4 ms·

Makes me wonder if DC wiring will ever catch on in newer homes. We don't have much need for AC anymore. The only places in a home where one needs AC is in the

Makes me wonder if DC wiring will ever catch on in newer homes. We don't have much need for AC anymore. The only places in a home where one needs AC is in the kitchen for large appliances, and garage/laundry room. And really that's just because of the motors. I'm not sure if those could be converted to DC motors and what powerloss that might entail. But the point stands; you could totally get away with building a new home where you drop AC to the kitchen and garage, and then 12VDC+5VDC everywhere else (12V on the wires, put a regulator to drop to 5V in the outlet for USB-C ports). The power-loss of DC in a home won't be that large. The end result is that the AC to DC transformer will be centralized to one location, where you can spend more money up front to get higher reliability, cleaner power, better safety, and better efficiency. Plus, if you have solar, you can avoid AC to DC conversation altogether, saving on a good chunk of powerloss there. The caveat, of course, is that lots of devices don't natively support DC input. Phones, tablets, and modern USB-C laptops are fine. Lighting is easy; just do permanent LED installations. The LEDs will last a very long time since they won't have regulators in them. Desktops are an issue. I believe the only desktops that support DC input are HTPC builds, using those micro PSUs. Perhaps there's an HTPC PSU that's got enough beef to power a normal desktop? You'd also have to find monitors that accept DC input, which do exist but that will narrow your market significantly. Rob Rhinehart is an early adopter (see: http://robrhinehart.com/?p=1331 http://robrhinehart.com/?p=1331) of this type of home. Sounds crazy, but it seemed like a glimpse at a hopeful future, at least everything outside of the kitchen.

mmagin 11y ago
Well, uh, AC vs DC and 100-250 volts versus 5-48 volts are two completely different dimensions to the problem here. For example, there has been some standardization of high voltage DC power distribution for datacenters, seeing as that could simplify providing battery backup, etc. But back to the residential case: As soon as you go to lower voltage power distribution, unless you spend a lot more on copper (larger conductors), you're really hurting as far as power distribution losses: your load uses 10 times as many amps running on 12 volts DC as it did on 120 volts RMS AC. Thus your loss due to the resistance of the wire is 100 times what it was, given the same wiring. (i.e. the same series resistance -- your loss is P = V * I = I^2 * R) And no, you don't suddenly get much greater efficiency in the power supply of the device - a lot of off-line power supply designs today are already 90% efficient, and even if you provide 12 volts (or 12 and 5) to the plug, there's going to be a lot of things you want to do in the device that does not satisfy, and if you want exactly 12, you're going to need some kind of DC-DC converter with regulation, because you cannot predict how the 12 volt supplied at the wall will go down due to other load at any given point in time -- so just like a laptop has various DC-DC converters from the 18 volts supplied by its power brick to the various internal circuits (Vcore logic, 1.8 volt logic, 3.3 volt, 5 volt USB, backlight circuits, etc) most devices will still have that. They might not require as much safety isolation, but you're not going to get them to be magically far more efficient than what we have today.
- jws 11y ago
  Lets not forget we could change the frequency. Running at 400Hz like aircraft do lets you shrink the capacitors, inductors, and transformers of your power supplies and your electric motors can make 10 times the power for the same weight. Going to 3-phase instead of single phase probably also helps for power supplies. The power delivered across time is uniform so a sufficiently clever design doesn't need to store energy between cycles. Sure, its another conductor, but they can be slightly smaller so you use the same amount of copper in the end. 50/60Hz is better suited to long distance transmission, but you could put an inverter to 400Hz for the last 50 meters. Smaller, lighter, cheaper devices but with the efficiency loss in the inverter. I suspect it would be a win. (Also, pick a new voltage, something in the ~100v+ range. High enough for efficiency, but then do the lethality tradeoff on picking the ultimate voltage. As long as its a new standard, build ground fault detection at the inverter as part of the standard. There are about 400 household electrocutions per year in the United States, so there is room to improve.)
walrus01 11y ago
You really don't want to use DC for distribution in your home. Go price out telcoflex copper cabling (from 0000 up to 4 gauge) for -48VDC datacenter use. Voltage drop over distance and losses to heat make it impractical in homes. You really want to pay the extra money to wire your home with 6AWG cable in the walls? That's a lot of copper. Centralizing an AC to DC transformer is pointless for consumer stuff since things run on DIFFERENT voltages. A lot of consumer grade stuff is 5VDC internally. Or 12VDC. Or 17.5VDC. Or 19.2VDC laptops. Or 24VDC. Or 48VDC. That's before we even get into the problem of "everything in the world is already standardized to run from 110-240VAC 50/60Hz". If you really want to do DC distribution in your home, do it with 802.3af/802.3at switches (or "dumb" midspan injectors") and cat5e/cat6 cable. You can get LED lightings and other things that will run off PoE voltages and amperages now.
- extrapickles 11y ago
  Also, with the new USB standard, its no longer only 5v, you can now use up to 20v @5A [1]. My laptop that has a USB-C port to charge uses the full 20v. 120/240VAC 50/60hz @ ~12A (steady state draw) is pretty much the only thing people agree on when it comes to consumer power. [1]: http://www.usb.org/developers/docs/ http://www.usb.org/developers/docs/
  - voltagex_ 11y ago
    I'm waiting for the first news stories about house fires caused by USB-C chargers. A faulty 5Vx1A charger will melt, 20Vx5A will be a bit more lively. The tests by people like Benson Leung [1] haven't given me any faith that manufacturers will actually care about getting the specs right. [1]: https://plus.google.com/collection/s0Inv https://plus.google.com/collection/s0Inv
    - walrus01 11y ago
      wait until we have USB-C charged hoverboards (and similar products), where not only can the charger and cable catch fire, but so will the low budget Li-Ion battery pack/charge controller/battery management system.

mmagin 11y ago

Well, uh, AC vs DC and 100-250 volts versus 5-48 volts are two completely different dimensions to the problem here. For example, there has been some standardization of high voltage DC power distribution for datacenters, seeing as that could simplify providing battery backup, etc. But back to the residential case: As soon as you go to lower voltage power distribution, unless you spend a lot more on copper (larger conductors), you're really hurting as far as power distribution losses: your load uses 10 times as many amps running on 12 volts DC as it did on 120 volts RMS AC. Thus your loss due to the resistance of the wire is 100 times what it was, given the same wiring. (i.e. the same series resistance -- your loss is P = V * I = I^2 * R) And no, you don't suddenly get much greater efficiency in the power supply of the device - a lot of off-line power supply designs today are already 90% efficient, and even if you provide 12 volts (or 12 and 5) to the plug, there's going to be a lot of things you want to do in the device that does not satisfy, and if you want exactly 12, you're going to need some kind of DC-DC converter with regulation, because you cannot predict how the 12 volt supplied at the wall will go down due to other load at any given point in time -- so just like a laptop has various DC-DC converters from the 18 volts supplied by its power brick to the various internal circuits (Vcore logic, 1.8 volt logic, 3.3 volt, 5 volt USB, backlight circuits, etc) most devices will still have that. They might not require as much safety isolation, but you're not going to get them to be magically far more efficient than what we have today.

jws 11y ago
Lets not forget we could change the frequency. Running at 400Hz like aircraft do lets you shrink the capacitors, inductors, and transformers of your power supplies and your electric motors can make 10 times the power for the same weight. Going to 3-phase instead of single phase probably also helps for power supplies. The power delivered across time is uniform so a sufficiently clever design doesn't need to store energy between cycles. Sure, its another conductor, but they can be slightly smaller so you use the same amount of copper in the end. 50/60Hz is better suited to long distance transmission, but you could put an inverter to 400Hz for the last 50 meters. Smaller, lighter, cheaper devices but with the efficiency loss in the inverter. I suspect it would be a win. (Also, pick a new voltage, something in the ~100v+ range. High enough for efficiency, but then do the lethality tradeoff on picking the ultimate voltage. As long as its a new standard, build ground fault detection at the inverter as part of the standard. There are about 400 household electrocutions per year in the United States, so there is room to improve.)

walrus01 11y ago

You really don't want to use DC for distribution in your home. Go price out telcoflex copper cabling (from 0000 up to 4 gauge) for -48VDC datacenter use. Voltage drop over distance and losses to heat make it impractical in homes. You really want to pay the extra money to wire your home with 6AWG cable in the walls? That's a lot of copper. Centralizing an AC to DC transformer is pointless for consumer stuff since things run on DIFFERENT voltages. A lot of consumer grade stuff is 5VDC internally. Or 12VDC. Or 17.5VDC. Or 19.2VDC laptops. Or 24VDC. Or 48VDC. That's before we even get into the problem of "everything in the world is already standardized to run from 110-240VAC 50/60Hz". If you really want to do DC distribution in your home, do it with 802.3af/802.3at switches (or "dumb" midspan injectors") and cat5e/cat6 cable. You can get LED lightings and other things that will run off PoE voltages and amperages now.

extrapickles 11y ago
Also, with the new USB standard, its no longer only 5v, you can now use up to 20v @5A [1]. My laptop that has a USB-C port to charge uses the full 20v. 120/240VAC 50/60hz @ ~12A (steady state draw) is pretty much the only thing people agree on when it comes to consumer power. [1]: http://www.usb.org/developers/docs/ http://www.usb.org/developers/docs/
- voltagex_ 11y ago
  I'm waiting for the first news stories about house fires caused by USB-C chargers. A faulty 5Vx1A charger will melt, 20Vx5A will be a bit more lively. The tests by people like Benson Leung [1] haven't given me any faith that manufacturers will actually care about getting the specs right. [1]: https://plus.google.com/collection/s0Inv https://plus.google.com/collection/s0Inv
  - walrus01 11y ago
    wait until we have USB-C charged hoverboards (and similar products), where not only can the charger and cable catch fire, but so will the low budget Li-Ion battery pack/charge controller/battery management system.