I wanted to share this opinion on Hackaday about a topic that is the usefulness of a something that has become ubiquitous relatively fast.
This techonolgyy has a lot of potential, what do you think?
I wanted to share this opinion on Hackaday about a topic that is the usefulness of a something that has become ubiquitous relatively fast.
This techonolgyy has a lot of potential, what do you think?
The problem is that nothing wants the same DC voltage. It wants 3.3V, or 5V, or 12V, or 48V, or 18.7V, or whatever. You end up with layers of conversion and save nothing in the end.
Let’s say you start with solar photovoltaic panels, a DC source. It feeds into a DC-DC inverter that puts out a steady 48V. Existing DC-AC microinverters can get 95% efficiency, and DC-DC conversion can be around the same.
In an AC system, we convert to DC at point of use (be it through a wall wort, a floor wort, a USB power port integrated into traditional AC plugs, or something else). This conversion can likewise be around 95% efficient.
In a DC system, we still have to do a DC-DC conversion to get the voltage you actually want at point of use. This is around 95% efficient, as well.
In the end, we stack the same number of conversions at around 95% efficiency no matter if we run AC or DC. Except that assumes we’re coming from a DC source in the first place, like solar photovoltaic. If we come from an AC source, like wind or hydro or pretty much anything besides a solar panel, then we only have transformer losses of converting the higher line AC voltage to what your house uses. Those aren’t 95% efficient; they’re closer to 98% efficient, so we’re better off.
Not only that, but we would still prefer AC for basically anything with a high draw motor, like air con or refrigerators. Now we’re doing DC-AC conversion, and that’s closer to 85% efficient. These are some of the highest draw items in a house–and they’re going to be used more as heat pumps for HVAC, water heaters, and clothes dryers become more common–so that drop in efficiency hits that much harder.
So DC home power sounds like a good idea until you break down how conversion efficiency hits things in practice. If we’re just going to get to the same place, why bother ripping out our current system?
That said, I would like to see PoE get used for residential more. There’s lots of devices that can run off 48V and can also use networking (like smart LED lights). Why not put it over the same plug and skip having to put those devices on a wireless network? Also, you don’t need a licensed electrician to run it. You can’t be an idiot about how to run and terminate it, but you don’t need a license. This would likely be alongside our existing AC wiring, though.
_ It wants 3.3V, or 5V, or 12V, or 48V, or 18.7V,
Exactly
That’s why if you had a 110VDC supply at the wall, you do a simple PWM step-down to the required voltage in every device.
LOADS cheaper/efficient than any USB-C PD circuit…
Saves on transformers, saves on dozens of USB PD wall outlets, saves on communication needed to communicate the PD required between each device and every USB PD wall outlet.
Much cheaper. More efficient.
If only the wall was 100VDC instead of AC
Why would 100VDC help over AC? You lose very little by rectifying AC.
And again, these aren’t the high draw items in the house. Stuff with motors are, like air con and refrigerators. Those are better left on AC. Why bother when the gains are small?
Stuff with motors are, like air con and refrigerators. Those are better left on AC.
No. Trend is they are all showing up with frequency drives. Of which those inverters are rectifying to DC before making their own AC.
Efficiency gains are massive of a frequency drive , hence why they are doing it.
Would be even better if they could drop the first rectifying circuit and just use the inverter portion only.
You lose very little by rectifying AC
You lose a lot actually in all the small cheap rectifiers that are in every device in the house.
Where a single purpose designed FET rectifier that is built for efficiency at the breaker would be drastically better.
In general, you don’t want DC or Ethernet cabling directly next to AC wiring. I forget the exact rules and distances, but you definitely don’t want them in the same conduit at least. Shielding only helps so much. Just a general note as you probably didn’t mean it quite so literally…
I do like PoE though! I have a server rack that powers a bunch of RPi 4s through a PoE+ switch. Had to make sure there was plenty of headroom as RPi 4s can pull just a wee bit of current under full load. I am just happy it works at all.
It’s running parallel to AC wiring. It’s usually not a big deal in practice, except for higher draw cable.
Your right. I was thinking about my job that runs 480VAC. Either way, testing for interference and noise when you run into issues can go a long way. I am just glad that, to my knowledge, CAT 7 is one standard with everything shielded. CAT 6 had so many variations and most packaging and online portals would not even tell you which ones they were using in the first place. Almost as bad as USB-C connectors.I gave up and ordered some short CAT 7 patch cables for the server so I wouldn’t stress over it. Ended up being a little cheaper than a lot of the cat 6 sets too.