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Data centers are transitioning from AC to DC

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Re: Data centers are transitioning from AC to DC

#341

Post by bonzini »

HWR_14 wrote: post #241
crote wrote: post #188

Earlier quoted context omitted.

Because the chassis is connected to ground (as in, a literal grounding rod hammered into the soil) and by definition your 0V reference point. The crucial difference is the direction in which the current is flowing: is it going "in to", or "out of" a hot wire? This becomes rather important when those wires are leaving the building and are buried underground for miles, where they will inevitably develop minor faults. W…

So, there is a true value for 0? Does that mean when you have electronics and use multiple dc-dc converters all the inputs and outputs share the same ground, it's not just the values for that pair of wires? And if I want to use a telephone on an incorrectly wired 48dc circuit, I could switch the positive and negative wires, as long as the circuit in the telephone is isolated and never touches ground? Thanks. Somehow…

> all the inputs and outputs share the same ground, it's not just the values for that pair of wires?

No, it depends on the converter. There are converters that leave 160V on the DC power rail for a 110V AC input, and 155V on the DC "ground" rail.

They are economic and you could find then when galvanic isolation is at least in theory not important, but they're terribly unsafe when used on PCBs that people might muck with.

If you have some "normal" converters and some of this kind, sharing the ground would be quite dangerous.

Re: Data centers are transitioning from AC to DC

#342

Post by kjs3 »

pdpi wrote: post #337
Xcelerate wrote: post #311

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…

> maybe with a more robust connector than RJ45 USB-C could be that connector, using USB-PD instead of PoE. Though I'm not sure I'd want to need that much smarts for every single power outlet.

Considering the number of times I've sheared off a USB-C connector vs ethernet, I wouldn't consider USB-C to be more robust than RJ45. YMMV.

Re: Data centers are transitioning from AC to DC

#343

Post by [deleted] »

jacquesm wrote: post #98
manwe150 wrote: post #93

Earlier quoted context omitted.

I suppose that still begs the question somewhat, since the US does have 240V (2 phase) already driving many appliances. Why hasn’t it ever become standard for luxury kitchens to have a European-style outlet for use with a European kettle? I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?

Well, as you say, it would not be according to code and the insurance company might have something to say about it. It's also single phase but not quite the way you do it in the USA, it would be a neutral and a phase whereas in the USA I think it is 2x110. Finally, it's 50 Hz rather than 60 which would work fine for resistive loads but not so well for inductive ones such as transformers and motors. In all likely not…

[deleted]

Re: Data centers are transitioning from AC to DC

#344

Post by zahlman »

wincy wrote: post #157
jacquesm wrote: post #53

Earlier quoted context omitted.

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…

I just wish I could run my air conditioner and my desktop computer at the same time without flipping the breaker. The RTX 5090 is a space heater and will easily peg at the 600W it’s rated for, and so with that and an air conditioner window unit, I have to run a long cable from another unused room if I want to do anything that stresses the video card.

If you're running an air conditioner and a "space heater" at the same time it might be worth reconsidering your priorities.

I can watch 1080p video on YouTube and it runs in an up-to-date web browser using less than 50% CPU on 12-year-old hardware with 8GB of RAM and a graphics card that was a budget option at the time (my searches indicate it draws at most 80W, though it expects a 500W PSU for some reason).

Re: Data centers are transitioning from AC to DC

#345

Post by matt-p »

Xcelerate wrote: post #311

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…

One of the main problems is conductor size. I wish we could access 22AWG copper in cheap and cheerful cat5e/cat6 format cable. 24AWG cat5e, sometimes CCA is not great for doing large amounts of POE.

Re: Data centers are transitioning from AC to DC

#346

Post by sholladay »

zarzavat wrote: post #314
sholladay wrote: post #302

Earlier quoted context omitted.

What qualifies as a strong motor here? Are you comparing to a brushed DC motor? Do you think a washer/dryer would have worse overall efficiency with a BLDC in a DC home compared to what we have today? If so, that’s news to me. Where can I learn more about that? The trade-off between, say, one (relatively) high voltage DC bus throughout the home vs many branches with lower discrete voltages is indeed a problem. With A…

Probably 90% of my devices run 5V DC or similar, but you can't run that through a home so you're back to needing AC. If you're going to have AC and DC then you might as well just have AC.

> Probably 90% of my devices run 5V DC or similar,

Indeed. And that’s quite normal. Our electrical system should serve our modern needs.

> but you can't run that through a home

5V might be too low for that length of wire. But you could most definitely have a low voltage line in your house that we could design around, maybe 12V. Electric vehicles are moving towards 48V for accessories. It seems like lack of a standard is holding us back more than anything else.

Or we could just keep doing 120V in the walls, with a DC supply. Modern DC-to-DC voltage converters are very efficient and small. But maybe I’m wrong. A lot of people seem to believe they are still not good enough yet for such a change to make sense.

> If you're going to have AC and DC then you might as well just have AC.

I arrive at the opposite conclusion. Most things are natively DC. So therefore, power in the walls should be DC and we should covert it to AC near the endpoint where necessary.

Re: Data centers are transitioning from AC to DC

#347

Post by Dylan16807 »

eqvinox wrote: post #324
rsync wrote: post #318

Earlier quoted context omitted.

"... 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 lighti…

> 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. That's not a constraint of physics, you can absolutely build a DC power supply that is efficient in a wide load range. (Worst case it might involve paralleling and switching between m…

> But of course something like that is more expensive...

More expensive than an inefficient unit, but it should still be a lot cheaper than 120 separate units, right?

And I expect one big fat unit to do a better job of smoothing out voltage and avoiding flicker than a bunch of single-light units. Especially because the output capacitors are sized for the entire system, but you'll rarely have all the lights on at the same time.

Though for efficiency I'd think you'd want 48v and not 12v.

Re: Data centers are transitioning from AC to DC

#348

Post by elif »

elif wrote: post #291
Animats wrote: post #118

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 mechan…

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.

Dear downvoters: softbank has been optimizing their datacenters for robotic technicians since 2020.

They are about to have fully human free datacenters by the end of this year.

When you are designing long term goals with datacenters, as I explicitly mentioned talking about, you can't ignore automation.

Re: Data centers are transitioning from AC to DC

#350

Post by balamatom »

wil421 wrote: post #211
boomskats wrote: post #202

Earlier quoted context omitted.

I mean yeah, but it's not like the guy's 'horrible attitude' came from nowhere. He naiively romanticised migrating to the US thinking the game was about scientific progress rather than capital, and so he got repeatedly screwed over by almost everyone around him for decades. If I was in his position I'm not sure I'd have taken it as well as he did.

There’s no way he suddenly developed autism or whatever mental illness plagued him upon arrival to American. Like most absolute geniuses he struggled in other areas. He said he had visions as a child.

But there is: his neurotype suddenly became considered "whatever mental illness" upon arrival in Eugenicsland.
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