Hacker News Reader

Low-power 12V or 24V DC is very doable around the house, for small-scale LED lighting, etc. But if you limit yourself to small connectors and thus reasonably low currents (like 10A, as I did), it's 120W or 240W per connector at the very top.

Serious power, in the kilowatt range, would require much higher voltage, and still much bulkier connectors and thicker conductors. OTOH 400V DC should be comparable in this regard with 220V AC, which has a 380V amplitude. The 400V DC standard is relatively widespread and well-supported by existing industrial equipment. Connectors are comparable in size to the (grounded) Euro plugs.

Certain things get a lot more complicated when you go from AC to DC. Two of the most significant issues for home use are connects that can be disconnected under load (arcing is a serious issue here) and turning DC power on/off with mechanical switches (arcing is also the issue here).

Industrial DC devices get around these issues with stricter rules and bulkier/more complex devices. E.g. electric cars use contactors to connect batteries rather than a simpler relay/switch.

This is indeed so.

But the standard clearance for air gaps is 1 mm / kV, and arching distance is below 0.4 mm / kV. More advanced and faster mechanical switches should work fine at 400V DC.

Also IGBTs may be a preferred way, especially with various smart switches.

Sockets and plugs seem to be the hardest part to make cheap and reliable. But industrial solutions can likely be adapted.

I have no idea what the average household load looks like.

I could imagine a scenario where every outlet also has a USB port. It could run your laptop and your lights. Obviously it can't run a fridge or a stove; maybe future fridges would run off the same current as the stove?

What I'm most unclear on is the middle range. I know you can't run a hair dryer or microwave that way. What about a food processor? Maybe a toaster?

I'm trying to figure out how much that middle range makes this a deal breaker.

Didn’t utilities in NYC offer DC service for a long time? See https://archive.nytimes.com/cityroom.blogs.nytimes.com/2007/...

Old buildings had elevators, lights, and so on, that operated on DC.

Yes, that was edisons original system.

Yeah I feel like this is very tractable problem. Most of my stuff runs on USB-C anyways, I just need USB power outlets everywhere. My lights, motor blinds, bathroom fans can run on POE, including data.

My oven should already have its own battery installed, or a capacitor bank for very fast preheat.

My fridge can do the same. It’s rarely actually compressing.

I’m mostly just trying to avoid needing to buy very expensive inverters.

Those types of appliances are coming:

Induction stoves with batteries built in, and why they matter

A conversation with Sam Calisch of Channing Street Copper Company and Wyatt Merrill of DOE.

https://www.volts.wtf/p/induction-stoves-with-batteries-buil...

And so we come full circle. Using a DC battery to power an inherently AC induction process. These are not your mother's home appliances.

Induction DC stove tops are also popular for off the grid cooking…when you just have solar panels and a car battery.

USB is too low a voltage to be useful. You will always need an adaptor to get from mains voltage to something useful for devices. There is nothing wrong with AC for mains, and the ease of transformers is not to be ignored.

Current voltage AC is still ideal for powering a house '

If USB PD were used, you would have up to 48V (240W) available, which should cover all but the largest appliances.

48 volts is not enough to cover a house without very large and expensive wires. And you still need to get higher voltage from the street to the house.

My fridge can do the same. It’s rarely actually compressing

Some new fridges seem to have much smalker compressors, which run all the time.

Their secret is variable speed compressors, advertised as "Inverter technology".

The compressor run continuously, it just changes speed so there is no noisy and inefficient start-up surge current.

Also common in heat=pumps, Air-conditioners, etc.

i could easily see USB 4 Power Delivery Extend Power Delivery and its successor become a de-facto standard. Many electrical outlets are already coming with usb ports nect to standard AC outlets. once that becomes standard on all new outlets you will see many more devices take advantage of that using USB for power then. after that you will see more demand for even higher voltage in future versions of the USB standard. once it reaches a tipping point it will make since to run DC throughout houses and instead of converting from AC to DC for the USB ports it will be reversed converting to ac for the legacy outlet next to the USB power ports

USB is too flimsy and awkward. A power profile negotiation using existing power sockets would be better.

USB-C might be that DC standard. It is easy to install aftermarket AC outlet modules with an embedded transformer feeding a pair of DC sockets. One could easily imagine a house wired with such USB power outlets, lacking the AC sockets - they'd presumably be supplied by buck converters from some higher bus voltage, likely 48v.

There are outlets with USB-A and USB-C ports. I don’t think there are any with USB-PD because chips are expensive for that. It would be possible to have multiple ports and no AC ports.

But problem is places with lots of devices, then would need power strip and might as well use AC one.

The problem is appliances that draw too much power for USB-C. They also draw too much power for 48V DC. There isn’t any advantage to switching the wall voltage.

> I don’t think there are any with USB-PD because chips are expensive for that.

Leviton makes a 60W unit now that supports PD. Be warned it's a little janky in that it tries to be "smart" and re-negotiate (well, outright drop to 5V) the port if your device stops drawing substantially less current than requested. This can confuse some devices - especially those without batteries. Otherwise I can say the 20V/3A profile works fine on my macbook.

I installed a few outlets last year which claimed to offer USB-PD at 18 watts. They were certainly more expensive than any other kind of receptacle, but not so much that I remember what I spent on them.

I don't think anyone would switch the wall voltage altogether; not in one generation, at least. But a majority of the devices we plug into AC outlets these days convert that power to DC before doing anything with it, and a majority of those devices do so using USB; so one could imagine that a house which had solar panels and batteries could also have DC power wiring and dedicated USB-PD receptacles, skipping the inverter and all the rectifiers.

The majority of devices might be USB powered, but the majority of energy use is from large AC appliances. USB is solved by adapter or special outlets.

Also, the DC voltage for house wires and batteries need to be much higher than USB voltage so will need conversion. Might as well have it be AC to DC converter.

There is a problem connecting solar panels to batteries and needing two inverters. But that could be solved with higher voltage DC between them.

A 48V dc circuit over a 12 AWG wire would provide less than 1/2 the wattage (power) available in a typical 120V AC circuit. You’re still going to need some circuits that can deliver 1500W to power appliances, space heaters, window AC, etc.