5 ms·

It has less to do with ac vs dc and more to do with the voltage and distance from source to load. If you wanted a dc bus inside a house you would need to have v

by conk 7y ago

It has less to do with ac vs dc and more to do with the voltage and distance from source to load. If you wanted a dc bus inside a house you would need to have voltages in the same range as ac power 120/240V in North America. At this point you have the same challenges of how do you reduce the voltage to something low and easy to work with for an end device like a light bulb or cell phone. Stepping down voltage is easy to do with AC power but difficult for DC which is why I don’t think it will ever be practical.

convolvatron 7y ago
48v dc bus and buck converters work just fine. generally power supplies that work off AC rectify and go through the same business - except they need larger inductors to sort out the zero crossing. i think the difference you're looking for is in volume of copper.
- jws 7y ago
  Maybe we should instead invent a domestic 3 phase distribution system. No more zero crossings requiring energy storage, just flat constant power. It would require a new, small four conductor plug to be designed. Total volume of copper would be a less for the same available power, since the three wires deliver twice the power as two single phase wires for the same conductor size. There would be more insulation involved so the wiring might grow or might shrink if outlets were held to 1500watts. The big savings would be in longer lived electronic devices. A sizable portion of digital electronics ultimately fail because the capacitors in their power supplies exceed their designed lifetime. Electrolytic capacitors (ticking time bombs) are cheap and compact for the capacity so they are used for the energy storage required in single phase systems, but if designing a three phase power supply less storage is required and maybe manufacturers wouldn't have to optimize the smaller, capacitors with electrolytics. I've had a 4k TV and a rather expensive musical instrument amp fail for capacitors this year, about $3000 of gear there. Looking back further there are a couple of professional powered sound reinforcement speakers (twice), an iMac G5 (three times). It's probably safe to say over the decades I've had $10k of electronics fail prematurely from electrolytic capacitor failure. These are all items which were not obsolete or worn out. Scale that up from one person to worldwide and it's easily in the hundreds of billions (10⁹) of dollars which could be saved. The problem is you can't get there from where we are. No one wants to drag more wires to residential houses, no one wants to shell out >$1k for a household phase converter and then rewire their house. You won't convince people to add three phase to a new house because it might be the future. And you won't convince the semiconductor houses to make a line of three phase power supply controller chips just because, well, maybe someone might use it. We're probably trapped at a suboptimal local maximum. Edit: In response to atoav's comment I found IEC 60309 and its extra low voltage variant which is a 42mm (1 2.3") 3 phase plug and connector in two compatible sizes good for 1.3kW and 2.6kW. Also, that Germans and Swedes did the engineering first and then built an electrical system and they get 480V 3 phase at 16A to their cooktops and stoves through a plug for a whopping 13kW!
  - gizmo686 7y ago
    Do we need to invent anything? My understanding is that most of the grid in the US operates on 3 phase, and some buildings (including residential) already have a 3 phase supply to operate AC and industrial applications. All we are missing is for it to be standard to wire the 3 phase distribution throughout buildings to every outlet (preferably in a backwards compatible manner; in theory converting 3-phase to single phase is just a matter of ignoring a wire. I would assume that a) the grid can handle people doing this and b) doing this with out current 3-phase standard would result in our current single phase standard,
    - Scoundreller 7y ago
      I hate those 3 phase residential buildings, because they usually deliver 208V to ovens and dryers instead of 240V. While the appliances are probably approved fo 208V, I doubt they’re drawing more peak current to make up for it.
  - atoav 7y ago
    I am not exactly sure what you imagine, but I (in Germany) have two 3 phase outlets (3x 16A @230V) in my flat and this is very common here. We use it for cook tops and ovens in the kitchen typically, and it makes the difference between 15 mins for boiling water (old single phase cook top) and (on my induction cook top) 1 min. Edit: and as an aside, why we probably don't do that everywhere: it makes for bigger plugs, and keeping safety standards can be a bit more expensive and space intensive with the potential 400V between phases.
    - jws 7y ago
      Well that's news to me! I'm jealous. I'll bet you can preheat an electric oven in less than 20 minutes. I see the successor to the 16A Perilex connectors you are referencing is IEC 60309 which has an "extra low voltage" version with a smaller, 42mm diameter (1 2/3") plug good for 16A or 32A. 16A devices will fit in a 32A socket, but not the other way around. So that seems to be a 1.3kW and 2.6kW solution. Sign me up!
benj111 7y ago
Dc to dc voltage voltage conversion is easy kind of, you simply need to convert it to AC and back. So as its going to become AC at some point anyway, why not use the existing wiring.

by conk 7y ago

convolvatron 7y ago

48v dc bus and buck converters work just fine. generally power supplies that work off AC rectify and go through the same business - except they need larger inductors to sort out the zero crossing. i think the difference you're looking for is in volume of copper.

jws 7y ago
Maybe we should instead invent a domestic 3 phase distribution system. No more zero crossings requiring energy storage, just flat constant power. It would require a new, small four conductor plug to be designed. Total volume of copper would be a less for the same available power, since the three wires deliver twice the power as two single phase wires for the same conductor size. There would be more insulation involved so the wiring might grow or might shrink if outlets were held to 1500watts. The big savings would be in longer lived electronic devices. A sizable portion of digital electronics ultimately fail because the capacitors in their power supplies exceed their designed lifetime. Electrolytic capacitors (ticking time bombs) are cheap and compact for the capacity so they are used for the energy storage required in single phase systems, but if designing a three phase power supply less storage is required and maybe manufacturers wouldn't have to optimize the smaller, capacitors with electrolytics. I've had a 4k TV and a rather expensive musical instrument amp fail for capacitors this year, about $3000 of gear there. Looking back further there are a couple of professional powered sound reinforcement speakers (twice), an iMac G5 (three times). It's probably safe to say over the decades I've had $10k of electronics fail prematurely from electrolytic capacitor failure. These are all items which were not obsolete or worn out. Scale that up from one person to worldwide and it's easily in the hundreds of billions (10⁹) of dollars which could be saved. The problem is you can't get there from where we are. No one wants to drag more wires to residential houses, no one wants to shell out >$1k for a household phase converter and then rewire their house. You won't convince people to add three phase to a new house because it might be the future. And you won't convince the semiconductor houses to make a line of three phase power supply controller chips just because, well, maybe someone might use it. We're probably trapped at a suboptimal local maximum. Edit: In response to atoav's comment I found IEC 60309 and its extra low voltage variant which is a 42mm (1 2.3") 3 phase plug and connector in two compatible sizes good for 1.3kW and 2.6kW. Also, that Germans and Swedes did the engineering first and then built an electrical system and they get 480V 3 phase at 16A to their cooktops and stoves through a plug for a whopping 13kW!
- gizmo686 7y ago
  Do we need to invent anything? My understanding is that most of the grid in the US operates on 3 phase, and some buildings (including residential) already have a 3 phase supply to operate AC and industrial applications. All we are missing is for it to be standard to wire the 3 phase distribution throughout buildings to every outlet (preferably in a backwards compatible manner; in theory converting 3-phase to single phase is just a matter of ignoring a wire. I would assume that a) the grid can handle people doing this and b) doing this with out current 3-phase standard would result in our current single phase standard,
  - Scoundreller 7y ago
    I hate those 3 phase residential buildings, because they usually deliver 208V to ovens and dryers instead of 240V. While the appliances are probably approved fo 208V, I doubt they’re drawing more peak current to make up for it.
- atoav 7y ago
  I am not exactly sure what you imagine, but I (in Germany) have two 3 phase outlets (3x 16A @230V) in my flat and this is very common here. We use it for cook tops and ovens in the kitchen typically, and it makes the difference between 15 mins for boiling water (old single phase cook top) and (on my induction cook top) 1 min. Edit: and as an aside, why we probably don't do that everywhere: it makes for bigger plugs, and keeping safety standards can be a bit more expensive and space intensive with the potential 400V between phases.
  - jws 7y ago
    Well that's news to me! I'm jealous. I'll bet you can preheat an electric oven in less than 20 minutes. I see the successor to the 16A Perilex connectors you are referencing is IEC 60309 which has an "extra low voltage" version with a smaller, 42mm diameter (1 2/3") plug good for 16A or 32A. 16A devices will fit in a 32A socket, but not the other way around. So that seems to be a 1.3kW and 2.6kW solution. Sign me up!

benj111 7y ago

Dc to dc voltage voltage conversion is easy kind of, you simply need to convert it to AC and back. So as its going to become AC at some point anyway, why not use the existing wiring.