How many "wall wart" power transformers do you have? Chances are you will get more. All modern electronics will operate happily from low-voltage DC. Halogen lights and electronic-ballast flourescents mean you don't need 120V AC for anything save a few big appliances like refrigerators and washing machines.
Even TV sets and computer monitors can be modified to use low voltage. So why not switch from dangerous, obsolete 120VAC to a house-wide 12 volt DC bus? Power losses from the wiring are more than made up for by eliminating step-down transformer losses. Save 120V for the three or so appliances that need them, and the central switching DC power supply. No more wall warts!
In response to comments (thanks!):
Assuming dry healthy skin, 12 volts is far too low to cause your muscles to contract. (If you doubt it, I will do a demonstration of your choice with a car battery.) 120VAC is the most dangerous voltage for contraction -- even more so than much higher voltages. The reversal of AC voltage does not make it safer than DC. A lot of this misinformation has propagated since the turn of the last century, when Edison and Westinghouse were duking it out over the emerging power standard. Edison (who promoted DC) went as far as to build the first electric chair, which used AC, natch.
I wouldn't use existing house wiring: I would larger gauge conductors to carry the higher DC currents with less IR-squared loss. I claim the total power will be moderately less because you can make a central switching DC power supply more efficient than a houseful of cheap transformers and wall warts (notice how warm they get -- that's wasted power).
Also, assuming a normal power factor, the characteristic impedance of house wiring at 60 Hz is not a factor.
You don't need a higher AC voltage to generate DC. Transformers can step-up just as easily as -down (this is how neon signs, which need high voltages, work from wall current). With modern switching power supplies, you don't even need AC: you can convert any DC to anything else you want.
I hadn't thought about the UPS issue, but low-voltage DC makes that easy as pie: a few car batteries, a power resistor for charging in parallel with a high-current diode and hey presto: uninterruptible power!
Addendum 8/15/00: Regarding current loads, please don't attempt to instruct your grandparent in the art of egg suction. High-power appliances like toasters clearly need high voltages; my argument is that many things we routinely use don't. For example, even 20W of compact flourescent lights is enough for the average room; use something similar for task lighting where necessary. [Note the electronic ballasts of compact flourescents work on DC!]-- rmutt,
Mar 30 2000
Why wall warts are used
http://www.fmraudio.com/FAQ.htm#question1An explanation of why the "Real Nice Compressor" (an audio device) uses a wall wart instead of an internal power supply. His reasons apply to many other devices, of course. [krevis, Mar 30 2000, last modified Oct 21 2004]
Home Power magazine
http://www.homepower.com/sysparts.htmHome power is the best magazine for folks building 12 volt houses [tenhand, Mar 30 2000, last modified Oct 21 2004]
Wanted: low power DC standard bus
http://www.kuro5hin...001/3/12/55716/4109 [egnor, Mar 30 2000, last modified Oct 21 2004]
Electric Current Needed to Kill a Human
http://hypertextboo.../2000/JackHsu.shtmlRelative deadliness of AC vs. DC - varying estimates. [hob, Oct 04 2004]
http://www.popularm...dustry/4220889.htmlWitricity [Shapharian, Sep 14 2007]
How Wireless Power Works
http://electronics..../wireless-power.htm [Shapharian, Sep 15 2007]
Let's go the other way.
High-tension_20mains [coprocephalous, Sep 15 2007]
http://www.greenplug.us/oneplug.htmlA smart power standard based off of usb. [talldave, Jun 14 2008]
For All (well most) your lighting needs
Single_20Source_20House_20Lightingmy own horn I be blowing [FlyingToaster, Oct 18 2008]
I wouldn't like to use a TV set which ran off 12V DC - or at least, I'd be pretty wary of doing any home wiring on any of the circuits it was connected to. One of the great things about AC is that you never get a very long shock from it, as the rapid reversal of the current causes your muscles to contract and jump away from it. On the other hand it's possible to get stuck to a DC power line as the constant current holds your muscles in spasm.-- hippo,
Mar 30 2000
How about 12VAC, then?
A rectifier is a lot smaller than
a stepdown transformer (right?).-- egnor,
Mar 30 2000
Doh! I have been thinking the very same thing for a couple of months now. You're dead on.
I talked to a better EE than I about the DC bus thing -- his advice was not to run DC over household wiring, b/c it's less efficient and more fire-prone. With AC, you're dealing with the characteristic impedence of the conductor, and with DC you're simply dealing with the resistance. Apparently, the latter is higher and thus more wasteful. This also makes the slope of the power curve (I^2 x R) steeper (because R is larger), and thus any overload condition will cause more rapid heating for DC distribution than for AC. I didn't understand why this wouldn't carry over to the circuit breaker and work out just fine, but my friend's visceral reaction to this idea as "very bad" stays with me.
Not that I've given up! I think you're right on with the basic idea that 120VAC household wiring is suboptimal these days. So, I've been thinking about what I might do with my own setup. Here's what I'm going to look into (hoepfully someone else here will chip in, even!):
1. I have to imagine that there's an easier form of AC to generate DC from than 1-phase 60 Hz 120VAC.
As you point out, much use could be made of 12VDC power. Most of the power supplies in my CPUs, etc have transformers that step 120VAC down to 24VAC. (You need a higher AC voltage to create a DC voltage in a power supply, in general.) At the very least, it might be cool to distribute 24VAC.
Even more intriguing to me is the idea that 3-phase distribution of low-voltage power might lead to less noisy power supplies. Most of what I want to do is power computer equipment that connects to my stereo system, so I'd like to eliminate 60Hz line noise. I suspect that a DC power supply optimized for 3-phase would be great at this, but I haven't done the research.
2. Even if it's dangerous to distribute DC through walls, it might be OK to have a DC rack-mount system in my basement with one monolithic power supply (maybe two w/ UPS for overengineering joy) and a number of rack-mounted components such as CPUs and stereo amplifiers, etc.
3. I haven't taken apart any of my stereo equipment yet, but I bet most of the non-amplified equipment (DVD player, etc.) runs on +/-12VDC and +/-5VDC. Another opportunity for central DC or low-voltage AC.-- heath,
Mar 30 2000
Yeah, rmutt, a EE prof I knew once told me that 60 Hz AC is actually even worse than Europe's 50 Hz standard. According to him, 60 Hz is closer to the resonant frequency of an adult human's hand-to-hand circuit.
Yeah, I already thought of the car battery idea, as well. I wonder about the need for a charger controller, though. I believe that lead-acid batteries
last longer if charged carefully. Maybe this is more of an issue in a car's electrical environment, though, I haven't checked.
You could also install one of those really *large* capacitors to smooth out any jaggies. Perhaps a couple of supercaps with it to get HF.
Which gets me to why I made the assumption that we'd want 24 or even 30 VAC if we ran AC instead of DC: I want as few switching power supplies in my house as possible. Ideally, there would be zero of them.
That's because part of what I want to do with this whole scheme is install some 12VDC audio componentry in various rooms. It may be nothing more than car amps and speakers hooked up to my normal DVD player's line out (so you can listen to the movie while you pee and nobody was nice enough to pause it), or it may include something like a laptop sending unstreamed Shoutcast into my amplifier. (Nice that laptop power supplies are off-board, right?)
With this in mind, I want as little noise in the power distribution system as possible. Right now, I've run ground lines to some equipment to circumvent crappy power supplies. In one such case (an LCD display), the power supply in question is a line-tumor (I crack myself up) type type, and so it inspired this whole train of thought about spreading the DC power. Anyway, this means that I want to avoid switching power supplies. I also want to be able to put 'dirty' devices somehow on isolated circuits. Not that I'm a freak or anything.
Amusingly, I had also just installed my first low-voltage lighting, which it seems you have, too. How synchronous.-- heath,
Apr 01 2000
Newer trains (like the Acela high speed train) have so much electronics on them that they need DC power wiring referred to as the Low Voltage Distribution Network. This network provides +72 Vdc, and is referred to as "low voltage" because you can imagine the voltage coming down through those overhead wires!
Devices in the vehicle draw power from the network and convert it to whatever they need. For instance, various parts of our device need 32, 15, 8, and 5 Volts, so we have a power supply board that handles this.-- Eeyore,
Apr 04 2000
the funny thing is that back before we had 120 VAC, the standard electrial service was in fact 12 VDC. tesla and edison had a fight over AC versus DC, tesla said DC, edison sais AC, and he won which is why we have ConEd...-- urbanmatador,
Apr 07 2000
Right idea, wrong players...Was Edison and Westinghouse. Westinghouse wanted AC, Edison wanted DC. Edison actually invented the electric chair as a way to show how dangerous AC was.
'AC is just the electric company's way of making you pay for the same electricity over and over'.-- StarChaser,
Apr 08 2000
Good ol' Ohm's law... you know, that I=E/R thing... You can also do the power (Watts) thing too as P=I*E.
Think about all of those not-so-large appliance thing in your house... vacuum cleaner, microwave oven, iron. A vacuum cleaner boasting a 6.9 Amp motor draws 828 Watts at 120VAC, at 12 volts, it would draw 10 times the current or 69 amps! How 'bout an electric iron (too many cotton shirts anyways!), it draws about 1200 Watts. At 12VDC, that would equate to 100 amps! Nothing like having the equivalent to automotive jumper cables running to a common iron. (No... I don't care to hear from the folks expounding on stereo "monster cable" as I'm sure many other EE's will chime in condemning their need).
On the positive side (no pun intended) our old camper had been wired for 12 volts to provide light whilst out in the woods... different lights, different plugs and outlets.
Apr 24 2000
dude... tesla was definitely involved. you may be right about who thought what, but tesla was definitely involved. in fact, for a while new york city has dc power plants every five blocks or so...-- urbanmatador,
Apr 29 2000
another thought... you mention a car as something which runs on 12 VDC... a car actually runs primarily on gasolene.-- urbanmatador,
Apr 29 2000
Tesla invented AC power, and sold it to Westinghouse.-- StarChaser,
Apr 29 2000
I vaguely remember now having read that it's more efficient to send high voltages over the lines and to transform them down to what one needs, than to send low voltages and have to transformer them up. That's why the US has 120 volt power as standard wall power and everybody else in the world has 220-240v...-- StarChaser,
May 04 2000
So you like the standard interface for 12 vdc, the lighter socket. Guess you never had troule with then slipping out, poor connections, on plastic housing meltdown under high current draw (a 10amp thermal electic cooler)-- scotty1969,
May 29 2000
I realize this only addresses part of the original poster's problem, but how about eliminating at least some wall warts by building the transformer into the surge supressor, UPS, etc.? I know that's where most of my wall warts are concentrated, so many that I bought a special Curtis surge suppressor that can accommodate up to eight. That power strip currently has five transformers (at least three of which are 12 VDC) plugged in.-- harmful,
Jun 12 2000
harmful: See the 2nd link for reasons why manufacturers go for wall warts instead of internal power supplies. As usual, worse is better.-- krevis,
Jun 12 2000
There are many problems with this:
1. A large current will be required, up to 100 Amps. With a normal current this large, circuit breakers will not be able to detect a short circuit. This could cause large losses, fires, long shocks, etc. this also means that connections must be very secure, or they will heat up and cause fires.
2. Changing DC to another voltage is very lossy compared to using pure AC.
3. A lot more metal will be required in house wiring, making it more expensive.-- DarthMal,
Jun 18 2000
Erm... this is a bit popular. The reason why 12v houses will never exist, is because all electronics companies make money from voltage-converters. If you could charge your laptop by blugging it DIRECTLY into the wall, the Dell would loose millions of money from their own brand of plug-transformer. Oh, and i dont know if this has been said, but DC is much more economical to transmit. So economical, that many companies are converting AC to DC, transmitting DC then converting it back to AC again.-- Parasheep,
Jun 22 2000
London underground runs on DC, primarily because AC current flows mostly through the surface of the rails and not all the way through the cross section ("skin effect"). DC is a much more efficient method of transmitting power to the trains.-- ashworth,
Jun 26 2000
For low-power devices, low-voltage operation is convenient. When much power is required, however, low-voltage operation will require heavier wiring or become less efficient than higher-voltage operation. Indeed, this is why most electric stoves and larger air conditioners run off 220 volts rather than 110 volts; the power demands are great enough that the losses from even 110 volt operation are unacceptable.
To see why low voltage operation is objectionable, consider the difference between a 6 volt and 12 volt automotive system. Assume that the wiring between the battery and each headlight has a resistance of 0.1 ohms and each headlight is supposed to use 72 watts at rated voltage.
A headlight that uses 72 watts at 12 volts will consume 6 amps (72 watts/12 volts) and have a resistance of 2 ohms (12 volts/6 amps). If the wiring resistance is 0.1 ohms then the total resistance will be 2.1 ohms, the resulting current will be 5.71 amps, and the light will end up getting 65.3 watts (5.71 amps^2 * 2 ohms) out of 68.6 watts drawn from the battery (5.71 amps * 12 volts). The wire will dissipate 3.27 watts, and the efficiency will be 95.2%.
A headlight that uses 72 watts at 6 volts will consume 12 amps (72 watts/6 volts) and have a resistance of 0.5 ohms (6 volts/12 amps). If the wiring resistance is 0.1 ohms then the total resistance will be 0.6 ohms, the resulting current will be 10 amps, and the light will end up getting 50 watt (10 amps^2 * 0.5 ohms) out of 60 watts drawn from the battery (10 amps * 6 volts). The wire will disspiate 10 watts and the efficiency will be 83.3%.
Note that in the lower-voltage case, not only is the efficiency much worse than in the higher-voltage case, but any power lost in the wire itself will turn into heat. If the power requirement were greater, the difference between 6 and 12 volt operation would be even more substantial. Suppose we wanted headlights rated for 144 watts at nominal voltage.
At 12 volts, such a light would be 1 ohm; total circuit resistance would be 1.1 ohm; net current would be 10.9 amps, light power would be 119 watts out of 131 (91% efficient) with 11.9 watts dissipated in the wire. At 6 volts, the light would be 0.25 ohm; total circuit resistance would be 0.35 ohm; net current would be 17.1 amps; light power would be 73.5 watts out of 103 (71.4% efficient) with 29.3 watts dissipated in the wire.
BTW, at 120 volts, a wiring resistance of 0.1 ohm would be no problem for even a 240-watt lamp: lamp resistance=60 ohms; total resistance=60.1 ohms; current would be 1.997 amps; light power would be 239.2 watts out of 239.6, (99.8% efficiency) with 0.4 watts dissipated in the wire.-- supercat,
Jun 27 2000
I love the 12-volt-house idea. Imagine: You could convert your vacuum cleaner to 12 volts DC; cover your ceilings with chicken wire; attach a long metal pole to the vacuum; then connect the chicken wire to your power source---just like those carnival dodgem-car rides. No more dragging awkward power cords or vacuum hoses around the house. Plus, the showers of sparks would keep the kids amused.-- Ander,
Jun 28 2000
Well, there *are* 12-volt (or 24v, or 48v) houses. People who generate their own power (because they're too far from the grid, or for fun, or because they're survivalists, or whatever) will sometimes retrofit their houses for lowish-voltage DC operation instead of using a big inverter. Lights are easy, and you can get retrofits for refrigerators and stuff.
(As for the rest of us, I like the wallwart-in-the-power-strip idea. Too bad wall warts all provide slightly different voltages/etc.)-- wiml,
Jun 28 2000
Ander, June 28, has the real halfbakery spirit I appreciate a lot!-- rrr,
Aug 15 2000
You could attack this problem on the other side: Make everything that runs on low voltage run on 12 volts. Then you can have just one type of wall wart that can be plugged into anything in your house. Companies would compete to make the most asthetic 12 volt power supplies, and pretty soon this isn't a problem any more.-- tenhand,
Sep 07 2000
I think it would be very unsuccessful to run homes off low voltages.
Most low voltage devices have microprocessors which require a VERY continuous ( no gap bigger than 1 microsecond) power supply with hardly any ripple. The amount of voltage fluctuations would be crazy with lots of devices turning on and off from a common 12v power supply.
Power supply units do more than just bring the voltage down - they act as 'buffers' and 'smoothers' for the power. If everything ran off a common 12v, you would have all the microprocessors resetting (crashing) all the time and devices becoming faulty more often (or alternatively, the power supplies would need much more electronics in them)
I would LOVE to see a S T A N D A R D WALL WART!
Make all wall-warts 12v and make then all the same polarity (tip=positive) and the same connector. Then they could easily be interchanged and competition would make them smaller and nicer. There are already some wall-warts that have switch-mode power supplies in them instead of the traditional big iron transformer. These are getting really small nowdays.
Andrew, Ba Elect Eng.-- goodie,
Sep 08 2000
You could have a switchable transformer built right into the outlet, hidden in the box - have the best of both worlds in an aftermarket product. They'd be more expensive, but no more expensive than a GFCI outlet, surely.-- Scott_D,
Sep 08 2000
Way off topic, but in the spirit of Ander's bumper sparky vacuum - Ceiling gas light fixtures, for a while, were used to power household appliances. There are ad. engravings of a furbelowed house with a long tube coming down from the chandelier and an iron, vacuum, hair-curler hissing away at the other end. Civilization survived that (theoretically); we could definitely do with sparky vacuum fun.-- hello_c,
Sep 08 2000
'Furbelowed'? I thought that was a rather disparaging way of referring to females...-- StarChaser,
Sep 09 2000
See my addition "Fibreoptic cable". It might have some relevance to this debate.-- rayfo,
Sep 10 2000
I can tell this debate is heavily populated by Americans! I don't mean that as a slam, but it is common for Americans to think in terms of domestic market only and miss the big picture. The "Wall Wart" - I like that, is actually popular because every country on the planet has it's own "Safety" standards (ie trade barriers) body that regulates we poor underappreciated designers. The regulatory body charges (extorts) large fees in order to test your product for safety compliance. You will see various approvals listed on your lowly "Wall Wart". By using one of these, the designer eliminates any further safety testing on the product because it connects to the low voltage ie safe side of the cube! So don't go blaming us engineers - it's politics! P.S. Yes ocassionally there is other reasons for using one - but this is the big one.-- MrEsoteric,
Oct 12 2000
P.S.S. Everyone objecting to the 12 volt house gets a star in physics - the rest of you stay in at recess!
P.S.S.S even twelve volts will be leaving us soon - your next generation cars - and I do mean combustion engine based, will be moving to 42 (ish) volts, to accomodate electric servo power steering and brakes. You guys need a few more techies in here!-- MrEsoteric,
Oct 12 2000
I've been living in a very successful solar heated home for 20 years, and last spring I added a modest photovoltaic (100 W) and windpower system (400 W) that charges a shared 440 ampere hour battery. The batteries are in an external "powerhouse" near the windmill mast, where 120 VAC is generated and supplied to a completely independent "power grid" with four nodes that supplies every corner of the home. The wiring is entirely by the code; It doesn't matter if you use 120 VAC or 12 VDC, if the wire's capacity is 15 Amp and you suse the input end at 20 Amp, you will have a fire. Thus, all of my fuses and breakers take that into account and do it conservatively, too (e.g., a 14 ga., 15 Amp wire run is protected with a 10 Amp fuse, etc.).
When I wired the powerhouse to the central node I added a 12 VDC, 15 Amp pair - fused both leads at 10 Amp - as an afterthought. The writer of this article is right, and he isn't talking about high current circuits. I've done this for real, and to my delight, the 12 VDC line turns out to be more in use than the 120 VAC outlets and is useful for all sorts of things, like LCD TVs, radios, battery chargers, two of my ham radio tranceivers, etc. I added a white LED illumination system (each lamp is a cluster of LEDs in series drawing the whopping current of 0.02 Amp), and I fused that system at 0.250 Amp (a meter fuse!).
This 120 VAC/12 VDC system is completely separate from our commercial power wires. Owing to the night lighting there is never a dark corner in the house at night, and I also added the lower power intrusion alarm to the solar circuit. 50 Watts is the upper limit (ever) on that 12 VDC circuit.
John R. Wright, Ph.D.
Professor of chemistry-- jwright,
Nov 10 2000
//12volts would be much more efficient for electronics. Since 20-30% of the power in a house today is used by electronics, eliminating the transformers will add a little more efficiency... Transformers are usually about 92-97% efficient.//
Most electronics internally use +5volts regulated or +3.3volts regulated, and possibly a higher unregulated voltage. If you feed in 12 volts to a typical cheap regulator, it will only be about 42% (5/12) efficient. If you use 9 volts input instead, your efficiency will improve to 55% (5/9). If you go with 6 volts (and your regulator can regulate with its input 1 volt above the output) efficiency improves to 83%.-- supercat,
Dec 10 2000
Wow talking about sparking a discussion! Lets start by saying Im totally for the 12vdc house. I have to begin by responding to what Ive read. To the Physicist who is worried about high current draw, extreme wattage and fires. When is the last time you used a window mounted air conditioner and felt the cord running to your 110vAC outlet or better yet just reach behind your refrigerator and feel the cord. Warm isnt it? The whole idea is not to overload the house with high current drawing circuits but lower voltage, lower current applications. Besides each those wall warts draw a pretty good current so in essence we already have a house full of the potentially "dangerous" DC. Now count up the electronic devices in your home verses pure AC driven appliances. Oh but wait... do not include lighting. The market is already saturated with perfectly safe low voltage lighting that draws a minimal current so lets not include them. On to irons, curling irons, hair dryers all of which have cordless "battery operated" counter parts that operate fairly efficiently. Now your down to Major appliances. How about gas stoves, dryers, or heat pumps? Now I think with what little is left we could expend our technological know how into refining the remaining dinosaurs. And by the way I believe the last statistics put the amount of home appliances with some type of microprocessor to over 80%. Anyone is welcome to correct this figure. So now that we have determined that we are already using DC for most of our house then how do we answer the fire in the wall issue. Lets start by saying I work for the Fire Dept in a Metropolitan City and I know for a fact that lots of fires start by faulty, old, or pest bitten AC wiring. The people that mentioned a DC distribution center have the right idea. It is in fact a stepdown system just like the wall warts but it is done before it gets to the outlet. By the time it runs through the walls the current will have already been dropped to a reasonable level. The main center would house the necessary circuits to clean the signal, buffer it, remove noise, offer spike protection and aha.... heat dissipation which I believe could be recycled. The final stepdown would be the outlet which would offer the lowest possible current to operate one or two devices that would run off of it. Overloading the outlet would be impossible because of the lack of current in the line. The device would simply not work as is true in DC circuits which at some point are all current limited, designed that way for safety and for extending the life of the device. My point to all this is to make technology fit our needs. If we need low cost, energy minded, low voltage devices then that is what should be produced. Dont let the power companies bully you into thinking that AC is necessary or the manufacturers talk you into multiple adapters to fit your house, car, or even airlines. By the way have you ever noticed that when you buy a cell phone you only get one adapter. Either a wall wart or a cigarette lighter plug but very seldom both. Instead you usually have to pay an additional "$30 + wow!" to buy the other adapter for something that cost them 2 bucks at the most to make.
P.S. If you follow safety guidelines in product developement and take all conditions into close scrutiny then you can design your house to use any voltage or current you want. By the way hats off to the one who used wind and solar power. There are definetly other energy sources to tap. How about every device having its own solid fuel energy source with a shelf life of a hundred years. No more wires!!! Yaa..ah baa.by!!-- cebreez,
Apr 17 2001
Great idea. We need to do the following:
Use gel cell batteries (like on boats and airplanes). Batteries could store energy you produce off solar/wind generation.
Save a little money on your bill. When you're not consuming the power your generating, run your meter backwards! You are allowed to add power to the grid and later, when you need power, you won't be charged for the amount you contributed.
These power outages - energy crisis in California have all of us re-thinking this 120 volt thing.-- wireless,
May 16 2001
I'm not sure what power conservation and home generation have to do with not using 120V. After all, if you want to run that two-way meter, you need the step-up.-- egnor,
May 16 2001
Telsa wanted AC, Edison wanted DC. Using 120 volts has nothing to do with the California 'energy crisis'. The only reason there is a problem is lack of power plants. The reason we use 120 volts is because it is more efficient than to distribute than a lower voltage. That's why there are voltages around 15,000 and up in power lines. A 1200 watt heater is going to use 1200 watts wether it is fed with 120 volts AC or 12 volts DC. The only difference is that at 120 Volts you only need 10 amps that can easily be carried by a normal size plug. At 12 volts it would draw 100 amps. Picture about 9 of normal size plug in wires bundeled together and thats about what you would need so they wouldn't melt or start a fire. I'm only 15 years old and I can see clearly why 12 volts DC running through a house is a bad idea.-- presto15,
Jun 01 2001
[presto15]: You've been here one day and you cannot yet see that the debate is at least as important as the idea. You're right, of course, but I imagine you'll be wrong eventually, just like the rest of us.-- angel,
Jun 02 2001
What about not going _entirely_
over to 12vdc - have a separate
240vac line (or 110v for the
Americans) used to power the
fridge, vacuum cleaner, air con,
TV/computer monitor and other
Then there could be a DC (_not_ 12
volts; ±24 would be better for
various reasons) line, maybe at
20--30, for supplying hi-fis,
computers, lighting, and anything
that needs a wall wart (or other
little dongly thing). Ideally,
each socket in the wall would be
short circuit-protected and
isolated from each other socket.
This DC voltage could be converted
by a large, efficient switching
power supply in the roof (or
wherever else is convenient) to
decrease energy wasted through
power lines.-- cp,
Jun 02 2001
[cp]: You suggest that 'each socket in the wall would be short circuit-protected and isolated from each other socket'. I assume that the required varistors, reservoir capacitors, and so on would be rated for the heaviest-draw appliance available, and would thus fit neatly into a box about the size of a wall-wart. Switch-mode power supplies work by rectifying the incoming AC and using the resultant DC to run a high-frequency oscillator whose output is then chopped to produce the required low voltage AC. This low voltage is then rectified again and smoothed. They are not particularly efficient, and they radiate huge amounts of RF noise, more so when they need to supply high current. They are used mainly because they are easy to design, and use small, lightweight parts which can be PCB mounted and are thus amenable to automated assembly. Note also that the majority of domestic electronic equipment requires several independent supplies, +12, -12, +9, and so on.-- angel,
Jun 02 2001
«Mister Highliter» - a
dual-voltage system is
more-or-less what I was suggesting.
«Angel» - DC voltage converters /
regulators are widely available
for things which require multiple
voltages. e.g. 7805 for +5v, 7812
for +12v, etc, will provide ~1amp
from a voltage that isn't _too_
much higher than what you're
starting with. Additionally, I
think you'll find that most
plug-packs are UNregulated, so
e.g. a 12v dongly thing might give
anything from 16--12v depending on
current draw and mains voltage (am
I right here, Mr Highlighter?) So
digital electronics or whatever
inside the equipment would have to
regulate the output from the
before they use it. (Most CMOS
and TTL beasts like around 5 volts.)-- cp,
Jun 04 2001
Several people are tossing out terms like "characteristic impedance" and "skin effect". Those effects are transmission line or high frequency effects that are not relevant at 60Hz.
Conversion from DC to another DC voltage can be very efficient. National Semiconductor makes DC/DC convertors which are on the order of 90% efficient.-- Orthonormal,
Jun 21 2001
Ok...first of all ... you want the SMALLEST current running through your house as possible. The US uses 120v because it is safer than 240v, but the current would be twice on the 120v system. The three phase idea won't work because in houses (residental buildings), the electrical lines are 120/240 two phase. The DC-DC converter comment is just rediculious ... 90% efficiency is great, but look at the amount of power they handle ... maybe a couple of watts. I am most definatly not saying that one can't build a high power DC-DC (I am in the process of building a 5kW 12v to 48v DC-DC for car stereo) but it will cost some money! Well...just figured I would through my thoughts out there.-- DJB,
Aug 24 2001
Actually the US is 120v because we did it first. It was later discovered that higher voltages are more efficient for transmission.-- StarChaser,
Aug 25 2001
I live on 12DC its great for most things. It would be great for the rest if DC was used more.-- AndyDoit,
Apr 21 2003
[AndyDoit], I guess you are using a generator-battery combo that provides 12V DC.
The problems highlighted above generally focus on safety and efficiency; the higher current associated with lower voltages being the problem. However, they miss out on another key feature of AC: its flexability.
With AC, you can easily transform the voltage to higher or lower voltages as required and rectify it to DC if that's what you need. If you start from DC, it's relatively expensive to step the voltage and to convert it to AC. Also 12V DC items are generally sold to the niche camping markets. That's why these items will always cost more than their mainstream AC counterparts.
I agree that if you depend on 12V DC as your standard, then yes, it'd be nice if the whole world followed your system, but in reality, that's never going to happen. I suggest next time you face a big capital outlay, you buy yourself an AC-capable generator, or failing that an inverter and take the opportunity to re-wire your home. You may save a fair bit of money in the long-run.-- FloridaManatee,
Apr 22 2003
There already are 12VDC homes. I call them Motorhomes/RVs. I know of people who have converted 5-wheel RVs to houses. They run 12VDC even for the frig, A/C, Heater, TV, VCR. etc. What I don't get is why a 12VDC TV/VCR costs more than a 120VAC one because you simply leave out parts to get the 12VDC unit. I have converted TV, VCR, Stereo, etc for friends. The RVs even have a Power Inverter for 120VAC for the unconverted appliances.-- chu467,
Apr 24 2003
(A five wheel RV) 2 on one side and 3 on the other. 2 at the front and 3 at the back.-- sufc,
Apr 24 2003
(A five wheel RV)? Off topic - The "fifth wheel" is what connects the two parts of articulated trucks in the UK...
The US is not the only place using 12V DC in homes. I have wired my home (mainly for lighting) with 12V distribution and hope to add solar charging in the future (near or far...) Ankara, Turkey-- agulesin,
May 22 2003
This is a great discussion and I'm sorry to just get in on it now. The idea of a 12V house is great. The National Electrical Code has no problem with free-floating unprotected (thus cheap) Class 2 wiring running through buildings. Remember, anything that is going to initiate a standard would need to be portable to office buildings as well (and they have stricter wiring requirements). I am envisioning a 12VAC distribution - get the advantage of the AC, and use it as well (I have a few wall warts which output 12VAC). Then, with a deep backbox in the wall, this could run into an ELECTRONIC transformer to make 12VDC. It would have to be very small capacity (20W or less) to fit even the smalles elec. converter into that backbox. This would leave us with a 12VAC and a 12VDC jack next to our standard 120V receptacle.
CONS to a 12V house:
This is a bad idea for a standard house because the decades-old loadcenter would need to be overhauled. I've dealt with the large electrical manufacturers, and such radical changes don't happen on a whim (if at all). Also, adequate fusing would be needed at all branches, and wire sizing for voltage drop would cease to be a no-brainer. These two factors restrict the 12V house to a project house that can only be utilized by true geeks.
Now, What about the PC station. My PC periphs have 6 - yes six - wall warts. I am going to dust off my EE design books and try to build a box that will handle multiple outputs at multiple voltages. Then dawn shall fall on the wall wart era!!-- keg,
Jun 09 2003
So basicly what your saying [keg] is; Geeks of the world unite, fight and invent their own standard?-- silverstormer,
Jun 09 2003
//This is a great discussion and I'm sorry to just get in on it now. The idea of a 12V house is great. The National Electrical Code has no problem with free-floating unprotected (thus cheap) Class 2 wiring running through buildings.//
I believe class 2 wiring must be current-limitted at 4 amps or less, at a voltage of 36 volts or less. You're thus limited to about 120 watts if you want to remain within U.L. class 2.
Even if you don't care about the U.L. requirements, trying to power a 240-watt device from 12 volts will require 20 amps. Cheap little 22-gauge bell wire isn't going to cut it. And if you want a 720-watt hair dryer? Forget it.-- supercat,
Jun 09 2003
Ok, folks, I can't resist adding my 2 cents' worth. How about this variation of the overall idea:
Consider that it is possible to wire electrical outlets so that each one gets its own circuit breaker at the distribution panel. Even the standard US duplex outlet has provisions for independent wiring, although it is seldom implemented in the field. That means that this idea will work best for new construction, not old (lots of extra wires would have to be run through the walls of existing houses, to provide those independent circuits). Either way, quite a lot of wire will be needed.
Next, consider that there are some companies out there working on transmission of data signals over the power lines. You can already buy communication gadgets you plug into the outlets and into your computers around your house, and they can talk to each other over the house power wiring.
Suppose all gadgets that are plugged into the outlets were given some rudimentary communication ability.
Now, consider the possibility of revising the distribution box utterly, so that it is a major electronically controlled power center. It receives Line Voltage from the power company, and distributes power over the house wiring, BUT ONLY to devices that are plugged in and request power. The initial data request would include the voltage requirements of the plugged-in device! A device that requests 3v gets it, just as a device that receives 240v gets it. Did you know that standard house wiring has a 600v rating? AND did you know that industrial systems frequently use 440v? With appropriately safe electrical construction (CONNECTION POINTS aren't usually protected up to 600v), I'd say to boost the House Line Voltage to 440 AND 3-phase, and let the central distribution controller handle the whole range from 3v to 440v, with either A.C. or D.C. available for the asking at any outlet! (YES, I do realize this heart-of-the-system is going to be one costly complicated contraption!) By the way, the data request from any plugged-in device might even include something about the maximum current rating for that device. (If a short develops, the control center can use THAT info -- current draw rising above that value -- to cut power, instead of waiting until so much current flows that a breaker trips. And Ground Fault Interrupt protection should also be available on every wiring circuit.)
There is, of course, a slight conundrum relating to how the gadget that has no power is going to communicate to request power, but this can be solved by the control center feeding all the circuits a trickle, say 2 volts, that mostly goes nowhere (no wastage), simply because the power circuit is not a complete circuit until something is plugged in. The 'something's rudimentary communications system could then use those 2 volts to send the power-request. Please note that the DC wire-resistance problem can be handled by having the power control center measure the voltage drop of the 2-volt circuit, so it can compute the resistance of the line between it and the gadget that wants power -- and it can boost the output voltage just a bit, to compensate. Yes, this means some extra wastage, over that of pure-A.C. You can't have everthing, but you can have quite a bit....
Note that to some extent, almost any gadget can use the standard wall-outlet plug; only those with extra power requirements (ranges, dryers, etc) would still need the specialized high-amperage outlets and heavier-gauge wiring that also tend to be associated with higher voltages. And, certainly standard 12-gauge house wire rated for 20 amperes can provide for the demands of all those different gadgets plugged into all those ordinary outlets -- each circuit is dedicated, remember!
As an example, consider an ordinary modern personal computer. It can plug into the wall and request 12v, after which its internal power supply can do conversion to 5v and 3v (it needs all three)...or the computer can connect to BOTH wall plugs of a duplex outlet, and request 12v from one and 5v from the other, and then its internal power supply only needs to convert 5v to 3v ... OR, with enough advance planning, houses could have quadplex outlets, and the computer could plug into three of them, requesting a different voltage at each.
It may now be seen the the biggest disadvantage will be the proliferation of wall outlets, combined with the much-lessened abiltiy to plug in multi-outlet power strips (one has to be very careful to ensure everything plugged into one has the same voltage rating! --AND the strip would have to have more-than-rudimentary communications, to tell the power control center that it is OK to boost amperage because more than one device is drawing.)
Naturally, when any gadget is unplugged (or even switched off!), the power circuit breaks, which should be signal enough for the house's power distribution center to once again supply only 2volts to that line (and power strips would have to be smart enough to deal with that, too).
Oh, and we do get some extra safety factor with this setup, because a child who plugs a key into a wall outlet will not feel a thing, since a key cannot provide the rudimentary communications signal needed to make the line powerfully "hot", and 2 volts is almost inherently unnoticeable.
Well, hope you liked it!-- Vernon,
Jun 10 2003
I do like it, thanks vern.-- Worldgineer,
Jun 10 2003
Just a quick note that I have been using a 120VDC-off-grid powered house for more than 23 years. I run lights, kitchen appliances, a full shop (lathe, milling machine, compressor,etc.) directly off the batteries. I use an inverter for my stereo system, washing machine, fridge, etc. and a generator only for my welder and of course the battery charger (sized to deliver about 3.5KW). The development of cheap off-line pwm supplies (including wall-warts) has greatly simplified my setup. I would need about $10,000CDN to replace this arrangement with an inverter big enough to supply all these loads. I have had exactly two power outages during the entire 23 years.
Jul 03 2003
Just found this item again & was amused to see [presto15]'s confident remark (from 2001) that the California energy debacle was caused by "not enough power plants." Heh... we were innocent in those days, weren't we. (For non-Calians - the state has since proved massive fraud on the part of energy suppliers, including but by no means limited to Enron, which cost the people between 3 and 9 *billion* bucks. Between that and the immoderate expenditures of the boom years, we are currently in deep, deep financial crap.)
Also, in the very first post [hippo] stated that DC electrocution is more dangerous because it keeps your muscles in spasm. I believe this is exactly backwards - muscle fibers only stay contracted if they are stimulated repeatedly, as happens with AC. AC is also more dangerous to heart rhythms. (link)-- hob,
Jul 03 2003
hello boys !
(because i think you probably all are, and i'm not)
(and a big ONE LOVE for all the americans on your
special day too : b all fireworky : you're really
celebrating the ancient celtic fire ritual of mid-
this is a most fascinating discussion, particularly
since i am considering setting up a wind generator
in my back garden, and thinking about how i am
going to use the power i garner...you know...should
i...shouldn't i...try to go low voltage ? i think that
although it's expensive i will probably buy that big
inverter, but it's so crazy : make DC, invert, pipe
to walls, draw by appliances : transform the power
again : either internally via "power regulators" or
externally via wall warts...but at least there are
SOME international standards of connection to make
things WORK in diff places, even if it involves
wasting BILLIONS of MU (monetary units) in forever
transforming and re-transforming electron flow...
keep up the banter : more is more...-- josiebelle,
Jul 04 2003
yes Josie, how exactly?, 8 ply wool and your pattern for cable stitch woiks hoW?-- The Kat,
Jul 04 2003
//low volt bus// Double-decker? That's one big boat [Rods]-- silverstormer,
Jul 04 2003
There is so much mis-information (some of it dangerous!) in all these comments, i don't know where to begin. Please don't share your thoughts on electricity unless you know what you're talking about. Somebody might get hurt or killed.
BTW, rmutt's idea is a good one, although fraught with more market hurdles than engineering ones.
Jul 05 2003
Well Cameron, please do share your thoughts once you figure out where to begin.-- hob,
Jul 05 2003
Rob: could you get in contact with me ? Email: email@example.com I have a few questions... and getting input from some one that has / Is doing it would be wonderful !
We are working very hard at getting off of the grid. So instead of buying a better vehicle, we have been driving real junk for a number of years to just to get our PV system going ! haha
We have run a PV system that produces 12v at 90 amps (full sun light) and we are using 0000 size coper wire ! For those of you unfamilure with wire size... this wire is about the size of a common garden hose and very tough to work with not to speak of expensive ! : )
We have just installed a 2 kw 120vdc PV array. I quickly found out that the only commercial inverters at 120vdc cost more than they should. A box of $300 worth of parts cost about $6,000 once they are soldered togeather ! haha
I will be building my own inverter, following the plans from some one who has ran his homebuilt 120vdc inverter for years.... but I'm un-happy with the design ( poor voltage output regulation and waveform )and hope to improve it when time permits.
As far as 120vdc being dangerous... So is hang gliding and other items... You must be aware of the danger, and train yourself to not go sticking your fingers in outlets or working with live voltages... haha It's really no more dangers than the deadly 120 / 240 vac that's in everyones homes ( which is indeed dangerous if not handled properly ) but everyone has accepted it.
Oct 26 2003
For converting 120VDC to 120VAC, have you considered cobbling together a rotary convertor?-- supercat,
Oct 27 2003
//VERY IMPORTANT: If any other companies want to use your standard, LET THEM. If you don't, it will never become THE standard.//
Indeed, Beta vs. VHS is hardly a new concept. In the early 20th Century (1908?), a guy named Mr. Robertson came up with a new improved replacement for the slotted screw. He didn't want anyone else to manufacture screws based upon his design, though. Later, in the 1930's, another guy named Mr. Philips came up with a different improved screw fastener. His wasn't as good as Mr. Robertson's, but he licensed the design to other manufacturers.
Mr. Robertson had something like a 25-year head start, but he never achieved anything near the market domination of Mr. Philips despite his superior product.-- supercat,
Nov 30 2003
Baked, baked, baked. But so what? I'm baffled at the idea that it's hard, complicated or dangerous. I wired my first house with #8-- and a bear it was too, as I used solid, not stranded. The only things I ran on 120vac were a record player (had a beautiful constant voltage transformer for that, lovely sin wave), the computer ran on a tripp lite (square wave, didn't seem to mind) and... And I think that was it. Lights were all 12 vdc, fridge was propane (quiet and cold), stove was gas. Worked a treat it did....-- hulot,
Dec 01 2003
Have been off the grid for 8 years and am wired for 12v. there is a way around every 120 volt problem. you just have to cut the" cord" to get there. solar has come way down and will continue to drop. at some point in the not to distant future it will be cheaper and then we`ll see a 12volt "revolution"-- 12volt dan,
Mar 30 2004
Did anyone mention that DC systems are more prone to electrolysis (sp?) induced corrosion?-- KiwiJohn,
Apr 02 2004
Has anybody considered the fact that not all DC appliances are 12v...? I've got a lot that are signficantly less than this.-- 5th Earth,
Jul 03 2004
What about using low-voltage AC at a frequency other than 60Hz? Transformers for higher frequencies don't have to be as large for a given current-carrying capacity, and so I would think there might be some possible efficiency improvements there. The biggest issues I would see would be (1) avoiding annoying audible noise; (2) avoiding harmonic interference on longwave communications if the frequency was high enough to deal with (1); (3) iron-core transformers have limits; 60KHz is fine, and 400Hz would be fine, but I won't know about 20KHz.-- supercat,
Jul 03 2004
I hate wallwarts too. (I sometimes call them "power bricks") I think the answer is to have a heavy duty 12v DC transformer built in to each AC wall plug. You could have a row of 5 or 6 12v positive center jacks running down the side of the plate, and all electronics would come with a double-ended cord instead of a wallwart.-- bobad,
Jul 03 2004
before i moved, i began building a 12 volt backup system for my house. 12 volt backup , charged by solar or by a charger, was almost a necessity because our power grid was shaky. true ,you arent going to run high power stuff off of 12v, but when the power goes down its nice to be able to have lights, a radio, or other small comforts. not mentioned here is also the fact that when your car battery is dead or if its cold outside and it does not want to start, you can always get a jump from your house...-- bobenhotep,
Jul 04 2004
I think the real problem this idea is trying to solve is the lack of standards and consistency with regard to wall warts/power supplies for various components -- I've got a cabinet full of them, all for different voltages and with inconsistent plug sizes.
Also, a 12V bus will likely be less efficient and more expensive than having 120VAC directly to all the components. I agree, at low currents, the wiring losses should still be relatively negligible compared to transformer losses. However the primary problem lies in the fact that not all equipment can be modified to run off 12V or any single voltage, for that matter. You're going to need a 120VAC -> 12VDC switching regulator for the home bus and then another 12VDC->5VDC or any other voltage--it's the combination of two conversion losses, versus just a single transformer using 120VAC directly. Switching power supplies also happen to be more complicated and probably more expensive for many of the basic applications where a simple transformer should work fine.
Combine that with the fact that we've already established that this must be a relatively *low current* line for wiring losses to be negligible, and it becomes evident that the additional work, expense, and negigible gain or even loss in efficiency to set up a 12VDC system in the house pretty much means there's not too much of a point to doing it.
Another point that should be noted about high-efficiency switching power supplies (both for the 120VAC-12VDC SMPS and the 12VDC-whatever DC-DC converters) -- unless you spend a lot of time doing design for such supplies, you're likely going to get a very electrically noisy system with lots of EMI/RFI, which might be unacceptable in many applications.
Back to my initial point--the biggest problem I see a lot of people trying to solve is really the inconsistency and inefficiency in many of the wall warts we have hanging around. It's not an easy problem to solve -- some believe that it's all just a huge conspiracy to charge the consumer lots of money for power supplies, but I personally suspect that the *PROFIT* / make - all - plug - heads - proprietary step of product development usually happens after the power supply design is finished. The biggest reason for having so many different adapters and plugs is simply because every product has different requirements. For example, the iPod has a proprietary dock connector with power not to make more money off the accessories but because it has extremely limited space requirements -- you'd take up a whole lot more space having a separate plug, and then you probably wouldn't be able to make/find a circular socket small enough to fit in the iPod. And then, of course, every device has different current, voltage, and noise requirements. We could try designing for every possible situation, but that'd be a futile exercise. Imagine lugging around a universal high current power supply the size of your laptop charger just to charge your phone -- not exactly the best way to go. Clearly, this is still a big problem to solve, and if anyone's got any better ideas, I'd really like to hear it.
-- edit, just read something in an above comment:
"$6000 for $300 of parts" does seem like a pretty absurd price for an inverter. But then again, as you mentioned, the output waveform was rather nasty--if an inverter is anything like a switching power supply, this is probably one of the most difficult steps and is the biggest difference between a simple DIY design and the commercial unit. In any switching supply, you not only need to consider the design of the circuit, but also the components (sometimes you'll need more expensive, low-ESR capacitors) and even the component layout (PCB design) in order to reduce the electrical noise and RFI/EMI emissions (in a commercial device, remember, you have to comply with Part 15 of the FCC regulations). For high-current applications, design becomes even more difficult, especially if you're also looking for higher efficiency.
That extra cost pays not only for better parts but also for the additional expense required for design.-- threepointone,
May 10 2007
Actually, I was just thinking that if one wanted to have a different standard for wiring, perhaps something like 36VAC@4A might be better. It would have the advantage over AC120 of being a non-hazardous voltage, but would only have to serve 1/3 the current of a 12 volt circuit.-- supercat,
May 11 2007
I have no idea how exactly this works but it is my understanding you can resonate and send power wirelessly. Electric toothbrushes for example between base and hand unit.
Why not make power wireless throughout your home. Whatever standard is established becomes the spec every device is made for.
wikipedia: MIT Witricity-- Shapharian,
Sep 14 2007
//Electric toothbrushes for example between base and hand unit.// Resonance has little to do with it - this is simply induction. The coupling is a simple transformer.-- coprocephalous,
Sep 15 2007
12 Volt wiring in a house is not practical however the need for a standard DC outlet that is compact and doesn't pulll out easily is a good idea. I used to have my workshop set up with quick-release terminals with 12V on them for experiments. I could see the advantage of 12V or maybe 24V wall sockets for consumer electronics that have a transformer unit and a fuse that snaps into the wall with similar dimensions of the common AC wall box - make it compatible with standard outlet covers.-- daniel_bingamon,
Oct 23 2007
Switching power supplies are becoming small and cheap enough that outlets that were rated to supply unregulated voltage at non-hazardous power levels might be useful. A switcher that takes 12-32VDC down to +5VDC wouldn't need to be as well protected as one designed for 120-240VAC.-- supercat,
Oct 23 2007
I gotta bun this for the half-bakedness but this could never be practical. There are so many variatons of how 12 volts are utilized in electronics that it would be tough to develop a standard. Many devices (like flat panel monitors) step up the voltage and/or amps and it relies on the strength of a 120V circuit to make up the difference.-- Jscotty,
Oct 24 2007
bigsleep: A step-down convertor that will generate 3.3 volts from anything in the range of 4 to 48 volts DC is pretty small, simple and cheap. A convertor that can directly accept up to 250 volts AC must be bigger and more complex.
Generally, I'd divide products that use wall-warts into three categories:
-1- Those that use the particular voltage from the wall wart for some purpose, and require some degree of precision.
-2- Those that use linear regulators and would accept any voltage above the minimum, except that power loss in the regulator will increase at higher voltages; this will typically cause a regulator to temporarily shut down when it overheats, though in some cases it may cause damage.
-3- Those that use switch-mode power supplies to produce any needed voltages; these will work from any voltage above the minimum up to a certain maximum, typically around 35-50VDC. These devices actually become more efficient at higher voltages.
Switched-mode supplies have shrunk considerably in size and cost over the last decade. If many devices start using such power supplies, a semi-universal 24-36VDC adapter may become practical.-- supercat,
Oct 27 2007
This is not a safe assumption:
"Assuming dry healthy skin, 12 volts is far too low to cause your muscles to contract. (If you doubt it, I will do a demonstration of your choice with a car battery.) 120VAC is the most dangerous voltage for contraction -- even more so than much higher voltages. The reversal of AC voltage does not make it safer than DC. "
Actually, voltage is simply the "availability of electricity" - like the size of a water pipe. Amperage is the force behind it (number of excited electrons), or how much water flows through the pipe.
Therefore, amperage is the killer. Any voltage can and will cause contraction of muscles (your body runs on micro-volts, and the muscles contract due to this). AC is far safer than DC - AC cycles to 0 voltages, based on the cycles per second - this means that one can escape the clutches of AC current. However, DC is at a constant voltage level and will not let go unless the power source is disconnected. I would take a hit from (and have) AC house wiring over a hit from a car battery anyday. One can weld with the current flow from a 50 - 70 Amp car battery - if someone survives that, they will have permanently damaged tissue (at the very least).
Now, 120V @ 70Amps will kill, as will 12VDC @ 70Amps. But the key here is the Amps, not the Volts. How ever, 3-phase 460VAC at 70 Amps will literally blow off limbs (and the victim will die) because there is a higher potential for electron flow (bigger water pipe)and the force is far greater than 120Vac or 12Vdc.
Just wanted to make sure we all understand this difference. It can save lives, appliances and houses.-- farmboy,
Feb 27 2008
//Now, 120V @ 70Amps will kill, as will 12VDC @ 70Amps// Now, that's a tricky one.I've seen a spanner glow red across the terminals of a car battery, but moments before, I picked the same battery up by the bare terminals. I wonder how you'd get 70amps through a human body with only 12 volts of potential? (ignore, for now if you will, that the potential was probably nearer 13 or 14 volts).[EDIT] You've probably guessed that I'm a) not deadb) not missing limbs-- AbsintheWithoutLeave,
Feb 27 2008
//Actually, voltage is simply the
"availability of electricity" - like the size
of a water pipe. Amperage is the force
behind it (number of excited
//Therefore, amperage is the killer//
//. AC is far safer than DC - AC cycles
to 0 voltages, based on the cycles per
second - this means that one can
escape the clutches of AC current.//
//I would take a hit from (and have) AC
house wiring over a hit from a car
Farmboy, you don't 'alf talk a load of
bollocks. Voltage is nothing like the
size of a water pipe; the closest
analogue would be water pressure. And
the electrons aren't "excited" - they are
permanently in the conduction band of
the metal anyway.
Amperage is not the killer, in the sense
you expressed. Listen, it's really quite
simple. What matters is the current
flowing through your body. Your body
has a certain resistance (typically
50-100kOhms between any two points
on dry skin; the skin contributes almost
all the resistance). Now, I=V/R and,
since R is constant, I (the current)
depends on V (the voltage).
If you happen to have a high resistance
in the circuit, then great. I can (and
regularly do, for reasons not worth
going into) handle a couple of kV with
bare hands, but it's going through a
10MOhm resistor. Since my body
resistance is only a hundredth of that,
there's only a voltage of about 20V
across my skin, and hence negligible
current. (If you prefer, think of it as
2kV going through 10.1MOhm -
current is about 10 microAmps).
As to the gonads about AC being easier
to escape from because the voltage
goes through zero - forget it. Your
muscles don't do anything much at 50
or 60 cycles per second, and the few
microseconds where the voltage is
crossing zero won't really be very
As for preferring to be shocked by 110
(or 220)V ac over a 12V car battery, you
really are very odd. Go now and stick
your fingers on the terminals of your
tractor's battery. You will feel precisely
bugger all. If you have a cut on one or
both fingers, you may just feel a tingle.
How is that so many people have such a
fundamental inability to understand
something so simple?-- MaxwellBuchanan,
Mar 01 2008
Well sounds like a lot of you need to do some research on AC/DC power. One reason why AC voltage is dangerous is that the frequency range of 50-70Hz is the most likely range to stop your heart. If the 45Hz standard had stuck when they were setting up the grid we would all be a lot safer (although crude motors would produce less low speed torque) . Instead we have the most dangerous possible ac power-volts and milliamps be damned.
A central DC system is not desirable because the lines would eat up the gain in efficiency. That said many RVs are essentially 12v homes.-- WcW,
Mar 01 2008
Putting your amp in the basement would require some serious low gauge wire for efficiency and quality reasons. Long wires eat acoustic quality.-- WcW,
Mar 01 2008
Touch the negative ground of a running car, then touch the coil lead. Unless the wires are brand new you get a pretty good impression of what bridging AC would feel like. It hasn't killed me yet but I avoid it.-- WcW,
Mar 01 2008
[WcW] sp. "Hz"What is interesting about this whole thread is that motor manufacturers are looking to increase the automotive standard from 12 to 48V, presumably in part to reduce the weight of copper they need to use.-- AbsintheWithoutLeave,
Mar 02 2008
//Touch the negative ground of a running
car, then touch the coil lead.// Yes, of
course. The coil is basically a crude step-
up transformer. Bridge the ground and
the 12V terminal of the battery and you
will feel exactly bugger all.-- MaxwellBuchanan,
Mar 02 2008
It's best that new standards are "evolutionary" instead of "revolutionary". I would suggest building off the USB standard.
The first product could be a wall outlet with a USB plug (not necessarily for data connectivity, but just for power) in between the two standard AC plugs. This would be accomplished with a small rectifier hidden away inside behind the outlet. Many things already charge off of the USB standard, so this could be used right away.
Next, for those with solar power, some DC current could stay DC current by providing power to the USB plugs. I don't know the details, but I've heard that converting the DC voltage from solar panels to AC for household appliances is a major source of expense.
Next, some simple connectivity, perhaps for fancy dimmer switches and 3-color LED lighting could be phased in.
These are just possible examples, but the key is small increments. In a free-ish market economy small increments is the way to solve chicken and egg problems.-- talldave,
Mar 02 2008
[Reposted from being falsely posted as a separate idea; sorry for the noise --admin]HELP PLEASE, we just got a house 650 sq. ft. that we wantto convert over to 12 vdc and we would love to get any helpwe can from all of you. We hope to do most of the workourselves, our home is in north Fla. not to much windbut lots of SUN. We plan to remove all inside wall covering.We would like to build our own converters, solor panels,hot water collectors, 12v water pumps, everything we canbuild we want to try and do ourselves. We need YOUR info.in our project and we hope to do this in 3 to 4 yrs. We livein a RV beside the home. I have some knowledge on homebuilding and little elec. Please email us at ,, firstname.lastname@example.org ,,, Thank you All,,-- tomrver,
Sep 23 2008
you just might wish to obfuscate your email and perhaps pop it onto your profile page.
welcome to hb and good luck!-- po,
Sep 24 2008
If you could keep the radiators electrically isolated, you could use the central heating feed and return pipes as conductors.You're going to need quite a lot of copper to carry the current.-- coprocephalous,
Sep 24 2008
I like that idea, [coprocephalous]. Use a plastic connector to join the radiator to the pipes, and you should be fine. I'd want to insulate all the pipework in that case, though - dropping a spanner across your central heating pipes could get nasty.-- Srimech,
Sep 24 2008
After a (very) quick look, it seems that an LED-based lamp which is roughly as bright as a conventional 100W incandescent lamp, uses about 3W. Even if this is wrong by a factor of 3, a 12V DC lighting circuit for LED lamps would have a smaller current requirement than your existing conventional 120V incandescent lighting circuit.
So, no wiring change needed. You just need to replace all your lamps with 12V LED ones, and put in a single 120/240AC->12DC 100W converter, which I suppose is more efficient than having ac->dc converters in every bulb.
Or, is it ? Maybe this is the Big Question. Are the Single converter efficiency gains greater than the low voltage cable losses ? I have no idea...
Of course every 120/240V LED bulb has a "mini-wart" nestling inside it. Which sounds like a lot of wasted components which have to be produced...
Anyway, this sounds as if it could become the First Step towards a 12V house - until you start running too much stuff on the lighting circuit !!-- VaquitaTim,
Oct 16 2008
Isn't permanent metal plumbing (such as central heating lines) supposed to be earthed, so it can't accidentally be made electrically live? It could probably still be used as the return, as long as currents aren't too high.-- spidermother,
Oct 16 2008
[tomrver] When you say 'convert', does that mean the house is currently connected to mains electricity? If so it may be financially and environmentally better to use the grid as an energy bank rather than use batteries to store energy.-- spidermother,
Oct 16 2008
//Isn't permanent metal plumbing (such as central heating lines) supposed to be earthed, so it can't accidentally be made electrically live? //Yes, but that's for dangerous touch-em-and-you're-dead mains voltages*.Here, the greatest danger is shorting two adjacent pipes, which, let's face it, are normally separated by the width of a radiator.
* that's 240V real mains, not the wimpy North American stuff.-- AbsintheWithoutLeave,
Oct 18 2008
<link> my system requires one transformer, if any, right at the source, for entire house lighting <smug look>-- FlyingToaster,
Oct 18 2008
//I wonder how you'd get 70amps through a human body with only 12 volts of potential?//
Large spikes...-- saedi,
Dec 12 2010
Solar homes and RVs already have 12 DC appliances.-- travbm,
Oct 29 2015