3 ms·

Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.

by adrr 6mo ago

bandrami 6mo ago
I've worked overseas a lot and one thing that's really different from 2 decades ago is that I simply don't need a step-down transformer anymore because every single thing I plug in converts to DC (or otherwise accepts dual-voltage) anyways. So I have a giant collection of physical plug adapters because every device I use just needs to fit into the socket and takes care of it from there. (My stand mixer is the lone sad exception)
- 747fulloftapes 6mo ago
  Agreed! I spent a few years getting flown out around the world to service gear at different datacenters. I learned to pack an IEC 60320 C14 to NEMA 5-15R adapter cable and a dumb, un-protected* NEMA 5-15R power strip. While on-site at the datacenters, an empty PDU receptacle was often easy to find. At hotels, I'd bring home a native cable borrowed from or given to me by the native datacenter staff or I'd ask the hotel front desk to borrow a "computer power cable," (more often, I'd just show them a photo) and they generally were able to lend me one. It worked great. I never found a power supply that wasn't content with 208 or 240V. Example adapters: https://www.amazon.com/dp/B0FD7PHB7Y https://www.amazon.com/dp/B0FD7PHB7Y or https://www.amazon.com/dp/B01IBIC1XG https://www.amazon.com/dp/B01IBIC1XG *: Some fancier power strips with surge suppression have a MOV over-voltage varistor that may burn up if given 200V+, rendering the power strip useless. Hence, unprotected strips are necessary.
ericd 6mo ago
Something to consider, and something I got a vivid demonstration of while playing with solar panels, DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe. My understanding is that DC breakers are somewhat prone to fires for this reason, too.
- bigiain 6mo ago
  Heh - I vaporised a fairly large soldering iron tip (probably 4mm copper cylindrical bar?), when I fucked up soldering a connector to a big 7 cell ~6000mAHr LiPo battery and shorted the terminals. Quite how I didn't end up blind or in hospital I don't know. It reinforced just how much respect you need to pay to even low-ish voltage DC when the available current was likely able to exceed 700A by a fair margin momentarily. I think those cells were rated at 60C continuous and 120C for 5 seconds.
  - ericd 6mo ago
    heh man, I'm glad you got out of that easy, I definitely wore safety glasses 100% of the time after my experience. I think a lifetime of experience with dangerous wall outlets and harmless little 1.5V/9V DC cells teaches us the wrong lessons about DC safety. I've since heard stories of wrenches exploding when they fall across EV high voltage battery terminals. Wrenches aren't supposed to be explosive. The electricians I was working with also told me stories about how with the really big breakers, you don't stand in front of it when you throw it, because sometimes it can turn into a cloud of molten metal vapor. And that's just using them as intended.
    - bluGill 6mo ago
      Amps - the old 48vdc telco data centers vaporized wrenchs once in a while.
    - jacquesm 6mo ago
      Those harmless 9V DC cells can do a lot of damage if you use them right.
      - sobjornstad 6mo ago
        This reminds me of the sailor who [decided](https://darwinawards.com/darwin/darwin1999-50.html https://darwinawards.com/darwin/darwin1999-50.html) to measure his internal resistance by pushing probes through the skin on his thumbs and electrocuted himself with the 9V multimeter battery.
kccqzy 6mo ago
That’s actually a recent phenomenon. Before the age of electronics most household appliances either worked with AC or DC equally well (like incandescent bulbs) or worked well with AC only given the technology at the time (think anything with a motor, fans, HVAC compressors etc).
- analog31 6mo ago
  Taking it to an extreme, the house I lived in while in grad school had wall lamp fixtures that doubled as electric and gas lamps. At some point I imagine it would have been possible to choose between using electric or gas by either flipping the switch or turning a valve. They said "Edison Patent" on them. We could have lit the house on AC, DC, or gas. Thinking about the failure modes gave me the heebie jeebies, but the gas had been disconnected ages prior.
  - jazzyjackson 6mo ago
    It’s kind of fun that light switches predate electricity. I think you used to turn a key, I guess you were turning a valve? Now that I think of it using a key to operate a valve makes a lot of sense but you don’t see it too often, well, I guess you want to turn things off without needing to find a key…
  - eszed 6mo ago
    I lived in a 19th century house in San Francisco that had gorgeous plaster work medallions on the ceilings - think cherubs and fruits - in the middle of which were the light fixtures. One day my dumb-ass flatmate made an ill-advised attempt to DIY his light fixture and cracked the still-active gas line embedded in the ceiling. Sometime in the 1920s - the date was printed on a sticker in the electrical panel - when they electrified the house, they'd wrapped the electrical wires around the gas pipes, and left them otherwise in situ. Crazy stuff.
torginus 6mo ago
I've had discussed with people familiar with the matter, and they convinced me its really not worth it for many reasons, the main one being safety - DC arcs are self sustaining - AC voltage constantly goes to zero, so if an arc were to form, it gets auto extinguished when the voltage drops. With DC this never happens, meaing every switch or plug socket can create this nice long arcs and is a potential fire hazard.
- adiabatichottub 6mo ago
  Really depends on what we're talking about. A lot of electrical safety equipment has a DC rating, usually something like 90VDC/300VAC. Also, most DC equipment just isn't going to have the stored energy to generate a big arc. Well, except batteries, and we're already piling them all around us.
  - torginus 6mo ago
    I mean it depends, but for dual rated stuff has both a voltage and current limit, both of which are way lower. Like typically a 230V/20A AC switch can switch 24VDC/2A. And the energy is not in the equipment, its in the mains (or batteries like you said, or PV panels)
    - adiabatichottub 6mo ago
      Right, but that's why I mentioned safety equipment. Your common DIN-mount UL-489 branch circuit breaker will be rated for the same trip current, same short circuit current rating (SCCR), but lower voltage. So you can use the same wiring and breakers as you might have with AC and your 48V battery bank won't vaporize the $5 hardware store toggle switch that somehow became a shunt.
      - torginus 6mo ago
        I mean, most AC circuit breakers use electromagnets to trip on overcurrent (as well as bimetallic strips using thermal methods for sustained high current). Electromagnets dont work for DC, so your breaker will never trip. For thermal protection, you need current, so that checks out, and it would make sense for it to be rated under 50V as thats considered the highest voltage thats not life threatening on touch. PV Batteries in general have a very high current (100s of A) at ~50Vish volts, so I dont think there's a major usecase for using household breakers for them. Im still not getting your point BTW, switches and breakers are two separate things, with different workings, and household (and datacenter) DC would be I think around 400ish V, which is a bit higher than the peak voltage of AC, but still within the arc limits of household wiring (at least in 230V countries). The advantage of DC is that you use your wiring more efficiently as the mean and peak wattage is the same at all times. Going with 48V would mean high resistive losses.
bigiain 6mo ago
Sure, maybe? If your house gets 800V DC you're still gonna need "bricks" to convert that to 5VDC of 12VDC (or maybe 19VDC) that most of the things that currently have "bricks" need. And if your house gets lower voltage DC, you're gonna have the problem of worth-stealing sized wiring to run your stove, water heater, or car charger. I reckon it'd be nice to have USB C PD ports everywhere I have a 220VAC power point, but 5 years ago that'd have been a USB type A port - and even now those'd be getting close to useless. We use a Type I (AS/NZS 2112) power point plug here - and that hasn't needed to change in probably a century. I doubt there's ever been a low voltage DC plug/socket standard that's lasted in use for anything like that long - probably the old "car cigarette lighter" 12DC thing? I'm glad I don't have a house full of those.
epx 6mo ago
Having a single big DC converter at a home would help a lot with power factor (LED lamps connected directly to AC have terrible power factor).
jwilliams 6mo ago
There are niches where DC makes sense - low-voltage lighting, USB/LED ecosystems. Once you get into higher power (laptops and up), switching and distribution get harder, so the advantages fade. For bigger appliances (fridge, etc), AC is fine + practical.
- adiabatichottub 6mo ago
  Your modern fridge is probably going to have an inverter-driven motor, so you're right back to using DC.
  - adrr 6mo ago
    All modern appliances and HVACs are using inverter drive motors for efficiency. Brushless DC motors are more efficient though.
    - userbinator 6mo ago
      "Brushless DC motors" are actually just AC synchronous motors.
Mistletoe 6mo ago
Modern bricks really aren’t that inefficient though. An Apple charger is like 90% efficient. A DC to DC converter is about that efficient or worse.
- catlikesshrimp 6mo ago
  The power adapters became so efficient that we have to transition to wireless charging to keep it down The irony...
flowerthoughts 6mo ago
I'm renovating a house, and have been considering 24V or 48V DC outlets in a few rooms. Semiconductors become more expensive above ~32V, so 24V might be the sweetspot. However, there's also PoE (24 or 48V!), so maybe that's the right approach. It's not like each outlet is going to run a heater anyway.
- fc417fc802 6mo ago
  Lower voltage makes voltage drop across the line proportionally worse. Depending on the purpose PoE is probably the way to go since the wiring and hardware is all standardized and safety certified. Unless you mean running AC and installing inverters in the wall? What is this even for? All my electronics are DC but critically they all require different voltages. The only thing I might benefit from would be higher voltage service because there are times that 15 A at 120 V doesn't cut it.
  - flowerthoughts 6mo ago
    No, I meant running separate DC wires. I'm Europe, so it's 240 VAC vs 24/48 VDC. For small devices, 24 V would be useful in that you don't require an isolated SMPS, so cheaper endpoints are possible. Slightly less risk of burning down the house with some cheap Chinese AC/DC. 24 V is still high enough to use USB PD/PPS at 20 V, and I doubt I'll run enough current that the losses due to lower voltage would be a problem. For PoE, I thought it was standardized at 48 V, but I see lots of cameras run at 24 V, and I think I've even seen 12 V. Seems a bit of a mess.

Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.

by adrr 6mo ago

Our houses should be DC. So wasteful to have all these bricks to change to AC to DC.

I've worked overseas a lot and one thing that's really different from 2 decades ago is that I simply don't need a step-down transformer anymore because every single thing I plug in converts to DC (or otherwise accepts dual-voltage) anyways. So I have a giant collection of physical plug adapters because every device I use just needs to fit into the socket and takes care of it from there. (My stand mixer is the lone sad exception)

747fulloftapes 6mo ago
Agreed! I spent a few years getting flown out around the world to service gear at different datacenters. I learned to pack an IEC 60320 C14 to NEMA 5-15R adapter cable and a dumb, un-protected* NEMA 5-15R power strip. While on-site at the datacenters, an empty PDU receptacle was often easy to find. At hotels, I'd bring home a native cable borrowed from or given to me by the native datacenter staff or I'd ask the hotel front desk to borrow a "computer power cable," (more often, I'd just show them a photo) and they generally were able to lend me one. It worked great. I never found a power supply that wasn't content with 208 or 240V. Example adapters: https://www.amazon.com/dp/B0FD7PHB7Y https://www.amazon.com/dp/B0FD7PHB7Y or https://www.amazon.com/dp/B01IBIC1XG https://www.amazon.com/dp/B01IBIC1XG *: Some fancier power strips with surge suppression have a MOV over-voltage varistor that may burn up if given 200V+, rendering the power strip useless. Hence, unprotected strips are necessary.

ericd 6mo ago

Something to consider, and something I got a vivid demonstration of while playing with solar panels, DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe. My understanding is that DC breakers are somewhat prone to fires for this reason, too.

bigiain 6mo ago
Heh - I vaporised a fairly large soldering iron tip (probably 4mm copper cylindrical bar?), when I fucked up soldering a connector to a big 7 cell ~6000mAHr LiPo battery and shorted the terminals. Quite how I didn't end up blind or in hospital I don't know. It reinforced just how much respect you need to pay to even low-ish voltage DC when the available current was likely able to exceed 700A by a fair margin momentarily. I think those cells were rated at 60C continuous and 120C for 5 seconds.
- ericd 6mo ago
  heh man, I'm glad you got out of that easy, I definitely wore safety glasses 100% of the time after my experience. I think a lifetime of experience with dangerous wall outlets and harmless little 1.5V/9V DC cells teaches us the wrong lessons about DC safety. I've since heard stories of wrenches exploding when they fall across EV high voltage battery terminals. Wrenches aren't supposed to be explosive. The electricians I was working with also told me stories about how with the really big breakers, you don't stand in front of it when you throw it, because sometimes it can turn into a cloud of molten metal vapor. And that's just using them as intended.
  - bluGill 6mo ago
    Amps - the old 48vdc telco data centers vaporized wrenchs once in a while.
  - jacquesm 6mo ago
    Those harmless 9V DC cells can do a lot of damage if you use them right.
    - sobjornstad 6mo ago
      This reminds me of the sailor who [decided](https://darwinawards.com/darwin/darwin1999-50.html https://darwinawards.com/darwin/darwin1999-50.html) to measure his internal resistance by pushing probes through the skin on his thumbs and electrocuted himself with the 9V multimeter battery.

kccqzy 6mo ago

That’s actually a recent phenomenon. Before the age of electronics most household appliances either worked with AC or DC equally well (like incandescent bulbs) or worked well with AC only given the technology at the time (think anything with a motor, fans, HVAC compressors etc).

analog31 6mo ago
Taking it to an extreme, the house I lived in while in grad school had wall lamp fixtures that doubled as electric and gas lamps. At some point I imagine it would have been possible to choose between using electric or gas by either flipping the switch or turning a valve. They said "Edison Patent" on them. We could have lit the house on AC, DC, or gas. Thinking about the failure modes gave me the heebie jeebies, but the gas had been disconnected ages prior.
- jazzyjackson 6mo ago
  It’s kind of fun that light switches predate electricity. I think you used to turn a key, I guess you were turning a valve? Now that I think of it using a key to operate a valve makes a lot of sense but you don’t see it too often, well, I guess you want to turn things off without needing to find a key…
- eszed 6mo ago
  I lived in a 19th century house in San Francisco that had gorgeous plaster work medallions on the ceilings - think cherubs and fruits - in the middle of which were the light fixtures. One day my dumb-ass flatmate made an ill-advised attempt to DIY his light fixture and cracked the still-active gas line embedded in the ceiling. Sometime in the 1920s - the date was printed on a sticker in the electrical panel - when they electrified the house, they'd wrapped the electrical wires around the gas pipes, and left them otherwise in situ. Crazy stuff.

torginus 6mo ago

I've had discussed with people familiar with the matter, and they convinced me its really not worth it for many reasons, the main one being safety - DC arcs are self sustaining - AC voltage constantly goes to zero, so if an arc were to form, it gets auto extinguished when the voltage drops. With DC this never happens, meaing every switch or plug socket can create this nice long arcs and is a potential fire hazard.

adiabatichottub 6mo ago
Really depends on what we're talking about. A lot of electrical safety equipment has a DC rating, usually something like 90VDC/300VAC. Also, most DC equipment just isn't going to have the stored energy to generate a big arc. Well, except batteries, and we're already piling them all around us.
- torginus 6mo ago
  I mean it depends, but for dual rated stuff has both a voltage and current limit, both of which are way lower. Like typically a 230V/20A AC switch can switch 24VDC/2A. And the energy is not in the equipment, its in the mains (or batteries like you said, or PV panels)
  - adiabatichottub 6mo ago
    Right, but that's why I mentioned safety equipment. Your common DIN-mount UL-489 branch circuit breaker will be rated for the same trip current, same short circuit current rating (SCCR), but lower voltage. So you can use the same wiring and breakers as you might have with AC and your 48V battery bank won't vaporize the $5 hardware store toggle switch that somehow became a shunt.
    - torginus 6mo ago
      I mean, most AC circuit breakers use electromagnets to trip on overcurrent (as well as bimetallic strips using thermal methods for sustained high current). Electromagnets dont work for DC, so your breaker will never trip. For thermal protection, you need current, so that checks out, and it would make sense for it to be rated under 50V as thats considered the highest voltage thats not life threatening on touch. PV Batteries in general have a very high current (100s of A) at ~50Vish volts, so I dont think there's a major usecase for using household breakers for them. Im still not getting your point BTW, switches and breakers are two separate things, with different workings, and household (and datacenter) DC would be I think around 400ish V, which is a bit higher than the peak voltage of AC, but still within the arc limits of household wiring (at least in 230V countries). The advantage of DC is that you use your wiring more efficiently as the mean and peak wattage is the same at all times. Going with 48V would mean high resistive losses.

bigiain 6mo ago

Sure, maybe? If your house gets 800V DC you're still gonna need "bricks" to convert that to 5VDC of 12VDC (or maybe 19VDC) that most of the things that currently have "bricks" need. And if your house gets lower voltage DC, you're gonna have the problem of worth-stealing sized wiring to run your stove, water heater, or car charger. I reckon it'd be nice to have USB C PD ports everywhere I have a 220VAC power point, but 5 years ago that'd have been a USB type A port - and even now those'd be getting close to useless. We use a Type I (AS/NZS 2112) power point plug here - and that hasn't needed to change in probably a century. I doubt there's ever been a low voltage DC plug/socket standard that's lasted in use for anything like that long - probably the old "car cigarette lighter" 12DC thing? I'm glad I don't have a house full of those.

epx 6mo ago

Having a single big DC converter at a home would help a lot with power factor (LED lamps connected directly to AC have terrible power factor).

jwilliams 6mo ago

There are niches where DC makes sense - low-voltage lighting, USB/LED ecosystems. Once you get into higher power (laptops and up), switching and distribution get harder, so the advantages fade. For bigger appliances (fridge, etc), AC is fine + practical.

adiabatichottub 6mo ago
Your modern fridge is probably going to have an inverter-driven motor, so you're right back to using DC.
- adrr 6mo ago
  All modern appliances and HVACs are using inverter drive motors for efficiency. Brushless DC motors are more efficient though.
  - userbinator 6mo ago
    "Brushless DC motors" are actually just AC synchronous motors.

Mistletoe 6mo ago

Modern bricks really aren’t that inefficient though. An Apple charger is like 90% efficient. A DC to DC converter is about that efficient or worse.

catlikesshrimp 6mo ago
The power adapters became so efficient that we have to transition to wireless charging to keep it down The irony...

flowerthoughts 6mo ago

I'm renovating a house, and have been considering 24V or 48V DC outlets in a few rooms. Semiconductors become more expensive above ~32V, so 24V might be the sweetspot. However, there's also PoE (24 or 48V!), so maybe that's the right approach. It's not like each outlet is going to run a heater anyway.

fc417fc802 6mo ago
Lower voltage makes voltage drop across the line proportionally worse. Depending on the purpose PoE is probably the way to go since the wiring and hardware is all standardized and safety certified. Unless you mean running AC and installing inverters in the wall? What is this even for? All my electronics are DC but critically they all require different voltages. The only thing I might benefit from would be higher voltage service because there are times that 15 A at 120 V doesn't cut it.
- flowerthoughts 6mo ago
  No, I meant running separate DC wires. I'm Europe, so it's 240 VAC vs 24/48 VDC. For small devices, 24 V would be useful in that you don't require an isolated SMPS, so cheaper endpoints are possible. Slightly less risk of burning down the house with some cheap Chinese AC/DC. 24 V is still high enough to use USB PD/PPS at 20 V, and I doubt I'll run enough current that the losses due to lower voltage would be a problem. For PoE, I thought it was standardized at 48 V, but I see lots of cameras run at 24 V, and I think I've even seen 12 V. Seems a bit of a mess.