Switching the mains to DC - Page 1
Forum section: electronics / general

author: torginus
author_rank: Newbie
timestamp: August 09, 2025, 11:23:12 pm
content: Hi!This is a bit of a pie in the sky thought, but I was just thinking about what would be the downsides/upsides of switching the mains voltage in our homes to DC (with the same voltage as our AC RMS)?Almost every device in our homes either uses DC voltages internally, or doesn't care. I think the last holdouts that do require AC were devices that had motors in them, like air conditioners, washing machines and the like, but even these are being replaced with ones that have BLDC motors internally.In fact, almost all devices sold currently use switching power supplies, which have rectifiers on their inputs to create high voltage DC to step down, and as far as I can tell, those would continue to just work from either DC or AC, reducing the logistical pain for consumers and manufacturers. On the infrastructure level, the switch could be carried out by installing an AC-DC converter at any point, from the local grid, to apartment, so this doesn't need to be an all or nothing effort.As for why, it's very simple - while this change would've made little practical sense years ago, now with the emergence of huge DC sinks (EVs) and sources (solar panels), I think having people purchase expensive and failure prone solar inverters is just bonkers. Solar panels are dirt cheap and if they could directly feed into the home circuit with just a voltage regulator, it'd change the economics massively, so I think there's cause to try this.The only downsides I can see is that DC safety equipment (breakers, RCDs) is more expensive than the AC equivalents.What do you think? Am I a bumbling idiot that has overlooked some fundamental flaws or is the idea sound and feasible? If it is, are there any pilot projects or proposals to do this?

author: bdunham7
author_rank: Super Contributor
timestamp: August 09, 2025, 11:34:42 pm
content: Quote from: torginus on August 09, 2025, 11:23:12 pmWell, there's the installed base of billions of induction motors, mains transformers and so forth that would become unusable. It is trivially easy to generate DC voltage from AC nowadays with PFC supplies so you really aren't gaining much--those new devices that work better with DC can obtain it easily enough. I don't think solar inverters are particularly unreliable and if they are, making them more robust surely can't be an insurmountable task. More than 90% of my stuff absolutely requires AC unless I do substantial modifications. I do have an old AC/DC radio, but I converted that to AC only input with DC internals using an isolation transformer and a HV linear PSU setup.

author: Circlotron
author_rank: Super Contributor
timestamp: August 09, 2025, 11:36:17 pm
content: Switches arcing.Electrolysis.More fuel for people that complain about 5G, smart meters, flat earth, and moon landing conspiracies.

author: Psi
author_rank: Super Contributor
timestamp: August 09, 2025, 11:40:28 pm
content: It might make sense in the far future if all motors move to brushless DC and if semiconductors for working with DC mains voltages at low Rds become cheaper than mechanical switches.As others have said there are mechanically switching problems with DC so that would all have to go.Electrolysis is an interesting one that I'd not considered, yeah would have to deal with that somehow.

author: coppercone2
author_rank: Super Contributor
timestamp: August 09, 2025, 11:51:03 pm
content: don't do this. The code is meant for 60Hz current. The behavior of plasma changes drastically at DC and basically requires special components to achieve the same performance levels as AC components.60Hz arcing likes to extinguish itself. DC does not. Because of this all switches take a beating and over heating.I am not sure how they feel about the insulation performance either (how much of a problem can it take at DC vs AC before it goes haywire.Same with the outlets (devices that spark when you plug them in).IMO you would need alot of testing to certify all that stuff. Look at how solar DC stuff is built and you will see how high current DC is different then AC.The corrosion issue is true too (the phone company has experience with this).Its NOT a little difference. Also there is the issue of inrush with bus capacitors. In his little demo the arc breaking distance looks to be... 15 times longer

author: David Hess
author_rank: Super Contributor
timestamp: August 10, 2025, 01:55:13 am
content: Various safety devices are rated for AC; switches and breakers and other things would need to be upgraded for DC operation.Based on my experience with ECMs (electronically commutated motors) which have replaced induction motors, they will be more expensive, and less reliable.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 10, 2025, 07:13:52 am
content: Biggest issue is switches and fuses, all incompatible, replacements 100x more expensive, and missing to replaceany single oneresults in house fire.

author: nctnico
author_rank: Super Contributor
timestamp: August 10, 2025, 09:32:23 am
content: Another problem with DC is that most loads are not constant but pulsating. So you'd still need the DC variant of power factor correction otherwise the 'DC' grid will probably start oscillating wildly due to impedance mismatches. In the end DC doesn't exist in the real world. 48V telecom equipment is a good example. There are strict rules for the frequency content of the current being drawn from the source.

author: Seekonk
author_rank: Super Contributor
timestamp: August 10, 2025, 11:16:43 pm
content: There was a coalition of companies that were trying to create a new standard for low voltage DC in the homes like a 30V range USB to power DC products. There would be one main converter for AC to DC instead of all these wall warts. Probably adaptable to solar too. Haven't heard anything about that in years.I have an off grid home and many of my inverters are DC out to run things. Much quieter and efficient.

author: TimFox
author_rank: Super Contributor
timestamp: August 10, 2025, 11:28:33 pm
content: I believe that the highest loads on the power to my house are AC induction motors:RefrigeratorFreezerCentral air conditioner compressor.Forced-air heating fans on gas-fired furnace.Vacuum cleaner.Clothes washing machine.Motor for gas-fired clothes dryer.What advantage to me is the expensive replacement of all of these to accommodate DC mains?Transformers may be heavy, but they can be extremely reliable compared to anything using solid-state power electronics.

author: Marco
author_rank: Super Contributor
timestamp: August 10, 2025, 11:36:58 pm
content: Quote from: Circlotron on August 09, 2025, 11:36:17 pmYou can use a two pole switch and some passive components. DC switch gets protected during turn off by a parallel capacitor, which then resonates with an inductor and a second capacitor so the other switch can turn off with AC, a resistor discharges the first capacitor.It turns something simple into something not so simple, but it's an option.Thisis what I'm talking about. There it's intended for a high powered circuit breaker, but I don't see why it wouldn't work for a simple bistable mechanical switch. The second capacitor isn't really needed I guess.

author: nctnico
author_rank: Super Contributor
timestamp: August 11, 2025, 07:32:30 am
content: Quote from: TimFox on August 10, 2025, 11:28:33 pmMost of those appliances use electronics to drive the motor nowadays. Even my 25+ year old washing machine has that.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 11, 2025, 07:55:01 am
content: Quote from: TimFox on August 10, 2025, 11:28:33 pmRefrigeratorFreezerBLDC drives are getting slowly more popular, AC induction motors still very popularCentral air conditioner compressor.Nearly all new designs have been BLDC for over 10 years.Vacuum cleaner.I don't think AC induction motors have ever been used for vacuum cleaners. They just need very high RPM, and therefore use brushed universal motors. Work fine with DC; have done exactly that - but power switch will possibly end up in flames so needs to be bypassed.Clothes washing machine.I have seen AC induction motor based clothes washing machine once: an ancient thing with dual-speed windings, and it left the clothes extremely wet because of crappy spin speed. Maybe they are more common in America, but really brushed universal motors are used because that's the only decent way to get the large dynamic range of different speeds, including spin cycle, with small and inexpensive motor.I'm not suggesting you could just run these appliances with DC supply. Significant modifications will be required nevertheless, even if they used motor types suitable for DC (inverter circuits which just rectify the mains, or brushed series-wound motors which run on DC and turn in the same direction regardless of polarity).

author: Gyro
author_rank: Super Contributor
timestamp: August 11, 2025, 12:25:52 pm
content: Quote from: Psi on August 09, 2025, 11:40:28 pmElectrolytic corrosion is something the London Underground system took very seriously from the start of its post-steam operation. The proximity of so many pipes etc. not to mention the cast iron tunnels themselves means that no traction current (@ 600V DC) is allowed to pass through the running rails. Instead, return current passes through a separate insulated conductor rail - the center one in the attached image. The live rail is the one furthest from the platform. Note the passenger fall refuge pit beneath the center rail (contrary to popular belief, you don't get fried if you touch it on the way down [as it is at nominally ground potential]).I don't know if other subway systems adopted the same practice.

author: David Hess
author_rank: Super Contributor
timestamp: August 11, 2025, 01:17:33 pm
content: Quote from: Seekonk on August 10, 2025, 11:16:43 pmI suspect any solution which requires more wire runs is uneconomical.

author: Zero999
author_rank: Super Contributor
timestamp: August 11, 2025, 01:31:07 pm
content: This has already been discussion.https://www.eevblog.com/forum/chat/will-ac-power-distribution-become-obsolete/In short. It's a bad idea and will never happen.

author: coppercone2
author_rank: Super Contributor
timestamp: August 11, 2025, 01:50:05 pm
content: it can happen with the right technology. Like an anti electron emissivity switch coating that makes arcing 10x more difficult to bring the switch in line with the AC switch. It would take a break through in materials science to make it possible for the same ease as AC. Otherwise you need some clever design that is more complex.Don't ask me how or if its possible to make something wanna arc less but also be a good contact. The alternative is some kind of quencher or diffuser for plasma. Kind of like blowing out a flame. Can it be done electromagnetically? Right now the best way is to use some kind of gas, or to make a trap that the plasma goes into and cools down in (parabola shapes).Tungsten silver is a very tough alloy for switch contacts, but you need to physically deal with the arc.

author: TimFox
author_rank: Super Contributor
timestamp: August 11, 2025, 02:47:29 pm
content: Quote from: nctnico on August 11, 2025, 07:32:30 amIn my case, none of them is rated for DC power input.“Cold, dead hands”

author: bdunham7
author_rank: Super Contributor
timestamp: August 11, 2025, 02:50:10 pm
content: Quote from: nctnico on August 11, 2025, 07:32:30 amI believe Tim was referring to his own household, not the current offerings in a European appliance store. In any case, the only one I think he is mistaken on is the vacuum cleaner.As for the other appliances, although there are BLDC/inverter options for many of them there are still also many of them sold new here in the US that still use PSC or cap-start induction motors. Air conditioning compressors, top-loading washers that use a transmission, dryers, refrigerators and freezers are all examples and in many cases, the old-school induction motors are only slightly less efficient, much less expensive and much more reliable. IDK exactly why, but that reliability gap seems to be a USA thing.The one application that seems to have gone mostly to BLDC is the furnace or air handler fan motor that circulates the air in a central HVAC system. These previously used a multi-speed induction motor and I think BLDC is actually cheaper to make.In any case, induction motors wouldn't be the only concern. DC would cause huge issues with other appliances. Ordinary toasters would go up in flames once your toast was done and a DC-capable toaster would probaby cost 10X what a typical disposable countertop toaster goes for these days. And then there are microwave ovens...

author: Zero999
author_rank: Super Contributor
timestamp: August 11, 2025, 03:17:31 pm
content: There's also an issue with RMS vs peak voltage. Some devices designed to work off rectified 230VAC, might require a higher voltage, than the RMS voltage. A mains powered LED lamp, might have over 100 LEDs in series, each with voltage drop of 3V, so will not work from 230V DC and will require over 300VDC.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 11, 2025, 03:38:51 pm
content: Quote from: Seekonk on August 10, 2025, 11:16:43 pmIt doesn't really work.First off, 30 V is a pretty nice choice. It definitely has arcing problems with switches but nowhere near as bad as even 48V, much less mains voltage DC.However, nothing actually runs on 30V. So everything still needs one or more step down converters to get to their operations voltages. These converters can be smaller and cheaper because they don't need as much bulk capacitance. They probably do need to be isolated to reduce ground loops but they don't need the same level of safety isolation as mains voltage supplies. You could get rid of wall warts, but the you couldn't use the skinny little power cords most wall warts have, you would need something like AWG16 lamp cord. Maybe you could use thinner insulation but the insulation is also physical protection against wear leading to short circuits which would be just as much of a problem.Except 30V is too low of a voltage for many applications. If we limit ourselves to the standard 15 amp (12 amp continuous) circuit ratings in the US, that is 360 watts per circuit. You can run small electronics and LED lighting off of that pretty easily. But it's not enough for something like a desktop computer, kitchen appliances, and so on. Even a laptop computer with a docking station, a couple external monitors and some other peripherals will tax a 30 V circuit.So you either need to have the low voltage DC exist alongside AC mains distributions which costs more, or bump the DC voltage up to something more like 120VDC. But then you get all the arcing problems in full force, plus all your points of load power supplies now need to be safety isolated. Which basically means all the wall warts would be back with a vengeance.There is a way you can do this. You can get power outlets with built in USB charge ports. Nobody uses them except at airports because 2 ports is hardly enogh. But you could make an in-wall low voltage power supply that had 10 USB-C ports, with up to 100 watts per port. I doubt they would be very popular either. If cable management is your goal it's better to build that into your desk with a single 120/240V cord going to the wall.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 11, 2025, 04:21:48 pm
content: Quote from: ejeffrey on August 11, 2025, 03:38:51 pmYeah. It's amazing how a relatively well-engineered, legal and safe 5-10W wallwart from universal 100-250VAC to 5V can be sold to end users for 5USD. Maybe the new fancy 30VDC system would reduce that to 3USD. And only if we do the full switch overnight to create the same economy of scales. Which also won't ever happen because we can't replace 100-240VAC with 30VDC at all; it would come as an additional extra system. All wiring work, sockets, switches, fuses etc. would also come as an extra over the existing AC system which cannot be removed.And I don't think running the 30VDC system even at 10-15A is practical at all. While amperage defines thermal limits for cables,energy efficiencyis important for other (obvious economic and environmental) reasons. And that is relative to voltagesquared. Given similar resistance of cables and connectors, 1V drop on 120V is mere 0.8% but 1V of 30V is 3.3%, not insignificant anymore. So such system would probably run at 5A max or something, also allowing nice small connectors. That's just 150W.But USB-C is quite nice already, allowing us to power phones and laptops of any brand and size from one standard connector, which does the really wise thing and autonegotiate the correct voltage - much more usable for product designers than some forced 30V system.

author: Zero999
author_rank: Super Contributor
timestamp: August 11, 2025, 05:11:32 pm
content: The thing is, it wouldn't even save much in terms of losses. The transmission losses might be slightly lower, but the DC:DC converters required to convert 132kV to 11kv to 230V DC etc. would be less efficient, compared to the equivalent transformers.

author: Marco
author_rank: Super Contributor
timestamp: August 11, 2025, 09:29:40 pm
content: Wouldn't have had problems with grid following and grid forming and associated stability problems though. At DC, everything would be grid forming.Geomagnetic storm induced low frequency currents just add or subtract a little power to a DC grid, very little, so those wouldn't have required expensive protection to protect against either.We're stuck with AC, but it has more problems than just the mismatch with inverter and DC loads.

author: TimFox
author_rank: Super Contributor
timestamp: August 11, 2025, 09:37:13 pm
content: DC is often used for long-distance transmission lines for grid-related reasons.However, switching from AC to DC at the customer end entails huge expense for no real benefit to the consumer.Other posters insist that the US switch the standard AC voltage at residential and low-voltage commercial service from 120 V to 240 V to make it more European, with a trivial ultimate increase in efficiency, but don't mention possible dangers of the higher voltage.Funny that no one insists that the other side switch from 50 to 60 Hz, or vice-versa.In Japan, they have lived with both standards (Tokyo at 50 Hz and Osaka at 60 Hz), which may have given Japanese electrical exporters an edge over mono-frequency countries.

author: David Hess
author_rank: Super Contributor
timestamp: August 11, 2025, 09:47:57 pm
content: Quote from: bdunham7 on August 11, 2025, 02:50:10 pmLarge parts of the US regularly get thunderstorms, with the associated power line spikes which happily destroy electronic ballasts and electronically commutated motors. I did not make the connection until I got a new refrigerator and had to change the EPA mandated ECM for the evaporator every year, which used to be a small shaded pole motor that never failed.

author: torginus
author_rank: Newbie
timestamp: August 11, 2025, 11:41:14 pm
content: Thanks for all the thoughtful replies, I've considered most of the replies, and I'm even more confident, that this is feasible - not only for new builds, but retrofitting existing homes as well, at reasonable costs.Yeah, AC loads would need to go, but as many people have pointed out, household appliances are already moving towards either BLDC or brushed motors, or have been using them in the first place.As for switches, I guess mechanical switches would need to go, but mains-rated mosfets are literally everywhere, they go into LED lights that barely cost anything. If you are somewhat more open to IoT, you don't even need mosfet wall switches, you can just tell the lights to switch themselves off via whatever input - they already have the mosfets in their power supplies.As for electrolysis, I'm not an expert, but I don't think it's a huge issue with PVC coated electrical cables.I think the insane cheapness of solar, and the falling cost of batteries means we have a potential future where most power for residential use is going to be produced either on-site, or within <10km of its intended place of consumption. Which is just as well, because it seems to me most of the world, save for China, has lost its appetite for investing into large scale basic infrastructure.

author: TimFox
author_rank: Super Contributor
timestamp: August 12, 2025, 12:50:27 am
content: To rewire a house, depending on size, by replacing the wiring and breaker box, typically costs between $8000 and $24,000 in the US.How much would your proposal cost, above replacing all the appliances?

author: ejeffrey
author_rank: Super Contributor
timestamp: August 12, 2025, 02:39:35 am
content: Quote from: torginus on August 11, 2025, 11:41:14 pmIt's definitely possible. Nobody here thinks its impossible. It's just that the advantages are not that great.Yes you might be able to save a few bucks on solar inverters. But it's not like you get rid of the inverter, you would be replacing it with a DC output converter. The only real difference is that you need less beefy storage capacitors.Likewise you might save a dollar on removing the PFC stage of power supplies. But the power supply is still there.Balanced over the whole system I don't know how those cost savings compare to the additional costs of switches and safety devices. I don't know if you designed a household power system from scratch in 2025 if you would use AC or DC. But it's definitely not worth a minimum of a trillion dollars or so in investment that could be spent on things like actually building more renewable power and better grid distribution.

author: Zero999
author_rank: Super Contributor
timestamp: August 12, 2025, 08:58:07 am
content: Quote from: torginus on August 11, 2025, 11:41:14 pmI suggest you read the arguments against again. Could you have subconsciously given more weight to ideas which reinforce your pre-existing opinion?QuoteNo, mechanical switches can't be replaced with semiconductors, because they have lower efficiency and safety reasons.Semiconductors have much higher voltage drop, compared to mechanical switches, especially when higher blocking voltages are required. A stack of IGBTs required to block 11kV will drop a couple of volts when on, compared to a mechanical switch which drops <100mV. This will result in increased power losses by a factor of 20 or more.Semiconductors have far too higher leakage currents and the slightest over voltage/current will cause them to fail short circuit. Mechanical switches are much safer because they physically isolate the conductors from one another. A mechanical switch can be subject to over-voltage, causing it to arc over and return to the open circuit state, once the voltage has returned to normal.It's not just switches which are the problem, but fuses and circuit breakers struggle to break a DC arc, compared to an AC arc which naturally extinguishes every time the current drops to zero.QuoteThat might be fine for powering appliances right next to the solar installation, but that doesn't mean it's a good idea to convert the entire grid to DC.

author: torginus
author_rank: Newbie
timestamp: August 12, 2025, 10:27:37 pm
content: You might be right on all these accounts, but switch efficiency doesn't matter that much considering all these switches are light switches, and the loads on those are tens of Watts. You could also wire the lights to be permanently on and use IOT signals to turn them off - 'smart' bulbs already work like this. And semiconductor switches have been used since time immemorial, in the form of triac dimmers.(And for switches that need to switch high loads with small loss, designs exist like the previous poster mentioned).I have also not suggested to turn the whole grid to DC (that really falls outside the scope of this discussion), merely remarked that in the future, power transmission might take place over far shorter distances from producer to consumer.And if your home and local grid use DC, and the solar farm that feeds it also uses DC, a step up conversion might be much simpler than turning the output of the solar farm into AC and transforming that up.

author: nctnico
author_rank: Super Contributor
timestamp: August 12, 2025, 10:51:31 pm
content: Quote from: Marco on August 11, 2025, 09:29:40 pmNo, because even on a DC grid, the current still has a large AC component which needs to be dealt with.

author: Marco
author_rank: Super Contributor
timestamp: August 12, 2025, 11:12:01 pm
content: Quote from: nctnico on August 12, 2025, 10:51:31 pmWhich requires reserves, but that's orthogonal to grid forming. Grid forming is about forcing the frequency and phase. When the frequency is DC, you can let everyone force those, can't go wrong.

author: nctnico
author_rank: Super Contributor
timestamp: August 12, 2025, 11:25:35 pm
content: Quote from: Marco on August 12, 2025, 11:12:01 pmI think you are wrong. With AC there is a single frequency to conform to. With DC, you only have voltage control and no idea what the frequency is. The critical part missing in your reasoning is that DCcurrentdoesn't exist.

author: Adrian_Taylor333
author_rank: Regular Contributor
timestamp: August 12, 2025, 11:32:31 pm
content: I did EXACTLY that some 15-20 years ago.Essentially, I stringed lead-acid 60Ah batteries in series to get the DC voltage of the mains peak ( 330-ish Vdc = some 24 batteries in series).I took a few shortcuts:- since any modern load can work with wide span of voltages, I didn't strictly regulate the voltage: I stringed akkus to get the battery voltage slightly below the mains peak. This way filling the batteries would be simple and self regulating (current fails as battery charges). And switchover is trivial - when mains go out, voltage is simply allowed to fall a bit to battery level.- no DC/AC conversion, whenever possible. Anything with modern switcvhing PSU works essentially off DC ( first thing there is the rectifier anyway)It worked GREAT, minus a caveat: It's not simple to rectify 230Vac to 330Vdc as trivial solution would be to simply use just a half of the period - simple did instead of greatz bridge.Power utility companies REALLY don't like this.Solution is to either do non-trivial conversion, or use the double battery string: 2x 330-ish V instead of 1.First approach complicates mains connection, the second gives you vastly more grid power for the same wiring, but complicates endpoints - you'd either have to convert each existing load point to 660Vdc, or make your own converter.But if you were to make your own solar with an option of EV charging, higher voltage would definitely be better.WIth 300+ish Vdc, even though in theory AC switches, fuses etc in theory don't really like DC, everything worked fine.

author: Marco
author_rank: Super Contributor
timestamp: August 13, 2025, 12:53:28 am
content: Quote from: nctnico on August 12, 2025, 11:25:35 pmThere is a bunch of grid forming generators fighting each other and the loads, trying to synchronize, and a bunch of followers. The followers only have the frequency the fighters are presenting them and some limits, no fixed internal reference to conform to.With DC, there really is a single frequency to conform to. If the load increases and a small generator has some power to spare because the voltage is near the upper limit, they can feel free to contribute their reserve ... they don't have to care about the frequency of the loads, only the frequency of the target voltage ... DC. Everyone can force DC, there is no need for formers and followers.

author: Zero999
author_rank: Super Contributor
timestamp: August 13, 2025, 08:03:34 am
content: Quote from: torginus on August 12, 2025, 10:27:37 pmWhat about circuit breakers? Those are a legal requirement to protect against shock and fire?How about isolators which enable an electrician to safely remove the power?And RCDs? These switch off the power in case of earth leakage. Whilst modern ones do sense DC, they're not designed to switch DC, which would be more expensive.QuoteI thought you were talking about the whole grid.You do know that power is mostly transmitted at 3 phase AC. DC is only used for very long distances, typically underground or submarine cables. Power is generated at around 11kVAC, stepped up to 110kV - 500kV for transmission over long distances, stepped down again to 11kV - 33kV, before it's finally stepped down to a low voltage, between 100V and 700V, for domestic and industrial purposes. In Europe low voltage is typically phase 400V phase-to-phase or 230V phase to neutral. In most countries, domestic consumers typically receive single phase, which is 230VAC to neutral.At which point do you think it should be DC?And how do you intend to deal with three phase consumers, who are used to 400VAC phase-to-phase and rely on it for their induction motors? Don't forget, in a tower block, will have 230V single phase for individual flats, with the lifts run off 400V three phase. The whole building will be supplied by one 400V three phase transformer.

author: torginus
author_rank: Newbie
timestamp: August 13, 2025, 10:26:08 am
content: QuoteDC breakers and GFCI devices can be bought in an electrical supplies store, I'm not sure what's the point you're trying to make. They're a bit more expensive but overall a small part of the whole system cost.QuoteI was talking about using DC on the house/apartment block level for residential purposes (and to some extent 'last mile' distribution). I did muse a bit about distribution, sorry, please ignore that, I don't want to defocus the argument.As for people commenting there's always AC in DC you are right - but please consider that most noise in the home grid is created by switching PSUs (including powerful ones, like aircons with BLDC inverters), and is high frequency and has nothing to do with the grid freq - same for DC. As for devices operating on the grid frequency (which is typical for motors) I'd argue it's worse since those create phase shift, for which you need PFC, and can't get rid of it with just a simple filter.

author: Zero999
author_rank: Super Contributor
timestamp: August 13, 2025, 12:17:15 pm
content: Quote from: torginus on August 13, 2025, 10:26:08 amThey're specifically designed for AC, not DC. DC breakers and RCDs are considerably more expensive at voltages above 24V. If you go for lower voltages, then cables become very bulky and expensive a 2400W kettle requires 100A at 24VDC.QuoteNo because a house still requires mechanical switches, in RCDs, circuit breakers, as mentioned above. Then there's the issue of requiring a separate network for businesses and residential. A farm which has lots of 3 phase equipment, would need a separate supply, to the few houses next to it.QuoteYes, that's true: irrespective of AC or DC mains, there will be high frequency noise from switching converters.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 13, 2025, 12:24:54 pm
content: Quote from: torginus on August 13, 2025, 10:26:08 amCan you share a link to such HVDC GFCI you can buy from an electrical supply store?I can buy type C RCD but not only it'sa lotmore expensive, it still onlydetectsDC leakage; still cannot be used in DC circuits.Maybe you are thinking about something else? All I have seen is application-specific custom, like circuitry within EV battery packs. It should be theoretically possible, with enough economy of scales, to make a HVDC GFCI which does not cost more than maybe "just" 5x more than the AC equivalent, but to my knowledge such product does not currently exist. It needs to combine fluxgate DC leakage sensing, which granted has finally became quite affordable, just 10x the price of AC equivalent, with the DC contactor technology (arc quenching), also some 10x more expensive.Can you share a link to what you mean?I mean, ideas are easy to throw around and I encourage doing that, but finally devil is in the small details.

author: Zero999
author_rank: Super Contributor
timestamp: August 13, 2025, 12:42:37 pm
content: Quote from: Siwastaja on August 13, 2025, 12:24:54 pmI'm not aware of any HV GFCI/RCD, either AC or DC.At voltages above 1kV, earthing is accomplished by a liquid resistor connected between the neutral of a transformer and earth, via a current transformer. The secondary of the current transformer is connected to a breaker, which interrupts the power, if too much current flows to earth.HVDC systems often use the earth as a return path, so I don't see why there would be any reason for one to exist.In low voltage DC systems, which don't use earth return, DCs RCDS/GFICS do exist (I've designed one myself, before it was possible to easily buy them off the shelf), but are not common. The most common use of DC earth leakage protection is an EV, in which case the system is normally bonded to earth (the chassis) via a high impedance: normally a high value resistor and low value capacitor in parallel. The voltage across the resistor is proportional to the the earth leakage current. It is monitored by a safety system which trips a breaker if the leakage current is too high. D

author: Siwastaja
author_rank: Super Contributor
timestamp: August 13, 2025, 01:20:31 pm
content: To clarify, I meant something around 400V with "HVDC". To my knowledge, leakage detection is application specific custom circuitry, such as within EV pack. I'm not aware of any inexpensive off-the-shelf DC RCD you can buy from "electrical supplies store".Some 20-30V system would be easy to design with, but that would only enable very small loads like lights. It would already struggle with large TV sets or gaming computer rigs, not even to talk about air conditioning, clothes washing or making food.

author: Zero999
author_rank: Super Contributor
timestamp: August 13, 2025, 01:49:27 pm
content: When discussing power distribution, high voltage is above generally 1kV, although this is somewhat dependent on the country: in the US it's 600V, whilst in Europe it's 1kV AC or 1.5kV DC.A type B RCD will provide protection against DC earth leakage, but finding one which can be powered off DC voltages and switch high DC currents at the requited DC voltage will be more challenging.https://www.electrical-installation.org/enwiki/Types_of_RCDs

author: torginus
author_rank: Newbie
timestamp: August 13, 2025, 02:04:19 pm
content: Quote from: Siwastaja on August 13, 2025, 12:24:54 pmApparently they are called Type B RCDs, and many vendors sell them.https://www.electrical-installation.org/enwiki/Types_of_RCDsI haven't really looked around but I found this ABB one for 250 euro (which is quite pricey imo), although this is a 2 circuit unit.https://www.amazon.de/-/en/F204-B-40-0-03-Circuit-Breaker/dp/B09LD1PJ9M?crid=7MAVQTWM0UHA&dib=eyJ2IjoiMSJ9.UTt2gs9uHy4VLvu65n63MRec7FAv7UUunNj2HqRQCFx1ZF1DHB3FeU12DhndwB5QfMCyVtd9anYBX4oZQwk3HHGAWnSPcpxEdmbZsewWPnEeHsTMQY3WkIuZeSFuQ7b7LeEVzbNfH2Ig2qXzPedBfEyVk8p8OuImqXcI1efyXKzE7NFmAfm0ixH-mn3j-PvN8mo6yh8SAZdMeSqxg7qVrr5BouzbODwx4KPm5b9IKZ_8R8L5HyoMr20ci3NKzqt62IXKm6DVBCIMavQVi70pEoaMjzKRc7lR4z2VFPa6mY0.BleJrYVJ4-4ILOvtrmOIPsnZ8aJR3_r2hN14mx1TLyw&dib_tag=se&keywords=Type+B+rcd&qid=1755093519&s=industrial&sprefix=type+b+rcd%2Cindustrial%2C89&sr=1-4There are Chinese equivalents for around 50 euro, if you are feeling adventurous.

author: Zero999
author_rank: Super Contributor
timestamp: August 13, 2025, 02:26:20 pm
content: Quote from: torginus on August 13, 2025, 02:04:19 pmJust because an RCD is sensitive to DC leakage, it doesn't mean it's specified to operate from DC voltage or switch the fully rated DC current.

author: Marco
author_rank: Super Contributor
timestamp: August 13, 2025, 02:46:44 pm
content: It's weird that cheap automatic fuses are explicitly rated for DC voltage, but they offer no RCDs for it.They have to exist, DC chargers have too much energy on the DC side to purely rely on the AC side. The relevant standard seems to be IEC TS 63053 but I can't quickly find actual devices.

author: IanB
author_rank: Super Contributor
timestamp: August 13, 2025, 02:55:21 pm
content: Quote from: Gyro on August 11, 2025, 12:25:52 pmJust FYI, both conductor rails on the London Underground are live. There is a resistive divider setting one at a nominal +420 V DC and the other at −210 V DC relative to earth.There is one case where the rails are at 0 V and +630 V (or +750 V), and that is on Network Rail track sections.Due to the Four Lines Modernisation project, the voltage in some areas has been increased from a nominal 630 V to a nominal 750 V. But there is still a voltage divider giving −250 V and +500 V.

author: Marco
author_rank: Super Contributor
timestamp: August 13, 2025, 03:14:34 pm
content: Couldn't you just mechanically couple a standard RCD with a DC rated automatic fuse and put them in series?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 13, 2025, 03:31:54 pm
content: Quote from: torginus on August 13, 2025, 02:04:19 pmNope. Wrong answer. Can't use that on DC - it will blow up in flames, just like type A or type AC RCDs.

author: Gyro
author_rank: Super Contributor
timestamp: August 13, 2025, 05:21:06 pm
content: Quote from: IanB on August 13, 2025, 02:55:21 pmInteresting. It makes me wonder about the sizing of the divider(s). They wouldn't want too much current flowing to earth, but at the same time, there's an awful lot of supply [Edit , insulation resistance, etc. to 'shift', compared to earthing the center rail at the substation.]

author: Sorama
author_rank: Frequent Contributor
timestamp: August 13, 2025, 05:39:07 pm
content: What about the law/regulation?Don't see it happen to get certified.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 13, 2025, 06:37:08 pm
content: Quote from: Sorama on August 13, 2025, 05:39:07 pmThanks to the proliferation of max 1kV DC systems like PV panels and home batteries, the laws, standards and regulations are there.So we would need to start with the practical work of:* Affordable HVDC GFCI/RCDs which do not exist AFAIK* Affordable HVDC switches, breakers and fuses; that's getting pretty good already* New type of user-pluggable, hotplug-safe, polarized HVDC plug, which needs to be handy, small and cheap.The last one is likely the biggest showstopper. Something like MC4 connectors are easy to plug in, but plugging them out by laymen results in massive number of very nasty deaths and house fires. I truly don't know how one would design such a connector, really.

author: Marco
author_rank: Super Contributor
timestamp: August 13, 2025, 09:40:32 pm
content: Quote from: Siwastaja on August 13, 2025, 06:37:08 pmhttps://www.mouser.co.uk/c/connectors/power-connectors/dc-power-connectors/?marcom=195486339&voltage%20rating=400%20VDC

author: TimFox
author_rank: Super Contributor
timestamp: August 13, 2025, 10:00:14 pm
content: So, with the existing topology of distribution grids, including high-voltage, somewhat high-voltage, about 3 kV, then 240 V center-tapped AC, which parts of your new improved DC distribution are at high voltage (to efficiently transport power over long distances), somewhat high-voltage (urban distribution), then lowish-voltage DC and what will replace the existing transformers that step down the voltage? Is it only the last domestic distribution leg to be done at DC to force me to replace my appliances? What about the new longer distribution infrastructure to transport power from rural wind and large-scale solar installations to urban customers?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 14, 2025, 06:49:25 am
content: Quote from: Marco on August 13, 2025, 09:40:32 pmJust 400V / 8.8A / 2.6kW max, meh

author: Silenos
author_rank: Regular Contributor
timestamp: August 14, 2025, 09:55:07 am
content: I was also severely disappointed after finding out that HVDC switches I would like to use in my pv installation are prohibitively expensive, and with maintenance features like replacable isolating ceramic elements. I ended up with isolating switches over inverters outputs, and with all HVDC connections sealed, and I'm still sour of it. I can only imagine what "low budget" pv installations look like.

author: Marco
author_rank: Super Contributor
timestamp: August 14, 2025, 11:12:13 am
content: Elmark 400V DC MCB is 4 euro.Can't use that as a frequently used switch, but fine for PV.

author: Silenos
author_rank: Regular Contributor
timestamp: August 14, 2025, 12:12:07 pm
content: Quote from: Marco on August 14, 2025, 11:12:13 amWhy do you people keep misinforming here with pasting those miniature breakers ment for 230 AC? They all have pictures with even visible Un printed on them which is 230 VAC. How do you imagine those tiny things quenching DC arc carrying +10 kW of power? And also, you don't disconnect 230 V loads with overcurrent/RCD breakers, it will damage them sooner or later.I admit I lost it in translation: by a "switch" I ment a power contactor, that's what makes them expensive. Manually actuated isolating (not power-connecting) switches for 1000 VDC are cheaper but more expensive than for 230 VAC

author: Siwastaja
author_rank: Super Contributor
timestamp: August 14, 2025, 12:45:03 pm
content: Quote from: Marco on August 14, 2025, 11:12:13 amI would be cautious - DC breaking current not specified at all. 400V DC voltage rating drops to mere 240V once you find the PDF datasheet instead of the web page. No data available supporting they are safe or legal for DC use.http://docs.elmarkholding.eu/LOW%20VOLTAGE%20POWER%20DISTRIBUTION/Circuit%20breakers/Miniature%20circuit%20breakers%20(MCB)/C60DC/Technical%20specification%20MCB%20C60DC.pdf- not rated for DC at all, even though name says "DC". Pretty confusing - just a name.Using fuses (or MCBs) for PV use is interesting - the supply itself is current-limited but also cannot offer the required short-circuit current to actually trip fuses, so fusing is useless; decorative.

author: Marco
author_rank: Super Contributor
timestamp: August 14, 2025, 04:08:09 pm
content: Schneider has 500V for little over 100 Euro. Chint is a Chinese brand with offices in the UK and sells a 500V one for 26 pound. There's some proper Chinesium brands on Amazon cheaper, but that's getting a little too dodgy.They could be used with a mechanical coupling to disconnect the strings on a AC trip. Or just as plain old switches, with a fuse function build in cause why not.Chintsays as much:Quote

author: Zero999
author_rank: Super Contributor
timestamp: August 14, 2025, 05:55:36 pm
content: Quote from: Marco on August 14, 2025, 04:08:09 pmThat's not far off ten times the the cost of the equivalent AC circuit breaker.And what about RCD/GFCIs which operate off DC, switch DC and can trip from DC leakage?

author: Sorama
author_rank: Frequent Contributor
timestamp: August 14, 2025, 06:10:00 pm
content: One of the (most important) reasons we use AC instead of DC is the necessity of bigger wires (in case of DC) and the transportation losses of DC.We all know that, don’t we?So why asking ?

author: Zero999
author_rank: Super Contributor
timestamp: August 14, 2025, 06:30:24 pm
content: Quote from: Sorama on August 14, 2025, 06:10:00 pmThat's not true. DC has lower losses than AC. There's no skin effect with DC and the dialectic losses are also lower. This is why DC is used for long distance underground/submarine cables.AC was primarily chosen because the voltage can be boosted or stepped down with simple, efficient transformers, which don't have moving parts. The only way to convert DC from one voltage to another was to use a motor generator set, which was comparatively inefficient and had moving parts to wear out. Nowadays switched mode converters can be used to step up/down DC, but they're more fragile and still less efficient compared to transformers. Secondly, AC was chosen because the current can be more easily interrupted with much less arcing, compared to DC. Finally AC was chosen because it can directly power AC motors, which lack brushes which wear out. Nowadays an inverter can be used to drive an AC motor from DC, but it's still much more efficient to power an AC motor directly, if speed control isn't required.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 14, 2025, 06:31:03 pm
content: Quote from: Sorama on August 14, 2025, 06:10:00 pmUm, no? Same Ohm's law and resistivity works out for both AC and DC (AC has additional skin effect, which is though quite manageable at 50-60Hz). Besides, HVDC is very successfully used for transport worldwide in all scales - longest HVDC line in China is over 3000km.

author: Marco
author_rank: Super Contributor
timestamp: August 14, 2025, 06:34:46 pm
content: Quote from: Sorama on August 14, 2025, 06:10:00 pmEven at the same RMS voltage, DC has an edge.

author: Sorama
author_rank: Frequent Contributor
timestamp: August 14, 2025, 06:43:24 pm
content: Common guys, cut the crap about skin effect.We all know that is only relevant in the kHz range.

author: bdunham7
author_rank: Super Contributor
timestamp: August 14, 2025, 06:58:00 pm
content: Quote from: Sorama on August 14, 2025, 06:43:24 pmNo, it's actually a thing at 60Hz for large transmission lines.

author: TimFox
author_rank: Super Contributor
timestamp: August 14, 2025, 08:20:43 pm
content: Quote from: bdunham7 on August 14, 2025, 06:58:00 pmThere's a rule-of-thumb that copper wires greater than 0.75 inch in diameter see important loss due to skin effect at 60 Hz.Hence, the largest such wire I have encountered is "500 mcm", which is about 0.94 inch in diameter, although 1000 mcm (1.4 x the diameter) exists.Depending on temperature, etc., 500 mcm wire is rated for 300 or 400 A current in raceway or conduit.I have seen rectangular bus bars in industrial buildings to reduce the skin effect for local power distribution, where the voltage cannot be increased.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 15, 2025, 05:36:15 am
content: Quote from: Sorama on August 14, 2025, 06:43:24 pmIt is only relevant in kHz rangein thin wires. Remember though that the power transmission cables are very thick! Skindepthis simply relative to the frequency. If it matters at 60kHz in a thin wire, then it matters at 60Hz in a 1000 times thicker wire.

author: uer166
author_rank: Super Contributor
timestamp: August 15, 2025, 06:00:57 am
content: Quote from: Siwastaja on August 15, 2025, 05:36:15 amReactive losses also dominate on long HVAC transmission lines (I2R losses due to current through parasitic capacitance to earth and adjacent conductors).Can't get rid of that one even if skin effect was non-existent, which of course is not true. The distance where DC gains make sense is very long, hence why it's extremely high voltage, long transmission lines that are a popular choice for it

author: RJSV
author_rank: Super Contributor
timestamp: August 15, 2025, 06:17:04 am
content: Even with some genuine new experiences, relating to off-grid Hawaiian life-styles, I tend to agree with other posts here, that express A LOT of doubts, about some simple shift overs. The AC power grid history is a long road of trial and error, and many folks seem to want to assume, that DC is just 'some other form' of electrical interchanges...it's not anywhere near that simple.I am, actually, shocked, a bit, by the high voltage ARC behaviors, in DC supplied systems, as that aspect hasn't been taught, heavily.Observing the low income cultural portions of the current SOLAR trends, it looks like things will, actually, get more wild and new feeling, as that trend takes form, around the world but in less prosperous areas, (often lacking formal power distribution.). The whole 'Solar Power is too Cheap' thing was a surprise, as we watch daytime power rates drop.So, maybe more surprise economics is yet to show ?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 15, 2025, 06:55:02 am
content: Quote from: uer166 on August 15, 2025, 06:00:57 amShorter HVDC links are useful to break up AC synchronous areas into smaller ones.

author: Zero999
author_rank: Super Contributor
timestamp: August 15, 2025, 07:05:06 am
content: Arcing is a huge problem for DC, especially when there's a bit of inductance, providing the high voltage transient to get the arc going. I remember testing a power supply to 50A, with a large wire wound resistor, which, to make it worse, had iron through the middle of the coil. I disconnected it by pulling the wire away from the terminal and it drew an bright arc several mm long, causing the insulation to burn. The open circuit voltage of the power supply was only 50V, but the inductance resulted in a transient voltage of several kV, which helped to strike the arc.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 15, 2025, 07:10:30 am
content: And remember that PV strings and general-purpose house power supply are very different. PV is inherently current limited; it has the efficiency it has (e.g. 20%); if you short circuit it, the current may increase like from 10A to 15-20A and efficiency obviously goes to zero, but that's pretty much it.But a general purpose house supply needs to be a voltage source, and the resistance needs to as low as possible to minimize losses and to allow fuse selectivity / clearing fuses in the defined time (by high enough short circuit current). But, that high breaking current is exactly what is way more difficult to arrange with DC.And the difference between the 20A 600V PV DC arc and the 10000A 600V DC arc is that former is very scary (look for videos) andmaykill, latter is truly very deadly.Remember that "for PV" DC isolation switches, fuses, MCBs (not that latter two make much sense to exist) are usually not safe to use on non-current-limited DC supplies. We need to read the specifications carefully and understand them. If something seems to be 10 to 100 times cheaper than the competitor, there probably is a reason for that - it is optimized to pass the requirements just in the specific use case it was intended for.

author: TimFox
author_rank: Super Contributor
timestamp: August 15, 2025, 02:11:08 pm
content: [quoteauthor=Siwastaja link=topic=467963.msg6012173#msg6012173 date=1755236175]Quote from: Sorama on August 14, 2025, 06:43:24 pmIt is relevant in kHz rangein thin wires. Remember though that the power transmission cables are very thick! Skindepthis simply relative to the frequency. If it matters at 60kHz in a thin wire, then it matters at 60Hz in a 1000 times thicker wire.The skin depth decreases with increased frequency, proportional tof-1/2.Therefore, at higher frequency, it is more important in thick wires, compared with lower frequency, in determining the AC resistance, since only the outer part conducts due to thinner skin depth.

author: Gyro
author_rank: Super Contributor
timestamp: August 15, 2025, 06:33:53 pm
content: Problem breaking DC? What problem?

author: Sorama
author_rank: Frequent Contributor
timestamp: August 16, 2025, 05:53:57 am
content: And the wires that would be used for domestic appliances would be rather thin.

author: Marco
author_rank: Super Contributor
timestamp: August 16, 2025, 09:55:31 am
content: You could ameliorate it a bit by going the UK way and taking it further. Plug? Fuse. Then also, socket? Fuse. Switch? Fuse. Every accessible node gets a fuse.

author: tooki
author_rank: Super Contributor
timestamp: August 16, 2025, 10:06:10 am
content: Quote from: Marco on August 16, 2025, 09:55:31 amThat’s affordable to do for AC fuses.DC-rated fuses are larger, more complex, and much more expensive.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 16, 2025, 12:19:58 pm
content: Quote from: Marco on August 16, 2025, 09:55:31 amWhen fuses for DC are more expensive, then the actual result would be the opposite, put fewer of them, not more. Or accept a significantly more expensive system, which is what OP wasn't anticipating.

author: Zero999
author_rank: Super Contributor
timestamp: August 16, 2025, 04:06:39 pm
content: Quote from: Siwastaja on August 16, 2025, 12:19:58 pmThat would be less safe.Also DC has will produce more of an arc flash which increases the fire risk.

author: jonpaul
author_rank: Super Contributor
timestamp: August 16, 2025, 06:05:47 pm
content: Old arguments:see 1890s War of the Currents:Thomas Alva Edison: DC (Pearl St NYC first)Nikola Tesla: AC (Niagara Falls)EnjoyJon

author: TimFox
author_rank: Super Contributor
timestamp: August 16, 2025, 07:35:01 pm
content: Quote from: jonpaul on August 16, 2025, 06:05:47 pmOf course, Pearl St in NYC was close to the loads in Manhattan.Niagara Falls had far more available power, but is farther from Manhattan.During the political and commercial war between the two approaches, New York State installed an electric chair for execution.Since it used AC, Edison wanted to call the method of electrocution "Westinghousing", claiming AC was more dangerous to the general public.

author: Circlotron
author_rank: Super Contributor
timestamp: August 16, 2025, 10:27:06 pm
content: A properly sized polarised snubber would look after switch contact arcing and maybe fuse clearing as well.And add even more to the cost, of course.

author: jonpaul
author_rank: Super Contributor
timestamp: August 16, 2025, 10:27:59 pm
content: Edison's first DC dist had very limited range, perhaps a few miles.The Manhattan DC distiruibution system persisted till the 1960s.Tesla conceived the HV AC T&D and later Charles Proteus Steinmetz at GE worked out the mathematics, and practical AC system by 1900-1920s.Jon

author: TimFox
author_rank: Super Contributor
timestamp: August 16, 2025, 10:37:59 pm
content: Quote from: jonpaul on August 16, 2025, 10:27:59 pmDC distribution in major Eastern US cities, including NYC and Boston, led to all sorts of "AC-DC" jokes, many of which are unsuitable for a technical forum.The "All-American Five" 5-tube AM radios could run on either (sending the AC or DC input through a tube half-wave rectifier and supplying the heaters in series from the then 110 V AC or DC), hence the term "AC-DC" for such radios. This included the famous E H Scott SLRM marine radio, since WW II merchant marine ships often had DC power.The commercial distribution of DC was ended after the utility companies supplied rectifiers to operators of elevators and other DC equipment.Funny how waves of the past are advertised as waves of the future...

author: Zero999
author_rank: Super Contributor
timestamp: August 17, 2025, 04:36:59 pm
content: Quote from: Circlotron on August 16, 2025, 10:27:06 pmThat will only reduce the effect of the inductance. It will not change the fact that the arc is more difficult to quench because the current doesn't periodically stop and change direction over a hundred times per second.

author: jonpaul
author_rank: Super Contributor
timestamp: August 17, 2025, 06:37:32 pm
content: DC breakers use arc chutes, compressed air, baffles to extinguish the arc.more difficult as V and I increase.Check breaker and fuse ratings.j

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 19, 2025, 04:01:15 am
content: As a compromise, how about pulsed DC? The interruptions would help suppress arcs the way AC does, while only requiring a single solid state switch to make the pulsed DC from constant DC.

author: Zero999
author_rank: Super Contributor
timestamp: August 19, 2025, 07:08:58 am
content: Quote from: NiHaoMike on August 19, 2025, 04:01:15 amWhat advantages would that have over AC?It is AC plus a DC bias. If it's squarewave, then there are high frequency components, which depend on the rise and fall times.I would also expect it to be not much better than DC, because the current doesn't change direction, the arc will still be harder to break, compared to DC.

author: Gyro
author_rank: Super Contributor
timestamp: August 19, 2025, 08:35:34 am
content: Agreed. It would only save 3 diodes over an AC SMPS and need the same size reservoir cap, effectively zero cost or size saving. It still wouldn't work with induction motors or transformers.Something I don't think anyone has mentioned is switch contact material migration with DC switches. A well known problem with car ignition contact breakers of old (with Tungsten contacts no less), resulting in a pip forming on one contact and a corresponding crater on the other. With the softer Silver based contact materials used in normal domestic switches, this migration would cause slower contact break, resulting in greater arcing, resulting in more migration, resulting in...

author: Marco
author_rank: Super Contributor
timestamp: August 20, 2025, 12:02:08 am
content: Quote from: jonpaul on August 17, 2025, 06:37:32 pmI feel they are too much designed like AC breakers, relying on the fault current to pass a mechanical stability point will always be kinda slow. It's the current squared which drives energy more than inductance after all.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 20, 2025, 01:40:49 am
content: Quote from: Zero999 on August 19, 2025, 07:08:58 amOnly requires one solid state switch to make from a constant DC source. And that can be on the low side to also keep the drive circuit simple.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 20, 2025, 10:18:02 am
content: Quote from: NiHaoMike on August 20, 2025, 01:40:49 amOf course it makes total sense to save $2 on a trivially cheap part and have to spend $200 elsewhere

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2025, 10:53:50 am
content: Quote from: NiHaoMike on August 20, 2025, 01:40:49 amIt will cost more than pure DC and three phase AC. All generators still need to be synchronized, as it's still AC, power can be only delivered part time and there's the additional complexity, inefficiencies of switched mode supplies. It appears as though you haven't thought it through.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 20, 2025, 11:53:30 am
content: Quote from: Zero999 on August 20, 2025, 10:53:50 amTo be fair, NiHaoMike said it would be a compromise. This would be a very typical textbook example of what acompromiseis, in political terms.

author: Marco
author_rank: Super Contributor
timestamp: August 20, 2025, 01:15:07 pm
content: Quote from: Gyro on August 19, 2025, 08:35:34 amI think a two pole switch with a couple passives would be similarly robust to a one pole switch with AC. Capacitor protects one switch during turn off, then the tank oscillates to let the other turn off with AC.

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2025, 05:09:08 pm
content: Quote from: Siwastaja on August 20, 2025, 11:53:30 amNot practical or technical then, purely political.

author: TimFox
author_rank: Super Contributor
timestamp: August 20, 2025, 05:38:29 pm
content: Again, the original question (perennially posed by novices) is whether to switch the mains (i.e., the power delivered to my house from the utility company) from 60 Hz AC to DC.I see no benefit to me from that expensive change in distribution from the 3 kV to 240 VCT transformer behind my house, fed from a local substation, and the longer distance transmission of relatively low voltage DC from that substation roughly one mile from my property.Should I need DC distribution within my house, I could pay for a suitable solid-state regulated rectifier and expensive circuit breakers or solid-state switches, but I see no benefit to me worth changing all of my appliances.

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2025, 07:00:32 pm
content: The advantage for large appliances would be not requiring the AC to DC conversion before the inverter which is driving the motor. I doubt that makes up for all of the disadvantages, and somewhere an even larger AC to DC conversion is necessary.Some data centers are setup this way, but they start the centralized AC to DC conversion at a much lower voltage.At the distribution level DC to DC conversion would replace AC transformers. Just the last stage of AC or DC to DC conversion from 2.4 to 32 kilovolts to 240 split phase, or whatever, is not easy with power electronics. Is this suppose to be economical and reliable compared to a large passive transformer made from copper, aluminum, and steel?A pig pole transformer might cost $10,000. Can it be replaced with a AC or DC to DC converter for that cost?

author: TimFox
author_rank: Super Contributor
timestamp: August 20, 2025, 07:07:17 pm
content: Unless the DC distribution voltage is fortuitously appropriate for the bus voltage needed by the inverter, a further step is needed inside the appliance anyway.With huge loads such as data centers, the engineers can design the power distribution with the building at will to match their equipment.

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2025, 09:23:20 pm
content: Quote from: TimFox on August 20, 2025, 07:07:17 pm"Low" voltage DC distribution is usually somewhere around 170 or 340 volts DC which allows the use of "universal" input AC power supplies with little or no modification. This voltage is also compatible with motor inverters intended for 120 and 240 volt AC motors.If safer but lower DC voltages are used, then wiring costs increase significantly.

author: TimFox
author_rank: Super Contributor
timestamp: August 20, 2025, 09:33:20 pm
content: Quote from: David Hess on August 20, 2025, 09:23:20 pmOr, I can connect my 120 V AC motor directly to my house wiring.

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2025, 09:40:29 pm
content: Quote from: David Hess on August 20, 2025, 09:23:20 pmIn Europe, low voltage AC power is normally 400V 3 phase, 230V to neutral. The tolerance is 90% to 120% of the nominal, so 207V to 253V single phase.Small 3 phase motors will either work off 230V (delta) or 400V (star) which is useful because it's possible to connect one to either 400V three phase (directly), or 230V, three phase generated from an inverter, run off 230V single phase.Larger motors are wound for 400V delta or 690V star, with the latter not commonly used.The peak voltage of 230VAC, 325VDC wouldn't be much use in industrial settings, where the peak of 400VAC, 566VDC would be more useful. Perhaps bipolar +/-305V would be a compromise, as 305V is the peak voltage towards the lower end of the 230VAC tolerance and 610V, is at the upper end of the 400VAC tolerance.This of course will never happen for the reasons discussed throughout this thread.

author: TimFox
author_rank: Super Contributor
timestamp: August 20, 2025, 09:45:09 pm
content: In my pre-retirement job, we often used high-power servo drivers to drive multi-phase servo motors with resolver feedback for commutation, for carefully-controlled motion.The power input went straight to the DC bus through a full-wave bridge, allowing DC or single-phase AC power.For higher current applications, we used an external 6-diode 3-phase bridge module from 208 V (line-to-line) three-phase power.The three-phase rectifier is a good solution, since it has much less inherent ripple than a single-phase rectifier.

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2025, 09:58:20 pm
content: Quote from: Zero999 on August 20, 2025, 09:40:29 pmIn the US most homes are limited to split phase 240 VAC, with each phase providing 120 VAC and the largest 240 VAC circuit being 30 to 50 amps for things like electric clothes dryers, air conditioners, and electric stoves. This limitation is usually by policy to prevent "industrial" operations from being conducted in residential areas, even if they are outside of city limits.Industrial areas can have anything starting with 3-phase 240 VAC. "High leg" 3-phase 240 VAC is common with the neutral attached between two legs to provide split phase 240 VAC and the high leg being 277 VAC to the neutral. Big office buildings might use the 277 VAC for lighting. 3-phase 480 VAC is common for larger machinery and I think for data centers now.

author: RJSV
author_rank: Super Contributor
timestamp: August 20, 2025, 11:26:21 pm
content: Here is an ironic way, for things to unfold, in future systems:Don't discount AC power distribution and use too recklessly, as I've seen examples of modes of (energy) use that keep the devices, and meanwhile manipulate the DC sourcing to essentially keep the overall AC distribution (and consumer devices) legacy.In that sense, has anyone estimated the numbers, to replace, say, a 120 vac beard shaver, with 120 VDC or all the myriad of other device replacements or outright unavailability of some consumer devices ?I'd like to see the numbers, aside from distribution, of all those devices, going INTO OUR LANDFILL DUMPS.

author: RJSV
author_rank: Super Contributor
timestamp: August 21, 2025, 12:29:40 am
content: (There's more)Thinking about how things, events sometimes unfold, I dread the day, when the excuse /reason for a big transition to 120 volts DC comes (by way of forced change):CLIMATE CHANGE.Now, you (we) get to argue against some agenda-driven system re-vamp. Watch those changes get trivialized. 'Yes', you might respond, "the proposal has some flaws...", "(but what else we gonna do ?)"...etc.You might comment that the people pushing for abandoning the AC systems are heavily, heavily, involved in politics, Governors of states, (and their mates and family) pushing somewhat strange-sounding agendas. "Those folks aren't taken seriously enough to do any damage." you might say...basically 'poo poo'ing' the cautions.Ok, then try Google 'History of Downtown Hayward LOOP'.I found some comments on REDDIT, involving THAT somewhat new'ish transportation system, in a traditionally congested and older downtown area filled with Massage Parlors, Pawn Shops, Dollar Discount Stores, and Massage Parlors. You can read comments like:"Hayward LOOP reform". (Huh ??).Point is, apparently there were enough folks active enough to convince city leaders, that a ROME STYLE roundabout could solve many traffic woes, in the square mile or so near and around the downtown. So now, you can listen to folks complain, about streets that end up facing other directions, all of a sudden, and other really odd configurations.Well, they. had to 'do something', or 'die' in traffic.(They got THE LOOP).

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: August 21, 2025, 02:14:09 am
content: The Currents War Reduxhttps://youtu.be/kue18AxK1tU?si=fFezZKJR0FNVhAsQ

author: Picuino
author_rank: Super Contributor
timestamp: August 22, 2025, 06:55:43 pm
content: Quote from: coppercone2 on August 09, 2025, 11:51:03 pmStunning!

author: Marco
author_rank: Super Contributor
timestamp: August 23, 2025, 08:31:04 pm
content: An arc across the switch is only a problem if you allow it to build.With more widespread use of DC there would be smarter switches (knife switches are very dumb indeed, even for AC).

author: Zero999
author_rank: Super Contributor
timestamp: August 23, 2025, 09:00:17 pm
content: Quote from: Marco on August 23, 2025, 08:31:04 pmYou appear to have missed the point: DC switches need arc suppression hardware, which makes them more costly than the equivalent AC switch. It has absolutely nothing to do with being smart.

author: Marco
author_rank: Super Contributor
timestamp: August 23, 2025, 09:59:12 pm
content: It's a point, but hardly the point of the video.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 24, 2025, 12:59:53 am
content: Quote from: Siwastaja on August 20, 2025, 10:18:02 amQuite a bit more than $2 for any substantial amount of power. 3 more solid state switches to get AC, 2 of which need high side drivers. On the other side, existing switching supplies just work, that includes fuses and switches. Or they can be changed to use a single diode instead of a bridge rectifier to get a slight bit more efficiency, probably not worth it.Quote from: Zero999 on August 20, 2025, 10:53:50 amCost more than pure DC until you consider the extra costs of DC rated switches and fuses that would be avoided. It would definitely be cheaper than 3 phase AC which would need 5 more solid state switches, which would be pointless for running switching power supplies.

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2025, 06:09:26 am
content: Quote from: NiHaoMike on August 24, 2025, 12:59:53 am3-phase inputs are common with big switching power supplies, and it can be done with 3 active switches with aVienna Rectifierto implement active power factor correction.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 25, 2025, 12:10:01 am
content: Quote from: David Hess on August 24, 2025, 06:09:26 amI don't see the advantage converting DC to 3 phase only to convert it back to DC. It's worth noting that even the really large AI servers use many single phase PSUs as opposed to a smaller number of 3 phase PSUs, there's a good reason for that.Reliability wise, the best is constant DC if the arcing issue can be mitigated, that unfortunately happens to be cost prohibitive in many situations. Pulsed DC would be almost as good, certainly much less complexity than AC.

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2025, 05:58:51 am
content: Quote from: NiHaoMike on August 25, 2025, 12:10:01 amI thought we were talking about data centers which use DC for distribution.High power DC to DC conversion often uses multiple phases, including for active power factor correction.

author: Zero999
author_rank: Super Contributor
timestamp: August 25, 2025, 11:55:26 am
content: Quote from: NiHaoMike on August 25, 2025, 12:10:01 amMultiphase buck converters effectively do this. The advantage is lower peak currents though the switches and inductors, leading to high efficiency.