Low voltage vs mains in the future - Page 1
Forum section: electronics / projects

author: calexanian
author_rank: Super Contributor
timestamp: March 17, 2014, 01:43:12 am
content: Just in a daydream today looking at my noticeably lower electricity bill after changing the majority of my house over to LED lighting, I had a thought. Bear in mind I live under a rock more or less (I live in Fresno California, not exactly a tech hot spot!) and this may already be happening out there, but how long until low voltage outlets start taking hold in homes? Honestly only large appliances and other big draws are the only need for mains anymore, and typically those do not run constantly save the heating/aircon. With cheap efficient switching converters I see great savings in lower voltages. DC itself in certain situations can have a galvanic effect of the condition of copper conductors, but low voltage AC can fix that. Heck, this 15 watt LED fixture gives a brighter better light than a 100 watt incandescent bulb. One thing I noticed though. The spectrum does not run my solar calculators as well! I have to use it on the bench under the flouro above my soldering area! At either rate, how long before the housing contractors realize you can effectively run a whole house worth of lights off a much smaller breaker and with much smaller conductors? Lower voltages would reduce the burden on LED drivers stepping down from mains reducing the complexity of the circuits. Perhaps standardize on LED forward voltage drop and string length to use simple circuits to drive them.Just a Utopian thought!

author: Fsck
author_rank: Super Contributor
timestamp: March 17, 2014, 02:01:18 am
content: the same time when north american builders wire outlets primarily for 230/240v since almost everything has universal voltage input.

author: IanB
author_rank: Super Contributor
timestamp: March 17, 2014, 02:08:14 am
content: Quote from: calexanian on March 17, 2014, 01:43:12 amHow do you find your eyes cope with this? I find such artificial light quite painful due to the lack of a continuous spectrum from red to blue/violet. Usually both CFLs and LEDs to me stick out like a sore thumb because the light is "wrong" and my eyes immediately pick up on that.If I dim an incandescent light, the light technically becomes yellow, but because it is still a continuous smooth spectrum it is possible for my brain to apply a color temperature correction and make it look "white". But with fluorescent light sources like LEDs or CFLs they don't have a smooth frequency spectrum and when the brain attempts to shift it and make it look "white" the attempt fails and the light ends up with a color cast, either green or red. This inability to balance the color and make it white leads to fatigue.For this reason I really dislike non-incandescent light sources and try to avoid them as much as possible.

author: Prime73
author_rank: Regular Contributor
timestamp: March 17, 2014, 02:08:32 am
content: Are you thinking to have a DC wiring in the house for the lights, etc or have a DC coming in? The latter was done by Edison back in a day and failed. DC is way more difficult to deliver over a long distances compare to AC.http://en.wikipedia.org/wiki/War_of_CurrentsI have all my lights converted to LEDs as well, however don't see much of a change on a bill - I guess I run a lot of other equipment that eats up a lot of power

author: Prime73
author_rank: Regular Contributor
timestamp: March 17, 2014, 02:10:29 am
content: Quote from: IanB on March 17, 2014, 02:08:14 amI've tried a few different ones starting with cheap ebay ones and ended up installing GU10 bulbs from ikea - to my eyes these are perfectly fine and really like them. I don't use dimmers though. I have multiple zones in my rooms ( 4 - 5) and I light the rooms as needed

author: dfmischler
author_rank: Frequent Contributor
timestamp: March 17, 2014, 02:21:22 am
content: Remember that power losses in the distribution system go up with the square of the current (P = I^2 * R), so it is far more efficient to distribute power at higher voltages. Even for relatively short runs. That is why IEEE 802.3af POE (power over ethernet) uses 48 volts. In the USA this is considered as high a voltage as you can have and still be covered by the "low voltage wiring" rules that cover things like ethernet.

author: calexanian
author_rank: Super Contributor
timestamp: March 17, 2014, 02:28:37 am
content: Agreed. The somewhat more expensive ones have a more natural light spectrum. I am envisioning something more like this. Power distribution is actually rather efficient as it is now. At your breaker box you have all of your high draw circuits running normally. Big loads, etc... Then you have a smaller power supply or a transformer. Perhaps the ubiquitous 13.4 VDC or perhaps 24VAC to prevent galvanic wire degradation of DC. this then runs to all of the various small loads. LCD tv's LED lighting, Computers, etc etc. As the power draw of these devices gets lower and lower as better technology is developed why do we need such large infrastructure in our houses? Additionally power supply design can get easier and more efficient. Isolation becomes easier.

author: calexanian
author_rank: Super Contributor
timestamp: March 17, 2014, 02:29:47 am
content: Quote from: dfmischler on March 17, 2014, 02:21:22 amThis is all assuming power draw of devices continues to drop as time goes on. As the load decreases, losses decrease as well.

author: dfmischler
author_rank: Frequent Contributor
timestamp: March 17, 2014, 03:05:01 am
content: Quote from: calexanian on March 17, 2014, 02:29:47 amSure, but is it really cost effective to have both a low voltage, low power distribution system and a higher voltage higher power system in the same area? In the USA the current National Electrical Code demands a 120V outlet on a 15A minimum circuit every 6 feet (1.8 meters) of usable wall with certain exceptions for hallways, doors, etc.: the so-called "vacuum cleaner rule". NEC has the force of law in areas where most people live in the USA so this is not something builders are free to change on their own.Also, mains distribution works very well and is quite reliable; do we need to worry about the possibility of low voltage supply failure killing lighting in large parts of a structure?

author: calzap
author_rank: Frequent Contributor
timestamp: March 17, 2014, 07:34:47 am
content: There is nothing in the electrical codes of most areas of North America that prevents wiring houses or other structures with low voltage wiring as long as mains 120 VAC or 240 VAC is included too. There are rules on keeping them separated in cables, boxes, etc. Some houses, mostly those off the grid, do have extensive low voltage wiring, usually 12 VDC. Dual wiring is present in many larger boats too. However, it would be difficult to ease into it on a wide scale. Most of the manufacturers of electronic devices that have internal power supplies would have to include a bypass cord or switch. There would also have to be agreement on voltage and connectors, and once power got to a certain level, a DC breaker panel would be needed. Low voltage may not be able to deliver a lethal shock, but at high currents, fires are possible. Don't hold your breath waiting for it to happen.BTW there was a trend a few years back to wire new houses in the USA with cat 5/6 cable. I think wireless has pretty much killed it.Those areas of the world that have 120 VAC as the primary mains voltage in homes have had enormous number of lives saved because of it. The downside: significantly more copper or aluminum needed to wire a house. The ultimate would be to use 48 VAC, but the trade-off is just too expensive.Mike in California

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 17, 2014, 08:42:22 am
content: What I would like to do.I'd like 48V dc for lighting and small things. Leave the main power outlets as 230v (Australia).I would put 2 or 3 230v to 48v convertors with sub distribution boards in the house.So much more wiring is in the lighting than in the power outlets. All the lighting and I guess some other stuff could all be changed to non lethal voltages. It uses less power too so the voltage drop wont be an issue.One day.

author: Kjelt
author_rank: Super Contributor
timestamp: March 17, 2014, 10:03:49 am
content: Actually the whole war of the currents is starting over. Now the electronics are here to make very high efficiency DC-DC converters there are already implementations for DC distribution, google for "DC grid".

author: electrodacus
author_rank: Super Contributor
timestamp: March 17, 2014, 07:33:54 pm
content: I just recently build my house. It is OffGrid and all my outlets are 24V DC (8 cell of LiFePO4) and can deliver up to 400W (16A) that is more than enough for most electronics.All my electronics have now a DC-DC converter like the laptops 24V - 28V in from battery and 19V out.And for lighting is the same 24V just 200W max for each fixture again an overkill since I have LED lights that do not use more than 30W on high.I have a power inverter that only works a few hours a day at most for large appliances in the kitchen usually for food preparation.Now I I will need to expand my small system in the future in order to heat the house with solar PV panels directly no battery involved here so that way is actually the least expensive option at the moment about 2.7cent/KWh if I can find a use for that power in summer.The heating part will be at much higher DC voltage to be able to use in floor electric heating cables and not spend that much on cables.

author: dfmischler
author_rank: Frequent Contributor
timestamp: March 17, 2014, 07:45:07 pm
content: Quote from: electrodacus on March 17, 2014, 07:33:54 pmCool. What did you use for outlets?

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2014, 07:52:55 pm
content: 120VAC/240VAC is low voltage. HV refers to >1kV.AC was only used for transmission because because the voltage can easily be changed using transformers. DC is more efficient because there is no skin effect or radiative losses. Nowadays switched mode powers supplies so high voltage DC distribution is more common.Now in theory it would be more efficient to power buildings off 120V/240VDC rather than AC but that's not going to happen because AC has been used for over 100 years and the infrastructure is st up for it.

author: katzohki
author_rank: Frequent Contributor
timestamp: March 17, 2014, 08:10:34 pm
content: Ugh, just what we need "cheap efficient switching converters" in every home! Yuck, no thanks. It would be terrible for HF radio I bet. Maybe as bad as the whole broadband over power lines thing?

author: Monkeh
author_rank: Super Contributor
timestamp: March 17, 2014, 08:49:40 pm
content: Quote from: calzap on March 17, 2014, 07:34:47 amhttp://www.esc.org.uk/industry/policies-and-research/statistics/Quotehttp://www.esfi.org/index.cfm/page/Injury-and-Fatality-Statistics/pid/12015Quotehttps://www.osha.gov/oshstats/commonstats.htmlQuoteSo that's 60 from consumer products, 66 from construction sites (okay, perhaps not all from 120V).. I haven't gone looking for those caused by faulty wiring, unsafe DIY work, and so on. You've already got as many fatalities as the UK per person, and twice as many in construction alone as all work related deaths in the UK. Where're these saved lives?

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2014, 10:27:22 pm
content: In addition, here in the UK, the most common voltage on construction sites is 110V which is either 55V or 63.5V with respect to neutral, depending on whether spilt phase or three phase is used.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 17, 2014, 10:48:32 pm
content: In the US, 240V is only marginally more dangerous from a shock perspective as it's two phases of 120V to ground. The only time it makes a difference is if both sides are contacted at the same time.

author: electrodacus
author_rank: Super Contributor
timestamp: March 18, 2014, 01:46:21 am
content: Quote from: dfmischler on March 17, 2014, 07:45:07 pmI used C19 panel mount power connector and of course C20 for the device even if I actually use a sort of multi outlet strip from C20 to multiple female XLR connectors since I have a lot of low power devices that need to be connected especially in my lab.If you are curios about the house you can see this videoHouse is still work in progress this is a short video with the build process.

author: johansen
author_rank: Super Contributor
timestamp: March 18, 2014, 01:47:35 am
content: dc is more efficient but not much more.single phase ac for instance, you pay for resistive losses at 120vac but you have to insulate for 168 volts dc.this isn't a problem for 120v but it is for 300KVac transmission lines, which have to be insulated for 500KV.so, i do believe there have been some dc grid installations where they used the same lines on dc at higher voltage, and since two dc lines can carry as much as three ac lines, plus the 41% increase in voltage, you can basically double your capacity.--but there are many systems where this can't be done because the insulators can't handle dc, so they have to replace them with new ones.the problem with dc of course is you need an inverter.while there are Thyrister stacks that have been in operation now for 40 years without a failure...try getting that reliability with 1200 volt igbts. ain't going to happen anytime soon...furthermore, you may not realize this but 60 hz transformers have been operating at 1KW per kilogram, at greater than 99.5% efficiency for 40 years now, provided they are at least 100MW in size.that kind of efficiency and cost (15$ per kilowatt) won't be beat by SMPS anytime soon.

author: Marco
author_rank: Super Contributor
timestamp: March 18, 2014, 02:25:43 am
content: Quote from: katzohki on March 17, 2014, 08:10:34 pmWe already have them in every home ... just not for the major appliances.The washing machine would probably run more efficiently on DC though because it's variable speed ... not that it will ever happen.

author: IanB
author_rank: Super Contributor
timestamp: March 18, 2014, 03:10:26 am
content: Quote from: johansen on March 18, 2014, 01:47:35 amI don't believe this is quite right?Suppose a two circuit AC transmission line (six conductors) operating at a given (RMS) phase voltage relative to ground. A three circuit DC transmission line using the same six conductors could deliver the same power at the same line currents and the same (DC) voltage relative to ground as the AC system. (I just did the math and verified this. I didn't know it before, but a DC circuit can deliver the same powerper unit weight of conductoras a three phase circuit if both circuits operate at the same line currents and same ground referenced voltages. The conductor size is the killer. To deliver the same total power over a two conductor circuit as a three conductor circuit with equal losses, the conductors have to be 50% thicker in the DC case.)Therefore increasing the voltage by 41% at the same maximum current would increase power by 41%, rather than doubling it. Still a useful increase, but not quite so stunning.

author: SL4P
author_rank: Super Contributor
timestamp: March 18, 2014, 03:23:17 am
content: There are also issues of galvanic corrosion and other physical / metallurgical factors.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 18, 2014, 04:24:10 am
content: Quote from: Marco on March 18, 2014, 02:25:43 amA lot of newer washing machines are in fact inverter drive.

author: calzap
author_rank: Frequent Contributor
timestamp: March 18, 2014, 04:27:29 am
content: Quote from: Monkeh on March 17, 2014, 08:49:40 pmFrom an epidemiological point of view, exposure has to be considered. The only rational way to look at it deaths per shock. The shock rate per capita probably varies considerably among countries; however, most shocks are likely unreported. In addition, RCD (aka GFCI) use varies considerably countries. My original statement was in past tense, so virtually all the 20th century has to be considered.As an analogy, if you look at gunshot deaths, the per capita rate in the US is terrible, but that is probably due mostly to gun ownership per capita being so high. If you want look at fundamental gun safety, the rate that should be considered is the deaths per gun or perhaps deaths per gun firing or deaths per gun user/owner. Don't know how the US would come out on that ... probably not so well.The shock rate per capita may well be higher in the US than many other countries. Part of it may be a phenomenon called risk compensation by actuaries. Basically, it means people push the limits of what they believe to be safe. I know a licensed electrician who thinks nothing of the occasional 120 VAC shock, but when it comes 240 VAC and higher, he is extremely careful. Says it bothers him, only if it happens in front of a customer. I think he's foolish not to be equally careful with 120 VAC, but he's survived so far. And, yup, if household mains voltage in the US was raised to 240 VAC, eventually folks would be more careful, but there would be a lot deaths in the interim.Likelihood of ventricular fibrillation, the cause of most shock deaths, is related to current flow through the heart. If you double the voltage, current flow will double. Actually, it's worse than the linear relationship of ohm's law. Body resistance to AC decreases as voltage increases.There's a reason why some countries have lower mains voltages in homes, and it's not because they like to spend money on copper and aluminum. But, hey, if 220 or 240 VAC is OK, let's raise it to 480 VAC and spend even less money on wiring.Mike in California

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2014, 04:58:11 am
content: Quote from: calzap on March 18, 2014, 04:27:29 amAnd yet the statistics just don't back your lower voltage. You have more fatal electrocutions, you have more electrical fires, you have higher losses and lower network reliability. Sorry, not convinced. Please join the 21st century.QuoteAnd now you're just being silly.

author: calzap
author_rank: Frequent Contributor
timestamp: March 18, 2014, 05:04:30 am
content: Quote from: Monkeh on March 18, 2014, 04:58:11 amThe main place that voltage matters in the negative outcomes you mentioned is in shock fatalities, and I made my statistical argument and consider it valid.The mention of 480 VAC was not to be silly but to emphasize that voltage matters when it comes to safety, which has been my main point .Mike in California

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2014, 05:16:29 am
content: Quote from: calzap on March 18, 2014, 05:04:30 amA statistical argument with no statistics. Very valid.QuoteCertainly, it matters. However it is quite apparent that your lower voltage system does not, at the end of the day, reduce overall fatalities over a 240V system. It almost certainly will reduce the number of fatalities per shock, but because people then begin to treat it like a 9V battery, the number of shocks goes up. You made that point yourself. The lower shock magnitude is outweighed by such factors. The system is no safer in practice.I could go into the number of electrical fires (both appliance and installation related), but that would just be adding insult to injury.

author: david77
author_rank: Frequent Contributor
timestamp: March 18, 2014, 06:10:12 am
content: Great idea having our homes filled with even more crappy chinese DC-DC converters that can fail.I'm not saying DC-DC converters are unreliable as such, but there's so much more scope to get it wrong when compared to a transformer & linear PSU. Especially when the manufacturers try to pinch every last penny out of a design to be more competitive.I recently converted our kitchen lights back to the >30 years old T8 fluoro fixtures that I ripped out in 2005 when we refurbished the kitchen because the new lights annoyed me so much, they kept blowing their T4 fluoro tubes or the electronic ballasts. Good thing I didn't throw the old ones out, I fully expect another couple of decades service from them seeing as there's no electronics in them that's likely to fail.Just for the record: The T4 fluoros were not cheapies, they came from a reputable German manufacturer, but still had only chinese crap inside. The T4 tubes also cost pretty much to replace and are rather hard to get. With all the repairs I had to do in the last 8 years I'm certain I did not save a cent, quite the opposite.

author: calzap
author_rank: Frequent Contributor
timestamp: March 18, 2014, 07:13:14 am
content: Quote from: Monkeh on March 18, 2014, 05:16:29 amSomehow I think more of us yokels in colonies would die being shocked by 240 VAC compared to 120 VAC. And risk compensation is never complete, so increasing safety margins does save lives; it's just a matter of how much we want to spend to save those lives. BTW, there are countries other than the US that have 120 VAC as the main household voltage. However, as I pointed out earlier, comparing shock deaths per capita between countries is not too useful unless shock rate, RCD use, etc. are taken into account, and those critical data are hard to come by.Mike in California

author: Kjelt
author_rank: Super Contributor
timestamp: March 18, 2014, 08:15:05 am
content: Quote from: david77 on March 18, 2014, 06:10:12 amTake a look at all the electronics of this century, they (almost) all have SMPS inside. Transformers have too much copper (expensive) and are being fased out already.So the whole point is that the first stage (rectifying and buffering) can be skipped resulting in even higher efficiencies. For instance lighting can all be done DC, tv, stereo, computers you name it. The only devices that still need ac for the moment are the washer and refridgerator but that is a small change to linear motors and dc compressors.And if you don't like the chinese DC-DC converters use the German, they have factories making very good switchers

author: rdl
author_rank: Super Contributor
timestamp: March 18, 2014, 03:21:38 pm
content: Quote from: electrodacus on March 18, 2014, 01:46:21 amAwesome video man.This should be on Hack a Day. Much more impressive thanall that Arduino crapwhat they usually post.

author: Fsck
author_rank: Super Contributor
timestamp: March 18, 2014, 03:34:59 pm
content: Quote from: Kjelt on March 18, 2014, 08:15:05 ampersonally I don't really about AC vs DC supplies in a home, I just want my >30kW in my work area for an "industrial"(very cliche term) UPS backed computers + electronics equipment.

author: Nerull
author_rank: Frequent Contributor
timestamp: March 18, 2014, 05:15:00 pm
content: "My friend is an idiot" is not really a valid commentary on relative safety.

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2014, 08:15:30 pm
content: Quote from: calzap on March 18, 2014, 07:13:14 amI suspect one of the reasons why the death rate from shock is lower in the UK, than the US, is because we have more stringent wiring regulations.Also one shouldn't forget that lowering the voltage, increases the current required which also increases the risk of cables overheating and fire, if they've not been sized appropriately.

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2014, 08:16:56 pm
content: Quote from: Hero999 on March 18, 2014, 08:15:30 pmWell, they have to size cables extremely conservatively in the US, because their volt drop concerns are extreme. We're already very conservative over here. Joints are the problem, really.

author: calzap
author_rank: Frequent Contributor
timestamp: March 18, 2014, 11:03:10 pm
content: When looking at electrocution rates in different countries, there are a huge number of factors that enter. Some are related to EE concerns like commonly accessible voltages, wiring methods and codes, use of RCD and arc-fault breakers, age of facilities, rate of new construction, availability of parts and devices that have certification, etc. Some are only partly or distantly related to EE concerns or totally unrelated: public education on electrical safety and first aid, tendency to do-it-yourself, code enforcement, inspection frequency, cultural attitudes about electricity and risk taking, quality of electricians and inspectors, centralization versus fragmentation of codes and enforcement, quality of emergency services and medical personnel, etc. It is really tough, maybe impossible, to sort these out when comparing two countries. However, within a country, a change in many of these factors has a predictable effect on whether electrocutions will increase or decrease, but quantification is an exercise in retrospection.Mike in California

author: richard.cs
author_rank: Super Contributor
timestamp: March 19, 2014, 11:27:59 am
content: Quote from: Hero999 on March 18, 2014, 08:15:30 pmThis is a key point to consider. Reducing the shock deaths has no value if you cause and equal or greater number of deaths from electrical fires. A meaningful analysis would include all of the electrical deaths not just shock.It is also necessary consider the benefits, a home without electricity gives zero shock risk but people accept a risk of electrical death in order to have a higher standard of living - a less extreme example is that 220-240V countries have more power available from general purpose outlets and perhaps an increase in risk might be an acceptable tradeoff to most people* (not saying there is or isn't an increase in risk) in the same way that people know driving to work 20mph faster carries an increased risk of death but they accept that for the benefit of getting up later.*Dedicated circuits not usually required for clothes driers, etc. Portable electric heaters become more practical, extension leads can be longer, kettles (yes, I know "what's that?") boil faster.

author: VK5RC
author_rank: Unknown
timestamp: March 19, 2014, 12:00:34 pm
content: A couple of points I would like to raise1. Higher voltage may not always be more dangerous, some 'intermediate' level high voltages can lead to ventricular fibrillation, the lethal heart arrhythmia, often if a bit higher voltage it defibrillates you at the same time! (I am not going to test this AGAIN! having once in my life connected myself, across the chest, national grid 240V AC active to earth, 1cm electrical burns on thumb)2. Some of the DC 'low' voltage used in off grid systems are getting up to potentially serious levels, 48V is not uncommon (to reduce copper losses)PS Work/Play safely; one hand in pocket, RCD device, master kill switch and learn CPR!

author: Kjelt
author_rank: Super Contributor
timestamp: March 19, 2014, 12:54:45 pm
content: Another point is that AC 50/60Hz is relatively safer then DC voltage because DC will contract the muscle, if you have a grip on some voltage conducting object you are less able to let go of it.Fail.Let-go current is the highest current at which subject can release a conductor. Above this limit, involuntary clasping of the conductor is present. It is 22 mA in AC and 88 mA in DC.

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 19, 2014, 01:04:21 pm
content: One of the real problems with DC (paticularly above 40V) is being able to break it reliably under load.This places a huge burden on the switches and they have to be designed for DC. This issue is often overlooked. 12V DC is no problem, but go a bit higher and it very quickly becomes troublesome.Trying to break a couple of hundred volts DC requires special switchgear. Using a normal large toggle switch just results in internal arcing and the switch goes up in smoke.Dick

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 19, 2014, 01:36:52 pm
content: Quote from: david77 on March 18, 2014, 06:10:12 amBut it could eliminate electrolytics, which are probably the most inherently unreliable component You can design a DC/DC with a pretty much unlimited lifetime - need for electrolytics makes this harder for low frequency AC.

author: madires
author_rank: Super Contributor
timestamp: March 19, 2014, 01:56:38 pm
content: I'd replace the 'vs.' with an 'and'. For low power stuff with wall warts and LED lighting a central low voltage DC PSU makes much more sense because of efficiency, reliability and costs. No cheap wall warts with bad efficiency anymore. No need for an AC-DC conversion in each LED light. You could add a backup, i.e. lead batteries, or photovoltaics. The low power low voltage wiring is less expensive than mains wiring. Most low power stuff in my home office is powered that way, simply by sharing a 80+Gold PSU of a server running 24x7 anyway. Overall the power consumption with that design is about the half of running everything on the cheap wall warts.High power low voltage DC is something for special cases because thick copper wires are expensive. You find those in data centers for telcos which run network elements on -48V DC. It's part of a large true online UPS. Some data centers, especially those running own servers, are considering mains voltage DC. Same wiring as for AC mains but the overall design with a central PSU incl. UPS increases the efficiency by some percent. If you pay monthly $250,000 for power 10% is a nice sum.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 19, 2014, 02:16:49 pm
content: Quote from: Kjelt on March 19, 2014, 12:54:45 pmNot true, 60Hz is actually right about the optimum frequency to stop the heart.

author: Kjelt
author_rank: Super Contributor
timestamp: March 19, 2014, 02:30:14 pm
content: Doh got it the wrong way aroundTime to re-take my NEN3140 examination again (was over three years ago)in the US they call this the let go threshold:Quote-

author: LukeW
author_rank: Frequent Contributor
timestamp: March 21, 2014, 06:54:55 am
content: I can see the appeal, if you look at the consumer electronics you're commonly using around the home.External hard drive which has a 12V plugpack.Two modern LCD monitors which each have a 12V plugpack.Laptop power supply, 17V DC or whatever that is.Phone charger, 5V DC plugpackTablet charger, 5V DC plugpackADSL modem, 5V DC plugpackAnother WiFi access point, 5V DC plugpack.You get the idea.I can see the appeal of low-voltage DC distribution for consumer electronics, freeing up the 240VAC outlets so that you've got one available to use when you want one, for the devices that really need it.Distribution at 48V might make sense, to reduce voltage drop and I2R losses whilst also staying within the "extra low voltage" political benchmark, just like POE.And then you might have a few local outlet modules - a couple in each room maybe - where a DC-DC converter converts the 48V into outputs at 12V and 5V DC. Or maybe something like 5V and 17V, and you have a whole bunch of output jacks running power out to your devices.For the ham radio aficionados concerned about interference, what's the worst that's going to happen? You're going to replace a dozen separate switchmode plugpacks which already exist with just 1 or 2.

author: Kjelt
author_rank: Super Contributor
timestamp: March 21, 2014, 08:09:33 am
content: The biggest challenge I see is to make the first in the house dc-dc converter a very high efficiency DC-DC converter that has to have a very high efficiency under any load not only under full load as most of the present types have.The next small problem is what the preventive replacement/service periods for these converters will be, every ten years? fifteen?

author: VK5RC
author_rank: Unknown
timestamp: March 21, 2014, 08:13:42 am
content: The only theoretical issue I can see as an amateur is the length of the "antenna"; the DC wiring becomes a radiator. With poor switch mode supplies they make the mains an antenna anyway so not much of a change. The real issue is crappy switch mode supplies (boost/buck DC converters/Inverters), if manufacturers try a bit they can make them properly, but some of the WHL guys will do anything to save a cent or 2.i think the real issue is there is no 'standard' for DC like there is for mains voltage (including fittings) although in amateur circles the "Anderson" connector is getting very close to being considered a 'standard' for the standard DC supply at '13.8V'.

author: madires
author_rank: Super Contributor
timestamp: March 21, 2014, 11:52:53 am
content: Quote from: VK5RC on March 21, 2014, 08:13:42 amMy setup with an ATX power supply and selfmade DC DC converters is tested with a shortwave receiver ;-)Quote40A connectors for a phone charger or DSL router? I'd think that the standard DC jacks found in nearly all devices would be the best choice.

author: dfmischler
author_rank: Frequent Contributor
timestamp: March 21, 2014, 12:02:33 pm
content: Quote from: madires on March 21, 2014, 11:52:53 amAnd which connector would that be? If you really look you will find they are not nearly as standardized as they would need to be.

author: richard.cs
author_rank: Super Contributor
timestamp: March 21, 2014, 01:14:03 pm
content: Quote from: dfmischler on March 21, 2014, 12:02:33 pmMore specifically what combination of pin diameter, barrel diameter and length would you like? Just sticking with the coaxial d.c. connectors there's >10 different types. And without any particular standard on their uses you probably can find a 24V power supply that will fit into your 5V cordless phone and make it go pop (but every 5V supply in your junk box won't fit).

author: madires
author_rank: Super Contributor
timestamp: March 21, 2014, 03:41:12 pm
content: Quote from: richard.cs on March 21, 2014, 01:14:03 pmMaybe the 2.1mm / 5.5mm with 9.5mm shaft, it's the most common. But it would make sense to define and design a larger and more robust connector supporting a lot of inserts/removals. Same for the socket. I would also define that dedicated connector to be used only for the DC power distribution with a specific range of voltage and current, e.g. 18-32V and 5A. Devices supporting that power input may use that connector too. Any other stuff would need an additional DC DC converter. As mentioned above the 2.1/5.5 type is used by >75% of all devices (at least over here). So it's easy to plug in the wrong wall wart anyway.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: March 21, 2014, 10:01:08 pm
content: There are pros and cons for all the power distribution systems world wide.Back in the 60's/70's it was worked out that over the projected life of a multi-storey office block it was cheaper to switch fluorescent lights off storey by storey, rather than room by room or zone by zone. The saving in cabling, switches etc. during construction and replacement of tubes & starters outweighed any apparent extra power consumption.The current rules outlawing incandescent lamps are supposedly to reduce overall energy consumption. An opposing view is that the energy used and relatively rare elements consumed to produce leds (amongst other solutions) never mind safe disposal and pollution issues do not justify the ban.Also consider that we, in this forum at least, have some understanding of the potential dangers of multiple supplies - the average man in the street has less understanding. Note I'm not saying stupid, just having less understanding.It would be interesting to estimate what the cost of retrofitting multiple supplies would be even for a small town, I think it would not be cost effective.Me I'm waiting for house wide induction charging

author: Dave Turner
author_rank: Frequent Contributor
timestamp: March 22, 2014, 12:30:38 am
content: Quote from: mojo-chan on March 21, 2014, 11:21:59 pmMojo - I tried to be very careful not to express a personal bias. Perhaps I chose an inappropriate example with regard to leds. My main issue is that there has been so much hype by vested interests regarding energy saving that the real 'truth', whether promoted by manufacturers or 'green' party opposition, is often obscured.

author: IanB
author_rank: Super Contributor
timestamp: March 22, 2014, 12:37:15 am
content: The factories that produced incandescent bulbs were clean, efficient, and highly automated, having been fine tuned over 100 years. Incandescent lamps are a simple and elegant engineering solution to a problem.The (Chinese) factories that produce CFLs and other electronic components are not subject to anything like the same environmental regulations. They generate toxic industrial waste and consume energy from coal fired power plants that generate CO2, acid gas and particulate pollution.The ban on incandescent bulbs has not provided an environmental improvement, it has merely shifted the problem to someone else's back yard and made it worse in the process.

author: Kjelt
author_rank: Super Contributor
timestamp: March 22, 2014, 06:14:03 pm
content: The EU has just recently passed a law that all smartphones shall have one and the same chargingconnector and voltage. So it could be done.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: March 22, 2014, 09:15:03 pm
content: The main reason for the law is to reduce the plethora of redundant chargers about, with just about every new phone requiring a different charger. That's laudable.However it may prove to be a restrictive nuisance to future innovation (as many of the EU laws appear to be).Personally I dislike the currently popular 'jack' plug solution. Imo they are too fragile for long term use. Maybe planned obsolescence has something to do with it, which somehow defeats to object of the law in the first place.As a matter of interest I'm told that the mains sewage filters in the UK (Greater London in particular) have often been blocked by obsolete mobile phones. Wonder what happened to the chargers!

author: calexanian
author_rank: Super Contributor
timestamp: March 25, 2014, 06:25:38 am
content: I think we can all agree that CFL's are terrible in nearly all respects. If its a choice of CFL or LED, there really is not much of a question which technology will be more long lived. Traditional Fluorescent tubes will go on if for no other reason than there are literally billions of fixtures out there they go in. CFL's can go away tomorrow and nobody would fret a bit over it since lamp base type LED's are good and widely available and despite the government "Banning" incandescent lamps they are still plentiful and cheap. I think it is silly the government even did anything as i believe people will discover as I did the benefits of the new LED designs and eventually make the change over naturally and leave the incandescent bulbs for fixtures that look best with them but are not used as primary light. I am a big believer in having a nice pretty fixture for looks and mood lighting, and then some high output crisp lighting (Now LED) for when I actually want them. I find the physical effect of not having the heat of a flouro tube or a traditional bulb soothing as well.I could go on for hours...

author: Monkeh
author_rank: Super Contributor
timestamp: March 25, 2014, 06:30:44 am
content: Quote from: calexanian on March 25, 2014, 06:25:38 amNope. But that's because I like 2D CFLs, which are actually quite good, if used correctly.

author: Kjelt
author_rank: Super Contributor
timestamp: March 25, 2014, 08:16:40 am
content: Quote from: AhhhChoo on March 25, 2014, 08:07:03 amIt all depends on the equipment, if you look around your house for electronic equipment I guess that about 80% (and probably even more) use an end voltage of 12VDC or lower which can be made with >90% efficiency from 24VDC if you compare that to the usually 70% efficiency of ac->dc converters that is pretty significant. Multiply that by 1 billion households....Yes there is always power hungry equipment that needs a higher voltage, i don't think it is smart to power your 2kW watercooker from 24VDC

author: han
author_rank: Frequent Contributor
timestamp: March 25, 2014, 09:12:00 am
content: why not use standard in telecommunication industry:48V DC for critical application, since it's easy to put a Battery Bank in the line240V for power hungry application like heater/ Air conditioner

author: mzzj
author_rank: Super Contributor
timestamp: March 25, 2014, 09:35:44 am
content: Quote from: dfmischler on March 17, 2014, 03:05:01 amLet's image for a second that NEC wouldn't limit our options in the future:We got a house with a roughly 20 meters (=40 meters or 80 feet round-trip) of wiring from power distribution box to farthest corner(hobby corner/workshop):4x30W for lightning (remember, this is eevblog hobby corner with smd work to do)5W for ADSL10W for external HDD30W for laptop=total 165 watts. =14 amps at 12vok, 14 amps you can probably do fine with 14G wiring regarding temperature rise. But with 12volts your wiring losses are 40% !To transfer the lousy 165 Watts efficiently(>98%) at 12 volts you need 1G wiring. 40 meters of 1G wiring is roughly 20 times more expensive than 14G wiring. Roughly $320 for 12v wiring instead of $8.So 12v wiring would be suitable for:-loads that are so small that the energy consumption is irrelevant in any case.-tiny apartments with dim lightning.

author: mzzj
author_rank: Super Contributor
timestamp: March 25, 2014, 09:58:48 am
content: Quote from: AhhhChoo on March 25, 2014, 09:46:57 amI think that instead 400Hz AC the 380vdc distribution would be much better. Some (or SoMe?)datacenters already run on 380vdc systems and there has been also talk about domestic 380vdc distribution systems.http://www.technologyreview.com/news/427504/edisons-revenge-the-rise-of-dc-power/

author: Kjelt
author_rank: Super Contributor
timestamp: March 25, 2014, 11:15:46 am
content: Quote from: mzzj on March 25, 2014, 09:35:44 amYeah but still your example is worst case and not adapted to low voltage.If you have the choice go for a higher voltage like 48VDC and thicker cables, but otherwise the trick is to use multiple cables and thus lower the amps per cable.Even new luxus houses that are build here with 230VAC bring their own individual cables to each outlet and switch which is much more future proof the one cable and branching off somewhere in the ceiling which they used to do.As an example I rebuild my livingroom, expanded with 3meters and added 15 led lamps of 7,5W each. I took a standard but high efficiency PC PSU and brought its 12V rail through 1,5mm2(16 gauge) copper to each fixture.The longest 12V wire I used was aprox. 20 meters one way.At the end I measured under load worst case 11,6V so a voltage drop op 0,4V on aprox. 600mA. So the loss in the wire is less then 3%.The efficiency of the PSU was >90% so instead of the provided 230VAC leddriver efficiency which was around 72%Still a gain in efficiency of around 15%.So the trick is to use multiple wires and thicker wires, or bring the DC voltage up.

author: VK5RC
author_rank: Unknown
timestamp: March 25, 2014, 11:28:29 am
content: The link re the high voltage DC distribution reminded me of a rather unusual very high voltage DC submarine cable crossing from the mainland to Tasmania in Australia. Photos of the distribution switching area get my hair standing on end! O0http://en.wikipedia.org/wiki/Basslinkhttp://www.usa.siemens.com/answers/en/_assets/pof106art06_pdf_1379750.pdf

author: ConKbot
author_rank: Super Contributor
timestamp: March 25, 2014, 11:52:09 am
content: Quote from: madires on March 21, 2014, 11:52:53 amNot gonna lie, I had to check your location to make sure it wasnt a Brit making that comment.That being said, if youre in the US, you can usehttp://www.powerwerx.com/powerpole-accessories/powerpole-outlet-cover-plate-electrical-box.htmlif youre so inclined. The main fault with that plate is that you cant put 2 devices into the top or bottom outlet separately. You have to snap the power poles together, then plug them into the outlet.If I had a bench with a elevated shelf for test equipment, and a power supply with rear terminals, I'd want to use something like that to get the test leads close, but still have the equipment out of the way, without the leads draped right in my face. Just crimp the remote sense wires in with the 12 awg wire, and run both pairs back to the power supply.

author: madires
author_rank: Super Contributor
timestamp: March 25, 2014, 02:17:52 pm
content: Quote from: ConKbot on March 25, 2014, 11:52:09 amI'll take that as a complimentQuoteLooks like a HAM's wet dream.Nearly 40 years ago my father installed wall sockets for loudspeakers in his living room. Each socket got four lovely 4mm banana jacks and fits perfectly in standard wall boxes. When DolbySurround came along I just had to plug in the additional speakers.

author: mzzj
author_rank: Super Contributor
timestamp: March 25, 2014, 02:21:49 pm
content: Quote from: Kjelt on March 25, 2014, 11:15:46 amYes, I did use worst-case( I bet I can do worse also!) scenario to show that power limits of the 12v system hit on your face perhaps sooner than you realize.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 25, 2014, 11:55:34 pm
content: Ok nobody in there right mind would use 12v. I take that as granted.But I think 36v and 48v are viable options.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: March 26, 2014, 12:29:13 am
content: Quote from: HackedFridgeMagnet on March 25, 2014, 11:55:34 pmNo no, clearly all appliances should be powered via USB. We can make new USB-Q and USB-W connectors rated for 50A and 150A respectively.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 26, 2014, 02:10:15 am
content: QuoteBut why not use existing USB connectors for the sake of compatability? We have enough USB connectors already.Was a Joke, like the quote.

author: TMM
author_rank: Frequent Contributor
timestamp: March 26, 2014, 02:51:54 am
content: Personally i like the idea of having a USB-style standard available at wall outlets. This way we hopefully get rid of the myriad of plugpacks/wallwarts that we use for low-power devices. Even with that it's probably better to have 1 powersupply (240VAC->xVDC) in each outlet, or for a number of closely located outlets.For everything else i don't think it really matters. Lighting ballasts are already cheap and efficient. Computers and Televisions etc are still going to need a powersupply unit to convert xVDC to 3.3v/5v/12v/whatever and having a big low voltage DC powersupply in your meter box is just adding one more thing to fail, require more breakers/fuses, beefier wiring/switches and increase transmission losses. Pretty much the only positive is that it increases user safety.Quote from: HackedFridgeMagnet on March 26, 2014, 02:10:15 amAn existing USB connector is going to handle 150A? Okay...

author: VK5RC
author_rank: Unknown
timestamp: March 26, 2014, 08:31:05 am
content: Even USB is not a 'standard' with different voltages on the middle pins to tell the device re power supply current capacity.

author: Kjelt
author_rank: Super Contributor
timestamp: March 26, 2014, 10:41:56 am
content: IMO USB is flimsy, not robust enough. You need something sturdy but not too large and able to handles currents upto 10Amps

author: madires
author_rank: Super Contributor
timestamp: March 26, 2014, 12:36:41 pm
content: Quote from: HackedFridgeMagnet on March 25, 2014, 11:55:34 pmWe should add some numbers to the discussion:The resistance of 20m 2.5mm² copper wire is about 0.14 Ohms, i.e. with 10A current we get a voltage drop of 1.4V and power loss of 14W. Now we have to double that for the return path, i.e. voltage drop of 2.8V and power loss of 28W. 20m should be reasonable for a wire from the central DC distribution to a room. 2.5mm² is the standard cross section for long mains wire (>20m at 16A) over here.OTOH, if we need 10A DC in a room we could assume 5 wall warts supplying 2A each. A cheap wall wart got an efficiency of about 60%. Now we mix some 5v and 12V types and assume an average voltage of 8V. The total loss would be 8V * 10A * 0.4 = 32W.Of course the central PSU doesn't run at 100% effiency, but the effective current for the DC distribution would be less than 10A because we have to take the higher DC voltage into account. And since most DC powered stuff got buck converters anyway (12V input from the wall wart, one buck for 5V and another for 3.3V for example) we may neglect power losses by additional converters, just have to build them for the higher input voltage. When running our DC power distribution with 24V instead of 12V we would half the effective current to 5A and also half the losses of the wiring, i.e. 16W.If we consider the numbers above it doesn't make much difference if using wall warts or a low voltage DC power distribution. The costs for the DC wiring would be much higher than the benefit of saving some Watts, actually a show stopper. And it should be clear that even a 24V DC power distribution is feasable. But if we add a PV system and some lead batteries the whole story changes dramatically. Also if you DC power just a single room like your home office or wherever most wall warts are located.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 26, 2014, 02:32:11 pm
content: Quote from: VK5RC on March 26, 2014, 08:31:05 amThe official standard just specs to short the pins together. Apple is the one using their own "standard".

author: 0odria
author_rank: Newbie
timestamp: March 26, 2014, 07:37:05 pm
content: Low frequency square wave AC, +48V and -48V. Although this may face opposition from true rms multimeter manufacturers.