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Low Voltage Power Distribution?

Cliff posted more than 8 years ago | from the wall-wart-motel dept.

237

thesp asks: "As I look around my apartment, I am continually struck by the plethora of high-voltage AC to low-voltage DC power adapters I use to power my various devices. At a recent estimate, around 30% of the power consumed in my house is via these adapters. From my laptop to my digital music player, and from my mobile telephone to my PDA, each device is down-converting its own power through its own adapter. Double this number to include my partner's devices. Many of these run hot, and are inconvenient to remove/replug to conserve power and outlets. Does Slashdot know of any moves to standardize power delivery to such devices, or of hobby/home-brew projects to distribute low-voltage power from a central power converter? Alternatively, are there reasons as to why this would not be a simple and effective solution to the proliferation of wall-warts.""On closer examination, these adapters seem to fall into four major categories, 7V, 5V and 3V, with the most common being 5V. Despite this, each device uses a different DC plug configuration, which makes efficient use of adapters difficult. It seems to me that, just as AC power is standardised, portable electronics power requirements should be also be standardised, with a standard wall outlet and car outlet at, say, 5V, and a standard device cable and interface. Electronics manufacturers would save money on power adapters, and the consumer would have the cost of the converter written in to home construction or automobile construction costs. No longer would we have to lug 4 separate power adapters with us on an overnight business stay to power our various equipment."

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Low Voltage DUPE distribution? (4, Informative)

TripMaster Monkey (862126) | more than 8 years ago | (#14746310)


Article is a dupe...original discussion can be found here [slashdot.org] , which amusingly enough, is itself a dupe of this [slashdot.org] discussion. Even more amusing is the fact that all of these submissions share the same editor.

Way to go, Cliff...a dupe hat trick. Zonk has nothing on you.

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

pjotrb123 (685993) | more than 8 years ago | (#14746633)

On Topic:

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

And ON really meant ON, and OFF meant OFF.

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

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

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

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

Re:Low Voltage DUPE distribution? (1)

SpaceLifeForm (228190) | more than 8 years ago | (#14747435)

Well, you can get that with a power strip, but, you're right, people are lazy. And, sure, it's inconvenient to use your car when you have multiple devices to charge, not to mention that many cars are not setup to give you a charging port these days. Maybe the best course is to avoid use of these portable devices, and pay attention to the real world around you.

Re:Low Voltage DUPE distribution? (2, Insightful)

Ossifer (703813) | more than 8 years ago | (#14746667)

So did any of these prior discussions come up with any useful results?

Re:Low Voltage DUPE distribution? (0)

Anonymous Coward | more than 8 years ago | (#14746761)


TMM is just pissed that he didn't get a first post in the other threads :)

Re:Low Voltage DUPE distribution? (1)

vsprintf (579676) | more than 8 years ago | (#14746686)

Have you ever considered that you might be spending way too much time here? It was news to me. Of course I have a life and a job and family and friends and a local bar, so maybe my priorities are all screwed up, and I should really be spending my time combing Slashdot for dupes.

Re:Low Voltage DUPE distribution? (1, Funny)

Anonymous Coward | more than 8 years ago | (#14746840)

What, the, fuck? Some dude posting at 8:00 PM on a Friday night is claiming to have a life? Right.

Re:Low Voltage DUPE distribution? (1)

Ossifer (703813) | more than 8 years ago | (#14746853)

Time zones, dude, time zones...

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

Jozer99 (693146) | more than 8 years ago | (#14746928)

The problem is that wires have resistance, which wastes power turning it into heat.  The amount of power wasted follows this equation

% Power loss = Power * Resistance / Voltage Squared

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

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

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

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

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

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

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

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

Re:Low Voltage DUPE distribution? (2, Interesting)

mysidia (191772) | more than 8 years ago | (#14747071)

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

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

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

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

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

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

Re:Low Voltage DUPE distribution? (1, Informative)

Jozer99 (693146) | more than 8 years ago | (#14747089)

Point taken, here the problem lies not in math, but in hardware. It is easy to change high voltage AC into low voltage DC with relatively high efficiency (70-80%). It is VERY hard to change the voltage of DC with high efficiecy, (like 30%). So you end up wasting lots of power that way. Plus, 120V AC current, if you get shocked, hurts like a B#TCH, but just leaves your ego bruised. 120V DC current will instantly cause your heart to stop. Better have a friend with a defibulator ready every time you plug in that laptop, or turn on that lamp.

Re:Low Voltage DUPE distribution? (0, Interesting)

Anonymous Coward | more than 8 years ago | (#14747392)

120V AC current, if you get shocked, hurts like a B#TCH, but just leaves your ego bruised. 120V DC current will instantly cause your heart to stop.

you are stupid and misinformed.

Re:Low Voltage DUPE distribution? (2, Insightful)

mysidia (191772) | more than 8 years ago | (#14747166)

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

See Wikipedia: Skin Effect [wikipedia.org]

Re:Low Voltage DUPE distribution? (1, Informative)

Jozer99 (693146) | more than 8 years ago | (#14747208)

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

BTW, Tesla was the oddball, he was all for wireless electricity. Sadly, his proposed wireless transmission device, the tesla coil, had a nasty habit of electrocuting people who steped within a 20 foot range. Not to mention it was hideously inefficient.

Re:Low Voltage DUPE distribution? (1)

germansausage (682057) | more than 8 years ago | (#14747399)

Which is why we use low frequencies for power transmission. There should be a mod for "true but completely irrelevant".

At normal distribution frequency 60 Hz North Am., 50 Hz Europe and elsewhere skin effect has no meaningful effect on resistance. From the wiki you thoughtfully linked to, skin depth in copper at 60hz is 8.57 mm. In other words, until the wire diameter hits 17.14 mm (about 3/4") skin effect is negligible. As a point of comparisom, standard house wire is 14 gauge with a diameter of about 1.6 mm.

Ohm's law (3, Insightful)

s800 (940543) | more than 8 years ago | (#14746313)

Good luck distributing 5Vdc over any distance.

Re:Ohm's law (1)

non-poster (529123) | more than 8 years ago | (#14746454)

What distance? A few hundred feet throughout the house? The loss would be neglegible over that distance.

If we're talking several hundred yards or more, then we might consider thinking about it.

Re:Ohm's law (1)

s800 (940543) | more than 8 years ago | (#14746569)

Do the math. It is very lossy unless your wires are huge. Remember that current will be larger by a square!

Re:Ohm's law (5, Informative)

toddbu (748790) | more than 8 years ago | (#14746630)

What distance? A few hundred feet throughout the house? The loss would be neglegible over that distance.

Depends on your current draw. Check out this table [windsun.com] . Remember that by time you wire your entire house, there will be several hundred feet of wire.

There's a reason we feed houses with AC.

Re:Ohm's law (2, Interesting)

Mattcelt (454751) | more than 8 years ago | (#14746862)

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

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

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

There's a reason we feed A/C to houses. That's not the same reason we feed A/C within houses.

Re:Ohm's law (1)

brokenin2 (103006) | more than 8 years ago | (#14746909)

Uhm.. The impedence of the device will dictate the current draw. You just need a powersupply that can send enough..

You could have a power supply that'll do 500 amps.. It's still not going to hurt your 2 volt LED if you only feed it 2 volts.

Re:Ohm's law (1)

Mysteray (713473) | more than 8 years ago | (#14747362)

You could have a power supply that'll do 500 amps.. It's still not going to hurt your 2 volt LED if you only feed it 2 volts.

I believe that's also known as an arc welder. How do you think your mp3 player with in-ear headphones would behave in the (very common) dead-short failure mode?

Probably not likely to obtain UL certification for powering consumer electronics anytime soon.

Re:Ohm's law (2, Informative)

stoborrobots (577882) | more than 8 years ago | (#14747033)

... according to the chart, a #10 (6mm^2) wire (which, while by A/C standards is huge, isn't really that big at all) will get you 216 feet at 10 amps.

You might note that that applies at 120 Volts, not 12V - at the lower voltage your #10 gets you a whopping 22 feet. For 200 feet at 12V you need 1/0 gauge wire, which is ten times the cross-section, and three-and-a-half times the diameter...

Again, not huge in real-world terms, but bigger than you imagine...

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

And thus your power source would be a fixed-voltage source, not a fixed current one. Technically, only raw components need to be protected from over-current situations - any (properly-designed) circuit should account for the max current going across any component within it, and prevent it from going overspec. Consider that most wall-warts do not limit the current being drawn from it - draw enough current, and you'll simply make the adapter overheat and melt down.

Re:Ohm's law (1)

TheCarp (96830) | more than 8 years ago | (#14746883)

Of course the question really is...

Is the loss of converting to DC centrally with a beefy power supply that can handle enough amperage to run all the houses devices and distributing via wires a few hundred feet more or less than distributing via AC and then converting it into DC with lots of little AC to DC converters?

Besides, sure you will have several hundred feet in a wired house, but... what if you say... put AC/DC converters in several places in the house to keep wire runs small? Or plan for more circuits through the house to decrease the length of each one?

It would be interesting to see the numbers run up on a few configurations to see whats more efficient (for all I know using many little wall warts is more efficient than one big switching power supply)

So anybody got the elctrical chops to run down some real figures on this?

-Steve

Re:Ohm's law (1)

InvalidError (771317) | more than 8 years ago | (#14747128)

Houses are fed with AC because:
1) simple power production: rotate a magnetized rotor in a multi-pole stator, completely brushless for reliability
2) simple power distribution: simple, relatively inexpensive and reliable laminated iron-core transformers (multi-megawatt DC-DC conversion was practical 30+ years ago anyway... and is rarely so even today)
3) compatibility: transformers cannot be plugged on a DC bus and many AC-DC converters have a voltage-doubling input topology that would be incompatible with DC input

So, AC distribution is going to stick around for simplicity, reliability, compatibility, economical and a bunch of other reasons.

A real problem (1)

Oldsmobile (930596) | more than 8 years ago | (#14746330)

I agree, this is a big problem that I have considered as well. The problem of course is that there is no standard.

I was however encouraged once when visiting a high tech summer house located off the coast. Though there was no electricity, they had a rather ingenious power system. A small windmill attached to a battery powered DC haloge lights throughout the compound, with cooking provided by gas and heting with wood.

It got me thinking, wouldn't having a low power DC system be rather energy efficient? Lighting and electronics with standardised DC, cooking with a 220AC and heating, well, oil or district.

Sounds good to me!

Re:A real problem (2, Informative)

drinkypoo (153816) | more than 8 years ago | (#14746374)

Actually, while there is no standard, I've definitely noticed that manufacturers are tending to use the same kind of plugs for the same voltages more and more. It seems like everything I've got that's 12VDC has the same plug, and I really mean everything, from my Radio Shack A/V transmitter unit, to the Intel webcam (from long long ago) that I connected to it, it's all the same size barrel connector. Obviously it's not standard but it's getting better.

I'm off-grid. (0)

Anonymous Coward | more than 8 years ago | (#14746842)

I have a 2,000 Ah deep-cycle battery bank charged via PV panels and wind generators. Because the distances from source to consumers aren't great, I elected to go with a 12V instead of 24V or 48V system.

Because of my work I'm lucky enough to get cable at no cost, so I over-specced it: 25 sq mm from the cells to the regulators, and 16 sq mm from PV panels and wind gens.

Lights are low-consumption flouros, and computers, radios, etc are direct from the supply. Cooking and heating is gas-powered, except water which is solar heated.

The few sub-12V devices I have are powered by custom controllers at the distribution board.

No problems or outages so far, and no bills from a powers co. The initial outlay isn't tiny, but I feel it's worth it in the long term, even in the satisfaction-value I get out.

Converters in outlets (1)

Punboy (737239) | more than 8 years ago | (#14746331)

I read somewhere about new poweroutlets that have "Universal AC/DC Adapters" built into them. They looked kind of neat, they had your regular outlets, and a retractable DC cord with multiple connectors on it. That would be much more efficient than distributing 5V around a house.

IMHO, USB will become the de facto power standard. (3, Insightful)

WoTG (610710) | more than 8 years ago | (#14746339)

Just a hunch, but my best guess is that we will slowly see the USB power "feature" become the standard for (very) lower power devices. You can already find cell phones, mp3 players, cameras, PDA's and a few misc. accessories that are USB powered - and I've seen USB "power only" hubs available for charging these devices while you're on vacation.

The natural next step is for more devices to switch to USB power. Routers and hubs and other things that are typically "near" a computer come to mind.

Re:IMHO, USB will become the de facto power standa (1)

MentalMooMan (785571) | more than 8 years ago | (#14746382)

This would be a very bad thing. USB was never designed as a power source, and it's not good to use it as if it was.

Re:IMHO, USB will become the de facto power standa (1)

Eideewt (603267) | more than 8 years ago | (#14746433)

Care to back that up? It sounds handy to me, and it's not like providing power through USB isn't included in the specification.

Re:IMHO, USB will become the de facto power standa (1)

MentalMooMan (785571) | more than 8 years ago | (#14746600)

"Care to back that up? It sounds handy to me, and it's not like providing power through USB isn't included in the specification."

Firstly, I see that I mis-read the original post. I didn't see the part about "very low power devices", but I think my point still stands.

It does sound handy to use USB for powering small devices, but not /that/ handy. USB provides power for a reason - to allow small devices to draw their required power from the host, and not require extra cables. It was never supposed to be used for solely supplying power. To have all your routers and other small devices plugged into your computer for power does seem a little strange to me, especially if you need them where there is no computer with USB connectivity (my router is across the room from me, and plugs into the wall there. It would be crazy for me to extend a cable along the floor and use USB to power it). To resolve this one might come up with a sort of USB hub that plugs directly into the wall and supplies power only, and no serial connection, but if you're going to go to those lengths, why not create a new standard and design it for powering things, instead of re-using an old standard?

Powering devices like LED lights that require a tiny amount of power to operate is okay, but when you move on to devices that would otherwise require a wall-wart (like the OP was suggesting), you're (ab)using USB for a completely different purpose to what it was made for. The USB specifications state that the maximum voltage that should be drawn by a single device is be 5.25 volts. Just looking around the room, I can find plenty of things (for example my network switch) that require more than that.

I am not suggesting that a universal power connector would be a bad thing at all, in fact, I can imagine that it would be hugely useful, but there are a couple of reasons why I doubt the emergence of such a thing.
Firstly, manufacturers can make a small amount of profit by making 'proprietary' plugs, because if you lose the one that came in the box, you have to go back and buy a new one instead of using a spare that you may have lying around.
Also, if all the connectors looked the same, then you would get people plugging the wrong type in and breaking something, and they'd complain about that.

Re:IMHO, USB will become the de facto power standa (1)

usrusr (654450) | more than 8 years ago | (#14747109)

> To resolve this one might come up with a sort of USB hub
> that plugs directly into the wall and supplies power only,
> and no serial connection, but if you're going to go to
> those lengths, why not create a new standard and design it
> for powering things, instead of re-using an old standard?

If there was any chance of this to happen then it would have already happened one or two decades ago. I see the obvious absence of such a standard as a very good proof that creating such a standard is not in the interest of the gadget manufacturers.

But with usb powering it is an entirely different story, manufacturers include the usb power option not because they have been waiting for a low-power plug standard all the time but because the devices need usb connectivity anyways and if you already have that then it's just convenient to have it as a power option too.

And being able to charge your phone, camera, mp3 player or pda virtually anywhere where power is available without bringing a vendor-specific cable would be such a great thing, sadly we are not there yet, most of those toys do not come with a standard usb type "b" jacks but need custom adaptor cables. and taking a powered hub + _one_ wall with you while traveling is definitely less of a mess than one for each device (multiply wall-warts by two for in-car power supply, but soon we will see usb blugs in cars, only for attaching mp3 media first but i guess once that becomes mainstream people/carmakers will soon understand the usefullness of a whole array of usb jacks under the dashboard, for powering stuff)

Oh, and i'd bet that before we see a specialized low-voltage short range (the first implies the second) power distribution standard that actually makes it to widespread real world use we will see an usb specification that is updated to the needs of more power-hungry applications, like quick-charging batteries.

Re:IMHO, USB will become the de facto power standa (1)

doj8 (542402) | more than 8 years ago | (#14746622)

Technically USB was designed to provide power, however, the limitations do preclude supporting many devices, since there is a 500mA limit for "high power" devices. Many devices need more than that. A group of devices would likely draw more than the source could provide, in any event. So, I agree USB is not a viable power distribution option.

http://www.usbdeveloper.com/UnderstandUSB/understa ndusb.htm#Power%20Distribution [usbdeveloper.com]

Re:IMHO, USB will become the de facto power standa (1)

dextromulous (627459) | more than 8 years ago | (#14746783)

USB 2.0 Spec download [usb.org]

Read 7.2 of usb_20.pdf
Devices default to low-power and as such can only pull one "unit load" (100mA.) If a device is configured to be High-power, it can draw five "unit loads" (500mA.) This is at 5V, so it will supply about 2.5W to a device (if you are lucky.)

IEEE 802.3af (better known as Power over Ethernet) would be a much better solution for the applications you mentioned (routers and hubs,) as well as others including IP phones, IP security cameras, and RFID tag readers. It provides power at 48V and around 15W. More info can be found here [cisco.com] .

Technically true... but my bet is still on USB. (1)

WoTG (610710) | more than 8 years ago | (#14746937)

I agree, 2.5 Watts isn't a whole lot of power with which to play. Technically, USB isn't a good choice. But because USB is already everywhere, I really think that it will inevitably be the closest thing that we have to a low power standard. There's no extra equipment required, and it's incredibly flexible -- it's pretty cool that with all the PC's around the house and office, I'm seldom more than 30 feet from a USB "charging" or "power" outlet. For longer term use, I imagine that cheap USB power hubs will be readily available. Plus, there's no reason for "wall warts" with USB connectors to cost more than any other 5V power adaptor (excluding a few dimes for the slightly more complex connector).

What would really make this work is some sort of higher power extension to USB, as you say, something in the range of 15 W. Heck, a 17inch LCD is right around 20W (I think)... maybe in "USB3".

Re:Technically true... but my bet is still on USB. (1)

dextromulous (627459) | more than 8 years ago | (#14747078)

1. Since when do you use a USB cable to transfer video to your monitor?
2. Most of the 17" LCDs I've seen are >40W (and need high voltages / negative voltages internally for the backlight, which draws a lot of that 40W.)
3. 40W at 5V = 8A == big cable & trickier to fuse. I'm not sure that the connectors on some of the USB cables could handle that.
4. Even if the specification were to allow for 40W on the bus, that would be 40W for the entire hub, not 40W per device attached to a hub (unless the hub was powered from the wall, instead of the device,) and you'd still be wanting more power. "If it can power my monitor, why not my 100W beast-of-a-laptop?"

Re:IMHO, USB will become the de facto power standa (1)

Dadoo (899435) | more than 8 years ago | (#14747319)

To be honest, I still can't imagine why it was necessary to invent Firewire and USB. Ethernet was already ubiquitous when they got popular and the chipsets were already cheap. If the IC industry could simply have invented some new protocols (e.g. for some of the Firewire capabilities) and a new connector (e.g. to provide power, like USB) they could have re-used existing chips and drivers to give us completely new functionality.

Honestly, how many serial buses do we need?

A few reasons... (3, Informative)

Tyler Eaves (344284) | more than 8 years ago | (#14746359)

1. You can't (simply) transform DC voltage to a different voltage. This can be done very efficiently with AC. The 120v to 5V (or whatever) in your power supply is done before the AC is rectified to DC.

2. Low voltage == High losses, esp. with DC.

Re:A few reasons... (1)

cnettel (836611) | more than 8 years ago | (#14746420)

I was under the impression that it, anyway, is usually more efficient to use a quickly oscillating crystal and then gate that to on and off. A capacitor construction after that will "smooth out" the square-wavish original signal. This is, for example, how you can set the DC voltage to your CPU. In contrast, getting a good efficiency in a simple transformer is actually kind of hard, if you want it to handle any impedance/DC load. If it's good at full load, it will waste energy if nothing is plugged in. If you have noticed, new transformers/chargers generally stay cool when plugged in, if they are not connected to the DC device, while older ones don't.

Re:A few reasons... (2, Informative)

amorsen (7485) | more than 8 years ago | (#14746426)

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

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

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

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

It would be very nice to have say 48V DC around the house. Devices could easily have 48V to 5V or whatever switching supplies built in -- they would be small enough and give off so little heat that they could be inside the box instead of being wall-warts.

Re:A few reasons... (4, Interesting)

plcurechax (247883) | more than 8 years ago | (#14746620)

Grandparent comment: You can't (simply) transform DC voltage to a different voltage.

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

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

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

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

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

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

Re:A few reasons... (1)

Seraphim1982 (813899) | more than 8 years ago | (#14747031)

Remember or learn Ohm's Law: Power (Watts) = Voltage (Volts) times Current (Amperes).

Ohm's Law is: Voltage = Current * Resistance

IIRC what your quoteing is Joule's Law with the time factor canceled out.

Re:A few reasons... (1)

Shimbo (100005) | more than 8 years ago | (#14746807)

It would be very nice to have say 48V DC around the house.

Well, that pretty much defines the Power over Ethernet niche (at least for smallish values of Power).

Re:A few reasons... (1)

adolf (21054) | more than 8 years ago | (#14746822)

Even if it were cheaper to regulate/switch/whatever DC than it is to transform, rectify, and filter AC (a notion that the retail market seems to disagree with), you seem to be missing two very important reasons why manufacturers like to use external AC adapters:

1. Small form factor devices. A cell phone WITHOUT a high-ratio DC-DC converter will always be smaller, lighter, and generate less heat than one WITH a high-ratio DC-DC converter. This is obvious. Therefore, under the suggested plan will either require larger devices, or DC-DC wall warts instead of the much-less-fashionable AC-DC wall warts that nobody likes.

2. Ease of safety approval. It is cheaper, easier, and SAFER to have Underwriters Laboratories inspect and certify one (1) 120VAC -> 7.5VDC wall wart which can power a thousand (1,000) different devices, than it is to certify 1,000 different devices individually.

Besides, I don't want high-current 48VDC around the house. That stuff will hurt you, and tends to hold on in ways that AC does not. And, simply by being in excess of twenty-five (25) volts, it is also considered high voltage in many jurisdictions, and so would need to be treated just like standard AC power in terms of permitting, licensing, and regulation. And so, this is why point #2, above, is still a Big Deal - all of those lovely internalized 48 -> 5 DC-DC converters will need approved.

I guess one could reduce the proposed voltage to, say, 24VDC, and include stiff current limiting to bypass some regulations. But then, the wiring would need to be twice as big, and thus at least twice as expensive. And then current goes up, which makes the connections more important and more prone to failure. And price per outlet goes up, because we need fuses, or breakers, or some other current-limiting apparatus. And so on, and so forth.

Who wants yet another cable plant in their house, anyway? We've already got Cat 5, satellite coax, OTA coax, cable modem coax, telephone, and multiple AC voltages in many rather basic houses.

I mean: Geez. This was all figured out a long time ago, with Edison vs. Westinghouse. Edison's Direct Current lost to Westinghouse's Alternating Current.

It was figured out again, years ago here on Ask Slashdot. It was a bad idea then, too, and nothing has changed since.

Re:A few reasons... (1)

TexVex (669445) | more than 8 years ago | (#14747425)

I don't want high-current 48VDC around the house. That stuff will hurt you, and tends to hold on in ways that AC does not.
I think you got that backwards. Why do you think AC is used in electric chairs and for electroshock therapy, but not used for electric fences?

Re:A few reasons... (1)

Tyler Eaves (344284) | more than 8 years ago | (#14747428)

DC will make your muscles contract....and STAY contracted. So you're quite likely to get a (literal) death grip on whatever is shocking you.

Re:A few reasons... (1)

nathanh (1214) | more than 8 years ago | (#14746479)

1. You can't (simply) transform DC voltage to a different voltage. This can be done very efficiently with AC.

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

Re:A few reasons... (1)

nathanh (1214) | more than 8 years ago | (#14746494)

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

Wrong! (1)

cr0z01d (670262) | more than 8 years ago | (#14746499)

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

Re:Wrong! (1)

nathanh (1214) | more than 8 years ago | (#14746537)

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

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

Re:Wrong! (0)

Anonymous Coward | more than 8 years ago | (#14746580)

HVAC also works wonderfully to maintain comfortable temperature and humidity.

Oh wait, acronym crossover!

Re:Wrong! (1)

speleo (61031) | more than 8 years ago | (#14746642)

The Pacific Intertie that supplies southern California with power from dams along the Columbia in Oregon is overland HVDC.

Re:Wrong! Wrong! Wrong! (0)

Anonymous Coward | more than 8 years ago | (#14746711)

The Wikipedia HVDC article is quite good: http://en.wikipedia.org/wiki/HVDC [wikipedia.org]

Toward the end it lists many HVDC installation spanning distances up to 1100 km and power up to 3150 MW.

While I'm sure that most power (units of MW*km ?) is transmitted as AC, HVDC provides more advantages than just avoiding power losses in capacitive underwater transmission lines.

From Wikipedia:
* Undersea cables. (e.g. 250 km Baltic Cable between Sweden and Germany).
* Endpoint-to-endpoint long-haul bulk power transmission without intermediate 'taps', for example, in remote areas.
* Increasing the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
* Allowing power transmission between unsynchronised AC distribution systems.
* Reducing the profile of wiring and pylons for a given power transmission capacity.
* Connection of remote generating plant to the distribution grid, for example Nelson River Bipole.
* Stabilising a predominantly AC power-grid,without increasing maximum prospective short circuit current.

Re:Wrong! (1)

shadowone (581691) | more than 8 years ago | (#14746588)

and it is more efficient to distribute DC Amps over long distances (constant current, rather than volts)

Re:A few reasons... (1)

njh (24312) | more than 8 years ago | (#14746859)

You're both talking nonsense: DC-DC conversion is standard technology, it's plausible that there are more DC-DC converters in your house than 50Hz transformers. Your computer power supply converts 450V DC to 5V DC.

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

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

http://en.wikipedia.org/wiki/HVDC [wikipedia.org]

Re:A few reasons... (2, Informative)

cr0z01d (670262) | more than 8 years ago | (#14746482)

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

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

Let's say you've got 12 AWG wire in your house (not uncommon). Resistance is .00187 ohm per foot. Let's further say you're running 5VDC across it, and the wire distance to transformer is 50 feet. A short circuit would suck:

(5 V)**2 / (.00187 ohm/ft * 50 ft) = 267 W

Divide this by two to get the maximum power draw from a device: 133W. Sounds like a lot of headroom, but at that point half your electric bill is going to heating the wires! This is why we have high voltage distribution systems.

On the other hand, I would like to see cool medium-high voltage DC distribution systems in the home. This would reduce the complexity of power supplies in our electronics: instead of having power drop out 60 times a second, they see 200VDC or something.

Re:A few reasons... (0)

Anonymous Coward | more than 8 years ago | (#14746564)

Urm, P=IV and the GP said: Low voltage == High losses

Re:A few reasons... (1)

typobox43 (677545) | more than 8 years ago | (#14746695)

And I=V/R. Therefore, P = V^2/R.

Re:A few reasons... (0)

Anonymous Coward | more than 8 years ago | (#14746607)

IANAEE, so help me out a bit here. Isn't this the old Westinghouse-Edison debate?

Let's say you've got 12 AWG wire in your house (not uncommon). Resistance is .00187 ohm per foot. Let's further say you're running 5VDC across it, and the wire distance to transformer is 50 feet. A short circuit would suck:

(5 V)**2 / (.00187 ohm/ft * 50 ft) = 267 W


Isn't the advantage of AC that the effective current is so much lower?

Re:A few reasons... (1)

Agripa (139780) | more than 8 years ago | (#14747270)

The advantage of high voltage is that the current is lower leading to lower transmission losses for a given resistance or size of wire.

The advantage of AC is the ability to use a simple transformer to change the ratio between the voltage and the current as well as it's generation and use in polyphase alternators and motors.

Re:A few reasons... (2, Informative)

Jeff DeMaagd (2015) | more than 8 years ago | (#14747441)

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

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

Incidental arcs with AC systems are easily broken and die automatically because the current goes to zero, breaking the current and the ionized path disperses too quickly for the reverse current to travel through it.

High voltage (2, Insightful)

JFbasta (722882) | more than 8 years ago | (#14746379)

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

Re:High voltage (1)

tricorn (199664) | more than 8 years ago | (#14746517)

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

I've wondered about whether it would be possible to create a low-power converter that would take in any voltage, any frequency, ignore polarity, and put out whatever internal voltage was required, that would use microwatts when not in use. Plug it in to anything, from solar cells, rechargeable batteries (1, 2, or 20), 12VDC, 48VDC, 120VAC, 240VAC...

I get tired of battery powered devices that are designed to run on alkaline, and think a NiMH battery is almost out because it runs at a slightly lower voltage.

Re:High voltage (2, Informative)

ralphclark (11346) | more than 8 years ago | (#14746538)

Let:

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

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

(1) P = V * I

By Ohm's Law,

(2) V = I * R

Therefore

(3) P = I ** R

So power dissipation is proportional to the square of the current. Given a requirement to deliver some arbitrary amount of usable power to the devices you have plugged in, by (1) you know that if you halve the voltage you must double the current to deliver the same amount of power. But, by (3) you also know that if you double the current you square the power dissipated by the resistance in the cabling. Hence if you step down from say 120V to 12V, you must deliver ten times the current and hence power losses are multiplied by a factor of 100.

This still wouldn't amount to much in reality as the sort of devices you're talking about are generally rated between 1-10W and therefore you're only delivering current on the order of an Ampere or two per device. Plus of course the resistance in your domestic cabling should be absolutely negligible.

However, it does explain why the power companies use high tension power lines (tens or hundreds of kilovolts) to transport electricity over long distances. Imagine the amount of current these things carry. When they step the voltage up by a factor of a thousand, the power loss due to resistance in the cables (and over hundreds of miles it'll be a lot) is reduced to a millionth of what it would be if transported at domestic voltage.

Re:High voltage (1)

Achromus (810984) | more than 8 years ago | (#14746638)

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

Aw, shoot. I guess I made this high-temperature superconductor for nothing then. What a waste.

Re:High voltage (1)

njh (24312) | more than 8 years ago | (#14746916)

Superconductors also have a maximum current rating, google 'Critical Current Density'. Work out the current required for low voltage (even 120V) distribution and work out how big the conductor would be (then estimate the cooling cost and compare with normal line losses).

iGo? (1)

AK__64 (740022) | more than 8 years ago | (#14746413)

Check out iGo, sold at Radioshack =( but manufactured by Mobility Electronics =) which is based in Phoenix (hence the smiley face...). May be helpful...

Standardised DC Power (2, Interesting)

nathanh (1214) | more than 8 years ago | (#14746452)

It seems to me that, just as AC power is standardised, portable electronics power requirements should be also be standardised, with a standard wall outlet and car outlet at, say, 5V, and a standard device cable and interface.

The 12VDC cigarette lighter plug is a de-facto standard. Redo all your devices to use 12VDC with a simple voltage leveller - eg, a zener diode followed by a 5V regulator IC - and then standardise on cigarette lighter sockets throughout the house.

Re:Standardised DC Power (1)

murderlegendre (776042) | more than 8 years ago | (#14746646)

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

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

Re:Standardised DC Power (1)

scatterbrained (144748) | more than 8 years ago | (#14747257)

Yeah, great idea - use the crappiest connector known to man to power
all of your electronics.

Not that there's anything wrong with that... (-1, Flamebait)

Anonymous Coward | more than 8 years ago | (#14746501)

thesp asks: "As I look around my apartment, I am continually struck by the plethora of high-voltage AC to low-voltage DC power adapters I use to power my various devices. At a recent estimate, around 30% of the power consumed in my house is via these adapters. From my laptop to my digital music player, and from my mobile telephone to my PDA, each device is down-converting its own power through its own adapter. Double this number to include my partner's devices.

Re:Not that there's anything wrong with that... (1)

November 1, 2005 (927710) | more than 8 years ago | (#14746549)

Actually, there is something wrong with it. Faggotry is disgusting and immoral.

Um...... so? (-1, Troll)

Anonymous Coward | more than 8 years ago | (#14746561)

I smell a red-stater.

Re:mod parent funny (0)

Anonymous Coward | more than 8 years ago | (#14746606)

mod parent funny. nice catch. and I do agree there's nothing wrong with it.

Good idea, but it'll never happen (1)

fm6 (162816) | more than 8 years ago | (#14746597)

It seems to me that, just as AC power is standardised, portable electronics power requirements should be also be standardised, with a standard wall outlet and car outlet at, say, 5V, and a standard device cable and interface. Electronics manufacturers would save money on power adapters, and the consumer would have the cost of the converter written in to home construction or automobile construction costs.
I like the idea, but forget about it ever happening. Manufacturers have no incentive to standardize. It might be cheaper to manufacture power supplies all with the same voltage, but not by much — power supplies are already pretty cheap.

Actually, such a change would cost manufacturers a huge amount, because they'd have to retool every gadget that doesn't fit the new standard!

Getting people to accept new standards is hard, even when there's a cost or safety benefit [cnn.com] . Wall power is standarized because the system wouldn't work without it. That's obviously not true for DC devices.

Re:Good idea, but it'll never happen (1)

elmegil (12001) | more than 8 years ago | (#14747209)

Do you think they retooled all the old gadgets that didn't fit the AC standard when it was finally arrived at?

Re:Good idea, but it'll never happen (1)

Mysteray (713473) | more than 8 years ago | (#14747389)

No, they just made everybody buy the same gadgets all over again. Although, IMHO, for good [straightdope.com] reasons [straightdope.com] .

Re:Good idea, but it'll never happen (1)

elmegil (12001) | more than 8 years ago | (#14747423)

Zackly my point.

3 or 4? (1)

TLouden (677335) | more than 8 years ago | (#14746681)

yeah, did you mean to add 12v to the list?

the real reason is already stated, efficiency of power distribution.

30 Percent? (1, Troll)

Gothmolly (148874) | more than 8 years ago | (#14746688)

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

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

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

I'd gladly settle for.. (2, Insightful)

murderlegendre (776042) | more than 8 years ago | (#14746697)

Standardized connectors. It's one thing to have a variety of devices that use different voltages, but having a variety of 5V devices each of which uses its own style of plug & jack defies all common sense.

For that matter, even on devices that use the same voltages and connectors, there is no standardization for polarity! Is it really that difficult to agree that ring is negative, and tip is positive, or even vice-versa?

Adaptor lock-in is just plain obnoxious.

Re:I'd gladly settle for.. (1)

scatterbrained (144748) | more than 8 years ago | (#14747277)

While we're fantasizing, how about standardized AC voltage,
frequency, connector, and safety approvals worldwide.

The big attraction of wall warts to a mfg. is that they
remove having to deal with all of the plugs, voltages, and
approvals and push it off on someone else.

If a mfg. just had to do one approval and one SKU, I
suspect a lot of wall warts would start to disappear.

Multiphase power (2, Insightful)

KonoWatakushi (910213) | more than 8 years ago | (#14746704)

As others have mentioned, DC is simply not a good alternative as you need very large conductors to make losses reasonable. This being the case, the best alternative would probably be 3-phase power.

3-phase AC is much more easily converted to DC, and also allows for simpler and more efficient motors. (So it is also ideal for things like air conditioners, refrigerators, furnaces, and such.) Overall, I think the advantages far outweigh the cost of an extra conductor, and it is unfortunate that it isn't more common outside of commercial settings.

Re:Multiphase power (2, Informative)

Skapare (16644) | more than 8 years ago | (#14747349)

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

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

Three phase is generally good for motors only above the 1 horsepower level. Many home appliances would not benefit from it. A few might (the big ones), but not all areas get three phase power, so the dominant appliance products use single phase power.

Re:Multiphase power (1)

Jeff DeMaagd (2015) | more than 8 years ago | (#14747456)

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

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

Surety you crave! Reality gives you none! (0, Troll)

Gothmolly (148874) | more than 8 years ago | (#14746725)

It seems to me that, just as AC power is standardised, portable electronics power requirements should be also be standardised

TYPICAL Euro-troll. Why can't everything be the same? (i.e. the way I want it) Isn't everything arbitrary> (so why not MY whim)

Other nice things:
One world currency
One world religion
One world governing body
One world form of government
New World Order

Re:Surety you crave! Reality gives you none! (2, Funny)

An Onerous Coward (222037) | more than 8 years ago | (#14746831)

Yeah, standardization is just a Satanic conspiracy.

Like that one time, Satan decided that all railroad tracks should be the same distance apart, so that every train could work on every track, so people would ride around on the trains, which sucked out their immortal souls.

Oh, and then they standardized screws and bolts, so that you didn't need to carry around one screwdriver for each screw manufacturer, which put some screwdriver makers out of business. Their children were thrown out to starve in the streets. Satan watched, and he laughed.

And home power standardized on 120V AC, so that everyone could plug their computers in anywhere, allowing Satan to tempt everyone with porn.

Don't even get me started on what Satan thinks of the USB 2.0 interface.

Re:Surety you crave! Reality gives you none! (1)

Russ Nelson (33911) | more than 8 years ago | (#14746992)

Satan was surely responsible for RS-232, and he's getting his britches into USB 2.0. Ever seen how many USB connectors and cable combinations there are?? It's RS-232 all over again. Some speculate that life on Earth is already hell. It isn't. Hell has no hope. Purgatory, on the other hand, gives you hope. That's why we keep clutching to new standards, because surely THIS one will solve all the old one's problems.
-russ

I for one (0)

Anonymous Coward | more than 8 years ago | (#14747121)

I for one welcome our new globally conspiring standardized power overlords.

Cable thickness (2, Interesting)

slavemowgli (585321) | more than 8 years ago | (#14746771)

IANAP, and I'm not good with anything hardware-related, but... isn't one of the reasons that you'd need thicker cables for lower voltages? When the voltage goes down, the current goes up, and thinner cables would melt. I distinctly remember being told that that's at least part of the reason why long-distance power cables uses voltages in the hundreds of kV range.

There's also neat experiments you can do in school with transformators - put a coil with, say, 5000 windings opposite of one with, say, 5, and you'll be able to quite literally melt nails. :) (Of course, don't do this at home, at least not until you know what you're doing and how to do it safely.)

Issues in low voltage power distribution (2, Informative)

Skapare (16644) | more than 8 years ago | (#14746802)

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

If you have a cluster of devices of all the same voltage at the same location, then it would make sense to have a common power supply. Otherwise, it makes more sense to use a higher voltage for distribution purposes. The electric utility generally brings power down to your street in the 11kv to 14kv range, and a permanent transformer drops it down to the 120 to 240 volt range you get into your home. Distributing power at 240 volts would not even be considered beyond at most 100 to 200 meters. Every time the voltage goes up by 2, the distant can go up by 4 since the current is cut in half, which means the voltage drop is cut in half, which has even less effect on twice the voltage. When they run the voltage at 50 to 100 times as much, they can deliver power over substantial distances. Cutting voltage to 1/10 as much means you can deliver the same amount power to only 1/100 the distance.

Incandescent lights actually work better at lower voltage, especially for bulbs of lower wattage. Normally a low wattage bulb requires greater resistance in the filament. That means the filament must be longer and/or thinner. That means it is more prone to mechanical shock damage. It also has to run at a lower temperature, producing a more orange light (which in some cases is what is desired). The lower temperature wastes power since more is emitted as infrared instead of usable light. By changing the bulb design to a low voltage like 12 volts, the same power level can have a shorter, thicker, hotter filament, which can run more efficiently, even making up for the loss involved in having a transformer converting the voltage.

The reason I mention low voltage lights is to point out that they are rather standard at 12 volts (a few use 24 volts), yet transformers are generally located close to where the lights are, rather than in a central location which would require the power be distributed in low voltage form. If a central low voltage source were practical, low voltage lighting would be the first to use it. But with very few exceptions, they don't do it this way.

I once considered running lots of stuff in my house on low voltage just to avoid the conversion if I was running it from emergency power or solar power. But once I learned more about all the issues involved, it actually makese sense to generate or produce power at a higher voltage (usually practical with battery arrays or wind generators), distribute it as AC (like from the windmills back to the house), and convert the voltage to what is needed, right where it is needed.

low voltage power distribution answers (1)

twitter (104583) | more than 8 years ago | (#14747404)

Read up on automotive and marine power distribution. All the issues you mention an more have been dealt with.

Standardized DC plug (1)

JohnWiney (656829) | more than 8 years ago | (#14746839)

I've thought about the same thing for years. It seems to me that a standad DC cord, with several connectors that would provide various voltages at specified currents, could make a lot of opportunities available. Standard DC transformers, with several outlets, could be used. Planes, etc., could provide standard plugs. Conference tables could be built with plugs provided for each seat. Battery replacements would look like standard batteries, with a cord that would plug into the standard outlet. Etc., etc. It seems to me that the place to pursue this is IEEE. I don't think Slashdot can help.

The Pessimist (2, Insightful)

Midnight Warrior (32619) | more than 8 years ago | (#14747069)

Have we all forgotten what companies charge for $2 wall warts? I've even seen a Brother label maker wall adapter that has an odd voltage (7.3v), odd amperage, a non-uniform center pin, and inverse polarity. They go overboard with the accessory business. This particular wall wart costs $24 at OfficeMax [officemax.com] . Then another $18 for the label cartriges. Then there are the power-hungry devices like cameras that don't come with a wall wart at all (computer controlled, time interval shots). Us mere mortals have to guess when we go down to the store what size connector to use. Face it, the money is in the connectors. If they can find a cheap way to make you use a new connector and charge outrageous amounts of money for adapters, they will. Cheer up. Atleast your iPod doesn't have any custom connector on it. Oh, wait. Never mind.

So maybe a better solution would be a single brick with different connectors for different voltages - this would conform to ISO standards. Then they could just pull the old printer "this box contains no cables" trick, and it would reduce the number of unused transformers out there eating away at copper supplies [foxnews.com] .

Here is what I'd do (1)

amliebsch (724858) | more than 8 years ago | (#14747170)

Buy one beefy transformer for your common DC voltages - start with 5 and 12 - at Radio Shack. If you are enterprising, you could also repurpose a PC power supply for this task. Then buy a couple of these [radioshack.com] adaptaplug extensions. For each device, buy the appropriate adaptaplug connector for that device, and a "y" connector [radioshack.com] . Use Y connectors and extensions to daisy-chain as many devices as you need to the appropriate voltage chain (careful not to go too long on the wires though), until you reach the current capacity of your transformer. For those pesky devices that have the cord attached inside the device, just lop off their crappy wall wart or connector and solder on a hobby connector [radioshack.com] .

Three major categories eh? (1)

fossa (212602) | more than 8 years ago | (#14747299)

I envy you if your devices fall into three major categories. I've been toying with the idea of building an equiptment rack with a few DC power buses for things like my DSL modem, TV antenna amplifier, mic preamp, router, various chargeable devices, etc. In addition to power, the rack would provide real power switches; many of my devices lack power switches. Since all the equipment will be in the same rack, transmission losses should not be great. Now, it may be the case that most of these devices can handle a fairly wide range of voltage input, but the provided adapters I've checked thus far include (DC unless otherwise noted): 16V AC (DSL modem and mic preamp), 16V (laptop), 15V (speakers), 12V (router), 7.8V (camcorder), 5V (TV antenna amp), and 4.3V (camera). My goal now is to have 120V AC, 16V AC, 16, 5, and one or two adjustable voltage sources. This isn't much better than individual transformers unplugged when not in use.

By the way, if anyone knows a supplier of small quantity panel mount voltmeters and ammeters of so-so or better quality that don't look like ass, please speak up.

Not for the house, but maybe for the rack (2, Interesting)

siegesama (450116) | more than 8 years ago | (#14747373)

I've been considering this since the last time this was on slashdot. While over any real distance DC is inefficient for power transmission, the inside of a rack might benefit. I figure with a large UPS and some sort of redundant power-supply, you could feed a number of computers with 12V lines and a picoPSU-120 12V DC-DC ATX power supply [mini-box.com] . Has anyone tried this yet? I've never worked with high-density hardware (like blades) but I'd imagine that each blade is certainly not using its own PSU.

You need these: (1)

virtualXTC (609488) | more than 8 years ago | (#14747442)

Since DC current can't travle far - you should really only convert to DC at each outlet. That accounted for - there's no reason we can't settle on 12V DC as it's already standard in the car and is even offered on buses, trains, planes etc. To convert at the outlet to 12 DC car plug you need this:
http://www.nugadgets.com/products/ProductDetails/4 .8956.1.html [nugadgets.com]

if you have multiple devices you'll need a spliter:
http://www.outletpc.com/c6331.html [outletpc.com]

if there are any devices that didn't come with a car adapter you can use one of these:

http://www.radioshack.com/product/index.jsp?produc tId=2102590&cp=&kw=dc+adapter&parentPage=search [radioshack.com]

Of course higher power versions of these cost more....
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