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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

#331

Post by zahlman »

Xcelerate wrote: post #311

I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment…

> Lighting, laptops, small/medium televisions. The current PoE spec allows up to 100 W, which covers like 80% of the powered devices in most homes.

I find it a little hard to imagine that those devices outnumber things like stoves, dishwashers, washers/dryers, kettles, hair dryers... by 4:1.

Unsure why PoE would be better for LED lighting than the standard approach of screwing a bulb directly into AC, either. How many lumens do you get out of strip lights these days? And you still have AC-DC conversion for whatever's sourcing power onto the Ethernet link.

Re: Data centers are transitioning from AC to DC

#332

Post by zahlman »

estimator7292 wrote: post #316
Xcelerate wrote: post #311

I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment…

I think we're slowly, slowly coming around to the idea of domestic DC distribution. The vast majority of consumer electronics would be perfectly happy to consume 12v. It's cheaper, safer, more efficient. Less design work and certification on inbuilt AC adapters. I think it's highly unlikely we'll see mass scale retrofits, but if enough momentum builds up, I can see it as a great bonus feature for new builds. I got lu…

> I think it's highly unlikely we'll see mass scale retrofits, but if enough momentum builds up, I can see it as a great bonus feature for new builds.

I imagine rooftop solar could also source DC for the house directly (or via a battery), before hitting the inverter... ?

The main problem I see is educating consumers. Maybe that starts with a standard for DC outlets and plugs that can't be confused with AC... ?

(Now I'm imagining desktop computers with much simpler power supplies; but you'd presumably have to wire for dozens of amps incoming...)

Re: Data centers are transitioning from AC to DC

#333

Post by formerly_proven »

zahlman wrote: post #331
Xcelerate wrote: post #311

I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment…

> Lighting, laptops, small/medium televisions. The current PoE spec allows up to 100 W, which covers like 80% of the powered devices in most homes. I find it a little hard to imagine that those devices outnumber things like stoves, dishwashers, washers/dryers, kettles, hair dryers... by 4:1. Unsure why PoE would be better for LED lighting than the standard approach of screwing a bulb directly into AC, either. How man…

PoE is also fairly bulky, requires large connectors, and either requires a wholly isolated PD or what's basically a class 2 DC/DC converter. That's why PoE-powered stuff usually has that big transformer cube in it with a lot of clearance, slotted PCB, 2-4 kV capacitors etc.

In practice PoE will have lower efficiency than mains powered, since it'll usually be at least double conversion, often three converters in series, plus the losses of the thin network wires, and the relatively high idle losses / poor low-load efficiency of the necessarily over-dimensioned PSE.

Re: Data centers are transitioning from AC to DC

#334

Post by sneak »

Xcelerate wrote: post #311

I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment…

I think Ubiquiti (makers of the UniFi wifi products, as well as some of the most popular managed PoE switches) also make a ton of other PoE products such as the usual stuff like cameras, ip phones, network switches, access card readers, door locks, and, now, ceiling lights (presumably due to the latest PoE standards delivering significant wattage).

It's super nice because you only need to put the UPS/ATS at the PoE switch and then you get power redundancy everywhere you have ethernet running (i.e. the phones don't go down).

Re: Data centers are transitioning from AC to DC

#335

Post by zahlman »

jacquesm wrote: post #53
KnuthIsGod wrote: post #49

Waiting 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 )

Not going to happen. For the same reason that the US never converted to a higher domestic voltage even though there are many practical advantages. The transition from one system to another at the consumer level would be terrible, even if there would be some advantage (and I'm not sure the one you list is even valid, you'd get DC-DC converters instead because your consumers typically use a lower voltage than the house…

... or we could have both sets of wiring, and use what's appropriate for the task/appliance?

Re: Data centers are transitioning from AC to DC

#336

Post by zahlman »

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.

"Wired"?

...There was some kind of switch involved, I hope?

Re: Data centers are transitioning from AC to DC

#337

Post by pdpi »

Xcelerate wrote: post #311

I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment…

> maybe with a more robust connector than RJ45

USB-C could be that connector, using USB-PD instead of PoE. Though I'm not sure I'd want to need that much smarts for every single power outlet.

Re: Data centers are transitioning from AC to DC

#338

Post by pyrale »

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).

> 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

The metal isn't going to disappear, but it won't be concentrated enough to be as easily retrievable.

Re: Data centers are transitioning from AC to DC

#339

Post by zahlman »

bregma wrote: post #180
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?

> but surely someone wanted hot tea faster No one in the USA drinks hat tea. The choices (and it tends to be regionally-based) is sweet or unsweet tea. No need to boil a kettle quickly for that.

> The choices (and it tends to be regionally-based) is sweet or unsweet tea.

... Unless you're buying it pre-made, does this not still start with making hot tea the regular way? Or what exactly are you doing with the tea bags and loose tea from the supermarket?

Re: Data centers are transitioning from AC to DC

#340

Post by crote »

Xcelerate wrote: post #311

I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC. Straight from the UPS as DC would work much better, and as I was teaching myself more about networking equipment, I was surprised to learn that most of it isn't DC input by default (i.e., each piece of equipment…

The problem is that all of those DC devices don't operate on 48V either. The vast majority of chips require a 5V or lower input, so with a 48V DC supply you're still going to need a per-device PSU to do DC-DC conversion. In other words: no getting rid of power bricks.

Efficiency isn't as straightforward either. You're still being fed by 120V/230V AC, so you're going to need some kind of centralized rectifier and down converter. It'll need to be specced for peak use, but in practice it'll usually operate at a fraction of that load - which means it'll have a pretty poor efficiency. A per-device PSU can be designed exactly for the expected load, which means it'll operate at its peak efficiency.

We also don't use 5V DC grids because the wire losses would be horrible, so a domestic DC grid should probably operate at pretty close to regular AC voltage as well. In practice this means the most sensible option would be to have a centralized rectifier and a grid operating at whatever voltage it outputs - but what would be the point?

As to PoE: I personally really like the idea, but I don't believe it'll have a bright future. For its traditional use the main issue is that there doesn't seem to be a future for twisted-pair beyond 10Gbps. 25GBASE-T might exist as a standard on paper, but the hardware never took off due to complete disinterest from the datacenter market, and it is too limited to be of use in offices and homes. I fully expect that 25G will arrive in the home and office as some form of fiber-optic interconnect - with fiber+copper hybrid for things like access points.

On the other hand, for a lot of IoT applications PoE seems to be too complicated and too expensive. It makes sense for things like cameras, but individual lights, or things like smoke sensors are probably better served in office/industrial applications by either a regular AC supply or a local DC one, plus something like KNX, X10, CAN, or Modbus for comms: just being able to be wired as a bus rather than a star topology is already a massive advantage. And for domestic use the whole "has a wire" thing is of course a massive drawback - most consumers strongly prefer using Wifi over running a dedicated wire to every single little doodad.

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