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How Tesla Batteries Will Force Home Wiring To Go Low Voltage
CIStud writes with a story at CEPro suggesting that solar power and home batteries like Tesla's PowerWall "will force the reinvention of home wiring from primarily AC high voltage to DC home-run low voltage to reduce power conversion loss," writing "To avoid the 20% to 40% power loss when converting from DC to AC, home wiring will have to convert to home-run low-voltage, and eventually eliminate the need for high-voltage 110V electrical wiring." As a former full-time Airstream dweller, I can attest to the importance of DC appliances when dealing with batteries.
You'd think the fight between Edison and Tesla would have ended long after their deaths. Clearly not. It is a good thing their graves aren't near each other, if they were, there would surely be lighting bolts going back and forth.
Kind of ironic. Nikola Tesla fought to champion AC power, and the company named after him will bring Edison's dream of DC-sourced homes to reality.
So, a company called Tesla is developing technology that will prove that in the long term that DC is the better choice for powering homes?
Low voltage is impractical for long runs. The amperage has to be too high and the voltage drop is too great.
High voltage DC is much more likely to happen, although my money is on higher efficiency conversion.
If you're using somewhere near the inverter's peak output, then you can get as much as 90% efficiency. Inverters are getting smaller all the time, which makes it more feasible to gang modules instead of using monolithic units which will provide very low conversion efficiency for low outputs.
It's still unfortunate to leave 10% on the table. But a lot of DC-DC power supplies are also not very efficient. Best-case, they are only around 95% efficient, and you can easily lose another 10-15% if you execute them poorly. So yes, optimally they have half the peak loss, and even bad ones are likely to be better, but we can make better inverters and we will as the demand increases.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Maybe they were both right and both wrong? http://en.wikipedia.org/wiki/W...
...albeit this has already happened on a smaller scale before. All you need to do is ask anyone who owns or has owned an RV or Camping trailer.
I dealt with it myself when I had an RV: a bank of huge batteries, an inverter, and a generator. In Tesla's instance, you replace "generator" with "local power grid", but otherwise it's the same routine: Your lights and similar are low-voltage (just like most RVs), but you use an inverter for any general consumer item (TV, computer/laptop, hair dryer, whatever).
I think the only diff would be in the appliances... most RV appliances (e.g. the refrigerator, furnace blower, AC units) are made to run off of 12v DC, but most RV appliances are pretty small when compared to their house-made counterparts.
Maybe ask folks who do the hardcore solar/wind thing?
Quo usque tandem abutere, Nimbus, patientia nostra?
It's not like there is one single standard DC voltage that everything runs off of. Switching between different DC voltages incurs a loss just like switching between the current AC standard and a given DC voltage incurs a loss.
If one were deploying everything from scratch, one could pick a standard. Right now, everyone is going to want to run the stuff they have, and the AC to DC converters on that stuff, even when they are exposed (i.e. wall-warts) instead of embedded in the device, are converting to a variety of different DC values.
With houses as big as they are, we ( USA ) need to think about going to 220v to save on copper.
Besides, inverters are easy to build, soon you'll beable to buy a Raseberry Pi kit to run a 10kw inverter.
I thought North America already was low voltage. 8P
230~240VAC FTW!
Will it be cheaper to buy 20-40% more batteries (or solar panels) or convert all your appliances? I suspect batteries will be far cheaper. But yes, I do know the importance of not converting. We spend a lot of time in the wilderness in our travel trailer and it really matters then. However, don't underestimate the loss with DC over the distance of a house. It won't be 20-40%, but 10% maybe...
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20% power loss for AC to DC? Someone is on crack here. A good inverter can hit over 97% efficiency. If there was a 40% loss, my comms room online UPS would have required a much bigger CRAC setup just to deal with that...
Forgive me if I have this wrong, but if we start wiring houses for low voltage DC, won't this mean huge fat copper cables to deal with the current implications of a washing machine or oven pulling tens, even hundreds of amps because of Ohms law?
I also call shenanigans on the 20%-40% inefficiency number -- a good DC/DC switching converter should be 85-90% efficient.
There just isn't enough lithium in the world to supply Tesla batteries to every US household, let alone the world.
Worrying about low-voltage appliances is delusional.
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Seems to me a better solution would be to research ways to convert from DC to AC more efficiently. Currently there's up to a 40% power loss. That's just begging for some research money....
You are correct, which is why the article is bs. USA needs to upgrade to 240 AC, not downgrade to 5 or 12 VDC.
If we were starting out then maybe, but there are just so many things that can be plugged into an AC socket. It's pretty amazing that you can take anything from the last 50 years or more that has the right plug on it, shove it into a wall socket, and off it goes. The current system is a very good standard, and it will be hard to change things. Further, one of the original reasons Tesla (Nikola) won out is that the induction motor is an extremely good motor design (safe, reliable, quiet). Lots of things still have AC induction motors (heatpumps, your fridge) and these require, well AC. If you don't have that then you need a motor driver for them (or brushes I suppose) which is just a three-phase inverter anyway.
Also 20-40% power loss is crazy. More like 5-10% with modern semi-conductors and getting better/cheaper all the time.
IIRC, Tesla Model S batteries are connected in series groups, resulting in a 350 Volt output. If Tesla made a home battery that put out 120 Volts, many resistive loads, universal motors and switched mode power supplies could run directly off battery power.
Have gnu, will travel.
Pair up with your neighbor and pay a midget to flip the switch 50 times a second?
As you know being a RV dweller doing this type of stuff you will have to upgrade the wiring size just to deal with current increase, and circuit break box. The only way would be in new homes.
While this would integrate well if using wind power and solar as a supplement to your home, those homes just using AC/DC will see high loss in total conversion requirements.
Unless your talking conversion to like 48VDC throughout house, or something that would just require half wave conversion and then current control on output into a battery bank as both a buffer and filter.
I'm not buying it. Voltage x Amperage = Wattage. So long as Wattage stays the same (think 1,800W hair dryers here), your Amperage must proportionately increase if the Voltage drops... This can only be accomplished by using LARGER wires to deliver the Amps... This is why wires on your car battery or golf cart are so large... Imaging the COST of wiring a home with large (lower Voltage) conductors like that... Ask yourself why Europe uses a ~230V/240V electricity in homes and how much cost savings there must be by delivering all the wattage at half the conductor size compared to the North American 120V household standard... Smarter people than us have all thought this stuff through many decades ago... Tesla is trying to push battery tech and if it were affordable and better than a $500 gas generator, we'd already have it installed. Cool technology, way too expensive and I'm not rewiring my house.
20 - 40% conversion efficiency, where the fuck did he get that from?
Also, there's the issue of much larger wire gauges, inability to run far more efficient and durable AC motors, more difficulty in converting between voltages (A DC microwave would be hilarious) the need to re-design every lamp ballast in existence and a host of other reasons why DC is a bad idea outside of data-centres and other niche applications.
We settled this a century ago.
Question for engineer / mathy types that can do the conversion loss calculations:
Given:
I think:
Would there be anything substantive to gain by putting in a maybe 10-12v, multi-amp power supply in the basement and running it to the various places you plug things in? Big-ass USB power supply @5v would cover a lot of things, but more stuff like streaming TV players, maybe laptops, and the like might be able to run from a bit higher voltage.
Granted, the opportunities for shorts, magic blue smoke release, and general safety issues are probably way more problematic than what you'd save in power conversion, and you will still need 110v to run big motors, and the like, but...
MB is already far ahead, as they actually transmit power from their dams as DC. https://www.hydro.mb.ca/corpor...
"Evil will always triumph over good, because good is dumb." - Dark Helmet (Spaceballs)
This is a very poorly researched article. They talk about getting 12V from a solar panel. No modern home-scale solar system runs at 12V. The power loss due to resistance is much too high until you use wires that are much too large.
The real solution would be to standardize on some type of home HVDC distribution in the 150-300VDC range. This would help keep the DC/DC conversion in roughly the 2:1 voltage ration range, which helps efficiency. It would also help keep the wire gauge reasonable. I'm not sure how the article's author envisions running things like a modern HE washing machine with build in heater from, say, 12V. It would take about 100-150 amps and require about 2/0 gauge wire to keep the losses manageable.
None of the methods have general and ubiquitous superiority. AC is key for centralized energy manufacturing. DC is instrumental for decentralized electric grids.
I think that prediction that home appliances will drift to DC is correct in a way that there will be more appliances that will start taking either AC or DC.
Next question is, however, on what will be the DC home grid voltage? Historic 12V? Electric car 48V? Anything in between?
If you look around, following voltages are common for DC using appliances:
- laptop 18V.
- Telephones, smartphones - 5V Usb
- I have two radios: one is 6*1.5V= 9V, other is 3 Volts
- Electric toothbrush: 3Volts
- Home security adapter - 24V
- other small appliances 1.5V battery
- Electric rechargeable drill 18V
Honestly I'm surprised this hasn't happened already. Most home devices these days run off of DC voltages (24,12,6,etc) such as LED lighting, computers, TV's, clocks, etc. And there are a LOT of losses running a bunch of small transformers in/around those devices. While I doubt 120AC is going to vanish anytime soon combined DC/AC house wiring with a centralized transformer or pulling straight off of a battery would seem to be a no brainer if a standardized connectors/devices can become commonplace.
The higher current draw (if a low voltage DC is used) will require much heavier cables than the typical (for US) 12 guage cable. That can get expensive and there would certainly be the need for DC-DC converters for funky voltages. Maybe it would be standardized over time but that's a long way off.
Maybe there will in fact be something like a 48V standard that would be some sort of compromise, although I think the Tesla batteries run around 220V to keep the motors relatively small. I don't know if there's any real problem with running higher voltage DC in the home although I'm pretty sure switches would need to be made differently to prevent arcing.
Seems like maybe more trouble than it's worth.
Many appliances run just fine on 120v DC power. Of course it's hard to tell which ones without either taking it apart and examining it or trying it and risking the magic smoke coming out.
Nothing high-current will ever switch to low voltage DC, I hope. I'm already annoyed at my 120v electric lawn mower; stupid extension cord is way heavier than my in-laws 240v electric lawn mower in Europe. Considering the cost of copper we should be switching to higher voltages, not lower.
Seems like the batteries could be redesigned to be higher voltage to reduce inverter losses. Just add more cells.
True sine wave IGBT converters are pretty efficient.
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NO. That will not happen. Power equals voltage times current. To deliver the same power load at a lower voltage would require higher current, and household wiring is already designed to carry as much current as it safely can. Lowering voltage would thus require new, much bulkier wiring, which can't easily be retrofitted in older structures. Conduits would be able to carry far less of it, so those two would have to be overhauled. Last but not least, wireless charging and better batteries will eliminate much of the need for the lower-power wiring in the first place. There are very few things that I can confidently predict about the future, but one of those things is that mains (110-220v) voltage is not going to change drastically anytime soon. I'd be willing to bet every single powered appliance in my home on it.
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I design homes as a hobby - how would I build my own? Most of my designs - except for the most "modernly practical" use DC power for at minimum lighting.
The one thing I need to work out - exactly how do we make a Lava Lamp work efficiently on DC power....
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Is it still the case that solar panels are wired to produce 12-V output? As I understand it, this was done historically for the convenience of interfacing with 12-V lead-acid batteries. This historical quirk has made almost everything else about solar more difficult and expensive, because it's a low-voltage, high-current architecture.
If, on the other hand, solar panels were wired to produce, say, 120 V DC output (i.e., the cells or panels wired more in series than parallel), then lots of things get easier and less expensive. All the wiring can be of much lighter gauge due to the lower current. The losses in the inverter would be lower because of lower resistive losses and more of 1:1 voltage ratio. Some components (capacitors, FETs and IGBTs) may be more expensive because of the higher voltage rating, but that is a relatively small incremental cost compared to the cost of copper.
It seems to me that a lot, if not the majority, of new residential solar installations are grid-tied with no battery attached. It seems that the system should be designed to make that easier and more efficient, rather than tie ourselves to historical off-the-grid designs. Plus, if Tesla and others are designing new style batteries for this market, they can design them for higher voltage.
if the battery power trend takes off, it must lead to a new paradigm in which homes will be powered more with low voltage wiring than line voltage electrical, according to a blog
A couple of real big if's there. Battery power is unlikely to take off in all but a few low latitude places where the climate is right and it's heavily subsidized. Even then, there are better alternatives than rewiring a house; and of course solar doesn't work for high density housing like a multi-story apartment building..
3-phase, while we're at it.
Home power is already low voltage... as is anything below 1kV.
https://www.eff.org/https-everywhere
I could use all my camping equipment in the comfort of my own home.
Yeah, the whole article is just terrible.
I'd need thick-ethernet-sized cables to safely power my array of computer gear, hoover, microwave etc. at that sort of voltage.
And 40% AC-DC conversion loss? My UPS gets much better efficiency than that and it's probably older than this house!
I don't know what bias or angle the author was aiming for but it doesn't seem to work out.
With homes having high load devices with large motors(washing machines, compressors in heat pumps, etc) and the large resistive loads like electric heaters, stoves, etc DC just is not the answer. Even with DC there would be a need for DC-DC converters which work by converting to AC... So given how easy it is to move AC voltages around and up/down I would think the question would be how do we optimize the losses in conversions. Maybe we need 5KHz instead of 50/60Hz.
"Anyone who stands out in the middle of a road looks like roadkill to me." --Linus
When my 3yr old sticks a forked prong in my DC electrical outlet, what is the safety factor compared to the current AC plugs?
Low voltage is not going to happen, if only because the costs for copper wire would be astronomical. If you take your standard 1500w electrical outlet, at 120v it only needs #14 gauge wire to run 54 feet @1800watts because it's only 15 amps. If you take that down to 24V, you need #2 gauge wire to run the same distance, and you are only getting 1200watts, at 50 amps! #14 wire is about $0.17 per foot, where as #2 wire is (from what I could find) about $7.50 per foot.
-Xoltri
If you're going for "low" voltage DC (24V), you're just shifting the losses from the conversion to the wiring. Anyone that has done any home automation, security systems or basic electronics knows that even over a relatively low distance you can have a severe voltage drop which has to be made up with more power draw.
Electricians do consider anything sub-400V, "low" voltage. To have your home outfitted with DC you wouldn't even need to replace wiring, you might need to replace outlets. IF your outlets are correctly wired, you could simply convert from 110VAC to 150-200VDC and most of your devices that are not inductive would continue to work. Incandescent light bulbs would work, fluorescents would not, LED light bulbs would, computers, phone, laptop chargers etc. all would. Your big apparatus' (laundry, fridge etc) would need some conversion work but would always almost work better with AC (AC motors are more cost efficient and less maintenance than DC motors, that's one of the reason's Tesla won).
Custom electronics and digital signage for your business: www.evcircuits.com
Absolutely correct. 12v is great for low power items. Try running your electric dryer or stove on it.
I'm not sure that home batteries will drive a switch to low voltage DC. There's a ton of inertia to overcome. The cost of retrofitting the wiring to handle the higher amperage of using lower voltage alone will be thousands of dollars for every single house, apartment, and office. A simple 20A 120V circuit changed over to 12V will draw 200A. You're going to need to upgrade to 4 or even 2 gauge wire at a minimum to handle that kind of current. And that's a lot of money.
The switch from AC to DC inside the home might be feasible but there's no way you can convert the entire grid. You'd have to rebuild the whole grid from scratch to convert from AC to DC. The transformers to step the voltages up or down simply don't work unless they're pushing AC so how do you handle industrial level supply being stepped down to household voltages at the neighborhood transformer? And who's going to pay for the switch? And what about the industrial users who don't need to run low voltage DC? How do you satisfy their demand?
Then you have to deal with how a substantial number of appliances are built. Many are designed for AC current and won't work with DC, regardless of the voltages. Sure, you can swap out the power supply in your desktop PC to take a DC feed without a lot of trouble. And if electronics retailers had a standard DC wall voltage to work with, you'd see most consumer electronics move to those standards. But how do you deal with a cable modem that needs 12V and a home router that takes 9V? Who wants to go out and replace all of their equipment that is running just fine right now? Who has the money to do that?
And here's the kicker. What real benefit do we gain from a switch over to low voltage DC in the house? Sure, some of the consumer electronics we use won't need that big wall vampire to supply them with power. And sure, we don't really need to run our lights from 120V when 12V can still drive enough light from LEDs without any trouble. But what about the appliances in the house that really draw the bulk of the power in the house? The 240V electric stove or the heat and AC systems? What about your refrigerator and your washer/dryer? Hell, can you imagine the amperage draw trying to recharge your electric car with 12V? And are you going to just skip using those appliances when you're running on battery power?
So if you're going to have to keep your 120V AC based house wiring for your major appliances, do you really want to spend all the money installing a low voltage subsystem for a few consumer electronic devices to supplement the wiring you already have? I know I wouldn't want to.
Like everything else that is poised to "fundamentally change the way we do things", the dreamers never consider the practical reality of actually making the change. In reality, I think we're going to have to deal with the inefficiency of converting from DC battery power to 120V AC for the home. There's just too many things to overcome for little to no benefit.
We already have 240V AC. We just have a split-phase system to provide it for the few special cases (dryers and ovens) that require it.
Lots of devices, like AC motors require AC to run. This includes air conditioning systems and refrigerators, which are the biggest power users in a typical home
Modern AC-DC power supplies are much more efficient than the article claims
But, the biggest reason this is silly is the ENORMOUSLY HUGE number of existing devices that run on AC
Maybe, maybe it might make sense for a VERY small number of VERY specialized devices in new construction
Less voltage = less eff. More voltage = more eff.
0.o
I think Tesla needs to go back to school. At low voltage, you can only push so many Watts before you run into resistance and heat issues. The higher the voltage, the more Watts you can push through the same size wire. This is why the car industry is moving towards 24 volt systems, because 12 volt systems max out at about 1.5KW's An ex. At 12 volts, my whats-a-ma-giger wants to consume 500 watts. for that much power, I will need to push ~"42" AMPS! Ho boy! Now that's an instant electrical fire! Now lets say my device runs on 110 volts and still consumes 500 watts. That's roughly about 5 amps we need to push (pull) down the line. Perfectly safe with standard house hold wiring.
And a second thing. DC requires MUCH THICKER CABLING at the same voltages and amperage than AC does. This is because you don't push the electrons in only one direction with AC, you push them back and forth and they never have to run all the way down the line leading to less long distance loss, and loss as heat. That is why we use AC. Could anyone imagine the size a DC cable would need to be at those high voltages?!
This Tesla company, there seem to be a bunch of "special" people working there. Just wow. lol
The USA is running on 220-250V AC for residential (exact voltage varies per locale). It's single-phase with a center-tap neutral, sometimes called "split phase"; Typically, a neighborhood will be on one phase of three-phase distribution system. Split phase allows one get two half-phases of about 120V (typical U.S. receptacle, a.k.a. "power outlet"), but you still have 240V available for large appliances: electric stoves/ranges, furnaces, installed heaters (baseboard or in-wall), clothes dryers, and/or sometimes a welding receptacle in the garage.
Split phase is occasionally incorrectly referred to as "two phase", which actually only exists with one old electrical distribution system near Niagra.
Having lived in an older home with aluminum wiring along with millions of others, this is not a bad thing esp as lighting transitions to LED's and PC's and TV's lower their power footprint. This could be the catalyst that has these older homes replace the sub par wiring to something more safe. Soon you may only have dedicated lines of AC voltage to things like HVAC systems, water softeners, hot tubs, electric stoves, but even these could be pushed over to DC.
Exactly. This sounds ridiculous. I wired up an inverter for a bar fridge in my trailer. The inverter has an 85% efficiency. The fridge draws 500 watts when the compressor first starts (measured with a Kill-A-Watt). When connected to just one battery with a 6 AWG cable (PLENTY to safely supply the 50 Amps I calculated), the voltage sags from 13.6 volts (full charge) to 10 volts and the inverter would cut out (3.6 volts loss at 120 volts doesn't matter, and it's still safe, so of course the electrical code was happy, but it does make a difference for a 12 volt system!). After connecting another THREE 6 AWG cables in parallel, giving me an effective ~2 AWG cable (Rated for 115 Amps by electrical code!), the voltage sag was negligible and everything ran well.
An 1800 watt hairdrier would be getting into the kcmil range to work reliably. When I worked installing wire at a factory, the largest pull I had to deal with was 500 kcmil. The puller machine bent the roof of the factory trying to get it around two 90s. Homeowners have never seen that. Cables the size of your toilet drain. Just a foot of that copper is a day's wages.
Keep in mind 2 AWG cable will cost you somewhere around $5 (or more) per foot and requires the sorts of holes in your studs you'd normally run drain pipes through. 14 AWG cable (the minimum allowed by code for a 120 VAC circuit here) costs about $1 per foot. The power whip for the fridge itself is 18 AWG (about $0.50 per foot).
Europe goes all the way with copper savings by permitting ring circuits.
Seems premature to me. An awful lot of things have to work out just right for whole-home battery systems to make much sense.
Even then low-voltage DC plants don't make much sense. Your microwave oven consumes 1100+ watts. Know what amperage that is at 5 volts DC? You'd barely be able to wrap your hand around the power cord.
Even at 48 volts DC, the power plant in a telephone company central office is really something to behold.
Also, AC/DC conversion isn't as dire as stated. Sloppy cheap converters do indeed operate at around 75% effeciency with the remaining 25% lost as heat. But look at the "80+" computer power supply standards. The "80+ platinum" standard requires 95% efficiency. Those power cost twice as much but "pure science" does not prevent their operation. They work as promised.
Moderating "-1, Disagree" is simple censorship. Have the guts to post your opinion.
Sure. And 1000 W appliance will draw 100 A. There is a reason why high voltage is needed.
This is strange. "20 to 40% power loss" seems to be an awfully poor inverter; existing inverters are 4-8 % loss.
Rather than rewire every house in America, wouldn't it make more sense to just design better inverters?
http://www.geoffreylandis.com
Ah. I kinda don't see this happening anytime soon.
There are millions (perhaps tens of millions) of buildings across the country. All running AC.
Tesla's batteries are somewhat attractive, but still a *VERY* niche product.
I really don't see them gaining a realistically large enough foothold to force this sort of transition and the type of power system infrastructure changes it would require.
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Add in to the mix that there is not enough copper in the world to give 7 billion people a first world lifestyle using 110V, and some US idiot thinks low voltage DC is the way to go.
Low voltage needs big wires. 40A 240V (stove outlet) would be 400A @ 24V, anything higher is no longer "low voltage" by code. No.
HVDC (240/300VDC) may be useful, but it needs different connectors and switches (Intel has done great work on that) because a DC arc doesn't self-extinguish (every outlet is a stick welder). A lot of things (except non-universal motors) would work OK on 120VDC or 240VDC because almost nobody uses big transformers anymore so the input section on most electronics is AC->400VDC->HiFreq transformer->Power, but every switch and outlet would need to be replaced.
lower voltages mean much higher wiring losses or much more expensive wiring (or likely a combination of both). DC at a given voltage is substantially more dangerous than AC because it is prone to arcing.
20% conversion efficiency is pretty shit by modern standards
http://www.apcmedia.com/salest... is an interesting read, it's aimed at datacenter UPS systems but many of the arguments would apply equally to a house battery system.
As for the posters mention of living in a caravan a house is much bigger than a caravan (though admittedly smaller than a datacenter). So the wiring losses are less of an issue.
note: i'm known as plugwash most places but i screwd up registering that here somehow in the past and now can't register
This sounds like fantasy from people who don't understand Ohm's law. Tesla's Powerwall voltage is around 400V. You have nothing to do with such voltage in the house, it is too dangerous. You need DC-DC or DC-AC converter to reduce voltage first, and you already have DC-AC for grid connection, and it is simpler.
Low voltage DC is used for lightning sometimes, like older halogen bulbs or outdoors. It may be nice to have extra sockets around the house for low power electronics, but there are no widespread standards for it, and it would be just waste of money for extra lines and outlets. You would need much more copper for low voltage/high amperage lines.
As someone who likes tea, and uses a kettle a lot, I'd rather North America move from 120V AC to 230V (given the same amp restrictions).
I haven't been able to find voltage specifics about the tesla battery system, but I've been expecting it will be more likely to lean towards AC. I would like to get the 10kwh pack for my off-grid system, but I don't yet know how to charge the tesla battery bank. Since they are clearly targeting the residential on-grid market, I expect AC charging to be more common. I wouldn't be surprised if I end up going the microinverter route with PC->AC going into the house and charging the battery bank, with an inverter. Has anyone found detailed installation specifics like this? I spent a good half hour looking after the price breakdown came out and couldn't find anything but a massive low-information media circlejerk.
I'm buying a massive house that is 1/3 the price it should be (ie, very good shape structurally, but is still half the price of per/square of "poor" quality; very high quality home, just hasn't been remodeled in many decades. Brand new roof though...heh). I'll be removing most of the sheetrock and replacing half of the wiring already, and am installing solar. I can't find a solar company that seems comfortable with DC circuits, low-voltage or otherwise. Coming off the solar it will be already DC; converting from DC to AC just to convert back to DC is likely why they claim the 20-40% loss - you're not losing in conversion just once, right? So then I just need some sort of power stabilizing factor - such as running through a battery or whatnot - thus why I clicked on this article at all. Any already know of a good book or resource with which I could inform myself before spending a good deal of money?
The extra copper needed for low voltage wiring will lead to home invasions just to strip copper from houses. Better get South Africa style home defense systems, which of course will mean still more copper.
This is so stupid. Telsa cars are a waste for a majority of the nation, as we like to drive beyond our city, or commute long distance. You know what's more efficient than wasting all this money on home electrical conversion and expensive batteries...? Gasoline. Super efficient means of moving energy from one place to another and lighter than a big nasty caustic battery, and I don't have to reconfigure my house to use gasoline.
And thats before even getting into the electrical merits pointed out by others.
>Ask yourself why Europe uses a ~230V/240V electricity
Apart from the economical reasons as outlined by yourself, I always assumed it was a safety issue. I was taught that current kills not Voltage. A static shock has huge tension but non-existent current whereas a toaster in the bathtub has (relatively) low voltage and high current.
Can a sparky weigh in on this for me?
Not that I'd go licking the sockets in any country.
Some additional to the copper is expensive arguments:
The Tesla Powerwall battery runs at 350-450V DC. So the home wiring will go low voltage because the battery itself is high voltage??
The Tesla Powerwall is only a battery. The inverter/battery charger will be (amongst others) Fronius Symo Hybrid (german, pdf). This neat little device combines a solar inverter/battery charger/battery inverter! DC-AC or AC-DC efficiency: 95-98%.
This must be the most idiotic technology prediction I ever read on slashdot!
AirStream user you may be, but an engineer you are NOT. Even with the conversion losses, it is MUCH cheaper to wire a facility for high-voltage, low-current usage - to provide the power to the appliance WITHOUT the concurrent IR-losses associated with low voltage power sources. A simple 0.1 ohm wire will lose (drop - dissipate - produce HEAT instead of usable power) more than 8 volts to power a 1KW device, providing only 4 volts to the appliance, which would then necissitate an additional current of 250 amps to provide the kilowatt of power - leading to additional IR losses - and effectively being totally unusable as a power source. With the same 0.1 ohm wire, @ 110 volts, @ 1000 watts, only 1 volt is lost (dissipated) by the wiring. THIS is a BEST-CASE model, since most house wiring approaches the 1 ohm level, hence the flicker / drop in brightness in kitchen lighting when the microwave kicks in, producing a 10 volt (or so) drop in the voltage to that particular circuit. The ONLY reason automotive systems are 12v-powered is because of the massive support industry of the 12-volt battery. MANY of the projected development systems for the near-future (10 years or so) are focussing on 48-volt systems, due to the increasing power consumption of the vehicle, and, for the SAME REASONING I JUST STATED - - - low voltage results in massively more LOST power through the conducting wiring than does HIGH(er) voltage. Hell, even 50 years ago, the commercial bus industry was using twinned, series batteries for 24-volt operation.
You keep repeating that. You continue to be wrong. You get two of three hot phases in home wiring, 120 degrees out of phase.
If they were the same phase you would get zero volts between them.
John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'
The Tesla Powerwall IS not that big of a deal and not the solution for Solar!
The 10kwh Powerwall is only good for 50 cycles a year! It is more of a house size UPS. The 7 will work for daily use but it is more expensive per kwh than the 10 and even Solar City is not going to sell the 7.
The Tesla power wall battery still sucks. It does suck less than other battery packs but only a little. The big improvment is one of packaging and frankly hype.
I know that this is going to go counter to the Church of Tesla's teachings but even the Model S really does not count. It is a 100K car for the very rich. Another fact is the simple truth that the Tesla car company is not successful car company yet. It has yet to make a profit.
No we do not need to move to low voltage wiring in our homes because of the "success" of the Powerwall. The Powerwall is the the solution to the solar production/demand problem. And frankly in most homes the biggest power users are things like AC, Hot water heaters, dryers, stoves, refrigerators, and so on. All of which work just fine on AC and I for one do not want to have to have a bus bar the size of my arm running to my dryer so it can work on 12 volts.
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
According to CE Pro Website, author of article is Jason Knott. According to LinkedIn, Jason Knott, Editor at CE Pro/EH Publishing, has a BA in Journalism from USC (1984). Also, from CE Pro's "About the Author" section: "Jason has covered low-voltage electronics as an editor since 1990. He joined EH Publishing in 2000, and before that served as publisher and editor of Security Sales, a leading magazine for the security industry." If The Onion wrote this article, the title might be:
"Area man parlays journalism degree into low-voltage DC career, then hypes low-voltage DC".
On the plus side, marine systems will likely stay DC for the foreseeable future. Perhaps Tesla batteries will be a boon to yacht owners? At the very least, it would make for a better article.
Here's the latest gimick to get us to buy new appliances! Throw away everything you have - washing machine, dryer, oven, cooktop, TV, and stereo. Buy new ones; you don't need the old, outmoded units. Hurry, be the first on your block! Err. By the way, how are they going to send the power cross-country to keep all these batteries charged?
I was taught that current kills not Voltage. A static shock has huge tension but non-existent current whereas a toaster in the bathtub has (relatively) low voltage and high current.
True.
Can a sparky weigh in on this for me?
Sure. The amperage coming through a 230V home outlet is still orders of magnitude higher than what's required to be lethal. The reduction by 1/2 from our 120V service has nothing to do with making it safe to stick a fork in the outlet ;-)
Current kills, yes. However, voltage provides the potential to get that current through your body. European homes still have more than enough current available to kill (in fact, those wimpy DC adapters everyone uses that aren't insulated at the connector also have enough current).
However, the reason that your DC adapter doesn't shock you is it takes more than 5 volts to push that current through your body. The standard is usually 48 volts, however, you WILL feel a very unpleasant shock at that voltage. Typical skin resistance means that 24 volts and under is not likely to cause any sensation. However, if you were to piece your skin, that 5 volt adapter could easily kill you because it is the current that kills, and once you are past the high resistance barrier (skin) and into low resistance areas (bloodstream) you don't need that potential to push the current through your body.
120 vac and 240 vac are both easily going to kill you from standard outlets, as there's way more than 100 mA available from them. 120 vac, however, is *less* likely to kill (but entirely still probable) since it hasn't got the potential as 240 vac to push the current through you. ie: Maybe at 120 vac you will get lucky and your shoes can insulate you enough.
To get to the point of "safe" high voltage (like a VanDegraaff generator), we would be looking at trying to keep the current low, say, 5 mA. That would require about 1 million volts to power your stove. At that voltage, other very odd things start to happen (eg: It will just arc through almost any sort of normal insulation and start fires).
I think the article is also talking about the fact that so many things are running low voltage today (and low amperage) that we are constantly throwing away energy in a solar situation to convert them back and forth. I have an off grid cabin where there are zero power lines as an option. Everything was originally designed for a generator. When I first put solar in, an inverter was a must to run a lot of things. My efficiency sucked, and I would have to budget power all of the time. Since then, I have switched to all LED bulbs. I put in a 12v dc stereo, and a 12v dc tv/dvd player. Additionally, I installed a car 12v DC to multi port USB charger. All of my music and movies run off a windows tablet running XBMC off of that USB hub. The fridge is 12v DC. The water is run off a 12v RV pump. Basically, I can do everything with no conversion from DC to AC to DC. There was an amazing amount of stuff that was either doing this through wall warts or internally in the device itself. That is all wasted electricity. The net result, I can run all of the stuff, all of the time, with the same number of panels. Amazing returns. I don't think anyone should be talking about switching high amperage devices over to DC. I left an AC line (and the inverter) in for that. But instead I have parallel low voltage AND low amperage DC lines for all of the stuff we use day to day. That would be the big gain in a solar home.
Getting 1500 watts out of 12 volts DC is WAY more dangerous than 1500 watts from 120 AC, by an order of magnitude.
1500w @15v == 100 amps. That means all your in home wiring would need to be ATLEAST 6 gauge wire to be able to carry the current, more likely its going to be 4
gauge wire, and its STILL GOING TO GET HOT.
At just 100 watts, you know, like a high powered light bulb, thats STILL 10 amps, which requires AT LEAST 10 gauge wire ... when most homes are wired with 12 or even 14 gauge!
We're not going to design homes around the Tesla charger and charging our iPhones, we're going to design it around our fridge, microwave, washer and dryer, and air-conditioning.
This entire article is stupid. The conversion losses are nothing compared to the resistive losses from carrying 10 or 100 amps across the wire, even only a 100 feet or so in your home.
I have several 3000 watt devices in my home, which is FILLED with 100 watt light bulbs. In the real world, this shit won't fly.
Persistent Volume manager for Kubernetes - https://github.com/dwimsey/openshift-pvmanager
We need to use HIGH voltage DC at about the same voltage as your house is now, forget about going "low voltage" DC. MOST things in your home will run JUST FINE on DC with a few notable exceptions. AC induction motors will NOT work, nor will anything that involves an old fashioned transformer, but most modern electronics with switching power supplies work great on anywhere between about 90V to 200V DC without modification. Most switching power supplies just convert the AC into DC right up front and won't know the difference. So, all you do is provide inverters for the things you cannot easily change (like for your appliances) and just feed DC to the rest of the stuff that doesn't care. What you DON'T do is go to low voltage DC and suggesting this is just crazy talk. Why?
1. Most stuff just works on high voltage DC as discussed above. Most switching power supplies simply don't know or care about AC or DC and due to their efficiency switching power supplies are used in almost everything electronic.
2. It's easier (and more efficient) to use high voltage DC for charging the batteries. All you need is a rectifier to convert that 220 into about 250V DC and charge the batteries, which is about as simple and efficient as it comes.
3. It's easer (and more efficient) to make an inverter that uses high voltage DC as input. It's pretty easy to just flip the current one way then the other to get AC sufficient to run most induction motors and transformer powered devices.
4. It's more efficient to use higher voltage in terms of wire size because IxR losses are less for the same power transfer. Chances are the same wires you have now will be fine, but if you go to low voltage (say 13.8V like in your car) you are going to need bigger conductors to avoid the voltage drops over long high current runs. Use higher voltage and lower current, and stick with the wires you have.
5. Current battery technology for EV's and hybrids uses about 200V DC to start with, so there are less modifications to the technology when adapting to a home use. If we stick with a common battery pack voltage it will increase the economies of scale in their production and allow the use of old automobile packs that have reduced capacity as power storage in homes where the size and weight of the battery is less important. If you go low voltage, you either have to convert the 200V down to 12 or 48 (and incur the conversion loss) or modify the battery pack to operate at the lower voltage.
I know that traditional DC systems run at multiples of 12 Volts because they are usually built on Lead-Acid batteries and that much equipment is commercially available that uses 12 and 48 volts based on this. But going to 12 or 48 volts is not the right answer. It's really just the traditional solution based on past thinking and limitations. Running 200V DC is a more viable and long term solution that will work fine with a lot of existing AC equipment, plus is compatible with a ready source of batteries which are commercially available (and if purchased used, pretty cheap).
So, NO, we DON'T want to start using low voltage DC... We want to use HIGH voltage DC.
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
I see a wonderful opportunity to separate lighting from power circuits. Expand the NEC to include some form of low-voltage low-power standard for lighting, and a much smaller solar/wind generation/storage solution could cover all needs. Your lighting always draws from the DC system, which is either fed from your locally charged battery system, or draws from a converter sitting on a standard AC grid circuit when necessary. Bonus: built-in battery backup for emergency (all) lighting when the power goes out for any reason. There is already low-voltage electrical wiring available and I bet most people reading this have some - cat5 cable. How hard would it be to standardize on some cable for lighting that draws 30-50w? Just take PoE and beef it up a little. It doesn't need to be as tiny as 22ga wire.
Pie-in-the-sky 100%+ generation at home is a nice dream, but this is a small cheap system that anybody could afford and save money/energy now. Seriously, a small 100W panel with maybe 2 car batteries would be enough that I'd rarely if ever need the AC/DC converter to contribute to my home lighting needs now that I switched to LED bulbs. Who needs multi-kW systems when all you are doing is picking the low-hanging fruit?
Yes, the whole premise is idiotic. Losses due to resistance would dwarf conversion losses; AC to DC conversion and DC to DC conversion are actually very efficient nowadays (if you care to spend the money; it's still cheaper to do it inefficiently)
With houses as big as they are, we ( USA ) need to think about going to 220v to save on copper.
Will never happen. Retrofit costs are far too high and I shudder to imagine the technical support nightmare that would cause.
A center-tapped transformer, fed with one of the three phases from power generation, yields two sine waves which are 180 degrees out of phase. As a whole, the output coil is in phase with the single input phase, but the two output sections give opposite voltage with respect to the common central tap.
This is strange. "20 to 40% power loss" seems to be an awfully poor inverter; existing inverters are 4-8 % loss.
Rather than rewire every house in America, wouldn't it make more sense to just design better inverters?
Or just run at 120V DC, as renewable energy systems did (and occasionally still do) before so many appliances were AC-only that it made sense to use an inverter.
Dropping voltage means you have to replace the copper wiring with MUCH HEAVIER wiring - by a square law - to carry a given amount of power with the same loss - and thus wiring heating inside the walls, where it can set the house of fire.
Switching to 120V just means using DC-capable appliances and replacing the breakers (DC is harder to interrupt) and must-be-GFCI outlets (normal GFCI devices use a transformer to sense unbalanced load).
The 48V standard was about having a voltage that was low enough that touching it was typically survivable, so working on or near it is (relatively) safe. The boundary between the hard part and the easy, "low-voltage", part of the electrical code is 50V (BECAUSE of phone companies B-) ). Medium power (>1KW) home Renewable Energy systems tend to be at 48V so much of the wiring falls under the easier part of the code, and because of the availability of
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
>Ask yourself why Europe uses a ~230V/240V electricity
Apart from the economical reasons as outlined by yourself, I always assumed it was a safety issue. I was taught that current kills not Voltage. A static shock has huge tension but non-existent current whereas a toaster in the bathtub has (relatively) low voltage and high current.
Can a sparky weigh in on this for me?
Not that I'd go licking the sockets in any country.
Increase the voltage (EMF) presented across a load, and your current increases.
I=E/R
So, no, it isn't safer. (Assuming Europeans have roughly the same electrical resistance of their skin as Americans)
The reason electrostatic charge is not normally harmful is because of how quickly the charge is dissipated. (usually microseconds)
--fatboy
In my neighborhood, the power lines are attached to a box in my house which distributes one phase to some rooms and the other phase to the other rooms, and some high-power appliances are attached to both phases.
These phases are 180 degrees out of phase. The three-phase power grid is converted to split phase at some point between the substation up the street and my house.
http://en.wikipedia.org/wiki/Split-phase_electric_power#North_America
But delta or wye?
This is silly. The article itself says that air conditioners, electric hot water heaters, and ovens/stoves run off of high-voltage A/C. Those items use at least 80% of a houses electricity. If you have a swimming pool, the pump also uses a lot of power and has, guess what, a high-voltage A/C motor.
I don't think it's cost-effective to re-wire a house for a 20% savings on 20% of the electricity. That's a 4% savings for the cost of a whole lot of copper and labor.
"We just have a split-phase system to provide it for the few special cases (dryers and ovens) that benefit from it."
My 1HP pool pump motor can be wired for 110v or 220v, depending on the circumstances. Since it is about 60 ft from the service, it's wired for 220v to better accommodate the length of the wiring. Ranges and dryers in the US are rarely wired for 100v due to the current needs.
Surprisingly, US electrical design is not entirely illogical or dysfunctional. Different choices.
deleting the extra space after periods so i can stay relevant, yeah.
To pump the same power at low voltages you must by necessity pump larger currents.
So for a low voltage DC circuit, you need bigger copper (expensive) wires or your Joule heating losses as the square of the current. (Power dissipated in the resistor = I^2 * R.
Higher voltages from AC grids pass less current so less is lost to resistive heating.
The example you were looking for was car-jumper-cable-sized...
Thick Ethernet has a big jacket, but inside is that tiny little center conductor. I thought that was a lousy analogy, but few people know what's going on inside coaxial cable, so what the heck.
deleting the extra space after periods so i can stay relevant, yeah.
At low voltages the current would be very high to run even moderately sized appliances. 220-240V was chosen, since many appliances would need very thick cables, and 60A+ fuses otherwise. There would also be the issue that conversion losses would just be moved elsewhere. Having a huge transformer that is underutilised most of the time would certainly not be efficient, and transmitting DC or low voltage over the grid is impractical for obvious reasons.
You typically do not get two of three hot phases. You get one phase, center tapped with the center tied to ground; the two hots are 180 degrees out of phase with respect to each other. You get two phases in some commercial circuits -- e.g. a lighting circuit might be two phases of a 3-phase wye with 208V between phases (120V between phase and center).
We'll need Monster Cables to make it all work.
At low loads even switchmode downconverters are routinely 80% or worse. You only see 90%+ when the loading on the converter is higher... a situation that is easy to arrange when you only charge a battery pack (say a tesla wall thingy) and shut down the charger/converter when not needed. Then use the DC from the wall thingy to run individual loads... it wouldn't make sense to run something like a 5ton Air Condidtioning unit from the DC system, so you'd just keep your 240AC feed to the residence.
That'd let you do away with all the little power bricks that are waiting to burn your house down. You'd now have smaller/cheaper and more efficient DC/DC only converters (98%+ efficiency since they don't need an input rectifier anymore), or nothing at all and power your stuff directly from the household battery bus.
Overall it'd probably be a net 3%-5% savings on consumption that'd probably NEVER pay for itself on its own... but if you could then run cheaper LED lights and other small loads (computer power supplies could be cheaper if they were just supplied with 12vDC only, etc...) you may be able to offset the battery replacements a little.
What it would do is let the power companies get by with fewer new power plants and that makes this similar to the reason behind phasing out incandescent lights in the home here in the States--Conserving Power/Energy as our population increases so infrastructure and the tree huggers can hammer out where all the new power we are demanding is going to come from.
Please go read the Tesla battery whitepaper - it clearly states the "Powerwall" battery is installed on the high voltage DC output of your PV array: http://www.teslamotors.com/powerwall
This operates at 350-350VDC and for good reason - copper losses.
PV inverters routinely meet 95-98% efficiency. Downstream AC-DC converters are capable of whatever efficiency you choose to pay for.
There are still millions of houses with hob and nail two wire... Most houses have some abhorrent mix of two wire and modern 3 wire.
It's gonna be a while before we through out that wiring entirely, and all the appliances built to use it (including appliances which could really use more power, but are artificially constrained by bad US wiring - like vacuums). Compared to power loss for a few pieces of disposable electronics my appliances are *very very very* expensive. And the cost to redo wiring is higher than that.
Maybe someday though. Wouldn't it be cool if anything that used power had to first request it similar to how it's done in USB. And the circuit breaker could also manage that to make sure that the last appliance that would require more than the allowed amount would be rejected.
I do this for a living as an facilities electrical engineer who works closely with electricians. The phase between lines on the primary side of a single-phase stepdown transformer is irrelevant to the secondary side. Indeed, sometimes the distribution lines are Y configuration rather than delta, so the inputs to the single-phase transformer is sometimes line-neutral instead of line-line. In most systems worldwide the single-phase transformer has two poles on the secondary side, one of which is grounded locally and is connected to the neutral conductor, the other pole is connected to the "hot" conductor or "line voltage". There is typically about 240V between hot on neutral. A main electrical panel for residential will have 2 bus bars in this case.
In the U.S., the transformer is typically has a three-pole secondary with a center-tap connected to the center of the secondary coil. The center tap is connected to local ground as well as the neutral conductor, and the other two poles at opposite ends are each hot conductors. Since there is only one coil on the transformer secondary this results in two hots that while measured against neutral are 120V, but each 180 degrees out of phase with the other for a result of 240V between lines. A main electrical panel will have 3 bus bars in this case. You can confirm this with a voltmeter. (If they were 120-degrees out of phase, you would measure a SQRT(3) ratio of V_lineline/V_lineneutral.
Occasionally in a commercial or industrial facility, you may find a 2-pole electrical panel that is a sub-circuit to a three-phase Y-configured panel (120/208V Typical configuration). These tend to be remodel conversions from when the building mains were swapped from single-phase to three-phase. In this one case, you will get the 120-degree difference between lines. When this is the case you have to be extra careful when connecting loads to the subpanel, because the difference in line-line voltage is less than what you would expect at first glance, and some equipment may fail to operate, or operate in a degraded state, because of that.
Just use silver, better conductivity.
You keep repeating that. You continue to be wrong. You get two of three hot phases in home wiring, 120 degrees out of phase.
If they were the same phase you would get zero volts between them.
He's not wrong. A simple Google search will support his statements. You are not using "phase" in the correct sense. On a generator with three windings, you will have three phases of electricity. If you center tap one of those windings, you achieve 1/2 the voltage. Combine the two halfs, and you have the full voltage of that ONE phase.
This article is wrong on so many levels it's not funny. Go to http://www.teslamotors.com/pow... and you will see that the Tesla home batteries are NOT low voltage. Efficient inverters are way cheaper than rewiring and relamping a house. Silly story.
When I installed solar panels, I did not connect the system to the grid because I was primarily after fault tolerance rather than lower costs or "greenness". Sine wave inverters (necessary to run motors, like in refrigerators) are expensive, and it made more sense to run a parallel 12 volt circuit to run things that are ok with 12 volts, than try to run an entire 110 - oriented house on 12 volts. Most non-motor appliances step 110 down to a low DC voltage anyway, and it seems wasteful to me to step up 12 DC to 110 AC and then back to 5 or 6 volts DC at the appliance end.
It turns out that there are a plethora of 12 volt choices at the local RV store. Even 12 volt CFLs. Any portable appliance can be run off a car adapter, and even appliances that aren't meant to be portable can be run off 12 volts with careful selection of the right adapter. (Voltage, noise, and current are important.)
Who knows, maybe some day we'll see major appliances with built-in inverters designed to plug right into a 12 volt circuit. Or maybe appliances with DC motors? Not really my area.
The only thing that worries me a little is the current requirements. Approx 1/10 the voltage, it seems to me, would mean 10X the nominal current for the same power, and I don't see running car-starter-cable gauge wire through the house. I'll have to do some measurements. For CFLs and electronics, it hasn't been an issue so far.
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
something not addressed in the comments so far, why would you need to rewire a home to accommodate DC? You'd prolly need to upgrade the circuit breaker, and upgrade the end appliances, but otherwise it's just copper, right?
Screw DC wiring, I'd much prefer high-power AC in the US. I've got the same model (but different power rating) electric grill both in Europe and in the US, and you can tell the difference between a standard wall socket on US 110V 15/20A vs EU 220V/16A when you're trying to grill a dozen things at once. And if you need it, you can then get 2-phase 380V power - bad for the utility bill but great for a high-power induction range.
Trying to get that kind of power out of a DC circuit on home wiring is gonna be like trying to suck an elephant through a straw. I guess the upside is that you won't have to heat your house, however, as you can just rely on the waste heat from the cable losses.
Apart from the economical reasons as outlined by yourself, I always assumed it was a safety issue. I was taught that current kills not Voltage.
That is a common saying but highly misleading and therefore dangerous.
What kills is current through the heart and to some extent the duration of that current. Since we can't really be sure what path current will take through the body during a fault we have to consider current through the body. That current is determined by
1: the impedance of the source
2: the open circuit voltage of the source
3: the impedance of the body
A very high impedance source or a source with minimal total energy available can have a very high open circuit voltage and yet not present a hazard. This is what we see with static electricity.
However when we are talking about shocks off the mains the impedance of the source is negligable. So the important factors are the voltage of the supply and the impedance of the body. A 230V supply is more likely to deliver a fatal shock than a 120V one. This is somewhat mitigated by the fact that things like shuttered sockets and plug cavities/pin insulation are the norm in much of the EU.
The advantages of the higher voltage are efficiency and lower fire risk.
note: i'm known as plugwash most places but i screwd up registering that here somehow in the past and now can't register
Low-voltage DC needs 10x more copper for the same power, and extending power runs to "home run" makes the wires even longer. Unless you pay for that extra copper, wiring losses will eat your savings. The big issue with ACDC conversion is that the AC is 60/50 Hz, which means energy storage of 8-10ms x wattage for efficient conversion is required. Better efficiency and lower wiring costs would come from using higher voltage DC and/or higher frequency AC. Aviation, submarines, spacecraft, trains and some industrial tools use 400 Hz AC - which allows for smaller transformers and motors. DCDC converters essentially have internal oscillators to perform the voltage conversion, and can choose an even higher frequency to minimize energy storage time. The reason we're still using 60/50 Hz is because it's the way things always were, just like train gauges are a good match to two horses side-to-side, and perhaps because 60/50Hz hum is less annoying than 400Hz hum - but hum just means that you're losing power to the environment, so it's power efficient to eliminate that anyway.
That being said, when retrofitting incandescent lighting systems with lower-power lighting, it could make sense to use existing wiring at a lower voltage AND LOWER POWER LEVEL. That way the power/voltage conversion could be grouped together in one or a few places so that higher-efficiency converters can be used, but still kept close to the points of use to minimize wiring loss. Unfortunately, the retrofit market is going for power conversion in individual lighting fixtures so one fixture at a time can be changed out.
Our revolutionary, world changing technology requires the world to change in order to work properly.
You're aware that lithium is a rare earth element, right?
lithium is an alkali metal, not rare earth element.
The rare earth elements are the lanthanides plus scandium and yttrium.
You're aware that lithium is a rare earth element, right?
First, lithium is not a rare earth element.
http://www.rareelementresource...
Second, you do know that the rare earth elements are not actually "rare," right? They are roughly the same abundance as copper.
There's no such thing as lithium ore.
Sure there are. "Ore" is just a word meaning "a mineral deposit containing a desired substance in economically recoverable concentrations." Lithium ores are typically lithium-containing phyllosilicate minerals, often in the form of evaporite deposits.
You strip mine millions of tons, process it and get a few tons in return.
http://www.geoffreylandis.com
What? Where? You can't be talking about the US. You get two single phase 115 VAC "legs" to any home not paying a premium for three phase service, which, as xfade551 noted, is directly from a center-tapped transformer. The neutral, which is tied to the white wire going to every 115 V outlet, is tied to the ground (green wire) as well as earth ground at the service entrance (and only at the the service entrance). I think in most neighborhoods you'll find three phase service and three phase transformers, with each house on a single phase and its own tap from a transformer. Nowhere that I've been will you find a residence connected to two of three phases, and I'll be surprised if anyone can document an example of that type of distribution.
I'm aware of some high-end residential neighborhoods where three phase service is common in the Phoenix area, primarily because of the economics associated with air conditioning 8000 square feet of floor space in a desert. Folks who can afford those houses don't generally have to worry about the higher base cost of three phase service.
The new type-C connector (although not required), updated cables, and USB Power Delivery specification may provide an improvement over "dumb" in-home 12V systems for convenient switchable low-voltage DC power distribution. Each device would need a chip that spoke the protocol in order to select the right voltage, but microcontrollers implementing this protocol will be very cheap. For legacy device support, an adaptor containing the smarts could be fashioned.
The spec (now at version 2.0 / Dec 2014) offers 5 useful profiles:
1: 5V @ 2A = 10W
2: 12V @ 1.5A = 18W
3: 12V @ 3A = 36W
4: 20V @ 3A = 60W (limit for micro-B connector)
5: 12V @ 5A / 20V @ 5A = 60W / 100W
For more see:
* http://www.usb.org/developers/powerdelivery/
* https://en.wikipedia.org/wiki/USB#USB_Power_Delivery
I'm not sure how efficiently one can convert Tesla battery pack voltage (somewhere around 375 volts) to the 21 volts or so that you'd want in home wiring for USB PD. Also you'd want relatively thick copper cables, maybe AWG 4 or even 2 I'd guess without looking.
Had the USA not had a power grid, but, each home had its own independent "power plant", the USA would have been on DC long ago. But, back then, it was decided, that it was better to have power generation done from a central location, and have it "piped" to the homes. Of course it became a business, & I seriously doubt the powers that be, will NOT allow home owners to have their own source of power, without some sort of BS tax. They will throw a ton of money at politicians, which do their bidding, and not the people.
Sounds like something built out of junk box parts.
I imagine this as a more efficient complement to AC systems and certainly not as a replacement. As others have pointed out, for high power and _many_ motors and appliances, you really need the AC and its associated benefits. But for computing, lighting, and entertainment, a complementary DC system may help improve efficiency for the solar collected power.
Just picking one brand, the nominal efficiency is 88 per cent (12 per cent loss) and the "line mode" efficiency is >95 per cent (http://www.theinverterstore.com/12000-watt-48-volt-low-frequency-inverter-charger.html#
small inverters have horrid losses, but once you get to house needs sizing they get better.
AC versus DC danger ... AC you jerk free of the wire, DC your muscles clamp. I've taken a 3000V AC hit when much younger through a green branch or I'd be likely dead anyway ... And I've taken a short impulse DC 800 volt hit from a large storage capacitor. I'll take the 3000 VAC through a tree branch thank you. Oh, and I've been hit by lightening (through contact with a wet building near its electrical feed, while walking to my nice safe Ford Faraday cage) and that is just no fun for anyone. Alas no super electrical powers or ESP or other comic book worth manifestations from it all.
It's awfully easy to find reasons to confiscate other people's money.
first, Tesla has to actually *complete* their "Gigafactory". Then they actually have to *sell* a whole lot of these power systems, enough to convince people that a LV system makes sense. Only then will these batteries "force" anything.
There are at least two assumed carts, before the horse here.
You don't get zero volts if you split your phase into two legs by using a center-tapped transformer.
Suppose that you number the connections to the secondary winding of the transformer from 1 to 3, with the center tap being number 2.
The waveform; let's call it "A"; found between connections 1 and 3, is exactly the same waveform you would get if there wasn't a center tap. If you didn't have a center tap, you would probably reference one of the two legs to ground to make a neutral, but that does not alter the waveform.
The waveform found between connections 2 and 3 is in phase with "A", but has half the amplitude.
The waveform found between connections 1 and 2 is also in phase with "A", and it also has half the amplitude.
In practice, the center tap is tied to ground to make a neutral. This has the effect of defining a polarity for the 120V circuits. As such, you would normally end up measuring one of these two wave forms with the opposite polarity to the other, resulting in it being 180 degrees out of phase to the first measurement. So, rather than measuring the waveform between 2 and 3, you would probably measure between 3 and 2 instead. It's the same waveform, but reversing the polarity makes it 180 degrees out of phase with "A".
You'd think that most of the "heating" devices in your home would work fine on DC with only a few modifications. Especially that water heater and ALL of the incandescent light bulbs in the house...
Did you know that a lot of your electronic devices work great on about 100V DC and wouldn't require any modifications? Most modern switching power supplies really don't care if it's AC or DC on the input, they work just the same either way. Don't just go out and hook up your expensive flat screen to the Prius battery (it can damage stuff sometimes) but chances are it would work... My Laptop charger, a PC desktop and LCD display along with a 30A 12VDC switching supply for my radios all worked just fine...
Personally, I think we should go with HIGH voltage DC, use it where it makes sense, and not freak out about having to convert it to AC when the need arises.
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
Someone is pushing some other agenda here.
I've fallen off your lawn, and I can't get up.
There are so many bogus claims in that article that it's hard to know where to start. But one good place would be the simple fact that the Powerwall is 450 volts DC.
It's got to be HIGH VOLTAGE because you're freaking trying to pull kilowatts out of it.
P = I * V
You want to run at 12 volts? Good, then you'll pull 10 times more current than running at 120 volts. That's going to require much thicker wiring. Think about those big fat cables coming off your car batter (or jumper cables) -- yeah, that's what you'll need to replace your current 120 volt AC wiring.
Other stupid thinks that the author claims:
-- Solar panels produce low voltage DC. No, the individual CELLS in a solar panel are low voltage. But the CELLS are stacked so that they create high voltage. Solar panels deliver HIGH VOLTAGE DC to the inverters because it's much less expensive than low voltage. It's much less expensive because the P=IV. IOW, HIGH VOLTAGE means that your cables are much smaller.
-- Power Inverters have a 20% efficiency loss. That's total nonsense. More like 2% than 20%.
That article is embarrassingly bad. The fact that it's featured on Slashdot is pretty sad.
DC to AC losses are on the order of 5%, not 20 to 40%.
Because you can't electrocute people with DC?
Actually it is easier to electrocute someone with DC the reason it rarely, if ever, happens is because most DC sources are very low voltage and cannot drive enough current through a human body to be a problem. A high frequency, alternating current is actually relatively safe because of something called the skin effect where only the outer surface of the object conducts the current. For a human this confines the current to your skin and away from vital organs like your heart. It is the reason why Tesla himself could discharge lightning bolts from his fingers without being electrocuted. However you do have to be careful since where the spark leaves your body can get burnt due to the heat of the plasma created.
You beat me to it. FAT wires. Just sayin'. It'll work just fine, so long as you live in a castle, and have one hell of a drill bit to install the wires in the wall.
I can see AC to the doorstep a big efficient whole house power supply that has 12vdc and 48vdc rails that are distributed thorough the house and battery backed, and few 220v "appliance circuits" off the AC.
48V and 12V lines are far too low to be sage and/or sensible. Remember that the power used is equal to the voltage times the current and that the heating of the wire carrying the current goes as the square of that current. Typical house wiring is good for ~30A of current and supplies several plugs in a room typically. With a 12V circuit you limit the power of all the devices connected to this circuit to 360W vs. the 6.6kW you get now (or 3.3kW if you live in North America). Even with a 48V circuit you only get 1.44 kW.
The result is that either you need to rewire the entire house with massively thick, and therefore expensive, cables to carry the far higher currents or you need to use a higher voltage for transmission. Even the factor of two reduction between Europe and Canada/US is noticeable for some devices: electric heaters are far punier than their European counterparts, kettles take far longer to boil, and Electric lawnmowers are practically useless etc. If you drop the voltage by another factor of 2-10 below even Canada/US then almost all devices will be impacted.
AC has it's advantages.
Mechanical switches for AC can run higher voltages and currents. Breaking the connection doesn't have to break a potential arc, since the voltages always goes down to zero. High voltage DC is dangerous and more difficult to switch.
Circuit breakers can too.
High power appliances need high voltages, the higher the voltage, the lower the current. High current means larger cables or more losses.
It's really easy to step up or down an AC voltage with a transformer.
You yanks already suffer boiling water with your 110V 1600W kettles. It's much quicker in 240V countries where 2400W appliances are common. The house wiring is only rated and fused for 16A for an entire circuit, since each outlet only supplies 10A.
http://en.wikipedia.org/wiki/High_voltage
High voltage (supply system) > 1000 Vrms > 1500 V electrical arcing
110V is low voltage.
Why doesn't the US just keep to a single 240V for all power outlets, rather than complicate things unnecessarily?
Why OpalCalc is the best Windows calc
Comment removed based on user account deletion
This is the stupidest thing I've read on /. in a long time. Those of you who understand things know why. Those of you who don't, never will.
Seems to me the author is understating his own argument, and missing the point, to some extent. The devices he excludes ("Appliances like electric ovens, electric water heaters, and air conditioners will [still] require 110VAC") are precisely the ones that take most of the power, probably 80% in aggregate. So, if you want significant savings, those would have to be DC as well, but it would have to be 220VDC or at least 110VDC, because for 12 volts you would need at least finger-sized copper bus running all through the house. In fact, the most efficient new air conditioners / heat pumps (e.g. Daikin Altherma) run on DC, i.e., they convert the AC to DC which then powers inverter-controlled synchronous motors. A water heater, even an existing one, could just as easily run on 110/220 VDC, you'd just need to replace the control unit. What you'd probably want is a system with at least 2 voltages, say 24V and 220V, each with its own battery charged by its own solar array, so you don't need to do DC/DC voltage conversion (which also has losses though probably not as much as an inverter). Most of the house would only have 24VDC wiring, 220VDC would only go to the kitchen and utility room, just as it does now in AC systems.
You may be thinking of commercial 3phase wiring where you get 110V phase to neutral and 208v phase to phase. In residential wiring, the final transformer coil is center tapped so you get 110 phase to neutral (center tap) and 220 phase to phase. Note that the two split phases are inverted with respect to each other because the neutral is a center tap.
"To avoid the 20% to 40% power loss when converting from DC to AC"
The original author, Self, has exactly zero idea what he is talking about.
The power loss in a modern inverter like the one in the PowerWall is about 2%. On the panel side, efficiency of 95% is no longer considered competitive. The numbers he's quoting are decades out of date.
This article completely ignores the fact that the DC wiring, for any decent distance, will need to be far thicker than AC wiring. More copper means more expense. Far cheaper to have a SMPS or transformer and rectifier at the points you need DC (which happens to be the present system).
When you're talking about 12Vdc then voltage drop is going to be a massive hit on any distance that needs to be run. Sure you can run higher DC voltages, but this article is focused on low voltage DC. If you do end up using higher voltage DC, then you will have to use a flyback converter to step the voltage down. You will get the same kind of losses in this case as if you had inverted to mains AC in the beginning.
On top of that DC switchgear will be far heavier to stop arcing and as the current will be higher. AC doesn't need as heavy switchgear as twice during a cycle the current is zero, making an interruption much easier to perform and with less chance of arcing. If you find a switch rated for both AC and DC, take a look at it: the rated DC voltage will be far lower than the rated AC voltage.
Sure HVDC is used in some places, but that is typically long distance transmission, especially underwater. Under water, the EMF causes the water surrounding the cables to ionise. If they used AC, the water ionisation would cause significant impedance when the current flows in the opposite direction. Over long runs, these losses are massive, hence they rectify to HVDC. DC doesn't have that impedance issue. Anyway, that is rather irrelevant to a residential situation.
HornWumpus read above or get a much better education before you slam someone!
I also am an Electrical Engineer; As xfade551 stated quite clearly standard residential is derived off on a single phase of a 3 phase distribution system. Your home gets its 120 VAC RMS from a centered tapped transformer where the neutral and ground are connected to the center of the transformer windings. This gives you 120 VAC RMS from each side of the transformer output to neutral/ground and 240 VAC RMS from each output terminal of the transformer. It has been this way for a hundred years; so you really should be able to find a lot of good reference material on this.
Strange name for a web site, but a good basic overview, with a transformer diagram:
http://www.beananimal.com/arti...
Note: voltages may vary depending on your local municipality.
One other issue I haven't seen discussed. Hi-Energy DC has switching issues as there is no voltage/current zero-crossing. Arc suppression becomes a real issue here with some real interesting failure modes!
6V*230AH = 1380 watts per battery. 10KW / 1.38 = 7.25 batteries I need to match their energy storage capacity. At $105 per battery that only costs $760. So, do you want to pay $3,000, or $760?
I could build the entire system, with an inverter, battery charger, and a couple solar panels for what they charge for just the battery.
The Tesla Powerwall battery packs is wired for a 350-400 volt range, and come bare bones except for some equalization circuitry, (no charger nor inverter). Any modifications to the battery pack itself would likely void the warranty. How ever adding a low voltage circuit does have it merits, but the Powerwall will not be a factor.
I have considered running a solar/battery backed up 32-35 volt DC supply into the house, and use a number of 5-pack LM2596S stepdown inverters. The adjustable nature of these DC buck converters can power DC fans, Security system, DVRs, Antenna amps, Sat boxes, night lights, laptops, LCD monitor, door bell, automation system, charging stations, etc. The higher distribution voltage keeps losses to a minimum while providing uninterrupted power.
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Ironically, Tesla (the new one) and Edison are on the same side this time... DC for the win ;^)
With the advent of leds, we need a new standard for lighting. Conventional phase cut dimmers dont work properly and 14awg wiring is way overkill now. Decide on a dc voltage, wire size and conductor count. Do we want smart switches where we encode control over the power leads for less conductors?
Also with leds wean alter the color temp if the units have multiple drivers in them. That control could be considered as well
eventually eliminate the need for high-voltage 110V electrical wiring.
Slashdot is so American it's pitiful. Ninety percent of the world runs on 220 volt 50 cycle power.
- Andy (Thailand)
A few years ago I owned a condo, and we got a letter that told us that if an outlet went out in the dining room, that we should not replace it ourselves, and that we should hire an electrician. That got me curious of course, so I got out a voltmeter, and measured 208V between the top and bottom hot wires in the outlet. As in, the top and bottom half of the outlet were on different circuits and on different phases.
We will have solar panels but lots of partial-array shading so no series-strings for us thus no high DC voltage and sadly, no Tesla Powerwall.
Instead, we'll go for a large 24V LiFePO4 of LiYFePO4 battery pack, and re-use some of our existing house circuits for 24 V DC for LED lights and 24V fridge and freezer. The 24V or 48V RV/Yacht fridges/freezers available are 5 to 10 times more energy efficient than standard "Energy Star" AC fridges.
Then we'll run a cheap DC/AC inverter or two for running laptops from the DC system.
Laptops, lights, (beer) fridge. In summer, what else do you need really?
Where are we going and why are we in a handbasket?
you are not wrong at all. the whole thing was written like someone just starting out. on a 12v system your highest regular charge controller is 80a, around about 1kw, on a 48v system you can do 4x more solar input on the same cables and controller. i use this online calculator alot - http://www.solar-wind.co.uk/cable-sizing-DC-cables.html
as it shows a 2kw kettle, with 1m of DC cables, would have to be 70mm2 cable to have little loss. or 16mm2 (still pretty expensive and large) for a 5% voltage loss. however, if you accept 5% loss but if your kettle is 5 metres away you're back to needing 70mm2.
using AC is not all about the appliances, it is mainly about the distribution - you can't possibly keep everything (inverter, batteries, fuse boards etc) all within the same space. also you can buy 3 chinese all-in-one inverter chargers for the price of a small DC fridge.
Generally commercial electricians are not familiar with DC power distribution, unless they are in the regular business of solar power installation, or work in an an industrial plant that still has some ancient DC distribution dating from the early 1900's.
Anyone thinking about using 120 volt DC needs to understand how equipment is rated, and the special wiring arrangements needed to ensure DC rated equipment will not explode when switched. Eaton sells one of the several lines of circuit breakers able to handle 120V DC. These are expensive compared to regular panel board breakers, and must be wired per the technical documents, or they tend to fail spectacularly (this is due to physics so this requirement to read the instructions applies to ALL brands).General DC Circuit Breakers
Such a small heating source could come from a soldering iron, and 12VDC soldering irons are not difficult to find.
How is the Riemann zeta function like Trump rallies? Both have an endless number of trivial zeros.
someone hear was clueless when he posted this a good ac inverter can be as good as 98% and make a better sine wave then the power company can provide meaning your power is even cleaner then grid. if you wired something like a house for dc thousands of square feet you would lose even more power from dc falloff then running a good ac inverted system. small system like rvs and cabins are only a few feet meaning running full dc is simply cheaper and those power lose is around the same.
yea that's way to hi no panel or charge controller goes that hi to charge the battery they need to wires these in a 12 to 48v option. granted with enough panels in serise you might get that voltage but no controller to charge not to mention none are program for lithium battery's the rest of the green world needs to catch up before the tesla wall is usefull..
"Occasionally in a commercial or industrial facility, you may find a 2-pole electrical panel that is a sub-circuit to a three-phase Y-configured panel (120/208V Typical configuration)"
Occasionally? Really? This is the common set up in nearly every urban area. If you live downtown you probably have 120/208V and you are probably in a networked area (the utility uses network protectors which sense a revers current flow to detect faults, the network protector opens and the electricity flows around, not through the damaged portion of the distribution system).
Now I can understand why you might think that 120/208V is rare if you are living in your Mom's basement in the suburbs...you might want to get out more.
A friend of mine rented an old Victorian house in downtown San Jose (Silicon Valley for the geographically challenged) that had 12V DC outlets. The wiring still worked. He plugged his CB radio by sticking the red and black wires directly into the outlet.
Thanks so much for this explanation. I studied as an electrical engineer, but we always stayed way out in theory land, and never once covered the concepts of how a house is wired, or where the 120/240 volt difference comes from. I've google enough that I finally figured it out, but your simple explanation still cleared some things up for me. Thanks!
Pretend that we could make graphene wire or ribbons in long lengths. Would this change the situation for home wiring (either retrofitting or new construction)?
A few facts that, for some reason, haven't been stated in this discussion:
1. EMI/RFI--AC systems radiate a lot of noise. Some come from lines discharging through a natural diode and the rest is the lower frequency 50/60 cycle AC and its harmonics. Even discounting the EMI-sensitive people out there (whether you believe them or not), there's no question that it affects receivers and some other electronics, and occasionally magnetics like a credit card. DC normally shouldn't have this problem.
2. Outside of motors and other heavy loads, most loads outside of factories and such are light loads, thus 48-60 volts with light gauge wiring might be sufficient for short (household or small business) distances.
3. A *BIG* safety issue no one has talked about is the increasing danger with voltage and going DC. This is a 2 pronged problem:
A. with AC the voltage goes down to zero every half-cycle, which is why switches can be made relatively simple under that 400 volts mentioned. But this disappears at DC and an arc or spark that fires WILL *STAY* FIRED as long as the power remains applied! I learned this at a GM discussion for mechanics when they were discussing the (new then) Chevy EV1 and its competition from Honda and Toyota when they talked about why they chose 36 volts for that car: its the highest voltage that won't carry a stable arc. The speaker pointed out that a pin hole, which would self-heal and not normally cause a problem on normal 12 volt circuit, would cause a self-maintaining arc at 48 volts if the hole came into contact with the frame. Of course, we all know what happened: the car failed due to lack of range (using lead acid!) and power (ohmic loss). But the safety issues remain, even on modern cars with high voltage DC battery packs, even though they seem to be solved...
B. Above 400 volts or so flash danger becomes a real threat, as lots of Youtube videos attest. Going to DC this could be a lot worse, I would think, as the arcs wouldn't self-extinguish. Combine this with heating inside the cells due to internal resistance and you could see a big BOOM!
If you power a few lights, fine.
If you want to power something in the range of 2000-3000 watts, like an oven or an AC, you either have huge losses and overheated cables, or you will need cables that cost about $100 per meter. And they're heavy, and you'll need lots of copper too.
Also the article states th solar panels provide 12 volt. Most home solar systems operate in the 100-600 volt range. Again, the cables would be really expensive if you did this differently.
The guy writing the source article has no idea what he is talking about.
In the 1940's, my grandfather ran his rural house and dairy farm on 12 volts DC, because utility power hadn't yet reached his location. Now we have utility power everywhere, but we don't like it any more, so we're going back to batteries. Funny how things go in cycles.
There's also capacitance loss. The two conductors constitute a capacitor. With AC that has to be discharged then recharged in the opposite polarity, for every cycle. This loss is negligible if the conductors are far apart as in a typical high voltage line, or short as in a building. But if the conductors are close together, or buried, or undersea, it's a big loss. So DC is useful especially for buried or undersea lines.
>Yeah, pretty much. Mains voltage in Oz is 240v AC for similar reasons, we can run a 2400w Clothes Dryer from a single phase, standard 10A outlet. IN the US this requires 2 phases IIRC.
Nope.
Residential service in the US is 240V single phase that get's split into two 120V 'legs'. That's why most people think that they have 120V service and two phases.
Your distribution box has two power busses, one bus is connect to leg-1 and one is connected to leg-2. If you want a 120V circuit then you use a connect to only one bus (through a circuit breaker of course). If you want 240V, you use a circuit breaker that connect across both busses.
As a rule, we don't do multi-phase residential service. You can get it but it's very uncommon.
You've already got 240V service. That's the US standard.
Standard US residential service is single phase 240V. That's what shows up inside your distribution box.
The distribution box has two bus bars. Each one is connected to one leg of the 240V service.
When you want a 120V circuit you install a 120V circuit breaker. That circuit breaker draws power from only one leg.
When you want a 240V circuit you install a 240V circuit breaker. That circuit breaker draws power from both legs. Some people think that a 240V circuit is a 'two phase' circuit. That's not correct.
Most of the circuits are 120V but you'll have 240V for any device that pulls a large amount of current.
> high-voltage 110V electrical wiring.
What, 110 volts as high voltage? Europe uses 230V / 50Hz AC.
I think US people are primarily afraid of AC in homes and offices because of the suspicion it causes brain tumors via EM fields. Some allege the doubly higher amperages used in american home wiring (due to only 110V /60Hz AC tension) are responsible for the discrepancy versus Europe (230V AC).
Some allege the some problem can be observed in Japan (I think they uses 100 volts 60Hz AC). Since japanese people are generally long-lived and eat healthy, cancer problems are easier to spot among them.
Even with switching power supplies, 12v is not optimal because of the losses in the diodes. Even Schottky diodes have a voltage drop of 0.3v or so.
I think it would be a good idea to standardize on something in the 40-50 volt range for the DC grid in the house, with some leeway for adjusting the actual charging voltage to what is convenient for the battery.
A 42-volt electrical system (http://en.wikipedia.org/wiki/42-volt_electrical_system#Choice_of_voltage) comes to mind. Even if it did not really take off the first time around.
C - the footgun of programming languages
Yes, Lets rewire all houses known to exist.
the quality of these articles has now reached a new low. GJ DICE.
*double facepalm*
Low voltage means high currents to get the same load...and higher currents means bigger losses in the cables that all need to get replaced to not burn up under the higher current. That proposal can come only from people who never wired anything. Dumb idea!
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Calculate your DC requirement to have bigger battery (by 20%) if running AC, vs cost of 'new' appliances and larger wire needed for the same power in DC. Whoever wins in that equation should (and in the long run will, IMHO) win.
This is true for solar panels and power from them to the battery charge circuits too. The further the DC power needs to go, the more it costs in losses of power or cost of wire.
... "When you pry the source from my cold dead hands."
The real win of the 400V system, btw is that you can travel about 4 kms from the transformer, which gives much more freedom designing the medium voltage network. The transformers are all three phase to keep the inbalance off from the medium voltage side (much less transformers, less chance to do blancing there).
In the US, that 3 phase Y is referred to as 208 3 phase. Each leg is 120 to neutral and 208 between any of the 3 phases. The low voltage referenced is the difference between 240V for a single phase 2 leg panel and a 3 phase panel of 208. A 240 Volt appliance will see 32 volts less than it was designed for. Ovens will be slower. Single phase window air conditioners will be running in a constant brown out condition and may stall, or draw excess current and burn out early.
Forgive me if I have this wrong, but if we start wiring houses for low voltage DC, won't this mean huge fat copper cables to deal with the current implications of a washing machine or oven pulling tens, even hundreds of amps because of Ohms law?
We can use copper girders instead of studs in the walls, and let them carry the current. Just thinking outside the box.
Star Trek transporters are just 3d printers.
We took advantage of this at one place where I lived. We had an electric dryer but the house was built for a gas dryer so initially instead of running a 240 volt circuit, we rewired one of the outlets in the room with the dryer to use the other phase and plugged the dryer in using two 120V plugs with hot and neutral going to one and the other hot going to the other. The dryer was also modified to halve the power drawn by the heating element to keep the current reasonable.
That could very well happen.
The voltage and the current from a test meter are both insignificant.
The reason why low voltage isn't dangerous usually, is because the skin is a damn good insulator requiring voltage above 100v to break (one of the argument invoked by countries using 100volts, whereas the rest is 220v).
The Darwin Award example did stick needle-like pointy ends of the probe *through* the skin. The skin's high insulation/resistance wasn't there any more to shield against "insignificant voltage". The serum of the blood isn't distilled water but is filled with electrolyte. Quite conducting mix. It also runs through the hearth. The rest of the fuilds inside a body are all rich with electrolytes too. That means that the *inside* of a body can conduct electricity quite well, and the hearth can easily get in its path (specially if you put each electrode pole at opposite side).
(one of the reason why it's not a bright idea to swim during a storm. the inside of your body is a *better* conductor that the water around you in the swimming pool, the skin is the only thing in the way blocking the electricity).
The actual delta-V needed for a muscle cell or a nerve to react is quite low (a few dozens of mili-volts are needed to rise above the threshold and cause contraction or impulse propagation). So with the skin barrier removed, it's quite likely that the remaining salty fuilds (mostly blood, but also extra-cellular fluids) can carry enough to cause a jolt to the hearth, enough to disrupt the normal rhythm.
"Sufficiently advanced satire is indistinguishable from reality." - [Tips: 1DrYakQDKCQ6y52z6QbnkxHXAocMZJE61o ]
I do wish Slashdot would let you edit posts, then I wouldn't have to reply three times!
I'll group the answers.
Then why doesn't it happen more often?
Well, you need to stick needles into the body quite big and deep to have a good contact (the probes mentioned in this Darwin award). And apply a sufficient voltage to them, for a long enough time. That's quite a convoluted way that doesn't happen in every day life.
(I hardly see example how it could happen, except deliberately as in the example).
Actually a healthy heart will regain rhythm easily.
Generally speaking, yes, I agree. A healthy heart should restart.
That's in fact the principle which is used by defibrillators:
- a firbillation: is a big electrical mess where the cells a completely desynchronised and are firing mostly at random each triggered by the mostly random fires of their neighbours. Electrically, the heart gives a signal that looks like white noise. Mecanically, the heart isn't beating in a coordinated manner, but instead its surface is more or less kind of "vibrating" making tons of small uncoordinated local micro-contraction (that's what fibrillation means).
- fire a charge a the heart
- the charge cause all the muscle cells (and the specialized muscle cells that serve as the heart's equivalent of nerves) to contract at the same time and stay contracted for the short duration of the charge.
- after the shock, most of the cell are more or less at the same position in the cycle. (and thus none will start miss firing due to other nearby miss-fires). They are more or less in "waiting state".
- natural rhythm generator generates impulse as usual, and now all the cell should follow the same impulse travelling along the heart (and its nerve-like specialised fibers).
- heart should contract in a coordinated manner and beat as it should.
BUT....
In the Darwin awards example, the current is constant. Which doesn't cause a "resync" as the single pulse that a defibrillator's shock is. Also, given the low resistance of the salty water medium, the current is probably quite high which is dangerous. (I mean relatively speaking).
There's a much higher risk of the heart going into fibrillation in this case.
Of course adding some heart disease could increase the likely hood of dying.
But the absence of disease isn't a definite guarantee to die from such shocks.
I've had quite a few jolts from 240 volt mains from one hand to the other. Explain why I'm not dead.
Basically: you got lucky.
Probably the shocks where short. Or by luck the travel path of the current didn't happen to reach the heart (I've once had a thunder struck patient that survived exactly because of that: the heart wasn't touched).
The fact that you survived previous shock and the fact that you don't have a heart disease doesn't necessarily make you immortal and doesn't guarantee that you won't die next time.
"Sufficiently advanced satire is indistinguishable from reality." - [Tips: 1DrYakQDKCQ6y52z6QbnkxHXAocMZJE61o ]
No one is forcing anything. Low Voltage is what all the high end reliable equipment for homes is sold in. People are speaking with their wallets and building better homes. I have Tesla charging stations on order for several homes and I've already received a request for a Powerwall. The best equipment for home automation is low voltage. Change is good, nowadays....
See subject "Forrest" & this -> http://tech.slashdot.org/comme...