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Data centers are transitioning from AC to DC

337 points by jnord 7mo ago

deleted 7mo ago
[deleted]
shdudns 7mo ago
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
- shiroiuma 7mo ago
  >- 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.
  - shdudns 7mo ago
    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.
    - bigiain 7mo ago
      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.
      - jacquesm 7mo ago
        Even your monster cable? ;)
        bigiain 7mo ago
        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!_
        jacquesm 7mo ago
        It's almost worth the experiment and your cables are a sacrifice I'm willing to make. For science, of course.
        bigiain 7mo ago
        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. :-)
        jacquesm 7mo ago
        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.
- adamking 7mo ago
  > 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
  - shdudns 7mo ago
    "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.
- prezk 7mo ago
  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.
  - bigiain 7mo ago
    > 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...)
- hrmtst93837 7mo ago
  [flagged]
bandrami 7mo ago
I stg if I see the kids talk about Westinghouse being batterymogged I'm leaving the Internet
Green-Jeans23 7mo ago
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otterley 7mo ago
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-instructions-for-a-dc-power-supply-unit https://www.dell.com/support/kbdoc/en-us/000221234/wiring-in...
- bluGill 7mo ago
  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.
  - mjuarez 7mo ago
    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.
    - SAI_Peregrinus 7mo ago
      Lots of amplifier circuits need a bipolar supply: both positive and negative voltages with respect to ground.
    - yostrovs 7mo ago
      Check out older English cars.
    - bluGill 7mo ago
      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?)
    - servo_sausage 7mo ago
stego-tech 7mo ago
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.
- arijun 7mo ago
  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.
- otterley 7mo ago
  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/publications/dc-power-distribution-and-grounding-in-the-5esstm-switch/ https://www.nokia.com/bell-labs/publications-and-media/publi...
  - stego-tech 7mo ago
    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”.
hristov 7mo ago
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.
- arijun 7mo ago
  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).
  - deleted 7mo ago
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  - themafia 7mo ago
    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.
- bluGill 7mo ago
  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.
- jacquesm 7mo ago
  Agreed, for the IEEE to go down this route is more than a little weird.
sghiassy 7mo ago
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
- cjbgkagh 7mo ago
  https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current
- adgjlsfhk1 7mo ago
  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.
  - arijun 7mo ago
    > 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.
    - adgjlsfhk1 7mo ago
      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)
umvi 7mo ago
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.
- bluGill 7mo ago
  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.
- throw0101d 7mo ago
  > 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_implementation https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i... * https://www.usailighting.com/poe-lighting https://www.usailighting.com/poe-lighting
  - elcritch 7mo ago
    And pay $60 per Ethernet POE+ light bulb.
    - throw0101d 7mo ago
      > And pay $60 per Ethernet POE+ light bulb. In the commercial/industrial space this may be worth it: how long do these bulbs last? how much (per hour (equivalent)) do you pay your facilities folks? how much time does it take for employees or tenants to report an outage and for your folks to get a ladder (or scissor lift) to change the bulb?
- fortran77 7mo ago
  Do you want your house to burn down? Lower voltages for LED lights mean higher current.
adrr 7mo ago
Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.
- bandrami 7mo ago
  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)
  - 747fulloftapes 7mo ago
    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 https://www.amazon.com/dp/B0FD7PHB7Y or https://www.amazon.com/dp/B01IBIC1XG 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.
- ericd 7mo ago
  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.
Aloisius 7mo ago
This article seems to imply that 800V DC is high-voltage DC, but that seems quite low.
- MathMonkeyMan 7mo ago
  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.
- bigiain 7mo ago
  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 https://www.youtube.com/watch?v=RoGbrgOhPes
KnuthIsGod 7mo ago
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 )
- jacquesm 7mo ago
  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.
  - manwe150 7mo ago
    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?
    - jacquesm 7mo ago
      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.
skullone 7mo ago
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.
b00ty4breakfast 7mo ago
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!
neoCrimeLabs 7mo ago
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.
- jeffbee 7mo ago
  It's obviously not new. ±400VDC architecture was presented at Open Compute last year, which is a fair indicator that the presenter had put it into practice at least 5 years prior to disclosing it. 48VDC distribution within a rack, and 48-to-1V direct regulators for CPUs, were both contributed to OCP 7 years ago, at which point they were both old hat. And 48VDC telco junk is, of course, totally ancient.
Animats 7mo ago
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/ai-factory-800vdc-reference-designs https://library.grid.gevernova.com/white-papers-case-studies... [2] https://www.youtube.com/watch?v=CQOreYMhe-M& https://www.youtube.com/watch?v=CQOreYMhe-M& [3] https://filecenter.deltaww.com/Products/download/2510/202510160921259104.pdf https://filecenter.deltaww.com/Products/download/2510/202510...
- rdtsc 7mo ago
  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.
  - Animats 7mo ago
    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.
amluto 7mo ago
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.
saltyoldman 7mo ago
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.
pugchat 7mo ago
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fredgrott 7mo ago
That is about like aying the band AC DC had its revenge..... can we stop vibe generating headlines?
flossly 7mo ago
AC is also waaaay safer for households: since the power drop to to zero 100x (50Hz) per second switches are cheaper and safer, and electrocution is less likely to happen.
pjdesno 7mo ago
90% of the power in our academic data center goes 13.8kV 3-phase -> 400v 3-phase, and then the machines run directly from one leg to neutral (230v). One transformer step, no UPS losses, and the server power supplies are more efficient at EU voltages. But what about availability? If you ask most of our users whether they’d prefer 4 9s of availability or 10% more money to spend on CPUs, they choose the CPUs. We asked them. There are a lot of availability-insensitive workloads in the commercial world, as well, like AI training. What matters in those cases is how much computing you get done by the end of the month, and for a fixed budget a UPS reduces this number.
- chromacity 7mo ago
  > and then the machines run directly from one leg to neutral (230v) And then every machine has a switching power supply to convert this to low-voltage DC, and then probably random point-of-load converters in various places (DC -> AC -> DC again) for stuff like the CPU / GPU core, RAM, etc. Each of these stages may be ~95% efficient with optimal load, but the losses add up, and get a lot worse outside a narrow envelope.
  - Dylan16807 7mo ago
    Yes, but it's not like any other layouts avoid those issues. You could feed your servers off fat 12/24/48 volt supplies but with how much power a modern server can pull you're already converting in bulk even if you don't do that, limiting the potential advantages. For running CPU/GPU/RAM, there is no other option. When you need hundreds of amps at 1-2 volts, you convert that centimeters away if at all possible. A datacenter using DC distribution is still using high voltages and stepping them down in layers. The hassle it avoids is in other aspects of power delivery.
- poemxo 7mo ago
  Really you're down for over an hour a year? Unscheduled?
  - ProllyInfamous 7mo ago
gwbas1c 7mo ago
Anyone notice that 400V and 800V are also used in EV battery architecture? I wonder if there's any sharing of technology?
notorandit 7mo ago
It does make a whole lot is sense. The amount of energy you loose to convert AC to DC can be humongous . And useless if you produce your own power (normally already in DC).
sholladay 7mo ago
Is there anything left in a modern home that really needs or is better on AC? We have some old ceiling and exhaust fans, but I know those can be replaced. Our refrigerator is AC, but extended family with an off-grid home has a DC refrigerator that cycles way less, probably due to multiple design factors but I’m sure the lack of transformer heat is part of it. I’m not as sure about laundry machine or oven/cooktop options but I believe those are also running on DC in the off-grid home without inverters. Most of these AC appliances also have transformers in them anyway for the control boards. It seems kind of insane to me that we are still doing things this way.
- Retric 7mo ago
  Of grid homes are vastly more concerned with the energy efficiency of their appliances and thus DC refrigerators generally have more insulation. Most AC customers prefer more internal volume for food over slightly increased efficiency. AC motors are using way more power than the puddly control boards in most home appliances. So you lose a little efficiency on conversion but being 80% efficient doesn’t matter much when it’s 1-5% of the devices energy budget. You generally gain way more than that from similarly priced AC motors being more efficient.
  - sholladay 7mo ago
    I agree with everything you said, except it seems like a false dichotomy. We can clearly build DC refrigerators with more or less insulation. We can clearly build them large or small. If you want to prioritize volume, then surely you could do that with DC. Right? I know that a long time ago DC-to-DC voltage converters were very large in size, which meant AC would win on space efficiency. But unless I’m mistaken, that’s no longer the case. Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator?
    - Retric 7mo ago
      > Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator? Sure, but it’s important to separate what could be built from what is being built based on consumer preferences and buying habits. The average refrigerator could be significantly quieter, but how often do people actually listen to what they are buying? People buying Tesla’s didn’t test drive the actual car they were buying so the company deprioritized panel gaps. And so forth, companies optimize in ways that maximize their profits not arbitrary metrics.
tibbydudeza 7mo ago
Have a solar system at home and from the panels it is DC into the batteries but then the inverter needs to convert it to 220V/50Hz AC for home use.
everdrive 7mo ago
"How can we turn this technical story into a story about people and their conflicts?"
BorisMelnik 7mo ago
its really wild at all the AC to DC changes. for those non electric engineers / hardware hackers (like myself) one of the biggest "examples" I've seen of this has been ceiling fans. Installing a ceiling fan used to be treacherous and so heavy. Also loud and buzzy after installed. Now the fans in these things are so lightweight and easy. seeing the same in many more areas (lighting, etc)
- hamdingers 7mo ago
  Would love to see more mainstream DC lighting options and an updated code to match. I just finished a remodel of my workshop and blew over a hundred bucks on 14/2 for a 15 amp lighting circuit that is unlikely to ever see more than a 1 amps load. The irony is all the recessed lights I picked out are DC, they all have little AC-DC boxes hanging off them using a proprietary connector. If I hadn't needed to pass a rough-in inspection going all DC would've been trivial.
p0w3n3d 7mo ago
Hard as a rock! Well it's harder than a rock!
Xcelerate 7mo ago
I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment tends to come with built-in AC-DC conversion). Then I started routing ethernet with PoE throughout my house and observed that other than a few large appliances, the majority of powered devices in a typical home in 2026 could be supplied via PoE DC current as well! Lighting, laptops, small/medium televisions. The current PoE spec allows up to 100 W, which covers like 80% of the powered devices in most homes. I think it would make more sense to have fewer AC outlets around the modern house and many more terminals for PoE instead (maybe with a more robust connector than RJ45). I wonder what sort of energy efficiency improvements this would yield. No more power bricks all over the place either.
- estimator7292 7mo ago
  I think we're slowly, slowly coming around to the idea of domestic DC distribution. The vast majority of consumer electronics would be perfectly happy to consume 12v. It's cheaper, safer, more efficient. Less design work and certification on inbuilt AC adapters. I think it's highly unlikely we'll see mass scale retrofits, but if enough momentum builds up, I can see it as a great bonus feature for new builds. I got lucky with my house and every room has a dedicated phone line meeting at a distribution panel (a couple of 2x4s with screw terminals) built in the 50s. I'm in the process of converting it to light duty DC power. The wiring is only good for an amp or two, but at 48v that's still significant power transmission.
  - zahlman 7mo ago
    > I think it's highly unlikely we'll see mass scale retrofits, but if enough momentum builds up, I can see it as a great bonus feature for new builds. I imagine rooftop solar could also source DC for the house directly (or via a battery), before hitting the inverter... ? The main problem I see is educating consumers. Maybe that starts with a standard for DC outlets and plugs that can't be confused with AC... ? (Now I'm imagining desktop computers with much simpler power supplies; but you'd presumably have to wire for dozens of amps incoming...)
sbhooley 7mo ago
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wolvoleo 7mo ago
Well they're kinda transitioning back. When I grew up most DCs (and telecom facilities) were running on 48V DC. Easy to back up with a big room full of lead acid batteries (just keep an eye on that hydrogen gas lol)
tezza 7mo ago
They were Thunderstruck?
wrecked_em 7mo ago
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Rapzid 7mo ago
I somehow made it to middle age without making the connection from AC/DC to electricity. Or I never thought about it till now.
redm 7mo ago
I guess we've come full circle. It was just 20 years ago that my datacenters gutted DC in favor of AC.
mikewarot 7mo ago
Ok, this is just plain nuts. 800 volts DC, at the megawatt power supply levels, implies fault impulses of more than a megajoule. Google tells me that's about 2 hand grenades worth of boom. That's an optimistic lower bound. The resulting copper plasma cloud is a burn and inhalation hazard, along with the overpressure. Let's say you get a 10 kiloamp fault current, this will then induce voltages everywhere you don't want it to go. If all the interconnects are fiber, that's really not a problem, but you have to have everything EMP shielded if you don't want boards popping randomly after such an event. The "efficiency" of removing the extra power conversions also removes filtering and surge suppression. It's entirely possible that one power supply over-voltage takes out half of your racks. The MOSFETs used tend to fail closed instead of open, making failures far worse than a simple outage. Very smart people are making very smart mistakes.
ykonstant 7mo ago
Soon they will replace all the iron railings with maiden.

337 points by jnord 7mo ago

deleted 7mo ago

[deleted]

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

shiroiuma 7mo ago
>- 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.
- shdudns 7mo ago
  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.
  - bigiain 7mo ago
    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.
    - jacquesm 7mo ago
      Even your monster cable? ;)
      - bigiain 7mo ago
        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!_
        jacquesm 7mo ago
        It's almost worth the experiment and your cables are a sacrifice I'm willing to make. For science, of course.
        bigiain 7mo ago
        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. :-)
        jacquesm 7mo ago
        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.
adamking 7mo ago
> 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
- shdudns 7mo ago
  "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.
prezk 7mo ago
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.
- bigiain 7mo ago
  > 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...)
hrmtst93837 7mo ago
[flagged]

bandrami 7mo ago

I stg if I see the kids talk about Westinghouse being batterymogged I'm leaving the Internet

Green-Jeans23 7mo ago

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otterley 7mo ago

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-instructions-for-a-dc-power-supply-unit https://www.dell.com/support/kbdoc/en-us/000221234/wiring-in...

bluGill 7mo ago
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.
- mjuarez 7mo ago
  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.
  - SAI_Peregrinus 7mo ago
    Lots of amplifier circuits need a bipolar supply: both positive and negative voltages with respect to ground.
  - yostrovs 7mo ago
    Check out older English cars.
  - bluGill 7mo ago
    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?)
  - servo_sausage 7mo ago

stego-tech 7mo ago

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.

arijun 7mo ago
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.
otterley 7mo ago
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/publications/dc-power-distribution-and-grounding-in-the-5esstm-switch/ https://www.nokia.com/bell-labs/publications-and-media/publi...
- stego-tech 7mo ago
  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”.

hristov 7mo ago

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.

arijun 7mo ago
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).
- deleted 7mo ago
  [deleted]
- themafia 7mo ago
  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.
bluGill 7mo ago
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.
jacquesm 7mo ago
Agreed, for the IEEE to go down this route is more than a little weird.

sghiassy 7mo ago

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

cjbgkagh 7mo ago
https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current
adgjlsfhk1 7mo ago
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.
- arijun 7mo ago
  > 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.
  - adgjlsfhk1 7mo ago
    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)

umvi 7mo ago

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.

bluGill 7mo ago
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.
throw0101d 7mo ago
> 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_implementation https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i... * https://www.usailighting.com/poe-lighting https://www.usailighting.com/poe-lighting
- elcritch 7mo ago
  And pay $60 per Ethernet POE+ light bulb.
  - throw0101d 7mo ago
    > And pay $60 per Ethernet POE+ light bulb. In the commercial/industrial space this may be worth it: how long do these bulbs last? how much (per hour (equivalent)) do you pay your facilities folks? how much time does it take for employees or tenants to report an outage and for your folks to get a ladder (or scissor lift) to change the bulb?
fortran77 7mo ago
Do you want your house to burn down? Lower voltages for LED lights mean higher current.

adrr 7mo ago

Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.

bandrami 7mo ago
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)
- 747fulloftapes 7mo ago
  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 https://www.amazon.com/dp/B0FD7PHB7Y or https://www.amazon.com/dp/B01IBIC1XG 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.
ericd 7mo ago
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.

Aloisius 7mo ago

This article seems to imply that 800V DC is high-voltage DC, but that seems quite low.

MathMonkeyMan 7mo ago
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.
bigiain 7mo ago
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 https://www.youtube.com/watch?v=RoGbrgOhPes

KnuthIsGod 7mo ago

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 )

jacquesm 7mo ago
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.
- manwe150 7mo ago
  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?
  - jacquesm 7mo ago
    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.

skullone 7mo ago

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.

b00ty4breakfast 7mo ago

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!

neoCrimeLabs 7mo ago

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.

jeffbee 7mo ago
It's obviously not new. ±400VDC architecture was presented at Open Compute last year, which is a fair indicator that the presenter had put it into practice at least 5 years prior to disclosing it. 48VDC distribution within a rack, and 48-to-1V direct regulators for CPUs, were both contributed to OCP 7 years ago, at which point they were both old hat. And 48VDC telco junk is, of course, totally ancient.

Animats 7mo ago

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/ai-factory-800vdc-reference-designs https://library.grid.gevernova.com/white-papers-case-studies... [2] https://www.youtube.com/watch?v=CQOreYMhe-M& https://www.youtube.com/watch?v=CQOreYMhe-M& [3] https://filecenter.deltaww.com/Products/download/2510/202510160921259104.pdf https://filecenter.deltaww.com/Products/download/2510/202510...

rdtsc 7mo ago
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.
- Animats 7mo ago
  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.

amluto 7mo ago

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.

saltyoldman 7mo ago

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.

pugchat 7mo ago

[dead]

fredgrott 7mo ago

That is about like aying the band AC DC had its revenge..... can we stop vibe generating headlines?

flossly 7mo ago

AC is also waaaay safer for households: since the power drop to to zero 100x (50Hz) per second switches are cheaper and safer, and electrocution is less likely to happen.

pjdesno 7mo ago

90% of the power in our academic data center goes 13.8kV 3-phase -> 400v 3-phase, and then the machines run directly from one leg to neutral (230v). One transformer step, no UPS losses, and the server power supplies are more efficient at EU voltages. But what about availability? If you ask most of our users whether they’d prefer 4 9s of availability or 10% more money to spend on CPUs, they choose the CPUs. We asked them. There are a lot of availability-insensitive workloads in the commercial world, as well, like AI training. What matters in those cases is how much computing you get done by the end of the month, and for a fixed budget a UPS reduces this number.

chromacity 7mo ago
> and then the machines run directly from one leg to neutral (230v) And then every machine has a switching power supply to convert this to low-voltage DC, and then probably random point-of-load converters in various places (DC -> AC -> DC again) for stuff like the CPU / GPU core, RAM, etc. Each of these stages may be ~95% efficient with optimal load, but the losses add up, and get a lot worse outside a narrow envelope.
- Dylan16807 7mo ago
  Yes, but it's not like any other layouts avoid those issues. You could feed your servers off fat 12/24/48 volt supplies but with how much power a modern server can pull you're already converting in bulk even if you don't do that, limiting the potential advantages. For running CPU/GPU/RAM, there is no other option. When you need hundreds of amps at 1-2 volts, you convert that centimeters away if at all possible. A datacenter using DC distribution is still using high voltages and stepping them down in layers. The hassle it avoids is in other aspects of power delivery.
poemxo 7mo ago
Really you're down for over an hour a year? Unscheduled?
- ProllyInfamous 7mo ago

gwbas1c 7mo ago

Anyone notice that 400V and 800V are also used in EV battery architecture? I wonder if there's any sharing of technology?

notorandit 7mo ago

It does make a whole lot is sense. The amount of energy you loose to convert AC to DC can be humongous . And useless if you produce your own power (normally already in DC).

sholladay 7mo ago

Is there anything left in a modern home that really needs or is better on AC? We have some old ceiling and exhaust fans, but I know those can be replaced. Our refrigerator is AC, but extended family with an off-grid home has a DC refrigerator that cycles way less, probably due to multiple design factors but I’m sure the lack of transformer heat is part of it. I’m not as sure about laundry machine or oven/cooktop options but I believe those are also running on DC in the off-grid home without inverters. Most of these AC appliances also have transformers in them anyway for the control boards. It seems kind of insane to me that we are still doing things this way.

Retric 7mo ago
Of grid homes are vastly more concerned with the energy efficiency of their appliances and thus DC refrigerators generally have more insulation. Most AC customers prefer more internal volume for food over slightly increased efficiency. AC motors are using way more power than the puddly control boards in most home appliances. So you lose a little efficiency on conversion but being 80% efficient doesn’t matter much when it’s 1-5% of the devices energy budget. You generally gain way more than that from similarly priced AC motors being more efficient.
- sholladay 7mo ago
  I agree with everything you said, except it seems like a false dichotomy. We can clearly build DC refrigerators with more or less insulation. We can clearly build them large or small. If you want to prioritize volume, then surely you could do that with DC. Right? I know that a long time ago DC-to-DC voltage converters were very large in size, which meant AC would win on space efficiency. But unless I’m mistaken, that’s no longer the case. Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator?
  - Retric 7mo ago
    > Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator? Sure, but it’s important to separate what could be built from what is being built based on consumer preferences and buying habits. The average refrigerator could be significantly quieter, but how often do people actually listen to what they are buying? People buying Tesla’s didn’t test drive the actual car they were buying so the company deprioritized panel gaps. And so forth, companies optimize in ways that maximize their profits not arbitrary metrics.

tibbydudeza 7mo ago

Have a solar system at home and from the panels it is DC into the batteries but then the inverter needs to convert it to 220V/50Hz AC for home use.

everdrive 7mo ago

"How can we turn this technical story into a story about people and their conflicts?"

BorisMelnik 7mo ago

its really wild at all the AC to DC changes. for those non electric engineers / hardware hackers (like myself) one of the biggest "examples" I've seen of this has been ceiling fans. Installing a ceiling fan used to be treacherous and so heavy. Also loud and buzzy after installed. Now the fans in these things are so lightweight and easy. seeing the same in many more areas (lighting, etc)

hamdingers 7mo ago
Would love to see more mainstream DC lighting options and an updated code to match. I just finished a remodel of my workshop and blew over a hundred bucks on 14/2 for a 15 amp lighting circuit that is unlikely to ever see more than a 1 amps load. The irony is all the recessed lights I picked out are DC, they all have little AC-DC boxes hanging off them using a proprietary connector. If I hadn't needed to pass a rough-in inspection going all DC would've been trivial.

p0w3n3d 7mo ago

Hard as a rock! Well it's harder than a rock!

Xcelerate 7mo ago

I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment tends to come with built-in AC-DC conversion). Then I started routing ethernet with PoE throughout my house and observed that other than a few large appliances, the majority of powered devices in a typical home in 2026 could be supplied via PoE DC current as well! Lighting, laptops, small/medium televisions. The current PoE spec allows up to 100 W, which covers like 80% of the powered devices in most homes. I think it would make more sense to have fewer AC outlets around the modern house and many more terminals for PoE instead (maybe with a more robust connector than RJ45). I wonder what sort of energy efficiency improvements this would yield. No more power bricks all over the place either.

estimator7292 7mo ago
I think we're slowly, slowly coming around to the idea of domestic DC distribution. The vast majority of consumer electronics would be perfectly happy to consume 12v. It's cheaper, safer, more efficient. Less design work and certification on inbuilt AC adapters. I think it's highly unlikely we'll see mass scale retrofits, but if enough momentum builds up, I can see it as a great bonus feature for new builds. I got lucky with my house and every room has a dedicated phone line meeting at a distribution panel (a couple of 2x4s with screw terminals) built in the 50s. I'm in the process of converting it to light duty DC power. The wiring is only good for an amp or two, but at 48v that's still significant power transmission.
- zahlman 7mo ago
  > I think it's highly unlikely we'll see mass scale retrofits, but if enough momentum builds up, I can see it as a great bonus feature for new builds. I imagine rooftop solar could also source DC for the house directly (or via a battery), before hitting the inverter... ? The main problem I see is educating consumers. Maybe that starts with a standard for DC outlets and plugs that can't be confused with AC... ? (Now I'm imagining desktop computers with much simpler power supplies; but you'd presumably have to wire for dozens of amps incoming...)

sbhooley 7mo ago

[dead]

wolvoleo 7mo ago

Well they're kinda transitioning back. When I grew up most DCs (and telecom facilities) were running on 48V DC. Easy to back up with a big room full of lead acid batteries (just keep an eye on that hydrogen gas lol)

tezza 7mo ago

They were Thunderstruck?

wrecked_em 7mo ago

[dead]

Rapzid 7mo ago

I somehow made it to middle age without making the connection from AC/DC to electricity. Or I never thought about it till now.

redm 7mo ago

I guess we've come full circle. It was just 20 years ago that my datacenters gutted DC in favor of AC.

mikewarot 7mo ago

Ok, this is just plain nuts. 800 volts DC, at the megawatt power supply levels, implies fault impulses of more than a megajoule. Google tells me that's about 2 hand grenades worth of boom. That's an optimistic lower bound. The resulting copper plasma cloud is a burn and inhalation hazard, along with the overpressure. Let's say you get a 10 kiloamp fault current, this will then induce voltages everywhere you don't want it to go. If all the interconnects are fiber, that's really not a problem, but you have to have everything EMP shielded if you don't want boards popping randomly after such an event. The "efficiency" of removing the extra power conversions also removes filtering and surge suppression. It's entirely possible that one power supply over-voltage takes out half of your racks. The MOSFETs used tend to fail closed instead of open, making failures far worse than a simple outage. Very smart people are making very smart mistakes.

ykonstant 7mo ago

Soon they will replace all the iron railings with maiden.