Data Centers And DC Power

mstansberry writes "In the final article in a series on the price of power in the data center, IT pros weigh the pros and cons of direct current-powered servers. A limited number of companies make servers with the power supplies removed with DC power distributed to multiple machines from a single unit. It saves power by skipping an extra conversion from alternating current (AC). Telcos have been using this method for years, but some data center pros are leery of taking on the new systems. It's not something people are familiar with and if they break down, you have to hire a specialized engineer to come fix them. But if they're saving even half of what they're reported to save on the electric bill, companies could afford to hire the engineers." We've reported on previous articles in the series.

Comments

Re:What about houses?

[n0dalus]

I thinks it's a really good idea.
If there were several pins, many different voltages would be possible, and a device could even use more than one voltage from one plug (eg, it could draw 2V for a relay, 4V for a power indicator, and the standard AC for the actual thing it's powering.)
By not having to have transformers and big resistors inside all the household devices, there would be huge savings in power, things wouldn't get so hot, wouldn't need such big heatsinks, there would be far less electromagnetic radiation around the place (which is probably responsible for a lot of people getting sick etc), and it's safer too (devices that only need a small DC power source won't electrocute you when you drop them in some water.)

Re:correction

[ArsenneLupin]

Either way, there is still only one conversion: 110AC -> 12/-12/5vDC.

Nope, you save two conversions.

Without DC distribution, you have AC->DC->AC in the central UPS, and then AC->DC in each computer's power supply.

With DC distribution, you have AC->DC in the central UPS, and no conversion in the computers.

You get down from 3 conversions to 1.

DC in Telco

[Comen]

I started working with IP in a small ISP. We were bought by a loal Telco and over the years have got used to having all our routers and switches running on DC current.
One thing telco companies do well is DC power, they have alot of skill in providing multiple DC feeds from DC power systems, with battery backup and generators all in line.
I would imagine that any big server farm would benefit from this kind of setup. Especially when you have people runnnig the lines that are as good as some of the guys in the telo world, they can really make the wiring look like a art in some places.

Re:What am I missing?

[GigsVT]

The DC step in the middle is so you can chop it into a high frequency square wave. You save power and space because you can vary the duty cycle of the square wave for regulation, and the high frequency allows for smaller components.

The first step

[dsginter]

The first step will be in the home office. Have you taken a look at the rat's nest under most desks? Most of it is AC/DC conversion. If the industry could just arrive at a DC power standard, we could start with a single AC/DC "box" under the desk with a standard plug end for all DC peripheraps. Add daisy chaining and wireless USB or Bluetooth, and that nest is largely eliminated.

At this point, we could start to build it into houses and other buildings.

Don't you still need a PSU for 48v DC?

[bigtrike]

Wouldn't you still need a power supply to convert to the various voltages required by a computer, which may change over time. Most DC power setups I've seen run at 48v, which still requires conversion to 12v, 5v, and 3.3v. You can buy a 48v power supply for most servers and other equipment today. With a switched power supply, you'd need larger capacitors or a higher switching frequency in order to smooth out the lower powered DC. It's very unlikely that you would eliminate any heat loss. I would assume that telecommunications equipment uses a 48v setup due to legacy issues and that it was a better idea before switching power supplies became cheap and efficient.

The downside with DC is that lower voltages require much thicker wires, and you're at much greater risk for fire. Circuit breakers and other things are also more complicated and expensive since DC tends to weld things together.

An EE I know just built a data center supplying 208v (2 branches of a 3 phase iirc) to all the racks. Almost all existing power supplies can take it, and it saves a bundle in wiring costs. I'm not sure about servers, but most desktop power supplies operate at a power factor of .8 or so, meaning 20% of the billable power is effectively wasted and could be recovered for a slight increase in cost.

Re:Forgot DC and AC power

[ThePowerGorilla]

Yes, real big iron still uses 3-phase power. I can only speak on behalf of large IBM system (zSeries, etc). These systems will accept 192VAC to 508VAC on the input, 3-phase Delta. This means no neutral required. Additionally, they will even run with one phase totally missing. The first power conversion stage in any piece of their 'big iron' is a very large AC to DC converter, rated for a 350VDC output at over 42kW. Actually it's six 7.5kW converters paralled, and these are redundant/hot swappable. Totally modular, with no cable connections. This block is about 95% efficient. This DC is then distributed to the rest of the system power supplies, with redundant cabling supplying all point of load converters. All point of load converters are also redundant and hot swap. These converters have a range of efficiencies, but are typically much better than industry standards. A DC/DC converter in the z9 can source 1000A alone on the CPU Vcore level (12 of these supplies are in the machine). Supplies are used for CPU nodes, I/O cages, blowers and refrigeration. All blowers are 3-phase DC-brushless type, with the 3-phase synthesized off the 350VDC feeds. The blowers are usually 300W or larger, each. The CPU refrigeration is also run by 3-phase compressors, this power also being synthesized off of 350VDC. This is done to allow a conventional off-the-shelf compressor to be run off any line voltage, and ride through phase losses (as this is seen by the bulk AC/DC converter instead). The 'big iron' also supports built in UPS cabability, allowing you to connect battery packs directly to the bulk AC/DC converters. A machine will handle six 400V@2.5Ah battery packs connected to it. This feature is used to ensure a system such as a z9 has true 100% availability, and won't suffer a hard shutdown due to careless datacenter workers or electricians. In short, the article is intend to address small white box systems that use $12 power supplies with very poor reliability and efficiencies. And to another poster that brought up 3-phase being more efficient for power conversion...that's not really true these days, as everything requires power-factor correction. Nothing in the IT uses huge three-phase bridge rectifiers and phase-regulated primaries anymore.

Re:What about houses?

[nido]

"Since when was non-ionizing EM radiation dangerous?"

It isn't.

don't be so sure... Living bodies are incredibly complex electrical devices. I think it arrogant to assume artificial electric fields cannot have an effect on their proper operation.

Now if you look at the question of: Are there biological effects, the engineers and the physicists say absolutely not. Their view in general of what living systems consist of is that the cells are little plastic bags filled with minestrone soup. And you can then with that sort of a concept calculate the field strength and the frequencies you would need to produce an effect on the minestrone soup. And this is exactly the concept that was employed after it became apparent that radar systems could heat up the human body. The physicists that were involved in answering the question: Are there effects? And at what level do they occur? And what would be a safe level? Basically, they followed a basic precept which was to consider a spherical cow, a circular oval object filled with conducting solution and composed of a skin that is transparent to the radio frequency waves that microwave generators produce. And on that basis, they asked: How much does it take to heat this up? Where does the cow's temperature start to rise?

And that number was calculated and confirmed in actual procedures in the lab using the spherical cow concept. They said, "OK, that's the number at which you are going to start heating people. Let's say that's not such a good idea and we'll set a level ten times lower as the safe levels."

That level was applied for several decades to everything that concerned electromagnetic pollution. Of course, this is not correct. Any biologist can tell you that the body is much more complicated than that and the work I had done up to that point had involved the body's actual use of electric currents generated in the body that regulated certain things like healing. Wound healing is associated with a rather specific electrical current and voltage. So, the premise that was applied by the physicists and the engineers was erroneous from the start.

That's number one. Number two, what would be the normal electromagnetic environment assuming that we're starting from scratch at Edison's time - and not Edison either because he went to DC current to light the light bulb. It was Nikolai Tesla who conceived of the system we presently use and who, incidentally, gets no credit for it: the 60 second electromagnetic field that is carried by power lines, the big lines that are strung across the country, and provides the current that comes into your home and appears in the wall socket and you use to run the coffee maker and the TV and all the rest of the things in the house 60 cycles. That didn't even exist one hundred years ago.

(emphasis added) From an interview of Robert O. Becker, M. D., who was a pioneer in the study of natural electrical currents in the human body.