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Slow Electricity: The Return of DC Power? (2016)
- bad_alloc 3y agoI wish there was some standard way to add DC wiring in parallel to AC. Seems like people who want to do this have to roll their own systems for now.
- amelius 3y agoYou could use USB wall sockets :)
- msandford 3y agoSame here. The problem is that there's no consensus on what voltages. I might prefer 48v for lower losses but you might want 24v since it's "safer" and my neighbor might want 192v since he's already an electrician.
- Szpadel 3y agoIMO just using the same voltage as in AC and multi voltage DC/DC adapter would be sweet spot
- PaulKeeble 3y agoThere are multiple things that we really need to make it viable. A standard for the plug that separates it from any AC standard, a standard voltage and current and then standard DC to DC convertors for adjusting the voltage. I guess also we need a completely different light bulb fitting socket too that only fits DC light bulbs. Lots of different commercial DC convertors of varying sizes to replace the AC convertors in all sorts of devices. I do wonder how much in practice would be gained given the DC to DC conversions are guaranteed for every device.
- eternityforest 3y agoWe do have a standard AC-DC converter, USB PPS, which can do most of these use cases just fine. DC-DC versions can be done too if one really wanted. But running low voltage DC power wiring is still probably not the best plan.
- adrianN 3y agoPower over Ethernet perhaps?
- cesarb 3y agoThere's already a somewhat common standard for DC wiring in homes and offices, though it's probably not exactly what you had in mind: it's Power over Ethernet (PoE), which provides around 48V over standard twisted pair Ethernet wiring, while still allowing it to be used for data.
- ianburrell 3y agoPoE is too low power to use for many things that would want DC power. 802.3bt tops out at 71W. You couldn't run a 100W USB-C adapter on it. Also, PoE is pretty high losses running power over Ethernet cable. The max power at source is 100W. PoE puts in higher voltage for account for the losses which means it isn't a straight 48V input to 48V output.
- JKCalhoun 3y agoWhen I built out a van into an RV, I got to run a new electrical system for it — one based around the 12V automotive battery. It turns out that there is a small industry out there that serves both RVs (and boats as well) that is 12V/DC based. Lights, pumps, refrigerators, fans, all running straight off a 12V power bank. "Cigarette lighter" outlets stand in for wall outlets for USB-style chargers, etc. The 12V/DC battery system in the van is of course charged from both solar on the roof of the van and from the van's alternator (when the van battery is topped off and the van is under power of course). I did add an inverter to supply 110V/AC for a pair of traditional electrical outlets I installed in the kitchen area of the van/RV. These are primarily used for plugging in wall-wart style chargers for the laptops. (My Kill-A-Watt suggests that my rice cooker and even the electrical kettle would, just barely, function on the current provided by the inverter but RV-life tends toward minimalism so those extra appliances I've left behind.) In any event, the whole experience did have me wondering if I could run a parallel 12V/DC electrical system in a new home and do away with a lot of the step-up/down of AC. Definitely could do with some kind of modern outlet (USBC?) rather than the cigarette lighter outlets, ha ha.
- Gibbon1 3y agoWhat would be nice is a residential power over Ethernet standard. With standard crimp connections. Some advantages power limited and low voltage means it's safer[1]. Ethernet means you can control lights and other devices. Smaller diameter wiring means it's cheaper. Not needing a licensed electrician to install it saves $$$. [1] Can imagine for a non North American not having to deal with 230VAC would be a big bonus.
- ianburrell 3y agoWhat would make the most sense to repurpose AC wiring for DC. The big problem is that only circuit goes to each spot and putting in duplicate circuits would be expensive. The standard AC wiring is probably enough for 720W with 48V. The problem with choosing 48V is lock to medium power. Appliances would require 240V or 480VDC to get enough power. The big problem is that there is no standard for DC power outlets or plugs. Would need to be different from AC and would also need to be different for different voltages.
- amelius 3y ago> Dutch researchers managed to reduce total cable length in a house down from 40 metres to 12 metres. They did this by moving the kitchen and the living room (where most electricity is used) to the first floor, just below the roof (where the solar panels are), while moving the bedrooms to the ground floor. They also clustered most appliances in the central part of the building, right below the solar panels Now this is dedication ...
- kabouseng 3y agoThat's not great, since entertaining guests it is preferable to have these rooms on the ground floor, and the bedrooms which can be private on the upstairs floor.
- Epa095 3y agoWhile upstairs has a better view, more light coming in through the windows, and heat rises up (so the bedrooms can be kept comfortable cool). I guess it depends on the house and it's surroundings:-)
- brtkdotse 3y ago> 40 metres to 12 metres So they sacrificed the freedom of design to save €100?
- deleted 3y ago[deleted]
- Scoundreller 3y agoWhat's happening in their living room to use so much electricity? I figured TVs, computers and lighting use a fraction of what they used to use. My mom is in a typical suburb tract housing development, and the kitchen is right above the service entrance and the HVAC/mechanical room is right at it. Great they're applying the same logic to solar-first systems, but it's not a new concept at all.
- walrus01 3y ago
- huppeldepup 3y agoSomething I didn’t find in the article is that in AC systems sparks are self-extinguishing because of the zero-crossing. There are a few domestic circuit breaker teardowns on youtube. I suggest watching one and then asking the question: how can we break a high current _DC_ surge?
- weare138 3y agoHigh voltage DC circuit breakers are a thing already.
- bluGill 3y agoThey exist, but are much more complex. they do things like pair with an air compressor to blow the arc out.
- adrian_b 3y agoYes, but they are more complex, thus more expensive.
- thsksbd 3y agoThey are far more expensive, and environmentally problematic [1], than an AC equivalent. [1] switchgear use SF6. DC will require the SF6 at far lower V than AC
- guenthert 3y ago"Because many modern devices operate internally on direct current (DC)" But notably the high power consumers like electrical stove, air conditioning, washing machines etc. do not. And it's not that with DC throughout there are no conversions. Solar cells' output varies greatly, hence it needs to be DC/DC converted to a fix voltage to be of any use. The same, albeit to a much lesser extend, applies to batteries. Further, there is no one single voltage, AC or DC, which is optimal for all uses. Even for devices which receive DC voltage, e.g. laptops, there are internal DC/DC converters. Removing the AC/DC conversion seems hardly worth the trouble. High efficiency AC/DC converters can be constructed. It's rather a question on how much one is willing to spend on such.
- kzrdude 3y agoWith more and more DC generation and consumption on the network, I think the AC mains is becoming very noisy, i.e. there are spikes, which we are not so used to handling.
- Liftyee 3y agoThat is true. There is a whole field of power factor correction and filtering that tries to reduce the noise injected into the mains (hello, EMC regulations) but some devices do that better than others.
- andix 3y agoMost of the high power consumers could run on DC power with only slight modifications (in design, not aftermarket). Heating elements can run on DC more or less unmodified. Also electric motors can run on DC efficiently (see electric cars). Back in the days 3-phase power was needed to run strong electric motors (very common in Europe, but i think it exists also in the US for factories and businesses). But there are many easy solutions nowadays to just run them on DC.
- Liftyee 3y ago> Heating elements can run on DC more or less unmodified. ..but to get the same power (heat) output you need more current in a low voltage DC system. And power loss in the supply cables scales with the square of current, so you'll need thick (expensive) wiring in the wall or you'll risk the walls becoming an equally effective heating element. Electric motors that run on DC are either brushed or have extra driver/conversion circuitry to pulse their coils in the right order. Both of these are not perfectly efficient.
- Physkal 3y agoWould this make DC appliances cheaper or smaller since there's no need for rectification circuits?
- andix 3y agoI don't think it would be significant.
- _fizz_buzz_ 3y agoI think it could make a difference. A lot of devices have power factor correction (pfc) now. To draw a current without harmonics from the grid. You wouldn’t need a pfc stage anymore.
- deleted 3y ago[deleted]
- andix 3y agoSome kind of voltage conversion would be needed anyway. Most electronic devices run at 5V, 3.3V or 1.8V. And that's limiting cable lengths to a few meters (probably less than 5m).
- _fizz_buzz_ 3y agoYeah of course, but the pfc stage boosts the voltage first up above the ac peak voltage and then a second stage steps it down to whatever voltage is needed. If one has a dc grid one doesn’t need the pfc stage (but of course still the second stage).
- limaoscarjuliet 3y agoAll this requires the DC appliances to be the same voltage, as transformers on DC is a tough task.
- _fizz_buzz_ 3y agoMost stuff is switched mode nowadays anyway, so this becoming less and less relevant. Not sure if there really are any transformer based appliances in my house anymore.
- Liftyee 3y agoTransformers on DC are already a solved problem with various switched-mode converters that can boost or decrease voltages at will. In fact, many AC-DC supplies (phone charger, etc.) are already using such converters, first rectifying the incoming AC. Not needing a bulky transformer makes them smaller and lighter.
- George2515 3y ago[flagged]
- George2515 3y ago[flagged]
- jakedata 3y agoJust sitting here speculating, not even a web search yet... In the USA we have both ground and neutral wires at every outlet along with the hot (120VAC nominal) wire. Why couldn't we raise the ground wire to +12VDC (or whatever) with regard to the neutral? The ground would have a very sensitive detector so that if electrical conditions exceeded some preset threshold it would collapse to zero nearly instantly, allowing the circuit protection to function as expected. You could make a plug that only has a neutral and ground pin to tap into the low voltage side, or use all three pins to provide low power standby mode. Now I'll do a search to find out that it is impossible because of a, b or c reasons or that it has already been patented somewhere and abandoned. Yay Internet...
- tzs 3y agoGround and neutral are tired together at the electrical panel.
- jakedata 3y agoThat's why this could work - the panel is the logical place to insert the DC supply. If ground and neutral were bonded in multiple places then it would just be a DC short.
- sokoloff 3y agoThey are bonded there for safety reasons and that bond needs to be low impedance. The reason is that you don’t want to allow a fault which puts a line voltage (120VAC) onto the chassis of a piece of equipment waiting for a human to come along and complete the circuit to ground. So, you use the protective earth to connect to the chassis, such that if a power line ever did contact it, it would be a dead short to ground, which would trip the OCPD (over-current protection device, typically a circuit breaker), clearing the fault. If you replace this safety mechanism with something that’s high-enough impedance to maintain a 12VDC differential, you’ve eliminated this important safety mechanism in your AC distribution system.
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- RetroTechie 3y agoNot mentioned so far: AC->DC adapters also provide galvanic isolation. In many power supplies, that electric isolation comes 'for free', as you don't want device(s) connected to high voltage wiring anyway. AC vs. DC as input isn't that big a deal really. In situations where power source (solar!), storage and most consuming devices are low-voltage DC, just use a DC based setup if more practical. I'm on a boat & most everything electric here is low voltage DC. But I do have a 12V->230V AC converter when needed. In short: AC & low voltage DC can live happily side-by-side. The DC vs. AC debate is kind of a moot point these days.
- dang 3y agoRelated: Slow Electricity: The Return of DC Power? (2016) - https://news.ycombinator.com/item?id=28216968 https://news.ycombinator.com/item?id=28216968 - Aug 2021 (230 comments)
- Animats 3y agoYeah, we did this already. Few devices other than switching power supplies are designed to work over a wide range of DC input voltages. There's an electric pump which will run slowly on an low input voltage and faster at a higher voltage.[1] Those are driven from windmills and solar. It's not cheap. It has to be self-protecting against too high and too low voltages. [1] https://www.dankoffsolarpumps.com/product/solar-slowpump/ https://www.dankoffsolarpumps.com/product/solar-slowpump/
- Johnny555 3y agoIf DC in houses became popular, it seems like they'd follow the same model as RV's -- low power devices like lighting, water pump, maybe refrigerator all run on 12VDC, high power devices like air conditioning, microwave, etc run on 120VAC (sometimes inverted from battery). That limits the high gauge wire to the short run from battery to inverter, otherwise you'd need very expensive and heavy large gauge cable running to those high power devices.
- amelius 3y agoWhy not step up the DC voltage instead of inverting to AC?
- Johnny555 3y agoIt's harder to step DC than AC, you'd probably end up using a switching power supply, which gets you most of the way to an AC inverter.
- thsksbd 3y agoThis is probably a bad idea by ppl who think things they understand scale without issue. Yes HVDC exist and are awesome for very long lines and for underwater uses. Yes, most appliances in a house today are DC. That doesn't mean that making the in-between DC makes sense.
- Podgajski 3y agoNot to mention the electric and magnetic fields that AC currents release. This alone is a health hazard that is ignored by most modern builders.
- Johnythree 3y agoDC Currents also create magnetic fields. And neither type are a health hazard.
- Podgajski 3y agoDC currents emit a static magnetic field with a frequency of 0Hz. This is not my concern since the magnetic field is so weak from a 12v system. Frequency is the issue with AC currents. because the EMF from AC lines are time varying, they can induce currents and voltages in nearby conductive objects, like people. The WHO seems to think ICNIRPs concerns are valid: https://www.icnirp.org/en/frequencies/low-frequency/index.html https://www.icnirp.org/en/frequencies/low-frequency/index.ht... Read papers 9-12 and let me know if you are still so certain. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2203969/#B9 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2203969/#B9
- walrus01 3y agoDC power never went away in serious ISP/telecom applications. It's more popular than ever. And things like the DC power distribution within an open compute platform standard rack, for large-scale numbers of individual small servers.
- blendo 3y agoJust to note, the USB 3.1 specification allows up to 240 Watts of 48 Volt, 5 Amp power. Easily enough power for a monitor/TV, or for a small desktop computer. https://audioxpress.com/news/usb-specification-revision-defines-up-to-240w-and-48v-of-power-delivery-over-usb-type-c https://audioxpress.com/news/usb-specification-revision-defi... And Anker now makes the honkin’ big hubs you need for that: https://www.anker.com/products/a2342-240w-gan-charger https://www.anker.com/products/a2342-240w-gan-charger
- nine_k 3y agoThis is part of the reason why a fully compliant USB-C cable is so expensive and stiff. It should carry thick power lines, and also a number of high-speed serial lines, and some electronics to configure and drive all that on either end.
- 20after4 3y agoCurrently the ideal balance of price, performance and availability of off the shelf components is 48v dc power. There is a telecom industry standard (perhaps only loosely standardized) for DC converters which are called "isolated DC-DC converters bricks."[2]. These are reasonably priced and reasonably high efficiency DC converters that fit into a set of standard form factors, e.g. 1/4 brick, 1/2 brick, etc. They are small sealed modules and a variety of outputs ratings are available for < $100 with efficiency > 85% and many newer examples are > 90% efficient. The setup I've settled on is the following, based on 48v nominal[2] system. Solar Array 80-100v | Solar Charger | LiFePo4 Battery [40-53v] | Circuit Protection | <- Standard house wiring to point of use | | --- [12v DC Brick] -- short wire --> 12v devices | | --- [5v DC Brick] -- short wire --> 5v devices Note that multiple devices could run on a single DC brick. It can, for example, provide an array of USB ports for devices to source power. The 5v or 12v power wiring is short so there isn't a need for oversized wire to combat voltage drop. 1. There are lots of sources for dc-dc "brick" converter modules, such as these: https://www.artesyn.com/power-supplies/cat/148/isolated-dc-dc-converters-for-telecommunications-applications https://www.artesyn.com/power-supplies/cat/148/isolated-dc-d... 1.1 Another affordable and available option is mean-well chassis-mount dc converters like this one: https://www.digikey.com/en/products/detail/mean-well-usa-inc/RSD-30H-5/7706233 https://www.digikey.com/en/products/detail/mean-well-usa-inc... 2. "48v nominal" means anywhere from something like 44v to 60v depending on battery chemistry, state of charge and current loads on the system.