Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Data centers are transitioning from AC to DC

spectrum.ieee.org

Post reply on HN
Print view View original

301–310 of 432 posts

Re: Data centers are transitioning from AC to DC

#301

Post by hamdingers »

BorisMelnik wrote: post #287

its really wild at all the AC to DC changes. for those non electric engineers / hardware hackers (like myself) one of the biggest "examples" I've seen of this has been ceiling fans. Installing a ceiling fan used to be treacherous and so heavy. Also loud and buzzy after installed. Now the fans in these things are so lightweight and easy. seeing the same in many more areas (lighting, etc)

Would love to see more mainstream DC lighting options and an updated code to match. I just finished a remodel of my workshop and blew over a hundred bucks on 14/2 for a 15 amp lighting circuit that is unlikely to ever see more than a 1 amps load.

The irony is all the recessed lights I picked out are DC, they all have little AC-DC boxes hanging off them using a proprietary connector. If I hadn't needed to pass a rough-in inspection going all DC would've been trivial.

Re: Data centers are transitioning from AC to DC

#302

Post by sholladay »

samus wrote: post #273
sholladay wrote: post #264

Is there anything left in a modern home that really needs or is better on AC? We have some old ceiling and exhaust fans, but I know those can be replaced. Our refrigerator is AC, but extended family with an off-grid home has a DC refrigerator that cycles way less, probably due to multiple design factors but I’m sure the lack of transformer heat is part of it. I’m not as sure about laundry machine or oven/cooktop opti…

Any appliance with strong motors should be more efficient with AC supply. But almost anything else can be regarded as a heater that doesn't care much as long as it is fed with the correct voltage. Which is actually the core issue. A DC household would have to choose a trade-off between multiple lines with different voltages or fewer voltages that need to be adapted to the appliances. And we're right back at the AC si…

What qualifies as a strong motor here? Are you comparing to a brushed DC motor? Do you think a washer/dryer would have worse overall efficiency with a BLDC in a DC home compared to what we have today? If so, that’s news to me. Where can I learn more about that?

The trade-off between, say, one (relatively) high voltage DC bus throughout the home vs many branches with lower discrete voltages is indeed a problem. With AC, we took the bus approach, running 120v everywhere (in the U.S., higher elsewhere). I’m inclined to say we should keep doing that for flexibility and predictability. But it’s a trade off, like you said. It would obviously help if regulatory and standards bodies came out with official recommendations.

Re: Data centers are transitioning from AC to DC

#303

Post by poemxo »

pjdesno wrote: post #227

90% of the power in our academic data center goes 13.8kV 3-phase -> 400v 3-phase, and then the machines run directly from one leg to neutral (230v). One transformer step, no UPS losses, and the server power supplies are more efficient at EU voltages. But what about availability? If you ask most of our users whether they’d prefer 4 9s of availability or 10% more money to spend on CPUs, they choose the CPUs. We asked t…

Really you're down for over an hour a year? Unscheduled?

Re: Data centers are transitioning from AC to DC

#304

Post by jacquesm »

Tempest1981 wrote: post #289
jacquesm wrote: post #184

Earlier quoted context omitted.

https://www.eevblog.com/forum/beginners/understanding-high-v...

Thanks Jacques. So creepage is when current flows/arcs across the surface of an insulator, vs through the air. And it's worse with DC due to its unidirectional nature. Worsens when pollution builds up, or the surface degrades.

Indeed. And it's a really nasty thing to properly protect against because that pollution, especially with stuff that is unattended for a long time has a habit of ending up much worse than your worst fantasies. I've taken more than one electrocuted mouse out of the HV section of older color TVs for instance. Up to 250V or so it is manageable, above that you can get the weirdest problems including completely invisible arcing where the only giveaway is the ozone smell and the occasional click. Looking at HV circuitry in the dark or by putting a flame near a suspect spot is a great way to spot these kind of issues.

Re: Data centers are transitioning from AC to DC

#305

Post by lostlogin »

fc417fc802 wrote: post #162
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?

Ahckhually US residential is split single phase, not two phase. https://en.wikipedia.org/wiki/Split-phase_electric_power I think the answer to your question is that it mostly doesn't matter for personal mug size quantities of hot water and if it does matter to you there are readily available competing options such as dedicated taps for your kitchen sink. Perhaps the biggest reason is that a traditional kettle on any…

I use an induction stove on maximum to boil water as I get irritated at the time it takes to boil water with 240v.

I’m surprised that American exceptionalism can tolerate half powered sockets.

Re: Data centers are transitioning from AC to DC

#306

Post by jacquesm »

sobjornstad wrote: post #237
jacquesm wrote: post #68

Earlier quoted context omitted.

Those harmless 9V DC cells can do a lot of damage if you use them right.

This reminds me of the sailor who [decided]( https://darwinawards.com/darwin/darwin1999-50.html ) to measure his internal resistance by pushing probes through the skin on his thumbs and electrocuted himself with the 9V multimeter battery.

Mythbusters time. Salty fluids can be remarkably conductive. Blood qualifies. What's interesting though is that you have to wonder if there isn't some contributing factor here, as a kid I did this quite a few times, so that's one more for that list of stuff that could have killed me. At the same time: I didn't have nice insulation piercing tips back then (I do now) and that may be what saved me. I will definitely not try this again.

Another story in the same line is that I heard that a horse got killed by contact with a lantern battery, but I don't have any reference for that, just a story by a family member that collected coaches.

Re: Data centers are transitioning from AC to DC

#307

Post by elif »

QuantumGood wrote: post #298
elif wrote: post #291

Earlier quoted context omitted.

As long as you can control for fire, electrical safety seems like a temporary condition as robots and intelligent machines are cheaper and more available long term solution to hot swap blades in datacenter racks.

I think you're being downvoted for speaking of a complex future possibility ("robots and intelligent machines ... solution") as if it was a proven commodity. There will be many twists and turns in the path to the possible reliability, scalability, and cost effectiveness of robots and intelligent machines.

Yea I literally said long term but HN voters have such a hate boner for anything adjacent to AI

Re: Data centers are transitioning from AC to DC

#308

Post by nkrisc »

card_zero wrote: post #234
nkrisc wrote: post #214

Earlier quoted context omitted.

That’s still not running out. It’s still there, just more effort to get.

"At 10 parts per quadrillion, the Earth's oceans would hold 15,000 tonnes of gold", says the Wikipedia page on gold. I'm inclined to think we've lost that gold.

Practically speaking, sure. It's obviously not cost-effective to extract it. But it's there if someone can get it. I don't expect anyone to be extracting gold from ocean water, but there are other source of other elements that may not be cost-effective now but could be in the future or may simply become necessary despite the cost.

Re: Data centers are transitioning from AC to DC

#309

Post by nkrisc »

PowerElectronix wrote: post #245
nkrisc wrote: post #214

Earlier quoted context omitted.

That’s still not running out. It’s still there, just more effort to get.

Effort high enough to consider that material lost to any practical purpose like a tv.

If prices of certain metals were high enough I bet people would stop throwing out TVs and dig up old ones from the dump.

Re: Data centers are transitioning from AC to DC

#310

Post by Liftyee »

jcalvinowens wrote: post #246
bluGill wrote: post #218

Earlier 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)…

I agree that the US voltage is safer (with the tradeoff of lower output powers available at your outlets). However, I suspect this is more than negated by the US plug design, which carries a much larger risk of shocks than almost all EU plug designs (Schuko, British/Type G, etc...)

- uninsulated metal pins make contact with supply while partially exposed - much smaller distance between metal pins and the edge of the plug

Post reply on HN