Data centers are transitioning from AC to DC • Hacker News Board

Re: Data centers are transitioning from AC to DC

#201

Post by eternauta3k » Wed, Mar 25, 2026, 11:40 AM UTC

15155 wrote: post #159

_fizz_buzz_ wrote: post #124

Earlier quoted context omitted.

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.

They chose 800VDC because it's a convenient multiple that is the peak possible with a two-level 650V (probably GaN) FET arrangement.

And why is 650V special?

Re: Data centers are transitioning from AC to DC

#202

Post by boomskats » Wed, Mar 25, 2026, 11:47 AM UTC

chrneu wrote: post #104

hristov wrote: post #9

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. Tesla understood that high voltage was needed for efficient long range transmission. He also understood that transformers were the inly remotely efficient way to climb up to and down from thes…

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, a…

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.

Re: Data centers are transitioning from AC to DC

#203

Post by [deleted] » Wed, Mar 25, 2026, 12:05 PM UTC

fecal_henge wrote: post #175

mjuarez wrote: post #35

Earlier quoted context omitted.

Not to be _that_ guy, but it was technically -48V DC. Honestly, that was pretty surprising to me when I had to work with some telco equipment a couple of decades ago. To this day, I don't think I've encountered anything else that requires negative voltage relative to ground.

I am STILL designing hardware for -48v telco standard. The first thing we do is convert -48 -> 48v. That's 4 square inches of PCB space we waste.

[deleted]

Re: Data centers are transitioning from AC to DC

#204

Post by jacquesm » Wed, Mar 25, 2026, 12:07 PM UTC

aidenn0 wrote: post #128

jacquesm wrote: post #98

Earlier quoted context omitted.

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…

> In all likely not worth the trouble. When I moved to Canada I gave away most of my power tools for that reason and when I moved back I had to do that all over again. If you ever have to do it again, you can probably get a transformer rated high enough for power-tools for cheaper than replacing all of your power tools.

Of course you can. That's kind of obvious. It is also highly impractical. Besides the frequency delta you end up having to lug a heavy transformer along and then you have to alternate it across your tools so you don't end up frying the transformer.

Re: Data centers are transitioning from AC to DC

#205

Post by ngvrnd » Wed, Mar 25, 2026, 12:14 PM UTC

elar_verole wrote: post #171

chrneu wrote: post #104

Earlier quoted context omitted.

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, a…

People need heroes. It's like the Keanu Reeves or Musk era, all the ""badass"" stories about this or that soldier / local hero / w/e that are very often overblown and get further and further away from the initial facts every time they resurface. No hate here, just noticing there is a weird visceral need to distill stories to their most essential, good vs evil, and the Tesla v Edison thing embodies this perfectly I th…

Except for Keith Moon. All the stories about him are true and if anything underplay the truth. :-)

Re: Data centers are transitioning from AC to DC

#206

Post by bananaflag » Wed, Mar 25, 2026, 12:17 PM UTC

mikkupikku wrote: post #178

AndrewDucker wrote: post #170

Earlier quoted context omitted.

Why would we run out of Ga?

There's a component of modern culture that trains and expects people to be extremely pessimistic about long term human development. It results in situations above, where without any further information people just assume by default that were going to run out of a thing and are on some collision course with not just a disaster, but every single conceivable one. (Gallium is a byproduct of aluminum production. We aren't…

On the other hand, it is possible to run out of a metal when all of it is either somewhere in some device or scattered among landfills (i.e. not concentrated in a place like a mine).

Re: Data centers are transitioning from AC to DC

#207

Post by fecal_henge » Wed, Mar 25, 2026, 12:21 PM UTC

eqvinox wrote: post #176

fecal_henge wrote: post #175

Earlier quoted context omitted.

I am STILL designing hardware for -48v telco standard. The first thing we do is convert -48 -> 48v. That's 4 square inches of PCB space we waste.

What do you need +48V for?

We go -48 -> 48 -> 12 -> 3v3,1v8 etc etc. If you went 48 straight to POL voltages then you would have horrific converter performance.

Re: Data centers are transitioning from AC to DC

#208

Post by 15155 » Wed, Mar 25, 2026, 12:22 PM UTC

eternauta3k wrote: post #201

15155 wrote: post #159

Earlier quoted context omitted.

They chose 800VDC because it's a convenient multiple that is the peak possible with a two-level 650V (probably GaN) FET arrangement.

And why is 650V special?

Historical, physical, engineering reasons.

Much of the world's mains-voltage electronics run at 240V (historical) and have PFC circuits (which are essentially just boost converters) that run at ~400V DC link voltages. 650V gives you enough headroom to tolerate overshoots and still have an 80% safety margin with a single level topology.

This voltage also coincidentally is a convenient crossover point where silicon MOSFETs start to become inefficient and GaN FETs have recently become feasible and mass-produced.

Re: Data centers are transitioning from AC to DC

#209

Post by boricj » Wed, Mar 25, 2026, 12:24 PM UTC

bluGill wrote: post #16

otterley wrote: post #7

DC power has been an option for datacenter equipment since I was a young lad racking and stacking hardware. Cisco, Dell, HPE, IBM, and countless others all had DC supply options. Same with PDUs. What’s old is new again. See e.g. https://www.dell.com/support/kbdoc/en-us/000221234/wiring-in...

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.

I'm working on stuff in that market, it's still largely is. DC Power System Design For Telecommunications is still a must read and it doesn't even cover the last 15 years or so of development, notably lithium batteries and high efficiency rectifiers.

I will say that this is a surprisingly deep and complex domain. The amount of flexibility, variety and scalability you see in DC architectures is mind-boogling. They can span from a 3kW system that fits in 2U all the way to multiples of 100kWs that span entire buildings and be powered through any combination of grid, solar and/or gas.

Re: Data centers are transitioning from AC to DC

#210

Post by eqvinox » Wed, Mar 25, 2026, 12:35 PM UTC

fecal_henge wrote: post #207

eqvinox wrote: post #176

Earlier quoted context omitted.

What do you need +48V for?

We go -48 -> 48 -> 12 -> 3v3,1v8 etc etc. If you went 48 straight to POL voltages then you would have horrific converter performance.

> If you went 48 straight to POL voltages then you would have horrific converter performance.

What's horrific converter performance in numbers?

An isolated flyback (to 12V) should be able to hit >92% and doesn't care if it's fed -48V or +48V or ±24V. TI webench gives me 95% though I'd only believe that if I'd built and measured it. What's the performance of your -48V → +48V?

[with the caveat that these frequently require custom transformers... not an issue with large runs, but finding something that can be done with an existing part for smaller runs is... meh]