>- 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.

> 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.

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.

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...

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.

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.

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).

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.

Agreed, for the IEEE to go down this route is more than a little weird.

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...

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.

> 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

Do you want your house to burn down? Lower voltages for LED lights mean higher current.

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.

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

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.

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)

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.

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).

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.

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.

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.

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.

Quite low compared to a power utility's HVDC, but quite high compared to the 5/12/24 V output of most AC/DC converters used for electronics.

I 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 proposed - 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

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.