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DC Power Saves 15% Energy and Cost @ Data Center
Krishna Dagli writes "Engineers at the Lawrence Berkeley National Laboratory and about 20 technology vendors this month will wrap up a demonstration that they said shows DC power distribution in the data center can save up to 15 percent or more on energy consumption and cost. The proof-of-concept program, set up at Sun Microsystems' Newark, Calif., facility, offered a side-by-side comparison of a traditional AC power system and a 380-volt DC distribution system, running on both Intel-based servers and Sun systems."
I, for one, would not be comfortable working around high power DC. Call me paranoid, but I rather enjoy my heart beating with its current interval. You can take all the precautions you want, but accidents do happen.
[sig]you really dont want the answers, trust me[/sig]
Read Stephen King's "Tommyknockers". You can do a lot of things if you go DC-only!
Where were you when the voynix came?
When they used to talk about DC power systems be less efficient, you have to remember that most of them were talking about 12-48 volt systems.
From the article:Not according to my electronics class, if they're really going to be running at 380 volts. They'll need more insulation instead. I'd also want to be real careful around those wires. DC will kill you much quicker than AC of the same voltage/amperage. Then again, you don't have to worry about shorting yourself to ground with DC.
For now.
I don't read AC A human right
15% seems compeling for DC power in new construction, but obviously this begs the question of switching costs. But 15% was just for the electricity used to power the servers, the article assumes as would I that there would be additional savings due to reduced cooling needs... that extra 15% electricity would have generated about that much heat. I'd like to see a breakdown of switching costs.
I definetely see advantages to go DC for server farms and such as there is always a lot of loss (heat) involved in all the AC->DC conversions, but dang, I sure as heck would not want to work around 380 volts DC.
Telephone Companies had known this for years. This is why you can get 48vDC versions of most systems.
In a telephon e exchange 48v DC is the norm.
They have huge batteries and standy generators to keep the phone syste, running.
I'd rather be riding my '63 Triumph T120.
Good to see some more DC in use. Tesla was right about AC for many applications but DC has its merits and any useful application of DC is a credit to Edison's scientific achievements.
... those claims of saving "up to 15 percent or more".
That pretty much covers the entire range of possibilities.
I often wonder why they didn't say something like "up to 50 percent or more" or "up to 99 percent or more". Those would be every bit as meaningful.
Those who do study history are doomed to stand helplessly by while everyone else repeats it.
I always thought the opposite was true. Here is a wiki quote that also supports that:
Taken from http://en.wikipedia.org/wiki/War_of_Currents/
You can also store DC whereas you cannot store AC, meaning UPS always need an AC-DC followed by a DC-AC stage. Since we have had large FET power transistors it has been possible to make DC/DC conversion very efficient - especially since, if you were beginning again, you would not choose 50 or 60 Hz for best efficiency.
In fact, already the PC is using a DC bus to power small peripherals (USB) and it works surprisingly well.
I may be wrong about this, but it was Edison who accused DC power of being more dangerous ("Westinghoused") only to have AC adopted for the pleasant US custom of humanely frying criminals.
Pining for the fjords
The only reason they save power here is because they increased the voltage, not because it's AC instead of DC. This allows them to reduce power line losses for really high draw equipment. Telcos already use -48v for all of their equipment which I think it simply too low for many modern switches. Some Lucent ATM switches draw over 3000 watts which is over 60 amps at -48 volts.
That stuff really hurts!
When asked his opinion, the ghost of Thomas Edison was Straight
n t.php?id=3456872&lid=1
forward and Direct about the conversion of the IT Closet to DC.
While it has been rumored that Mr. Nikola Tesla is spinning in
his grave and refuses to give a comment
http://www.ieee-virtual-museum.org/collection/eve
--- Relax, that mass muderer is just trying to reduce our carbon footprint, one fetus at a time...
The article didn't really describe technically what they did. Can someone explain to me how moving to DC helps? AFAIK:
- This eliminates the need for a AC->DC rectifier in each component
- But they still need to have the transformers to step down the voltage
- DC requires twice as many wires
Is the elimination of the rectifier a significant efficiency increase? Or is the real benefit in the move to a higher voltage? But doesn't that just mean they need bigger transformers to step down to the 12V they really need? Or are they using equipment that runs on higher voltages anyway?
Would be interesting to know what the efficiency is of a 380 -> 12/5 DC-DC converter, compared to a traditional 110 AC -> 12/5 DC converter. This is of course only just a part of the total picture, but in the past this has often been mentioned as the reason for _not_ going DC. Maybe with modern switching power supplies, that problem has disappeared.
Browsers shouldn't have a back button!! It's all about going forward...
This issue has a been a hot topic at conferences for data center professionals, with a lot of debate about timetables. Several facility designers are advocating DC distribution as the solution to the current power/cooling challenges. Corporate data center managers like the cost savings projections, but want to see it work in someone else's facility before they put their neck on the line and pitch a DC conversion to their bosses. That's the real value of the Livermore project discussed in TFA - it provides a working model.
Right now the cost of power is remaking the landscape of the data center industry. Yesterday there was another announcement of a huge data center in central Washington State. Sabey will invest $100 million in a facility right up the street from where Microsoft and Yahoo have data centers under construction. It's all about cheap hydro power. Both Microsoft and Yahoo have contracted for more than 40 megawatts of power from the local utility. That's why DC is one of the solutions that will begin to get serious consideration.
RichM
Data Center Knowledge
The article talked about multiple changes back and forth between AC and DC. That makes it sound to me like the power is always running from the batteries through an inverter. So the power comes through the inverter all the time. The solution is to take the power from the mains almost all the time. The losses in the rectifier and the inverter go away. When there's a power failure the inverter comes on line. That can happen smoothly enough that the load (ie. all the computer equipment) never notices the difference.
So, you might have to buy new inverters but you wouldn't have to rewire the data center. Usually, rewiring costs way more than equipment. A clever power management module could even obviate the need to buy new inverters. There are ways that the data center could actually save money on electricity and they don't involve dc distribution.
Ummm... Transformers don't work with direct current.
Ooo man the floppy drive is broken. No wait. The computer is just upside down.
Depending on where you are in the world 3 phase AC is 415V or 480V, and in industry we have no problem handling that. 380 VDC doesn't seem much of an issue to me with regards to insulation safety etc and I have dealt with control panels that have operator controls running at 240VDC (and grabbed them accidently and lived to tell the story) Though now days operator controls are being specced as 24VDC.
.. Bzzt .. Nope. grounding yourself is always an issue with ground referenced power systems. And I would never rely on any power system being perfectly isolated from ground. That sort of misguided thinking leads to nasty surprises.
But as for DC killing you quicker, I would disagree that its the type of system that kills you, it will depend on the type of damage that the shock causes. You can use a 9VDC battery to kill yourself if you apply it in a manner that a small current (mA level) flows to your heart and I would guess that the same level of AC current would also do the trick. On the other hand if you pass a large current through your body that causes physical damage (major burns etc) then it won't matter if its AC or DC if the so much of the body is destroyed as you will die eventually.
As for not worrying about grounding yourself with DC
I am Slashdot. Are you Slashdot as well?
From the article:
(emphasis mine)
The power lost in the cables varies as the resistance of the cable and the current in the cable.
The power delivered to the equipment varies as the current in the cable and the voltage on the cable.
A 380 volt DC system can deliver as much power per unit current in the cables as a 380 volt AC system (assuming a near-unity power factor).
Ergo, the size of the cables for a 380VDC system will be the same as the size of cables for a 380VAC system.
So, if the comparison is against a 240VAC system, then a 380VDC system will have SMALLER cables, not larger. Only if the system being compared against is a 440VAC system will the cables be larger.
Also - a 380VRMS AC system will have a peak voltage of about 540 volts (two significant digits in, two significant digits out), and thus will require MORE insulation than a 380VDC system.
Also - the first things a switching power supply does is rectify the AC into DC and dump it into a capacitor (and usually do power factor correction): so a power supply designed to run from DC needs neither the power factor correction nor the big capacitor (a smaller cap will still be needed, but not one that can carry the system through the bulk of the AC cycle when the voltage is below peak). This makes the power supply simpler, and removes switching losses from the rectifier (granted, a modern synchronous rectifier based on IGBJTs will have a very low loss - but it still is a loss.)
Also - creating a backup for 380VDC is pretty easy - you use a battery bank floated at the 380VDC level. No need to "switch" from mains power to battery - you are ALWAYS running on battery, and the mains power is just charging the battery. This is how the phone company does it - the central office has a bank of batteries providing 48VDC, which is float charged from the mains. Lose mains power, and the system doesn't even blink.
(Yes, you need to have fusing to prevent those batteries from going nuclear if shorted, but that is a much simpler problem to solve than the issues of switching to backup power for an AC system.).
Yes, you have to design the equipment to run off the 380VDC - so you need different power supply front ends: most power supplies are split into 2 parts - the front end that takes mains power and makes about 300VDC on a cap, and the back end that makes the lower voltages from that - so the back end of the power supply does not need to be redesigned. Moreover, most power supplies use an off-the-shelf front end module, and any "magic" is in the back end - so this is NOT a major issue.
www.eFax.com are spammers
... find http://yro.slashdot.org/article.pl?sid=06/08/06/13 3203this useful.
Warning: Corny karma killing post above.
Traditional 110V cables will draw 3.5 times the current 380V does. That means 110 will produce more heat along the wire. Also using DC will cause you to not have to rectify the AC when it enters the powersupply of the device you are powering.
That being said, you have to GET to 380V. My guess is they are simply rectifying 440VAC to DC.
Seems like a cleaver, efficient idea.
--fatboy
Hell yeah, son. Tesla was on top of his game, he made Edison look like a child at the science fair. Edison spent a lot of time trying to publicly discredit Tesla, while Tesla was busy being an electical bad ass.
I wonder if you would see the same 15% power saving if a home was outfitted for DC use ? When you think about it most electronic devices in the home have power supplies embedded which are nothing more than AC-DC coverters, which in and of themselves waste energy.
A DC power home would lend itself more readily to home based power generation. I believe most solar panels and windmill generate DC power which then has to be converted back to AC before it can be put on a powerline or used with conventional home appliances. With the new high efficiecy LED DC lights available the AC light bulb (a hundred year old device) is a real power hog and also generates enomrmous amounts of heat.
100 yrs ago when they were first bring electrical power to the masses perhaps AC was the right answer, but I believe our needs and priorities have changed in the past 100 yrs and perhaps the way we generate, distribute and use electricity is due for a new analysis.
1. DC/DC conversion is cheaper and simpler bacause with a 60Hz AC signal, you have *no* power during the zero crossing. The PS has to store the energy in a capacitor or a coil to deliver during the 120 "outages" a second. A DC/DC converter operates at hundreds of kHz, so components are much smaller, and since the conversion uses square waves, it does not have the "outages" a sine function has on the input.
2. A lot of AC/DC switching power supplies is a constant power load on the grid. It tends to draw more Amps as the Voltage decreases, producing a lot of harmonics in the mains power line, and a worse power factor than regular "resistive" equipment. Therefore the mains must be overdesigned to support this kind of load.
2. 220V AC means 220V *RMS*; 110V is just one of the wires tied to ground. The peak-peak is around 311V. Not that different from 380V
"Fix it"
"His [Thomas Alva Edison] method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90 per cent of the labor. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense." --Nikola Tesla stating that DC current (which Edison prefered) was ineffencet to AC current (which Tesla prefered). (Source wikipedia)
The Rapture is NOT an exit strategy.
Comment removed based on user account deletion
Most computer equipment is still powered by 110VAC while mearly all of it is not only capable of running on 220VAC it runs more efficiently .
At my last job we were expanding our data center and put in a small handful of 220V circuits, by hooking up our biggest servers to 220 we were able to increase our UPS runtime by almost 10% and reduce our HVAC duty cycle by a bit in the process.
BITD when I went through Compaq ASE training the instructor mentioned that some server configurations (maxed out drive bays) you only had N+1 redundant power supplies if you powered the server with 220VAC. IIRC this server had three power supplies and two were enough to keep the server running in most configurations, but with the maximum load they could only keep up if you fed them 220.
From the Merck Medical Manual "...The effects of AC on the body depend largely on the frequency. Low-frequency currents of 50 to 60 Hz (cycles/sec), which are commonly used, are usually more dangerous than high-frequency currents and are 3 to 5 times more dangerous than DC of the same voltage and amperage. DC tends to cause a convulsive contraction, often forcing the victim away from the current's source. AC at 60 Hz (household current) produces muscle tetany, often freezing the hand to the current's source; prolonged exposure may result, with severe burns if the voltage is high...."
A 15 minute call could save you 15% or more on your power costs
This reminds me of a recent discussion I overheard here at work, yesterday. Some vendors were talking about an experiment they had heard of, where an entire office building was converted from fluorescent lighting over to LED lights. They claimed that the long-term cost was higher for LEDs due to an unexpected increase in heating costs, since the ballasts from the fluorescents had been helping to heat the building in the winter.
Here in Wisconsin, the heat "wasted" by computer systems isn't a complete loss during cold weather (which is the larger portion of the year). Yes, it's more expensive than using the heating system, but it may not be enough of a difference to justify the expense of non-standard equipment.
Speaking of conductor sizes, the article said this:
A DC system also would mean having to bring in larger cables than now exist with AC power.
I challenge this notion. Conductor size is not related to whether the power is AC or DC or what frequency of AC it might be; it is related to current.
Larger cables are needed when more current is passed. Traditionally, you need larger cables for DC, because traditionally, DC power systems were lower voltages (12, 24, 48) than AC systems, and these lower voltages required larger currents for same power (e.g. 100W= 830mA at 120V, but 8.3A at 12V). Running at 380V, however, you get to lower the current (excluding the reduced current caused by the 15% power savings) versus a 120V system.
Expanding on that, the reduced conductor size is proportional to the square of the reduced current. Simply by going from 120V to 380V (a factor of 3.17), you change the current flow downward by a factor of .32. This means you can change the cable cross-section area to by a factor of .1; you reduce the cable to one-tenth its original size; one tenth the copper.
www.wavefront-av.com
Edison use to stage public demonstrations where he'd electrocute dogs with AC current to show how evil and dangerous it was.
He was bonkers at times, but a crazy marketing wizard. Telsa just wasn't a people person, although AC did win out in the end.
I see their results, but I come to a different conclusion.
My headline would read "DC Power Results in 15% Increase in Equipment in Data Centers"
I'm sure they might be able to refit their computer rooms for less than $1billion.
When you sympathize with stupidity, you start thinking like an idiot.
100 yrs ago when they were first bring electrical power to the masses perhaps AC was the right answer, but I believe our needs and priorities have changed in the past 100 yrs and perhaps the way we generate, distribute and use electricity is due for a new analysis.
Sorry dude, but you really need to learn more about power distribution before making blanket statements like that. Maybe a dedicated AC to DC converter in the home may be useful, but for the purposes of power distribution AC is the only choice.
As an example, do you have any idea how big a breaker would need to be for a DC system at substation becuase there is no zero crossing in DC?
Or the do you know the benefits or three phase?
How about the advantages of high voltage low current power lines?
Tesla knew.
"Karma can only be portioned out by the cosmos." -Homer Simpson
DC is good for short-haul power distribution
:)
m issionh tml
Please tell that to Manitoba Hydro.
"The two transmission lines, each nearly 900 km long, operate at +/- 450 kV and +/- 500 kV DC, with converter stations at Gillam and Sundance, and the receiving terminal near Rosser. The combined capacity of the two HVDC lines is 3420 MW, or about 68% of the total generation capacity in the province."
http://en.wikipedia.org/wiki/Manitoba_Hydro#Trans
http://www.hydro.mb.ca/our_facilities/ts_nelson.s
Why do you use DC for long-haul lines? Because the high voltage AC lines act line gigantic antennas. They started at AC and had to convert everything to DC because of that. It is a big problem converting that much power back and forth from DC to AC, but it is better than having most of it gone to space.
I once had an electronics professor tell me that if we had DC flowing through the walls of our buildings instead of AC, everything capable of being magnetized would be. I've never researched this, but it would really suck if all my paper clips, screwdrivers, etc. were constantly sticking together.
If you honestly don't see the difference between Edison and Mengele then you're an idiot.
Don't hydrogen fuelcells generate DC? I can't wait to hook my home gaspipe to more than just my stove, and suck in the MWs direct to my devices. Without all those AC adapters left over from the 20th Century cluttering my home, getting hot, drawing power when "off", getting lost and mixed up...
Maybe we can use the old AC network as a 3rd broadband line, after telco and cableco.
--
make install -not war
They can deliver a DC-powered rack that will do the A/C conversion in the rack using a rectifier, so you save power by making the conversion only once. They also can take DC to the rack, and put pretty much whatever you want into the systems. Not to mention the high density you can get.
Blade enclosures also use a similar trick, the blades all get DC. And many data centers also have DC available already, you just have to ask.
http://www.rackable.com/
Instead of using a 380-volt DC distribution system, why not use the telephone standard: 48V? Then you could use the same 48V connectors (STD equipment, lower cost) to plug into converters that would be in the same form factor as regular AC power supplies. Then, if you really what to save money, have solar panels (or other means of power generation) to charge batteries that would feed the 48V system. Built-in UPS!
Hum, I might be too idealist, here...
Obama's legacy: (N)othing (S)ecure (A)nywhere and (T)error (S)imulation (A)dministration
I don't think you need to worry about arcing for 380V.
r ge
38kV maybe...
http://en.wikipedia.org/wiki/Electrostatic_discha
you do if you're switching, you can "strike an arc", which means creating ionized plasma that can carry the arc farther and farther as you move two conductors apart. Big switches have "arc chutes" that carry the arc over seperated plates to try to lengthen and cool the arc at the same time. Sometimes these switches can be defeated by repeatedly making and breaking contact so large amounts of ionized air are around the switch, sometimes then arcs between opposite phases (AC) or poles (DC) can occur.
To get AC, you spin a coil in a magnetic field.
To get DC you, um, spin a coil in a magnetic field, then rectify it, then put a huge capacitor on there to flatten out the humps.
There's just no good method for generating DC. And even if there were, electric companies aren't going to run two new phases (DC+ and DC-) to get it to you from the source.
Instead, the power is going to come to near you as 3-phase, then be rectified. There is a loss in that rectification, but sadly, you can't eliminate it, just change where it happens. Moving it to the other side of your power meter will have an advantage since you theoretically wouldn't have to pay for the losses, although the electric companies would surely change their rates to recoup this lost money. But note that even if they don't change their rates, you haven't saved any energy, just not paid for as much.
So my guess is this experiment bought into this fallacy, that they measured their power usage at DC levels, found it was lower and reported that as a win, when without a source of DC power that doesn't involve rectification it really isn't.
I'm sure they save some electricity due to the increased voltage. That reduces current, which decreases power lost. This is the same reason electric companies use high voltages for power transmission.
The article seems to imply that power supplies convert 120VAC to 381VDC internally. This just isn't true. They never raise the voltage, and 120VAC peaks at 175V or something like that. Even 240V input would peak at 350V. So I don't get this. I think they just messed up a few numbers and really in the experiment connected rectified 240V (UK 240V, which is one phase double high, not the US one 120V phase over another) directly into the power supplies after the point where the rectifier would normally be.
From what I can tell, going to DC just would save you the cost of lots of little rectifiers in favor of the cost of one big one. To be honest, since the small rectifiers come in commodity ATX power supplies, you're paying almost nothing for them anyway. So I don't see that it's all that valueable to consolidate them.
I would recommend that if we wanted to save the most power on servers, we should just go to 3-phase 440V AC power supplies. A new connector would have to be designed, as the current 440V 3-phase connector would barely fit on the back of a tower, and wouldn't fit on a 1U server. This would save the most possible in losses without having to buy external rectifiers or force the electric companies to install one on site (and charge you back in increased rates).
http://lkml.org/lkml/2005/8/20/95
Aren't they from Australia?
Yeah, because we all know that cable, component lead and semi-conductor junction reactance allow for perfect square waves.
"Soylent Green is IT people!"
Anything that can be switched to 220V should be. I helped a friend redo his woodworking shop. Every electric motor that had the option was switched to 220V from 110V. Doing this uses less power to generate the same or more power from the motor, either as horsepower or torque (which is really a better description). The electric bill for his shop was cut by 40% a month by this simple change. It was simple, switching outlets and breakers was the main issue after moving a wire or two in each motor. The whole shop was wired with 12GA wire so that was not an issue.
One thing I have wondered about computers? Would things run smoother with different cycles? On my submarine in the late 70's the electricians switched a circuit roem the 60hertz grid to the 400hertz (sonar ran on 400). That was the only thing done and the difference in the stereo on the mess deck was amazing. We had a very high end Sansui system and the tape "fuzz" was undetecable. Everything sounded smooter and more clear. I wonder what effect this would have on hard drives and optical drives?
Professional Politicians are not the solution, they ARE the problem.
So it's O.K. to pee on the black wire?
..........FULL STOP.
DC isn't any more dangerous than AC of similar voltage and current.
380 VDC isn't going to fry you any more dead than 120VAC.
You also may have a misconception that DC requires large currents. Well, yes, at 48V. And at those currents you can easily, like, weld a wrench to a rack rail before a breaker trips.
I've always been a fan of 240V. 99% of equipment made today will run on anything between 100 and 240 volts, and at 240 you need half the current. Whenever I bring this up as part of a data center design, I'm met with blank, puzzled stares. Good luck with HV DC.
Give a man a fish and you have fed him for today. Teach a man to fish, and he'll say "WHERE'S MY FISH, YOU IDIOT?"
and mod the GP down, he has it ass backwards and may actually end up killing someone with his idiotic misinformation. Mods, do you want that death on your hands? Get the right info out. kthxby
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
The problem is not only the high voltage but specificzally the "DC-ness", so the parent was right. The difference between AC and DC is that in AC the voltage and thus (resistive) current goes to zero every now and then (50/60Hz) and a DC current doesn't. When you switch off the current it is possible that an arc forms between the switch contacts, in other words, current keeps flowing through the air. This arc will remain as long as the current is not cut externally. For AC this means that it will immediately disappear as soon as the voltage goes through zero. In DC systems it can remain forever, hence the danger.
Clearly there are enough slashdotters here to settle this debate. All those in favor of DC run out and grab the connectors of your car battery, those who say AC is safer please stick your tongue in a socket. Those who can please hurry back and post. I promise to mod you up.
"I love his boyish charm, but I hate his childishness" - Leela
So were you on the short list for a Darwin Award? Were you sorry to find out your brother's actions disqualified you?
Instead of 60Hz hum in improperly filtered circuits, you'll get 400Hz hum. Whee!
My understanding is that as the frequency increases, you have a greater problem with inductive loss.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Sounds counter-intuitive to me. I mean you've got billions of 3.3vdc logic elements in a data center. Getting from 380vdc to 3.3v is no small matter. Current is current. Think about it.
Heard any good sigs lately?
...remove a rectifier from server PSU and remove an DC to AC converter from your UPS and save 15% (wich btw. are the loss in the DC to AC converter...) I'm impressed... but wait... now you can't use your server anywhere else...
Simply move your datacenter up the mountain, farther North, or perhaps underground.
The situation these data centers have is the legacy of Bill Gates, as implemented by legions of white-paper writing vendors, magic quadrant touting analysts, and the pointy haired managers who relied on them. We now have thousands of 1U 'servers', each running at most a single application, or part of an application. Each has its own complete copy of the operating system in and GUI sitting in memory, its own power supply and, in the vast majority of cases, each has its own directly-attached storage. The industry as a whole just blindly 'follows-the-leader'.
I am afraid that the 380 Volts DC figure that was mentioned seems to be really out in left field.
ALL of the DC powered servers available from Sun and Dell are 48VDC. I did some Googling for other DC powered servers and found that they are also ALL 48V DC. 48VDC is a worldwide standard for powering telco equipment, although some telco equipment operates at 24VDC. I saw 90 volts tossed out in a post as a telco voltage -- 90 volts is the AC RINGING voltage (the nominal ringing voltage is 88 volts at 20 Hz); the normal voltage on an idle telephone line is 48 volts DC. The discussion in TFA regarding the use of larger conductors for DC powered servers makes more sense if you are talking about 48 volts rather than 380 volts.
It's okay to pee on any wire. The urine stream breaks up into individual droplets a foot or so away from the origin, so it won't conduct. Or so say Mythbusters, but God knows they aren't the most reliable folks. Perhaps you should try it out and get back to us to confirm or deny the Mythbusters conclusion?
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
The freq switch smoothed out the motor in the tape drive. There was almost no hum detectable compared to 60 hertz. When listening to Soviet boats we would alter 60 hertz up or down (58, 59, 61, 62) to alter our own background noise and unmask tones on that line from the contact.
When operating on exercises with our own or allied forces we used a special transducer and amp to play tapes of various Soviet boats. I wish I had the 500watt McIntosh tube amp we used.
Professional Politicians are not the solution, they ARE the problem.
Reliability is exactly what I'm interested in. I use a cluser which is plagued by node failures due to the small, cheap PSUs it contains. I have to wonder, what is the point of having 100 PSUs in the cluster? Couldn't we just have one big PSU (plus a failover) for each rack, with a couple of 12v leads for each node? Does anybody sell such a thing for a reasonable price?
No, he just had good marketing. People keep repeating a lot of things he never actually invented, just proposed some vague idea, together with other things that proved totally impractical. I wonder why they never quote this:
"The aeroplane is fatally defective. It is merely a toy-a sporting play-thing. It can never become commercially practical. It has fatal defects."
Nikola Tesla
Edison, it's true, had his personality defects. In many cases he was not quite ethical. He was wrong in trying to push DC technology at that time, although with modern electronic components transmission of DC at very high voltages is not only possible but the only practical alternative in many cases.
Now consider Tesla's idea of bladeless turbines for instance, impractical at the time, still impractical today. In order to work with reasonable efficiency, it needed a set of disks with a tenth of a millimiter in thickness separated by less than a half millimeter. Try sending a flow of high pressure steam into such a machine, a fraction of a second later you'll have a big mess of crumpled metal foil. Or how about what is possibly Tesla's most famous experiment, a wireless system for transmitting electric power. It radiated energy away in all directions, to be received here and there by special antennas. With luck this system could use maybe a fraction of a millionth of the total power transmitted. A few cities in the early 20th century had Edison's impractical DC power distribution system, but Tesla's wireless system was never adopted anywhere because it was so extremely inefficient.
The main difference between Edison and Tesla is that Edison made research with practical applications in mind. Tesla proposed many ideas without even building prototypes, Edison made painstaking trials until he got it working. For instance, in his incandescent light bulb, Edison's lab tested more than a thousand different filament types before finding one that worked. Edison's main invention that Tesla ignored was a system for developing applications for new ideas. It's not enough to have brilliant ideas like Tesla did, one must put those ideas to practice, like Edison did.
I already saved 15% by switching to Geico.
Forget DataCenters.
How about 12V DC at home, so that I can get rid of the half dozen little tranformers plugged-in under my desk?
What are the real objections to 12V in the home?
The most sensible one I've heard is most digital devices need a fairly fixed voltage drop, which probably means that need to be in parallel. That pushs your current thru the entire system up, perhaps to dangerous levels.
The article seems short of detail like the interweb in general. I guess only the redundant "ac to dc rectifcation" at the smps(s) was eliminated. I found this other site useful. http://www.energyandpowermanagement.com/CDA/Archiv es/afdf1ed0fdcb9010VgnVCM100000f932a8c0____
They can have my command prompt when they pry it from my cold dead fingers.
My Bluetooth headset uses it too.
Rich
n/t
sigs are for losers (except to point out that sigs are for losers)
AC is what grabs you, DC will blow you clear.
INCORRECT. The lower the frequency the deeper current will penetrate a conductor (which is what your body would be when you are electrocuted), and DC will go right through you. When DC current travels through your muscles (including your heart) they will CONTRACT and STAY contracted. DC is what grabs you, NOT AC.
What makes AC dangerous is the specific frequency. Ironically, 50 to 60 Hz is probably the most hazardous to people--we ended up with that frequency becasue of economics more than anything else (I believe early Canadian AC power worked at 25Hz interestingly enough. Since lights flickered badly it was abandonded). If you grew up on a farm you know how electric fences work--they are essentially very low frequency AC--you get a pulse of current followed by no current at about 1 Hz. You get thrown from the fence not because of the "DC" pulse, but becasue of the RELEASE of the power (your brain is trying to tell your muscles to release but the electricity is contracting them--when the electricity goes away your brain is still telling you to release and you jump back--like the rope breaking in a game of tug-of-war).
What makes 60Hz deadly is that it is low enough frequency that the "skin effect" is not evident enough to keep current from reaching your heart, yet it is too high for your muscles to respond to the change in current--in the case of your heart it is right in that zone that would cause fibrillation, so that when you cut the power your nervous system is still confused. If the AC frequency was much lower--20Hz or less maybe? not sure but there is a point--the body would perceive it as a vibration and your muscles would have time to respond to the change in current so you could let go--plus the risk of fibrillation would be much lower. However, if you could feel the vibration you could also SEE it--lighting would be noticeably flickery. Low frequency AC electrocution would be much less fatal but could cause seizures, plus it is much less efficient.
Very HIGH frequency AC would also be safer because it is TOO fast to induce fibrillation in your heart, plus it causes what is called the "skin effect" on any conductor through which it passes, so VERY high frequency current would pass over the surface of your body and cause bad burns and such, but not reach your heart at all. As a result of this effect, your (or any other conductor's) "AC resistance" is much higher than your "DC resistance" at higher frequencies as well, so the effective current passing through your body at the same voltage is HIGHEST at DC and gets LOWER as the frequency goes up. This effect is why large, high-voltage/high power conductors in AC power systems are hollow copper tubes--it is a waste of metal when only the surface actually carries the electricity and the rest just gets warm, so the inside is just air (or cooling oil or whatever non-conductor). Because of the skin effect and increased AC resistance, and the fact that induction motors would run far too fast, very high frequency AC is not used becasue it as impractical as DC.
DC is what they use in lighting systems at TV studios because it is easier and safer to work with "live".
This is also WRONG. I have been in the studio environment before and can tell you that AC lighting is probably MORE common than DC lighting in many studios, which is actually HARDER to deal with than AC in most cases. DC is used NOT because it is safer (becasue it is often more complicated to use and no safer than AC), it is used for technical reasons, such as:
* mobile lighting uses batteries which supply DC
* Certain lighting powered by AC could perhaps flicker at rates too high for the human eye, but enough that film or video will catch it--particularly in the case of film becasue 60Hz doesn't sync well with 24 frames/sec. However tungsten glows pretty persistenly so it shouldn't be very susceptible to flicker.
* Lighting control (dimming etc) for some lighting might be easier do
> I call bullshit. The installed cost of the LED lighting might not be made up
;-)
> by the power savings over its lifespan, but the energy bills will go down,
> no matter what. There's simply no way to tip that balance, unless gas gets
> more expensive than electric heat, which has never been the case.
Assume the following calculation:
Cost of electricity: 10 Cent/KWh
Cost of heaing-oil : 3 Cent/KWh
__Led__ __fluor._
$10000 $2000 Cost of Lamps and maintenance over 10 Years
$10000 $20000 Energy cost over 10 Years (1E5/2E4 KWh)
==============
$20000 $22000 total cost ==> Led wins !
However, with the Leds, you need to buy extra heating oil in order
to generate 100,000 extra KWh you got for "free" with the fluorescent
lamps, which will cost you an extra $3000.
Thus, the cost for the LED solution rises to $23,000, so now the
fluorescent solution is cheaper - in Wisconsin that is, not Florida !
However, the numbers in this example were made up.
In reality, I doubt that Leds can already challenge fluorescent lighting
on a cost basis, as it does not yet really have an efficiency advantage over
fluorescent tubes, unless you need colored light, or many small lamps.
Discaimer:
In case I goofed somewhere in these calculations,
then I am an anonymous coward from Antarctica
A 120VRMS system is 170 VP - that is, the PEAK voltage across the pairs is 170 volts. However, AC also REVERSES - so you also get a -170 V Peak. You use a bridge rectifier, and you get the difference of BOTH PEAKS, or about 340 volts - and this MOST DEFINITELY is what you will find on the main cap of a switching power supply. Don't believe me? Get out a voltmeter and measure it yourself.
Since you OBVIOUSLY have never designed a power supply in your life, why don't you visit Vicor and read up on how it is really done.
www.eFax.com are spammers
What I could see happenning, though, is special small size switching transformers built into a standard electrical junction box, which are "smart" in some manner to know when a plug is plugged into them, which connects the switching transformer in, and that supplies, say, 12V at 10A or something to a common downconvertor system or something that all the other peripherals plug into (that, or each peripheral converts the 12VDC independently). In a way, I built something like this, once, for a desk I had: I hooked up an old Sun Computer pizza-box (Sparcstation?) powersupply and created a "bus" of electrical wires running under the desk, hooked up to screw terminal bus strips every so often. I ran the 12V, 5V, and ground lines via this bus along the length of the desk, so then I could get 12V, 7V, and 5V feeds from this system. Hooked up all my peripherals that had wall warts to the bus, and ran a "power on" green LED to the front of the desk for status. Worked pretty well.
Reason is the Path to God - Anon
There's nothing like working on a phone line at the junction box on your house with bare hands, then the phone rings - zzzzt!! Yow!
Except perhaps getting shocked by 110VAC, or the distributor/coil on your car...ouch!
Reason is the Path to God - Anon
I am quite surprised that Slashdot even ran a story that would sully the beliefs of one of their Gods, namely Mr. Tesla.
In some cases flat solid busbars can be used that maximise surface area, but most modern systems just do not have enough space.
It also really is very important in SELV (safety extra low voltage) applications to minimise volt drop by reducing resistance as far as possible. When I started designing equipment which used 12V and 5V DC buses (back in the 80s!) it was hard to get wiremen to use sufficiently heavy gauge wire because they did not appreciate that, for instance, the tolerance on commercial TTL was from 4.75 to 5.25V. Dropping even a quarter volt down the bus could mean that, with circuit board losses, many components were on out of tolerance voltage. It really was necessary to wire point to point to every board independently or use very heavy gauge wires for buses.
The problem is particularly severe with 12 and 24V systems with battery back up. Ten years ago a lot of these systems were designed with an allowed 10% volt drop for the most remote component. Now 3% is considered desirable. If you find it hard to see why, guess which is the most expensive: to increase the size of your generator/alternator by 7% and increase the number of batteries in your UPS (since lower voltage will mean higher current or longer running is needed), or to use thicker wire in the bus?
Pining for the fjords
A DC motor is using a split commutator to convert the input AC into rectified AC.
If you spin it, it will generate rectified AC, not DC. Actually, due to the leading advance built into the motor, it'll likely not switch at the right point. But you could make it switch at the right point.
Rectified AC useful too, but it's not DC and you can't treat it as such.
Anyway, having a split commutator is problematic when you want to produce a lot of power. It's easier to diode rectify.
http://lkml.org/lkml/2005/8/20/95
Many people on here have been talking about how DC is safer then AC, because you can grab one leg of a DC circuit and be safe so long as you don't touch the other leg. They then say that AC is more dangerous, because touching only one leg will shock you. This is simply not true, have you ever seen birds on a power line? These lines are AC, are bare Al in most cases, and are AC powered. When a bird lands on this line, it is not shocked even though its one leg of an AC circuit. Get it? I do wish more people would think around here, that is think something besides "Boy, I am sure an expert on all topics" you sound like my brother in law.
"To be positive is to be wrong at the top of your lungs." - wow, what an ass you are.
The test obtained 15% at the facility level.
The test could be 15% at the facility level if they considered the facility to receive DC power and still be subject to the caveats I mention. This is unrealistic today, but it might be in their assumptions since they want to prove that a major change should be effected . Saying "facility level" does not negate what I said.
The test was conducted in the U.S.
This means nothing. They are trying to explain how major-level plant changes can be effective in helping efficiency. There's no reason to precluse the idea of using UK-style 240V AC if that would make it more efficient.
It is not a stretch to assume that their power-factor-correcting 480VAC input facility UPSs have 380VDC internally.
Actually, 480VAC input facilities have greater than 380VDC internally, guaranteed. I didn't think 480 or 440VAC facilities were a large enough part of the market to care about (figured 208VAC was more common), but it appears I am wrong about that.
No, they are aware that the same active rectification that is so popular with variable speed drives (electric motors) due to good power factor can achieve 97% efficiency.
If rectification (and inversion) were 97% efficient (and perhaps it is), then there would be no way to save 15% on your power used, and switching to DC would be near pointless. Want to modify your statement?
Honestly, if all you want to do is raise the efficiency from your UPS to the racks, then either rig it to output UK-style 240V AC or 3-phase AC. Better yet, get inside and turn off the inverter so it generates 240V rectified AC (lumpy DC). You won't even have to modify the equipment in your racks, and you should save on inversion losses. Next step would be to turn off the sine wave shaper in your racks, your equipment probably would still survive. Best to leave in short 0 pulses from time to time or you may find that you are unable to soft-off your equipment due to the Triacs inside never shutting off.
You're essentially outputting unregulated high voltage DC now, perhaps with gaps in it. You'll save some money I suppose, something is better than nothing.
http://lkml.org/lkml/2005/8/20/95
For those of you just entering this thread, let me present a handy summary:
* Edison was a fraud, Tesla was a badass.
* AC and DC are both dangerous. When approaching a power line, use the back of your hand, in case of electricity-induced muscle clenching.
* DC distribution systems? What??
If there's fifteen different 12V appliances in my bedroom, does it make sense to do this conversion once instead of jamming every outlet with block transformers?
No answer.
Telecom companies have been using DC distribution systems for DECADES because they don't have to lose energy converting back and forth between AC and DC. It's about time the computer industry is catching on.
The reason why "DC distribution" isn't being done is because the onus is on device manufacturers to all use the same kind of plugs for DC power-in and to use a restricted set of voltages.
Manufacturers would rather provide an AC/DC converter that does exactly what the device needs and no more or no less.
But since most many devices are starting to support USB connectivity (music players, cameras, etc.) it would make sense if they could standardize on the USB connector itself to deliver power.
You can just buy a cheap powered USB hub as a mini-power strip to power usb-powerable devices.
I've actually seen a few devices that come with a DC->USB connector for just this purpose. It's usually desk toys from geek websites.
THIS THING CAN TURN ON A DIME, MACROSSZERO STYLE ALSO FUCK BETA, ~NYORON
i think most people are missing the point of this
AC is good for long runs as you can step up and down the voltage very easily (with a transformer). doing this with DC involves turning it back into AC, changing the voltage with somthing like a transformer, then rectifing it back to DC
so of course a power company is going to use AC for long runs, by bieng able to change the voltage they can keep down the losses by going High voltage for country wide distrabution then switch it to somthing lower for suburb then lower and more useful for home usage
the reason to use DC in data centers is quite simple, you can deal with less power supplies and focus more on each one. i assume they would still use AC to get power to each rack then regulate it to DC for the entire rack. that way you can keep everything cooler (only one or two power supplies to keep cool, if placed at the top then you could use a 120mm fan or two to keep things a bit quiter) and each rack mount PC benifits because sudennly there isnt an AC power supply being cooled by a 40mm fan in the case so the CPU can run cooler.
in the enda PC needs DC. i would say this is more about power and heat managment than a AC vs DC slug fest. by reducing the amoun of power supplies and shuffling around of where the heat is generated you could reduce noise and heat.
It is a shame, that every piece of electronic device comes with its own power adapter — slightly different from the others like it.
Imagine washing-machine manufacturer saying: "We have determined, that our equipment works best using 101V at 37Hz. Here is a converting device — never mind its size (about the same as the washer), and noise."
It is a pitiful failure of standartization, that we don't have an agreed-upon voltage (and minimum amperage high enough for laptops and TVs) and connector shape to avoid having to use dozens of AC-DC "bricks" around the house.
Power-over-USB seems promising (and Blackberry wisely uses it to recharge its devices)... One can only hope...
In Soviet Washington the swamp drains you.