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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? More

Low Voltage Power Distribution?

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  • Low Voltage DUPE distribution? (Score:4, Informative)

    by TripMaster Monkey ( 862126 ) * on Friday February 17, 2006 @07:53PM (#14746310)

    Article is a dupe...original discussion can be found here [slashdot.org], which amusingly enough, is itself a dupe of this [slashdot.org] 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.

    • Re:Low Voltage DUPE distribution? (Score:5, Insightful)

      by pjotrb123 ( 685993 ) on Friday February 17, 2006 @08:54PM (#14746633)
      On Topic:

      Just about every device needs power in the 5 to 20 volt DC range to operate. No matter if it is 25 days old, or 25 years old.
      In the old days there was a transformer and an AC/DC rig to achieve this. And a big fat Power switch, to connect the transformer to the high voltage AC supply.
      This used to be all built into the device - think: big old fat radio, stereo, or TV. Because it was easy and convenient, because it was a big fat apparatus anyway.

      And ON really meant ON, and OFF meant OFF.

      Then came Stand-by mode. OFF suddenly meant: a little bit ON.
      Goodbye to the big fat Power switch. Enter the apparatus that consumes power all day long.

      Then, everything started shrinking, to become portable, "personal", etc.
      So now we have the i-Pod, mobile phone, MP3 player, laptop computer, Discman, PDA, GPS. "We" want to take them wherever we go, so they have to be light, Battery powered, nobody wants a big heavy transformer inside of course. Enter thousands of battery chargers. And because we are lazy, we keep the chargers plugged in, all year long.

      It's a trend. Not one that I necessarily like.

      Why are there no chargers that we can keep plugged in, with true mechanical ON/OFF switches?

      • Well, you can get that with a power strip, but, you're right, people are lazy. And, sure, it's inconvenient to use your car when you have multiple devices to charge, not to mention that many cars are not setup to give you a charging port these days. Maybe the best course is to avoid use of these portable devices, and pay attention to the real world around you.
    • So did any of these prior discussions come up with any useful results?
    • Have you ever considered that you might be spending way too much time here? It was news to me. Of course I have a life and a job and family and friends and a local bar, so maybe my priorities are all screwed up, and I should really be spending my time combing Slashdot for dupes.
      • I pay a lot less attention to the Ask Slashdot questions than Cliff does, yet I remeber seeing this exact retarded question at least twice before. Possibly a couple times before that. It seems to me that Cliff ought to be able to remember it, I mean it's his job, and I'm just an occasional website visitor.

    • Re:Low Voltage DUPE distribution? (Score:5, Insightful)

      by Jozer99 ( 693146 ) on Friday February 17, 2006 @09:52PM (#14746928)
      The problem is that wires have resistance, which wastes power turning it into heat.  The amount of power wasted follows this equation

      % Power loss = Power * Resistance / Voltage Squared

      So, with a length of wire that has a resistance of 10 Ohm, with 120V at 1 amp (120W), you lose

      %P = 120W * 10 Ohm / 120V^2

      or 8.3% of the total power, about 10W.

      If you were to run the same amount of power over a 5V line (120W, or 24A), you would lose

      %P = 120W * 10 Ohm / 5V^2

      or a whopping 48% of your power, about 58 Watts.  So you see, having all those transformers is actually more efficient.  This is the reason why we have high voltage lines.  The power that comes into your house is 120V, but if it were to be 120V all the way from the power plant 20 miles away, most of the power would be lost.  So, power is sent on high tension wire at about 200,000V, then steped down to several thousand volts on main streets, then to less than 1,000V for your side street, then finally transformed down to 120V (or 240V if you live in some countries) right before it goes to your house.  This minimizes loss.

      On the other hand, if you have lots of devices that all use the same voltages right next to eachother, it can be efficient to get a single transformer.  Musicians (like me), who have dozens of effects pedals that run on 9V, can buy special power bricks that power up to 6 devices.  You can buy these from musician's supply stores (like musiciansfriend.com).  You can even make one from parts at radioshack.  You have to make sure you have a beefy transformer, then wire on several plugs in parallel.

      If you want more info about power line waste, there is good info at:
      http://www.bsharp.org/physics/stuff/xmission. html

      • 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

      • AC and DC have different characteristics, too. Depending on the properties of the wire, the same piece of wire may have a noticeably higher resistance when AC flows through it than that some wire would have when AC were flowing through it, because high frequencies of AC avoid travel through most of the wire's cross-sectional area. This can be a substantial increase in resistance, one disadvantage of using AC.

        See Wikipedia: Skin Effect [wikipedia.org]

        • Yes, but this does not outweight the advantage of better transformers for AC. Back in the early 1900's, there was a hugh battle over whether our power infrastructure would be AC or DC. Many great minds had a huge stake in this debate. Eventually, AC won out, mostly because it was easier to tranform to higher or lower voltages, making sending it long distances much more efficient.

          BTW, Tesla was the oddball, he was all for wireless electricity. Sadly, his proposed wireless transmission device, the tesl
    • Complaining about dupes accomplishes only one thing: it generates far more duplicate traffic in the form of repetetive dupe complaints than the dupe articles themselves.

      Dupe complaints are hypocrisy.

  • Ohm's law (Score:3, Insightful)

    by s800 ( 940543 ) on Friday February 17, 2006 @07:54PM (#14746313)
    Good luck distributing 5Vdc over any distance.
  • I read somewhere about new poweroutlets that have "Universal AC/DC Adapters" built into them. They looked kind of neat, they had your regular outlets, and a retractable DC cord with multiple connectors on it. That would be much more efficient than distributing 5V around a house.
    • > and a retractable DC cord with multiple connectors on it

      And exactly how long will it take till someone sues whoever installed the outlets because he fried his expensive gizmo by using the wrong voltage, polarity, connector, ...? Sounds like a very stupid idea to install those outlets in the houses of typical dumbheads.

      Greetings from 230V-AC-land.

  • IMHO, USB will become the de facto power standard. (Score:4, Insightful)

    by WoTG ( 610710 ) on Friday February 17, 2006 @07:58PM (#14746339) Homepage Journal
    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.

  • A few reasons... (Score:4, Informative)

    by Tyler Eaves ( 344284 ) on Friday February 17, 2006 @08:01PM (#14746359)
    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.
    • I was under the impression that it, anyway, is usually more efficient to use a quickly oscillating crystal and then gate that to on and off. A capacitor construction after that will "smooth out" the square-wavish original signal. This is, for example, how you can set the DC voltage to your CPU. In contrast, getting a good efficiency in a simple transformer is actually kind of hard, if you want it to handle any impedance/DC load. If it's good at full load, it will waste energy if nothing is plugged in. If yo
      • Completely wrong. An ideal transformer has 100% efficiency. A real transformer has some nonideal effects, but a well-constructed one generally has >98% efficiency. A REALLY good switching power supply can get maybe 90% efficiency, in reality it's more like 60% with typical supplies.

        The thing you are noticing (adapters getting warm) is losses from inefficient transformers. A switcher is less efficient when it's on, but it can shut off completely with no load. A cheap transformer will waste a lot of p

    • Re:A few reasons... (Score:3, Informative)

      by amorsen ( 7485 )
      You can't (simply) transform DC voltage to a different voltage.

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

      The 120v to 5V (or whatever) in your power supply is done before the AC is rectified to DC.

      The 120V to 5V transformation is done by treating the AC as a fluctuating DC signal, and doing DC conversion. It is less efficient than proper DC to DC conversion, but not much, and it's way more efficient than using a traditional transformer.

      It would be very nice t

      • 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).
        • A 12VAC bus would be pointless and stupid. You would be wasting just as much power as with DC, without any benefits whatsoever. In fact, the transformers would cost more because they would require high-current windings on both sides, with more turns on both to achieve the required inductances.
      • It would be very nice to have say 48V DC around the house.

        Well, that pretty much defines the Power over Ethernet niche (at least for smallish values of Power).
      • Even if it were cheaper to regulate/switch/whatever DC than it is to transform, rectify, and filter AC (a notion that the retail market seems to disagree with), you seem to be missing two very important reasons why manufacturers like to use external AC adapters:

        1. Small form factor devices. A cell phone WITHOUT a high-ratio DC-DC converter will always be smaller, lighter, and generate less heat than one WITH a high-ratio DC-DC converter. This is obvious. Therefore, under the suggested plan will either r
        • I don't want high-current 48VDC around the house. That stuff will hurt you, and tends to hold on in ways that AC does not.
          I think you got that backwards. Why do you think AC is used in electric chairs and for electroshock therapy, but not used for electric fences?
    • 1. You can't (simply) transform DC voltage to a different voltage. This can be done very efficiently with AC.

      That is pure nonsense. You are perhaps confused with power transmission; DC transmission over long distances is inefficient compared to AC.

      • PS: and the reason why is because it's easier to step AC voltages up, and higher voltages have lower losses due to lower current.

      • Wrong! Google HVDC... there's plenty of DC power distribution (read: across many km).
        • Wrong! Google HVDC... there's plenty of DC power distribution (read: across many km).

          HVDC is only used in rare situations, such as undersea power cables where capacitance works against AC. Power transmission across land is almost without exception HVAC.

          • The Pacific Intertie that supplies southern California with power from dams along the Columbia in Oregon is overland HVDC.
      • You're both talking nonsense: DC-DC conversion is standard technology, it's plausible that there are more DC-DC converters in your house than 50Hz transformers. Your computer power supply converts 450V DC to 5V DC.

        http://en.wikipedia.org/wiki/Switched-mode_power_s upply [wikipedia.org]

        DC is more efficient and more useful over long distances because you don't have a) inductive losses, b) capacitive losses, c) no need to synchronise phases at both ends. On the downside, you need an inverter at each end. AC wins in the co

    • Re:A few reasons... (Score:3, Informative)

      by cr0z01d ( 670262 )
      1. Yes, you can simply transform DC voltages to different voltages. They're called switching power supplies, and you find them EVERYWHERE. You get them off the shelf or build your own, they're cheap, they're light, and they're efficient (90% is not uncommon). Your computer does NOT step down AC to a low voltage then rectify it... it rectifies it to high voltage DC, then steps it down.

      2. Losses have nothing to do with AC or DC, it's just a function of current.

      Let's say you've got 12 AWG wire in your house

      • Re:A few reasons... (Score:3, Informative)

        by Jeff DeMaagd ( 2015 )
        AC transformers are even more efficient than DC-DC converters, 99%+ efficient is not uncommon. 90% efficiency on DC is available, but for the cut-throat consumer electronics market, the extra cost means that they go with cheaper units with maybe 70% efficiency.

        There are still some nearly unsolvable problems with higher voltage DC as a distribution system. For one, arcs start easier on a 48VDC system, and arcs are harder to break because current can just follow the ionized trail and is easily sustained. T

  • High voltage (Score:2, Insightful)

    by JFbasta ( 722882 )
    Power is transported at high voltage to diminish losses in cables, any long-range transportation with low voltage is inherently lossy.

    • True, but this is about distributing low-voltage DC throughout the house, NOT transmitting it long distances. You'd still want high-voltage in the house for high-power applications (electric dryer, AC, electric stove), but low voltage DC would be better for most electronics, maybe even for lighting if you switch over to LEDs or other "cold" lighting, where you don't need all that excess power to produce heat.

      I've wondered about whether it would be possible to create a low-power converter that would take i

    • Re:High voltage (Score:3, Informative)

      by ralphclark ( 11346 )
      Let:

      P = power dissipation
      I = current
      R = resistance
      V = potential difference (voltage)

      We know that power is a function of power and current. For direct current,

      (1) P = V * I

      By Ohm's Law,

      (2) V = I * R

      Therefore

      (3) P = I ** R

      So power dissipation is proportional to the square of the current. Given a requirement to deliver some arbitrary amount of usable power to the devices you have plugged in, by (1) you know that if you halve the voltage you must double the current to deliver the same amount of power. But, by (

  • Standardised DC Power (Score:3, Interesting)

    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.

    • While that sounds like a nice idea, it's extremely wasteful.

      If your global supply is 12V, and you want to run a 5V device, you need to blow off 7 volts.. that's more power wasted than actually delivered to the load. Kirchoff's & Watt's laws will get you everytime.

    • Are you an idiot or do you not have a clue? A zener diode has to obey ohm's law just like anything else. Therefore, a 7V zener diode or regulator chip with an amp flowing through it (barely enough to charge an ipod) would be dissipating 7W, and the iPod would be receiving only 5W.

  • 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.

    I like the idea, but forget about it ever happening. Manufacturers have no incentive to standardize. I

  • 30 Percent? (Score:2, Troll)

    by Gothmolly ( 148874 )
    At a recent estimate, around 30% of the power consumed in my house is via these adapters.

    You're new here, aren't you. By "new", I mean, new to this planet. Apparently you have no idea how much a TV uses, or how much a refridgerator or microwave uses.

    So this article is a "tripe", and also has a stupider premise than the others. Thanks, "editors".

  • I'd gladly settle for.. (Score:3, Insightful)

    by murderlegendre ( 776042 ) on Friday February 17, 2006 @09:04PM (#14746697)

    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.

    • I continue to cling to the delusion that positive tip/negative ring is the standard, and everyone who does it the opposite way is backwards. Just imagining that this standard exists and is frequently violated makes me feel better than the idea that something so simple has never been standardized.
  • As others have mentioned, DC is simply not a good alternative as you need very large conductors to make losses reasonable. This being the case, the best alternative would probably be 3-phase power.

    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 mor

    • Re:Multiphase power (Score:3, Informative)

      by Skapare ( 16644 )

      DC does not require any larger conductors than AC does, for the same voltage and current. You must be assuming low voltage in reference to DC.

      Three phase is only marginally better than single phase for converting AC to DC. And unless the power supply is a very complex and expensive type, it will result in a high level of harmonics and a low power factor on the AC source due to the rectification cycles. On a large scale this could also overload the neutral conductor.

      Three phase is generally good for mot

      • DC does not require any larger conductors than AC does, for the same voltage and current. You must be assuming low voltage in reference to DC.

        Low voltage as in safe DC voltage. 120VDC is unsafe for home use. Start an arc and you can't stop it short of tripping a circuit breaker. The same arc on an AC system, 120VAC RMS, the arc dies before the zero crossing.

  • 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.)

  • Issues in low voltage power distribution (Score:3, Informative)

    by Skapare ( 16644 ) on Friday February 17, 2006 @09:23PM (#14746802) Homepage
    There certainly are some difficulties:
    1. There are a lot of different voltage needs I have seen, including: 3v, 4.5v, 6v, 7.5v, 9v, 10v, 10.5v, 12v, 14v, 15v, 16v, and 18v. Some things need (or can accept) AC, others need DC (some can take it filtered while most want reasonably smooth). It would be nice if the voltages were better standardized, but this is not always an option. And often where it is an option, it ends up being traded off with a loss in efficiency.
    2. Voltage drop is more dramatic at lower voltages. Given a specific current and a specific wire resistance, the voltage drop is a constant. Home wiring typically sees voltage drops in the range of 2 to 3 volts with high current loads, which is not much of an issue with 120 volts (less so with 230 volts). But at even 12 volts, that's a rather dramatic drop in voltage.
    3. For the same amount of power, devices at lower voltage use more current, which means even more voltage drop.
    4. Fault current can be an issue. If you have a lot of devices, the total current you might need could be very high. A power supply would need to deliver such current. A short circuit on a high current source can result in significant damage to everything from the power supply to the house. Surely you would fuse protect each branch circuit. The small "wall wart" power supplies have very small fault current as seen by the small arc if you short them out (don't try this at risk of blowing a tiny fuse they may have inside). But a power supply that can deliver 25 amps to a normal load can deliver much more than that under a short circuit condition, resulting in damaging arcs.
    5. A central power supply (or transformer if AC is all you need) is going to have its own level of power waste, anyway. While it can probably be designed with better efficiency, it won't really make up for what's lost in the wiring.

    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

  • The Pessimist (Score:3, Insightful)

    by Midnight Warrior ( 32619 ) on Friday February 17, 2006 @10:22PM (#14747069) Homepage

    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 [officemax.com]. 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 [foxnews.com].

    • Round the voltage to the nearest volt and go with that. The tolerances on those things are like +/- 40%. I bet the 7.3V adapter is putting out 15V when it's unloaded and 5V when outputting rated current. The odd voltage ratings are used to discourage the use of universal adapters, the device will always have a regulator inside.

    • 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.

      None of which should pose any trouble at all for a universal AC adapter. I run 6V devices at 4.5V, and vice versa with few side-effects. Any universal AC adapter will have a setting for 7.5V. Ditto for the amperage... it really doesn't matter as long as it's close, preferably slightly above what's necessary. Polarity is a complete non-issue. Finally, the connec

  • Buy one beefy transformer for your common DC voltages - start with 5 and 12 - at Radio Shack. If you are enterprising, you could also repurpose a PC power supply for this task. Then buy a couple of these [radioshack.com] adaptaplug extensions. For each device, buy the appropriate adaptaplug connector for that device, and a "y" connector [radioshack.com]. Use Y connectors and extensions to daisy-chain as many devices as you need to the appropriate voltage chain (careful not to go too long on the wires though), until you reach the current
    • If you've actually done this, you will find out what a horrible idea it is when you connect two of the devices together and set something on fire. It is a _really_ bad idea to do this, since most devices are designed to run from an isolated power supply. They often take a 20V power supply and use it to create two 12V rails, with the ground being the midpoint. Connect a single-supply device to this which uses 0V as its ground rail, and you will short things out.

      Just so you know, this is precisely why engi

  • I envy you if your devices fall into three major categories. I've been toying with the idea of building an equiptment rack with a few DC power buses for things like my DSL modem, TV antenna amplifier, mic preamp, router, various chargeable devices, etc. In addition to power, the rack would provide real power switches; many of my devices lack power switches. Since all the equipment will be in the same rack, transmission losses should not be great. Now, it may be the case that most of these devices can han

    • A quick glance around my house, in order by voltage:

      15v DC, proprietary connector (iSub USB subwoofer)
      12v and 5v DC, proprietary connector (USB hard drive)
      12v DC, tip positive (speakers, ionic air purifier thing, wireless router, Ethernet switch)
      12v DC, ring positive (speakers)
      9v DC, tip positive (cordless phone)
      9v DC, ring positive (speakers)
      9v AC (original old-school Nintendo)
      7.5v DC, tip positive (USB hub, cordless screwdriver, Ethernet switch)
      6.22v AC, hard-wired (Dust Devil mini vacuum cleaner)
      5.9v AC,

  • 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.

    • 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.

      Check out the specs on telco equipment. A lot of them run on 48 vdc with special 48vdc power supplies. You can get a lot of networking gear that come with 48vdc power supplies. I think there

  • I would like to propose that we extend the work that has been done for Power over Ethernet (IEEE 802.3af) to higher power levels for consumer electric products.

    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 [wikipedia.org] 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 outlet
  • You probably already use plug strips that have a switch on them. While it may be inconvenient to plug/unplug them on a regular basis, it's rather easy to hit the power switch. Just get 2 or 3 strips and categorize the plugs. One for things that have to stay on (answering machine), one for things that are only on while home or only when awake (router, dsl modem, cordless phone), etc.
    When you leave home, hit the switch. When you go to bed, hit another switch. When you're getting busy in the bedroom...oh wait
  • There is a new 12VDC connection system being used by ham radio geeks that seems to fit your ticket: http://www.andersonpower.com/ [andersonpower.com]

    Distance is still a problem.. why do you think that you have a big fat wire on your car battery? A lot of car manufactures are looking at using 47v or something for cars in the near future to reduce the weight of wire in cars.

  • My own centralization attempt (Score:4, Interesting)

    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.

  • Forget low voltage DC, low voltage AC is a path (Score:5, Interesting)

    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.

  • I've also wanted to do this for a long time. It's been a lot of work over several years, so I'm not sure if it was a worthwhile obsession, but I have combined a DC power bus with battery backup and supplemental solar power.

    http://ecloud.org/index.php?title=DC_power_system [ecloud.org]

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