywhere in the world. The PSU may even operate more efficiently when fed with full three phase power (the full cycle nature of three phase power reduces the level of filtering needed for smooth DC).
Running DC is NOT a crackpot idea. It just needs to be studied correctly, in its various possible forms, and compared to CORRECT designs of AC wiring, in its various possible forms. The choice of 400VDC for distribution within a data center to the individual PSUs is a reasonable one, given that the existing PSU designs go through a conversion to 340VDC to 380VDC, anyway. But these same PSUs, especially in the larger form of one per rack, could just as well be designed to operate from 380 VAC, 400 VAC, 416 VAC, or 480 VAC.
Maybe DC is the right choice. Or maybe AC can still be the right choice when engineered correctly (which far too often is not done, sometimes due to ignorance, sometimes due to budget limitations which would never go for DC anyway, and sometimes just due to mental inertia).
Re:The arguments of olde (Score:5, Interesting)
I think Tesla would be just fine with DC power if he saw what we're using it for today. Back then, there wasn't much stuff that cared which way the current flowed. Lights and electric heaters work fine either way, and motors are more efficient on AC, as is any power source that depends on spinning a generator (almost everything besides solar cells). But once you start throwing diode junctions and electrolytic capacitors into the mix, things change.
Re:terrible indeed (Score:3, Interesting)
The highest drawing stuff in the home often works better on AC. The motors that run the compressor on refridgerators and air con are more efficient that way. Any electric heaters (potentially stoves, water heaters, and furnance, depending on the setup) are more efficient on AC (I think--it'll be about equal at worst). Incandecent bulbs don't care, and flurecents can use either one (though the ballast has to be setup specifically for AC or DC). LED lights would care, but those are really expensive, anyway.
That leaves computers and home entertainment equipment. However, they use a multitude of different voltages, so there's going to be some DC-DC conversion involved. The difference between AC-DC and DC-DC conversion efficiency isn't that big. Certainly not big enough to justify putting in extra DC-dedicated wiring.
You're better off buying high efficiency power supplies on your computer and fully shutting off entertainment stuff (which you can often only do by unplugging it).
Re:What about a _home_ standard for DC power? (Score:5, Interesting)
There is one already: USB power. Fairly low current, but a host of consumer devices from bluetooth headsets to GPS devices to iPods use it as their standard charging source.
It's a little awkward because there are more pins than ought to be strictly necessary, but it's a relatively reasonable compromise over the former solution of no common standard at all.
Is this really new? (Score:3, Interesting)
I work in the telecommunications industry. It has always been standard practice (at least where I work) to use DC power supplies for data equipment if they are co-located with voice equipment, since most voice equipment uses -48 V DC power.
This has the additional advantage of utilizing the battery backup system (required for voice) to also back up the data equipment's power.
Re:48VDC pros/cons (IMHO) (Score:3, Interesting)
I've often wondered why the ups is *before* the computer power supply, anyway. It seems to me that a couple of lithium cells in the right places could keep the important bits going for just long enough to get through short power hiccups.
e.g. keep just the ram and proc going for a few seconds before suspending to ram, followed ultimately with some kind of chipset-powered auto-hibernate when cell voltage indicates that it can't hold the suspend much longer and still retain the option of hibernation.
Re:terrible indeed (Score:3, Interesting)
You're better off buying high efficiency power supplies on your computer and fully shutting off entertainment stuff (which you can often only do by unplugging it).
Well, tube warmers used to be the major source of abuse, but other then CRT TVs is there really any equipment with a meaninful power draw in "standby"?
DC-DC converters (Score:3, Interesting)
The responses to this here where highly predictible, and many af them are quite naive.
Modern DC-DC converters have excellent Efficiency over a wide dynamic range of loads. This holds true for the small, nice isolating ones which every designer of instruments likes very much, and also for larger ones. No transformers, smaller capacitors, easier redundant designs, easier buffering. In a time when computers are more and more designed to vary their input power according to their load, all these things could provide a savings of energy (and money). Even if this saves only a few percent, the investment will be payed off in a reasonable time.
Re:Nonsense (Score:3, Interesting)
One advantage is that switching PSUs seem to be more efficient with the higher voltage input. It's not a lot, like maybe 2% on most PSUs, but still. If you have 50kW worth of computers, 2% savings is not trivial, since it also = less heat output.
Re:The arguments of olde - don't carry much weight (Score:3, Interesting)
220 to 110 is not a transformer operation. It is using two legs of 3-phase AC and a ground instead of one leg, a neutral, and a ground(grounds are electrically optional, safety required).
Anytime you convert energy from one state to another using a larger device to power many smaller devices you have the ability to realize net energy savings. This is why electric cars, charged off the grid, are better than just relocating the pollution to a centralized site. Similarly using a train or a cargo ship is better for long haul transportation than using semi-trucks. Larger aircraft typically move more people/cargo for a given amount of fuel (assuming full utilization)
Using a large DC converter in an adjacent space with copious forced air cooling and proper AC for your servers will probably be the best of both worlds. Short electric run and better utilization of existing cooling capacity.
Just my $0.02.
Phil