Well they're kinda transitioning back. When I grew up most DCs (and telecom facilities) were running on 48V DC. Easy to back up with a big room full of lead acid batteries (just keep an eye on that hydrogen gas lol)
Data centers are transitioning from AC to DC
321–330 of 432 posts
Re: Data centers are transitioning from AC to DC
#322I 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…
> 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.
With double-conversion, generally yes.
I recently ran across the (patented?) concept of a delta conversion/transformer UPS that seems to eliminate/reduce the inefficiencies:
* https://dc.mynetworkinsights.com/what-are-the-different-type...
* a bit technical: https://www.youtube.com/watch?v=nn_ydJemqCk
* Figures 6 to 8 [pdf]: https://www.totalpowersolutions.ie/wp-content/uploads/WP1-Di...
The double-conversion only occurs when there's a 'hiccup' from utility power, otherwise if power is clean the double-conversion is not done at all so the inefficiencies don't kick in.
Re: Data centers are transitioning from AC to DC
#323Earlier quoted context omitted.
> 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 req…
-48 to 48 claims something like 97% (load dependent of course). It also needs to arbitrate between two input supplies for glitchless redundancy, plus have PM bus and other spec mandated stuff. There is no technical reason why you cant go -48 -> 12 as you state with good efficiceny, but we cant get hold of a part that ticks all the boxes. Horrific performance by my definition would be 48v to say 1v. We only realistica…
I'm just surprised that either input isolation isn't on your spec, or it still somehow works out better with isolated to +48V than straight to 12V... but I guess if your spec requires other things, it makes sense.
(Thanks for the info!)
Re: Data centers are transitioning from AC to DC
#324I 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…
> 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 multiple PSUs that target different load ranges.) But of course something like that is more expensive...
Re: Data centers are transitioning from AC to DC
#325Earlier quoted context omitted.
Of grid homes are vastly more concerned with the energy efficiency of their appliances and thus DC refrigerators generally have more insulation. Most AC customers prefer more internal volume for food over slightly increased efficiency. AC motors are using way more power than the puddly control boards in most home appliances. So you lose a little efficiency on conversion but being 80% efficient doesn’t matter much whe…
I agree with everything you said, except it seems like a false dichotomy. We can clearly build DC refrigerators with more or less insulation. We can clearly build them large or small. If you want to prioritize volume, then surely you could do that with DC. Right? I know that a long time ago DC-to-DC voltage converters were very large in size, which meant AC would win on space efficiency. But unless I’m mistaken, that…
> Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator?
Sure, but it’s important to separate what could be built from what is being built based on consumer preferences and buying habits. The average refrigerator could be significantly quieter, but how often do people actually listen to what they are buying? People buying Tesla’s didn’t test drive the actual car they were buying so the company deprioritized panel gaps. And so forth, companies optimize in ways that maximize their profits not arbitrary metrics.
Re: Data centers are transitioning from AC to DC
#326Earlier 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…
Do you also happen to why this is not more common? Must be useful for more than just telephone wires.
It is! Look up "impressed current cathodic protection": you apply a small DC voltage to, say, pipelines to prevent corrosion.
Re: Data centers are transitioning from AC to DC
#327Earlier 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.
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 be unlucky and have a power outage with 3% battery on your phone...
Re: Data centers are transitioning from AC to DC
#328Earlier quoted context omitted.
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…
> 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!
Re: Data centers are transitioning from AC to DC
#329They were Thunderstruck?
Re: Data centers are transitioning from AC to DC
#330Earlier 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…
Do you also happen to why this is not more common? Must be useful for more than just telephone wires.
I ran into a guy at a hardware store who ran just such a power supply attached our city's water (or was it natural gas?) infrastructure. I was incredulous, but the idea that it helped prevent corrosion did make sense.