Low Voltage Power Distribution?

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."

Comments

Low Voltage DUPE distribution?

[TripMaster Monkey]

Article is a dupe...original discussion can be found here, which amusingly enough, is itself a dupe of this 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?

[pjotrb123]

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?

[Jozer99]

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?

[Hardwyred]

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
actually that is not entirely correct. 10ma of current across your heart period will cause serious issues be it DC or AC. In fact, DC is actually safer then AC when it comes to turning yourself into a light bulb. When the power grid was first being created, DC proponents used to fry small animals to prove that AC was unsafe while DC would do no damage. Granted, a DC power grid would need a power generation station almost every 3 blocks.
As a side, don't be fooled, 110v AC can kill you dead just like 400v AC can. It's all about your bodies internal resistance mostly due to moisture and the path the power takes.

Re:Low Voltage DUPE distribution?

[RzUpAnmsCwrds]

It is VERY hard to change the voltage of DC with high efficiecy

Not true. DC-DC converters have existed for years, and they are highly efficient. Take, for example, the DC-DC convertor on your motherboard - if it were only 30% efficient, it would be dissipating more heat than the CPU. Fortunately, DC-DC converters are generally closer to 90-95% efficient.

Take, for example, the picoPSU - it outputs 120W at various voltages (from a DC source) and it doesn't even have a heatsink.

Ohm's law

[s800]

Good luck distributing 5Vdc over any distance.

Re:Ohm's law

[toddbu]

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. 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.

IMHO, USB will become the de facto power standard.

[WoTG]

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

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

A few reasons...

[Tyler Eaves]

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...

[plcurechax]

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).

My own centralization attempt

[jolshefsky]

I've got a Kill-A-Watt tester and I thought the same thing about my wall-warts for things like USB hubs, my PDA charger, cell-phone charger, etc. I plugged them all into a power strip and they use 16 watts total. I then wired up an empty PC case with a switching supply to power most of the devices. I just used diodes to drop 0.6V at a time from the various taps (12V, 5V) to get to the levels I needed for the oddball devices (the few that need something other than 12V or 5V).

I wired it all up and: 16 watts again.

It was exactly the same between using all the individual supplies and using the centralized PC supply. Admittedly, 16 watts isn't exactly ideal for a 90-watt supply (hmm ... maybe I'll try a smaller source supply ...) but at least I get a nice solid 5 volts going to the USB hubs.

If you get one of those Kill-A-Watt (or equivalent) meters, it's a great help in figuring out what you might want to put on a power strip and switch off manually. My stereo components when off drew a total of about 50 watts so I started switching them all off. The battery chargers in the basement used about 10 watts total, but since I was only using them to keep batteries topped-off, I could reduce it by putting them on a timer and running them an hour a day instead.

In essence, do your experiments and figure out how much you'll really save.

Forget low voltage DC, low voltage AC is a path

[Maljin Jolt]

Recently, I did my own experiments on low voltage power distribution, mainly because I plan to install a large scale solar power charger with a lot of Pb accumulators. The best result is: 24V/35kHz AC home backbone, with a lot of switching voltage changers on rooms, those provide multiplicity of output voltage of 5V, 6V, 9V, 12V DC as well as 230V/50Hz for UPSes and consumer grade devices. LED lights are quite fine with low voltage already. It will take some 6-9 years to return the costs, but only because I design and build the circuitry myself.

Unlike DC or 50/60Hz AC, 35kHz (or even more) AC requires a lot cheaper wiring, very small transformers and have very little losses.