Comment by eigenvector | Hacker News Reader

Comment by eigenvector | Hacker News Reader

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As it is, typical home electrical systems have no active components. There are just wires, panels and bimetallic circuit breakers. These systems are nearly maintenance-free over a lifespan similar to that of the structure.

A DC distribution system in the home would require both a high power rectifier at the main panel to something like 125 VDC, then many smaller DC/DC converters throughout the home for your usable voltages like 5/9/15/20 V that are too low to be effectively distributed.

All of those things would need to be maintained and upgraded over the years, because there is no such thing as power electronics that last forever. After a few electrician visits, you might find that you haven't saved any money at all.

Even if you have solar, you still need a DC converter because it will not output a constant voltage let alone all of the DC voltages you need for your devices. And generation any further away than your own rooftop is going to need to be stepped up to higher-than-home voltages and then back down for use in your home - all of which is exactly why we currently use AC for distribution.

You forgot the magnetic trip of the breakers and the now-mandatory RCDs. The latter are far more complex than a simple rectifier would be.

And even then, there's no reason such a rectifier module couldn't be a pluggable module. They still last 10~20 years, easily.

I don't see what all those low voltage rails should be for. Computers typically work fine on 300~350 V DC, and if anything, there is reason to go from 12 V to a higher supply bus voltage, actually deployed in some modular servers by now (with a 48 V bus between the local battery backup modules, AC-fed supplies, and motherboards).

The ostensible benefit to DC distribution in homes is to be more economical and simpler for devices that already run on DC - not to redesign ever device ever made to accept mains-voltage DC. If your iPad and your laptop and your blender still need a power brick to work, what's the point?

Using high-voltage unnecessarily to avoid using a DC converter is also not going to save money. Yeah, you can use a 300 V DC motor in a coffee grinder, but why? It's just going to cost more money to make.

90% of things in your home would happily run from 150V DC, even though they aren't rated for it.

Source: I sometimes connect my solar panels direct to my AC wiring without an inverter, and my house works entirely except my washing machine and fridge (both of which have AC motors in). Even my vacuum cleaner works (although it's on-off switch doesn't work, since it uses a thrysistor!). Phone charger, laptop charger, oven, microwave, doorbell, furnace, routers, TV, monitors, desktop pc, all work fine.

If some country declared tomorrow that all electrical devices must accept AC or DC, not that much would have to change.

I had no idea about this. Can it damage things that won't work (eg things with AC motors). I've been building out electrical in a campervan and always wonder if there were DC equivalents to a lot of things.

Yes. AC motors will normally blow their fuses immediately.

But a small AC motor (eg. a fishtank water pump) will burn out before the fuse blows.

Surge protector strips sometimes have isolation transformers. These will also blow their fuses immediately.

My point is, that the European accidentally-DC-capable mains equipment can be expected to complain/sustain overcurrent damage, provided it isn't able to handle US residential voltages.

Hence you might as well take the opportunity and switch to a higher in-house distribution voltage than the typical 120 V.

And that 300 V DC motor may actually be cheaper, as you could run a BLDC driver directly from the DC supply with just minimal filtering.

The enhanced power density and copper-efficiency of these high-frequency 3-phase motors may make up for the cost of said inverter, even neglecting the considerably increased energy efficiency over a typical single-phase-capable "oldschool" motor.

48V DC has always been the standard for DC-fed rack mount servers as far as I am aware. Telcos have used -/+ 48V since A. G. Bell.

Yes, but single-stage conversion from 48 V to ~1.2 V core/memory voltages is inefficient with the typical buck topology, due to the low duty cycle.

There are solutions based on ZCS (+ZVS) (semi-)resonant switched capacitor topologies that could (technically) do this in essentially one stage. But because they are still somewhat recent and rely on either GaN enhancement-type FETs or low-average-blocking-voltage topologies that make use of e.g. small 5V-capable IC process nodes and some tricks to have the individual power transistors floating.

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