3 ms·

I'm skeptical of their DC vs AC commentary It's not about DC vs AC, it's high-voltage vs low-voltage. The power dissipation by wire resistance scales with the

by tremon 4y ago

I'm skeptical of their DC vs AC commentary It's not about DC vs AC, it's high-voltage vs low-voltage. The power dissipation by wire resistance scales with the square of the current ($P=RI^2$), and low line voltage means that you need large currents to transmit the same amount of power.

xpe 4y ago
Yes. Thanks for catching that. Also, DC and AC have differences in power transmission independent of resistance, some due to first principles (reactivity), and others related to devices for stepping voltage up or down (eg transformers).
cogman10 4y ago
Whether or not that's feasible is going to depend a lot on the application. I don't think we'd ever fully rid homes of AC sockets, it's too useful for things like vacuum cleaners or space heaters. But what about the sub 100W or even 200W applications? That's where I think something like 48VDC would start to shine. Every light in a home, phone chargers, tablet chargers, computer monitors, televisions, computers? (maybe not gaming rigs, but certainly laptops and nucs).
- midoridensha 4y ago
  >But what about the sub 100W or even 200W applications? That's where I think something like 48VDC would start to shine. How so? Exactly what benefit does it have over the current AC mains? With 48VDC, you'd still need to use DC-to-DC converters to power everything. I fail to see how that's any kind of improvement over the current switch-mode power supplies used. Instead, it'll just be less efficient because you'll get higher line losses in the power lines in the walls and all the way from wherever that 48VDC is coming from. If that's from a big SMPS in a closet somewhere, that's going to have its own losses. Overall, the entire system will have lower efficiency compared to the current system. Exactly what problem are you trying to solve with this idea? If you think you're going to eliminate SMPSs in all your electronic equipment, you're not; that's a fantasy. Everything needs a power supply because electronics only work at very low voltages (5V, 3.3V, even 1.8V in places, now 20V with USB3) and most equipment has some kind of peculiar voltage requirements, and usually multiple different requirements inside the same device. There's no improvement in efficiency by running a computer, for instance, from 48VDC vs. 120VAC or 240VAC, in fact it's probably worse.

by tremon 4y ago

xpe 4y ago

Yes. Thanks for catching that. Also, DC and AC have differences in power transmission independent of resistance, some due to first principles (reactivity), and others related to devices for stepping voltage up or down (eg transformers).

cogman10 4y ago

Whether or not that's feasible is going to depend a lot on the application. I don't think we'd ever fully rid homes of AC sockets, it's too useful for things like vacuum cleaners or space heaters. But what about the sub 100W or even 200W applications? That's where I think something like 48VDC would start to shine. Every light in a home, phone chargers, tablet chargers, computer monitors, televisions, computers? (maybe not gaming rigs, but certainly laptops and nucs).

midoridensha 4y ago
>But what about the sub 100W or even 200W applications? That's where I think something like 48VDC would start to shine. How so? Exactly what benefit does it have over the current AC mains? With 48VDC, you'd still need to use DC-to-DC converters to power everything. I fail to see how that's any kind of improvement over the current switch-mode power supplies used. Instead, it'll just be less efficient because you'll get higher line losses in the power lines in the walls and all the way from wherever that 48VDC is coming from. If that's from a big SMPS in a closet somewhere, that's going to have its own losses. Overall, the entire system will have lower efficiency compared to the current system. Exactly what problem are you trying to solve with this idea? If you think you're going to eliminate SMPSs in all your electronic equipment, you're not; that's a fantasy. Everything needs a power supply because electronics only work at very low voltages (5V, 3.3V, even 1.8V in places, now 20V with USB3) and most equipment has some kind of peculiar voltage requirements, and usually multiple different requirements inside the same device. There's no improvement in efficiency by running a computer, for instance, from 48VDC vs. 120VAC or 240VAC, in fact it's probably worse.