OK, since you insist on beat this dead horse…
From my previous link, an Energy Star 2 - rated 200W power supply requires 70+% efficiency at 5W load. So, you would be consuming 7.14W. This would undoubtably be a big savings over having 10 unloaded power supplies, each consuming .5W scattered around the house.
The efficiency isn’t the problem - it’s everything else.
But you would still have all the unloaded power supplies around the house. In fact, you would have more because there would be several in every room.
Well, everything else plus this doesn’t really help.
Unloaded supplies could use various tricks, such as disconnecting the transformer when not in use, or having several transformers of different size that could be disconnected individually.
None of those tricks are used in wallwarts for two reasons: a) phantom power is hippy hype that doesn’t affect GW or our wallets (but let’s ignore that for now) b) the dozens of wallwarts are each made as cheaply as possible. A centralized DC converter could afford to use more advanced (but still inexpensive) technology, or a hippy homeowner could invest in the technology that he’d like.
You also don’t need a converter in every outlet. That was a spur-of-the-moment response to a strawman argument. Electronics don’t draw much power, don’t need high currents, and hence wouldn’t see resistive losses in the wires.
Let’s recap some of the advantages of DC wall power:
[ul]
[li]DC-DC converters are much more compact and efficient than AC-DC converters. (This 150W computer power supply outputs four different voltages, attains 96% efficiency, and is the size of a pack of gum.)[/li][li]Be cheaper. Each device will not need its own proprietary adapter, and manufacturers won’t be able to gouge you for losing one. (This is China’s motivation behind the cell-phone law.) Of course, electronics themselves will become less expensive.[/li][li]Be more efficient. Cheap-ass wallwarts were never designed for efficiency, either during operation or during standby. Unlike some claims, distributing DC power from one source will not be inefficient. Wire losses arise when carrying a great deal of amps, which is not what this distribution system is designed for.[/li][li]Provides opportunity for new safety technologies. A USB plug communicates with its receptacle to ask for power before taking it, to protect against overloads. A house circuit would do the same thing.[/li][li]Provides opportunity for world standardization. Currently, even the countries that use 220V AC have half a dozen or so different sockets shapes. It’s madness. This is not directly related to DC, but should be mentioned.[/li][li]Be more convenient. Not only are wallwarts unsightly, but only two can fit into an outlet plate. In contrast, many small DC ports can fit into a wall. DC current can even be daisy chained.[/li][/ul]
Of course, ideally you would not want devices which connect to computers to have an additional cable going to the wall. (Unless such devices connect wirelessly.) The model of USB, of a combined data and power link, is a good one. The killer problem with USB is that it can only put out 2W. If the adoption of Firewire, which can carry 30W, had been more widespread, the evolutionary path would be more obvious. As it is, there is a huge chicken-and-egg/barrier-to-entry problem. A problem that is reasonable to say cannot be overcome in the short-term.
When using a combined data/power connector, HorseloverFat brought up an excellent and overlooked point, regarding security. Any USB-like standard would have to address it, such as by having different shaped connectors (a power connector would be visibly missing the data pins).
Still, there are many advantages to DC power, and I find it strange that some people argue that none exist at all.
The only way I could see such a system as economically sensible is if it was fed from solar panels on your roof. Then you could use them to provide 12V DC to a couple of places in your house, like a PC, printer, etc. in your office and a TV/music/home theatre setup in your living room.
But even then, you would have to wire your house for this, and purchase equipment that can run from 12VDC. (Except for laptops, that isn’t common currently, and is more expensive.) You would also have to provide some battery storage in the system, for use at times when the sun isn’t shining. Or you could provide a large AC-to-DC converter from the main AC power, to run this when needed.
I don’t think this would pay back economically, given the current prices of solar panels, copper wiring, etc. Possibly it would in the future. Especially, if lots of people began doing it.
Something interesting I’d also like to mention is ways that AC power could be made friendlier to electronics.
For one thing, AC-DC power supplies could be a lot more compact if the AC frequency wasn’t a pathetically low 60Hz. 16ms is an eternity that necessitates big inductors and big capacitors to bridge the timegap.
For another, a low-voltage AC source would provide some of the advantages of a low-voltage DC one (especially in regard to allowing electronics to safely house conversion circuitry internally).
I’ve never heard low-voltage high-frequency AC distribution being contrasted with DC, so I wouldn’t rule it out. Of course it’s probably inferior overall, but I felt like mentioning it for completeness and to hint at what is strictly about “DC” and what isn’t. In fact, many of the benefits I mentioned aren’t so much about current/voltage either (standardized plugs, etc.). But one big change can roll up many little ones.
Four out of five EEs agree, DC…
for home power distribution…
sucks.
They also emit a lot of EMI.
Cordless devices like vacuums and other cleaning paraphenalia would go well there.
Cordless tool chargers?
Have you been to a kitchen store recently? Crikey, the number of cordless kitchen tools are growing by leaps and bounds.
I’d bet that you have a significant number of 120v outlets unused in your house as well. Yet, the electrical code requires them to be there. If you’re proposing a code standard for DC outlets, I would lay good odds that the final standard would require the DC outlets in nearly every place there is an AC outlet.
I’ve half a mind to take you up on that. From conception to fully approved standard in less than 50 years? Considering I’ve seen it take three code cycles to resolve safety issues, implementing a standard for something that very few people think is necessary would take much longer than half a century.
All prices from Home Depot.com
Double gang electrical box - 2.16 (one side for AC, one for DC)
Duplex receptacle - .59
Double gang wall plate -$.89
Universal DC power supply $78 (Leviton 12-Volt Universal Mini DC Power Supply)
Cost per outlet - $81.64
Any questions?
I have sitting under my desk, plugged in, a Condor Class 2 AC transformer outputting 200mA @12VAC. It’s running a Pelco video switcher. I’m not going to take the time to open the switcher to see what happens inside.
No, I use a properly designed power strip to accomodate the transformers. It’s much more affordable and considerably simpler than attempting to change the world.
In that case, why not lobby the hard drive manufacturers to install pass-through power on their product? I’d think that would be a pretty smart first step.
You’ve answered your own question right there. Even with no output connected, there is a complete circuit in the input side of the transformer. An unloaded transformer essentially becomes an inductor.
See above. If it retails at $70, I would hazard the guess that wholesale is around $35. But it’s not a question of wholesale. My contractor isn’t going to charge me a wholesale price for the materials in my house.
To minimize line losses and to control costs, I’d guess you’d want one per room. Maybe two in a dedicated office space, but who knows which room will become the office over time? But code requires that such connections and devices be accesible, so it’ll either have to be engineered to fit in a single-gang box or each room will have to have it’s own low voltage panel so the device can be easily accessed.
Keep in mind that the NEC has much stronger requirements for devices that are permanently installed, so the R&D costs of developing your technology will likely offset any savings in mass manufacture. Not to mention that the first company to successfully develop the device gets the patent and the monopoly.
>Universal DC power supply $78 (Leviton 12-Volt Universal Mini DC Power Supply)
Yep, there’s your deal breaker right there. Instead of the 5 or 6 wall warts I have right now, code will dictate 10 of these things in my house. We’re looking at several thousands dollars of product and labor so some guy can have less wall warts in his house.
Oh, I think you guys are neglecting economies of scale.
These could easily be made for $2. Look at all the price of current wallwarts.
But, I think that this is not what the OP was suggesting, which was to have a single DC power supply, and pump 12v (or 5v, or whatever) all over the house.
It’s pretty clear that just moving the current wallwarts into the wall is pretty pointless.
Nope. A 5W wallwart is one thing; A 200W power supply is a very different thing and you are not getting it for $2.
That was dismissed as expensive and impractical early in the thread due to voltage drop and/or huge copper wires.
That is pretty much where we all agree.
No. that must be tiny. Look:
And 40W does not come even close to being anything “universal”. You’d need five times that.
And the way things go with electronics a few won’t work when you need them and they will all be obsolete in 8~12 years and will need replacing.
No it wasn’t. Thanks for purposely not reading any of my posts. Voltage drops only due to high current. No one is feeding a 2kW microwave through 12VDC, so this isn’t a fn issue.
>Oh, I think you guys are neglecting economies of scale.
EoS isnt magic. For this stuff to be up to whatever codes, safety regulations, RoHS, etc its still gong to cost something significant. Lets say half: $40. At least for early adopters. Maybe in 20 years it’ll be 10 dollars or so.
Even then, human labor doesnt scale. The union guys pulling DC wire through my house and installing these things is still going to cost me $150 an hour. Whats 20 outlets cost you in labor alone? Lets say one hour each and lets throw in the wires and conduit for free. $3,000 in labor and 800 dollars in parts. So the lowball estimate is $3,800.
Im not holding my breath.
Ok, let’s do some math. What size wires do you need to feed 200 W at 12V over a distance of 100’ with 5% voltage drop max?
The answer is 10 times more section than at 120 V. Do you know what the going price of copper is?
Do you insist this is an economical solution? (To a non-existent problem?)
Do you want to continue pricing this?
OK, let’s do.
[quote=“Alex_Dubinsky, post:65, topic:500891”]
[li]DC-DC converters are much more compact and efficient than AC-DC converters. (This 150W computer power supply outputs four different voltages, attains 96% efficiency, and is the size of a pack of gum.)[/li][/quote]
I dispute every one of those claims. It does not regulate 150 W but more like 60 W, max, tops, and that is with adequate refrigeration. When temp exceeds 65C you needs to derate. The “150 W” claim is simply put, false, because it does not regulate the 12 V line at all. It implies a separate regulator for that line.
[quote=“Alex_Dubinsky, post:65, topic:500891”]
[li]Be cheaper. Each device will not need its own proprietary adapter, and manufacturers won’t be able to gouge you for losing one. (This is China’s motivation behind the cell-phone law.) Of course, electronics themselves will become less expensive. [/li][/quote]
We are going around in circles. One more time: you can do that with cell phones because the power they require is insignificant and because they pretty much all work at the same voltage to begin with. You cannot do that with a range of devices which use a range of different voltages and substantial amounts of power because you would need to supply the sum total of all power required and at different voltages. It would be extremely economically inefficient to have all that DC power available only to use a tiny fraction of it.
[quote=“Alex_Dubinsky, post:65, topic:500891”]
[li]Be more efficient. Cheap-ass wallwarts were never designed for efficiency, either during operation or during standby. [/li][/quote]
They are designed to be cheap which is what people want. Anything you propose will be more expensive.
Let us stop with the handwaving and general assertions and put some numbers on this. Please tell me what exactly you propose. How much power at what voltage distributed how? Numbers please.
[quote=“Alex_Dubinsky, post:65, topic:500891”]
[li]Provides opportunity for new safety technologies. A USB plug communicates with its receptacle to ask for power before taking it, to protect against overloads. A house circuit would do the same thing. [/li][/quote]
Well, that’s very nice. A heart attack also provides opportunities for doctors to practice their trade. That does not make heart attacks a good thing.
Now you want a DC system which has intelligent power management? Really? Ok, give me more details. I can guarantee that the drawbacks and problems far outweigh any gains.
[quote=“Alex_Dubinsky, post:65, topic:500891”]
[li]Provides opportunity for world standardization. Currently, even the countries that use 220V AC have half a dozen or so different sockets shapes. It’s madness. This is not directly related to DC, but should be mentioned.[/li][/quote]
Good luck getting countries to go along. There are many homes in America which still do not have breakers or grounded systems and it has been decades since those things were introduced. But I am sure America will go metric any day now.
[quote=“Alex_Dubinsky, post:65, topic:500891”]
[li]Be more convenient. Not only are wallwarts unsightly, but only two can fit into an outlet plate. In contrast, many small DC ports can fit into a wall. DC current can even be daisy chained.[/li][/quote]
DC can be daisy chained just as well as AC. This is a mechanical thing which has nothing to do with electricity.
It would make much more sense for the computer PS to supply an additional DC output for accessories and this has not happened because people want to save money as much as they can and do not want to pay for things they might not need. You can preach all you want but most people will go for the cheapest option.
Good luck with all this.
No. No one is arguing there are no advantages. What I am arguing is that the advantages are smaller than the disadvantages. A pogo stick also has many advantages but not as an intercontinental mode of transportation.
Maybe that worked because it was a good idea, with obvious advantages, had manufacturers behind it, and the tech public was clamoring for a solution to device interconnection problems, and they really wanted it.
Besides, nobody modified their computers to wait for USB. The new versions just incorporated it, for the reasons given above.
We like wall warts (we like wall warts)
You like wall warts (we like wall warts)
(sax solo follows)