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Comment by oakwhiz | Hacker News Reader

PC power supplies can be in the 2200W range already. What's wrong with that?

The external power you're talking about would be like 1 volt at hundreds of amps. What's the point of that? The connector and cable would be huge, think copper feeders. The existing set up where a higher voltage (12v) is stepped down to all dynamic target voltages (Vcore, memory etc) is fine and there isn't anything wrong with that. No need to reinvent the wheel. I don't want 1 external power supply per graphics card, what is the point of a modular internal power supply then?

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On the other hand, I wish eGPUs were more popular/standard. Having a separate enclosure is nice when the GPU is the main outlier to a modern system.

The rest of the PC can run off, what, 200 watts, and fit on a nano motherboard with basic cooling? Then comes the big ass space heater GPU that draws most of the power and disrupts airflow for everything else. Why not have it in its own little cage, almost like a game console? It can get better cooling that way, its own power supply that maximizes output instead of efficiency, and easy upgrades. Connect it when you wanna game or do AI stuff, leave it completely off the rest of the time.

If it had its own little web enabled controller, maybe you could even rent it out for processing workloads in the clouds.

I haven't looked at the eGPU space in a while, but the convenience of being able to move a very expensive GPU between machines without taking apart the machines or having excess power is definitely an interesting idea especially now that ML models are so popular.

What's the current state of eGPUs these days? I had a quick look, and wow, there aren't many eGPU enclosures going about, and what there are, are expensive.

I always saw them as intended for laptops rather than desktops - are there any downsides or performance penalties compared to slotting directly into a PCIe slot?

> are there any downsides or performance penalties compared to slotting directly into a PCIe slot?

Latency, for one. All signals must at least pass through two Thunderbolt/USB4 chipsets on their way to and from the GPU, and at least for anything but high profile AMD CPUs Thunderbolt is connected to the southbridge instead of northbridge (where the x16 GPU slot is).

Are there none that still use pcie, just through a cable instead of a slot?

That's too bad, if so :(

PCIe can only go to like 14 inches in trace length, and that's already challenging enough to do for risers and extender cables without compromising signal integrity.

[1] https://www.protoexpress.com/blog/pci-express/

There is a way to solve this with optical but the cost is still high and it's not terribly compact. Usually you can only get 4 lanes directly into one optic. Most implementations I have seen rely on a 2-port PCIe packet switch chip, and they rely on SRIS/SRNS clocking and hotplug/"surprise removal" support is provided by that switch (don't want a crash if you yank the cable)

I see. Thanks for the explanation!

(Not a hardware guy. Didn't realize there physical/electrical limits to these.)

otoh, many risers are out of spec and still work

There's a difference between "appears to work" and "works at advertised speeds". PCIe is surprisingly tolerant but it will downgrade the link speed during initial training.

The solution of "huge beefy modular power supply" involves starting with a power supply that is way overkill; here, we can expand piecemeal. Nothing is more modular than a separate unit. Modular power supplies don't allow you to "upgrade" them, only to reduce cabling.

Re: voltages. I mean the opposite. The idea here is that we could supply, say, 50V for the graphics card to step down now that we're no longer constrained by system voltages. Now there is much less current going through the fiddly connector. A 2200W power supply constrained by 12V is delivering at least 180A.

I could get behind this idea. Open Compute has a 48 volt rack specification, negative 48V is common in telecom since forever, PoE standards use roughly 48V, and 48V is at the upper limit of what's often considered "safe" by various standards and many (but not all) regulatory bodies across the world.

What hurts 48V adoption is typically component cost. In the past there was a large price jump between 12V and 48V-60V capable circuits, with a lot of competition and demand at 24V from industrial stuff but less at 48V. Part of the problem is the huge ratios of 10x-50x between the voltages and the idea that the semiconductor switching elements have to be able to handle the peak voltages encountered in the system. In order to realize a 48V system at minimum cost you kind of need a flyback style power converter, leaning on a transformer's winding ratio to help. Dealing with custom magnetics sucks and engineers have in the past related to me how much they try to avoid dealing with magnetics. The frequency you want to use is high and this makes the magnetics smaller but increases the stress on the switching element (MOSFETs). The power you get off a flyback-buck like this can be a little noisy if not postregulated so you might need clever tricks to regulate it better to reduce that in the first place. I have noticed that high powered PoE adoption and lithium battery pack demand (like for electric bikes etc) is driving some of the costs on these things down a bit.

> PC power supplies can be in the 2200W range already. What's wrong with that?

For starters - a typical 15amp outlet is only supposed to have a 1,440W continuous load, 1,800W peak.

> For starters - a typical 15amp outlet is only supposed to have a 1,440W continuous load, 1,800W peak.

Luxury! Where I live the typical socket is only 10A, and the most common standard voltage is 127V (it varies by city, some places have 220V), so the maximum would be around 1,2kW.

(There's also a 20A socket, with slightly larger pins, but it's mostly found on sockets dedicated for window air conditioners.)

In domestic North American environments. You can have 20 amp outlets and higher voltage outlets such as 208V or 220-240V. Most power supplies accept universal voltages, and I have personally seen a demonstration from a manufacturer of a workstation PC designed for 20 amps at 120V.

Sure, you can. But 20A circuits outside of kitchens and bathrooms are exceedingly rare in north america. Heck - even on a 20A kitchen circuit, I don't know that I've ever seen one with a 20A receptacle - they always have standard 15A receptacles.

240v is even less common.

So ... yeah, you can do it, but you're talking about the equivalent work to having an electric car charger put in your office.

> PC power supplies can be in the 2200W range already. What's wrong with that?

I've been building PCs since I was a kid, and I'd still rather gouge my eyes out with a rusty spoon than have to change a PC power supply - it's just so, so damned fiddly and time consuming in almost every case I've ever seen :(

Treat yourself, buy the largest case you can find and nice custom cables :)

I currently have a large tower case. But even with such cases, it's typically really difficult to even get access to the PSU.

I recently rebuilt my PC, and things have changed substantially in recent years.

Where we used to fit all the components from the same side of the case, modern cases have the PSU fitted from the reverse side, allowing the cabling to be concealed yet reasonably easy to access. I believe this was intended to make things pretty for the glass-window enthusiast crowd, but it also makes changing the power supply easier.

There are also substantially fewer components in general. Things like networking and sound have been on the motherboard for decades, of course - but now 5.25-inch drive bays are also gone, with 3.5-inch bays in decline. And of course with M.2 you might not need any other drives.

All of which means there are fewer power cables to plug in than ever before!

"glass-window enthusiast crowd" - I'm about to go off topic, but I really wish that they would metallize the plastic/glass windows on these cases to improve EMC (or get a hair closer to TEMPEST compliance). I miss the 5.25 inch bays as well since that was a fun way to customize the front of a case with accessories and hotswap bays.

I have an NZXT H7 Elite case. Access to the PSU is pretty easy. Pop the side panel, undo the 4 screws holding the PSU to the case, slide it out.

I've literally never had a problem changing a PSU in a non-SFF case. Disconnecting all the molex connectors takes longer than actually swapping the PSU.

It could be even faster if manufacturers would standardize on modular connector pinouts. You could do half the unplugging. Unfortunately there is not really any compatibility between modular cables, to the point of being partly responsible for exploding PC incidents.

yeah, that would make it trivial

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