4 ms·

I think you’re underestimating the resistive losses at lower voltage. For the same amount of power (volts x amps) resistive losses are inverse square to the vol

I think you’re underestimating the resistive losses at lower voltage. For the same amount of power (volts x amps) resistive losses are inverse square to the voltage so losses are 100x greater at 10V x 10A than at 100V x 1A. Resistance is inverse to the cross sectional area of the wire so to compensate you need thicker wire, 10x the diameter (100x the area) for 1/10th the voltage x 10x the current. That’s why the wire that connects to your car battery is so much thicker than the mains wire in your home. You could have high voltage DC in your home but then you still need the transformer so I’m not sure it really buys you anything.

yazaddaruvala 3y ago
Have you ever had an issue with the resistive losses in your long ethernet cords? If you're prefer you can think of it as: each room gets its own Tesla powerwall, and therefore the battery to wall socket resistive losses are negligible.
- laurencerowe 3y ago
  Power over Ethernet usually supplies milliamps of current. Resistive losses are proportional to the square of the amps so they’re not a big problem for most things you power over PoE. Latest standards seem to max out at 90W. https://www.analog.com/en/technical-articles/ltpoe-extends-poe-to-90w-with-reliable-and-easy-to-use-standard.html https://www.analog.com/en/technical-articles/ltpoe-extends-p... Over the 100M max cable length voltage will drop 25% from 56V input to 48V output. http://poe-world.com/Calculator/ http://poe-world.com/Calculator/ For the same power draw, losses are 4x as high as at 110V, and 16x as high as at 220V. DC/DC power adapters are more efficient at low power (a few watts), so PoE might conceivably be marginal efficiency win for powering a bunch of low power VoIP phones. But as soon as you want to do something like power a laptop or even fast charge a mobile phone, you’re going to be better off plugging it into the mains with a modern AC/DC adapter that can be 95% efficient. It’s not that AC is better than DC, it’s that higher voltages are far more efficient than lower voltages as soon as you need even moderate amounts of power over moderate distances.

yazaddaruvala 3y ago

Have you ever had an issue with the resistive losses in your long ethernet cords? If you're prefer you can think of it as: each room gets its own Tesla powerwall, and therefore the battery to wall socket resistive losses are negligible.

laurencerowe 3y ago
Power over Ethernet usually supplies milliamps of current. Resistive losses are proportional to the square of the amps so they’re not a big problem for most things you power over PoE. Latest standards seem to max out at 90W. https://www.analog.com/en/technical-articles/ltpoe-extends-poe-to-90w-with-reliable-and-easy-to-use-standard.html https://www.analog.com/en/technical-articles/ltpoe-extends-p... Over the 100M max cable length voltage will drop 25% from 56V input to 48V output. http://poe-world.com/Calculator/ http://poe-world.com/Calculator/ For the same power draw, losses are 4x as high as at 110V, and 16x as high as at 220V. DC/DC power adapters are more efficient at low power (a few watts), so PoE might conceivably be marginal efficiency win for powering a bunch of low power VoIP phones. But as soon as you want to do something like power a laptop or even fast charge a mobile phone, you’re going to be better off plugging it into the mains with a modern AC/DC adapter that can be 95% efficient. It’s not that AC is better than DC, it’s that higher voltages are far more efficient than lower voltages as soon as you need even moderate amounts of power over moderate distances.