I do hope he is joking.

And average (ish) PC uses around 300 watts (I'm picking this figure out of the air) when it is working. If you try to run the PC from a 'remote' power supply this power need to come down the wires at 12V - this equates to 12V @ 25A. The longer the cable the more power is lost.
Say for instance that the total cable run from wall to PC has a resistance of 0.05 ohms (reasonable if you include the connectors at both ends). You would waste current squared times resistance (or 31.25W)
That is why the electricity on the grid is 72000V not 220V or 110V.

Just for comparison 240V 300W 0.05R, will waste 0.078W

Many off-grid homes use 12V and 120V, but the 12V is carried using large-guage wire. Practical for the length of a house, but not for something like a factory. Then Rhyuso's comments ring true.

Those homes use the 12V for lighting and things like answering machines, so their inverters can switch to a low-power mode until higher amperage 120V appliances are needed. Otherwise they would need to be "on" all the time.

So really Felsenstein's "idea" isn't new at all - its been in use for decades.

There are more cost effective ways to get rid of wall warts. The volume of a wart, and the part that creates the phantom load is the transformer to convert the 120 or 240 volt AC down to some lower voltage, say 5 or 18 which is then converted to DC for your electronic device.

For no more than $2/wart it could have a circuit in it to detect when there is no load and disconnect the transformer from the mains until a load is applied. This will not happen until a regulatory agency requires it. Wall warts are a horribly competitive industry with a margin in the pennies.

There are other ways of converting AC to DC that do not require a transformer and would not create the phantom load. The down side is that they are also not isolated from the mains and certain failures in them could lead to lethal voltages on the outputs. I don't expect to see these getting UL approval, with good cause.

The 12v PC power supply is a bit of a mystery me. The integrated circuits are still going to need 5v, 3.3v, and probably a lower one yet for the CPU. There will have to be a DC/DC converter on the board to do these, much like there is one for the CPU voltages today. Each converter is going to be less than 100% efficient. I suspect the improvement is in making a really good 120vac-12vdc power supply and not losing as much power there. Google is a special case, in a giant machine room they could use very efficient 3 phase AC to 12 V DC converters and run power busses up the racks. That won't apply in homes.

How in the world is 12v safer?? 12v in a car could kill you fairly easily (with enough amperage) and difibulators runon DC as well. Yeah, a defib would save you, but hit you with one right now and your going to the ER.

anyhow see http://en.wikipedia.org/wiki/War_of_Currents

Hey everybody, I have an idea! Let's take 20 years of PC power supply design, and throw it out the window because someone vaguely famous (who is probably not an electrical engineer) said so!

Let's step back for a moment and look at this logically. It's true that replacing a typical desktop PC power supply with one that outputs 12 volts only is completely possible, and quite easy. However, not everything runs on 12 volts. This means motherboards, processors, ram, hard drives, optical drives, video cards, sound cards, etc.; nearly EVERY piece of electonics in the computer would need to be redesigend for 12 volts, or it would need to include a voltage step-down transformer or voltage regulator in it's circuit. Transformers and regulators are always inefficient. Moving away from a system that has a few transformers centrally located to a system that uses many transformers (all over the place) is not only more energy inefficient, but it is also more prone to failure. On top of the energy ineffiencies introduced by tossing transformers and extra voltage regulators everywhere, there's also the issue of increased thermal inefficiency.

I just don't see this happening - at least not for consumer gear. Perhaps a much more reasonable modification would be the addition of a (perhaps shunting) circuit into power supplies that allows you to connect a 12 volt (DC) source (from either a building-based transformer, or smaller source (solar/wind), instead of the typical 120/240 volt (AC) source. In this scenario, the power supply would function as a central voltage regulator and distributor. This would enable nearly the same desired end result while requiring a redesign of the power-supply ONLY. This means it could work with current off-the-shelf PC components and provide consumers/businesses with choice.

The traditional telco equipment voltage is, if I remember right, 54V DC or something in that neighborhood, up at the limit for reasonably safe (for professionals) work on live conductors. The equipment runs right off the batteries, no UPS inverter needed. DC/DC convert inside the equipment. DC distribution makes for much simpler connections to redundent power, with just diodes to isolate things.

geekpdx, So if it is so much trouble to run everything off one voltage, how does my notebook computer do it from a single transformer block?

This is too big a subject to cover in this format, but I would like to hit a couple of high points (which I will number, of course.)

1. DC to DC converters for small currents and low input and output voltages can be very efficient, and if run using a high switching frequency, do not need much bulky filtering to produce a clean output.

2. Telco is nominally 48 volts, but while the batteries are being charged constantly the voltage is close to 54. The currents are in the tens of thousands of amps in a big old technology telco central office. More modern equipment and smaller PBX installations may use 24 volts DC instead.

3. It is current that kills, not voltage. Twenty milliamps of current at the right frequency across the right path in the body can kill. But 12 volts is low enough that there is no way that it could drive enough current across the resistance of your skin to kill you. The car steps up that voltage to 10,000 volts or more to drive the spark plugs and hybrids and pure electrics use battery pack voltages as high as 500 volts DC. 12 volts applied directly to the heart through implanted electrodes might be enough to kill you, but that should not happen as you are working on your car. On the other hand, the battery can drive enough current through a short circuit such as a wrench or your wedding ring to make a lot of heat and sparks and burn you badly!

4. Powering home appliances that use wall warts from a 12 volt DC system would be practical. Powering computers at full bore CPU operation would only make sense if you have bus bars and short interconnects.

5. The wall wart when not connected to what it is powering, or when what it is powering is turned off completely (not just listening for a remote control, which is another issue) does not get very warm or use very much power, but although the current that flows through its transformer windings does not represent a large power loss there, it does cause resistive losses in the house and utility wiring. For this reason, utilities often put large capacitor banks, called power factor correctors, in key locations, usually on the high voltage transmission side of your local transformers.

5. A single transformer can have multiple output windings which produce different AC voltages, but modern computer power supplies, called switching power supplies, can use the transformer to create a fairly high isolated DC voltage which then goes into numerous DC to DC convertors that provide all of the output voltages. Or you can provide a non-isolated DC which uses isolated DC to DC convertors.

6. Non-isolating DC to DC convertors do not need transformers, only inductors, and they can be fairly small and low loss because the frequencies (or pulse widths) involved are small. You do not need a lot of iron or a large amount of copper if the frequency is high enough.

7. In summary, the concept is worth looking at more deeply, and many of the objections raised here make no sense, just as some objections are quite reasonable (the 300 watt example among them.)
A dual voltage supply system, with the 12 volts produced locally at each building, and with 120 volts available where needed for high power uses could be practical.

Lloyd, great question!

The components in laptops and PCs perform the same functions. However, at the same time, desktops are generally far more powerful. More imporantly (to most consumers) the components and total cost are vastly different.

When considering a server (as Google certainly is), one must balance performance, cost and reliability. A laptop cannot match a desktop or rackmount computer in those terms. In general, a desktop PC can have one or all of it's hardware components replaced as needed with other off-the-shelf hardware - this is very difficult to do with a laptop. Other than hard drives and RAM, most laptop components are specific to the make and model laptop you have purchased. This leaves you at the mercy of the manufacturer, should you encounter a problem or desire to upgrade.

I use a laptop at work (right now, in fact :). It is a bit underpowered for my needs, but I make it through the day. For me, a slower system that isn't as reliable or extensible is an acceptable trade-off for the portability. For many home users, especially gamers, the cost and performance of a laptop doesn't make sense. Laptops pretending to be servers in data centers doesn't work out very well either.

On a side note, when I turn off my desktop PC, it does not continue to consume power (though some desktop PCs do). When I turn off my laptop, the transformers still burn power. For convenience, I have a transformer in my cubicle, in my photo room, and I have two at home. If I do not unplug them, they'll suck up small bits of power juice all day and night. More transformers do not make this world more efficient, however, being able to run a laptop directly from batteries charged by solar or wind power... That's treehugger. Which is why I made the case for deskptop PC power supplies to also be able to be used with 12 volt DC power. I just wish solar/wind power was feasible at my house. (Ironically, the trees in my yard prevent me from using either.)

It seems to me he could just buy all 48v equipment, there is plenty available already since telco stuff all uses it. All Cisco gear is available with 48v power supplies.
Sure you can't run 12v dc long distances, but since the high line voltage is dropped to 220 with a center tapped 120v leg at the transformer on the pole outsiede each home it would be very easy to tap off a 12v line then bring it in, rectify it and filter it smooth to eliminate all the wall warts.
I'm working on a 12v home system myself, I have my home server running from 12v (A mini-ITX board with a 12v in supply from a company called minibox whom I think Apple copied the mac mini design), my wireless router, cable modem, battery chargerts, etc all run from 12v. I'm going to run them straight from battery power to create a true online UPS then charge the battery from a small solar panel with a relay to kick in a 120v laine transformer if the solar call can't keep up with the load.

geedpdx I'm afraid you didn't Lloyd's question at all.

Llyod, the real answer is that your laptop power supply puts out high current low voltage DC from 110V AC, that requires a bulky heat producing component that laptop manufacturers and owners don't want inside their computers, especially when its being used as a portable off batteries.

The exact voltage the power supply produces is matched to whatever the battery pack of the system produces which nowadays is usually some multiple of the 3.7V or so that a single Li-Ion cell produces.

Inside your computer there are other DC-DC converters and regulators to produce the many other DC voltages needed for the computer components - from 3.3V, 5V to 12V. These are small and usually more efficient and hence don't output as much heat - compared to the CPU which effecitvely dissipates all its power consumption as heat they negligible.