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

Re: Data centers are transitioning from AC to DC

#51

Post by bluGill » Wed, Mar 25, 2026, 2:29 AM UTC

MathMonkeyMan wrote: post #42

bluGill wrote: post #16

Earlier quoted context omitted.

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.

Yeah I always heard that the phone lines carried their own power, and in Florida the phones did keep working when the power went out, but I never knew why. So the grid was always charging up the lead acid batteries, and the phone lines were always draining them? Or was there some kind of power switching going on where when the grid was available the batteries would just get "topped off" occasionally and were only dra…

Grid charging batteries, phone draining them as I understand. Of course there were switches all over the us so I can't make blanket claims but from what I hear that was normal.

Re: Data centers are transitioning from AC to DC

#52

Post by bluGill » Wed, Mar 25, 2026, 2:31 AM UTC

mjuarez wrote: post #35

bluGill wrote: post #16

Earlier quoted context omitted.

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.

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.

positive ground used to be in all cars. When they went from 6 volts to 12 the disadvantages became appearant fast and so everyone went negative ground then (mid 1950s). I am not clear why positive ground was bad (maybe corrosion?)

Re: Data centers are transitioning from AC to DC

#53

Post by jacquesm » Wed, Mar 25, 2026, 2:31 AM UTC

KnuthIsGod wrote: post #49

Waiting for home DC. It is silly to have AC to DC converters in all of my wall connected electronics ( LED bulbs, home controller, computer equipment etc )

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.

Re: Data centers are transitioning from AC to DC

#54

Post by servo_sausage » Wed, Mar 25, 2026, 2:32 AM UTC

mjuarez wrote: post #35

bluGill wrote: post #16

Earlier quoted context omitted.

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.

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.

Is that something other than a labelling convention? Is ground actually connected to a earth stake?

Re: Data centers are transitioning from AC to DC

#55

Post by jacquesm » Wed, Mar 25, 2026, 2:34 AM UTC

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…

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

Re: Data centers are transitioning from AC to DC

#56

Post by CamperBob2 » Wed, Mar 25, 2026, 2:35 AM UTC

servo_sausage wrote: post #54

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.

Is that something other than a labelling convention? Is ground actually connected to a earth stake?

Cathodic protection against corrosion was the goal of using -48V, in the telcos' case.

Re: Data centers are transitioning from AC to DC

#57

Post by AbanoubRodolf » Wed, Mar 25, 2026, 2:36 AM UTC

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...

[flagged]

Re: Data centers are transitioning from AC to DC

#58

Post by Mistletoe » Wed, Mar 25, 2026, 2:36 AM UTC

adrr wrote: post #23

Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.

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.

Re: Data centers are transitioning from AC to DC

#59

Post by bigiain » Wed, Mar 25, 2026, 2:36 AM UTC

fortran77 wrote: post #27

umvi wrote: post #17

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. I imagine the light bulb cartel wouldn't really like that.

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

That's traded off against the increase efficiency of LED lighting, at least compared to incandescent lighting. An LED "equivalent replacement" for a typical incandescent globe is down around 1/10th of the power. A 7Watt LED bulb is typically marketed as "60W equivalent". If that configured as a bunch of LEDs in series (or series/parallel) that need 12VDC, it's right about the same current draw as the 120V 60W incandescent equivalent. (Or perhaps double the current for those of us who get 220VAC out of our walls.)

(Am I just showing my age here? How many of you have ever bought incandescent globes for house lighting? I vaguely recall it may be illegal to sell them here in .au these days. I really like quartz halogen globes, and use them in 4 or 5 desk lamps I have, but these days I need to get globes for em out of China instead of being able to pick them up from the supermarket like I could 10 or 20 years ago.)

Re: Data centers are transitioning from AC to DC

#60

Post by gizmo686 » Wed, Mar 25, 2026, 2:38 AM UTC

umvi wrote: post #17

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. I imagine the light bulb cartel wouldn't really like that.

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.