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Power Hardware

Sensibly Powering DC Technology? 90

Posted by Cliff
from the do-away-with-the-wall-warts dept.
splatnet asks: "Having upgraded my PC to a Mac Mini all my IT kit is now DC. The Mini, my flatscreen, external USB HDD, USB DVD writer, JBL speakers, ADSL/Wireless Router. I have practically the same amount of space taken up for transformers as I do computer equipment! Has anyone found/invented a way to power multiple DC devices (all with slightly different power requirements)? I'm thinking in terms of space/convenience/running costs etc." It would be neat if there was a DC power source that could be tuned to a specific voltage, as well as modular plugs to fit your various devices. Is there anything out there that comes close?
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Sensibly Powering DC Technology?

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  • by TristanBrotherton (857376) on Wednesday April 20, 2005 @09:22AM (#12292111) Homepage
    1) Take power bricks and place in pile. 2) Cover in duct tape. 3) Continue wrapping of duck tape over cables. 4) Spray paint blue. Voila, a uni power brick... Seriously, i have this problem too, its even worse for traveling with devices. Most of the time the power brick is bigger than the gadget. I ended up building my powerbricks into my table, (underneath the desk) looks neater. Not much more functional. -tris me [kyivpost.com]
  • Dupe (Score:3, Insightful)

    by Game Genie (656324) on Wednesday April 20, 2005 @09:22AM (#12292117)
    This has been discussed before [slashdot.org]. That being said, good luck. Having read the last discussion, I think you'll need it.
  • Yes (Score:4, Insightful)

    by infernalC (51228) <matthew@mellon.google@com> on Wednesday April 20, 2005 @09:24AM (#12292132) Homepage Journal
    Your typical PC AT power supply comes very close. It outputs 12V and 5V DC (most of what you need) and can handle a lot of current if it isn't a cheapo. Go to Radio Shack, get some plugs and some solder and have fun.
    • Re:Yes (Score:1, Interesting)

      by Anonymous Coward

      My high-school electronics lab used a powersupply from an old IBM PC to provide power to an entire room of students. It was perfect for all the 12V ICs, etc.
    • No! (Score:2, Interesting)

      by klossner (733867)
      Your typical PC AT or ATX power supply will fall on its face if your power network doesn't resemble a PC's. In my lab, we power a lot of 3.3V and 5V systems with COTS ATX supplies. We have to put big resistive loads on the 12V lines to get adequate current.
      • "We have to put big resistive loads on the 12V lines to get adequate current."

        Ummmm... so, you're just wasting power then. The current rating on a power supply is the maximum current the supply can give you before it blows a fuse or catches fire. Similarly, the current rating on the device is how much the device needs to run.

        If the device requires more current than the PSU, you need a bigger power supply.

        If the device requires less, it will be fine. You don't need to put a bunch of extra load on the p
        • If the device requires more current than the PSU, you need a bigger power supply. If the device requires less, it will be fine. You don't need to put a bunch of extra load on the power supply for it to work right.

          Logically, that makes sense, but ten years of experience has shown this to be untrue. For example, I have here a "JGE ATX-250W PC-12V" power supply from "A+GPB INC.". It's the cheapest ATX supply my purchasing department found one day. It's rated to produce 20A at +3.3V, 22A at +5V, 10A at

          • Grandparent post:
            "...if it isn't a cheapo."

            You:
            "It's the cheapest ATX supply my purchasing department found one day."

            QED.

            • Include the context:
              can handle a lot of current if it isn't a cheapo
              I'm talking about voltage, not current. I measure voltage sag when drawing only a few milliamps of current, far less than the rating of the cheapest supply. Try it yourself.
        • FALSE (Score:3, Informative)

          by Andy Dodd (701)
          Certain types of basic switching regulators actually have a MINIMUM load that allows them to maintain regulation.

          Many ATX-type switchers use a flyback-style arrangement, where each of the voltages is obtained from a tapped transformer. Regulation is often performed by monitoring the voltage on one line, and if the loads on the other lines are within the design specifications of the supply then the other lines are guaranteed to be regulated if one is.

          In any PC, it's pretty easy to guarantee that the loads
        • Ummmm... so, you're just wasting power then

          Approx 20W. Not a big deal.

          If the device requires less, it will be fine. You don't need to put a bunch of extra load on the power supply for it to work right, unless you're just trying to heat your lab with expensive resistors.

          Not true. Most switching power supplies specify a minimum load in order for them to regulate properly. If you don't have the proper load, you will see the voltage regulation problem the grandparent mentioned.
    • by nwanua (70972)
      The PC AT power supply does sound like the most efficient way to do it. Even if you've got a couple of devices that don't run off 12V or 5V, you can always slap a diode here and there to drop the voltage to your desired level; even if you're off by 0.3V, you'll be OK.

      The only trouble would be any devices that need higher than 12V, for that, you could try connecting two AT supplies (GND - 12V-GND - 12V), so the max difference would be 24V. Do be careful: if the grounds cannot be "decoupled", you'll have a n
      • Actually, ATX power supplies have a -12V output. Combining this with +12 or +5V terminals, you can create 24V and 17V outputs at relatively low current values to supply devices which do not need a common ground (i.e., which will not be connected to any one of the other devices which is also being powered from the same ATX supply).
  • by ka9dgx (72702) on Wednesday April 20, 2005 @09:29AM (#12292170) Homepage Journal
    You've got all sorts of equipment, with all sorts of hidden assumptions about what ground means. In the best case scenario, you actually have no weird assumptions, or nasty surges when devices get turned on, and it all works.

    I've learned, the hard way, that the coaxial power plugs used on most devices these days will temporarily SHORT when you plug them it, which means, at a minimum, a separate current limited regulator for each plug.

    Accept the things you cannot change, this is one of them.

    --Mike--


  • A Froogle search for Universal Power Adapter [google.com] found this: Coby CA-33 Universal 110-/220-Volt AC Power Adapter [buy.com], but it only supplies one voltage at a time.

    It would be great if these were available to supply multiple voltages. A problem, however, would be that all devices powered would need to have the same ground, a condition that might not exist. Deciding whether all devices had the same ground might be tricky.
    • Hm, that Coby adapter seems to only output to one device at a time.

      What if we made the submitters question easier? I have 2 identical ethernet switches that use identical power. Can you get a wall wart that has multiple "tails" for providing identical voltage to multiple identical devices?

      I've thought about using some workbench DC powersupplies around the house, but these are a bit more expensive than what I'd be interested in buying, and wouldn't fit in a rack for work.
  • by mewyn (663989) on Wednesday April 20, 2005 @09:40AM (#12292288) Homepage
    If you don't know anything about power electronics, linear and switching supplies, and transformers and rectifiers you won't be able to pull this off. You will need to find all the different specs for power, produce switching supplies for each device, and make sure you provide very clean power. I've been thinking about doing this myself, but never doing it, partly out of lazyness with how much work it will take.
  • When houses will be wired for DC for just this reason. Imagine a nice plug that's secure in the wall like 110v so it won't be flopping around, and having a 12vdc and 5vdc wall plate. Any other requirements could be done by stepping voltage down.
    • Unlikely. The wire would need to be huge in order to get any kind of transmission efficiency. There's a reason power transmission systems were set up as AC in the first place. Maybe high voltage DC would work, but you'd still need converters.
    • by Gilk180 (513755) on Wednesday April 20, 2005 @11:04AM (#12293073)
      >Any other requirements could be done by stepping voltage down.h

      You can't just step down DC power, that is one of the many reasons AC is ubiquitous when most electronics operate on DC.

      • With AC, voltages can be stepped down or up.
      • AC can be more easily transmitted over longer distances because it is transmitted at very high voltage(and therefore low current), then transformed near the destination to 110/220/whatever you might use.
      • AC can easily be converted into DC. Give me a good diode. Or even better, 4 diodes and a capacitor. The inverse it not true.
      • I know I'm forgetting some things...
      • * I know I'm forgetting some things...

        AC won't fry the living sh*t out of you like DC. You have a far better chance of living through an AC electrocution.
        • Remebering my days on the floor of the hospital and responding to codes, Zoll (tm) defib machines (and all defibs actually) are dc and provide a range of power-typically 300 Joules. This is enough to kill (by forcing repolarization of the cardiac tissue during the wrong point of the cycle thus inducing lethal arrhythmias such as ventricular tachycardia or more likely ventricular fibrilliation. DC ain't nothing to fool with.
      • You can't just step down DC power,

        Actually, with switching power supplies, you can.

        As far as I understand them, switching power supplies operate by "topping off" a capacitor that your DC-operated-device drains power from. If your device sucks a lot of power, the power supply has to "switch" and top off the capacitor more often. If it doesn't suck much power, it switches less-often.

        The beauty of this is that it doesn't require a transformer for stepping down the AC and they don't require a linear

    • Unfortunately, that day was sometime before 1890, when Westinghouse/Tesla's AC system took over.
  • Requirements (Score:4, Informative)

    by justanyone (308934) on Wednesday April 20, 2005 @09:41AM (#12292298) Homepage Journal

    The requirements seem to be:

    * 5 output ports;
    * for each port (or via a central control panel) configuration for output voltage on that port, continuously variable from 2 VDC to 24 VDC;
    * each port capable of 50 watts without significant voltage drop;
    * a handful of accessory connectors / converters including 1 plug male -> 4 plugs female, big diameter plug to small plug, extension cables, etc.
    * silent power supply if possible / air cooled, or very, very quiet fan

    I'd think that a sealed design with a large external heat sink is best. I have a cat and the cat hair ends up all over things on the floor, which is the power bricks and one of my PC's, making cleaning a regular (once / 2 months) thing to lengthen lifespan / prevent overheating).

    I don't care about weight too much. It should be well grounded.

    Another wonderful idea is the ability of it to use as input a 12VDC car/marine-deep-cycle battery, so if the power goes, I can still use my accessories.
    • Let us examine the implications of each of your requirements in turn to see what impact they will have on the final design:
      5 output ports
      In and of itself, not a real problem - but it does imply that the final output circuits will have to be replicated 5 times, which will increase the bill of materials.

      This also runs afowl of the "0-1-infinity" rule - if you provide N ports, the user will need N+1 ports - and will bitch mightily that "you were a moron for only supplying N ports since everybody knows you

      • Re:Requirements (Score:3, Informative)

        by alienw (585907)
        That is really a very wide voltage swing. If the main internal power bus is less than 26V, it means each output module must be a buck/boost converter (which is more complex and expensive than the other solutions, as well as less efficient).

        The main power bus will be about 170VDC, since the power brick will presumably be AC powered.

        However, for 2V a 50W supply is 25A - that takes BIG wire to carry, and special connectors.

        Generally, devices don't require much more than 10A. However, they often do requi
        • I've personally seen two PlayStations get fried because they were connected to different phases of an AC line of an apparently miswired house and were connected together with a link cable.

          I doubt you've seen a house with multiple power phases in it. Pretty much every US house is going to have a single 240V feed split into two 120V legs (+/-) at the pole by a transformer with a grounded center tap. That 240V feed comes off of one of the three phases that travel on the poles, not multiple ones.
          • Technically, that makes the 240V system a two-phase system. However, in that particular case, it was most likely due to a swapped hot and neutral at the outlet.
          • Re:Requirements (Score:2, Interesting)

            by rot26 (240034)
            I think he misused the term "phase". Actually, I don't know what is correct, but I've heard them referred to as "legs", and generally about half of the house is wired from one leg, and the other half from the remaining leg. According to the code, they're not supposed to be adjacent to each other, but using extension cords or some other creative stupidity, it IS possible to end up powering two interconnected devices from separate legs, and running the risk (esp. with unpolarized plugs) of putting 240v thro
          • I live in one. Actually, it's an apartment. The electrical circuits are fed by two separate phases of a three-phase distribution system. About half of the circuits are on one phase, the rest are on another phase.

            I found out about it during a power outage where they lost one of the phases. The site electrician and the tech from the power company both confirmed that the complex used a three-phase distribution system and that I was one of the lucky people that was connected to more than one phase.

        • The main power bus will be about 170VDC, since the power brick will presumably be AC powered.

          Not necessarily - remember the requirement to accept 12VDC input? You can do one of two things - you can run from the 12V bus, or you can have a second DC/DC converter to take 12VDC to the higher voltage.

          Besides, you wouldn't generate 170VDC, but 300VDC - you full wave rectify the signal and dump the +170VDC into one cap, and the -170VDC into another.

          80% efficiency is unacceptable here. With decent quality compo

          • I agree, having it run off of 12VDC is a stupid idea. It will not work simply due to the very large required currents.

            Besides, you wouldn't generate 170VDC, but 300VDC - you full wave rectify the signal and dump the +170VDC into one cap, and the -170VDC into another.

            A full-wave rectifier would produce 170V, not 300V. You can only get 300V if you use a voltage doubler circuit.

            Only for a fixed output voltage design running off a high voltage main bar.

            Fixed or variable doesn't make much of a differen
            • First of all - have you ever designed a power supply, or worked with people who have? I do.

              I suggest you go look at Vicor's web site to get some basic information about modern switched power supplies, as you don't seem to know as much as you think you do.

              120VAC is 170Vpeak-center or 340 Vp-p. Full wave rectifying the voltage gives you about 300V (minus losses). If you doubt me, do the math on sine wave to RMS.

              It is *not* just a matter of varying the duty cycle of a PWM supply - the very long pulse widths
              • You are right about the efficiency problems. However, you are mistaken on your definition of a full-wave rectifier. You are probably thinking of a voltage doubler (which are commonly used in SMPSs). A full-wave rectifier is just 4 diodes, and it will produce 120V * sqrt(2) which is approximately 170Vpeak. The waveform from it looks like abs(sin(120*pi*t)). It can then be filtered, and the voltage will be ~170VDC. A voltage doubler charges one capacitor with the positive voltage swing and another with
                • No, the circuit labeled "voltage doubler" is incorrectly labeled - it is a full wave recitfier, just not the "classical" configuration.

                  Look up "Rectifier" in Wikipedia - they got it right.

                  Actually, most switching power supplies use a modification and combination of the two approaches - for a nominal 120VAC they use the 2 diode configuration and feed the other leg into the common point between both caps, and for a nominal 240VAC they feed the other leg into a second pair of diodes - allowing 300VDC to be g
        • All the fried hardware.
          If you can switch voltage you can bet someone will set it wrong. Not only that but a lot of devices I have seen will connect vcc straight to the adapter plug!
    • Re:Requirements (Score:3, Interesting)

      What about building this into a UPS? Say you took a bunch of 1.5 volt cells and arranged them in series. Then you could take off from between any given pair depending on how much voltage each device required. You could charge them all at once with only a single pair of connections to the terminals at the extreme ends.

      I'm envisioning something like this, assuming 1.5 volts per cell (should be obtainable with the right industrial deep-cycle batts):

      [okay, that was anticlimactic. I just spent 10 minutes t
      • What's wrong with doing it this way?

        The cells drain unequally but charge equally, meaning you will overcharge the cells you don't use, and likely you'll never fully charge the cells you do use. The pack will die more quickly. (For this reason, even with conventional designs, some people who assemble battery packs will put in the effort to sort cells by their tested capacity and match them.)

        Other issues are that you only get the available power from the cells you use, and you have differing ground potent

  • by Mr_Dyqik (156524) on Wednesday April 20, 2005 @09:47AM (#12292350)
    Lots of guitarists use something similar to power multiple FX pedals on stage. However FX pedals tend to be fairly low power, and all at simialr voltages (as they mostly run on 9V square batteries).

    Contact someone who puts together racks of FX for guitarists/stage musicians?
    • The big ol' line of effects pedals all run at 9VDC, and you can even get nice little runs of cable to link them in parallel to the one transformer.

      Which is bugger all use for this situation, where everything wants its own different voltage, unfortunately.
    • Well, this hypothetical device is the holy grail of electronic musicians. There are no guitarists in my band, but there's a fair number of stompboxes and other electronics distributed among 5 people. If they were all manufactured by (if we were sponsored by!!!) Boss, then everything would be running at 9V DC, as specified immediately above. However, our stuff varies as much as the original Ask/.er, so there's just NO HOPE. My bass microsynth runs at 15V DC. The Handsonic pulls an amp at 12V. Only about 1/3
    • No, we're back to the ground issue. Almost everything musicians use up to the mixing board is Hi-Z, unbalanced, which means (among other things) common ground. There's no guarantee you can have common ground with the computer setup described.

      Frankly I'm surprised Apple hasn't solved this issue for themselves.
  • It depends how much you're willing to spend. You could get a 66000 rack-mount multiple-output DC power supply from Agilent for $2K plus $300/channel. Max total power output is 1200W.
  • Quit the idiocy to put the PSU in an extra box! So all you need is the normal 230 V current and the standard power cords. And we could have real power switches instead of standby-buttons again.
  • take one of your old pc's and remove its 500w, manually switched, multiple voltage power supply and hope everything you've got can run at some combination of (i think) 5v, 12v, -5v and -12v. you could make several combinations (12 - -5 = 17v, 12 - 5 = 7v), i belive all it would take is a voltmeter. i've used these for hobby power supplies for years and the only trouble ive had is that they require some load to work properly.
  • What you're asking for is technically possible, but would have several problems.

    Firstly, setting the voltages would be awkward. By far the easiest thing would be to give the user a switch with settings for 12v, 9v, 6v, 5v and 3v. But there are plenty of peripherals that need voltages like 14.1v. So a switch is right out. You could have a control knob, but you'd need some way for the user to know when the voltage was correct. Then you get into the domain of voltage meters, LCD displays and digital controls.
    • But there are plenty of peripherals that need voltages like 14.1v.

      Generally, a voltage requirement like 14.1V means the peripheral will accept anything from 12V to 16V but they don't want you using a third-party adapter. Even switching adapters are usually off by half a volt or more, and regular transformer bricks are +/- 30% or more.

      Also, you don't need heavy transformers to put out high currents. Read about switching power supplies sometime. With those, the transformer size depends mainly on switchi
      • Even switching adapters are usually off by half a volt or more, and regular transformer bricks are +/- 30% or more.

        I wasn't aware voltage error was that high! Presumably that's for unregulated power supplies?

        One would certainly expect such deviation from an unregulated supply (in Europe, the tolerences on the standard 230V AC are such that you can get 220 to 240 volts and still be within specification) but I'd have hoped regulated supplies would be more accurate!

        As you suggested, I looked into switching
        • I wasn't aware voltage error was that high! Presumably that's for unregulated power supplies?

          Most power bricks (the ones that plug directly into an outlet and have a transformer inside) are completely unregulated. The voltage that's printed on them is strictly nominal, and the internal resistance of the transformer is so high that the voltage drops considerably with load. For instance, a randomly picked adapter out of my junkbox says 3V on it. It actually puts out 3.88V no load, which is a 30% error.
          • The reason a UPS will have a huge transformer is because it has to put out a 50 or 60Hz sine wave, and not DC. Transformers running at 60Hz need far more inductance than ones running at, say, 500kHz (a common frequency for switching power supplies).

            You seem to know a lot about this; I'd like to pick your brains, if I could.

            My question is: Could you make a switching supply to convert 12VDC to 120VDC then transform that to AC with Pulse Width Modulation (like in some AC motor controllers, I understand)?

            Ch
  • Forget it (Score:2, Insightful)

    by duffbeer703 (177751)
    If you follow some of the posters here and solder yourself a custom power regulator for everything you own, and it subsequently burns your house down, you will get $0 from your insurance company when they figure it out.

    • Re:Forget it (Score:3, Interesting)

      by justanyone (308934)
      If you...solder yourself ... and it subsequently burns your house down, you will get $0 from your insurance company when they figure it out.

      The insurance industry doesn't quite work that way.

      You can burn down your house by misusing matches (or a propane torch, or a hand grenade) and you'll still get your insurance adjustment. As long as you don't do it ON PURPOSE you're covered. That means if you accidentally knock the lit candle into the paper-shredder-basket, it's covered. If you trip over the c
  • What we need is a NEMA or IEC standard for low voltage DC. As an example, IEC 320 C-13 Style Straight Receptacle is the standard for the connector on your computer power supply.
  • by cybereal (621599)
    The electrical aspect of this problem makes it, shall we say, untenable. So, I suggest solving the problem in an architectural way. Suppose you develop a form factor for transformers, where the plug from the transformer to the AC source is not attached directly to the transformer, something common on laptop ac adapters. The plug itself is removable and OEM's can provide varying sizes for your needs. And the connector on the transformer for the power cable (AC Source) is standardized so that someone coul
  • I'm not aware of a solution to your exact problem. But based on previous experience [slashdot.org] if someone wants a submission accepted, wait a couple months and ask this question again.

    Sad-- seemed like it was just yesterday when that went up. (and by sad, I mean on my part) And all sarcasm aside-- there's more info. there should someone want to look.
  • by aaarrrgggh (9205) on Wednesday April 20, 2005 @11:57AM (#12293577)
    is the iGo power adapters. To really meet your needs you would have to reverse-engineer something, though.

    What makes the iGo solution work is the "tips" which apparently provide feedback to the DC-DC voltage regulators as to what the desired voltage for that tip is.

    What makes it suck is that you can only have two "tips", and it has so many cords that it is almost worse than the original two wall warts you had to carry around.

    My solution would be to reverse-engineer an iGo system, have a common high voltage DC bus and modular DC-DC regulators that can stack, with integrated ports for additional cords and "tips". It isn't perfect; you still have way more cords than a sane person would want, and if your device requires multiple voltages (I think the mac mini is in this category) you will need to do something fancier...
  • by macz (797860) on Wednesday April 20, 2005 @12:09PM (#12293746)
    Get a big tesla coil and broadcast the power wirelessly to your devices. Try not to worry about the side effects.
  • The closest thing I've seen to what the poster is looking for are power bricks (like the VoodooPower) for guitar pedalboards. But that kind of thing generally only works because the devices are all relatively low-current devices and they all share the same voltage (9 volt) rating.

    Personally, I'd be happy if some manufacturer would just start making power strips with 20 outlets all spaced far enough apart from each other that you can plug all your AC-DC bricks into it without them bumping into each other o
  • by QuietRiot (16908) <cyrus.80d@org> on Wednesday April 20, 2005 @01:05PM (#12294343) Homepage Journal
    Someday we will have devices that - IF they need to be plugged in - will communicate with the power supply its needs in terms of power handling, voltage, and ripple requirements (or desires). While adapters could provide a means for some time to power the devices that will not communicate (use a switch to manually select), eventually things should be plugNplay - just like your USB mouse. (It's too bad USB can't handle more power at this point....)

    This power supply could provide a few hundred watts, run off any voltage (AC or DC) to step (buck or boost) and switch [altera.com] (provided the current on the supply side is available) to the proper output voltage. 3-6 wires and some sort of universal plug would be sufficient to provide a serial comms link and power/ground for a few different supplies to a number of devices.

    I can imagine having to buy a large one for your computer desk, and maybe a smaller one for your phone/answering machine/etc. (If they're still around).

    The connectors should be bisexual so you can connect a number of cords together without worrying about which end is which (or having to buy matched pairs and end up with extras for DIYers) to get to your device. Feedback from the device on power quality or voltage drop would be nice (expensive however) to compensate at the supply for bad contacts or extra long runs.

    NatSemi will eventually come out with an integrated controller that takes care of the signaling (including PHY), all control functions, and the kitchen sink - all somebody has to do is provide the transformer, diodes, filter caps, and case. This will make these easy to manufacture and then companies can compete on form factor, efficiency and cost rather than trying to get you to buy their proprietary cables and yet another wall wart for your [whatever].

    A controller that could plug into a spare ATX power supply that would properly load it and provide a number of different voltages and a cabling system with converters to a number of different barrel connector sizes and polarities would be nice :) to start however. Happy 420!
    • There is a safety aspect to this also. By distributing power only in the amount, manner and moment that a device requests it, we wouldn't need to have 120V outlets active throughout our buildings at all times. Electrocution could almost be eliminated if power was intelligently distributed and monitored for noise, over-current, and ground faults.

      - The full 120V (or whatever the device needs) is only sent when the device actually needs it. You could drop a plugged-in hair drying into the tub and if it was
  • Over the years I've considered this many times.

    Most recently I wanted something to tame the mess of wall warts and table-top clutter of multiple PDA's, cell phones, digital cameras, etc. I thought of having a stylish box with a power strip inside where you'd plug all the warts into, and then on top would be an angled shelf with dividers where you would "dock" your phone, pda, etc and the power cord would be held right there so you always knew where to plug in.

    Turns out there is a similar device being sol
  • Solar enthusiasts (Score:4, Interesting)

    by ferralis (736358) on Wednesday April 20, 2005 @02:48PM (#12295459) Homepage Journal
    If someone comes up with a workable solution, there are probably any number of solar power enthusiasts who would pay $$$ for a working product that would allow them to wire a circuit their house with DC of a fixed voltage which could then be converted for each device. Wall warts (and many other transformers) leak current due to their design (and usually also to their generally cheap components). This is a parasitic load- it does nothing for you and is using power even when the wall wart is disconnected. So, those of you who have the right background and ideas, consider this: A single, ultra-high efficiency transformer that generates,say, a clean 24 VDC with a stable ground. Low resistance (say 10-gauge?) wiring throughout the house with special outlets. Universal adapters (similar to RV or Car adapters) that plug in to these special outlets, then into the appliance. These could be quite small, because there would be no need for a lossy/bulky step-down transformer. Something to think about, anyway...
  • Couldn't a solution to this be charging over USB? Apple now does this with the iPods, my Palm Tungsten C does it, and so does my cell phone.

    What are the pitfalls for manufacturers to adopt USB as a universal charging device?

    • Each USB port on a powered hub is supposed to provide up to 0.5A at just under 5V. The USB standard encourages designers to set current limits higher but devices still need to stay below that limit. Many devices use more power when charging and so charging them through USB would slow down charging. Some also require different voltages and so they would need to have added circuitry to convert 5V from USB to whatever voltage they need.
  • There doesn't seem to be any readily available commercial multi-bank DC adapters out there. This is quite surprising since the solution is pretty simple. The solution requires a switching power supply that generates a DC voltage that is somewhat higher (at least 3V) than the highest voltage required to be generated, and a bank of LM317 [national.com] programmable voltage regulators. In this configuration, each LM117 can provide up to 1.5A of current. If necessary, LM318 or LM150 devices that support higher current can b
  • by stienman (51024) <adavis AT ubasics DOT com> on Wednesday April 20, 2005 @08:15PM (#12298529) Homepage Journal
    One problem here is that it is impossible to provide a fool-proof way to get the right of power to the right devices given stupid consumers. You likely have two devices that have the same plug. Are they the same polarity? Same voltage? Do they have special needs such as inrush current limiting, special filtering, etc? Can you trust yourself to program a "universal power brick" to do everything correctly when the laptop manufacturer won't give you complete information? Can you trust joe average? Do you want to pay a lot of money up front to include every kind of connector that there exists, or do you want to special order each connector for $5 each after spending $300 on this power supply? When the manufacturer stops supporting your model with the latest connectors, are you going to swallow another $300 unit, or complain again?

    No manufacturer is going to take this on because of the customer service issues, even if liability wasn't a problem.

    Further, it would have to be mass produced to even approach the cost of buying seperate bricks, and many, if not most, consumers would rather save the 20% increase and deal with a few extra bricks.

    Finally, such a supply could not be nearly as efficient as seperate bricks and still be remotely cost effective. The most efficient supplies are switching power supplies. The most efficient switching power supplies are fixed voltage, and have a peak efficiency at a particular current. Each brick is designed for the device it powers. While one can design an adjustable output supply it is optimizable for one voltage and one current - the rest of the range is very poor. This makes for a hotter brick, nevermind the cost of the additional electricity.

    The best option is to have a universal supply at one voltage which can easily be converted by the target device into the power that it needs.

    This is called AC distribution, and works quite well.

    The real problems are consumers who complain to manufacturers that they want light/smaller/portable devices, and manufacturers who fulfill those requests by taking the AC power converter out of the device.

    No, we're not going to run DC around the house because you either need high DC voltages (which can be more dangerous than AC due to muscle dynamics) or high currents which are a greater fire hazard.

    No, we're not going to create a 'universal power supply' because universal for you is not universal for joe average, and even if you would be willing to pay $300 to power 5 devices, it's not a mass market item.

    No, manufacturers aren't going to put the power supply back in the laptop/cellphone/monitor/etc. It's cheaper with the bricks, and they can sell worldwide with different bricks instead of completely different parts.

    -Adam
  • I've read through some of the other posts and don't think anyone else has mentioned this yet. I could be wrong.

    Has anyone thought about using a standard DC power supply (computer supply, etc.) and then using solid-state voltage regulators to produce the required voltages for different devices?

    Let's say you have an ATX power supply that puts out +5, +12, and -12. You might even be able to do it with a big brick that just puts out 12VDC, depending on what regulators you buy. Then you use solid-state DC-D

  • by sakusha (441986) on Wednesday April 20, 2005 @09:42PM (#12299080)
    Check a ham radio supplier, any decent shop will carry many different power supply units that are designed to address this precise problem.
    For example, I googled and the first entry under "ham radio supplies" was aesham.com, their catalog is downloadable as a PDF. On page 82, they have power supplies from Astron, Daiwa, Diamond, AIM, etc. Most of them only output a single voltage but are adjustable, however a few units have multiple voltage outputs. Many of these units have big geeky analog gauges on the front indicating the power draw, for extra nerd appeal.
    A few pages later (pg 84) they have power distribution busses, for feeding multiple units from the same voltage. Just what you're looking for. And Hams are totally obsessed with clean power, so you can set up rigs with pure, clean power and no grounding problems.
    Check out some other Amateur Radio suppliers and gaze through the catalogs, and stand in awe at true hardware geeks that have been doing this for about 3 times as long as computers have even existed. I learned more about electronics from Ham Radio catalogs than anywhere else.
  • There's a standard for this, established for airline in-seat power outlets. Those provide 15VDC, and up to 10 amps.

    This works fine, but it's overkill for most applications. A box with four Empower outlets would need a 600W power supply.

    This might catch on if cars start coming with Empower outlets at the seats.

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