This article seems to imply that 800V DC is high-voltage DC, but that seems quite low.
Data centers are transitioning from AC to DC
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Re: Data centers are transitioning from AC to DC
#42DC 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.
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 drained when the power went out?
Re: Data centers are transitioning from AC to DC
#43This article seems to imply that 800V DC is high-voltage DC, but that seems quite low.
Quite low compared to a power utility's HVDC, but quite high compared to the 5/12/24 V output of most AC/DC converters used for electronics.
Re: Data centers are transitioning from AC to DC
#44Earlier 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.
Check out older English cars.
Re: Data centers are transitioning from AC to DC
#45Earlier quoted context omitted.
Something to consider, and something I got a vivid demonstration of while playing with solar panels, DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe. My understanding is that DC breakers are somewhat prone to fires for this reason, too.
Heh - I vaporised a fairly large soldering iron tip (probably 4mm copper cylindrical bar?), when I fucked up soldering a connector to a big 7 cell ~6000mAHr LiPo battery and shorted the terminals. Quite how I didn't end up blind or in hospital I don't know. It reinforced just how much respect you need to pay to even low-ish voltage DC when the available current was likely able to exceed 700A by a fair margin momentar…
heh man, I'm glad you got out of that easy, I definitely wore safety glasses 100% of the time after my experience. I think a lifetime of experience with dangerous wall outlets and harmless little 1.5V/9V DC cells teaches us the wrong lessons about DC safety. I've since heard stories of wrenches exploding when they fall across EV high voltage battery terminals. Wrenches aren't supposed to be explosive.
The electricians I was working with also told me stories about how with the really big breakers, you don't stand in front of it when you throw it, because sometimes it can turn into a cloud of molten metal vapor. And that's just using them as intended.
Re: Data centers are transitioning from AC to DC
#46Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.
There are niches where DC makes sense - low-voltage lighting, USB/LED ecosystems.
Once you get into higher power (laptops and up), switching and distribution get harder, so the advantages fade.
For bigger appliances (fridge, etc), AC is fine + practical.
Re: Data centers are transitioning from AC to DC
#47Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.
Having a single big DC converter at a home would help a lot with power factor (LED lamps connected directly to AC have terrible power factor).
Re: Data centers are transitioning from AC to DC
#48Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.
I've had discussed with people familiar with the matter, and they convinced me its really not worth it for many reasons, the main one being safety - DC arcs are self sustaining - AC voltage constantly goes to zero, so if an arc were to form, it gets auto extinguished when the voltage drops. With DC this never happens, meaing every switch or plug socket can create this nice long arcs and is a potential fire hazard.
Really depends on what we're talking about. A lot of electrical safety equipment has a DC rating, usually something like 90VDC/300VAC. Also, most DC equipment just isn't going to have the stored energy to generate a big arc. Well, except batteries, and we're already piling them all around us.
Re: Data centers are transitioning from AC to DC
#49Waiting 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 )
Re: Data centers are transitioning from AC to DC
#50I've been hearing this line for over a decade, now. "Immersion cooling will make data centers scale!" "Converting to DC at the perimeter increases density!" Yes, of course both of those things are true, and yes, some data centers do engage in those processes for their unique advantages. The issue is that aside from specialty kit designed for that use (like the AWS Outposts with their DC conversion), the rank-and-file…
At least for servers, power supplies are highly modular. It just takes 1 moderately sized customer to commit to buying them, and a DC module will appear.
Looking at the manual for the first server line that came to mind, you can buy a Dell PowerEdge R730 today with a first party support DC power supply.