Way back in the early days of the electrification of America, Thomas Edison advocated using direct current to transfer power from utilities to homes. In this he was opposed by George Westinghouse (and his former employee Nikola Tesla) who favored alternating current. Westinghouse and Tesla won that battle for very good technical reasons, and 120V AC became the standard power available in American homes. And AC works great for powering the sort of appliances that were invented to use the new technology: incandescent lights, electric toasters, and the like.
But AC is no good for sophisticated electronics, and so every single one of them ships with a device to convert AC to DC… a power brick. These things are ugly, they take up a lot of space, they’re easily lost, they get hot, and they add expense. AC remains the right choice for transmitting power over long distances, but why hasn’t anyone devised a standard for plug-in direct current power inside the home, with a master converter located just past the meter? A plug with a 12V rail, a 5V rail, and a ground would satisfy the needs of most electronics. Why isn’t this done? I’m sick of wall warts.
Expense.
The voltage would have a noticeable drop across an average home.
Electronics like computers would not do well with power drops.
You then have to plug in multiple voltages. Don’t forget you’ll want +5v, -5v, +12v, -12v, and 3.3v.
Surely one (or a few) in-wall AC-to-DC converters would be less expensive than one for every single electronic device in the house
Okay, so put the DC outlets right next to the AC outlets, with the conversion happening right on the spot rather than trying to run DC through the walls.
Not sure I buy this. Electronic devices use a wide variety of voltages because they can, because they all come with their own bricks. If they were designed to work with standardized outlets, I bet the designers could make do with a smaller set of voltages. Three rails (+5V, +12V, and ground) would give you -5V, -12V, +7V, and -7V if you needed them.
edit: and I’m not proposing getting rid of AC outlets, either. If a device (like a computer) really needed a wide range of specific voltages, it could stick with its old-fashioned AC power supply.
If you’re not going to do it at every AC outlet, how do you decide which outlets do get them? Do you do it at construction time or on an add-when-needed basis? There’s a large stock of buidlings that only have AC wiring and outlets now.
Also, it sounds like this could lead to even more ‘vampire power’; any AC-DC in-wall converter will be drinking power all the time, even when nothing is plugged in and in use, unless you build a switch into it (more expense)
Your overall question has a number of answers, but just for one – the “brick” you so despise is a great invention. Electronics can be made the same for every country in the world, then shipped with the right brick for that country’s voltage and plug shape. Much cheaper from a manufacturing standpoint.
Electronics have been powered internally by different voltages over the years. If my house was wired in the 1950s according to your DC proposal of multiple voltages, it would probably have AC of 12.6 volts (for tube filaments) and 300 DC volts for plates in some radio devices. Think of how useless that would be today. Thank goodness I can plug in today’s computer and run it on the same 120VAC power supply my house was wired for in the 1950s.
Its still expensive as you will need twice as many outlets and wiring for both your 120ac and 12vdc. A lot of good that 12v will do for a 48v phone.
The brick as pay per item, so it makes buying a home cheaper and it comes with different voltages and connectors. 16v for my laptop and 6v for my flashlight or 4v drill.
>bet the designers could make do with a smaller set of voltages.
Yeah now that 6v flashlight needs a, you guessed it, brick to step down the voltage from the 12 house feed. Pot meet kettle. Not everything will run at 12v. Im not going to wait 4 hours for my laptop to charge instead of 1 because of low voltages. Im not going to lug around both DC and AC bricks because I dont know what crazy scheme the owner of the house or hotel will have when Im traveling.
Not to mention most of these bricks for higher end goods do both 120 and 220 volts, so I can travel internationally and only use a basic adapter if need be.
>Electronic devices use a wide variety of voltages because they can
A 8v processor or electric motor doesnt require that voltage because "it can.’ Its a requirement in the design.
My 1950’s style doorbell runs on DC. There’s an AC wire that runs to a small DC transformer in the basement just beneath the front door. But when you get right down to it, what’s the difference between that and a wall wart?
If you assume that electronic companies settle on lets say 12 vdc.
Either the utility provides you with both AC and DC, which will increase your bill. Or each house will have to have built in a converter. And the house will have to have an ac and dc power distribution system, which will require much more wire and labor to install. This would be on new construction. On remodeling or older homes it would be a major issue.
The US uses 240/120 systems, Europe O be;oeve uses 220, most computers have a switch on the back.
It’s pretty much a “It’s works. Why change it? Just for cosmetic reasons?” While in the end DC might be more convenient, it would be very difficult to force every electronic device to use a certain DC voltage when they’ve been able to use whatever voltage is necessary now. Heck, it was hard enough trying to force people to switch to their TV’s to HD.
It really is more work for everyone involved, and, as some have suggested above, the benefit is pretty small. I mean, if you don’t eventually get rid of any of the AC line, then all you are doing is making the wiring of a house more complicated. And if you do get rid of it, you’re forcing the 100+ million houses in the country to be rewired. And people don’t like to be forced to spend money.
Tesla won that AC/DC battle for very good technical reasons. Nothing to do with 120v per se; the US would have been better off with 220-240v like virtually everyone else.
You think it is a good idea to bury an electronic device inside the wall just to keep it out of sight? Really? So when one fails you have a major remodeling job? (Not to mention that adapters are all different in voltages, current and other characteristics like whether they are stabilised, limited, protected, etc. And many are low voltage AC anyway.
This thread points out there might be a reason to include the adapter inside the device being powered, not in the wall and many devices do just that. The reason many do not is quite simply that a device which only has very low voltage inside it is subject to fewer safety rules than one which has mains voltage inside. So you can make the brick power supply to those standards and not have to make the entire low voltage device.
It’s really a chicken and egg type problem. Electronics manufacturers can’t change their product designs because there is no universal DC supply standard and nobody will make in-wall AC-DC supplies because electornics are not standardized enough.
But I do see a light at the end of the tunnel. As low-voltage LED lighting becomes more widespread, I can easily see home builders begin to wire houses for DC. Then, electronics manufacturers can piggyback on whatever standard is adopted for LED lighting.
I gotta say, most of these objections seem pretty picayune.
By considering what makes sense? The outlets that are placed to power your refrigerator or washer/dryer probably don’t need an associated DC outlet. The outlets in the office probably do.
Either-or. Construction time seems to make the most sense, but whatever. Does it matter?
There are also things called “powerstrips”, which have an AC plug at one end and a line of AC sockets at the other. These are useful for situations where the building does not have enough AC sockets where they’re needed. Do you see where I’m going with this?
You got a source for this? It’s been a long long time since I studied EE, but I believe all of these power bricks start with an AC transformer. If there’s an open circuit on one side of the transformer, it shouldn’t be drawing any current. I’m betting that even if I’m mistaken about this and some power is consumed by an AC-to-DC power supply even when it’s not connected to anything, the quantity is negligible.
Having a standardized DC outlet doesn’t change this… in fact, it makes it even simpler. All of these devices that have multiple bricks for different locales terminate in a connector that expects a particular DC voltage. If that voltage were available at the wall, then instead of shipping a brick, the manufacturer only needs to ship a cord. If some locales don’t have that available, the manufacturer can fall back on the brick.
You’re looking at it backwards. I’m certain that there have been engineers working on AC powered devices who have, at times, wished they had different voltages available, but because 120VAC is all they had to work with, they made do. DC, on the other hand, being unstandardized, has resulted in wide varieties of devices using different voltages. If a standard set of DC voltages were available, we’d see more devices using those standard voltages and less variation.
Well, you got me there… adding DC outlets to the home would increase the cost of a house, no question about that. For a particularly inexpensive home, these costs might rise as high as one tenth of one percent of the total costs… but I doubt it.
Yes, because flashlights need to work on 6V power. 5V (the potential between a +5 rail and a ground rail) will not do, nor will 7V (the potential between a +12V rail and a +5V rail). Flashlights need exactly 6V to work, it’s the first thing they teach you in electrical engineering school. If you tried to make a flashlight that worked on even a single volt more or less, a plague of locusts would overrun the land.
I do not think it means what you think it means.
So plug in your damn brick. Why do you believe that I proposed eliminating AC?
Oh yes, and had the engineers been handed design requirements such as “must work on 12VDC”, they would have been stymied. Flummoxed. Right? :dubious:
Who said it would?
There’s more than consmetics involved. Underneath my desk is a rat’s nest of a dozen bricks and four powerstrips, necessary because the AC-to-DC conversion needs to happen 12 times instead of once. With a DC outlet standard, devices could be built to daisy-chain power, so you could plug one device into the next, rather than needing to run every device to the wall. (In theory this could be done with 120VAC but it’s much less practical because of the size of the wires necessary to safely carry it.) I’m betting there would be efficiency improvements from doing the AC-to-DC conversion on a multi-device scale, too.
The two situations are not parallel… and in fact HD adoption was quite high long before people were forced to adopt it. But we’re not talking about consumers, we’re talking about device manufacturers, and historically manufacturers have been quite eager to adopt standards, and with good reason: using standardized components saves them money.
You could make the same argument about wiring a house for cable. Or telephone. Neither of them eliminated the AC line, either, and they made house wiring more complicated. But that wasn’t all they did, any more than a DC standard would do nothing but make wiring more complex without eliminating AC. And it didn’t matter that wiring for cable or telephone didn’t eliminate AC, because they were intended to serve different purposes. Just as wiring for DC would serve a different purpose, too.
Please read what I wrote more carefully. I didn’t say that 120V had anything to do with the victory, all I said was “…and 120VAC became the standard.” Which it did. A different voltage would have worked as well; a DC voltage would not have.
No, not “just” to keep it out of sight. For several other reasons, one of which is to keep it singular rather than requiring a dozen devices that all do the same thing.
An AC-to-DC power converter is a very simple solid-state device which hardly ever fails. External power bricks, on the other hand, can be stepped on, have their prongs bent, and above all, lost.
Really? Name some.
If you put it inside the device, you’re still having one per device rather than one shared among many devices.
Internalizing the power supply also increases its the device’s weight and size, makes it less internationalizable, and presents problems for heat dissipation.
The solution to the chicken-and-egg problem is to have simple powerstrips, like existing AC-to-DC powerstrips, that have a row of DC outlets rather than AC outlets, which would allow people to take advantage of DC outlets with no rewiring or remodeling required.
This may well be the killer app that eventually leads to DC in the home, but LED lighting will have to come down in price by a significant amount before there’s hope of that happening.
Yes, and don’t forget in automobiles as well, most of which have a 12VDC outlet, often occupied by a cigarette lighter but there are plenty of devices designed to take advantage of the availability of DC in the automobile.
Actually some places are supplying AC and DC outlets. Last time I had to travel both the airport, and the hotel I stayed in had “charging” USB ports next to the AC outlet. Let you charge all those accessories without having to drag out the brick.
USB standard will not work for everything, but it does a good job for alot of stuff. You don’t need an in-wall converter for it. Just plug it into your computer.
Yes, I should have mentioned this. USB has made good strides towards being a standard power connector, to the point that when I purchased a Bluetooth helmet I was irritated that it had a proprietary power connector (5VDC, yet). But as you say, it’s not suitable for many things. The only voltage it supplies is 5V, at a maximum of 500mA. (This is rising to 900mA in USB 3, which will be better but still unsuitable for many applications.)