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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

#361

Post by matt-p »

crote wrote: post #340
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…

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.

Re: Data centers are transitioning from AC to DC

#362

Post by bigiain »

swamp_donkey wrote: post #158
jacquesm wrote: post #96

Earlier quoted context omitted.

I have a couple of those narrow escapes one of which led me to put a significant chunk of Eastern Amsterdam out of power. Another involved Beryllium oxide. 9 lives are barely enough.

Ah! Perhaps you are a member of the gigawatt club? Eligible for entry once you have accidentally tripped off 1000 MW of load or generation! No sweeping that under the table

Somehow I simultaneously desperately want to be in that club, and never want to be responsible for an event that would let me join that club...

Re: Data centers are transitioning from AC to DC

#364

Post by lillecarl »

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.

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

Re: Data centers are transitioning from AC to DC

#365

Post by Dylan16807 »

crote wrote: post #328
jcalvinowens wrote: post #246

Earlier quoted context omitted.

> When the system is AC ground makes no difference. With AC it's about where the ground is attached along the length of the transformer secondary. In the EU they ground one of the ends of the secondary, in the US we ground the center point. I don't get to say this very often ... but the US way is objectively safer with no downside: 99% of human shocks are via ground, and it halves the voltage to ground (120V vs 240V)…

In the EU it is quite common for houses to have three-phase power. If you squint a bit, the grounded neutral of the Y transformer isn't entirely unlike the grounded center tap in the US. The voltage is a lot higher, of course!

> If you squint a bit, the grounded neutral of the Y transformer isn't entirely unlike the grounded center tap in the US.

Yes, but you only get the safety benefit on three phase equipment.

In the US there aren't a lot of 240V plugs, but if you get some installed you can get the safety benefits with plain old consumer goods.

Re: Data centers are transitioning from AC to DC

#366

Post by [deleted] »

margalabargala wrote: post #280
ta9000 wrote: post #262

Earlier quoted context omitted.

Yes, my curiosity was about when we run out, because I didn’t know if we would run out. That was the whole point of the question. Have some leniency, we’re not all experts about everything.

> 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.

[deleted]

Re: Data centers are transitioning from AC to DC

#367

Post by ssl-3 »

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.

That'd be neat. But there's no standard for voltage for home solar: The batteries might be 12, 24, 48v, 60v, or even much more. Meanwhile, the panel arrays commonly output anything as low as 0V and up to ~600V. There's not much for rules and norms here.

Even if we were to standardize a low (But, sure -- we can play it out. So let's say we have an in-home 48VDC distribution standard and decide that this is the path forward and we enshrine it in law.

We need to convert whatever the solar system has available to 48VDC. Then, we need to distribute that 48VDC using a completely separate network of cabling. Finally, we still need to convert 48VDC to whatever it is that devices can actually use.

That's not representative of a reduction in steps, or an increase in efficiency.

That is instead just an increase in installed infrastructure expense, and a decrease in device compatibility. It takes what we have, which is simply universal (at least within any given geographical area) and adds complexity.

And for what? What's the perceived benefit?

Re: Data centers are transitioning from AC to DC

#368

Post by ta9000 »

margalabargala wrote: post #280
ta9000 wrote: post #262

Earlier quoted context omitted.

Yes, my curiosity was about when we run out, because I didn’t know if we would run out. That was the whole point of the question. Have some leniency, we’re not all experts about everything.

> 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?

Re: Data centers are transitioning from AC to DC

#369

Post by ta9000 »

adrian_b wrote: post #297
margalabargala wrote: post #248

Earlier quoted context omitted.

It's a byproduct of aluminum production. The earth's crust is 8% aluminum. We will have bigger problems before hitting this one.

That is true, but gallium is present in the aluminum and zinc ores only in minute quantities. We will not remain without gallium, but it is impossible to scale up the gallium production to a higher level than provided by the current productions of aluminum and zinc. So there is a maximum level of gallium that can be used per year and it would not be possible to increase the production of blue and white LEDs and of po…

Thanks for providing a real answer.

Re: Data centers are transitioning from AC to DC

#370

Post by Dylan16807 »

chromacity wrote: post #238
pjdesno wrote: post #227

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 t…

> 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 envelop…

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.

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