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Sensibly Powering DC Technology?

Cliff posted more than 9 years ago | from the do-away-with-the-wall-warts dept.

Power 90

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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Sticky tape and elmers (4, Funny)

TristanBrotherton (857376) | more than 9 years ago | (#12292111)

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]

Re:Sticky tape and elmers (1)

photon317 (208409) | more than 9 years ago | (#12293274)


The duct tape will restrict airflow to the little vent slots on some adapters, causing the transformers in them to overheat and fail early.

Re:Sticky tape and elmers (2, Funny)

TristanBrotherton (857376) | more than 9 years ago | (#12293392)

Yes, that is true in theory. I neglected to mention the use of the Elmers. The elmers glue is used to attatch large purple heatsinks. . Na na na naaa

Re:Sticky tape and elmers (1)

Hard_Code (49548) | more than 9 years ago | (#12294505)

1.5) add 1 extra power brick, and attack computer case fans to brink and to assembly

Dupe (3, Insightful)

Game Genie (656324) | more than 9 years ago | (#12292117)

This has been discussed before [slashdot.org] . That being said, good luck. Having read the last discussion, I think you'll need it.

Re:Dupe (1)

Game Genie (656324) | more than 9 years ago | (#12292174)

Also, there is some more interesting discussion of DC power here [slashdot.org] .

Yes (3, Insightful)

infernalC (51228) | more than 9 years ago | (#12292132)

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 (1, Interesting)

Anonymous Coward | more than 9 years ago | (#12292666)


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! (2, Interesting)

klossner (733867) | more than 9 years ago | (#12293226)

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.

Re:No! (0)

k4_pacific (736911) | more than 9 years ago | (#12294695)

"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 power supply for it to work right, unless you're just trying to heat your lab with expensive resistors.

Re:No! (1)

klossner (733867) | more than 9 years ago | (#12294818)

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 +12V. When I connect the 3.3V and 5V but not the 12V, I measure 3.1V on the the 3.3V line. A big 7.5ohm resistor on the 12V eliminates the sag.

Re:No! (1)

bluephone (200451) | more than 9 years ago | (#12295089)

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

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

QED.

Re:No! (1)

klossner (733867) | more than 9 years ago | (#12295293)

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 (2, Informative)

Andy Dodd (701) | more than 9 years ago | (#12295270)

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 are within specs, as the load ranges of a properly designed supply are quite wide. Unfortunately, it is basically impossible to maintain regulation in these designs if some of the lines have zero load, ESPECIALLY the line that is monitored.

Higher-end PC power supplies (Such as some of the top-end Thermaltake and Antec units) use independently controlled switching supplies for each output, and will run fine with zero load on some of their lines, but 90%+ of ATX supplies are not built this way because it's significantly more expensive.

If this doesn't make sense, I suggest reading up on switching power supply theory. For optimum operation, switching power supplies depend on there ALWAYS being current flowing through an inductor. Whether this happens is dependent on switching frequency, inductor size, and the value of the load resistance. The higher the load resistance is, the higher the inductor size and frequency needed to keep current always flowing in the correct direction. If an ideal (no resistive losses) power supply is operated within this region, its output voltage will always be a direct function of the input voltage and the ratio of on/off times of the switching element. If the load resistance is too high, this no longer holds true and the switching circuit is no longer regulated. In non-ideal circuits, resistive losses in the inductor and switching element will impose a maximum load in addition to minimum load.

If you add circuitry that monitors the output of the switching circuit and changes the switching waveform appropriately if it is out of tolerance, you can maintain regulation outside of the aforementioned regions of operation (specifically the low-load conditions), although efficiency will often suffer in these regimes. As I mentioned before, most PC power supplies do not implement this independently for each output simply because it is not necessary, in any situation the PS was designed for, regulation on one line will imply regulation on all lines because of the way the loads are balanced. But if you leave one line totally unloaded, regulation is no longer guaranteed.

Re:No! (1)

MarkGriz (520778) | more than 9 years ago | (#12295451)

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.

Re:Yes (1)

nwanua (70972) | more than 9 years ago | (#12293480)

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 nice short on your hands.

On a related topic, I recently started chopping off my wall warts and replacing them with two USB plugs and some electronics, so when I travel with my gadgets I only need one hydra cable which I plug into my laptop. Provided you stay within the USB limits on current draw, you'll be fine.

Cheers.

Re:Yes (1)

nokiator (781573) | more than 9 years ago | (#12297978)

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).

You're asking for Trouble! (4, Insightful)

ka9dgx (72702) | more than 9 years ago | (#12292170)

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--

Froogle search: Universal Power Adapter (2, Informative)

Futurepower(R) (558542) | more than 9 years ago | (#12292249)


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.

Re:Froogle search: Universal Power Adapter (1)

Qzukk (229616) | more than 8 years ago | (#12304963)

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.

Power electronics can be tricky (2, Informative)

mewyn (663989) | more than 9 years ago | (#12292288)

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.

I'm waiting for the day (2, Funny)

Bin_jammin (684517) | more than 9 years ago | (#12292290)

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.

Re:I'm waiting for the day (1)

asquared256 (637499) | more than 9 years ago | (#12292903)

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.

Re:I'm waiting for the day (1)

FLEB (312391) | more than 9 years ago | (#12292974)

In-wall adaption at the plug might be a decent solution.

Re:I'm waiting for the day (5, Informative)

Gilk180 (513755) | more than 9 years ago | (#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...

Re:I'm waiting for the day (2, Informative)

Strange Ranger (454494) | more than 9 years ago | (#12293425)

* 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.

Re:I'm waiting for the day (0)

Anonymous Coward | more than 9 years ago | (#12294118)

Not to be a nit picker but no one lives through electrocution.
Meaning [reference.com] of electrocution.

Re:I'm waiting for the day (0)

Anonymous Coward | more than 9 years ago | (#12294852)

...no one lives through electrocution.

I was raised on the electricity, bitch!

Re:I'm waiting for the day (1)

tankenator (803647) | more than 9 years ago | (#12296640)

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.

Re:I'm waiting for the day (0)

Anonymous Coward | more than 9 years ago | (#12294400)

You obviously wouldn't want to do away with the 110V (or 240V) AC lines. DC step-up / step-down is not that big of a problem. Most of the devices which the submitter listed can probably deal with a wide range of input voltages. I know many small routers (but not all!) do.

The two biggest problems are:

1) Keeping the voltage clean: You have to make sure that a short or burst consumption during plugin doesn't affect other devices. Takes active electronics to do that. On the other hand, you're already regulating each socket individually, so it could be added in with little overhead.

2) Low voltage -> high current -> high losses over longer distances. DC needs to be created from AC close to the consumer. This means you would probably have the equivalent of a switching power supply in every DC socket. This could still be a good idea if it meant that device manufacturers agree on two, maybe three, standard voltages and connectors. But it's a long, long way and seeing how people still try to "save" a buck by buying cheap wal warts instead of the modern switching PSU ones, I'm not too optimistic regarding any power savings.

It's really an economics of scale problem. The electronics to do something like that are dirt cheap once mass produced.

Re:I'm waiting for the day (1)

jemenake (595948) | more than 9 years ago | (#12365166)

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 voltage regulator. Have you noticed that Radio Shacks newer Adaptaplug adaptors (thanks to switching electronics being cheap enough) are now really small and light (like... smaller than the transformer that's no longer inside them?) and can supply surprising amounts of current. They've got a 9V adaptor that can supply 1500mA and it's the size of two Zippo lighters... whereas they used to sell two transformer-based ones. One could supply about 300mA and looked like a normal adaptors and the "heavy-duty" one could give you 800mA and was the size and weight of a baseball!

This also should give you power savings and less heat because of the way linear voltage regulators work. If you step a 110V AC signal down (and rectify it) to 12V DC and then run it through a 9V regulator, the regulator does this, essentially, by acting as a variable resistance between the transformer and the load. So, if your 9V device is drawing 1 amp, then 1 amp must be going into the voltage regulator... which means that the voltage regulator has to burn up 3V x 1A = 3Watts. That's why voltage regulator ICs almost always have heat sinks on them. :)

When you think about this, you realize that they only way to prevent this heat generation is if you can decrease the current going into the regulator by the same amount that you're decreasing the voltage coming out. Linear voltage regulators can't do this, but switching power supplies achieve it by quickly turning on and off to top off a capacitor. So, it's more like a pulse-width-modulation method of providing a certain voltage level.

Anyway, to respond to the parent of the parent, I had the same idea of household-wide-DC a few years ago. My EE friend set me straight, though. Typical house wiring is good for 20, sometimes 30, amps per circuit. Go tally up the current requirements for all of your devices (starting with your Mac mini and LCD). Chances are you'll quickly exceed 30 amps. So then you've got a choice: Do you wire the walls of your house with jumper-cable-sized cable, or do you have multiple DC circuits to complement your multiple AC circuits? Not a very attractive set of options.

Re:I'm waiting for the day (1)

sakusha (441986) | more than 9 years ago | (#12298979)

Unfortunately, that day was sometime before 1890, when Westinghouse/Tesla's AC system took over.

Requirements (3, Informative)

justanyone (308934) | more than 9 years ago | (#12292298)


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.

Re:Requirements (1)

wowbagger (69688) | more than 9 years ago | (#12292489)

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 need N+1 ports you 'tard!"

Each port variable from 2V to 24V
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).
each port capable of 50 watts without significant voltage drop
The term "voltage drop" is meaningless in this context - what you really mean is "with good regulation." Voltage drop would be the loss due to resistance from the power module to the device being powered. Now, for 24V a 50W supply is 2 amps - not a really big problem. However, for 2V a 50W supply is 25A - that takes BIG wire to carry, and special connectors. If you are willing to specify that power in terms of a given voltage (e.g. 50W max at 24V, max 4A current) this problem goes away.


Then there is the fact that your 5 ports at 50W each is 250W of power delivered to the devices - allowing for a total effeciency of 80% that is 313W input from the wall, and 63W of heat dissipated in the power system.

a handful of accessory connectors / converters including 1 plug male -> 4 plugs female, big diameter plug to small plug, extension cables, etc.
No real problem except that this is more stuff to lose - you would want to sell these things seperately and let the end user buy what he needs when he needs it.
silent power supply if possible / air cooled, or very, very quiet fan.
See the power requirements - you are going to have a problem without forced air cooling, and if you want that to be quiet you have to have a fairly large device so that you can move lots of air slowly.
Use a 12VDC battery as input
Again, this means that each section has to be a buck/boost converter. You also are going to be pulling 26A from that battery - you will need, again, heavy wires and special connectors for this. You also run into the problem of supplying a battery box for this - you will NOT get UL/CE approval if you just allow Jethro to set a wet cell car battery down on the floor next to this thing. You also run into the problem of adding charging circuits (more cost) to the power supply, adding short-circuit protection on the battery terminals, and the fact that you may need to draw as much as 600W to run all the gizmos and charge the battery.


You also have the problem that, in general, the efficiency of a DC/DC converter goes down as the input voltage goes down - you are MUCH more efficient making power from a 300V rail than from a 12V rail.



You also run into the possiblity of ground loops - you have one ground path from the computer to the gizmo, and one ground path from the gizmo to the power supply. The noise pickup will be a function of the loop area, which will be very large, and of the noise injection of all the other devices. Seperate transformers break the ground loop by not having a DC path from the gizmo to the wall. While it is possible to break the ground loop the same way with a bus power device like this, it increases the cost of the final output stages.

Now, IF we could convince the gizmo makers to standardize on a small set of standard voltages, and IF we could get them to design their devices with the possiblity of ground loops and power supply noise in mind, we could have a device that made those standard voltages and a distribution mechanism for them.

And if all the /bots would boycott bad Star Wars films George Lucas would stop making them.

/me breaths deeply.

I'm not holding my breath.

Re:Requirements (2, Informative)

alienw (585907) | more than 9 years ago | (#12292795)

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 require up to 50W. Anyway, this should not be a problem.

See the power requirements - you are going to have a problem without forced air cooling, and if you want that to be quiet you have to have a fairly large device so that you can move lots of air slowly.

80% efficiency is unacceptable here. With decent quality components, you should be able to get up to about 95% efficiency out of a switching power supply, and perhaps even more. Besides, average power should be a lot less than 50W, more like 12W.

You also run into the possiblity of ground loops - you have one ground path from the computer to the gizmo, and one ground path from the gizmo to the power supply.

A shared ground is absolutely unacceptable in this application. This won't just cause noise, it will cause lots of smoke. All devices powered by a DC adapter assume they are running off of a transformer-type power brick, so they connect the grounds as they see fit. If the grounds are not isolated and you connect one device to another, chances are good their ground arrangements won't be compatible and you will short out something and fry one or both devices. 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. Apparently, the designers didn't think to isolate the console from ground in the power supply (although it could have been grounded through something else, like the TV).

A good solution would be to have an isolated switching supply (one that uses a transformer) for each output port. This will be almost impossible to do cheaply, though. I doubt such a device could be made for under $150, even with mass production in China.

Re:Requirements (1)

pyite (140350) | more than 9 years ago | (#12293061)

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.

Re:Requirements (1)

alienw (585907) | more than 9 years ago | (#12294096)

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 (2, Interesting)

rot26 (240034) | more than 9 years ago | (#12294336)

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 through something. I was made well aware of this phenomenon back in my garage band days, when that "something" would often be ME. 120v hurts. 240v can kill you, or make your lips numb for a couple of days if, for instance, you are holding a guitar connected to an amp running off of one leg and trying to sing into a mic running through a PA connected to the other leg. There's nothing like a severe electric shock to help you remember that kind of stuff.

Re:Requirements (1)

Detritus (11846) | more than 9 years ago | (#12296823)

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.

Re:Requirements (1)

wowbagger (69688) | more than 9 years ago | (#12293488)

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 components, you should be able to get up to about 95% efficiency out of a switching power supply...


Only for a fixed output voltage design running off a high voltage main bar. If you want to support a wide range of voltages (like the requirements state) you lose efficiency, and if you want to run off a low voltage buss you lose efficiency, and if you want to cascade supplies (either 120VAC to 300VDC to 12VDC to output, or 12VDC to 300VDC to output, as required to allow for both AC mains and battery operation) your efficiency goes down as the product of the stages.

A shared ground is absolutely unacceptable in this application.

And if you noticed, I addressed this - you can do this, but then each of your final output stages needs to be a fully galvanicly isolated flyback design - which is more expensive and less efficient than the other possible topologies that do not provide ground isolation.

Re:Requirements (1)

alienw (585907) | more than 9 years ago | (#12294072)

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 difference (it's just a matter of changing the PWM duty cycle), and neither does using a buck/boost topology. The main losses are in the switching elements and the transformers, and are mainly determined by how much you are willing to pay. Of course, running it off of a very low voltage like 12V won't be very efficient due to the high currents involved.

Re:Requirements (1)

wowbagger (69688) | more than 9 years ago | (#12294448)

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 saturate the coil and cause losses, and the very short duty cycles cause increased switching losses due to the rise time of the switches.

Re:Requirements (1)

alienw (585907) | more than 9 years ago | (#12295865)

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 the negative swing, so you double the voltage. Here's a link [gsu.edu] to a voltage doubler circuit. This [osha.gov] is a full-wave rectifier.

Re:Requirements (1)

wowbagger (69688) | more than 9 years ago | (#12296655)

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 generated from both 120VAC and 240VAC with a single switching circuit.

Of course, in a modern power supply design neither of these are acceptable as they BOTH generate a terrible power factor due to the caps only charging at the voltage crests - hence the need for a power factor correction circuit before the rectifiers in order to get certification for the EU.

One other problem.. (1)

LWATCDR (28044) | more than 9 years ago | (#12297444)

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 (2, Interesting)

Daniel Boisvert (143499) | more than 9 years ago | (#12293878)

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 trying to get slashcode to take my ASCII art and failed miserably. Any ASCII art experts care to respond with tips on how to make it work?]

You could come within .75V or so of the input spec of any given device, which is probably within tolerances, and the deep-cycle batts should provide more than enough current. They'd also double as a handy-dandy UPS. You can charge the whole set from the ends, so charging is relatively easy.

What's wrong with doing it this way?

Re:Requirements (1)

rcw-home (122017) | more than 9 years ago | (#12298096)

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 potentials between equipment.

Oh, and lead-acid batteries are nominally 2.0 volts per cell, not 1.5 volts.

Guitarists might have some ideas (3, Interesting)

Mr_Dyqik (156524) | more than 9 years ago | (#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?

Re:Guitarists might have some ideas (3, Informative)

iainl (136759) | more than 9 years ago | (#12292397)

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.

Re:Guitarists might have some ideas (3, Interesting)

marcelmouse (74690) | more than 9 years ago | (#12293139)

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 of our devices share a voltage, and it's a real shame, because no 1 person has 2 9V DC boxes. Therefore, a concentrated power solution doesn't really work. So, we wind up making do with little velcro strips and gaff tape.

Somewhere, I saw an interview with the sound/tech guy for one of those bands that is a vaguely electronic pop/rock band. (It wasn't Radiohead, but it was some similar band.) They had a whole 9U rack devoted to a power solution for the whole band. It had a power conditioner in it, as well as a serious UPS. It provided clean power for the whole band, across a whole range of DC voltages, in different amperages, as well as AC. I priced out JUST those parts that were commercially available, not even counting the homebrew stuff, and it worked out to be something like fifteen hundred dollars.

So, the answer to your Ask Slashdot?

"Get rich & famous, then hire somebody else to tame your cables."

Re:Guitarists might have some ideas (1)

Roadkills-R-Us (122219) | more than 9 years ago | (#12294858)

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.

about that mini (0)

Anonymous Coward | more than 9 years ago | (#12292447)

if I read correctly, mac minis use 18v for power, and have a very non-standard power connector.

hopefully there is somebody out there willing to trivialize both of these setbacks.

Expensive solutions abound (1)

jsproul (4589) | more than 9 years ago | (#12292524)

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.

Best solution for the problem: (1)

Kosi (589267) | more than 9 years ago | (#12292553)

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.

get a soldering iron & a voltmeter (1)

ryanelm (787453) | more than 9 years ago | (#12292647)

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.

Watch those neg.-voltage current limits! (0)

Anonymous Coward | more than 9 years ago | (#12294804)

PC Power supplies typically have VERY LOW current limits on the negative voltages. This means combos like +12 tied to -12 for 24V swing also has a very low maximum current.

Sure, you can probably get 7V by tying +5 to +12, but even then I'd say be careful.

All in all this project only works well if you have a power supply that natively cranks out the voltages you need in the currents you need.

You may luck out, some devices may "want" 6V, which corrosponds to 4 battieries, but tolerate 4.8V, which corrosponds to 4 1.2V batteries. In this case, 5V from a PC power supply will do the job. Likewise, some 5V devices may tolerate 4.5V or 6V. Caveat user. No warranties. All manufacturers warranties void. Etc. etc.

This could be done but probably shouldn't. (1)

Mike1024 (184871) | more than 9 years ago | (#12292648)

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. Everything gets really complex. Oh, and the unit has to have a cover or something, so you can't accidentally change voltage with your feet.

Second, plugging in wouldn't be very user-friendly. You'd have lots of identical cables coming from an identical unit. How would you know which one you'd set to what?

Third, what current would you want it to work at? Too low and the thing would be useless because you couldn't attatch everything to it. Too high and the unit becomes very heavy (since transformers have lots of metal in, and for a large current you'd need a large transformer). The final device could end up as large and heavy as the power supplies it replaces.

Fourth, unless the user was fairly knowledgable, every cable from the device would have to be the largest of the cables being replaced (in case that output was used for a high current) and also the longest (in case the device was far away).

Fifth, some devices have unusual/proprietry power connectors. The device would have to come with an assload of interchangable connectors. Mobile phone connectors could be particularly annoying.

etc. etc.

Anyway, my point is: This is possible electronically, but would be hard to make into a cheap, easy to use device.

Re:This could be done but probably shouldn't. (2, Informative)

alienw (585907) | more than 9 years ago | (#12292888)

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 switching frequency.

You do bring up a valid point. I think the main reason nobody makes such a device is because it's impossible to make idiot-proof. If someone doesn't set the voltage or polarity properly, they will be very pissed when they fry the device. When you have multiple outputs, this is extremely easy to do.

Re:This could be done but probably shouldn't. (1)

Mike1024 (184871) | more than 9 years ago | (#12293416)

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 power supplies - it's certainly interesting technology!

The reason I assumed a large transformer would be needed was from a UPS unit I repaired a few months ago. It was only about 3 years old, but it contained a transformer that was heavier than a house brick!

You're quite right, of course; for a multiway power supply like this a switched-mode power supply sounds like the way to go!

Cheers,

Michael

Re:This could be done but probably shouldn't. (1)

alienw (585907) | more than 9 years ago | (#12294402)

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. Generally, these are meant to be used with a regulator inside the device.

A switching power supply that powers my speakers (this one is regulated) is rated for 18V and actually puts out 18.7V no load. This is only a 3.8% error, which is to be expected given the component tolerances in it. But specifying 14.1V for a device implies a 0.3% tolerance, which is far too much to expect from an inexpensive power brick.

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). More inductance means lots of metal and lots of turns of thick wire. At high frequencies, you can get away with small transformers using just a few turns of wire. It's also easier to rectify and filter 500KHz square waves than 60Hz sine waves (although the interference problems are very challenging). A computer power supply is a switching design, which is why it can put out 300W at multiple voltages and not weigh a ton.

Re:This could be done but probably shouldn't. (1)

Mike1024 (184871) | more than 8 years ago | (#12304646)

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)?

Cheers,

Michael

Forget it (1, Insightful)

duffbeer703 (177751) | more than 9 years ago | (#12292662)

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 (2, Interesting)

justanyone (308934) | more than 9 years ago | (#12294909)

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 cat and do the same thing, you're still covered. But if you decide, "Hey, I don't like my stuff anymore!" and do it on purpose, you're not covered.

This leaves aside the stupidity of purposefully burning down your own house. Most policies cover 80% of actual (demonstrated) losses, with some very-much-higher priced policies covering 80% of replacement costs. In both cases you have to prove what you owned. This is usually quite difficult to reconstruct from ashes. One good trip 30-minute around the house with a video recorder and sending the tape to your favorite sibling/parent/safe-deposit-box supposedly means the difference between getting bubkus and actually being able to state (and prove!) you owned relatively new 25 button-down shirts at 50% of their expected lifespan at $30 each = $15 * 25 * .8 = $300. Extend that to underwear, ties, shoes, etc. and you end up with huge dollars involved in just replacing what you have.

Remember the reimbursement price for lots of things is basically garage-sale prices, which isn't much considering you'll have to go out and actually find it all again.

Fires suck. Insurance sucks, too, except when you need it, and then it's the best thing there ever was. I dated a gal a long time ago that lost everything in a tornado. She got new stuff, but not very much of it, and she lost all the pics she'd ever taken, etc.

So: It's okay to solder your own Power Supply. It's okay with your insurance company (probably, IIRC) to use it. But, it's wise to test the sucker and probably leave it plugged in for a couple of days on a concrete floor with no combustibles around and a good circuit breaker protecting things.

My advice: Simplify things. Buy a set of 5 outlet strips, use the provided screws to affix them to a piece of plywood, plug them into each other (cascade them; they have built in circuit breakers themselves), plug all your bricks into this arrangement, and put a very nice smoke detector right over the whole thing.

IEC / NEMA standard (1)

metoc (224422) | more than 9 years ago | (#12292866)

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.

Ahem. (0, Troll)

o0zi (652605) | more than 9 years ago | (#12293126)

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?
Ahem.
IF THERE WERE!!!
(Sorry, not having a good day regarding the subjunctive...)

Re:Ahem. (0)

Anonymous Coward | more than 9 years ago | (#12298488)

Actually, "if there was" is acceptable if he is implying that it is fairly likely. The subjunctive is used when you are trying to imply that it is unlikely.

Re:Ahem. (1)

o0zi (652605) | more than 9 years ago | (#12300672)

Actually, no. The subjunctive is used in any event of uncertainty, whether that uncertainty be small or great.

Saturable reactors (0)

Anonymous Coward | more than 9 years ago | (#12293281)

Or synchronous rectifiers... Someone needs to design a switching supply with multiple outputs that runs off one transformer but has multiple independently regulated variable outputs.

More likely solution (2, Insightful)

cybereal (621599) | more than 9 years ago | (#12293376)

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 could make a 'rack' of sorts to plug that transformer into directly (with cooling space and so forth). Size variation needed by larger applications would work just like rackmount cases, in unit format i.e. 1u for your mac mini, 3u for your 500 watt 7.1 digital surround processor and receiver.

The problem I have is with the powerstrips and their utter lack of a good transformer solution. I'll get around to this one day but I intend to get a series of short (3-6") extension cables to make it so one power strip will hold all of my various transformers. Then I'll probably just hang them somewhere on the side of my desk or tie them together with those nifty little velcro strips.

Another wish of mine is that everyone would use the same stupid form factor for transformers. If you look at Apple's transformer it's perfect for the usual powerstrip configuration, same thing with Nokia's latest charger adapters. They are no wider than the regular plugs out there and they grow in such a direction that you can put them side by side without issue. Now one example where they came close but completely screwed up is Linksys. At least some of their products have this thin power adapter that looks a lot like it would be great on powerstrips but it's turned 90 degrees. This provides excellent wall plug support but that's really not where you should be plugging these in! Now, if they used this format and made it so the blades could be rotated 90 degrees then it would probably be my favorite.

*sigh* sorry for the book.

Re:More likely solution (1)

elkyle (875715) | more than 9 years ago | (#12295529)

D-Link has similar "thin" transformers...love 'em.

Re:More likely solution (1)

R2.0 (532027) | more than 9 years ago | (#12297858)

"I'll get around to this one day but I intend to get a series of short (3-6") extension cables to make it so one power strip will hold all of my various transformers. Then I'll probably just hang them somewhere on the side of my desk or tie them together with those nifty little velcro strips."

http://www.cyberguys.com/templates/searchdetail. as p?T1=121+2535

http://www.samash.com/catalog/showitem.asp?itemi d= 22104

Re:More likely solution (1)

Trevin (570491) | more than 9 years ago | (#12313847)

APC Professional SurgeArrest [apc.com] . Depending on how many transformer outlets you need, it's halfway there.

Based on previous experience (1)

stoolpigeon (454276) | more than 9 years ago | (#12293519)

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.

The closest consumer solution (2, Interesting)

aaarrrgggh (9205) | more than 9 years ago | (#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...

Tesla broadcast (2, Funny)

macz (797860) | more than 9 years ago | (#12293746)

Get a big tesla coil and broadcast the power wirelessly to your devices. Try not to worry about the side effects.

Power bricks for guitar pedalboards (1)

c0d3h4x0r (604141) | more than 9 years ago | (#12294023)

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 or covering nearby outlets. There's got to be demand for such a thing, so why hasn't any manufacturer made one?

Re:Power bricks for guitar pedalboards (1)

dj_virto (625292) | more than 9 years ago | (#12296385)

Fry's has power strips like that..

Re:Power bricks for guitar pedalboards (1)

man_ls (248470) | more than 9 years ago | (#12297111)

When I came to college, I bought a 6-foot power with around 20 outlets spaced about 4 inches apart, down the length of it.

Cost me $49.95, but it's been worth it. It lives behind my desk and gives me a straight drop of power to whatever I need.

Auto-voltage selection magical box in the corner (2, Interesting)

QuietRiot (16908) | more than 9 years ago | (#12294343)

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!

Re:Auto-voltage selection magical box in the corne (1)

fred fleenblat (463628) | more than 9 years ago | (#12295412)

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 off at the time there would be no danger.

- If the aforementioned hair dryer was on at the time, the power usage would change from 80% resistive and 20% motor to 100% resistive and the amount of current drawn would increase, and there would be a ground fault. Halt power delivery on any unexpected change in usage parameters.

- A toddler sticking a fork into an outlet would be safe. Unless the fork specifically knows how to ask for power, none would be sent.

- Devices that only need 5V only get 5V. You can charge your electric razor next to the sink and not worry about it.

I think we've all thought of this before... (1)

greywire (78262) | more than 9 years ago | (#12294921)

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 sold at drug stores that I saw recently... its plastic and kinda retarded looking and only holds three devices but its exactly the same idea.

Wont work for me though (between me and the wife, that's two cells and two pdas)..

Solar enthusiasts (3, Interesting)

ferralis (736358) | more than 9 years ago | (#12295459)

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...

USB Charging? (1)

gozar (39392) | more than 9 years ago | (#12295590)

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?

Re:USB Charging? (1)

enosys (705759) | more than 9 years ago | (#12302955)

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.

One way to implement it... (1)

nokiator (781573) | more than 9 years ago | (#12298114)

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 be used. LM117s package sell for about 50c each, so this would be a relatively low cost solution.

This is a problem that will not be solved. (2, Interesting)

stienman (51024) | more than 9 years ago | (#12298529)

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

DC-to-DC Voltage Regulators (1)

Kadin2048 (468275) | more than 9 years ago | (#12298613)

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-DC regulators to produce the specific voltages you need for each device. For the more common voltages you could use off-the-shelf fixed regulators (Radioshack even sells a few), and for the less common ones you can use variable regulators and set the voltage with some resistors and capacitors. An example part is LM2734 from National, although I'm sure there are lots of others.


The obvious downside from this is that the max voltage you'd be able to deliver is slightly over 12V (some regulators can produce Vout higher than Vin, but not by much), and the current is limited by the regulators. Also, they need heatsinking, and waste a fair amount of energy I think. But given that DC power supplies are fairly cheap, this might not be a bad thing.


Of course you'd have to get the ATX supply, if that's what you'd choose to use, to produce power in the first place. Sometimes as other people have noticed, they won't work without a load. I use one on my workbench, and in order to get it to produce power at all I have an ancient 5.25" hard drive that I keep plugged in to one of the outputs as a load. I'm sure I could fake the load with resistors or something if I wanted to, but why bother.


Anyway, just a thought for the enterprising hobbyist or experimenter. I'm pretty sure you could use this to power all your small DC devices like peripherals. For large current-draw devices like computers or displays, this might not be an appropriate solution.

Ham Radio suppliers carry these power supplies. (3, Informative)

sakusha (441986) | more than 9 years ago | (#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.

The Empower standard for DC distribution (1)

Animats (122034) | more than 9 years ago | (#12314694)

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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