8 ms·

> In practice, inverters probably also need partial redesign I'd also love for appliances to entirely adopt DC. - Homes should run on batteries. - Batteries

> In practice, inverters probably also need partial redesign I'd also love for appliances to entirely adopt DC. - Homes should run on batteries. - Batteries should be trickle charged from the grid with a cheap rectifier.

ianlevesque 3y ago
I agree on more DC appliances. Can't really escape having a failure-prone component in the mix though. For utility-scale you still need AC for transmission. For small-scale you need a switching regulator to even out the output voltage.
gtvwill 3y ago
Been tossing around the idea of Poe Eth to 100w usb-c wall ports. I'd love to see more Poe DC gear. In aus we have laws where if it's <100v and x amperage you don't need a license to work on it. Would make rolling out a house or shop install/fitout able to be done using regular labourers not expensive sparkies. Hell sneak some data in and you have smart control of all these connected usb-c cabled devices too. Make for game changing smart home rollout. Gimme lamps, lights, speakers, fans, window motors, TVs all on usb-c power plus data pls.
- ianburrell 3y ago
  Power over Ethernet can't do 100W. The 802.3bt supports 51W (Type 3) or 71W (Type 2). PoE uses pretty small currents, Type 4 is 960mA. Also, PoE does have significant loss over longer distances. It isn't a problem with low power devices but would be a huge issue for higher power. It is almost certainly more efficient to send power as 120V AC and convert to USB-C. The alternative is outlets with USB-C ports, or power strips with USB-C. Places that use 12V/48V DC have much thicker cables. They also have shorter lengths on RV, boat, or cabin.
- conk 3y ago
  I think if there was large scale adoption of PoE to power stuff outside of network equipment the regs would eventually catch up and it would have similar requirements line voltage wiring. 100W is more than enough to start a fire. 100W at 100V is enough to kill someone. There just aren’t as many regs because it’s new and not widely used. Building codes and standards are written in blood. One an apartment burns down because a bad RJ-45 connector started a fire the codes will catch up.
- Gibbon1 3y ago
  > In aus we have laws where if it's <100v and x amperage you don't need a license to work on it You're the first other person I've seen to point this out. Better even is negotiated power means normally the wire would only deliver 15W which isn't going to burn down anything. I'm also seeing more and more cordless appliances. A cordless vacuum doesn't need much power when charging.
kibwen 3y ago
Extremely amusing to see that the war of the currents is back on, between cheap solar panels and the advent of high-voltage DC power transmission. Edison might still get the last laugh.
- kccqzy 3y ago
  Today's DC electric components use such advanced electronics (like IGBT) that Edison would find very alien.
laurencerowe 3y ago
What’s the advantage of DC? You presumably still need to step down from high voltage or you end up with expensive thick wiring to avoid resistive losses.
- culopatin 3y ago
  You seem to imply that you can’t have high voltage DC. Why wouldn’t you be able to have 200v dc at home?
  - thsksbd 3y ago
    Because its nasty stuff! switching off a low Z 200V DC carrying 20 A in an emergency is not trivial. AC arcs self extinguish every 100 or 120 Hz.
- yazaddaruvala 3y ago
  I'm just talking about DC inside the home. To the meter it should still be AC, then pushed into a battery bank. The house should only use the battery bank (i.e. different battery packs that are dedicated for different parts of the house - like the breaker box - the battery packs exchange power between each other and the grid as needed. This way DC -> DC fast charging could be a thing, also my DC -> DC oven could pull a lot more Amps and pre-heat very quickly. Inputs: - Solar Panels -> Battery Bank - Grid <-Inverter-> Battery Bank Outputs: - Battery Bank -> Washing Machine - Battery Bank -> Lights - Battery Bank -> Induction Stove - Battery Bank -> USC-C to charge devices (my devices could charge so fast!)
  - ianburrell 3y ago
    Why do you think DC to DC fast charging will be better than AC to DC fast charging? Both involve voltage conversion and the conversion has about the same efficiency. The one advantage is that could choose higher DC voltage, like 480V, and send more power on same wires. But that won't get you DC fast charging, will still take a couple hours to charge. A lot of the things you are talking about will require conversion. LEDs will still need conversion from line voltage. Any incandescent lights will need AC conversion. The USB-C adapter will still exist, and there would no effect on charging speeds. You can get most of the benefit by having DC power cables between the battery, solar panels, and inverter.
ars 3y ago
So you want to replace the cost of an inverter with the cost of a battery? That seems like a bad trade-off to me. Batteries live 5 years? Inverters live 20+. Inverters are also cheaper than batteries. I'm not seeing any advantage to your idea.
- dgacmu 3y ago
  LFP batteries have a much longer lifespan.
  - ch_sm 3y ago
    Also a Li-Ion with a good BMS lives far longer than 5 years
deleted 3y ago
[deleted]
ianburrell 3y ago
The problem is that there is no standard for house-scale DC power. It has to be higher voltage than 12V or 48V that are used off-grid. There are no standard plugs or sockets, and it has to be different than AC. The big problem is that everyone has AC sockets, and it isn't worth the trouble to switch. It is going to be huge expense to buy new appliances for potential small efficiency gain. The in-wall voltage is going to mean that need adapters for other DC uses. A better approach is to have a standard for DC power between AC side, batteries, and solar panels. Then have a single big inverter between AC and DC. It also makes possible to have DC-only in places like cabins that aren't connected to the grid. Finally, many houses and apartments can't add batteries or solar panel. Not everyone has space like a basement. Like there is efficiency advantage like with utility solar, it might make sense to put batteries in substations where can use containers.
- marssaxman 3y ago
  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.
  - ianburrell 3y ago
    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.
    - phil21 3y ago
      > 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.
thsksbd 3y ago
Anything with a motor will get a lot more expensive. AC motors are dirt cheap. Also safety is harder on DC. For one the relays must be made much larger to withstand the nasty arcing. Arc extinguishing is much harder too. Efficiency is a toss up. On one hand, rectifiers are very efficient and you could get by with one rectifier instead of many. On the other, they're not 100% efficient and the voltages are much lower -> more copper. Reliability wont be as good. Rectifiers go all the time (think PC's CPU), there's no comparable failure component in the AC home. Overall the idea has merit, mainly because the most home loads are DC nowadays anyway. But your AC, washer, fridge, garage opener, pool pump, furnace blower, refrigerator, dryer and dishwasher will not be pleased.

ianlevesque 3y ago

I agree on more DC appliances. Can't really escape having a failure-prone component in the mix though. For utility-scale you still need AC for transmission. For small-scale you need a switching regulator to even out the output voltage.

gtvwill 3y ago

Been tossing around the idea of Poe Eth to 100w usb-c wall ports. I'd love to see more Poe DC gear. In aus we have laws where if it's <100v and x amperage you don't need a license to work on it. Would make rolling out a house or shop install/fitout able to be done using regular labourers not expensive sparkies. Hell sneak some data in and you have smart control of all these connected usb-c cabled devices too. Make for game changing smart home rollout. Gimme lamps, lights, speakers, fans, window motors, TVs all on usb-c power plus data pls.

ianburrell 3y ago
Power over Ethernet can't do 100W. The 802.3bt supports 51W (Type 3) or 71W (Type 2). PoE uses pretty small currents, Type 4 is 960mA. Also, PoE does have significant loss over longer distances. It isn't a problem with low power devices but would be a huge issue for higher power. It is almost certainly more efficient to send power as 120V AC and convert to USB-C. The alternative is outlets with USB-C ports, or power strips with USB-C. Places that use 12V/48V DC have much thicker cables. They also have shorter lengths on RV, boat, or cabin.
conk 3y ago
I think if there was large scale adoption of PoE to power stuff outside of network equipment the regs would eventually catch up and it would have similar requirements line voltage wiring. 100W is more than enough to start a fire. 100W at 100V is enough to kill someone. There just aren’t as many regs because it’s new and not widely used. Building codes and standards are written in blood. One an apartment burns down because a bad RJ-45 connector started a fire the codes will catch up.
Gibbon1 3y ago
> In aus we have laws where if it's <100v and x amperage you don't need a license to work on it You're the first other person I've seen to point this out. Better even is negotiated power means normally the wire would only deliver 15W which isn't going to burn down anything. I'm also seeing more and more cordless appliances. A cordless vacuum doesn't need much power when charging.

kibwen 3y ago

Extremely amusing to see that the war of the currents is back on, between cheap solar panels and the advent of high-voltage DC power transmission. Edison might still get the last laugh.

kccqzy 3y ago
Today's DC electric components use such advanced electronics (like IGBT) that Edison would find very alien.

laurencerowe 3y ago

What’s the advantage of DC? You presumably still need to step down from high voltage or you end up with expensive thick wiring to avoid resistive losses.

culopatin 3y ago
You seem to imply that you can’t have high voltage DC. Why wouldn’t you be able to have 200v dc at home?
- thsksbd 3y ago
  Because its nasty stuff! switching off a low Z 200V DC carrying 20 A in an emergency is not trivial. AC arcs self extinguish every 100 or 120 Hz.
yazaddaruvala 3y ago
I'm just talking about DC inside the home. To the meter it should still be AC, then pushed into a battery bank. The house should only use the battery bank (i.e. different battery packs that are dedicated for different parts of the house - like the breaker box - the battery packs exchange power between each other and the grid as needed. This way DC -> DC fast charging could be a thing, also my DC -> DC oven could pull a lot more Amps and pre-heat very quickly. Inputs: - Solar Panels -> Battery Bank - Grid <-Inverter-> Battery Bank Outputs: - Battery Bank -> Washing Machine - Battery Bank -> Lights - Battery Bank -> Induction Stove - Battery Bank -> USC-C to charge devices (my devices could charge so fast!)
- ianburrell 3y ago
  Why do you think DC to DC fast charging will be better than AC to DC fast charging? Both involve voltage conversion and the conversion has about the same efficiency. The one advantage is that could choose higher DC voltage, like 480V, and send more power on same wires. But that won't get you DC fast charging, will still take a couple hours to charge. A lot of the things you are talking about will require conversion. LEDs will still need conversion from line voltage. Any incandescent lights will need AC conversion. The USB-C adapter will still exist, and there would no effect on charging speeds. You can get most of the benefit by having DC power cables between the battery, solar panels, and inverter.

ars 3y ago

So you want to replace the cost of an inverter with the cost of a battery? That seems like a bad trade-off to me. Batteries live 5 years? Inverters live 20+. Inverters are also cheaper than batteries. I'm not seeing any advantage to your idea.

dgacmu 3y ago
LFP batteries have a much longer lifespan.
- ch_sm 3y ago
  Also a Li-Ion with a good BMS lives far longer than 5 years

deleted 3y ago

[deleted]

ianburrell 3y ago

The problem is that there is no standard for house-scale DC power. It has to be higher voltage than 12V or 48V that are used off-grid. There are no standard plugs or sockets, and it has to be different than AC. The big problem is that everyone has AC sockets, and it isn't worth the trouble to switch. It is going to be huge expense to buy new appliances for potential small efficiency gain. The in-wall voltage is going to mean that need adapters for other DC uses. A better approach is to have a standard for DC power between AC side, batteries, and solar panels. Then have a single big inverter between AC and DC. It also makes possible to have DC-only in places like cabins that aren't connected to the grid. Finally, many houses and apartments can't add batteries or solar panel. Not everyone has space like a basement. Like there is efficiency advantage like with utility solar, it might make sense to put batteries in substations where can use containers.

marssaxman 3y ago
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.
- ianburrell 3y ago
  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.
  - phil21 3y ago
    > 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.

thsksbd 3y ago

Anything with a motor will get a lot more expensive. AC motors are dirt cheap. Also safety is harder on DC. For one the relays must be made much larger to withstand the nasty arcing. Arc extinguishing is much harder too. Efficiency is a toss up. On one hand, rectifiers are very efficient and you could get by with one rectifier instead of many. On the other, they're not 100% efficient and the voltages are much lower -> more copper. Reliability wont be as good. Rectifiers go all the time (think PC's CPU), there's no comparable failure component in the AC home. Overall the idea has merit, mainly because the most home loads are DC nowadays anyway. But your AC, washer, fridge, garage opener, pool pump, furnace blower, refrigerator, dryer and dishwasher will not be pleased.