How Tesla Batteries Will Force Home Wiring To Go Low Voltage 597
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.
Will This Fight Ever End? (Score:5, Funny)
Re:Will This Fight Ever End? (Score:5, Funny)
Re: (Score:2)
20% to 40% ??? No. Just no. (Score:5, Insightful)
Someone is pushing some other agenda here.
Re: (Score:3)
Re: (Score:3)
With the advent of power FETs, we were able to get rid of the 0.7 volt drop x two = 1.4 volts lost on bridge rectification. Even Germanium and Shottky diodes had 0.3- 0.4 x two = 0.6 to 0.8 volts wasted in rectification. With 12 Volts AC this is a high loss.
Now they use FETs as switches for "synchronous rectification", a very old concept from the dawn of electricity and used in switching power supplies, with toroidally wound coils which allows for efficiency in the 97%+ range. Look here for data http://b [bit.ly]
Re: (Score:2)
Well, Edison did have a point that AC is more dangerous. There is a dead elephant to prove it.
Re:Will This Fight Ever End? (Score:5, Insightful)
There is a dead elephant to prove it.
If he had simultaneously ran DC to a 'control' elephant and it remained unharmed, you might be on the way to proving something.
Re: (Score:3)
Lightning is DC. Not many survive that
Re:Will This Fight Ever End? (Score:5, Informative)
Well, that doesn't seem to be completely true
1999 Darwin Awards - Resistance is Futile [darwinawards.com]
and that was only a 9v battery.
Skin effect: DC more deadly at same voltage (Score:3)
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 [wikipedia.org] 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 hims
Re:Will This Fight Ever End? (Score:5, Interesting)
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.
I have that Thinkgeek t-shirt actually...
It is mildly amusing that DC, Edison's favorite, might be better suited to an application named after the major proponent of AC, Tesla...
Re: (Score:3)
It is mildly amusing that DC, Edison's favorite, might be better suited to an application named after the major proponent of AC, Tesla...
Yes, that DC is still in business is truly a MARVEL.
Re: (Score:3)
This is a load of hooey. Low-voltage wiring is a PITA, and losses due to conversion aren't as high as is being claimed. The loss from just charging the battery is bigger. I'm afraid we are stuck with 120/240 VAC, and Tesla is the winner.
Tesla enables Edison to win the endgame? (Score:5, Insightful)
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.
Re:Tesla enables Edison to win the endgame? (Score:5, Insightful)
Worth noting that this is still forced to work within the Edison system's restrictions: the power source encouraging DC must be local. Which is cool when we all have our own power storage and generation capabilities.
Re:Tesla enables Edison to win the endgame? (Score:5, Insightful)
Everything I have read here makes me angry. First, there were technical reasons why Tesla wanted AC, and economic reasons why Edison wanted DC.
Second, HVDC lines exist. This is for BOTH technical and economic reasons.
Third, you can run AC and DC on the same lines and filter one from the other. With modern SiC tech this isn't even a challenge.
Re: (Score:3, Informative)
Running both AC+DC works but they both still add up to the same tolerable breakdown voltage before it arcs over in an undesirable manner.
Re:Tesla enables Edison to win the endgame? (Score:5, Informative)
DC in the home is only viable due to recent advances in power silicon. AC has its problems, but the genius of AC power is that you can controll it with nothing more than carefully arranged windings of wire and big chunks of metal. Transformers, inductors, capacitors, and resisters can all be made with nothing more than properly arranged and chosen wires and metal blocks. There was no practical DC-DC conversion in Edison's day. Even AC/DC conversion was tricky, often requiring an AC motor with a shaft mechanically linked to a DC generator.
Edison did not have the IGBT
http://en.wikipedia.org/wiki/Insulated-gate_bipolar_transistor
Today, that's different.
You can make tiny, tiny, cheap little AC-DC or DC-DC converters that are dozens of times cheaper and many more times efficient than their counterparts made even a decade ago. What used to require large arrays of MOSFETs and many many pounds of expensive copper windings (And the design/volume/heatsinks/fans to deal with all the waste heat!) is now handled by a much smaller transformer, a handful of inductors, and some advanced switching silicon controlled by a fairly smart processor. You also, thanks to increased efficiency, don't need to overbuild with expensive heat tolerant components so much. (Heat shortens component lifetimes, particularly caps)
And they're already deeply commoditized because, guess what, the chinese are big in to solar. (They know they are going to need it. They're quite aware that traditional energy can't economically fully meet their future demand.)
Re:Tesla enables Edison to win the endgame? (Score:5, Funny)
Sounds like the fight about currents has been rectified then?
Re:Tesla enables Edison to win the endgame? (Score:4, Informative)
Absolutely false, ultra high voltage DC is the most efficient way, and smarter countries are building such systems. Brazil is building a system that will have a 1500 mile long line, India is building them too
Re:Tesla enables Edison to win the endgame? (Score:5, Informative)
HVDC works well for long trunk lines between a distant large power source and a population center, but it much less useful for a grid system with many interconnect points. That's why the primary usage has been between hydro plants and distant cities and for international interconnects (especially where the local grids of the two sides do not share a common standard).
Re: (Score:3)
Look up the Celilo Converter Station [wikipedia.org] and the Pacific DC Intertie [wikipedia.org] for examples of HVDC in the US. I like how they used +-500kV to ground so that the insulators to the grounded tower could be smaller than if they'd used +1MV to ground.
Re:Tesla enables Edison to win the endgame? (Score:5, Informative)
The parasitic losses of DC over long distance is reason enough that it's not done
Siemens quotes 3.5% loss per 1,000km for +-800kv DC vs 6.7% for 735kv AC systems, exactly the opposite of your claim. I think I'll trust one of the biggest names in power over someone with a free bitcoin scam in their signature.
Re:Tesla enables Edison to win the endgame? (Score:5, Informative)
This is why there are only a handful of DC transmission lines in the world
How big are your hands? Wikipedia [wikipedia.org] has a "few" (200+) examples of HVDC transmission lines. And a here's a cool map [wmflabs.org] showing the inverter stations.
Re: (Score:3)
200+ vs MILLIONS of installations of AC
yes, 200 is a handful in comparison.
Re:Tesla enables Edison to win the endgame? (Score:4, Informative)
There's two main sets of losses, as I understand: Resistive losses and radiative losses. You can get into other issues, such as power factor and phase error related losses. The two biggies that hit you almost before you get started are resistive and radiative losses, though, if you just consider a single transmission line driving a resistive load.
You combat resistive losses by going up in voltage, so you can send more power with less current. Since resistive losses are proportional to the square of current, each doubling of voltage reduces your resistive losses by a factor of 4. That's why long haul transmission lines are high voltage.
Radiative losses are different. Whenever you accelerate a charged particle, you generate an electromagnetic wave. With respect to wires carrying current, that corresponds to changing the amount of current. (Current measures the rate at which electrons flow, so changing current means accelerating or decelerating electrons.) That's how radio transmitters works, for example.
In an AC system, that current is continuously changing, so those transmission lines are continuously radiating away some amount energy. But that's not all. If there are any conductors nearby, those E-M waves can induce a current in those conductors, and the resulting E-M waves from that induced current can drag on the AC line further. This mutual induction is how transformers work. But, along an AC transmission line, unwanted coupling results in transmission losses. So, an AC system has a built in, inherent source of losses in the alternating current itself.
In a DC system, with a fixed, perfectly resistive load, the current doesn't change, so there's no radiative losses. In the real world, though, the loading on the system is continually changing, so the actual current demand on the DC system will vary over time, and some energy will be radiated away. To some extent that can be filtered, but that's limited by the amount of storage you can put near the ends of the transmission.
The reason AC won out over DC in the early days is that we didn't have practical means to step DC voltages up and down. But, we had just invented the first practical transformers, and those can step AC to higher and lower voltages trivially.
HVDC is practical now since we've had 100 years to develop better technology for converting DC voltages on the grand scales required.
Re: (Score:3)
Do you know what the most efficient switch is for voltages over a kilovolt? I'll give you a hint: it's not based on semiconductors. Especially for high power. There's this little matter of "breakdown voltage," for one. Also "channel resistance." When someone comes up with a transistor [1] that can do
Re: Tesla enables Edison to win the endgame? (Score:5, Funny)
If the Tesla Powerwall starts shining, it's best to move away from it as quickly as you can.
Too low: don't forget the power requirements! (Score:5, Insightful)
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.
20-40% overblown (Score:2)
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 p
Re:20-40% overblown (Score:5, Informative)
> If you're using somewhere near the inverter's peak output, then you can get as much as 90% efficiency
These days inverters are much better than that. To use a random product that is currently shipping, an SMA Sunny Boy 5000 runs at 95.5-97% efficiency. Bigger inverters are even better with some commercial scale monsters at 98% efficiency.
The original article is pure nonsense. There are already three port inverters on the market. Those ports are: your 120V AC, your solar array, your battery bank. If the energy is going from the solar array to the battery there is simply no intermediate conversion to AC. With a three port inverter, there is only ever a single conversion from DC to AC. And, as I previously mentioned, will only get hit with a 3-4.5% loss. There is simply no way the world is going to change how electricity is delivered to avoid that.
Since the Tesla Power Wall is pretty much for sure going to be a high volume product, there are inverter manufacturers falling all over themselves to design and build three port inverters specifically optimized for the Tesla product.
This has been played out before... (Score:5, Informative)
...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?
Re: (Score:2)
Re: (Score:2)
Boat people use 36 or 48V in larger vessels. There is a lot of work done in high voltage DC for people with lots more money than sense.
The higher DC voltages seem to work well for everything except household-class heater appliances like dryers. But 12V isn't going to cut it for house-sized objects. Yes, you can do it - but why would you want to?
For one thing, high amp copper cable is expensive and a PITA to install.
Re: (Score:3)
RVs tend to have two rails. A 12 volt set of circuits, and 120 VAC. However, because it is only 3-4 meters at most, one can get away with using low-amp appliances on that rail.
A house, with its far longer runs should be on 120 for everything, and if 12 volts is needed... put a rectifier in the room. No need to use big fat meth-head attracting cables.
If one wants the advantage of clean power without needing a power supply for every box... this is a long since solved problem. Telcos have been using 48VDC
Important Question: WHICH DC? (Score:4)
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.
Re: (Score:3)
Or you could just buy a socket with a built in USB charger and swap them out. For example in the UK you can get these
http://www.screwfix.com/p/lap-... [screwfix.com]
They even retro fit in to 25mm deep back boxes. I can't believe that similar sockets are not available in other countries.
Re: (Score:3)
Call me when you figure out how to run a house air conditioner or full sized refrigerator off of 5v@1A
Re: (Score:3)
Therein lies the problem with LVDC in the home. There's a reason why we use high voltage to transmit power - either HVAC or HVDC. You lose a crapload of power at low voltages because losses increase with the square of the current. So double the voltage, halve the current, quarter the losses! (It's called IIR losses). Lower currents also mean your wires can be thinner (though your insulation needs to be thic
Bad Idea (Score:2, Insightful)
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.
Low voltage? (Score:2)
I thought North America already was low voltage. 8P
230~240VAC FTW!
Re: (Score:2)
60 HZ FTW!
Which raises the question, if we have installing inverters, why not 400 HZ?
Re: (Score:2)
Re:Low voltage? (Score:5, Funny)
640Hz should be enough for everybody.
Re: (Score:2)
440hz sounds like a better idea to me, though.
Re:Low voltage? (Score:5, Funny)
Just because we're all dim bulbs doesn't mean we're low voltage. There is a lot of resistance around here.
Re: (Score:2)
North American homes use a split-phase system which means they have both 120v and 240v. Typically high-power appliances use the 240v, such as dryers, large air conditioners, ovens, etc.
Re: (Score:3)
When I return home to the States from my current assignment, 220 outlets in my kitchen will be a top priority. Sure, I could buy a new kettle and a new coffee maker, but running off of 220 is so much better.
It will come down to economics. (Score:2)
Current? Fat cables? (Score:5, Insightful)
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?
Re: (Score:2)
Re:Current? Fat cables? (Score:5, Informative)
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.
Re:Current? Fat cables? (Score:5, Informative)
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.
A niche product in a niche market (Score:2)
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.
Save in conversion, pay for copper (Score:2)
.
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....
Re: (Score:2)
So you move the cost of losses from the DC to AC conversion to the cost of significant increases in the amount of copper needed to wire a house and the internals of power-hungry appliances.
Yeah I've been wishing it wasn't so ridiculously hard to change mains voltage. If only we could distribute at 220V, or get 220V feed lines to build 220V circuits. Europe has all these 15 amp appliances like steam irons that you can't get in the US because you'd need 30-35 amps to run them--they're 15A at 220V. Same appliances in America are low-power (1800W), and operate as if they're severely defective.
High-voltage, low-current is the way to go. We have 20 amp bedroom circuits; we don't need 20V 120
AC is the standard (Score:5, Insightful)
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.
Why Low Voltage DC? (Score:2)
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.
Re: (Score:3)
With modifications. A lot of things like those motors and LED lighting depends upon inductive current limiting. Give them DC at what seems the right voltage and they'll probably catch fire.
DC (Score:2)
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
Not buying it, Copper wire is exspensive (V*A=W) (Score:5, Interesting)
Lose the bricks? (Score:2)
Question for engineer / mathy types that can do the conversion loss calculations:
Given:
I think:
Manitoba Hydro (Score:2, Informative)
MB is already far ahead, as they actually transmit power from their dams as DC. https://www.hydro.mb.ca/corpor... [hydro.mb.ca]
Poorly researched article (Score:5, Insightful)
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.
AC and DC complement each other (Score:2)
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:
lots of copper? (Score:2)
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
Some appliances run fine on DC (Score:2)
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
A thousand times NO. (Score:4)
I've been planning this for years. (Score:2)
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....
Solar Panel Voltage (Score:2)
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 eas
if, and if, and if, then blog (Score:3)
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..
Replace 110 outlets with cigarette lighter outlets (Score:2)
the real question might be which AC frequency (Score:2, Informative)
What about safety? (Score:2)
When my 3yr old sticks a forked prong in my DC electrical outlet, what is the safety factor compared to the current AC plugs?
Copper wiring. (Score:5, Insightful)
High Voltage DC more likely (Score:3)
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).
Re: (Score:3)
A lot of inertia (Score:5, Insightful)
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.
Silly article (Score:3)
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
with so many people responding so strongly... (Score:3)
Use High voltage DC stupid... (Score:5, Interesting)
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.
Re: (Score:3)
Heh I should have read your whole post before replying to the first line, but let me pick you apart in another one instead.
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.
Absolutely wrong. The first thing most power supplies do is step down from high voltage AC to something in the general range of whats needed on the highest output value. They step down with a transformer. That transformer only works with AC, if you put DC in it, you're just going to burn it up as it turns into a magnet carrying more current (because its not AC, so the there is no ind
Re: (Score:3)
We need to use HIGH voltage DC at about the same voltage as your house is now, forget about going "low voltage" DC.
No, we don't.
120v AC will kick you off of it if you touch exposed wires.
120v DC will cause you to clamp down if you grab onto a wire or device that electrocutes you, and worse still, it'll kill you at much lower voltages than AC.
Um, no, it's exactly the opposite situation. Both AC and DC can shock and kill at high enough voltages, but AC is what you cannot let go of and DC is what usually bumps you off. DC induces all your muscles to contract at the same time all at once which cause a quick jerk which often disconnects the victim, AC has the effect of pulsating all the muscles, which incapacitates the victim but not inducing one big jerk. The rule of thumb is that AC is about twice as lethal at the same current/voltage over DC.
Wrong. Tesla batteries are 350-450 volts (Score:3)
Re: (Score:3)
Yeh, for anything that produces heat, and hence requires a lot of power, this really isn't going to work. 250A cabling to a little electric fire place is a non-starter.
Re: (Score:2, Informative)
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. Power (in watts) is a function of voltage and current, it's relatively easy to juggle 100-300v on fairly light cable, but there's a good reason car starter motor cables are half an inch in diameter, they need to be to handle the 200plus amp current the starter motor needs at a nominal 12v. Low voltage is fine for lighting
Re: (Score:3)
48V is a common telecoms voltage, may as well work with an existing standard (it's 48V because you don't need an electrician's license to work with low-voltage, defined as under 50V).
Re: (Score:3)
Re: (Score:3)
Even with a few meters, it will require fat, all copper cables (A/C, one can use CCA due to the skin effect.) These are not cheap, and even the big fat ones are not run for more than a few feet.
As an RV-er, I'm familar with both 12 volt and 120 volt systems. For a LED TV or other low wattage appliance, 12 volt is better, just because it directly comes from the batteries. However, for a load like a microwave, A/C, heater, or anything above 300 watts, trying to run that on 12 volts would require very fat,
Re:Impractical (Score:5, Interesting)
This is largely what I was thinking.
As it currently stands, commercial buildings often have 277V lighting circuits (this is in the US) because it involves installing less copper in the ceilings.
From this, one can intuit that lowering the voltage will significantly increase the amount of copper, but let's take an example and make it more solid.
Let's say, for the sake of example, that we were considering 48V DC as an alternative to 120V AC (I personally would not want to consider anything lower than 48V in a home environment). If you need to deliver 1200W from point A to point B, it will require 10A at 120V, and 25A at 48V.
That 10A could be safely delivered on a 14 ga. wire in most domestic contexts, but will probably be delivered on 12 ga. For 25A, however, you're going to need 10 ga.*
A 250' roll of wire is ~$43 for 14 ga, $95 for 12 ga., and $138 for 10 ga. See the problem?
For the next challenge, you will also need to use different, more expensive switches and circuit breakers, or drop back to using fuses. This is because an AC arc self-quenches in half a cycle or less, and won't re-establish until the contacts are brought close enough together. The DC arc, on the other hand, is continuous, and requires additional effort to quench. Just for the record, there is an arc every time that a circuit breaker or switch is opened under load. This is the reason why you will often see switches and breakers labelled "AC Only".
Now, this is not to say that these problems won't be overcome or that a different variant might come about. Who knows? Maybe they'll gravitate towards 120V AC or some such, in which case it will be 1915** all over again.
(*For the non-Americans and uninitiated, US wire gauge is backwards: larger numbers are smaller wires. 14, 12 and 10 gauge are ~2.1, 3.3 and 5.3 mm^2, respectively)
(**There is nothing special about 1915, but I live in a house that was built in 1915 and was electified from day one. It would have had DC delivered to it in those early days, courtesy of Mr. Edison's various efforts in my current home town of Schenectady.)
Re: (Score:2)
Can't the electric company supply both AC (for home appliances) and DC (for electric cars)? They could also add a state tax to the DC meter charging 1.5 cents road tax for certain amount of kWh charged by the vehicle. Gasoline cars pay 30 cents per gallon for road tax, so it's time for EVs to start paying too.
Re: (Score:2)
What do electric cars have to do with anything? The article is talking about *home* batteries.
Re:oh the Irony (Score:4, Informative)
DC has very rapid power loss over any kind of distance.
No it doesn't. Losses are related to current, not AC vs. DC. A higher current in the same sized conductor equates to higher loss. You can get around this by raising the voltage (traditionally easier with AC), thus transferring the same amount of energy with less current, or you can increase the size of the conductor. DC can actually transfer more energy than AC on a similar sized conductor because it doesn't have to deal with skin effect.
I could link all of these terms to applicable articles for you but I'm feeling lazy and this is all common knowledge stuff anyway.
Re:oh the Irony (Score:5, Funny)
Well, as soon as someone invents the AC battery we can switch back...
Re: (Score:2)
Premature (Score:4, Insightful)
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.
Better inverters needed (Score:5, Informative)
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?
Even if you go DC, stay at 120V (Score:5, Interesting)
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
Re:Even if you go DC, stay at 120V (Score:5, Interesting)
(Continuing after brushing the touchpad posted it for me. B-b) ... equipment at that voltage. (Small systems are often 12V due to the availability of 12V appliances.)
But back to inverters:
Current inverter and switching regulator (they're pretty much the same stuff) technology is SO efficient that large PC boards in computing and networking equipment may run the power through as many as THREE DC-DC converters, because you lose less power to heat as losses in the inverters than you would to resistance running it a few inches through a printed circuit board power plane.
So the '"20-40% loss" number seems to me to be utterly bogus.
(Consider this: A Tesla automobile IS AC motors driven by inverters from batteries. A horsepower is almost exactly 750 watts. If they had 20-40% losses in the inverters, how do you keep the car from being on fire after a jackrabbit start? Let alone recover enough power on braking to reuse on acceleration to make a substantial difference?) If ANYBODY knows how to handle inverters it's Tesla. B-) )