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Comment by sowbug | Hacker News Reader

As I understand it, 48V makes sense for the long cable runs of PoE and server racks, as well as the varying voltage needs of cars. But a PC doesn't have such runs, and 12V is already higher than any PC component's voltage. It seems like a good tradeoff.

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This is correct. I see a future where there is an optional 48VDC line that is run in our homes to power stuff like LED lights and dedicated USB ports. This can become especially important for homes that use solar and stored electricity where you might be having to go from 48VDC -> 120/240VAC -> 12VDC -> 5VDC (see note) with each conversion resulting in the loss of some power due to the fact that these cannot be 100% efficient.

Note: a lot of flyback-style transformers are setup to step down the AC voltage 1/10th (12V in 120VAC, 24V in 240VAC) because transformers are cheap/abundant for that. It’s cheaper often to put a buck converter that takes any voltage from 12-24V and convert it to a fixed required voltage.

If we’re moving to a new standard I’d much rather we standardize around 240V DC with an improved plug design.

You’d have HUGE savings on the copper required for a standard home, plus you’d get a substantial increase in power capacity.

240VDC conversion to any low voltage (1V for cpu/gpu) won't happen.

Most of the copper is spent on carrying hundreds of amps at low voltage not the 12V lanes.

240VDC is way too dangerous for residential use. And really it's not super practical to drop that down to 5v for charging your widgets. 48V makes much more sense.

And for that matter, I wouldn't want 240VDC on utility poles either. If a line goes down, it's so much more dangerous.

The more sane solution would be a high capacity DC converter installed next to the line transformer that feeds your street. DC infrastructure inside the home makes total sense at moderate voltages. City scale DC at line voltages is honestly terrifying.

All of Europe uses 220v-240v for residential use.

That’s AC, not DC.

Irrelevant. It’s virtually the same risk, the only minor difference between 240V AC and DC is a hypothetical arc is harder to extinguish in DC (AC benefits from the oscillation slightly), but if were to the point that wires are arcing we’ve already got major problems.

Huh? DC is generally considered safer than AC at a given current or voltage:

https://en.m.wikipedia.org/wiki/Electrical_injury

It is, however, considerably more complex to make DC circuit breakers or ground fault detection devices.

Nonsense. I have 600v DC from my solar panels. It’s not magic, just needs proper insulation.

Utility poles are 10’s of thousands of volts (AC), I guarantee you that will cook your goose AC or DC.

Why not just throw in a DC/DC converter from 48 to 12V? You need protection anyway (so that failure won't take down your whole 48V microgrid) and perhaps even management.

No, 12V is already too low for the most power-hungry PC components (GPUs), as witnessed by the trouble nVidia has had with power connectors on the 4090.

If they're going to go to the trouble of coming up with a new standard, it's asinine to base it on 12 volts, which is already known not to be sufficient. They need to use 48V.

The GPU runs at 1V (sub 1V usually). The issues with the power delivery and the nvidia connector are their own.

That's not how it works. The GPU receives power at 12V via the PCIe 8/6+2 connector at 20-30 amps or so. It then steps that down to ~1 volt at the point of load, at hundreds of amps, but that's irrelevant.

The problem is that safely handling "20-30 amps or so" cannot really be done with cheap consumer-level Molex connectors, or at least should not be done, ideally. More expensive connectors are needed, so what they are doing now is asking for trouble. However, the voltage doesn't determine how hot it gets; only the current influences that. If they were distributing power at 48 volts, the current would be about 1/4 what it is now, and overheating at the connector would not be an issue.

says 600W GPU, that's 50A. Screw based connectors would do just fine - delivery 48V would require to step it down to some other (sub 20) voltage first. That part would be at the GPUs.

Also I do understand how it works.

Yes, certainly, using better connectors would head off overheating problems. That's not free. Something else that isn't free is extra copper in the wire harnesses from the PSU.

Meanwhile, it's true that point-of-load regulation from 48V directly to 1V will be less efficient (well, maybe; see nimish's link below). But by the same token, regulation in the PSU would be more efficient if it didn't have to go all the way down from 150-300 VDC on the primary side down to 12 at the output.

A good compromise would probably be the geometric mean between a few hundred volts and the voltage at the load with the highest current. Assuming 250 volts on the primary as a compromise between 120/240VAC operation and 1V all the way downstream, that would be about 16 volts. Doesn't seem like a big improvement, but it would be enough to lower the current at the GPU input connector by about 1.8x compared to 12 volts.

Either way, sticking with 12 volts in any new standard is just stupid. 48 has another advantage, which is that automotive is going to (finally) start moving to it over the next few years. There could be a lot of room for parts-sharing between the two industries.

I’ll take the over on 3 years for automotive to switch to 48VDC.

At 50A, those screw connectors should be properly torqued. 50A is serious current. (20A is more than enough to start fires due to small-scale arcing.)

>properly torqued

Indeed - drop the phillips head already. Hex or torx, please. 50A is really on the very high side, though.

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