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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

#371

Post by marcosdumay »

matt-p wrote: post #361
crote wrote: post #340

Earlier quoted context omitted.

The problem is that all of those DC devices don't operate on 48V either. The vast majority of chips require a 5V or lower input, so with a 48V DC supply you're still going to need a per-device PSU to do DC-DC conversion. In other words: no getting rid of power bricks. Efficiency isn't as straightforward either. You're still being fed by 120V/230V AC, so you're going to need some kind of centralized rectifier and down…

What if all homes had battery storage and or solar? You could then simply use it's rectifier as needed or direct 48v from the solar panels. That would be even more efficient than 230v.

I'm not sure converting the solar and battery to 48V, distributing it around, and converting it to the needed voltage at the point of use is any more efficient than inverting it into 230V and distributing it around.

Also, you'll need wires that 5 times thicker. Instead of needing a reasonably 1mm^2 for a normal 16A line, you'll need 5mm^2 for the same power.

Re: Data centers are transitioning from AC to DC

#372

Post by margalabargala »

ta9000 wrote: post #368
margalabargala wrote: post #280

Earlier quoted context omitted.

> my curiosity was about when we run out, because I didn’t know if we would run out You still seem to be missing the point. If you talk about "when we run out", you are presenting yourself as an expert stating "we will run out" and asking about the aftermath. It would be appropriate, and better received with more leniency, for you to ask whether we would run out.

That’s not rational. Why would I be asking such a simple question if I were an expert?

Exactly, that self-contradiction is part of why you were downvoted so heavily. Because you presented yourself to the world as irrational.

Re: Data centers are transitioning from AC to DC

#373

Post by marcosdumay »

bluGill wrote: post #218
tinyhitman wrote: post #197

Earlier quoted context omitted.

Do you also happen to why this is not more common? Must be useful for more than just telephone wires.

Most large scale systems are AC because transformers are relatively cheap, low maintenance, and efficient. When the system is AC ground makes no difference. With DC systems you generally think about the issues - which is why modern cars are negative ground. However other than cars most people never encounter power systems of any size - inside a computer the voltages and distances are usually small enough that it does…

> because transformers are relatively cheap, low maintenance, and efficient

And because that problem of galvanic corrosion the GGP talked about, and the mirror one of material aggregation don't happen. And it also makes switches more reliable.

Both are less dangerous on telephone lines. But are very important on electricity ones.

1 - It won't break your posts, but can easily short small contacts.

Re: Data centers are transitioning from AC to DC

#374

Post by marcosdumay »

myrmidon wrote: post #217
ta9000 wrote: post #160

Earlier quoted context omitted.

Does that mean when we run out of Ga there are no more LED TVs?

Sidenote: Whenever someone tells you that (vital) reserves of some ressource are going to run out soonish (implying drastic consequences), you should be extremely skeptical: Such predictions have an abysmal historic track record, because we tend to find workarounds both on the supply side (=> previously undiscovered reserves) as well as flexibility on the demand side (using substitutes). This applies historically for…

"Reserves" are the name of something that exists only at a set price. Change the price, and the reserves change too.

The people that rush to tell you that reserves are running out tend to omit what price they are talking about. That way of expressing oneself is normally called "a lie".

Re: Data centers are transitioning from AC to DC

#375

Post by HWR_14 »

bonzini wrote: post #341
HWR_14 wrote: post #241

Earlier quoted context omitted.

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 w…

I have done some projects that needed some generic dc-dc converters from aliexpress (eg stepping down 12v to 5 or 3.3) I alway treated the output of each step down as a pair of wires that share no ground. It sounds like that would be overkill if they were reputable but it's probably best to not try tying the grounds together.

I figured any happenstance from the multimeter that the grounds match was transitory and not to be trusted.

Re: Data centers are transitioning from AC to DC

#376

Post by shiroiuma »

rsync wrote: post #318
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…

"... 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…

These days, you should not be using transformers to power small loads at all, you should be using switching power supplies. They have negligible power draw when there's no load attached.

Re: Data centers are transitioning from AC to DC

#377

Post by mschuster91 »

bluGill wrote: post #286
mschuster91 wrote: post #223

Earlier quoted context omitted.

> Such predictions have an abysmal historic track record, because we tend to find workarounds both on the supply side (=> previously undiscovered reserves) as well as flexibility on the demand side (using substitutes). That's a classic example of the "preparedness paradox" [1]. When no one raises the alarm in time or it is being ignored, resources can go (effectively) exhausted before alternatives can be found, or co…

I've seen articles from the 1880s claiming oil will run out by 1890. 140 years latter... Yes we can run out of oil, but nobody really knows if or even when that will happen. Right now I'm guessing we won't run out because wind and solar is so much cheaper for most purposes everyone is shifting anyway - this will take decades to play out.

> Yes we can run out of oil, but nobody really knows if or even when that will happen.

We can run out of cheap and accessible oil very, very fast if the shitshow in MENA continues to escalate. Qatar already lost 20% of their LNG capacity in a single strike.

The US may have enough domestic oil production to sate its domestic demand, but the prices would still skyrocket even for them. Europe meanwhile, we're straight fucked here. Technically the oil hasn't run out, it's still in the oil fields of the journalist-butcher country and other sheikdoms, but that doesn't matter if it cannot be pumped out any more because the wells got blasted to pieces or if it cannot be transported thanks to Iranian mines, Europe is still running out of oil in practice.

Re: Data centers are transitioning from AC to DC

#378

Post by shiroiuma »

lillecarl wrote: post #364
matt-p wrote: post #361

Earlier quoted context omitted.

What if all homes had battery storage and or solar? You could then simply use it's rectifier as needed or direct 48v from the solar panels. That would be even more efficient than 230v.

We live on societies, switching from AC to DC because your low-power home appliances doesn't need AC makes no sense. Home power usage is dominated by heating and cooling not by your 45w laptop charger. DC infrastucture makes sense in highly specialised environments.... Like new gigawatt AI farms

Large home appliances probably mostly need DC power these days too. Look at clothes washers: they all have variable-speed reversing motors, so they're probably using brushless DC motors (which use motor drives that are fed with DC, and output variable-frequency and variable-amplitude sinusoidal waves to drive the motor). HVAC seems to be similar, with variable-speed motors and compressors.

I don't think that much stuff is left which actually needs AC power (usually to run an AC induction motor).

Re: Data centers are transitioning from AC to DC

#379

Post by shiroiuma »

eqvinox wrote: post #327
divbzero wrote: post #36

Earlier quoted context omitted.

Interesting, so this is why the phone line still worked when power was out across the whole town.

Yeah, it used to be that you could still make calls (particularly to emergency services) even in complete power outages, for as long as your local exchange has batteries for. (AFAIR that tended to be on the order of hours, but probably differs quite a bit across locations and regulatory domains/countries.) Another thing we lost in the age of VoIP landlines, but then again mobile towers also have batteries. Just don't…

Luckily, phone batteries and phone power consumption seem to have improved a lot in the last half-decade.

Re: Data centers are transitioning from AC to DC

#380

Post by shiroiuma »

samus wrote: post #320
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…

Things like washing machines, dryers, dishwashers, air conditioners, or fridges spend a lot of energy by running powerful electrical motors, which should benefit from AC. Everything else I can think of in a typical household is basically a mere heater that in principle works equally well with AC and DC of the correct voltage. Even computers can be said to mostly care about the correct voltage since AC->DC conversion…

>Things like washing machines, dryers, dishwashers, air conditioners, or fridges spend a lot of energy by running powerful electrical motors, which should benefit from AC.

No, they don't, not at all.

Most modern appliances have variable-speed motors these days. You can't do that by just connecting AC to a motor; you need a control board to generate the waveforms necessary to make the motor turn at the speed and direction you want. That control board has to be fed with DC power. (Source: I used to design BLDC motor control systems)

Only really simple appliances, like old-fashioned horribly-inefficient clothes dryers, still use AC induction motors, and those are mostly being phased out. (Bathroom fans also need AC; they're usually cheap synchronous reluctance motors.)

So it really doesn't matter much whether the incoming power is AC or DC these days, unless you have a bunch of ancient appliances that still use induction motors. If it's AC, it's going to be rectified and fed into a DC-to-DC converter to create the lower DC voltages needed. If it's a higher DC voltage, we can skip the rectification step and not worry much about ripple.

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