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."

Comments

Safety

[TimeTrav]

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.

Re:Safety

[cswiger2005]

Obviously, you don't work on live circuits if you have a choice of working with them off instead, but good habits mean you treat even dead circuits as if they were live until fully isolated & disconnected, just as you should treat a gun as being loaded until you've confirmed that it is not.

Well-designed power supplies often have a bleeder resistor across the primary filter caps to drain them of juice, but note that the vaccuum tube in a CRT makes an excellent capacitor as well (it's being charged to 20 kilovolts or more), and it's dangerous to try to dead-short it to drain the residual current. 120VAC current shock can be fatal but that is very uncommon; however, the voltages inside a CRT are probably the most dangerous level of current most people have around in their homes or work environments.

Re:Safety

[Anonymous Coward]

>So you also failed electrical theory, as well.

Yourself also?

ANY electrical path must be joined from source to drain or no power will flow. It doesn't matter if it is DC or AC. Period.

An AC path, however, has an easier to isolate ground because it works with simple transformers. A 1:1 transformer will allow you to grab a 220 volt line without being shocked, assuming you do not touch any path that leads back to the other side of the transformer. This is why in the ICU in hospitals you will find them being used: If a patients equipment shorts in a manner that the electricity reaches the patient, it will not shock the patient unless the patient grabs ahold of the equipment.

Unfortunately DC does not offer this sort of simplicity of isolation.

Edison was a sadistic nutbag that actually enjoyed electrocuting animals like cats, dogs, and elephants by joining them to an AC power path. His DC power was no less dangerous, the only reason it never electrocuted the animals was that the voltage was low enough skin (or fur) resistance did not allow enough current to pass through the animal's body to kill them. Furthermore, due to the low voltage/high current nature of his system, the amount of energy wasted through heating the conductors limited electricity runs to less than about 2 km.

The exact same ridiculousness in power cable AWG requirements can be seen in "modern" car stereo upgrades. People will run a 4 AWG cable to their subwoofer amplifier to power an "800 watt" 12 VDC amplifier. The same 800 watts can be generated from a 16 AWG cable hooked into a 120 VAC amplifier. The difference being that the car amplifiers are often unfused because fuses in the 100 - 200 Amp range are expensive, and circuit breaks even more so, and that 15 amp fuses and circuit breakers for home electricity are incredibly cheap. The unfused car system when shorted will burn the car down in no time. The fused circuit in houses when shorted will burn nothing down, and, when repaired, the wiring can even be reused.

Edison created a useless power system that never worked properly for anyone at all. He also enjoyed electrocuting animals for no apparent reason other than to hookwink customers. He also helped develop one of today's most popular capital punishments: The electric chair. Oh, and he stole credit for several inventions (not the least of which is the light bulb). All around, he's just not a cool guy.

So, basically, for Edison's idea to have worked, we'd all have 0000 AWG cables running to our homes, and we'd probably be melting several of them causing fires, not to mention that the DC power will cause the conductors to be damaged through electroplating. But, we wouldn't get shocked. Of course, the exact same benefits, along with the additional benefit of no electroplating, could be had by running the same conductors with the same voltage AC current at a frequency outside of 50 - 60 Hz.

Of course, at 50 - 60 Hz AC power is most dangerous. But then again, at the voltage levels required for modern electricity, the frequency makes very little difference.

The Telcos have known this for years

[RotateLeftByte]

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've always liked ...

[jc42]

... 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.

Re:Edison

[John Hasler]

> 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.

For 19th and early twentieth century technology Tesla and Westinghouse were entirely right. They had no practical method of changing voltage.

BTW you don't want to look too closely at Edison's scientific achievements. You might find that there is less there than meets the eye.

Re:Edison

[Svartalf]

Edison didn't have all that many scientific acheivements.

The record player was really the only truely unique thing he did. Everything else was a duplication of someone else's efforts where he succeeded and the others failed- or was something one of his employees came up with. Did you know that he'd "Westinghouse" a cat "to show the dangers of AC power" during the time where he was trying to compete with AC power versus his DC system (From which ConEd initially came from...)? This would entail hooking up a grid of alternating plates with some small amount of insulating gap to an AC power connection, place them inside a cage that one's keeping a cat and then plug it in. Edison's NOT someone to be holding up as an example of scientific achievement- unless you want to hold Mengele up as well. Sure, we got a lot further in medical science because of that "Doctor", but how he got his information, I'd rather he didn't do what he did- and it's not a good example of a scientific achievement.

DC and AC both have their place. DC is good for short-haul power distribution, but if you short out the lines you'll destroy the entire power run. AC doesn't do that anywhere near as bad- which is why electric power is distributed as AC- it doesn't have the same safety issues and it can be transmitted long distances without major losses as it's being transmitted down the wire, not conducted.