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Comment by ashleyn | Hacker News Reader

most household circuits can only support 15-20 amps at the plug. there will be an upper limit to this and i suspect this is nvidia compromising on TDP in the short term to move faster on compute

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So you are saying that Nvidia will finally force USA to the 220V standard? :)

Many American homes already have 240V sockets (eg: NEMA 14-30) for running clothes dryers, car chargers, etc. These can provide over 7200W continuous power!

I guess PC power supplies need to start adopting this standard.

You can't use a NEMA 14-30 to power a PC because 14-30 outlets are split-phase (that's why they have 4 prongs - 2 hot legs, shared neutral, shared ground). To my knowledge, the closest you'll get to split-phase in computing is connecting the redundant PSU in a server to a separate phase or a DC distribution system connected to a multi-phase rectifier, but those are both relegated to the datacenter.

You could get an electrician to install a different outlet like a NEMA 6-20 (I actually know someone who did this) or a European outlet, but it's not as simple as installing more appliance circuits, and you'll be paying extra for power cables either way.

If you have a spare 14-30 and don't want to pay an electrician, you could DIY a single-phase 240v circuit with another center tap transformer, though I wouldn't be brave enough to even attempt this, much less connect a $2k GPU to it.

As far as I’m aware (and as shown by a limited amount of testing that I’ve done myself), any modern PC PSU (with active PFC) is totally fine running on split-phase power: you just use both hots, giving you 240v across them, and the ground. The neutral line is unnecessary.

If you installed a European outlet in a US home then it would be using the same split phase configuration that a NEMA 14-30 does. But many appliances will work just fine, so long as they can handle 60 Hz and don't actually require a distinct neutral and ground for safety reasons. Likewise NEMA 10-30, the predecessor to NEMA 14-30 which is still found in older homes, does not have a ground pin.

I thought the main purpose of providing the neutral line was to be able to power mixed 240V and 120V loads.

I feel like every time I read about USA standards I inevitably discover that any and all SI standards are actually adopted somewhere in the USA - measures in the NASA, 24h clock in the army etc. Just not in the general populace. :)

The entire residential electrical grid in the USA uses 240v, split phase. One hot wire at 120v, one neutral at 0v, and one hot at -120v, out of phase with the other hot. Very rare to have anything else. It’s just that inside the building, the outlets/lights are connected to one side of the split phase connection or the other, giving you only 120v to work with. But then we have special outlets for electric clothes dryers, EV chargers, etc, which give you both hot connections in a single receptacle, for 240v.

PC power supplies already support 240V. Their connectors can take 120V or 240V.

Yes, but a standard household wall socket in the US supplies 120V @ 15A, for a max continuous power of 1.4 kW or so. So typical power supplies are only designed to draw up to that much power, or less.

If someone made a PC power supply designed to plug into a NEMA 14-50 you could run a lot of GPUs! And generate a lot of heat!

You just need the right adapters to connect the C14 connector on most PSUs to NEMA 14-50R. Use these two:

https://www.amazon.com/IronBox-Electric-Connector-Power-Cord...

https://www.amazon.com/14-50P-6-15R-Adapter-Adaptor-Charger/...

As long as the PSU has proper overcurrent protection, you could get away with saying it is designed for this. I suspect you meant designed for higher power draw rather than merely designed to be able to be plugged into the receptacle, but your remark was ambiguous.

Usually, the way people do things to get higher power draw is that they have a power distribution unit that provides C14 receptacles and plugs into a high power outlet like this:

https://www.apc.com/us/en/product/APDU9981EU3/apc-rack-pdu-9...

Then they plug multiple power supplies into it. They are actually able to use the full available AC power this way.

A (small) problem with scaling PSUs to the 50A (40A continuous) that NEMA 14-50 provides is that there is no standard IEC connector for it as far as I know. The common C13/C14 connectors are limited to 10A. The highest is C19/C20 for 16A, which is used by the following:

https://seasonic.com/atx3-prime-px-2200/

https://seasonic.com/prime-tx/

If I read the specification sheets correctly, the first one is exclusively for 200-240VAC while the second one will go to 1600W off 120V, which is permitted by NEMA 5-15 as long as it is not a continuous load.

There is not much demand for higher rated PSUs in the ATX form factor most here would want, but companies without brand names appear to make ones that go up to 3.6kW:

https://www.amazon.com/Supply-Bitcoin-Miners-Mining-180-240V...

As for even higher power ratings, there are companies that make them in non-standard form factors if you must have them. Here is one example:

https://www.infineon.com/cms/en/product/promopages/AI-PSU/#1...

The U.S. has been 240V for over a century. It uses split phase which has opposite phases on each hot line to let you take one and connect it to neutral to get 120V. If you connect both hot lines, you get 240V. For some reason, people in Europe and other places are unaware of this despite this having been the case since electrification happened in the early 20th century.

People are aware of this, but the regular sockets are connected to 120V only. You can (easily) hack an electrical circuit ("consumer unit" in UK) to deliver 240V on an existing plug, but that would be a very serious code violation. SO unless you hack your house circuits, you have 120V on regular sockets.

You can replace the receptacles with ones meant for 240VAC at the same time you modify the wiring. Then it should be okay. Replacing the NEMA 5-15 receptacles with NEMA 6-15 receptacles would work.

Then you could also say that Europe uses 400 V. You get three-phase power with 230 V phases in your home, and high-powered appliances are often designed to use all three phases.

But when people speak of voltages, they usually mean what you get from a typical socket.

This explains why a number of people in Europe seem to love the idea of having triple phase to DC on board chargers on electric cars, even though it makes more sense to have those at the charging points.

That said, a typical socket likely varies more in the U.S. than in Europe since anything that is high draw in the U.S. gets 240VAC while Europe's 220VAC likely suffices for that. I actually have experimented with running some of my computers off 240VAC. It was actually better than 120VAC since the AC to DC conversion is more efficient when stepping down from 240VAC. Sadly, 240VAC UPS units are pricy, so I terminated that in favor of 120VAC until I find a deal on a 240VAC UPS unit.

I wonder if they will start putting lithium batteries in desktops so they can draw higher peak power.

There's a company doing that for stovetops, which I found really interesting (https://www.impulselabs.com)!

Unfortunately, when training on a desktop it's _relatively_ continuous power draw, and can go on for days. :/

Yeah that stove is what I was thinking of!

And good point on training. I don't know what use cases would be supported by a battery, but there's a marketable one I am sure we will hear about it.

They already use capacitors for that.

Batteries and capacitors would serve different functions. Capacitors primarily isolate each individual chip and subsystem on a PCB from high frequency power fluctuations when digital circuits switch or larger loads turn on or off. You would still need to use capacitors for that. The purpose of the batteries would be to support high loads on the order of minutes that exceed the actual wall plug capacity to deliver electricity. I am thinking specifically of the stove linked in your sibling comment, which uses lithium batteries to provide sustained bursts of power to boil a pot of water in tens of seconds without exceeding the power ratings of the wall plug.

It is the same function on different time scales. If you had a big enough capacitor, you could achieve the same thing. Not coincidentally, the capacitors in PSUs are huge, although not battery sized in terms of capacity. The purpose of the capacitors in the PSU is to keep things powered during a power outage to allow for a UPS to switch to battery. The technical term for this is PSU hold up time.

I consider smoothing out high frequency power fluctuations and providing power over a period of minutes that exceeds the capacity of the wall plug to be conceptually two different functions, even if they have similarities.

You’re right that a large enough capacitor could do that, and I’ve worked with high voltage supercapacitor systems which can provide tens of watts for minutes, but the cost is so high that lithium batteries typically make more sense.

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