In When Hardware is Free, Power is Expensive, I referenced a Google whitepaper (pdf) that explained why typical PC power supplies are not particularly efficient:
This is a companion discussion topic for the original blog entry at: http://www.codinghorror.com/blog/2007/05/upgrading-to-a-high-efficiency-power-supply.html
For ages I have been using computer hardware that runs with -48V DC (that is: “TELCO gear”,) these days I am converting all my telematic gizmos to 13.8V DC (“12V” lead acid battery float charge) bus. Instant integrated UPS within the systems.
Nothing new in having some DC bus voltage inside the systems.
The new Sun/Fujitsu M9000 mainframe system has common intermediate 48V DC bus powering all modules, and all power supplies in system feed the same bus. Conversion efficiency optimization is very important when total power consumption is up to 45 kW per machine.
In commodity-hardware the +12V DC is definitely obvious choice.
For quite a while the CPU core supply switcher has been non-isolated DC-DC converter on system board next to the CPU. Efficiency has been 94-96% in most designs, and boosting it couple percent is in the realm of possibility (ever lower output voltages at high currents is difficult enough challenge.)
Still 5% of 120 Watts is 6 Watts, which is still hefty amount to blow away with the wind, but less difficult than the 120 Watts in the CPU…
Say you get that main-to-12V DC at 90% efficiency, multiply by 95% and total system efficiency is 86% If both converters are running at 95%, the net result is 90% total conversion efficiency.
(The result is the same when there are lot of output converters.)
Is it possible to make 95% efficient mains-AC-to-12VDC supply ? Most likely it is. A 300 Watt supply would still have 15 Watt waste power to blow away.
Engineers view on the issue is that yes, single optimized converter from mains-AC-to-intermediate-DC plus a number of non-isolated very high efficiency DC-DC converters does make very much sense.
The mains supply converter has required 2000 Volt isolation (which is an added difficulty with lots of output voltages), while final converters need not be isolated at all.
Stand-by power generation can be separate 10 Watt supply in the mains converter performing at 80% efficiency without being noteworthy.
For embedded uses there is already amazingly small “picoPSU” by mini-box.com. Various models drink up 12V DC or 6-26V or whatever, and the entire power converter fits on top of motherboard power connector. The lovely wonders of “mini-itx”…
Good to know. Anyway, many PCs spend hours off, so we should also disconnect completely our PC while it is supposed to be off (as you mention), as an extra way to save energy… for us and for the planet…
Depending on where you live, who cares about efficiency?
In my area, I am paying to heat my house 9ish months of the year.
100% of the energy consumed by my PC is released as either heat, or light. The light is there for functionality, and the heat is where the “inefficiency” goes.
All of that energy “lost” by my PC is floating around my office in the form of heat, and comes directly off the portion of my energy bill devoted to heating my environment.
Now the situation is obviously different if you own and operate an air conditioner, or otherwise don’t want the heat, but for the sizable portion of the world that needs that heat, the situation is far less grim.
Or am I missing something?
i just read google’s paper. something odd strikes me: they remove the multiple voltage part of the power supply, only to place it on the motherboard.
i do understand that current motherboard already includes this part, so they are effectively removing one converting step. i also do understand that, when the voltage regulators are included on the motherboard, the manufacturer can size their regulator to draw the most efficiency out of them.
but then, do motherboard manufacturers care about efficiency ? do we have any study or any numbers on motherboard efficiency ?
rektide: Um. Did you even read his post? The power draw COMING OUT OF THE PLUG AND INTO HIS COMPUTER was ~10% lower in its various uses. That’d suggest that the system is in fact more efficient.
Dave: As someone else stated, electrical heating is not very efficient compared to other methods. Also, the heat released by your computer isn’t forced and doesn’t radiate nearly as well as a device made for heating your home (ie your furnace), so that heat energy being thrown away by your computer is still very much a waste.
Nacho: I’d suggest using Jeff’s second suggestion which is to just flip the rocker switch at the back of the PSU. Unplugging your computer is probably not worth it for the 5w power draw. @ 5w, assuming $.10/kWh, you’d have to leave the computer on for 3 months before it cost you a dime. It’s probably not worth it at that point to be getting on your hands and knees to unplug the thing.
Another option is to plug it into a switched power strip/bar, and flip the switch on that after the computer’s completed its shutdown sequence.
Erm. 5w draw @ $.10/kWh would cost you $.40/mo or so. I got my numbers backwards.
sulks into corner
How much power does it use in standby low-power mode? That’s the mode my PC is in the majority of the time and it would seem reducing the power in that mode is the best way to save energy.
Dave, even when all the heat is welcome, electricity is usually not the most economic way of heating.
Rien, on the efficiency thingy. There could be the possibility to design the onboard converterts more closely to the actual load, but then there are the PCI slots which consume unknown amounts. At least the bigger converters are more efficient, because higher voltage means less current and hence less losses.
Another thing for google may be to do away with the separate power supply for each PC and have a big one for each rack; bigger supplies are easier to get efficient. The telco people traditionally power their racks with some 48V dc because that makes it lot easier to run the stuff on battery.
dnm: untrue - heating your house with electricity is 100% efficient.
I bought a Seasonic 380w power supply about a year ago. On top of being more efficient, it’s also less noisy, produces less heat and is ROHS compliant (less toxic metals in it).
Great buy.
I’d also be interested in the power consumption in Sleep/Hybrid Sleep mode. Sleep appears to be working much better in Vista than it did in XP - my computer has never crashed coming out of it. Could be my new computer, of course.
I’m quite happy with my 80 PLUS power supply - the SilverStone ST50EF (500W). When I was deciding on it a couple months ago, the price difference for upgrading to an 80 PLUS model was about the same as switching from non-modular cabling to modular.
Good to see that everyday energy handling is entering in our mind ! But I’am still frightened about the energy used for doing nothing visible. There is the AMULET microprocessor, a ARM9 microprocessor (a very well designed CPU, and a real pleasure to work with, GP2X my love) without clock, it is indeed asynchronous. With this design, the energy used is related to the amounh of computing you are performing. One or two more ideas like this, and maybe we will be able to code without less ecological consciousness problem 
Via has been doing its part to help as well, example:
http://www.linuxdevices.com/news/NS8508116370.html
Somehow I think that if there were more of a collaboration between Via, Intel, AMD, etc. some amazing things could be done in terms of CPU, chipset, and memory “power” per watt.
Of course in such a world we might not even have the options we do now, since commercial competition truly can drive innovation. Hopefully more than it squelches innovation to appease the greedy shareholders. And yes I realize without greed there would be no shareholders. One could hope for a somewhat less “Ferengi” economy though.
Harold: That’s true. Doesn’t mean its good for the environment or your wallet though. (Unless your going for an electric heat pump).
Harold/Dave: Only the last step in electrical heating - the conversion of electricity to heat - is 100% efficient. The electricity is usually generated at a pretty disappointing level of efficiency - 35% to 40%. So every unit of heat you get in the house sends almost two more units up a smokestack somewhere, along with the attendant C02 and other pollutants. Unless your house uses electrical resistance heating, its heating system is likely to give you much better efficiency, and the waste heat from your appliances is truly waste.
I have a Corair HX 620, it costs an arm and a leg at $120 but it is completely silent and it is the highest performance PSU on the consumer market [that I know of]. 5 year warranty is another reason; it will last as long as my computer does.
this seems falacious to me. most of the power demands of a reasonably energy efficient system are going to come from the cpu. a 12v supply motherboard is still going to have to convert the 12v into the ~1.3v required by the cpu. requiring huge frigging mosfets on the motherboard just seems like you are moving the problem from the power supply to the mobo. sure your power supply is now 85% efficient (which is already available, but is significantly more expensive with conventional dual rail ATX’s), but now your mobos voltage regulators are tossing off gobbs of waste heat too.
the notion of cheaper high efficiency power supplies is very alluring, and i do hope to see it become a possibility. but please consider the complications involved.
note: the Corsair HX 520W and Corsair HX 620W PSUs are also made by Seasonic.
You won’t be able to buy such computers for a while,
Not exactly. Why not just get an EPIC and NANO board which already do this and have for some time? They are not Core Duo 2 but some models can use single volt 12v PSUs. I love that google pretends they invented though. Makes the server farm cowpokes feel special!
I find it amazing that we have abstracted the consumption of energy to just kwh and $$. Depending on whether you’re using renewable (hydro/wind/solar) energy or not, the depletion of fossil fuels and global warming are way more important than the money. A 65 watt computer left running full time consumes a barrel of oil (equivalent) in a year. 5,500,000 btu/barrel / 10,000 btu/kwh / 8760 hrs/year = 63 watts. How many hours a day do you run your SUV PC, Jeff?
I know you need high performance for games but for normal info-appliance usage, 237 or 215 watts is way overkill. So go get yourself a laptop or a Mac Mini. My mini uses about 20 watts, way less energy than the 75 watt new Dual Core desktop which I just sent packing.
Leave in alone and it goes to sleep at less than a watt, not 5 watts like your box or my HP all-in-one printer which gobbles about 10 watts turned off. My previous desktop ran 10 watts in sleep mode. What’s wrong with this picture?
Bonus? My new Mac Mini Core Duo is faster on XP than my other new desktop was on Vista, and it’s QUIET!