5 ms·

Every so often, I come back to the "I should have DC power on demand in my house!" until I'm reminded that DC power loss over a distance can hurt bad, even 48VD

Every so often, I come back to the "I should have DC power on demand in my house!" until I'm reminded that DC power loss over a distance can hurt bad, even 48VDC telecom power. Perhaps USB-C PD might help? USB power adapters are compact and PD offers standard, useful high power DC. If the adapters become ubiquitous, you could see "USB-C lightbulbs".

Someone1234 8y ago
Slight tangent but "in-building DC" exists, and is rapidly gaining popularity but not via the medium many assumed: Power Over Ethernet. You can buy PoE LED light fixtures now, which are both powered and controlled over ethernet. You buy a single PoE switch, run some low voltage Cat6, and you can power an entire floor's worth of lighting. EEPoE (Energy Efficient PoE) offers more efficient PoE too which claims up to 94% efficiency. Definitely a space to watch. Particularly as the cost savings of running low voltage Ethernet cable compared to high voltage electrical cable (110v) are substantial.
- baybal2 8y ago
  Definitely watching. I once was in the LED industry when it was still hot. The company was called Zega. They tried every random thing, including putting a small real ARM server on the bloody thing to do remote control. It was back then when I first stumbled on Espressif people and Teo. They got lightyears ahead of us with all-in-one SoC.
- jws 8y ago
  EEPoE is new to me: Microsemi's exclusive EEPoE technology cuts the power losses on Ethernet cables by 50%, through the utilization of all the copper available on cable when a Microsemi EEPoE PSE IC or Midspan is used. It is 100% compatible with IEEE802.3at, and the savings work with ANY IEEE 802.3at Type 2, Type 1 or IEEE 802.3af compliant PD. In practice, devices that consume 25.5W would consume less than 27.75W, instead of the worst case 30W when a non-EEPoE PSE is employed. So they use all 8 wires for power instead of just 4 to halve the power loss on the wire. For the worst case device that makes the 20% loss be a 10% loss.
  - TorKlingberg 8y ago
    Does that mean you cannot use it for any regular Ethernet data signaling at the same time, or is the signal overloaded on the DC?
    - poopchute 8y ago
      You can. I used to work for an ISP and every WiFi access point I installed had Ethernet+DC over the same cat6 cable. Still got 100 megabit speeds
- HeyLaughingBoy 8y ago
  you can power an entire floor's worth of lighting ? Must be either very low current lighting or that's some pretty beefy Cat6. I think the average Cat6 cable is only 24 gauge and that won't carry a lot of current very far.
  - bronson 8y ago
    Star topology
    - jandrese 8y ago
      Isn't this like saying you could light the world if you had a big enough switch and unlimited cable?
      - bronson 8y ago
        Where did you get that? GP is talking about lighting a floor in a building.
        jandrese 8y ago
        He's talking about running a separate cable for each and every bulb. It's a wasteful solution compared to running all of the lights off of a single circuit (or limited number of circuits) like a normal building.
        Someone1234 8y ago
        No I wasn't. PoE+ can support half a dozen LED panels off of a single Cat6 run.
  - FooHentai 8y ago
    PoE+ will deliver 30W to the far end of up to 100M network cabling. Given that those cables radiate out to endpoint devices from a central point, rather than powering multiple devices in a ring/loop topology, the potential to power lots of devices over a wide area is huge. Biggest problem tends to be accommodating the central power delivery device. Those big PoE switches run hot and loud.
- noveltyaccount 8y ago
  TIL about PoE lighting. I always imagined homes would migrate to 12VDC and converge electronics with RVs.
  - FooHentai 8y ago
    A small DC-input PoE switch in your RV might be the next logical evolution :)
vvanders 8y ago
Isn't that a function of voltage and not modulation? There might be a cost argument, I'm not sure if solid state step-down DC-DC converters are cheaper than good old cheap transformers.
- Filligree 8y ago
  It's a function of both. At equivalent voltage, DC has much lower loss than AC.
- tlb 8y ago
  Yes, it's entirely a function of voltage. But the safe limit for DC voltage is lower for two reasons: - A shock from a DC supply will cause heart fibrillations at lower voltage than AC, because of the way muscles receive signals from nerves - An electrical arc from a DC line will burn continuously, while an AC arc tends to self-extinguish at each zero-crossing. So in practice, 120 VAC or 48 VDC are the limits for household wiring.
  - robocat 8y ago
    > So in practice, 120 VAC or 48 VDC are the limits for household wiring About 20% of the world uses 110-120 V and 60Hz. The rest uses mostly 240V at 50Hz. Although 110V is safer, the US seems to ignore many of the safety features I see used elsewhere in the world. How that translates to deaths per million people per year comparing to similarly rich countries, I don't know.
  - upofadown 8y ago
    >A shock from a DC supply will cause heart fibrillations at lower voltage than AC, because of the way muscles receive signals from nerves That is opposite to my understanding. The extra shock hazard of AC vs DC was an argument used against AC power distribution back in the day. The 50V limit is to prevent shock altogether.
pitaj 8y ago
> until I'm reminded that DC power loss over a distance can hurt bad, even 48VDC telecom power. If you had AC to your house, then a rectifier for a 100V/200V DC circuit through your house, the losses wouldn't be any worse. DC losses are less than AC losses at the equivalent voltage, because the resistance seen by DC is less than the AC impedance.
- sevensor 8y ago
  Certainly at the household scale this is true. I cringe at the inefficiency of rooftop solar panels, hooked up to inverters, powering transformers that supply phones, lights, and electronics. AC in the house is great for an electric oven, vacuum cleaner, or fridge compressor, but so many modern electronic devices would be happy to run off of 5V or 12V.
  - ip26 8y ago
    Look on the bright side- in terms of real power, the electric oven, vacuum cleaner, AC compressor, and fridge compressor totally swamp the entire load, waste and all, of those 5V devices. In a perfect world we'd have both AC & DC, and could use whichever was most appropriate. We could feed DC straight from the solar panels to the cell phone. But in terms of what consumes most of the power, in the typical home it's AC loads.
    - dsfyu404ed 8y ago
      >Look on the bright side- in terms of real power, the electric oven, vacuum cleaner, AC compressor, and fridge compressor totally swamp the entire load, waste and all, of those 5V devices. This isn't an appropriate comparison. Those appliances actually do useful things that need to get done so the energy isn't just wasted like it is with power supply inefficiency. Sure a 12vdc circuit would be nice. It wouldn't be nice enough or efficient enough to be worth paying for.
      - ip26 8y ago
        The point is the power delivery system we have does a good job for 99% of real power consumed (or whatever the number really is). I hate waste; my mains-connected smoke detectors (1% efficient) and garage door opener (15W standby) gnaw at my soul. But that's scope for improvement, not an efficiency crisis.
setquk 8y ago
Also to note that your 1KW appliances need 83 amps in a 12V DC system. This is a huge amount of current and requires special cabling (which has a not insignificant voltage drop due to the resistance of the wire) and special connectors.
dreamcompiler 8y ago
Power loss (I^2R loss) over distance is not caused by DC; it's caused by the combination of low voltage and high current. If current usage and distance are both small (as they would be in an LED-lighted house), wiring a house for DC is a perfectly reasonable thing to do.
rb808 8y ago
Yes Please for DC power. Especially if it can remove all the power adapters. I think I have more adapters than wall sockets in my house now. Phones, Tablets, electric toothbrushes, shaver, router & switch, wifi access point, rasp pi, cameras, Laptop, Monitor, streaming device, reading light, electric piano, toy train. good grief

Someone1234 8y ago

Slight tangent but "in-building DC" exists, and is rapidly gaining popularity but not via the medium many assumed: Power Over Ethernet. You can buy PoE LED light fixtures now, which are both powered and controlled over ethernet. You buy a single PoE switch, run some low voltage Cat6, and you can power an entire floor's worth of lighting. EEPoE (Energy Efficient PoE) offers more efficient PoE too which claims up to 94% efficiency. Definitely a space to watch. Particularly as the cost savings of running low voltage Ethernet cable compared to high voltage electrical cable (110v) are substantial.

baybal2 8y ago
Definitely watching. I once was in the LED industry when it was still hot. The company was called Zega. They tried every random thing, including putting a small real ARM server on the bloody thing to do remote control. It was back then when I first stumbled on Espressif people and Teo. They got lightyears ahead of us with all-in-one SoC.
jws 8y ago
EEPoE is new to me: Microsemi's exclusive EEPoE technology cuts the power losses on Ethernet cables by 50%, through the utilization of all the copper available on cable when a Microsemi EEPoE PSE IC or Midspan is used. It is 100% compatible with IEEE802.3at, and the savings work with ANY IEEE 802.3at Type 2, Type 1 or IEEE 802.3af compliant PD. In practice, devices that consume 25.5W would consume less than 27.75W, instead of the worst case 30W when a non-EEPoE PSE is employed. So they use all 8 wires for power instead of just 4 to halve the power loss on the wire. For the worst case device that makes the 20% loss be a 10% loss.
- TorKlingberg 8y ago
  Does that mean you cannot use it for any regular Ethernet data signaling at the same time, or is the signal overloaded on the DC?
  - poopchute 8y ago
    You can. I used to work for an ISP and every WiFi access point I installed had Ethernet+DC over the same cat6 cable. Still got 100 megabit speeds
HeyLaughingBoy 8y ago
you can power an entire floor's worth of lighting ? Must be either very low current lighting or that's some pretty beefy Cat6. I think the average Cat6 cable is only 24 gauge and that won't carry a lot of current very far.
- bronson 8y ago
  Star topology
  - jandrese 8y ago
    Isn't this like saying you could light the world if you had a big enough switch and unlimited cable?
    - bronson 8y ago
      Where did you get that? GP is talking about lighting a floor in a building.
      - jandrese 8y ago
        He's talking about running a separate cable for each and every bulb. It's a wasteful solution compared to running all of the lights off of a single circuit (or limited number of circuits) like a normal building.
        Someone1234 8y ago
        No I wasn't. PoE+ can support half a dozen LED panels off of a single Cat6 run.
- FooHentai 8y ago
  PoE+ will deliver 30W to the far end of up to 100M network cabling. Given that those cables radiate out to endpoint devices from a central point, rather than powering multiple devices in a ring/loop topology, the potential to power lots of devices over a wide area is huge. Biggest problem tends to be accommodating the central power delivery device. Those big PoE switches run hot and loud.
noveltyaccount 8y ago
TIL about PoE lighting. I always imagined homes would migrate to 12VDC and converge electronics with RVs.
- FooHentai 8y ago
  A small DC-input PoE switch in your RV might be the next logical evolution :)

vvanders 8y ago

Isn't that a function of voltage and not modulation? There might be a cost argument, I'm not sure if solid state step-down DC-DC converters are cheaper than good old cheap transformers.

Filligree 8y ago
It's a function of both. At equivalent voltage, DC has much lower loss than AC.
tlb 8y ago
Yes, it's entirely a function of voltage. But the safe limit for DC voltage is lower for two reasons: - A shock from a DC supply will cause heart fibrillations at lower voltage than AC, because of the way muscles receive signals from nerves - An electrical arc from a DC line will burn continuously, while an AC arc tends to self-extinguish at each zero-crossing. So in practice, 120 VAC or 48 VDC are the limits for household wiring.
- robocat 8y ago
  > So in practice, 120 VAC or 48 VDC are the limits for household wiring About 20% of the world uses 110-120 V and 60Hz. The rest uses mostly 240V at 50Hz. Although 110V is safer, the US seems to ignore many of the safety features I see used elsewhere in the world. How that translates to deaths per million people per year comparing to similarly rich countries, I don't know.
- upofadown 8y ago
  >A shock from a DC supply will cause heart fibrillations at lower voltage than AC, because of the way muscles receive signals from nerves That is opposite to my understanding. The extra shock hazard of AC vs DC was an argument used against AC power distribution back in the day. The 50V limit is to prevent shock altogether.

pitaj 8y ago

> until I'm reminded that DC power loss over a distance can hurt bad, even 48VDC telecom power. If you had AC to your house, then a rectifier for a 100V/200V DC circuit through your house, the losses wouldn't be any worse. DC losses are less than AC losses at the equivalent voltage, because the resistance seen by DC is less than the AC impedance.

sevensor 8y ago
Certainly at the household scale this is true. I cringe at the inefficiency of rooftop solar panels, hooked up to inverters, powering transformers that supply phones, lights, and electronics. AC in the house is great for an electric oven, vacuum cleaner, or fridge compressor, but so many modern electronic devices would be happy to run off of 5V or 12V.
- ip26 8y ago
  Look on the bright side- in terms of real power, the electric oven, vacuum cleaner, AC compressor, and fridge compressor totally swamp the entire load, waste and all, of those 5V devices. In a perfect world we'd have both AC & DC, and could use whichever was most appropriate. We could feed DC straight from the solar panels to the cell phone. But in terms of what consumes most of the power, in the typical home it's AC loads.
  - dsfyu404ed 8y ago
    >Look on the bright side- in terms of real power, the electric oven, vacuum cleaner, AC compressor, and fridge compressor totally swamp the entire load, waste and all, of those 5V devices. This isn't an appropriate comparison. Those appliances actually do useful things that need to get done so the energy isn't just wasted like it is with power supply inefficiency. Sure a 12vdc circuit would be nice. It wouldn't be nice enough or efficient enough to be worth paying for.
    - ip26 8y ago
      The point is the power delivery system we have does a good job for 99% of real power consumed (or whatever the number really is). I hate waste; my mains-connected smoke detectors (1% efficient) and garage door opener (15W standby) gnaw at my soul. But that's scope for improvement, not an efficiency crisis.

setquk 8y ago

Also to note that your 1KW appliances need 83 amps in a 12V DC system. This is a huge amount of current and requires special cabling (which has a not insignificant voltage drop due to the resistance of the wire) and special connectors.

dreamcompiler 8y ago

Power loss (I^2R loss) over distance is not caused by DC; it's caused by the combination of low voltage and high current. If current usage and distance are both small (as they would be in an LED-lighted house), wiring a house for DC is a perfectly reasonable thing to do.

rb808 8y ago

Yes Please for DC power. Especially if it can remove all the power adapters. I think I have more adapters than wall sockets in my house now. Phones, Tablets, electric toothbrushes, shaver, router & switch, wifi access point, rasp pi, cameras, Laptop, Monitor, streaming device, reading light, electric piano, toy train. good grief