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"... 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!"

We installed 120 LED ceiling lights in our home circa 2020, all of which were run with high voltage (romex) and accompanied by 120 little transformer boxes that mount inside the ceiling next to them.

Later ...

We installed outdoor lighting with low voltage, outdoor rated wiring and powered by a 12V transformer[1] and I felt the same way you did: why did we use a mile of romex and install all of those little mini transformers when we could have powered the same lights with 12V and low voltage wire ?

I then learned that the energy draw of running the low-volt transformer all the time - especially one large enough to supply an entire house of lighting - would more than cancel out energy savings from powering lower voltage fixtures.

You don't have this problem with outdoor lighting because the entire transformer is on a switch leg and is off most of the time.

So ... I like the idea of removing a lot of unnecessary high voltage wire but it's not as simple as "just put all of your lights behind a transformer".

[1] https://residential.vistapro.com/lex-cms/product/262396-es-s...

> 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.

With double-conversion, generally yes.

I recently ran across the (patented?) concept of a delta conversion/transformer UPS that seems to eliminate/reduce the inefficiencies:

* https://dc.mynetworkinsights.com/what-are-the-different-type...

* a bit technical: https://www.youtube.com/watch?v=nn_ydJemqCk

* Figures 6 to 8 [pdf]: https://www.totalpowersolutions.ie/wp-content/uploads/WP1-Di...

The double-conversion only occurs when there's a 'hiccup' from utility power, otherwise if power is clean the double-conversion is not done at all so the inefficiencies don't kick in.

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.

The power connectors will be on the far side of the rack from the service side so shouldn’t be a problem for humans touching the third rail so to speak.

With that sort of voltage you should be able to use a capacitive or inductive sensor to activate a relay.

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.

An EV fast charger can do 1000V, so with a bit of logic that sounds doable.

Or maybe you can require technicians to be in full-protection electrical suits.

As long as you can control for fire, electrical safety seems like a temporary condition as robots and intelligent machines are cheaper and more available long term solution to hot swap blades in datacenter racks.

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.

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.

800V DC is definitely not "old".

[dead]

> 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.

Really you're down for over an hour a year? Unscheduled?

I recommend reading these two:

https://developer.nvidia.com/blog/nvidia-800-v-hvdc-architec...

https://blogs.nvidia.com/blog/gigawatt-ai-factories-ocp-vera...

almost everybody in the industry is embracing 800V DC mostly because of Vera Rubin and the increased electricity requirements.

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...

Immersion cooling was/is so fucking impractical it is only useful for very specific issues. If you talk to any engineer who worked on CRAY machines that were full of liquid freon, they'll tell how hard it is to do quick swaps of anything.

Its much cheaper, quicker and easier to use cooling blocks with leak proof quick connectors to do liquid cooling. It means you can use normal equipment, and don't need to re-re-enforce the floor.

A lot of "edge" stuff has 12/48v screw terminals, which I suspect is because they are designed to be telco compatible.

For megawatt racks though, I'm still not really sure.

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.

It is weird to me how far from the state of the art mainstream server equipment is. I can't imagine anything worse than AC-AC UPS, active PDUs, and redundant AC-DC supplies in each rack unit, but that's still how people are doing it.

These are GigaWatt data centers. For a single one they buy equipment by the container ship. Nothing is niche about it.

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.

Any appliance with strong motors should be more efficient with AC supply. But almost anything else can be regarded as a heater that doesn't care much as long as it is fed with the correct voltage. Which is actually the core issue.

A DC household would have to choose a trade-off between multiple lines with different voltages or fewer voltages that need to be adapted to the appliances. And we're right back at the AC situation, but worse since DC voltages are more difficult to change.

But consumers like datacenters can very well plan ahead and standardize on a single DC voltage. They already need beefy equipment to deal with interruptions, power sourges, non-sinus components, and brownouts, which already involves transformers, condensators, and DC conversion for battery storage. Therefore almost no additional equipment is required.

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.

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.

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.

Assuming you live in a "large" western home, it's impractical. Remember, Edison's first power grid operated at 110/220v DC to the home. If there was lower voltage (IE, 12 volts) going from the street to your walls, the line loss would be significant. It only works in RVs and shacks because the wires are short.

Thus, even if you had DC in the walls, it would be 100+ volts, and you'd still have conversion down to the lower voltages that electronics use. If you look at the comments in this thread from people who work in telco, they talk about how voltage enters equipment at -48V and is then further lowered.

It's called USB power delivery

home appliances have lower voltage, like 12V or 5V. The wire loss and heat would be a problem.

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.

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

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.

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.

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.

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.

because shorts and voltage loss are a real issue at that scale.

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.

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)

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.

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).

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.

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.

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.

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.

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

> 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

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.

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.

>- 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.

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.

>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

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.

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).

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.

Yeah this isnt an argument. It was far simpler to wrap some copper wire around a chunk of metal than it was to fire up a mosfet fabrication plant in the 1800's.

You can have the best idea in the world, but if you cant manufacture it you're SOL.

Title is clickbait. Edison is not mentioned anywhere else in article. I am okay with it.

Ok, we've deposed Edison from the title above.

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.

But there was an equivalent: a mechanical switch. Or an electromechanical relay. Or a spinning wheel with electrical contacts.

Note that one could email the mods to de-clickbait/enrage the title, especially with such a concrete point as this comment’s. (I haven’t done so as TIL is a poor basis for such an argument.)

Agree, clickbait.

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.

yes, this! thank you good post

> 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.