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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

#111

Post by toast0 »

ericd wrote: post #28
adrr wrote: post #23

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

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.

> 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.

It would have self-extinguished if you waited long enough for the probe to vaporize.

Re: Data centers are transitioning from AC to DC

#112

Post by SAI_Peregrinus »

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.

Lots of amplifier circuits need a bipolar supply: both positive and negative voltages with respect to ground.

Re: Data centers are transitioning from AC to DC

#113

Post by jacquesm »

bigiain wrote: post #101
jacquesm wrote: post #94

Earlier quoted context omitted.

It's almost worth the experiment and your cables are a sacrifice I'm willing to make. For science, of course.

You're _so_ right! I'm pretty sure you have my delivery address from when I bought sorted Lego from you about 10 years back. Let me know when to expect the 100,000Amp test equipment! I shall make sure I wear better PPE than just my reading glasses. :-)

This would be the funniest thing to do. 100K Amps is doable, the question is for how long. That would be one very impressive bank of capacitors. And to turn a 00 into plasma would have some spectacular side effects, such as raining molten copper across a sizeable area. Just your reading glasses would indeed not be enough, there probably isn't any PPE that I would consider entirely safe other than sufficient distance from ground zero. But now I'm really curious. I have a spot welder that will do bursts of 5KA and that will happily throw the breaker every so many welds. 100KA sustained will be a fair engineering challenge.

Ah, that lego project... that was one I always wondered if I should have industrialized it but sourcing enough lego was a real problem.

Re: Data centers are transitioning from AC to DC

#114

Post by jacquesm »

bigiain wrote: post #103
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.

I would read that book...

'Stupid stuff I've done and survived'...

Re: Data centers are transitioning from AC to DC

#115

Post by ianburrell »

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.

What voltage do you use? Most DC stuff wants low voltage (5-48V), but appliances need higher voltage like AC-level to get enough power over existing wiring. The result is DC-DC converters every place that have transformers now.

The gain from DC-DC converters is small and DC devices are small part of usage compared appliances. There is no way will pay back costs of replacing all the appliances.

Re: Data centers are transitioning from AC to DC

#116

Post by [deleted] »

arijun wrote: post #38
adgjlsfhk1 wrote: post #19

Earlier quoted context omitted.

AC is less efficient than DC at a given voltage. The advantage of AC is that voltage switching is cheap, easy and efficient. Switching DC voltage is way harder, more expensive, and less efficient. However the switching costs are O(1) and the transmission losses are O(n) so for some distance (currently somewhere around 500 km) it's worth paying the switching cost to get super high voltage DC. The big thing that's chan…

> AC is less efficient than DC at a given voltage To expand on this, a given power line can only take a set maximum current and voltage before it becomes a problem. DC can stay at this maximum voltage constantly, while AC spends time going to zero voltage and back, so it's delivering less power on the same line.

[deleted]

Re: Data centers are transitioning from AC to DC

#117

Post by myself248 »

CamperBob2 wrote: post #56
servo_sausage wrote: post #54

Earlier quoted context omitted.

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.

And the telegraph lines before that.

Re: Data centers are transitioning from AC to DC

#118

Post by Animats »

800V to each rackmount unit, with hot plugging of rack units? That's scary. The usual setup at this voltage is that you throw a hulking big switch to cut the power, and that mechanically unlocks the cabinet. But that's not what these people have in mind. They want hot-plugging of individual rackmount units.

GE has a paper about the power conversion design, but it doesn't mention the unit to rack electrical and mechanical interface. Liteon is working on that, but the animation is rather vague.[2] They hint at hot plugging but hand-wave how the disconnects work. Delta offers a few more hints.[3] There's a complex hot-plugging control unit to avoid inrush currents on plug-in and arcing on disconnect. This requires active management of the switching silicon carbide MOSFETs.

There ought to be a mechanical disconnect behind this, so that when someone pulls out a rackmount unit, a shutter drops behind it to protect people from 800V. All these papers are kind of hand-wavey about how the electrical safety works.

Plus, all this is liquid-cooled, and that has to hot-plug, too.

[1] https://library.grid.gevernova.com/white-papers-case-studies...

[2] https://www.youtube.com/watch?v=CQOreYMhe-M&

[3] https://filecenter.deltaww.com/Products/download/2510/202510...

Re: Data centers are transitioning from AC to DC

#119

Post by jacquesm »

tbrownaw wrote: post #108
manwe150 wrote: post #93

Earlier quoted context omitted.

I suppose that still begs the question somewhat, since the US does have 240V (2 phase) already driving many appliances. Why hasn’t it ever become standard for luxury kitchens to have a European-style outlet for use with a European kettle? I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?

> I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before? How expensive would a proper AC->DC->AC brick for that power level be?

Not so simple, you'd have to use a 'drier' or 'welder' socket for that otherwise you won't have enough power. A single circuit in Europe is 240V 16A or 3840W!

A pure sinewave inverter for that kind of power is maybe 600 to 1000 bucks or so, then you'd still need the other side and maybe a smallish battery in the middle t stabilize the whole thing. Or you could use one of those single phase inverters they use for motors.

Re: Data centers are transitioning from AC to DC

#120

Post by jacquesm »

jcalvinowens wrote: post #110
manwe150 wrote: post #93

Earlier quoted context omitted.

I suppose that still begs the question somewhat, since the US does have 240V (2 phase) already driving many appliances. Why hasn’t it ever become standard for luxury kitchens to have a European-style outlet for use with a European kettle? I know the US already has a different 240V plug shape, so it might have to be an unlicensed installation, but surely someone wanted hot tea faster and did that calculus before?

I wired a UK kettle to an unused 240V range outlet in the US once. It was amazing, boiled a liter of water in just under a minute. Obviously kinda sketchy.

That's more like it :)
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