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Low Voltage Power Distribution? 237

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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  • Ohm's law (Score:3, Insightful)

    by s800 ( 940543 ) on Friday February 17, 2006 @07:54PM (#14746313)
    Good luck distributing 5Vdc over any distance.
  • 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.
  • High voltage (Score:2, Insightful)

    by JFbasta ( 722882 ) on Friday February 17, 2006 @08:06PM (#14746379)
    Power is transported at high voltage to diminish losses in cables, any long-range transportation with low voltage is inherently lossy.
  • 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?

  • by Ossifer ( 703813 ) on Friday February 17, 2006 @08:59PM (#14746667)
    So did any of these prior discussions come up with any useful results?
  • 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.

  • Multiphase power (Score:2, Insightful)

    by KonoWatakushi ( 910213 ) on Friday February 17, 2006 @09:05PM (#14746704)
    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 more common outside of commercial settings.

  • 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
  • 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].

  • by mysidia ( 191772 ) on Friday February 17, 2006 @10:41PM (#14747166)

    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]

  • by Anonymous Coward on Saturday February 18, 2006 @12:20AM (#14747494)

    "the problem lies not in math, but in hardware."

    This is geeky cluelessness at its best.

    Folks, the problem lies with marketing departments worldwide. They WANT you to have to spend another $15-20 to buy yet another nonstandard wallwart, preferably at the checkout counter or on the end-cap where you can't compare it to a generic or universal device that will do the same job cheaper.

    This is extra-item-selling defined. It allows a nearly marginless industry to make a little extra back.

    Yes, of course it sucks for consumers, but nobody - absolutely nobody with a lick of business sense is going to get on a standardization bandwagon.

  • by Anomalous Poltroon ( 588279 ) on Saturday February 18, 2006 @12:23AM (#14747502)
    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).


    1. Enhanced safety because unused outlets provide a high-impedance (power-limited) source
    2. 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


    1. Power controllers will always waste power
    2. 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.

  • by AaronLawrence ( 600990 ) on Saturday February 18, 2006 @07:03AM (#14748605)
    It's the current that kills you not the voltage
    Pardon me, but saying something like this just makes you sound ignorant.
    It's not like you can a current "by itself". It's directly related to voltage. The higher the voltage, the more current will flow through a given resistance. So, arguing which one of the two kills you is like saying that the speed of a car hitting you doesn't matter, it's the weight.

Never say you know a man until you have divided an inheritance with him.