This makes me wonder if we shouldn't have an AC and DC circuits in the house. I mean, it could be all AC coming in, but at the box it splits into (at least) two different circuits (an AC one and a DC one).
AC circuit would still be used for things that have motors, but everything else uses DC.
Imagine how simple LED lighting could be on a DC circuit. Just an LED and resistor.
I only took a few electrical engineering classes so correct me if this is a bad idea.
Having an AC to DC converter at the mains to your house would be great. Using a reasonably safe 48V DC in the home seems reasonable. Modern high efficiency motor driven appliances all use internal AC->DC converters and a 3-phase DC->AC driver anyway. I'm still on the fence about what the DC voltage should be - upwards of 60-80 are still nice and require less current for a given load but you don't want your PC and TV to need too many stages to get low voltage.
It would be nice if some people got together and wrote a standard for DC powered homes. Preferably without a bunch of patented stuff included in the standard. Then all the pieces could be produced by various industry players and we could switch.
I have a big 48 port PoE switch (Ubiquity) and power tons of devices from it. You can get a GbE PoE “uninjector” which will give you a 5V micro USB output and use that to power tons of things all over the house, while also leaving the GbE usable at full speed (on Amazon). I also buy PoE versions of things whenever possible. I even have PoE switches powered by the core switch and home automation gear powered by PoE (e.g. Control4). Great low wattage DC distribution, and getting greater with PoE++ (I have just one 4 port PoE++ for now, but it is also 10GbE.)
A current limiting resistor isn't ideal for LEDs bright enough for home lighting. It's not very efficient compared to a proper constant-current LED driver. Losing the terrible power supplies in most LED lamps wouldn't be a bad thing, though.
The breadth of products like this [1] tells me you're far from the first person to think of that problem. Distributed circuits for DC is already a reality. Now we just need more light USB LED lighting solutions for around the home.
Right, but my question is would it be better to do the conversion once for the entire house or to make every single device bundle in its own transformer and rectifier as we are currently doing?
I was not clear. The point I was trying to make was that transformers are not perfect in the conversion even when there is no load there is some power loss in the form of heat. Not sure if it is a real problem or not.
You need the transformer to step down the voltage For example: going from 120V AC (in US) down to something the rectifier can use to produce the DC line voltage like 5V. An AC to DC converter will have both a transformer and rectifier.
For one, you don't need a transformer for stepping down voltage, as you can see in essentially every piece of consumer electronics nowadays. Your typical CPU nowadays runs in the 1-2 volt range, but PC and laptop power supplies and batteries provide various voltages between 3.3 and 20 V. Your typical desktop mainboard takes most of its power to feed the CPU from the power supply's 12 V rail. Yet, you won't find a single power transformer outside the power supply--the only transformers you will find on a mainboard are probably Ethernet signal transformers.
All of that is done by switching regulators, and those work perfectly fine for regulating 120 V down to 5 V as well.
Then, rectifiers really don't have a problem rectifying 120 V. Some of the cheapest diodes you can find are perfectly capable of rectifying 120 V mains voltage. In fact that works so well that almost every power supply, at least for consumer electronics, nowadays does just that: The input is fed through a rectifier and a filtering capacitor to first to procude (in the case of 120 V input) ~ 170 V DC. After that comes some sort of oscillator that then generates more or less AC from that, but at a much higher frequency, in order to feed that through a transformer--primarily for isolation, but if you have to have a transformer anyway, you might as well use it for reducing the voltage as well. The output from the transformer then is rectified again for most applications, which is a lot more difficult to do efficiently due to the high frequency and the low voltage.
I have 48vdc on my phone line which is thin wire and plenty enough power (amps) for very bright lights. This 48vdc phone line has been in my house for twice as long as I've been alive.
It seems like an efficient house would at least want a "lighting circuit" where you have a single transformer/rectifier/controller driving a bunch of LEDs all throughout your house. That type of lighting scheme seems like it could last decades if you use quality LEDs.
The usefulness seems questionable. LEDs have to be driven with current, so either you would have to have all LEDs in your house in series, with short-circuit switches for light switches, or you still have most of the electronics in every lamp/bulb anyway (saving only the rectifier and maybe needing only a smaller input filtering cap). The former is highly impractical (complete rewiring, one broken lamp makes all lamps in the house go dark, massive peak voltages if you have many lamps, ...), the latter isn't worth it either in device costs nor in efficiency gains (a shottky full-bridge rectifier probably eats less than half a percent of the lamp's power consumption at ~ 100 V supply voltage, less at higher voltages).
AC circuit would still be used for things that have motors, but everything else uses DC.
Imagine how simple LED lighting could be on a DC circuit. Just an LED and resistor.
I only took a few electrical engineering classes so correct me if this is a bad idea.