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Low Voltage Power Distribution? 237

Posted by Cliff
from the wall-wart-motel dept.
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."
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Low Voltage Power Distribution?

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  • by nathanh (1214) on Friday February 17, 2006 @08:19PM (#14746452) Homepage
    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.

    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.

  • Re:A few reasons... (Score:5, Interesting)

    by plcurechax (247883) on Friday February 17, 2006 @08:51PM (#14746620) Homepage
    Grandparent comment: You can't (simply) transform DC voltage to a different voltage.

    Parent comment: Actually transforming DC is way cheaper and more efficient than transforming AC...

    You can simply transform AC voltage using the simple and low-tech electronic device called a transformer. Just a bounce of wire wound a metal core.

    I assume you are referring to solid state DC-DC converters which can be (far) more efficient (less waste, less heat) than a linear power convert, but they are not simplier.

    Distribution to businesses and houses will remain AC because AC is easier to distribute over long distance. High power (wattage) is easier (more efficient) to distribute (power transmission) with a high AC voltage than high voltage DC. This goes back to the famouse Edision vs. Telsa fight over DC / AC power distribution near the previous turn of the century.

    It is possible to distribute low voltage AC (say 12 VAC) within a house for electronic usage. Using high efficiency power supplies (i.e.: don't waste a lot of engery producing wasted heat as a by-product of the conversion process) such as found in newer laptop power supplies would be another positive step. Otherwise I don't know if we'll see the elimimation of inefficient wall-warts.

    To the submitter: Don't forget about electric applicants that are high power (e.g. 1000W or higher), in my case that includes: electric force air heating, electric stove (aka range/oven) for cooking, air conditioning, refridgerator, microwave, toaster, hair dryer, and coffee maker. These devices would not work (easily) at a lower voltage without a large increase of current. Remember or learn Ohm's Law: Power (Watts) = Voltage (Volts) times Current (Amperes).
  • Cable thickness (Score:3, Interesting)

    by slavemowgli (585321) on Friday February 17, 2006 @09:17PM (#14746771) Homepage
    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.

    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. :) (Of course, don't do this at home, at least not until you know what you're doing and how to do it safely.)
  • Re:Ohm's law (Score:3, Interesting)

    by Mattcelt (454751) on Friday February 17, 2006 @09:37PM (#14746862)
    I don't know - according to the chart, a #10 (6mm^2) wire (which, while by A/C standards is huge, isn't really that big at all) will get you 216 feet at 10 amps. Most of the DC devices we use wall-warts for an average of no more than 1 to 1.5 amps, so you could theoretically wire a room for low-amp DC with a single cord.

    If you wire your house intelligently - converting your A/C to D/C in a central location and radiating each a line to each room from there - only very large houses will have a throw distance of more than 200 feet. (Remember that the chart accomodates the return trip already.) This makes using D/C internally seems like a very feasable proposition.

    I think the biggest pitfall is making sure you don't deliver too much (or little) current to the devices you plug in. It would be very bad to deliver 10 amps to a device which is expecting 300 milliamps, or 300mA to a device expecting 2A.

    There's a reason we feed A/C to houses. That's not the same reason we feed A/C within houses.
  • by mysidia (191772) on Friday February 17, 2006 @10:23PM (#14747071)

    Ok, that's all well and good, but why not use a higher voltage DC to the outlet then? Say 50-100 volts.

    Perform this conversion where service enters, along with stabilizing the power, filtering any noise, to protect sensitive electronics, etc, the resistance down the household wiring should be low enough that the heat waste on the wire is small, so that the convenience matters, and high voltage offers some flexibility.

    Then have each kind of wall outlet include components to reduce the voltage to fit the requirements of the device that will be hooked into it; or have the device contain a simpler adapter to regulate the voltage down from the standard high voltage.

    I.E. you might have a plate on your wall that has a few generic sort of connector ports, such that the plate is designed to plug a whole outlet panel into. And the kind of panel/faceplate you choose to plug in determines how many ports you get and what voltage and amperage each port is allowed.

    In theory, you might even have a protocol for the device to signal the modular port to tell it what voltage to use. (The outlet detects when a device has initially been plugged into it and starts at a standard 3v, until the device confirms a voltage change or requests the outlet be turned off for a certain duration, or something like that)

    The cost of transformers may be cheap, but once you've got hundreds of devices that have to use them, because almost everything requires DC, it seems like a huge waste --- not necessarily so much of electricity, but of the natural resources and work required to build the devices.

  • by siegesama (450116) on Friday February 17, 2006 @11:39PM (#14747373) Homepage

    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 [mini-box.com]. 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.

  • by Anonymous Coward on Friday February 17, 2006 @11:45PM (#14747392)
    120V AC current, if you get shocked, hurts like a B#TCH, but just leaves your ego bruised. 120V DC current will instantly cause your heart to stop.

    you are stupid and misinformed.
  • by Hardwyred (71704) on Saturday February 18, 2006 @12:37AM (#14747548) Homepage
    Plus, 120V AC current, if you get shocked, hurts like a B#TCH, but just leaves your ego bruised. 120V DC current will instantly cause your heart to stop
    actually that is not entirely correct. 10ma of current across your heart period will cause serious issues be it DC or AC. In fact, DC is actually safer then AC when it comes to turning yourself into a light bulb. When the power grid was first being created, DC proponents used to fry small animals to prove that AC was unsafe while DC would do no damage. Granted, a DC power grid would need a power generation station almost every 3 blocks.
    As a side, don't be fooled, 110v AC can kill you dead just like 400v AC can. It's all about your bodies internal resistance mostly due to moisture and the path the power takes.
  • by jolshefsky (560014) on Saturday February 18, 2006 @01:14AM (#14747672) Homepage
    I've got a Kill-A-Watt tester and I thought the same thing about my wall-warts for things like USB hubs, my PDA charger, cell-phone charger, etc. I plugged them all into a power strip and they use 16 watts total. I then wired up an empty PC case with a switching supply to power most of the devices. I just used diodes to drop 0.6V at a time from the various taps (12V, 5V) to get to the levels I needed for the oddball devices (the few that need something other than 12V or 5V).

    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.

  • by Maljin Jolt (746064) on Saturday February 18, 2006 @02:16AM (#14747884) Journal
    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.

  • by Anonymous Coward on Saturday February 18, 2006 @03:55AM (#14748213)
    Depending on conditions, your body actually has a decent amount of capacitance.

    DC will cause a charge to build up, increasing your resistance and shutting down current flow. So you feel an initial shock when the current is connected and then nothing until it's cut off, when you get a second shock.

    AC, OTOH, does not cause a charge to build up because the polarity is constantly changing. As a result, you feel shocks constantly. (twice per cycle)

    I would be a little surprised if that built up charge had some significant detrimental effect on your nervious system, but not too surprised.

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