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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

#401

Post by flowerthoughts »

fc417fc802 wrote: post #165
flowerthoughts wrote: post #149

Earlier quoted context omitted.

I'm renovating a house, and have been considering 24V or 48V DC outlets in a few rooms. Semiconductors become more expensive above ~32V, so 24V might be the sweetspot. However, there's also PoE (24 or 48V!), so maybe that's the right approach. It's not like each outlet is going to run a heater anyway.

Lower voltage makes voltage drop across the line proportionally worse. Depending on the purpose PoE is probably the way to go since the wiring and hardware is all standardized and safety certified. Unless you mean running AC and installing inverters in the wall? What is this even for? All my electronics are DC but critically they all require different voltages. The only thing I might benefit from would be higher volt…

No, I meant running separate DC wires. I'm Europe, so it's 240 VAC vs 24/48 VDC. For small devices, 24 V would be useful in that you don't require an isolated SMPS, so cheaper endpoints are possible. Slightly less risk of burning down the house with some cheap Chinese AC/DC. 24 V is still high enough to use USB PD/PPS at 20 V, and I doubt I'll run enough current that the losses due to lower voltage would be a problem.

For PoE, I thought it was standardized at 48 V, but I see lots of cameras run at 24 V, and I think I've even seen 12 V. Seems a bit of a mess.

Re: Data centers are transitioning from AC to DC

#402

Post by matt-p »

ssl-3 wrote: post #367
matt-p wrote: post #361

Earlier quoted context omitted.

What if all homes had battery storage and or solar? You could then simply use it's rectifier as needed or direct 48v from the solar panels. That would be even more efficient than 230v.

That'd be neat. But there's no standard for voltage for home solar: The batteries might be 12, 24, 48v, 60v, or even much more. Meanwhile, the panel arrays commonly output anything as low as 0V and up to ~600V. There's not much for rules and norms here. Even if we were to standardize a low ( But, sure -- we can play it out. So let's say we have an in-home 48VDC distribution standard and decide that this is the path f…

Almost all home batteries are 48v, I think it would be reasonable to standardise on that.

Re: Data centers are transitioning from AC to DC

#403

Post by matt-p »

marcosdumay wrote: post #371
matt-p wrote: post #361

Earlier quoted context omitted.

What if all homes had battery storage and or solar? You could then simply use it's rectifier as needed or direct 48v from the solar panels. That would be even more efficient than 230v.

I'm not sure converting the solar and battery to 48V, distributing it around, and converting it to the needed voltage at the point of use is any more efficient than inverting it into 230V and distributing it around. Also, you'll need wires that 5 times thicker. Instead of needing a reasonably 1mm^2 for a normal 16A line, you'll need 5mm^2 for the same power.

Solar and battery are already at 48v in most cases, so you are avoiding converting it to AC.

I agree, it's unserious to suggest a cooker or something high power is going to run off of 48v. But for loads like lights, PC/Laptop/TV/Audio 16a at 48v is ~770W which is adequate for these devices.

Re: Data centers are transitioning from AC to DC

#404

Post by matt-p »

shiroiuma wrote: post #378
lillecarl wrote: post #364

Earlier quoted context omitted.

We live on societies, switching from AC to DC because your low-power home appliances doesn't need AC makes no sense. Home power usage is dominated by heating and cooling not by your 45w laptop charger. DC infrastucture makes sense in highly specialised environments.... Like new gigawatt AI farms

Large home appliances probably mostly need DC power these days too. Look at clothes washers: they all have variable-speed reversing motors, so they're probably using brushless DC motors (which use motor drives that are fed with DC, and output variable-frequency and variable-amplitude sinusoidal waves to drive the motor). HVAC seems to be similar, with variable-speed motors and compressors. I don't think that much stu…

[HVAC] true for the fans and controllers but surely you wouldn't DC feed a compressor.

Re: Data centers are transitioning from AC to DC

#405

Post by phantom784 »

Dylan16807 wrote: post #347
eqvinox wrote: post #324

Earlier quoted context omitted.

> I then learned that the energy draw of running the low-volt transformer all the time - especially one large enough to supply an entire house of lighting - would more than cancel out energy savings from powering lower voltage fixtures. That's not a constraint of physics, you can absolutely build a DC power supply that is efficient in a wide load range. (Worst case it might involve paralleling and switching between m…

> But of course something like that is more expensive... More expensive than an inefficient unit, but it should still be a lot cheaper than 120 separate units, right? And I expect one big fat unit to do a better job of smoothing out voltage and avoiding flicker than a bunch of single-light units. Especially because the output capacitors are sized for the entire system, but you'll rarely have all the lights on at the…

Plus you save money on the conductors running to the lights.

Re: Data centers are transitioning from AC to DC

#406

Post by ssl-3 »

matt-p wrote: post #402
ssl-3 wrote: post #367

Earlier quoted context omitted.

That'd be neat. But there's no standard for voltage for home solar: The batteries might be 12, 24, 48v, 60v, or even much more. Meanwhile, the panel arrays commonly output anything as low as 0V and up to ~600V. There's not much for rules and norms here. Even if we were to standardize a low ( But, sure -- we can play it out. So let's say we have an in-home 48VDC distribution standard and decide that this is the path f…

Almost all home batteries are 48v, I think it would be reasonable to standardise on that.

So 48v it is.

Is the juice worth the squeeze, though? Two sets of home wiring voltages? Substantially bigger copper wire inside the walls instead of existing copper, in order to do the same work? Two sets of appliances (of all sizes) on shelves at the store? More adapters?

Billy now needs to bring 2 wall warts to make sure he can charge his portable gear at a friend's house instead of just 1, because he's never sure until he gets there if they've got a 120 or 240v house like they all used to be, a combination house, or if it's one of those solar-only places that only has the weird plugs.

What we have now is 1 cable plant connecting the rooms of a home, and an increasing number of hybrid solar inverters that -- on a sunny day -- cheerfully convert solar power directly from whatever the panels are outputting to the 120/240 VAC wiring that both existing and future appliances know how to use. At night, these hybrid systems do do the same thing from whatever voltage the battery uses and convert that to AC. There's only 1 voltage, and only 1 plug; Billy brings 1 wall wart and knows he can charge his stuff.

To be sure: What we have not strictly ideal, but then neither is changing things without a clear positive benefit.

Again: What's the qualitative advantage of changing this, other than change for the sake of change?

DC might feel nice and neat, but in reality it doesn't seem to be shaped that way at all to me.

Re: Data centers are transitioning from AC to DC

#407

Post by contravariant »

rdtsc wrote: post #135
Animats wrote: post #118

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 mechan…

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…

The phrase "when it is detected" makes me nervous.

Re: Data centers are transitioning from AC to DC

#408

Post by marcosdumay »

matt-p wrote: post #403
marcosdumay wrote: post #371

Earlier quoted context omitted.

I'm not sure converting the solar and battery to 48V, distributing it around, and converting it to the needed voltage at the point of use is any more efficient than inverting it into 230V and distributing it around. Also, you'll need wires that 5 times thicker. Instead of needing a reasonably 1mm^2 for a normal 16A line, you'll need 5mm^2 for the same power.

Solar and battery are already at 48v in most cases, so you are avoiding converting it to AC. I agree, it's unserious to suggest a cooker or something high power is going to run off of 48v. But for loads like lights, PC/Laptop/TV/Audio 16a at 48v is ~770W which is adequate for these devices.

Both solar and batteries voltages vary wildly and require a converter to use.

Re: Data centers are transitioning from AC to DC

#409

Post by wat10000 »

the_cosmos wrote: post #399
wat10000 wrote: post #288

Earlier quoted context omitted.

There is a true zero potential. You can detect this because two charged objects with zero delta between them will still repel each other. I think a circuit should mostly care about the deltas, but when you’re talking about things like phone lines, the earth becomes part of your circuit. You can’t influence its potential (it’s almost exactly neutral because any charge imbalance gets removed by interaction with the int…

Voltage is _always_ relative; you only ever measure differences between two points. Voltmeters have two probes. Ground is just a convenient reference, not a universal zero. And while Earth can act as a reference or return path in some systems, it’s not perfectly neutral or fixed...it’s just large enough to approximate that in practice. (The interplanetary medium aka aether doesn't exist) Objects don’t repel because t…

Can't you define zero as the limit of the potential at infinity? And neutral charge bodies in empty space are generally close to that.

The interplanetary medium absolutely exists. I'm not talking about aether. I'm talking about the soup of dust, gas, and particles that fills space in the solar system. It contains a lot of charged particles, which is what keeps Earth extremely close to neutrally charged. Any deviation from neutral starts attracting positively charged particles and repelling negative, or vice versa, which equalizes the charge.

I didn't say objects repel because they're at the same potential. I said that objects at the same potential will still repel each other if that potential isn't zero.

Seriously, what is this reply? Aether? Objects repelling because they're at the same potential? You seem to have read a comment very different from what I wrote.

Re: Data centers are transitioning from AC to DC

#410

Post by kjs3 »

Brian_K_White wrote: post #382
kjs3 wrote: post #358

Earlier quoted context omitted.

I'm not talking about unplugging. Normal use.

And in normal use, how often do you handle or cycle an rj45 vs a usb? Even when it's your job the usb are still handled and cycled way more often. You might handle 100 ethernet jacks today, but it won't be the same one 100 times. You plug it in and don't touch that one again for 5 years.

You mean the ethernet cable in my laptop? Couple of times a day. The box under my desk? Often? How about the hundreds of devices I work with that have RJ45 connectors for serial access? All the time? Are you seriously telling me you hold up a (decently made) ethernet cable next to a USB-C connector and think "yeah...the one a fraction of the size of the other is obviously mechanically stronger". Is this some Apple shill campaign to try and get people to think "no, no...the smaller, thinner, narrower and shallower the connector is the better it will be someplace where people bump it all the time"?
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