It is absolutely stupid to talk about this as edisons revenge. If Tesla had the modern high power transistors needed to get high voltage dc out of the ac produced from a spinning turbine he would be all for high voltage dc too. Tesla understood that high voltage was needed for efficient long range transmission. He also understood that transformers were the inly remotely efficient way to climb up to and down from these high voltages. And transformers only work with ac. So he designed an ac system and even designed some better transformers for it.
If there was anything like a high power transistor back then he would have used that. High power transistors that are robust enough to handle the grid were designed inly recently over 100 years after the tesla/edison ac/dc argument.
>It is absolutely stupid to talk about this as edisons revenge. If Tesla had the modern high power transistors needed to get high voltage dc out of the ac produced from a spinning turbine he would be all for high voltage dc too.
This!
The soon people realized these facts the better. The pervasive high rise buildings did not happen before the invention of modern cranes.
Exactly twenty years ago I was doing a novel research on GaN characterization, and my supervisors made a lot money with consulations around the world, and succesfully founded govt funded start-up company around the technology. Together with SiC, these are the two game changing power devices with wideband semiconductor technology that only maturing recently.
Heck, even the Nobel price winning blue LED discovery was only made feasible by GaN. Watch the excellent video made by Veritasium for this back story [1].
[1] Why It Was Almost Impossible to Make the Blue LED:
There's a component of modern culture that trains and expects people to be extremely pessimistic about long term human development. It results in situations above, where without any further information people just assume by default that were going to run out of a thing and are on some collision course with not just a disaster, but every single conceivable one.
(Gallium is a byproduct of aluminum production. We aren't going to run out.)
On the other hand, it is possible to run out of a metal when all of it is either somewhere in some device or scattered among landfills (i.e. not concentrated in a place like a mine).
My understanding of most elements is if we want more it’s either pretty easy to make from something else we have a lot of, or we need to redo the Big Bang, the latter being, in my opinion, a bit of a disaster scenario.
From your earlier comment, your curiosity was more about what happens after we run out.
In your question you stated the running out as a given fact ("When" we run out, not "if").
If that was what you wanted to say I can't tell you, but that's definitely how it was received and thus you also got the harsh response. Since it reads a lot like doomsday thinking.
(Example: Does that mean when we run out of oxygen there are no more humans?
the internet really needs to stfu about tesla and get over that oatmeal comic that spawned a billion internet myths. dude was a decent inventor but suffered from chronic mental health issues and, in his lifetime, wasted so much time/energy/money and burned so many bridges with his horrible attitude. there's a reason most people didnt like him in his day, he was a depressed asshole who alienated everyone around him, and yes I know he was likely gay in a time when that wasn't cool. the fact still remains; his inventions are massively overblown by internet nerds.
the podcaster Sebastian Major from "Our Fake History" did a looonnngg patreon episode on tesla and debunked most of the weird myths around tesla. Sebastian doesn't have a vendetta or anything, it's just amazing how much of the Tesla stuff is just nonsense or is viewed through a very weird bias nowadays. Major also briefly touches on the weird Edison stuff and how the internet has twisted Edison into a villain.
People need heroes. It's like the Keanu Reeves or Musk era, all the ""badass"" stories about this or that soldier / local hero / w/e that are very often overblown and get further and further away from the initial facts every time they resurface.
No hate here, just noticing there is a weird visceral need to distill stories to their most essential, good vs evil, and the Tesla v Edison thing embodies this perfectly I think.
Keanu Reeves and Nikola Tesla to a degree as well, are decent figures.
Aside from all the cult classics Keanu is part of like john wick and the matrix, even discounting that, he is a good person in it of itself who is genuinely humble and might be one of the best persons within hollywood.
What I feel pissed about is that people like Andrew Tate and others like them took the concept of Matrix and the contributions Keanu did within that movie and tried to capitalize on that cult classic decades after in the most toxic form that might be the issue if we are talking about an era
To be honest, Nikola tesla is also a great person within the context of his time. GGP's comment is still true but Tesla's contributions can hardly be reinstated and I'd much rather people believe these to be the heros (Keanu/Tesla) rather than Tate/Musk etc.
If I take anything from Keanu, I would like to take his humility/humbleness.
I mean yeah, but it's not like the guy's 'horrible attitude' came from nowhere. He naiively romanticised migrating to the US thinking the game was about scientific progress rather than capital, and so he got repeatedly screwed over by almost everyone around him for decades.
If I was in his position I'm not sure I'd have taken it as well as he did.
Tesla was an outstanding technologist, but a poor businessman. He had a "vision" (actually more than one) about how his ideas could transform the world. Some of his ideas were amazing, but he was swindled out of his patents because the investors knew he had a passion and wanted to see them in use. The polyphase AC motor or fluorescent light bulb could have made him millions.
IMHO, the vision he had about universal free electricity (transmitted wirelessly) was the dumbest. It was a novel idea, and he invested a lot (his time and other people's money) in it. The problem with his idea is that there was no way to monetize it (and profit from it). (There were also the technical issues of the power loss over distance (1/R^2), the harm to the environment, and the interference with radio communications.)
Edison was quite a villain. He stole many of his "inventions", and orchestrated a PR campaign against Tesla touting the "evils" of AC power. AFAIK, the electric chair was either invented or inspired by him.
I know these things because I've read many books on various topics related to Tesla, and all of this knowledge predates the Internet.
Essentially none of this is true. The war of the currents was between Edison and Westinghouse, not Tesla. Tesla's downfall was that he turned into a crackpot who rejected modern science, such as Maxwell's equations, and started defrauding investors. Edison was an outspoken opponent of the death penalty, and the electric chair used AC simply because it is much more deadly.
> The war of the currents was between Edison and Westinghouse [...]
Thank you for quashing the gross misinformation. I was going to post this, but searched and found your comment. `\m/`
(I learned of the "Current War" in the 70's, since the Edison Museum was in my "backyard" -- and was a common destination of local school field trips.)
Edison did not invent the electric chair. When the inventors were trying to choose between using AC or DC he helped them decide on AC as part of his PR campaign.
Also, if anything would have been Edison's revenge it would have been HVDC, where they're sending power long distances with DC. (But as you said, even there it wouldn't make a ton of sense, since they were arguing in a different era).
The two primary reasons to do that are to allow the intertie of two AC grids that are not otherwise synchronized, and to take advantage of "earth return" paths when necessary to double the capacity of the line. The latter you may need to consider just to make the line cost effective over an equivalent AC span.
sure, and also Montezuma didn't actually plan on diarrhea ruining people's vacations, but vernacular usage being what it is we have the phrase Montezuma's revenge.
I only found Edison in the headline, I didn't find it anywhere in the body, nor did I find Tesla. Glancing through the article it almost seems like someone tried to make a catchy headline to get clicks.
Yes, but a rectifier only rectifies. That's not going to give you DC-DC conversion - let alone converting it to a higher voltage for long-distance transmission.
DC power has been an option for datacenter equipment since I was a young lad racking and stacking hardware. Cisco, Dell, HPE, IBM, and countless others all had DC supply options. Same with PDUs. What’s old is new again.
48vdc was common in phone exchanges. They filled the basement with lead-acid batteries and to could run without the grid for a couple weeks. In turn the phone was 99.999% reliable for decades.
I'm working on stuff in that market, it's still largely is. DC Power System Design For Telecommunications is still a must read and it doesn't even cover the last 15 years or so of development, notably lithium batteries and high efficiency rectifiers.
I will say that this is a surprisingly deep and complex domain. The amount of flexibility and scalability you see in DC architectures is mind-boogling. They can span from a 3kW system that fits in 2U all the way to multiples of 100kWs that span entire buildings and be powered through a combination of grid, solar and/or gas.
Not to be _that_ guy, but it was technically -48V DC.
Honestly, that was pretty surprising to me when I had to work with some telco equipment a couple of decades ago. To this day, I don't think I've encountered anything else that requires negative voltage relative to ground.
Well if it's negative 48V the electricty flows out of your circuit and back to the grid, so you need to make it positive to have the electricity come in.
Yes, and that tiny little difference can cost you a lot of expensive gear if you run it off the battery and plug in a serial port or something like that. You'll also learn first hand what arc welding looks like without welding glass.
Some old guitar effects used -9V DC.[1] And the convention with guitar effects power adapter is the barrel is center negative (which is motivated with facilitating easy wiring of the socket's switch to connect to a 9V battery inside).
Because the chassis is connected to ground (as in, a literal grounding rod hammered into the soil) and by definition your 0V reference point.
The crucial difference is the direction in which the current is flowing: is it going "in to", or "out of" a hot wire? This becomes rather important when those wires are leaving the building and are buried underground for miles, where they will inevitably develop minor faults.
With +48V corrosion will attack all those individual telephone wires, which will rapidly become a huge maintenance nightmare as you have to chase the precise location of each, dig it up, and patch it.
With -48V corrosion will attack the grounding rod at your exchange. Still not ideal, but monitoring it isn't too bad and replacing a corroded grounding rod isn't that difficult. Telephone wires will still develop minor faults, but it'll just cause some additional load rather than inevitably corroding away.
positive ground used to be in all cars. When they went from 6 volts to 12 the disadvantages became appearant fast and so everyone went negative ground then (mid 1950s). I am not clear why positive ground was bad (maybe corrosion?)
Yeah I always heard that the phone lines carried their own power, and in Florida the phones did keep working when the power went out, but I never knew why.
So the grid was always charging up the lead acid batteries, and the phone lines were always draining them? Or was there some kind of power switching going on where when the grid was available the batteries would just get "topped off" occasionally and were only drained when the power went out?
The phone grid predated the electrical grid. There was no other choice for power.
Actually, there was one. Even earlier phones had their own power. A dry-cell battery in each phone, and every 6 months, the phone company would come around with a cart and replace everyone's battery. Central battery was found to be more convenient, since phone company employees didn't have to go around to everyone's site. Central offices could economize scale and have actual generators feeding rechargeable batteries.
Grid charging batteries, phone draining them as I understand. Of course there were switches all over the us so I can't make blanket claims but from what I hear that was normal.
It's a pretty decent chunk of power down a POTS cable too, as it was designed to ring multiple big chunky metal bells in the days of yore.
I was wiring in a phone extension for my grandma once as a boy and grabbed the live cable instead of the extension and stripped the wire with my teeth (as you do). I've been electrocuted a great number of times by the mains AC, but getting hit by that juicy DC was the best one yet. Jumped me 6ft across the room :D
The teeth. Yikes! But yeah, I remember having the rotary phone disassembled and touching the wires adjusting something when a ring came. Gave me enough of a jolt to remember.
The batteries and phone lines were one system at -48v with power supplies converting AC power to DC while grid / generator is up.
The batteries are floated at the line voltage nothing was really charging or discharging and there was no switchover.
This is similar to your cars 12v dc power system such the when the car is running the alternator is providing DC power and the batteries float doing nothing except buffering large fluctuations stabilizing voltage.
Obviously 48VDC has been around and internally they will probably still step down to 48V. But these 48V islands are nowadays inter connected by regular AC grid. They want to replace that interconnection with a 800VDc bus. I kind of assume they chose 800vdc because there are already bunch of stuff available from EVs which also have 800vdc battery packs now.
Much of the world's mains-voltage electronics run at 240V (historical) and have PFC circuits (which are essentially just boost converters) that run at ~400V DC link voltages. 650V gives you enough headroom to tolerate overshoots and still have an 80% safety margin with a single level topology.
This voltage also coincidentally is a convenient crossover point where silicon MOSFETs start to become inefficient and GaN FETs have recently become feasible and mass-produced.
800V to each rackmount unit, with hot plugging of rack units? That's scary.
The usual setup at this voltage is that you throw a hulking big switch to cut the power, and that mechanically unlocks the cabinet. But that's not what these people have in mind.
They want hot-plugging of individual rackmount units.
GE has a paper about the power conversion design, but it doesn't mention the unit to rack electrical and mechanical interface. Liteon is working on that, but the animation is rather vague.[2] They hint at hot plugging but hand-wave how the disconnects work.
Delta offers a few more hints.[3] There's a complex hot-plugging control unit to avoid inrush currents on plug-in and arcing on disconnect. This requires active management of the switching silicon carbide MOSFETs.
There ought to be a mechanical disconnect behind this, so that when someone pulls out a rackmount unit, a shutter drops behind it to protect people from 800V. All these papers are kind of hand-wavey about how the electrical safety works.
Plus, all this is liquid-cooled, and that has to hot-plug, too.
> When it is detected that the PDB starts to detach from the interface, the hot-swap controller quickly turns off the MOSFET to block the discharge path from Cin to the system. After the main power path is completely disconnected, the interface is physically detached, and no current flows at this time
> For insertion, long pins (typically for ground and control signals) make contact first to establish a
stable reference and enable pre-insertion checks, while short pins (for power or sensitive signals)
connect later once conditions are safe; during removal, the sequence is reversed, with short pins
disconnecting first to minimize interference.
I've been hearing this line for over a decade, now. "Immersion cooling will make data centers scale!" "Converting to DC at the perimeter increases density!"
Yes, of course both of those things are true, and yes, some data centers do engage in those processes for their unique advantages. The issue is that aside from specialty kit designed for that use (like the AWS Outposts with their DC conversion), the rank-and-file kit is still predominantly AC-driven, and that doesn't seem to be changing just yet.
While I'd love to see more DC-flavored kit accessible to the mainstream, it's a chicken-and-egg problem that neither the power vendors (APC, Eaton, etc) or the kit makers (Dell, Cisco, HP, Supermicro, etc) seem to want to take the plunge on first. Until then, this remains a niche-feature for niche-users deal, I wager.
As seen on HN a few days ago, immersion cooling is dead: turns out the risks of getting sued to oblivion due to widespread PFAS contamination isn't worth it. [0]
DC doesn't have such a killer. There are a decent bunch of benefits, and the main drawback is gear availability. However, the chicken-and-egg problem is being solved by hyperscalers. Like it or not, the rank-and-file of small & medium businesses is dying, and massive deployments like AWS/GCP/Azure/Meta are becoming the norm. Those four already account for 44% of data center capacity! If they switch to DC can you still call it "specialty kit", or would it perhaps be more accurate to call it "industry norm"?
It is becoming increasingly obvious that the rest of the industry is essentially getting Big Tech's leftovers. I wouldn't be surprised if DC became the norm for colocation over the next few decades.
Those vendors all have DC power supply options, to my knowledge. It’s hardly new; early telco datacenters had DC power rails, since Western Electric switching equipment ran on 48VDC.
That’s just it though, telco DCs != Compute DCs. Telcos had a vested interest in DC adoption because their wireline networks used it anyway, and the fewer conversions being done the more efficient their deployments were.
Every single DC I’ve worked in, from two racks to hundreds, has been AC-driven. It’s just cheaper to go after inefficiencies in consumption first with standard kit than to optimize for AC-DC conversion loss. I’m not saying DC isn’t the future so much as I’ve been hearing it’s the future for about as long as Elmo’s promised FSD is coming “next year”.
I think the real reason is because battery power didn't have to be converted twice to be able to run the gear in case of an outage, so you'd get longer runtime in case of a power failure, and it saves a bunch of money on supplies and inverters because you effectively only need a single giant supply for all of the gear and those tend to be more efficient (and easier to keep cool) than a whole raft of smaller ones.
At least for servers, power supplies are highly modular. It just takes 1 moderately sized customer to commit to buying them, and a DC module will appear.
Looking at the manual for the first server line that came to mind, you can buy a Dell PowerEdge R730 today with a first party support DC power supply.
Surely if it makes sense for the big players, they will do it, and then the benefits will trickle down to the rest? Like how Formula 1 technology will end up in consumer vehicles.
Not going to happen. For the same reason that the US never converted to a higher domestic voltage even though there are many practical advantages. The transition from one system to another at the consumer level would be terrible, even if there would be some advantage (and I'm not sure the one you list is even valid, you'd get DC-DC converters instead because your consumers typically use a lower voltage than the house distribution network powering your sockets) it would be offset by the cost of maintaining two systems side by side for decades.
You could wire your house for 12, 24 or 48V DC tomorrow and some off-grid dwellers have done just that. But since inverters have become cheap enough such installations are becoming more and more rare. The only place where you still see that is in cars, trucks and vessels.
And if you thought cooking water in a camper on an inverter is tricky wait until you start running things like washing machines and other large appliances off low voltage DC. You'll be using massive cables the cost of which will outweigh any savings.
> Not going to happen. For the same reason that the US never converted to a higher domestic voltage even though there are many practical advantages.
It would be relatively easy for the US to go to 240V: swap out single-pole breakers for double-pole, and change your NEMA 5 plugs for NEMA 6.
For a transition period you could easily have 240V and 120V plugs right next to each other (because of split phase you can 'splice in' 120V easily: just run cable like you would for a NEMA 14 plug: L1/L2/N/G).
What would be the real challenge would be going from 50 to 60Hz.
I suppose that still begs the question somewhat, since the US does have 240V (2 phase) already driving many appliances. Why hasn’t it ever become standard for luxury kitchens to have a European-style outlet for use with a European kettle? I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?
Well, as you say, it would not be according to code and the insurance company might have something to say about it. It's also single phase but not quite the way you do it in the USA, it would be a neutral and a phase whereas in the USA I think it is 2x110. Finally, it's 50 Hz rather than 60 which would work fine for resistive loads but not so well for inductive ones such as transformers and motors.
In all likely not worth the trouble. When I moved to Canada I gave away most of my power tools for that reason and when I moved back I had to do that all over again.
> In all likely not worth the trouble. When I moved to Canada I gave away most of my power tools for that reason and when I moved back I had to do that all over again.
If you ever have to do it again, you can probably get a transformer rated high enough for power-tools for cheaper than replacing all of your power tools.
Of course you can. That's kind of obvious. It is also highly impractical. Besides the frequency delta you end up having to lug a heavy transformer along and then you have to alternate it across your tools so you don't end up frying the transformer.
I wired a UK kettle to an unused 240V range outlet in the US once. It was amazing, boiled a liter of water in just under a minute. Obviously kinda sketchy.
No one in the USA drinks hat tea. The choices (and it tends to be regionally-based) is sweet or unsweet tea. No need to boil a kettle quickly for that.
You can run 240V circuit to kitchen for kettle and put in NEMA 6 outlet. But few people care about fast boil and importing European kettle. Most people use the microwave or stovetop, and 120V kettles are fine in most cases. It will never become a standard thing.
I think the answer to your question is that it mostly doesn't matter for personal mug size quantities of hot water and if it does matter to you there are readily available competing options such as dedicated taps for your kitchen sink.
Perhaps the biggest reason is that a traditional kettle on any half decent electric range will match if not exceed the power output of any imported electric kettle. Many even go well beyond that with one burner marked "quick boil" or similar.
> I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?
How expensive would a proper AC->DC->AC brick for that power level be?
Not so simple, you'd have to use a 'drier' or 'welder' socket for that otherwise you won't have enough power. A single circuit in Europe is 240V 16A or 3840W!
A pure sinewave inverter for that kind of power is maybe 600 to 1000 bucks or so, then you'd still need the other side and maybe a smallish battery in the middle t stabilize the whole thing. Or you could use one of those single phase inverters they use for motors.
I'm not sure it's likely, but I could see DC lighting start to happen in new construction. Have a single AC-to-DC converter off the main service entrance that powers hard-wired LED lighting fixtures in the house. Would probably be better than running the individual (and usually very low quality) converters in dozens of standard LED light bulbs. Would need to be standardized, codified, etc. so probably not happening soon.
I just wish I could run my air conditioner and my desktop computer at the same time without flipping the breaker. The RTX 5090 is a space heater and will easily peg at the 600W it’s rated for, and so with that and an air conditioner window unit, I have to run a long cable from another unused room if I want to do anything that stresses the video card.
Well, having spent some time operating a 12VDC system last year when I moved into some shacks, I will say that I find it a lot more convenient to run 120VAC.
I end up converting stuff anyhow, because all my loads run at different voltages- even though I had my lights, vent fan, and heater fans running on 12V I still ended up having to change voltages for most of the loads I wanted to run, or generate a AC to to charge my computer and run a rice cooker.
Not to mention that running anything that draws any real power quickly needs a much thicker wire at 12V. So you're either needing to run higher voltage DC than all your loads for distribution and then lowering the voltage when it gets to the device, or you simply can't draw much power.
Not that you can't have higher voltage DC; with my newer system the line from my solar panels to my charger controller is around 350VDC and I can use 10awg for that... but none of the loads I own that draw much power (saws, instapot, rice cooker, hammond organ, tube guitar amp) take DC :D
The lesser-known instance of this is RV power. When you're running off small batteries and solar, you want to make the best use of the watt-hours you have, and that means avoiding the DC-to-AC-to-DC loop wherever possible. So you run 12V (or in newer models, higher voltage) versions of everything, upconverting as necessary.
I am really skeptical that 12VDC power distribution in RVs actually saves power compared to a high-quality (hah!) higher voltage AC or DC system. 12V is absurdly low and you can’t easily lose quite a few percent in resistive losses even with fairly large cables, and those large cables are quite unpleasant to work with and rather dangerous.
I wonder how much of the benefit is simpler redundant power equipment. For AC, you have standby UPSes and line-interactive UPSes and frequency and phase synchronization. And everything needs a bit more hold-up time because, in case of failure, your new power supply might be at a zero crossing.
For 800V DC, a simple UPS could interface with the main supply using just a pair of (large) diodes, and a more complex and more efficient one could use some fancy solid state switches, but there’s no need for anything as complex as a line-interactive AC UPS.
They're still converting from AC to DC at the datacenter, it just isn't being stepped down at the perimeter. There is no transmission of HVDC going on. This isn't really Edison's revenge, more like his consolation price, ha!
I don't understand why new houses don't just have one high quality AC/DC converter so you can just use LED lighting without every bulb needing its own AC/DC converter. I imagine the light bulb cartel wouldn't really like that.
With modern technologies, that's power over ethernet or USB-C. Other comments in this thread point out that the telephone service also routinely used 48V for the ring signal.
However, higher DC voltage is riskier, and it's not at all standard for electrical and building code reasons. In particular, breaking DC circuits is more difficult because there's no zero-crossing point to naturally extinguish an arc, and 170V (US/120VAC) or 340V (Europe/240VAC) is enough to start a substantial arc under the right circumstances.
Unfortunately for your lighting, it's also both simple and efficient to stack enough LEDs together such that their forward voltage drop is approximately the rectified peak (i.e. targeting that 170/340V peak). That means that the bulb needs only one serial string of LEDs without parallel balancing, making the rest of the circuitry (including voltage regulation, which would still be necessary in DC world) simpler.
> I don't understand why new houses don't just have one high quality AC/DC converter so you can just use LED lighting without every bulb needing its own AC/DC converter.
IEEE 802.3bt can deliver up to 71W at the destination: just pull Cat 5/6 everywhere.
Every decent LED would then need … a switching power supply. LEDs are current-driven devices, and you get the best efficiency if you use an actual current-controlled supply. And those ICs are very, very cheap now.
The part that would genuinely be cheaper is avoiding problematic flicker. It takes a reasonably high quality LED driver to avoid 120Hz flicker, but a DC-supplied driver could be simpler and cheaper.
What voltage do you use? Most DC stuff wants low voltage (5-48V), but appliances need higher voltage like AC-level to get enough power over existing wiring. The result is DC-DC converters every place that have transformers now.
The gain from DC-DC converters is small and DC devices are small part of usage compared appliances. There is no way will pay back costs of replacing all the appliances.
LED light bulbs exist exclusively for compatibility with Edison sockets. Every LED fixture I have seen had a single transformer for the entire fixture; and that transformer was reasonably separate from the LEDs themselves.
It wouldn't work. leds need low voltages, meaning massive wires. you can run the voltage change on ac or dc. Ac just needs a few capacters to smooth the wave out.
That's traded off against the increase efficiency of LED lighting, at least compared to incandescent lighting. An LED "equivalent replacement" for a typical incandescent globe is down around 1/10th of the power. A 7Watt LED bulb is typically marketed as "60W equivalent". If that configured as a bunch of LEDs in series (or series/parallel) that need 12VDC, it's right about the same current draw as the 120V 60W incandescent equivalent. (Or perhaps double the current for those of us who get 220VAC out of our walls.)
(Am I just showing my age here? How many of you have ever bought incandescent globes for house lighting? I vaguely recall it may be illegal to sell them here in .au these days. I really like quartz halogen globes, and use them in 4 or 5 desk lamps I have, but these days I need to get globes for em out of China instead of being able to pick them up from the supermarket like I could 10 or 20 years ago.)
If your house gets 800V DC you're still gonna need "bricks" to convert that to 5VDC of 12VDC (or maybe 19VDC) that most of the things that currently have "bricks" need.
And if your house gets lower voltage DC, you're gonna have the problem of worth-stealing sized wiring to run your stove, water heater, or car charger.
I reckon it'd be nice to have USB C PD ports everywhere I have a 220VAC power point, but 5 years ago that'd have been a USB type A port - and even now those'd be getting close to useless. We use a Type I (AS/NZS 2112) power point plug here - and that hasn't needed to change in probably a century. I doubt there's ever been a low voltage DC plug/socket standard that's lasted in use for anything like that long - probably the old "car cigarette lighter" 12DC thing? I'm glad I don't have a house full of those.
Something to consider, and something I got a vivid demonstration of while playing with solar panels, DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe.
My understanding is that DC breakers are somewhat prone to fires for this reason, too.
Heh - I vaporised a fairly large soldering iron tip (probably 4mm copper cylindrical bar?), when I fucked up soldering a connector to a big 7 cell ~6000mAHr LiPo battery and shorted the terminals. Quite how I didn't end up blind or in hospital I don't know. It reinforced just how much respect you need to pay to even low-ish voltage DC when the available current was likely able to exceed 700A by a fair margin momentarily. I think those cells were rated at 60C continuous and 120C for 5 seconds.
heh man, I'm glad you got out of that easy, I definitely wore safety glasses 100% of the time after my experience. I think a lifetime of experience with dangerous wall outlets and harmless little 1.5V/9V DC cells teaches us the wrong lessons about DC safety. I've since heard stories of wrenches exploding when they fall across EV high voltage battery terminals. Wrenches aren't supposed to be explosive.
The electricians I was working with also told me stories about how with the really big breakers, you don't stand in front of it when you throw it, because sometimes it can turn into a cloud of molten metal vapor. And that's just using them as intended.
A bunch of those big breakers require two people. One person in a flash suit and another with a 2m long pole around the first person. That way if an arc flash happens, the second person can yank the first person to safety without also getting hurt.
Ruins the fun and interrupts instilling respect deep into the bones of interns.
Allegedly
While on "work experience" from high school I was put on washing power lines coming straight out of the local power station near the ocean - lots of salt buildups to clear.
Same deal, flashover suits and occasional arcs .. and much laughter from the ground operators who drifted the work bucket close.
I have a couple of those narrow escapes one of which led me to put a significant chunk of Eastern Amsterdam out of power. Another involved Beryllium oxide. 9 lives are barely enough.
Ah! Perhaps you are a member of the gigawatt club? Eligible for entry once you have accidentally tripped off 1000 MW of load or generation! No sweeping that under the table
I'm the idiot that sent a fairly high voltage spike into the grid setting off a cascade. Even years later I do not fully understand how it could happen, you'd think the grid would be low impedance enough to absorb a spike like that. But it set off a cascade on a part of the local grid that was known to be weak.
> DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe.
It would have self-extinguished if you waited long enough for the probe to vaporize.
I've worked overseas a lot and one thing that's really different from 2 decades ago is that I simply don't need a step-down transformer anymore because every single thing I plug in converts to DC (or otherwise accepts dual-voltage) anyways. So I have a giant collection of physical plug adapters because every device I use just needs to fit into the socket and takes care of it from there.
I spent a few years getting flown out around the world to service gear at different datacenters. I learned to pack an IEC 60320 C14 to NEMA 5-15R adapter cable and a dumb, un-protected* NEMA 5-15R power strip. While on-site at the datacenters, an empty PDU receptacle was often easy to find. At hotels, I'd bring home a native cable borrowed from or given to me by the native datacenter staff or I'd ask the hotel front desk to borrow a "computer power cable," (more often, I'd just show them a photo) and they generally were able to lend me one. It worked great. I never found a power supply that wasn't content with 208 or 240V.
*: Some fancier power strips with surge suppression have a MOV over-voltage varistor that may burn up if given 200V+, rendering the power strip useless. Hence, unprotected strips are necessary.
I've had discussed with people familiar with the matter, and they convinced me its really not worth it for many reasons, the main one being safety - DC arcs are self sustaining - AC voltage constantly goes to zero, so if an arc were to form, it gets auto extinguished when the voltage drops. With DC this never happens, meaing every switch or plug socket can create this nice long arcs and is a potential fire hazard.
The 'what is safer' question for DC and AC at the same effective current and power has a mixed set of answers depending on conditions. For instance, DC is more likely to cause your muscles to contact and not let go (bad), but AC is more likely to send your heart into ventricular fibrillation (sp?, also bad).
AC arcs are easier to extinguish than DC arcs, but DC will creep much easier than AC and so on.
From a personal point of view: I've worked enough with both up to about 1KV at appreciable power levels and much higher than that at reduced power. Up to 50V or so I'd rather work with DC than AC but they're not much different. Up to 400V or so above that I'd much rather have AC and above 400V the answer is 'neither' because you're in some kind of gray zone where creep is still low so you won't know something is amiss until it is too late. And above 1KV in normal settings (say, picture tubes in old small b&w tvs and higher up when they're color and larger) and it will throw you right across the room but you'll likely live because the currents are low.
HF HV... now that's a different matter and I'm very respectful of anything in that domain, and still have a burn from a Tronser trimmer more than 45 years after it happened. Note to self: keep eye on SWR meter/Spectrum analyzer and finger position while trimming large end stages.
Really depends on what we're talking about. A lot of electrical safety equipment has a DC rating, usually something like 90VDC/300VAC. Also, most DC equipment just isn't going to have the stored energy to generate a big arc. Well, except batteries, and we're already piling them all around us.
I mean it depends, but for dual rated stuff has both a voltage and current limit, both of which are way lower.
Like typically a 230V/20A AC switch can switch 24VDC/2A. And the energy is not in the equipment, its in the mains (or batteries like you said, or PV panels)
Right, but that's why I mentioned safety equipment. Your common DIN-mount UL-489 branch circuit breaker will be rated for the same trip current, same short circuit current rating (SCCR), but lower voltage. So you can use the same wiring and breakers as you might have with AC and your 48V battery bank won't vaporize the $5 hardware store toggle switch that somehow became a shunt.
I mean, most AC circuit breakers use electromagnets to trip on overcurrent (as well as bimetallic strips using thermal methods for sustained high current).
Electromagnets dont work for DC, so your breaker will never trip. For thermal protection, you need current, so that checks out, and it would make sense for it to be rated under 50V as thats considered the highest voltage thats not life threatening on touch.
PV Batteries in general have a very high current (100s of A) at ~50Vish volts, so I dont think there's a major usecase for using household breakers for them.
Im still not getting your point BTW, switches and breakers are two separate things, with different workings, and household (and datacenter) DC would be I think around 400ish V, which is a bit higher than the peak voltage of AC, but still within the arc limits of household wiring (at least in 230V countries).
The advantage of DC is that you use your wiring more efficiently as the mean and peak wattage is the same at all times. Going with 48V would mean high resistive losses.
That’s actually a recent phenomenon. Before the age of electronics most household appliances either worked with AC or DC equally well (like incandescent bulbs) or worked well with AC only given the technology at the time (think anything with a motor, fans, HVAC compressors etc).
Taking it to an extreme, the house I lived in while in grad school had wall lamp fixtures that doubled as electric and gas lamps. At some point I imagine it would have been possible to choose between using electric or gas by either flipping the switch or turning a valve. They said "Edison Patent" on them. We could have lit the house on AC, DC, or gas.
Thinking about the failure modes gave me the heebie jeebies, but the gas had been disconnected ages prior.
I lived in a 19th century house in San Francisco that had gorgeous plaster work medallions on the ceilings - think cherubs and fruits - in the middle of which were the light fixtures. One day my dumb-ass flatmate made an ill-advised attempt to DIY his light fixture and cracked the still-active gas line embedded in the ceiling. Sometime in the 1920s - the date was printed on a sticker in the electrical panel - when they electrified the house, they'd wrapped the electrical wires around the gas pipes, and left them otherwise in situ. Crazy stuff.
It’s kind of fun that light switches predate electricity. I think you used to turn a key, I guess you were turning a valve? Now that I think of it using a key to operate a valve makes a lot of sense but you don’t see it too often, well, I guess you want to turn things off without needing to find a key…
I'm renovating a house, and have been considering 24V or 48V DC outlets in a few rooms. Semiconductors become more expensive above ~32V, so 24V might be the sweetspot.
However, there's also PoE (24 or 48V!), so maybe that's the right approach. It's not like each outlet is going to run a heater anyway.
Lower voltage makes voltage drop across the line proportionally worse. Depending on the purpose PoE is probably the way to go since the wiring and hardware is all standardized and safety certified.
Unless you mean running AC and installing inverters in the wall? What is this even for? All my electronics are DC but critically they all require different voltages. The only thing I might benefit from would be higher voltage service because there are times that 15 A at 120 V doesn't cut it.
I think there'a a regulatory "Low Voltage" definition of "below 50V", which has implications around whether you need to be a licensed electrician to install it or not. Anything above that is - for at least some purposes - considered "High Voltage".
Other people, of course, have other definitions of high voltage:
"This resonant tower is known as a Tesla coil. This particular one is just over 17 feet tall and it can generate about a million volts at 60,000 cycles per second."
and:
"This pulse forming network can deliver a shaped pulse of over 50,000 amps with a total energy of about 1,057 times the tower primary energy"
AC is less efficient than DC at a given voltage. The advantage of AC is that voltage switching is cheap, easy and efficient. Switching DC voltage is way harder, more expensive, and less efficient. However the switching costs are O(1) and the transmission losses are O(n) so for some distance (currently somewhere around 500 km) it's worth paying the switching cost to get super high voltage DC. The big thing that's changed in the last ~30 years is a ton of research into high voltage transistors, and fast enough computers to do computer controlled mhz switching of giant high power transistors. These new super fancy switching technologies brought the switching costs down from ludicrous to annoyingly high.
To expand on this, a given power line can only take a set maximum current and voltage before it becomes a problem. DC can stay at this maximum voltage constantly, while AC spends time going to zero voltage and back, so it's delivering less power on the same line.
Maybe if by "same voltage" we mean DC voltage the same as AC peak voltage. When we talk about AC voltage we are referring to root-mean-square (RMS) voltage. It's kind of like saying the average, though for math reasons the average of an unbiased sine wave is 0. Anyhooo, 1 VRMS into a load will produce the same power as 1VDC. If AC delivered less power than DC at the same voltage then life would be very confusing.
That’s true, but my understanding is the main contributor is skin effect, since AC travels only on the surface of the wire, while DC uses the whole area, resulting in lower resistance loss (https://en.wikipedia.org/wiki/Skin_effect)
this iirc is the smallest of 3 problems. the other 2 are skin effect (AC wires only store power on the outside of the wire) and capacitive effects (a write running parallel to the ground is a capacitor and AC current is equivalent to constantly charging and discharging the capacitor)
The primary benefit of AC is it's really easy to change the voltage of AC up or down.
The transmission efficiency of AC comes from the fact that you can pretty trivially make a 1 megavolt AC line. The higher the voltage, the lower the current has to be to provide the same amount of power. And lower current means less power in line loss due to how electricity be.
But that really is the only advantage of AC. DC at the same voltage as AC will ultimately be more efficient, especially if it's humid or the line is underwater. Due to how electricy be, a change in the current of a line will induce a current into conductive materials. A portion of AC power is being drained simply by the fact that the current on the line is constantly alternating. DC doesn't alternate, so it doesn't ever lose power from that alternation.
Another key benefit of DC is can work to bridge grids. The thing causing a problem with grids being interconnected is entirely due to the nature of AC power. AC has a frequency and a phase. If two grids don't share a frequency (happens in the EU) or a phase (happens everywhere, particularly the grids in the US) they cannot be connected. Otherwise the power generators end up fighting each other rather than providing power to a load.
In short, AC won because it it was cheap and easy to make high voltage AC. DC is comming back because it's only somewhat recently been affordable to make similar transformations on DC from High to low and low to high voltages. DC carries further benefits that AC does not.
Important factor is that AC at given nominal voltage V swings between 1.41V and -1.41V, so it requires let's say 40% better/thicker insulation than the equivalent V volts DC line. This is OK for overhead lines (just space the wires more) but is a pain for buried or undersea transmission lines; for that reason, they tend to use DC nowadays.
> I always thought AC’s primary benefit was its transmission efficiency??
There are many factors involved, and "efficiency" is only one. Cost is the real driver, as with everything.
AC is effective when you need to step down frequently. Think transformers on poles everywhere. Stepping down AC using transformers means you can use smaller, cheaper conductors to get from high voltage transmission, lower voltage distribution and, finally lower voltage consumers. Without this, you need massive conductors and/or high voltages and all the costs that go with them.
AC is less effective, for instance, when transmitting high power over long, uninterrupted distances or feeding high density DC loads. Here, the reactive[1] power penalty of AC begins to dominate. This is a far less common problem, and so "Tesla won" is the widely held mental shortcut. Physics doesn't care, however; the DC case remains and is applied when necessary to reduce cost.
How is DC better than a three phase delta 800Vrms, at 400Hz?
- Three conductors vs two, but they can be the next gauge up since the current flows on three conductors
- no significant skin effect at 400Hz -> use speaker wire, lol.
- large voltage/current DC brakers are.. gnarly, and expensive. DC does not like to stop flowing
- The 400Hz distribution industry is massive; the entire aerospace industry runs on it. No need for niche or custom parts.
- 3 phase @ 400Hz is x6 = 2.4kHz. Six diodes will rectify it with almost no relevant amount of ripple (Vmin is 87% of Vmax) and very small caps will smooth it.
As an aside, with three (or more) phase you can use multi-tap transformers and get an arbitrary number of poles. 7 phases at 400Hz -> 5.6kHz. Your PSU is now 14 diodes and a ceramic cap.
- you still get to use step up/down transformers, but at 400Hz they're very small.
- merging power sources is a lot easier (but for the phase angle)
- DC-DC converters are great, but you're not going to beat a transformer in efficiency or reliability
"now run that unshielded wire 50 meters past racks of GPUs and enjoy your EMI"
Multipole expansion scales faster than r^2.
Also, im not in the field (clearly) but GPUs cant handle 2.4 kHz? The quarter wavelength is 30km.
"nothing in that catalog is rated for 100kW–1MW rack loads at 800Vrms"
Current wise, the catalog covers this track just fine. As to the voltages, well that's the whole point of AC! The voltage you need is but a few loops of wire away.
"you still need an inverter-based UPS upstream, which is the exact conversion stage DC eliminates"
So keep it? To clarify, this is the "we're too good for plebeian power, so we'll transform it AC->DC->AC", right?
"SiC solid-state DC breakers are shipping today from every major vendor"
Of course they do. They're also pricey, have limited current capability (both capital costs and therefore irrelevant when the industry is awash with GCC money) and lower conduction, and therefore higher heat.
They're really nice though.
"wide-bandgap converters are at 95%+ with no moving parts"
transformers have no moving parts. Loaded they can do 97%+ efficiency, or 2MW of heat eliminated on a 100MW center.
400Hz is an aircraft hack. In a data center, where batteries and most of the stuff behind the PSU already want DC, cutting conversion stages and a bunch of UPS weirdness is a boring win even if DC breakers are nastier and pricier. If you want switchgear with aerospace pricing in a building full of racks, AC at boutique frequencies is one way to get there.
An advanced AI rack might use 100kW = 800V 125A, requiring gauge 2, quarter inch diameter---this isn't your lol speaker wire. Actually, I apologize, I realized I may be talking to a serious audiophile, didn't mean to disrespect your Monster cables.
The skin depth by the way is sqrt(2 1.7e-8 ohm m / (2 pi 400Hz mu0))=~3mm for copper---OK for single rack, but starts to be significant for the type of bus bars that an aisle of racks might want.
As for efficiency, both 400Hz transformers AND fancy DC-DC converters are around 95% efficient, except that AC requires electronics to rectify it to DC, losing another few percent, so the slight advantage goes to DC, actually.
As for merging power, remember that DC DC converter uses an internal AC stage, so it's the same---you can have multiple primary windings, just like for plain AC.
> I realized I may be talking to a serious audiophile, didn't mean to disrespect your Monster cables.
I am a recovering audiophool.
I do own a pair of 2m long Monster Cable speaker cables (with locking gold plated banana plugs). I am fairly certain I've used welders with smaller cables.
(In my defence, I bought those as a teenager in the late 80s. I am not so easily marketed to with snake oil these days. I hope.)
(On the other hand, I really like the idea of a reliably stable plus and minus 70V or maybe 100V DC power supply to my house. That'd make audio power amplifiers much easier and lighter...)
>- no significant skin effect at 400Hz -> use speaker wire, lol.
What are you talking about? There's a very significant skin effect at 400Hz. Skin effect goes up with frequency. These datacenters use copper busbars, not cable, so skin effect is an important consideration.
At 100 000 A for a 100 MW data center at 1000 V, speaker wire is a joke.
You obviously need at least a dozen stands in parallel!!
Clearly skin effect scales with frequency but, 400 Hz is still low, only 2.5x lines frequency (the scale is by the root); so the skin depth is 3mm. 3mm on each side makes for a pretty hefty rectangular cross-section.
If you could get that 100,000Amps flowing through your speaker wire, the vaporised copper and the plasma channel would probably keep your 100MW flowing, at least until your building caught fire.
This would be the funniest thing to do. 100K Amps is doable, the question is for how long. That would be one very impressive bank of capacitors. And to turn a 00 into plasma would have some spectacular side effects, such as raining molten copper across a sizeable area. Just your reading glasses would indeed not be enough, there probably isn't any PPE that I would consider entirely safe other than sufficient distance from ground zero. But now I'm really curious. I have a spot welder that will do bursts of 5KA and that will happily throw the breaker every so many welds. 100KA sustained will be a fair engineering challenge.
Ah, that lego project... that was one I always wondered if I should have industrialized it but sourcing enough lego was a real problem.
Holy crap. That's a whole series of bad ideas extremely well executed. That guy probably has never seen what a lead acid battery can do when it explodes. He keeps hiding away from the hot metal but in the path of ~half of those batteries. Ignorance is bliss.
Transitioning? It already happened decades ago. Only smaller scale/generic or less proficient "we bought all Dell and HP" use AC. At large scale it's been a ton of DC for literally decades. And for 70 years in telco and network gear.
The large brick you have on all your tech when you plug it in is the converter. AC works great for some applications, none of them really technical in nature.
It is absolutely stupid to talk about this as edisons revenge. If Tesla had the modern high power transistors needed to get high voltage dc out of the ac produced from a spinning turbine he would be all for high voltage dc too. Tesla understood that high voltage was needed for efficient long range transmission. He also understood that transformers were the inly remotely efficient way to climb up to and down from these high voltages. And transformers only work with ac. So he designed an ac system and even designed some better transformers for it.
If there was anything like a high power transistor back then he would have used that. High power transistors that are robust enough to handle the grid were designed inly recently over 100 years after the tesla/edison ac/dc argument.
>It is absolutely stupid to talk about this as edisons revenge. If Tesla had the modern high power transistors needed to get high voltage dc out of the ac produced from a spinning turbine he would be all for high voltage dc too.
This!
The soon people realized these facts the better. The pervasive high rise buildings did not happen before the invention of modern cranes.
Exactly twenty years ago I was doing a novel research on GaN characterization, and my supervisors made a lot money with consulations around the world, and succesfully founded govt funded start-up company around the technology. Together with SiC, these are the two game changing power devices with wideband semiconductor technology that only maturing recently.
Heck, even the Nobel price winning blue LED discovery was only made feasible by GaN. Watch the excellent video made by Veritasium for this back story [1].
[1] Why It Was Almost Impossible to Make the Blue LED:
https://youtu.be/AF8d72mA41M
Does that mean when we run out of Ga there are no more LED TVs?
Why would we run out of Ga?
There's a component of modern culture that trains and expects people to be extremely pessimistic about long term human development. It results in situations above, where without any further information people just assume by default that were going to run out of a thing and are on some collision course with not just a disaster, but every single conceivable one.
(Gallium is a byproduct of aluminum production. We aren't going to run out.)
On the other hand, it is possible to run out of a metal when all of it is either somewhere in some device or scattered among landfills (i.e. not concentrated in a place like a mine).
My understanding of most elements is if we want more it’s either pretty easy to make from something else we have a lot of, or we need to redo the Big Bang, the latter being, in my opinion, a bit of a disaster scenario.
You know, you could have just said:
> (Gallium is a byproduct of aluminum production. We aren't going to run out.)
I was genuinely curious.
Edit: wow, I get harassed and then I’m the one that gets downvoted.
From your earlier comment, your curiosity was more about what happens after we run out.
In your question you stated the running out as a given fact ("When" we run out, not "if").
If that was what you wanted to say I can't tell you, but that's definitely how it was received and thus you also got the harsh response. Since it reads a lot like doomsday thinking.
(Example: Does that mean when we run out of oxygen there are no more humans?
Why would we run out?)
I've heard the EV charging has played a big role in the maturation of GaN / SiC.
Yes, EV and high frequency electronics (microwave, mmWave, photonics) that require very fast switching capability.
And military radars love GaN
https://shrunk.ai/research-journals/f/cranes-skyhooks-and-it...
What are some novel processes or technologies you see becoming more important in the next 5-10 years?
the internet really needs to stfu about tesla and get over that oatmeal comic that spawned a billion internet myths. dude was a decent inventor but suffered from chronic mental health issues and, in his lifetime, wasted so much time/energy/money and burned so many bridges with his horrible attitude. there's a reason most people didnt like him in his day, he was a depressed asshole who alienated everyone around him, and yes I know he was likely gay in a time when that wasn't cool. the fact still remains; his inventions are massively overblown by internet nerds.
the podcaster Sebastian Major from "Our Fake History" did a looonnngg patreon episode on tesla and debunked most of the weird myths around tesla. Sebastian doesn't have a vendetta or anything, it's just amazing how much of the Tesla stuff is just nonsense or is viewed through a very weird bias nowadays. Major also briefly touches on the weird Edison stuff and how the internet has twisted Edison into a villain.
People need heroes. It's like the Keanu Reeves or Musk era, all the ""badass"" stories about this or that soldier / local hero / w/e that are very often overblown and get further and further away from the initial facts every time they resurface. No hate here, just noticing there is a weird visceral need to distill stories to their most essential, good vs evil, and the Tesla v Edison thing embodies this perfectly I think.
Except for Keith Moon. All the stories about him are true and if anything underplay the truth. :-)
Keanu Reeves and Nikola Tesla to a degree as well, are decent figures.
Aside from all the cult classics Keanu is part of like john wick and the matrix, even discounting that, he is a good person in it of itself who is genuinely humble and might be one of the best persons within hollywood.
What I feel pissed about is that people like Andrew Tate and others like them took the concept of Matrix and the contributions Keanu did within that movie and tried to capitalize on that cult classic decades after in the most toxic form that might be the issue if we are talking about an era
To be honest, Nikola tesla is also a great person within the context of his time. GGP's comment is still true but Tesla's contributions can hardly be reinstated and I'd much rather people believe these to be the heros (Keanu/Tesla) rather than Tate/Musk etc.
If I take anything from Keanu, I would like to take his humility/humbleness.
I mean yeah, but it's not like the guy's 'horrible attitude' came from nowhere. He naiively romanticised migrating to the US thinking the game was about scientific progress rather than capital, and so he got repeatedly screwed over by almost everyone around him for decades.
If I was in his position I'm not sure I'd have taken it as well as he did.
Tesla was an outstanding technologist, but a poor businessman. He had a "vision" (actually more than one) about how his ideas could transform the world. Some of his ideas were amazing, but he was swindled out of his patents because the investors knew he had a passion and wanted to see them in use. The polyphase AC motor or fluorescent light bulb could have made him millions.
IMHO, the vision he had about universal free electricity (transmitted wirelessly) was the dumbest. It was a novel idea, and he invested a lot (his time and other people's money) in it. The problem with his idea is that there was no way to monetize it (and profit from it). (There were also the technical issues of the power loss over distance (1/R^2), the harm to the environment, and the interference with radio communications.)
Edison was quite a villain. He stole many of his "inventions", and orchestrated a PR campaign against Tesla touting the "evils" of AC power. AFAIK, the electric chair was either invented or inspired by him.
I know these things because I've read many books on various topics related to Tesla, and all of this knowledge predates the Internet.
Essentially none of this is true. The war of the currents was between Edison and Westinghouse, not Tesla. Tesla's downfall was that he turned into a crackpot who rejected modern science, such as Maxwell's equations, and started defrauding investors. Edison was an outspoken opponent of the death penalty, and the electric chair used AC simply because it is much more deadly.
> The war of the currents was between Edison and Westinghouse [...]
Thank you for quashing the gross misinformation. I was going to post this, but searched and found your comment. `\m/`
(I learned of the "Current War" in the 70's, since the Edison Museum was in my "backyard" -- and was a common destination of local school field trips.)
Edison did not invent the electric chair. When the inventors were trying to choose between using AC or DC he helped them decide on AC as part of his PR campaign.
We’re talking about Nikola Tesla, not Elon Musk, and I don’t think Musk is gay.
I think you need to read the post you are responding to again.
Also, if anything would have been Edison's revenge it would have been HVDC, where they're sending power long distances with DC. (But as you said, even there it wouldn't make a ton of sense, since they were arguing in a different era).
The two primary reasons to do that are to allow the intertie of two AC grids that are not otherwise synchronized, and to take advantage of "earth return" paths when necessary to double the capacity of the line. The latter you may need to consider just to make the line cost effective over an equivalent AC span.
It's just a fun title, you are overthinking it
sure, and also Montezuma didn't actually plan on diarrhea ruining people's vacations, but vernacular usage being what it is we have the phrase Montezuma's revenge.
I only found Edison in the headline, I didn't find it anywhere in the body, nor did I find Tesla. Glancing through the article it almost seems like someone tried to make a catchy headline to get clicks.
Agreed, for the IEEE to go down this route is more than a little weird.
It was Westinghouse who pushed the AC grid against his rival Edison's DC approach. Tesla was a minor figure working for both of them for a bit.
Tesla also design the modern induction motor which needs ac. Though these days we often run them on a phase generator which has a dc step.
> If there was anything like a high power transistor back then he would have used that.
Mercury arc rectifiers were used long before his death.
Yes, but a rectifier only rectifies. That's not going to give you DC-DC conversion - let alone converting it to a higher voltage for long-distance transmission.
DC power has been an option for datacenter equipment since I was a young lad racking and stacking hardware. Cisco, Dell, HPE, IBM, and countless others all had DC supply options. Same with PDUs. What’s old is new again.
See e.g. https://www.dell.com/support/kbdoc/en-us/000221234/wiring-in...
48vdc was common in phone exchanges. They filled the basement with lead-acid batteries and to could run without the grid for a couple weeks. In turn the phone was 99.999% reliable for decades.
I'm working on stuff in that market, it's still largely is. DC Power System Design For Telecommunications is still a must read and it doesn't even cover the last 15 years or so of development, notably lithium batteries and high efficiency rectifiers.
I will say that this is a surprisingly deep and complex domain. The amount of flexibility and scalability you see in DC architectures is mind-boogling. They can span from a 3kW system that fits in 2U all the way to multiples of 100kWs that span entire buildings and be powered through a combination of grid, solar and/or gas.
Not to be _that_ guy, but it was technically -48V DC.
Honestly, that was pretty surprising to me when I had to work with some telco equipment a couple of decades ago. To this day, I don't think I've encountered anything else that requires negative voltage relative to ground.
I am STILL designing hardware for -48v telco standard. The first thing we do is convert -48 -> 48v. That's 4 square inches of PCB space we waste.
What do you need +48V for?
We go -48 -> 48 -> 12 -> 3v3,1v8 etc etc. If you went 48 straight to POL voltages then you would have horrific converter performance.
Well if it's negative 48V the electricty flows out of your circuit and back to the grid, so you need to make it positive to have the electricity come in.
Likely as a basis for converting to other useful DC voltages.
Yes, and that tiny little difference can cost you a lot of expensive gear if you run it off the battery and plug in a serial port or something like that. You'll also learn first hand what arc welding looks like without welding glass.
Some old guitar effects used -9V DC.[1] And the convention with guitar effects power adapter is the barrel is center negative (which is motivated with facilitating easy wiring of the socket's switch to connect to a 9V battery inside).
[1] https://www.analogisnotdead.com/article26/what-is-going-on-w...
Can you explain why it's -48 VDC as opposed to 48 VDC with the + and - inputs mislabeled?
Because the chassis is connected to ground (as in, a literal grounding rod hammered into the soil) and by definition your 0V reference point.
The crucial difference is the direction in which the current is flowing: is it going "in to", or "out of" a hot wire? This becomes rather important when those wires are leaving the building and are buried underground for miles, where they will inevitably develop minor faults.
With +48V corrosion will attack all those individual telephone wires, which will rapidly become a huge maintenance nightmare as you have to chase the precise location of each, dig it up, and patch it.
With -48V corrosion will attack the grounding rod at your exchange. Still not ideal, but monitoring it isn't too bad and replacing a corroded grounding rod isn't that difficult. Telephone wires will still develop minor faults, but it'll just cause some additional load rather than inevitably corroding away.
Do you also happen to why this is not more common? Must be useful for more than just telephone wires.
In short, ground.
Lots of amplifier circuits need a bipolar supply: both positive and negative voltages with respect to ground.
RTL and DTL both needed negative-voltage relative to ground, as do many analog circuits.
Is that something other than a labelling convention? Is ground actually connected to a earth stake?
Cathodic protection against corrosion was the goal of using -48V, in the telcos' case.
And the telegraph lines before that.
positive ground used to be in all cars. When they went from 6 volts to 12 the disadvantages became appearant fast and so everyone went negative ground then (mid 1950s). I am not clear why positive ground was bad (maybe corrosion?)
Check out older English cars.
Yeah I always heard that the phone lines carried their own power, and in Florida the phones did keep working when the power went out, but I never knew why.
So the grid was always charging up the lead acid batteries, and the phone lines were always draining them? Or was there some kind of power switching going on where when the grid was available the batteries would just get "topped off" occasionally and were only drained when the power went out?
The phone grid predated the electrical grid. There was no other choice for power.
Actually, there was one. Even earlier phones had their own power. A dry-cell battery in each phone, and every 6 months, the phone company would come around with a cart and replace everyone's battery. Central battery was found to be more convenient, since phone company employees didn't have to go around to everyone's site. Central offices could economize scale and have actual generators feeding rechargeable batteries.
Grid charging batteries, phone draining them as I understand. Of course there were switches all over the us so I can't make blanket claims but from what I hear that was normal.
It's a pretty decent chunk of power down a POTS cable too, as it was designed to ring multiple big chunky metal bells in the days of yore.
I was wiring in a phone extension for my grandma once as a boy and grabbed the live cable instead of the extension and stripped the wire with my teeth (as you do). I've been electrocuted a great number of times by the mains AC, but getting hit by that juicy DC was the best one yet. Jumped me 6ft across the room :D
I discovered the same exact thing wiring a second phone line to my bedroom as a teenager. I jumped into a pile of fiberglass insulation! :/
The teeth. Yikes! But yeah, I remember having the rotary phone disassembled and touching the wires adjusting something when a ring came. Gave me enough of a jolt to remember.
The batteries and phone lines were one system at -48v with power supplies converting AC power to DC while grid / generator is up.
The batteries are floated at the line voltage nothing was really charging or discharging and there was no switchover.
This is similar to your cars 12v dc power system such the when the car is running the alternator is providing DC power and the batteries float doing nothing except buffering large fluctuations stabilizing voltage.
Interesting, so this is why the phone line still worked when power was out across the whole town.
-48V! :-)
I still have a bunch of 48vdc comms gear in my powerplant.
Why do you have a powerplant?
Obviously 48VDC has been around and internally they will probably still step down to 48V. But these 48V islands are nowadays inter connected by regular AC grid. They want to replace that interconnection with a 800VDc bus. I kind of assume they chose 800vdc because there are already bunch of stuff available from EVs which also have 800vdc battery packs now.
They chose 800VDC because it's a convenient multiple that is the peak possible with a two-level 650V (probably GaN) FET arrangement.
And why is 650V special?
Historical, physical, engineering reasons.
Much of the world's mains-voltage electronics run at 240V (historical) and have PFC circuits (which are essentially just boost converters) that run at ~400V DC link voltages. 650V gives you enough headroom to tolerate overshoots and still have an 80% safety margin with a single level topology.
This voltage also coincidentally is a convenient crossover point where silicon MOSFETs start to become inefficient and GaN FETs have recently become feasible and mass-produced.
800V to each rackmount unit, with hot plugging of rack units? That's scary. The usual setup at this voltage is that you throw a hulking big switch to cut the power, and that mechanically unlocks the cabinet. But that's not what these people have in mind. They want hot-plugging of individual rackmount units.
GE has a paper about the power conversion design, but it doesn't mention the unit to rack electrical and mechanical interface. Liteon is working on that, but the animation is rather vague.[2] They hint at hot plugging but hand-wave how the disconnects work. Delta offers a few more hints.[3] There's a complex hot-plugging control unit to avoid inrush currents on plug-in and arcing on disconnect. This requires active management of the switching silicon carbide MOSFETs.
There ought to be a mechanical disconnect behind this, so that when someone pulls out a rackmount unit, a shutter drops behind it to protect people from 800V. All these papers are kind of hand-wavey about how the electrical safety works.
Plus, all this is liquid-cooled, and that has to hot-plug, too.
[1] https://library.grid.gevernova.com/white-papers-case-studies...
[2] https://www.youtube.com/watch?v=CQOreYMhe-M&
[3] https://filecenter.deltaww.com/Products/download/2510/202510...
It is a pretty clever design
> When it is detected that the PDB starts to detach from the interface, the hot-swap controller quickly turns off the MOSFET to block the discharge path from Cin to the system. After the main power path is completely disconnected, the interface is physically detached, and no current flows at this time
> For insertion, long pins (typically for ground and control signals) make contact first to establish a stable reference and enable pre-insertion checks, while short pins (for power or sensitive signals) connect later once conditions are safe; during removal, the sequence is reversed, with short pins disconnecting first to minimize interference.
Yes, I read that. There had better be a backup system. MOSFETs tend to fail ON, and there's a megawatt going into each rack.
Somehow this seems the wrong approach to AI.
Or maybe you can require technicians to be in full-protection electrical suits.
I've been hearing this line for over a decade, now. "Immersion cooling will make data centers scale!" "Converting to DC at the perimeter increases density!"
Yes, of course both of those things are true, and yes, some data centers do engage in those processes for their unique advantages. The issue is that aside from specialty kit designed for that use (like the AWS Outposts with their DC conversion), the rank-and-file kit is still predominantly AC-driven, and that doesn't seem to be changing just yet.
While I'd love to see more DC-flavored kit accessible to the mainstream, it's a chicken-and-egg problem that neither the power vendors (APC, Eaton, etc) or the kit makers (Dell, Cisco, HP, Supermicro, etc) seem to want to take the plunge on first. Until then, this remains a niche-feature for niche-users deal, I wager.
As seen on HN a few days ago, immersion cooling is dead: turns out the risks of getting sued to oblivion due to widespread PFAS contamination isn't worth it. [0]
DC doesn't have such a killer. There are a decent bunch of benefits, and the main drawback is gear availability. However, the chicken-and-egg problem is being solved by hyperscalers. Like it or not, the rank-and-file of small & medium businesses is dying, and massive deployments like AWS/GCP/Azure/Meta are becoming the norm. Those four already account for 44% of data center capacity! If they switch to DC can you still call it "specialty kit", or would it perhaps be more accurate to call it "industry norm"?
It is becoming increasingly obvious that the rest of the industry is essentially getting Big Tech's leftovers. I wouldn't be surprised if DC became the norm for colocation over the next few decades.
[0]: https://thecoolingreport.com/intel/pfas-two-phase-immersion-...
Those vendors all have DC power supply options, to my knowledge. It’s hardly new; early telco datacenters had DC power rails, since Western Electric switching equipment ran on 48VDC.
https://www.nokia.com/bell-labs/publications-and-media/publi...
That’s just it though, telco DCs != Compute DCs. Telcos had a vested interest in DC adoption because their wireline networks used it anyway, and the fewer conversions being done the more efficient their deployments were.
Every single DC I’ve worked in, from two racks to hundreds, has been AC-driven. It’s just cheaper to go after inefficiencies in consumption first with standard kit than to optimize for AC-DC conversion loss. I’m not saying DC isn’t the future so much as I’ve been hearing it’s the future for about as long as Elmo’s promised FSD is coming “next year”.
I think the real reason is because battery power didn't have to be converted twice to be able to run the gear in case of an outage, so you'd get longer runtime in case of a power failure, and it saves a bunch of money on supplies and inverters because you effectively only need a single giant supply for all of the gear and those tend to be more efficient (and easier to keep cool) than a whole raft of smaller ones.
At least for servers, power supplies are highly modular. It just takes 1 moderately sized customer to commit to buying them, and a DC module will appear.
Looking at the manual for the first server line that came to mind, you can buy a Dell PowerEdge R730 today with a first party support DC power supply.
These are GigaWatt data centers. For a single one they buy equipment by the container ship. Nothing is niche about it.
Surely if it makes sense for the big players, they will do it, and then the benefits will trickle down to the rest? Like how Formula 1 technology will end up in consumer vehicles.
I stg if I see the kids talk about Westinghouse being batterymogged I'm leaving the Internet
Waiting for home DC.
It is silly to have AC to DC converters in all of my wall connected electronics ( LED bulbs, home controller, computer equipment etc )
Not going to happen. For the same reason that the US never converted to a higher domestic voltage even though there are many practical advantages. The transition from one system to another at the consumer level would be terrible, even if there would be some advantage (and I'm not sure the one you list is even valid, you'd get DC-DC converters instead because your consumers typically use a lower voltage than the house distribution network powering your sockets) it would be offset by the cost of maintaining two systems side by side for decades.
You could wire your house for 12, 24 or 48V DC tomorrow and some off-grid dwellers have done just that. But since inverters have become cheap enough such installations are becoming more and more rare. The only place where you still see that is in cars, trucks and vessels.
And if you thought cooking water in a camper on an inverter is tricky wait until you start running things like washing machines and other large appliances off low voltage DC. You'll be using massive cables the cost of which will outweigh any savings.
> Not going to happen. For the same reason that the US never converted to a higher domestic voltage even though there are many practical advantages.
It would be relatively easy for the US to go to 240V: swap out single-pole breakers for double-pole, and change your NEMA 5 plugs for NEMA 6.
For a transition period you could easily have 240V and 120V plugs right next to each other (because of split phase you can 'splice in' 120V easily: just run cable like you would for a NEMA 14 plug: L1/L2/N/G).
What would be the real challenge would be going from 50 to 60Hz.
> What would be the real challenge would be going from 50 to 60Hz.
Other way around, no? The US is already 60Hz.
Edit: I mostly remember this because the SNES games I used to buy in the US and brought back to Europe ran noticeably slower.
I suppose that still begs the question somewhat, since the US does have 240V (2 phase) already driving many appliances. Why hasn’t it ever become standard for luxury kitchens to have a European-style outlet for use with a European kettle? I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?
Well, as you say, it would not be according to code and the insurance company might have something to say about it. It's also single phase but not quite the way you do it in the USA, it would be a neutral and a phase whereas in the USA I think it is 2x110. Finally, it's 50 Hz rather than 60 which would work fine for resistive loads but not so well for inductive ones such as transformers and motors.
In all likely not worth the trouble. When I moved to Canada I gave away most of my power tools for that reason and when I moved back I had to do that all over again.
> In all likely not worth the trouble. When I moved to Canada I gave away most of my power tools for that reason and when I moved back I had to do that all over again.
If you ever have to do it again, you can probably get a transformer rated high enough for power-tools for cheaper than replacing all of your power tools.
Of course you can. That's kind of obvious. It is also highly impractical. Besides the frequency delta you end up having to lug a heavy transformer along and then you have to alternate it across your tools so you don't end up frying the transformer.
I wired a UK kettle to an unused 240V range outlet in the US once. It was amazing, boiled a liter of water in just under a minute. Obviously kinda sketchy.
That's more like it :)
> but surely someone wanted hot tea faster
No one in the USA drinks hat tea. The choices (and it tends to be regionally-based) is sweet or unsweet tea. No need to boil a kettle quickly for that.
You can run 240V circuit to kitchen for kettle and put in NEMA 6 outlet. But few people care about fast boil and importing European kettle. Most people use the microwave or stovetop, and 120V kettles are fine in most cases. It will never become a standard thing.
Most important comment here!! I would love to buy like a 6kw battery induction kettle for the states. As far as I can tell, they don’t exist.
Ahckhually US residential is split single phase, not two phase. https://en.wikipedia.org/wiki/Split-phase_electric_power
I think the answer to your question is that it mostly doesn't matter for personal mug size quantities of hot water and if it does matter to you there are readily available competing options such as dedicated taps for your kitchen sink.
Perhaps the biggest reason is that a traditional kettle on any half decent electric range will match if not exceed the power output of any imported electric kettle. Many even go well beyond that with one burner marked "quick boil" or similar.
> I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?
How expensive would a proper AC->DC->AC brick for that power level be?
Not so simple, you'd have to use a 'drier' or 'welder' socket for that otherwise you won't have enough power. A single circuit in Europe is 240V 16A or 3840W!
A pure sinewave inverter for that kind of power is maybe 600 to 1000 bucks or so, then you'd still need the other side and maybe a smallish battery in the middle t stabilize the whole thing. Or you could use one of those single phase inverters they use for motors.
I'm not sure it's likely, but I could see DC lighting start to happen in new construction. Have a single AC-to-DC converter off the main service entrance that powers hard-wired LED lighting fixtures in the house. Would probably be better than running the individual (and usually very low quality) converters in dozens of standard LED light bulbs. Would need to be standardized, codified, etc. so probably not happening soon.
I just wish I could run my air conditioner and my desktop computer at the same time without flipping the breaker. The RTX 5090 is a space heater and will easily peg at the 600W it’s rated for, and so with that and an air conditioner window unit, I have to run a long cable from another unused room if I want to do anything that stresses the video card.
You can use nvidia-smi to reduce the powerdraw of the card to just below what will trip the breaker.
Well, having spent some time operating a 12VDC system last year when I moved into some shacks, I will say that I find it a lot more convenient to run 120VAC.
I end up converting stuff anyhow, because all my loads run at different voltages- even though I had my lights, vent fan, and heater fans running on 12V I still ended up having to change voltages for most of the loads I wanted to run, or generate a AC to to charge my computer and run a rice cooker.
Not to mention that running anything that draws any real power quickly needs a much thicker wire at 12V. So you're either needing to run higher voltage DC than all your loads for distribution and then lowering the voltage when it gets to the device, or you simply can't draw much power.
Not that you can't have higher voltage DC; with my newer system the line from my solar panels to my charger controller is around 350VDC and I can use 10awg for that... but none of the loads I own that draw much power (saws, instapot, rice cooker, hammond organ, tube guitar amp) take DC :D
Catch me wiring my house with 20V USBC ;)
The lesser-known instance of this is RV power. When you're running off small batteries and solar, you want to make the best use of the watt-hours you have, and that means avoiding the DC-to-AC-to-DC loop wherever possible. So you run 12V (or in newer models, higher voltage) versions of everything, upconverting as necessary.
I am really skeptical that 12VDC power distribution in RVs actually saves power compared to a high-quality (hah!) higher voltage AC or DC system. 12V is absurdly low and you can’t easily lose quite a few percent in resistive losses even with fairly large cables, and those large cables are quite unpleasant to work with and rather dangerous.
I tried using a microwave off the RV batteries, your inverter needs 4/0 cable. Very "fun".
It's called USB power delivery
home appliances have lower voltage, like 12V or 5V. The wire loss and heat would be a problem.
I wonder how much of the benefit is simpler redundant power equipment. For AC, you have standby UPSes and line-interactive UPSes and frequency and phase synchronization. And everything needs a bit more hold-up time because, in case of failure, your new power supply might be at a zero crossing.
For 800V DC, a simple UPS could interface with the main supply using just a pair of (large) diodes, and a more complex and more efficient one could use some fancy solid state switches, but there’s no need for anything as complex as a line-interactive AC UPS.
The datacenter I built in 2007 was DC.
Many datacenters I'd been to at that point were already DC.
Didn't think this was that new of a trend in 2026, but also acknowledge I did not visit more than a handful of datacenters since 2007.
It just seemed like a undenyably logical thing to do.
They're still converting from AC to DC at the datacenter, it just isn't being stepped down at the perimeter. There is no transmission of HVDC going on. This isn't really Edison's revenge, more like his consolation price, ha!
I don't understand why new houses don't just have one high quality AC/DC converter so you can just use LED lighting without every bulb needing its own AC/DC converter. I imagine the light bulb cartel wouldn't really like that.
With modern technologies, that's power over ethernet or USB-C. Other comments in this thread point out that the telephone service also routinely used 48V for the ring signal.
However, higher DC voltage is riskier, and it's not at all standard for electrical and building code reasons. In particular, breaking DC circuits is more difficult because there's no zero-crossing point to naturally extinguish an arc, and 170V (US/120VAC) or 340V (Europe/240VAC) is enough to start a substantial arc under the right circumstances.
Unfortunately for your lighting, it's also both simple and efficient to stack enough LEDs together such that their forward voltage drop is approximately the rectified peak (i.e. targeting that 170/340V peak). That means that the bulb needs only one serial string of LEDs without parallel balancing, making the rest of the circuitry (including voltage regulation, which would still be necessary in DC world) simpler.
> I don't understand why new houses don't just have one high quality AC/DC converter so you can just use LED lighting without every bulb needing its own AC/DC converter.
IEEE 802.3bt can deliver up to 71W at the destination: just pull Cat 5/6 everywhere.
* https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i...
* https://www.usailighting.com/poe-lighting
And pay $60 per Ethernet POE+ light bulb.
Every decent LED would then need … a switching power supply. LEDs are current-driven devices, and you get the best efficiency if you use an actual current-controlled supply. And those ICs are very, very cheap now.
The part that would genuinely be cheaper is avoiding problematic flicker. It takes a reasonably high quality LED driver to avoid 120Hz flicker, but a DC-supplied driver could be simpler and cheaper.
What voltage do you use? Most DC stuff wants low voltage (5-48V), but appliances need higher voltage like AC-level to get enough power over existing wiring. The result is DC-DC converters every place that have transformers now.
The gain from DC-DC converters is small and DC devices are small part of usage compared appliances. There is no way will pay back costs of replacing all the appliances.
LED light bulbs exist exclusively for compatibility with Edison sockets. Every LED fixture I have seen had a single transformer for the entire fixture; and that transformer was reasonably separate from the LEDs themselves.
It wouldn't work. leds need low voltages, meaning massive wires. you can run the voltage change on ac or dc. Ac just needs a few capacters to smooth the wave out.
Do you want your house to burn down? Lower voltages for LED lights mean higher current.
That's traded off against the increase efficiency of LED lighting, at least compared to incandescent lighting. An LED "equivalent replacement" for a typical incandescent globe is down around 1/10th of the power. A 7Watt LED bulb is typically marketed as "60W equivalent". If that configured as a bunch of LEDs in series (or series/parallel) that need 12VDC, it's right about the same current draw as the 120V 60W incandescent equivalent. (Or perhaps double the current for those of us who get 220VAC out of our walls.)
(Am I just showing my age here? How many of you have ever bought incandescent globes for house lighting? I vaguely recall it may be illegal to sell them here in .au these days. I really like quartz halogen globes, and use them in 4 or 5 desk lamps I have, but these days I need to get globes for em out of China instead of being able to pick them up from the supermarket like I could 10 or 20 years ago.)
because shorts and voltage loss are a real issue at that scale.
Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.
Sure, maybe?
If your house gets 800V DC you're still gonna need "bricks" to convert that to 5VDC of 12VDC (or maybe 19VDC) that most of the things that currently have "bricks" need.
And if your house gets lower voltage DC, you're gonna have the problem of worth-stealing sized wiring to run your stove, water heater, or car charger.
I reckon it'd be nice to have USB C PD ports everywhere I have a 220VAC power point, but 5 years ago that'd have been a USB type A port - and even now those'd be getting close to useless. We use a Type I (AS/NZS 2112) power point plug here - and that hasn't needed to change in probably a century. I doubt there's ever been a low voltage DC plug/socket standard that's lasted in use for anything like that long - probably the old "car cigarette lighter" 12DC thing? I'm glad I don't have a house full of those.
Something to consider, and something I got a vivid demonstration of while playing with solar panels, DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe.
My understanding is that DC breakers are somewhat prone to fires for this reason, too.
Heh - I vaporised a fairly large soldering iron tip (probably 4mm copper cylindrical bar?), when I fucked up soldering a connector to a big 7 cell ~6000mAHr LiPo battery and shorted the terminals. Quite how I didn't end up blind or in hospital I don't know. It reinforced just how much respect you need to pay to even low-ish voltage DC when the available current was likely able to exceed 700A by a fair margin momentarily. I think those cells were rated at 60C continuous and 120C for 5 seconds.
heh man, I'm glad you got out of that easy, I definitely wore safety glasses 100% of the time after my experience. I think a lifetime of experience with dangerous wall outlets and harmless little 1.5V/9V DC cells teaches us the wrong lessons about DC safety. I've since heard stories of wrenches exploding when they fall across EV high voltage battery terminals. Wrenches aren't supposed to be explosive.
The electricians I was working with also told me stories about how with the really big breakers, you don't stand in front of it when you throw it, because sometimes it can turn into a cloud of molten metal vapor. And that's just using them as intended.
A bunch of those big breakers require two people. One person in a flash suit and another with a 2m long pole around the first person. That way if an arc flash happens, the second person can yank the first person to safety without also getting hurt.
Why don't they use the pole to flip the breaker from 2m away?
Ruins the fun and interrupts instilling respect deep into the bones of interns.
Allegedly
While on "work experience" from high school I was put on washing power lines coming straight out of the local power station near the ocean - lots of salt buildups to clear.
Same deal, flashover suits and occasional arcs .. and much laughter from the ground operators who drifted the work bucket close.
Amps - the old 48vdc telco data centers vaporized wrenchs once in a while.
Those harmless 9V DC cells can do a lot of damage if you use them right.
You got super lucky.
Yep. Super super lucky. I suspect my reading glasses are the only reason I can still see anything.
I have a couple of those narrow escapes one of which led me to put a significant chunk of Eastern Amsterdam out of power. Another involved Beryllium oxide. 9 lives are barely enough.
Ah! Perhaps you are a member of the gigawatt club? Eligible for entry once you have accidentally tripped off 1000 MW of load or generation! No sweeping that under the table
I'm the idiot that sent a fairly high voltage spike into the grid setting off a cascade. Even years later I do not fully understand how it could happen, you'd think the grid would be low impedance enough to absorb a spike like that. But it set off a cascade on a part of the local grid that was known to be weak.
I would read that book...
'Stupid stuff I've done and survived'...
> DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe.
It would have self-extinguished if you waited long enough for the probe to vaporize.
I've worked overseas a lot and one thing that's really different from 2 decades ago is that I simply don't need a step-down transformer anymore because every single thing I plug in converts to DC (or otherwise accepts dual-voltage) anyways. So I have a giant collection of physical plug adapters because every device I use just needs to fit into the socket and takes care of it from there.
(My stand mixer is the lone sad exception)
Agreed!
I spent a few years getting flown out around the world to service gear at different datacenters. I learned to pack an IEC 60320 C14 to NEMA 5-15R adapter cable and a dumb, un-protected* NEMA 5-15R power strip. While on-site at the datacenters, an empty PDU receptacle was often easy to find. At hotels, I'd bring home a native cable borrowed from or given to me by the native datacenter staff or I'd ask the hotel front desk to borrow a "computer power cable," (more often, I'd just show them a photo) and they generally were able to lend me one. It worked great. I never found a power supply that wasn't content with 208 or 240V.
Example adapters: https://www.amazon.com/dp/B0FD7PHB7Y or https://www.amazon.com/dp/B01IBIC1XG
*: Some fancier power strips with surge suppression have a MOV over-voltage varistor that may burn up if given 200V+, rendering the power strip useless. Hence, unprotected strips are necessary.
I've had discussed with people familiar with the matter, and they convinced me its really not worth it for many reasons, the main one being safety - DC arcs are self sustaining - AC voltage constantly goes to zero, so if an arc were to form, it gets auto extinguished when the voltage drops. With DC this never happens, meaing every switch or plug socket can create this nice long arcs and is a potential fire hazard.
The 'what is safer' question for DC and AC at the same effective current and power has a mixed set of answers depending on conditions. For instance, DC is more likely to cause your muscles to contact and not let go (bad), but AC is more likely to send your heart into ventricular fibrillation (sp?, also bad).
AC arcs are easier to extinguish than DC arcs, but DC will creep much easier than AC and so on.
From a personal point of view: I've worked enough with both up to about 1KV at appreciable power levels and much higher than that at reduced power. Up to 50V or so I'd rather work with DC than AC but they're not much different. Up to 400V or so above that I'd much rather have AC and above 400V the answer is 'neither' because you're in some kind of gray zone where creep is still low so you won't know something is amiss until it is too late. And above 1KV in normal settings (say, picture tubes in old small b&w tvs and higher up when they're color and larger) and it will throw you right across the room but you'll likely live because the currents are low.
HF HV... now that's a different matter and I'm very respectful of anything in that domain, and still have a burn from a Tronser trimmer more than 45 years after it happened. Note to self: keep eye on SWR meter/Spectrum analyzer and finger position while trimming large end stages.
> DC will creep much easier than AC
Can you say more about "creep"? Is the resistance changing? Or is material actually migrating?
Also curious why it's worse using DC.
https://www.eevblog.com/forum/beginners/understanding-high-v...
Really depends on what we're talking about. A lot of electrical safety equipment has a DC rating, usually something like 90VDC/300VAC. Also, most DC equipment just isn't going to have the stored energy to generate a big arc. Well, except batteries, and we're already piling them all around us.
I mean it depends, but for dual rated stuff has both a voltage and current limit, both of which are way lower. Like typically a 230V/20A AC switch can switch 24VDC/2A. And the energy is not in the equipment, its in the mains (or batteries like you said, or PV panels)
Right, but that's why I mentioned safety equipment. Your common DIN-mount UL-489 branch circuit breaker will be rated for the same trip current, same short circuit current rating (SCCR), but lower voltage. So you can use the same wiring and breakers as you might have with AC and your 48V battery bank won't vaporize the $5 hardware store toggle switch that somehow became a shunt.
I mean, most AC circuit breakers use electromagnets to trip on overcurrent (as well as bimetallic strips using thermal methods for sustained high current).
Electromagnets dont work for DC, so your breaker will never trip. For thermal protection, you need current, so that checks out, and it would make sense for it to be rated under 50V as thats considered the highest voltage thats not life threatening on touch.
PV Batteries in general have a very high current (100s of A) at ~50Vish volts, so I dont think there's a major usecase for using household breakers for them.
Im still not getting your point BTW, switches and breakers are two separate things, with different workings, and household (and datacenter) DC would be I think around 400ish V, which is a bit higher than the peak voltage of AC, but still within the arc limits of household wiring (at least in 230V countries).
The advantage of DC is that you use your wiring more efficiently as the mean and peak wattage is the same at all times. Going with 48V would mean high resistive losses.
That’s actually a recent phenomenon. Before the age of electronics most household appliances either worked with AC or DC equally well (like incandescent bulbs) or worked well with AC only given the technology at the time (think anything with a motor, fans, HVAC compressors etc).
Taking it to an extreme, the house I lived in while in grad school had wall lamp fixtures that doubled as electric and gas lamps. At some point I imagine it would have been possible to choose between using electric or gas by either flipping the switch or turning a valve. They said "Edison Patent" on them. We could have lit the house on AC, DC, or gas.
Thinking about the failure modes gave me the heebie jeebies, but the gas had been disconnected ages prior.
I lived in a 19th century house in San Francisco that had gorgeous plaster work medallions on the ceilings - think cherubs and fruits - in the middle of which were the light fixtures. One day my dumb-ass flatmate made an ill-advised attempt to DIY his light fixture and cracked the still-active gas line embedded in the ceiling. Sometime in the 1920s - the date was printed on a sticker in the electrical panel - when they electrified the house, they'd wrapped the electrical wires around the gas pipes, and left them otherwise in situ. Crazy stuff.
It’s kind of fun that light switches predate electricity. I think you used to turn a key, I guess you were turning a valve? Now that I think of it using a key to operate a valve makes a lot of sense but you don’t see it too often, well, I guess you want to turn things off without needing to find a key…
There are niches where DC makes sense - low-voltage lighting, USB/LED ecosystems.
Once you get into higher power (laptops and up), switching and distribution get harder, so the advantages fade.
For bigger appliances (fridge, etc), AC is fine + practical.
Your modern fridge is probably going to have an inverter-driven motor, so you're right back to using DC.
All modern appliances and HVACs are using inverter drive motors for efficiency. Brushless DC motors are more efficient though.
"Brushless DC motors" are actually just AC synchronous motors.
I'm renovating a house, and have been considering 24V or 48V DC outlets in a few rooms. Semiconductors become more expensive above ~32V, so 24V might be the sweetspot.
However, there's also PoE (24 or 48V!), so maybe that's the right approach. It's not like each outlet is going to run a heater anyway.
Lower voltage makes voltage drop across the line proportionally worse. Depending on the purpose PoE is probably the way to go since the wiring and hardware is all standardized and safety certified.
Unless you mean running AC and installing inverters in the wall? What is this even for? All my electronics are DC but critically they all require different voltages. The only thing I might benefit from would be higher voltage service because there are times that 15 A at 120 V doesn't cut it.
Having a single big DC converter at a home would help a lot with power factor (LED lamps connected directly to AC have terrible power factor).
Modern bricks really aren’t that inefficient though. An Apple charger is like 90% efficient. A DC to DC converter is about that efficient or worse.
The power adapters became so efficient that we have to transition to wireless charging to keep it down
The irony...
This article seems to imply that 800V DC is high-voltage DC, but that seems quite low.
I think there'a a regulatory "Low Voltage" definition of "below 50V", which has implications around whether you need to be a licensed electrician to install it or not. Anything above that is - for at least some purposes - considered "High Voltage".
Other people, of course, have other definitions of high voltage:
"This resonant tower is known as a Tesla coil. This particular one is just over 17 feet tall and it can generate about a million volts at 60,000 cycles per second."
and:
"This pulse forming network can deliver a shaped pulse of over 50,000 amps with a total energy of about 1,057 times the tower primary energy"
https://www.youtube.com/watch?v=RoGbrgOhPes
Quite low compared to a power utility's HVDC, but quite high compared to the 5/12/24 V output of most AC/DC converters used for electronics.
I’ve always wondered about these new High-Voltage DC (HVDC) transmission lines.
I always thought AC’s primary benefit was its transmission efficiency??
Would love to learn if anyone knows more about this
AC is less efficient than DC at a given voltage. The advantage of AC is that voltage switching is cheap, easy and efficient. Switching DC voltage is way harder, more expensive, and less efficient. However the switching costs are O(1) and the transmission losses are O(n) so for some distance (currently somewhere around 500 km) it's worth paying the switching cost to get super high voltage DC. The big thing that's changed in the last ~30 years is a ton of research into high voltage transistors, and fast enough computers to do computer controlled mhz switching of giant high power transistors. These new super fancy switching technologies brought the switching costs down from ludicrous to annoyingly high.
> AC is less efficient than DC at a given voltage
To expand on this, a given power line can only take a set maximum current and voltage before it becomes a problem. DC can stay at this maximum voltage constantly, while AC spends time going to zero voltage and back, so it's delivering less power on the same line.
Maybe if by "same voltage" we mean DC voltage the same as AC peak voltage. When we talk about AC voltage we are referring to root-mean-square (RMS) voltage. It's kind of like saying the average, though for math reasons the average of an unbiased sine wave is 0. Anyhooo, 1 VRMS into a load will produce the same power as 1VDC. If AC delivered less power than DC at the same voltage then life would be very confusing.
That’s true, but my understanding is the main contributor is skin effect, since AC travels only on the surface of the wire, while DC uses the whole area, resulting in lower resistance loss (https://en.wikipedia.org/wiki/Skin_effect)
this iirc is the smallest of 3 problems. the other 2 are skin effect (AC wires only store power on the outside of the wire) and capacitive effects (a write running parallel to the ground is a capacitor and AC current is equivalent to constantly charging and discharging the capacitor)
The primary benefit of AC is it's really easy to change the voltage of AC up or down.
The transmission efficiency of AC comes from the fact that you can pretty trivially make a 1 megavolt AC line. The higher the voltage, the lower the current has to be to provide the same amount of power. And lower current means less power in line loss due to how electricity be.
But that really is the only advantage of AC. DC at the same voltage as AC will ultimately be more efficient, especially if it's humid or the line is underwater. Due to how electricy be, a change in the current of a line will induce a current into conductive materials. A portion of AC power is being drained simply by the fact that the current on the line is constantly alternating. DC doesn't alternate, so it doesn't ever lose power from that alternation.
Another key benefit of DC is can work to bridge grids. The thing causing a problem with grids being interconnected is entirely due to the nature of AC power. AC has a frequency and a phase. If two grids don't share a frequency (happens in the EU) or a phase (happens everywhere, particularly the grids in the US) they cannot be connected. Otherwise the power generators end up fighting each other rather than providing power to a load.
In short, AC won because it it was cheap and easy to make high voltage AC. DC is comming back because it's only somewhat recently been affordable to make similar transformations on DC from High to low and low to high voltages. DC carries further benefits that AC does not.
Important factor is that AC at given nominal voltage V swings between 1.41V and -1.41V, so it requires let's say 40% better/thicker insulation than the equivalent V volts DC line. This is OK for overhead lines (just space the wires more) but is a pain for buried or undersea transmission lines; for that reason, they tend to use DC nowadays.
BTW, megavolt DC DC converters are a sign to behold: https://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jp...
> I always thought AC’s primary benefit was its transmission efficiency??
There are many factors involved, and "efficiency" is only one. Cost is the real driver, as with everything.
AC is effective when you need to step down frequently. Think transformers on poles everywhere. Stepping down AC using transformers means you can use smaller, cheaper conductors to get from high voltage transmission, lower voltage distribution and, finally lower voltage consumers. Without this, you need massive conductors and/or high voltages and all the costs that go with them.
AC is less effective, for instance, when transmitting high power over long, uninterrupted distances or feeding high density DC loads. Here, the reactive[1] power penalty of AC begins to dominate. This is a far less common problem, and so "Tesla won" is the widely held mental shortcut. Physics doesn't care, however; the DC case remains and is applied when necessary to reduce cost.
[1] https://en.wikipedia.org/wiki/Electrical_reactance
https://en.wikipedia.org/wiki/High-voltage_direct_current
How is DC better than a three phase delta 800Vrms, at 400Hz?
- Three conductors vs two, but they can be the next gauge up since the current flows on three conductors
- no significant skin effect at 400Hz -> use speaker wire, lol.
- large voltage/current DC brakers are.. gnarly, and expensive. DC does not like to stop flowing
- The 400Hz distribution industry is massive; the entire aerospace industry runs on it. No need for niche or custom parts.
- 3 phase @ 400Hz is x6 = 2.4kHz. Six diodes will rectify it with almost no relevant amount of ripple (Vmin is 87% of Vmax) and very small caps will smooth it.
As an aside, with three (or more) phase you can use multi-tap transformers and get an arbitrary number of poles. 7 phases at 400Hz -> 5.6kHz. Your PSU is now 14 diodes and a ceramic cap.
- you still get to use step up/down transformers, but at 400Hz they're very small.
- merging power sources is a lot easier (but for the phase angle)
- DC-DC converters are great, but you're not going to beat a transformer in efficiency or reliability
> no significant skin effect at 400Hz -> use speaker wire, lol
now run that unshielded wire 50 meters past racks of GPUs and enjoy your EMI
> The 400Hz distribution industry is massive; the entire aerospace industry runs on it
nothing in that catalog is rated for 100kW–1MW rack loads at 800Vrms
> 3 phase @ 400Hz is x6 = 2.4kHz... Your PSU is now 14 diodes and a ceramic cap
you still need an inverter-based UPS upstream, which is the exact conversion stage DC eliminates
> large voltage/current DC breakers are.. gnarly, and expensive. DC does not like to stop flowing
SiC solid-state DC breakers are shipping today from every major vendor
> DC-DC converters are great, but you're not going to beat a transformer in efficiency or reliability
wide-bandgap converters are at 95%+ with no moving parts
"now run that unshielded wire 50 meters past racks of GPUs and enjoy your EMI"
Multipole expansion scales faster than r^2.
Also, im not in the field (clearly) but GPUs cant handle 2.4 kHz? The quarter wavelength is 30km.
"nothing in that catalog is rated for 100kW–1MW rack loads at 800Vrms"
Current wise, the catalog covers this track just fine. As to the voltages, well that's the whole point of AC! The voltage you need is but a few loops of wire away.
"you still need an inverter-based UPS upstream, which is the exact conversion stage DC eliminates"
So keep it? To clarify, this is the "we're too good for plebeian power, so we'll transform it AC->DC->AC", right?
"SiC solid-state DC breakers are shipping today from every major vendor"
Of course they do. They're also pricey, have limited current capability (both capital costs and therefore irrelevant when the industry is awash with GCC money) and lower conduction, and therefore higher heat.
They're really nice though.
"wide-bandgap converters are at 95%+ with no moving parts"
transformers have no moving parts. Loaded they can do 97%+ efficiency, or 2MW of heat eliminated on a 100MW center.
400Hz is an aircraft hack. In a data center, where batteries and most of the stuff behind the PSU already want DC, cutting conversion stages and a bunch of UPS weirdness is a boring win even if DC breakers are nastier and pricier. If you want switchgear with aerospace pricing in a building full of racks, AC at boutique frequencies is one way to get there.
An advanced AI rack might use 100kW = 800V 125A, requiring gauge 2, quarter inch diameter---this isn't your lol speaker wire. Actually, I apologize, I realized I may be talking to a serious audiophile, didn't mean to disrespect your Monster cables.
The skin depth by the way is sqrt(2 1.7e-8 ohm m / (2 pi 400Hz mu0))=~3mm for copper---OK for single rack, but starts to be significant for the type of bus bars that an aisle of racks might want.
As for efficiency, both 400Hz transformers AND fancy DC-DC converters are around 95% efficient, except that AC requires electronics to rectify it to DC, losing another few percent, so the slight advantage goes to DC, actually.
As for merging power, remember that DC DC converter uses an internal AC stage, so it's the same---you can have multiple primary windings, just like for plain AC.
> I realized I may be talking to a serious audiophile, didn't mean to disrespect your Monster cables.
I am a recovering audiophool.
I do own a pair of 2m long Monster Cable speaker cables (with locking gold plated banana plugs). I am fairly certain I've used welders with smaller cables.
(In my defence, I bought those as a teenager in the late 80s. I am not so easily marketed to with snake oil these days. I hope.)
(On the other hand, I really like the idea of a reliably stable plus and minus 70V or maybe 100V DC power supply to my house. That'd make audio power amplifiers much easier and lighter...)
>- no significant skin effect at 400Hz -> use speaker wire, lol.
What are you talking about? There's a very significant skin effect at 400Hz. Skin effect goes up with frequency. These datacenters use copper busbars, not cable, so skin effect is an important consideration.
At 100 000 A for a 100 MW data center at 1000 V, speaker wire is a joke.
You obviously need at least a dozen stands in parallel!!
Clearly skin effect scales with frequency but, 400 Hz is still low, only 2.5x lines frequency (the scale is by the root); so the skin depth is 3mm. 3mm on each side makes for a pretty hefty rectangular cross-section.
If you could get that 100,000Amps flowing through your speaker wire, the vaporised copper and the plasma channel would probably keep your 100MW flowing, at least until your building caught fire.
Even your monster cable? ;)
Well, it'd still vaporise, but it'd sound smoother and more musical as it did it, and the soundstage from the plasma arc would be _stunning!_
It's almost worth the experiment and your cables are a sacrifice I'm willing to make. For science, of course.
You're _so_ right!
I'm pretty sure you have my delivery address from when I bought sorted Lego from you about 10 years back.
Let me know when to expect the 100,000Amp test equipment!
I shall make sure I wear better PPE than just my reading glasses.
:-)
This would be the funniest thing to do. 100K Amps is doable, the question is for how long. That would be one very impressive bank of capacitors. And to turn a 00 into plasma would have some spectacular side effects, such as raining molten copper across a sizeable area. Just your reading glasses would indeed not be enough, there probably isn't any PPE that I would consider entirely safe other than sufficient distance from ground zero. But now I'm really curious. I have a spot welder that will do bursts of 5KA and that will happily throw the breaker every so many welds. 100KA sustained will be a fair engineering challenge.
Ah, that lego project... that was one I always wondered if I should have industrialized it but sourcing enough lego was a real problem.
Ho ho ho, you asked for it:
https://www.youtube.com/watch?v=OC7sNfNuTNU
Holy crap. That's a whole series of bad ideas extremely well executed. That guy probably has never seen what a lead acid battery can do when it explodes. He keeps hiding away from the hot metal but in the path of ~half of those batteries. Ignorance is bliss.
That's low voltage lightning :)
He was gifted an arch flash suit by the guys from Lightening on Demand :D
"The gift of life". Complete madness.
See also (as posted elsethread): https://www.youtube.com/watch?v=RoGbrgOhPes
Transitioning? It already happened decades ago. Only smaller scale/generic or less proficient "we bought all Dell and HP" use AC. At large scale it's been a ton of DC for literally decades. And for 70 years in telco and network gear.
That is about like aying the band AC DC had its revenge.....
can we stop vibe generating headlines?
The large brick you have on all your tech when you plug it in is the converter. AC works great for some applications, none of them really technical in nature.