4 ms·

Is there anything left in a modern home that really needs or is better on AC? We have some old ceiling and exhaust fans, but I know those can be replaced. Our

Is there anything left in a modern home that really needs or is better on AC? We have some old ceiling and exhaust fans, but I know those can be replaced. Our refrigerator is AC, but extended family with an off-grid home has a DC refrigerator that cycles way less, probably due to multiple design factors but I’m sure the lack of transformer heat is part of it. I’m not as sure about laundry machine or oven/cooktop options but I believe those are also running on DC in the off-grid home without inverters. Most of these AC appliances also have transformers in them anyway for the control boards. It seems kind of insane to me that we are still doing things this way.

Retric 7mo ago
Of grid homes are vastly more concerned with the energy efficiency of their appliances and thus DC refrigerators generally have more insulation. Most AC customers prefer more internal volume for food over slightly increased efficiency. AC motors are using way more power than the puddly control boards in most home appliances. So you lose a little efficiency on conversion but being 80% efficient doesn’t matter much when it’s 1-5% of the devices energy budget. You generally gain way more than that from similarly priced AC motors being more efficient.
- sholladay 7mo ago
  I agree with everything you said, except it seems like a false dichotomy. We can clearly build DC refrigerators with more or less insulation. We can clearly build them large or small. If you want to prioritize volume, then surely you could do that with DC. Right? I know that a long time ago DC-to-DC voltage converters were very large in size, which meant AC would win on space efficiency. But unless I’m mistaken, that’s no longer the case. Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator?
  - Retric 7mo ago
    > Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator? Sure, but it’s important to separate what could be built from what is being built based on consumer preferences and buying habits. The average refrigerator could be significantly quieter, but how often do people actually listen to what they are buying? People buying Tesla’s didn’t test drive the actual car they were buying so the company deprioritized panel gaps. And so forth, companies optimize in ways that maximize their profits not arbitrary metrics.
samus 7mo ago
Any appliance with strong motors should be more efficient with AC supply. But almost anything else can be regarded as a heater that doesn't care much as long as it is fed with the correct voltage. Which is actually the core issue. A DC household would have to choose a trade-off between multiple lines with different voltages or fewer voltages that need to be adapted to the appliances. And we're right back at the AC situation, but worse since DC voltages are more difficult to change. But consumers like datacenters can very well plan ahead and standardize on a single DC voltage. They already need beefy equipment to deal with interruptions, power sourges, non-sinus components, and brownouts, which already involves transformers, condensators, and DC conversion for battery storage. Therefore almost no additional equipment is required.
- sholladay 7mo ago
  What qualifies as a strong motor here? Are you comparing to a brushed DC motor? Do you think a washer/dryer would have worse overall efficiency with a BLDC in a DC home compared to what we have today? If so, that’s news to me. Where can I learn more about that? The trade-off between, say, one (relatively) high voltage DC bus throughout the home vs many branches with lower discrete voltages is indeed a problem. With AC, we took the bus approach, running 120v everywhere (in the U.S., higher elsewhere). I’m inclined to say we should keep doing that for flexibility and predictability. But it’s a trade off, like you said. It would obviously help if regulatory and standards bodies came out with official recommendations.
  - zarzavat 7mo ago
    Probably 90% of my devices run 5V DC or similar, but you can't run that through a home so you're back to needing AC. If you're going to have AC and DC then you might as well just have AC.
    - sholladay 7mo ago
      > Probably 90% of my devices run 5V DC or similar, Indeed. And that’s quite normal. Our electrical system should serve our modern needs. > but you can't run that through a home 5V might be too low for that length of wire. But you could most definitely have a low voltage line in your house that we could design around, maybe 12V. Electric vehicles are moving towards 48V for accessories. It seems like lack of a standard is holding us back more than anything else. Or we could just keep doing 120V in the walls, with a DC supply. Modern DC-to-DC voltage converters are very efficient and small. But maybe I’m wrong. A lot of people seem to believe they are still not good enough yet for such a change to make sense. > If you're going to have AC and DC then you might as well just have AC. I arrive at the opposite conclusion. Most things are natively DC. So therefore, power in the walls should be DC and we should covert it to AC near the endpoint where necessary.

Retric 7mo ago

Of grid homes are vastly more concerned with the energy efficiency of their appliances and thus DC refrigerators generally have more insulation. Most AC customers prefer more internal volume for food over slightly increased efficiency. AC motors are using way more power than the puddly control boards in most home appliances. So you lose a little efficiency on conversion but being 80% efficient doesn’t matter much when it’s 1-5% of the devices energy budget. You generally gain way more than that from similarly priced AC motors being more efficient.

sholladay 7mo ago
I agree with everything you said, except it seems like a false dichotomy. We can clearly build DC refrigerators with more or less insulation. We can clearly build them large or small. If you want to prioritize volume, then surely you could do that with DC. Right? I know that a long time ago DC-to-DC voltage converters were very large in size, which meant AC would win on space efficiency. But unless I’m mistaken, that’s no longer the case. Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator?
- Retric 7mo ago
  > Wouldn’t a DC refrigerator with equivalent insulation and interior volume have nearly identical exterior dimensions as an AC refrigerator? Sure, but it’s important to separate what could be built from what is being built based on consumer preferences and buying habits. The average refrigerator could be significantly quieter, but how often do people actually listen to what they are buying? People buying Tesla’s didn’t test drive the actual car they were buying so the company deprioritized panel gaps. And so forth, companies optimize in ways that maximize their profits not arbitrary metrics.

samus 7mo ago

Any appliance with strong motors should be more efficient with AC supply. But almost anything else can be regarded as a heater that doesn't care much as long as it is fed with the correct voltage. Which is actually the core issue. A DC household would have to choose a trade-off between multiple lines with different voltages or fewer voltages that need to be adapted to the appliances. And we're right back at the AC situation, but worse since DC voltages are more difficult to change. But consumers like datacenters can very well plan ahead and standardize on a single DC voltage. They already need beefy equipment to deal with interruptions, power sourges, non-sinus components, and brownouts, which already involves transformers, condensators, and DC conversion for battery storage. Therefore almost no additional equipment is required.

sholladay 7mo ago
What qualifies as a strong motor here? Are you comparing to a brushed DC motor? Do you think a washer/dryer would have worse overall efficiency with a BLDC in a DC home compared to what we have today? If so, that’s news to me. Where can I learn more about that? The trade-off between, say, one (relatively) high voltage DC bus throughout the home vs many branches with lower discrete voltages is indeed a problem. With AC, we took the bus approach, running 120v everywhere (in the U.S., higher elsewhere). I’m inclined to say we should keep doing that for flexibility and predictability. But it’s a trade off, like you said. It would obviously help if regulatory and standards bodies came out with official recommendations.
- zarzavat 7mo ago
  Probably 90% of my devices run 5V DC or similar, but you can't run that through a home so you're back to needing AC. If you're going to have AC and DC then you might as well just have AC.
  - sholladay 7mo ago
    > Probably 90% of my devices run 5V DC or similar, Indeed. And that’s quite normal. Our electrical system should serve our modern needs. > but you can't run that through a home 5V might be too low for that length of wire. But you could most definitely have a low voltage line in your house that we could design around, maybe 12V. Electric vehicles are moving towards 48V for accessories. It seems like lack of a standard is holding us back more than anything else. Or we could just keep doing 120V in the walls, with a DC supply. Modern DC-to-DC voltage converters are very efficient and small. But maybe I’m wrong. A lot of people seem to believe they are still not good enough yet for such a change to make sense. > If you're going to have AC and DC then you might as well just have AC. I arrive at the opposite conclusion. Most things are natively DC. So therefore, power in the walls should be DC and we should covert it to AC near the endpoint where necessary.