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Low Voltage Power Distribution?
thesp asks: "As I look around my apartment, I am continually struck by the plethora of high-voltage AC to low-voltage DC power adapters I use to power my various devices. At a recent estimate, around 30% of the power consumed in my house is via these adapters. From my laptop to my digital music player, and from my mobile telephone to my PDA, each device is down-converting its own power through its own adapter. Double this number to include my partner's devices. Many of these run hot, and are inconvenient to remove/replug to conserve power and outlets. Does Slashdot know of any moves to standardize power delivery to such devices, or of hobby/home-brew projects to distribute low-voltage power from a central power converter? Alternatively, are there reasons as to why this would not be a simple and effective solution to the proliferation of wall-warts."
"On closer examination, these adapters seem to fall into four major categories, 7V, 5V and 3V, with the most common being 5V. Despite this, each device uses a different DC plug configuration, which makes efficient use of adapters difficult. It seems to me that, just as AC power is standardised, portable electronics power requirements should be also be standardised, with a standard wall outlet and car outlet at, say, 5V, and a standard device cable and interface. Electronics manufacturers would save money on power adapters, and the consumer would have the cost of the converter written in to home construction or automobile construction costs. No longer would we have to lug 4 separate power adapters with us on an overnight business stay to power our various equipment."
Article is a dupe...original discussion can be found here, which amusingly enough, is itself a dupe of this discussion. Even more amusing is the fact that all of these submissions share the same editor.
Way to go, Cliff...a dupe hat trick. Zonk has nothing on you.
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~ |rip/\/\aster /\/\onkey
Good luck distributing 5Vdc over any distance.
Just a hunch, but my best guess is that we will slowly see the USB power "feature" become the standard for (very) lower power devices. You can already find cell phones, mp3 players, cameras, PDA's and a few misc. accessories that are USB powered - and I've seen USB "power only" hubs available for charging these devices while you're on vacation.
The natural next step is for more devices to switch to USB power. Routers and hubs and other things that are typically "near" a computer come to mind.
1. You can't (simply) transform DC voltage to a different voltage. This can be done very efficiently with AC. The 120v to 5V (or whatever) in your power supply is done before the AC is rectified to DC.
2. Low voltage == High losses, esp. with DC.
TODO: Something witty here...
Actually, while there is no standard, I've definitely noticed that manufacturers are tending to use the same kind of plugs for the same voltages more and more. It seems like everything I've got that's 12VDC has the same plug, and I really mean everything, from my Radio Shack A/V transmitter unit, to the Intel webcam (from long long ago) that I connected to it, it's all the same size barrel connector. Obviously it's not standard but it's getting better.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Power is transported at high voltage to diminish losses in cables, any long-range transportation with low voltage is inherently lossy.
The 12VDC cigarette lighter plug is a de-facto standard. Redo all your devices to use 12VDC with a simple voltage leveller - eg, a zener diode followed by a 5V regulator IC - and then standardise on cigarette lighter sockets throughout the house.
Standardized connectors. It's one thing to have a variety of devices that use different voltages, but having a variety of 5V devices each of which uses its own style of plug & jack defies all common sense.
For that matter, even on devices that use the same voltages and connectors, there is no standardization for polarity! Is it really that difficult to agree that ring is negative, and tip is positive, or even vice-versa?
Adaptor lock-in is just plain obnoxious.
There's a Starman, waiting in the sky / He'd like to come and meet us, but he hasn't got the time.
3-phase AC is much more easily converted to DC, and also allows for simpler and more efficient motors. (So it is also ideal for things like air conditioners, refrigerators, furnaces, and such.) Overall, I think the advantages far outweigh the cost of an extra conductor, and it is unfortunate that it isn't more common outside of commercial settings.
IANAP, and I'm not good with anything hardware-related, but... isn't one of the reasons that you'd need thicker cables for lower voltages? When the voltage goes down, the current goes up, and thinner cables would melt. I distinctly remember being told that that's at least part of the reason why long-distance power cables uses voltages in the hundreds of kV range.
:) (Of course, don't do this at home, at least not until you know what you're doing and how to do it safely.)
There's also neat experiments you can do in school with transformators - put a coil with, say, 5000 windings opposite of one with, say, 5, and you'll be able to quite literally melt nails.
quidquid latine dictum sit altum videtur.
If you have a cluster of devices of all the same voltage at the same location, then it would make sense to have a common power supply. Otherwise, it makes more sense to use a higher voltage for distribution purposes. The electric utility generally brings power down to your street in the 11kv to 14kv range, and a permanent transformer drops it down to the 120 to 240 volt range you get into your home. Distributing power at 240 volts would not even be considered beyond at most 100 to 200 meters. Every time the voltage goes up by 2, the distant can go up by 4 since the current is cut in half, which means the voltage drop is cut in half, which has even less effect on twice the voltage. When they run the voltage at 50 to 100 times as much, they can deliver power over substantial distances. Cutting voltage to 1/10 as much means you can deliver the same amount power to only 1/100 the distance.
Incandescent lights actually work better at lower voltage, especially for bulbs of lower wattage. Normally a low wattage bulb requires greater resistance in the filament. That means the filament must be longer and/or thinner. That means it is more prone to mechanical shock damage. It also has to run at a lower temperature, producing a more orange light (which in some cases is what is desired). The lower temperature wastes power since more is emitted as infrared instead of usable light. By changing the bulb design to a low voltage like 12 volts, the same power level can have a shorter, thicker, hotter filament, which can run more efficiently, even making up for the loss involved in having a transformer converting the voltage.
The reason I mention low voltage lights is to point out that they are rather standard at 12 volts (a few use 24 volts), yet transformers are generally located close to where the lights are, rather than in a central location which would require the power be distributed in low voltage form. If a central low voltage source were practical, low voltage lighting would be the first to use it. But with very few exceptions, they don't do it this way.
I once considered running lots of stuff in my house on lo
now we need to go OSS in diesel cars
Yeah, standardization is just a Satanic conspiracy.
Like that one time, Satan decided that all railroad tracks should be the same distance apart, so that every train could work on every track, so people would ride around on the trains, which sucked out their immortal souls.
Oh, and then they standardized screws and bolts, so that you didn't need to carry around one screwdriver for each screw manufacturer, which put some screwdriver makers out of business. Their children were thrown out to starve in the streets. Satan watched, and he laughed.
And home power standardized on 120V AC, so that everyone could plug their computers in anywhere, allowing Satan to tempt everyone with porn.
Don't even get me started on what Satan thinks of the USB 2.0 interface.
You want the truthiness? You can't handle the truthiness!
Have we all forgotten what companies charge for $2 wall warts? I've even seen a Brother label maker wall adapter that has an odd voltage (7.3v), odd amperage, a non-uniform center pin, and inverse polarity. They go overboard with the accessory business. This particular wall wart costs $24 at OfficeMax. Then another $18 for the label cartriges. Then there are the power-hungry devices like cameras that don't come with a wall wart at all (computer controlled, time interval shots). Us mere mortals have to guess when we go down to the store what size connector to use. Face it, the money is in the connectors. If they can find a cheap way to make you use a new connector and charge outrageous amounts of money for adapters, they will. Cheer up. Atleast your iPod doesn't have any custom connector on it. Oh, wait. Never mind.
So maybe a better solution would be a single brick with different connectors for different voltages - this would conform to ISO standards. Then they could just pull the old printer "this box contains no cables" trick, and it would reduce the number of unused transformers out there eating away at copper supplies.
I've been considering this since the last time this was on slashdot. While over any real distance DC is inefficient for power transmission, the inside of a rack might benefit. I figure with a large UPS and some sort of redundant power-supply, you could feed a number of computers with 12V lines and a picoPSU-120 12V DC-DC ATX power supply. Has anyone tried this yet? I've never worked with high-density hardware (like blades) but I'd imagine that each blade is certainly not using its own PSU.
what the hell is a 'junk character', anyway?
As some may know, this standard provides for approximately 15W of power at a nominal 48V. See http://en.wikipedia.org/wiki/Power_over_Ethernet for an introduction.
We can reuse and/or extend the probe/negotiation phase to provide additional power levels, let's say up to 150W (approximately 4A max).
Advantages
1. Enhanced safety because unused outlets provide a high-impedance (power-limited) source2. Unified power connector for low-voltage/low-power appliances
3. DC outlets could be provided either through centralized power controllers, plug-in power strips, or wall-box mounted controllers
Disadvantages
1. Power controllers will always waste power2. Centralized power controllers will require point-to-point wiring
3. Significant additional component cost compared to linear regulators
4. Modest additional component cost compared to DC/DC regulators
Some device manufacturers won't want to support this because it would increase the size of the in-device charge controller. For example, I have an iPod, a Treo, and a Bluetooth headset. All support a wide range of input voltages for charging (this implies an internal DC/DC regulator), but none support an input voltage higher than approximately 15V. Designing a DC/DC regulator that supports 48V requires more robust (therefore larger) components. In addition there will be an in-device power controller to communicate with the central power controller. Fortunately this last part is already available for 802.3af applications.
You heard it here first.
I wired it all up and: 16 watts again.
It was exactly the same between using all the individual supplies and using the centralized PC supply. Admittedly, 16 watts isn't exactly ideal for a 90-watt supply (hmm ... maybe I'll try a smaller source supply ...) but at least I get a nice solid 5 volts going to the USB hubs.
If you get one of those Kill-A-Watt (or equivalent) meters, it's a great help in figuring out what you might want to put on a power strip and switch off manually. My stereo components when off drew a total of about 50 watts so I started switching them all off. The battery chargers in the basement used about 10 watts total, but since I was only using them to keep batteries topped-off, I could reduce it by putting them on a timer and running them an hour a day instead.
In essence, do your experiments and figure out how much you'll really save.
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Recently, I did my own experiments on low voltage power distribution, mainly because I plan to install a large scale solar power charger with a lot of Pb accumulators. The best result is: 24V/35kHz AC home backbone, with a lot of switching voltage changers on rooms, those provide multiplicity of output voltage of 5V, 6V, 9V, 12V DC as well as 230V/50Hz for UPSes and consumer grade devices. LED lights are quite fine with low voltage already. It will take some 6-9 years to return the costs, but only because I design and build the circuitry myself.
Unlike DC or 50/60Hz AC, 35kHz (or even more) AC requires a lot cheaper wiring, very small transformers and have very little losses.
There you are, staring at me again.
A question of DC vs AC for electricity distribution was the subject of conflict between Edison an Tesla in 19th century. You can read more on that:
/ >
<URL:http://en.wikipedia.org/wiki/War_of_Currents
Yes there is. A 1200W microwave draws 10 amps at 120V. At 12V it would draw 100A. You have any idea how thick the wire has to be to handle 100A?
Conclusion: the Empire squashes the Federation like a bug. Accept it.
Edison, for some unknown reason, hated Tesla and tried to kill his ideas of AC power distribution. He apparently had the (AC-powered) electric chair created as a PR stunt so that people would know that AC power was being used to kill people -- but it turned out to be relatively difficult to reliably kill people with AC power because an AC charge turns out to be an impromptu defibrulator, so you essentially have to cook your victim.
DC on the other hand, causes the heart to go into a constricted mode which is harder to recover from. I was taught to always handle AC with one hond only, if at all possible (to avoid a possible circuit across the heart).
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