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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

#241

Post by HWR_14 »

crote wrote: post #188
HWR_14 wrote: post #154

Earlier quoted context omitted.

Can you explain why it's -48 VDC as opposed to 48 VDC with the + and - inputs mislabeled?

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…

So, there is a true value for 0?

Does that mean when you have electronics and use multiple dc-dc converters all the inputs and outputs share the same ground, it's not just the values for that pair of wires?

And if I want to use a telephone on an incorrectly wired 48dc circuit, I could switch the positive and negative wires, as long as the circuit in the telephone is isolated and never touches ground?

Thanks. Somehow I got in my head that all circuits were just about the delta from neutral and therefore nothing outside them mattered.

Re: Data centers are transitioning from AC to DC

#242

Post by superxpro12 »

bluGill wrote: post #16
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...

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.

This reminds me of the early google data centers that directly soldered those massive duracell lantern batteries directly to the motherboards as a primitive battery backup. I'm struggling to google examples of it, this would have been back around 2008, but i have a vivid memory of it.

edit: found it https://www.cnet.com/tech/tech-industry/google-uncloaks-once...

Re: Data centers are transitioning from AC to DC

#243

Post by superxpro12 »

Animats wrote: post #144
rdtsc wrote: post #135

Earlier quoted context omitted.

It is a pretty clever design > When it is detected that the PDB starts to detach from the interface, the hot-swap controller quickly turns off the MOSFET to block the discharge path from Cin to the system. After the main power path is completely disconnected, the interface is physically detached, and no current flows at this time > For insertion, long pins (typically for ground and control signals) make contact first…

Yes, I read that. There had better be a backup system. MOSFETs tend to fail ON, and there's a megawatt going into each rack. Somehow this seems the wrong approach to AI.

Fail spectacularly

Data center workers are gonna need those big yoink sticks and those thick arc-fault bibs that furnace operators wear.

Re: Data centers are transitioning from AC to DC

#244

Post by throw0101d »

elcritch wrote: post #168
throw0101d wrote: post #22

Earlier quoted context omitted.

> 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. IEEE 802.3bt can deliver up to 71W at the destination: just pull Cat 5/6 everywhere. * https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i... * https://www.usailighting.com/poe-lighting

And pay $60 per Ethernet POE+ light bulb.

> And pay $60 per Ethernet POE+ light bulb.

In the commercial/industrial space this may be worth it: how long do these bulbs last? how much (per hour (equivalent)) do you pay your facilities folks? how much time does it take for employees or tenants to report an outage and for your folks to get a ladder (or scissor lift) to change the bulb?

Re: Data centers are transitioning from AC to DC

#245

Post by PowerElectronix »

nkrisc wrote: post #214
bananaflag wrote: post #206

Earlier quoted context omitted.

On the other hand, it is possible to run out of a metal when all of it is either somewhere in some device or scattered among landfills (i.e. not concentrated in a place like a mine).

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.

Re: Data centers are transitioning from AC to DC

#246

Post by jcalvinowens »

bluGill wrote: post #218
tinyhitman wrote: post #197

Earlier quoted context omitted.

Do you also happen to why this is not more common? Must be useful for more than just telephone wires.

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). A neutral isn't required if there aren't 120V loads.

Re: Data centers are transitioning from AC to DC

#247

Post by KaiserPro »

chrneu wrote: post #104
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…

the internet really needs to stfu about tesla and get over that oatmeal comic that spawned a billion internet myths. dude was a decent inventor but suffered from chronic mental health issues and, in his lifetime, wasted so much time/energy/money and burned so many bridges with his horrible attitude. there's a reason most people didnt like him in his day, he was a depressed asshole who alienated everyone around him, a…

> he was a depressed asshole who alienated everyone around him,

enough Edison bashing!

Look, Tesla was a weirdo, but, he was a very good inventor who actually invented shit.

Edison was an industrialist, who knew the price of everything, and wasn't above spending a lot of money to destroy a rival.

Do I idolise Tesla? no, but I respect his understanding of high frequency electronics with really primitive tooling.

Do I despise Edison? also no, but he is a massive prick. Excellent buisness man, but an abrasive prick never the less.

Re: Data centers are transitioning from AC to DC

#248

Post by margalabargala »

bananaflag wrote: post #206
mikkupikku wrote: post #178

Earlier quoted context omitted.

There's a component of modern culture that trains and expects people to be extremely pessimistic about long term human development. It results in situations above, where without any further information people just assume by default that were going to run out of a thing and are on some collision course with not just a disaster, but every single conceivable one. (Gallium is a byproduct of aluminum production. We aren't…

On the other hand, it is possible to run out of a metal when all of it is either somewhere in some device or scattered among landfills (i.e. not concentrated in a place like a mine).

It's a byproduct of aluminum production.

The earth's crust is 8% aluminum.

We will have bigger problems before hitting this one.

Re: Data centers are transitioning from AC to DC

#249

Post by throw4847285 »

chrneu wrote: post #104
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…

the internet really needs to stfu about tesla and get over that oatmeal comic that spawned a billion internet myths. dude was a decent inventor but suffered from chronic mental health issues and, in his lifetime, wasted so much time/energy/money and burned so many bridges with his horrible attitude. there's a reason most people didnt like him in his day, he was a depressed asshole who alienated everyone around him, a…

Software engineers idolize Tesla because they see themselves as the Tesla (a selfless devotee of the abstract idea of technology) against evil Edisons (businessmen who only care about money and steal other people's ideas). They've basically projected the Jobs/Woz divide back onto two historical figures who, in reality, barely interacted.

The funniest part is that The Oatmeal comic didn't invent this concept, but drew on pre-Internet narratives put forward by The Tesla Society, who were mailing busts of Tesla to universities around the country since the 70s at least. And that organization is explicitly nationalistic and religious, tied to other Serbian-American heritage organizations, and doing events with the Orthodox church.

Re: Data centers are transitioning from AC to DC

#250

Post by crimshawz »

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…

Agree, clickbait.
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