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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

#61

Post by jacquesm »

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.

Yes, and that tiny little difference can cost you a lot of expensive gear if you run it off the battery and plug in a serial port or something like that. You'll also learn first hand what arc welding looks like without welding glass.

Re: Data centers are transitioning from AC to DC

#62

Post by bluGill »

ericd wrote: post #45
bigiain wrote: post #39

Earlier quoted context omitted.

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 electrician…

Amps - the old 48vdc telco data centers vaporized wrenchs once in a while.

Re: Data centers are transitioning from AC to DC

#63

Post by bigiain »

Aloisius wrote: post #41

This article seems to imply that 800V DC is high-voltage DC, but that seems quite low.

I think there'a a regulatory "Low Voltage" definition of "below 50V", which has implications around whether you need to be a licensed electrician to install it or not. Anything above that is - for at least some purposes - considered "High Voltage".

Other people, of course, have other definitions of high voltage:

"This resonant tower is known as a Tesla coil. This particular one is just over 17 feet tall and it can generate about a million volts at 60,000 cycles per second."

and:

"This pulse forming network can deliver a shaped pulse of over 50,000 amps with a total energy of about 1,057 times the tower primary energy"

https://www.youtube.com/watch?v=RoGbrgOhPes

Re: Data centers are transitioning from AC to DC

#64

Post by jacquesm »

stego-tech wrote: post #24
otterley wrote: post #10

Earlier quoted context omitted.

Those vendors all have DC power supply options, to my knowledge. It’s hardly new; early telco datacenters had DC power rails, since Western Electric switching equipment ran on 48VDC. https://www.nokia.com/bell-labs/publications-and-media/publi...

That’s just it though, telco DCs != Compute DCs. Telcos had a vested interest in DC adoption because their wireline networks used it anyway, and the fewer conversions being done the more efficient their deployments were. Every single DC I’ve worked in, from two racks to hundreds, has been AC-driven. It’s just cheaper to go after inefficiencies in consumption first with standard kit than to optimize for AC-DC conversi…

I think the real reason is because battery power didn't have to be converted twice to be able to run the gear in case of an outage, so you'd get longer runtime in case of a power failure, and it saves a bunch of money on supplies and inverters because you effectively only need a single giant supply for all of the gear and those tend to be more efficient (and easier to keep cool) than a whole raft of smaller ones.

Re: Data centers are transitioning from AC to DC

#65

Post by idiotsecant »

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.

I still have a bunch of 48vdc comms gear in my powerplant.

Re: Data centers are transitioning from AC to DC

#66

Post by adiabatichottub »

jwilliams wrote: post #46
adrr wrote: post #23

Our 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.

Your modern fridge is probably going to have an inverter-driven motor, so you're right back to using DC.

Re: Data centers are transitioning from AC to DC

#67

Post by jacquesm »

bigiain wrote: post #39
ericd wrote: post #28

Earlier 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…

You got super lucky.

Re: Data centers are transitioning from AC to DC

#68

Post by jacquesm »

ericd wrote: post #45
bigiain wrote: post #39

Earlier quoted context omitted.

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 electrician…

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

Re: Data centers are transitioning from AC to DC

#69

Post by torginus »

adiabatichottub wrote: post #48
torginus wrote: post #31

Earlier quoted context omitted.

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.

I mean it depends, but for dual rated stuff has both a voltage and current limit, both of which are way lower. Like typically a 230V/20A AC switch can switch 24VDC/2A. And the energy is not in the equipment, its in the mains (or batteries like you said, or PV panels)

Re: Data centers are transitioning from AC to DC

#70

Post by Georgelemental »

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…

It's just a fun title, you are overthinking it
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