5 ms·

Generally this doesn't work too well because low-voltage distribution is very inefficient. Even at very modest currents, you're going to need huge conductors o

Generally this doesn't work too well because low-voltage distribution is very inefficient. Even at very modest currents, you're going to need huge conductors or else deal with lots of voltage drop. Compare that to a typical switch-mode power supply, which is already very efficient. The quiescent current of a modern, reasonably well designed power supply is basically negligible. The problems of 'vampire draw' have basically been solved for the actual power supply (devices that don't 'sleep' are still an issue, but that's no fault of the supply). Recently I modified some LED fairy lights with a LDR/transistor setup. The quiescent draw during the day is about a tenth of a watt, vs. 6 watts under load. Left plugged in for a year in 'off' mode, that would cost me less than 10 cents. This 'variable clock' switch-mode supply is all about squeezing every bit of battery life you can with a device. It's about making sensors that can be deployed without a power source that last for years instead of months.

mulmen 10y ago
This is exactly the type of response I was hoping for, thank you. Is this a similar reason to why long distance power lines are of a much higher voltage?
- lutusp 10y ago
  > Is this a similar reason to why long distance power lines are of a much higher voltage? Long-distance power conductors use the highest practical voltage to avoid what are called "I squared R" losses, so named because the power dissipated in a resistance (like a transmission line) is equal the the square of the current times the resistance. For a given power level, one can obtain that same power with a very high voltage and a proportionally lower current, thus greatly reducing resistive losses in the lines. This is why a million volts is by no means out of the question for long power transmission lines.
- euyyn 10y ago
  Correct. And why AC won over DC: It's much easier to step the voltage up for power transmission.
  - zkms 10y ago
    > It's much easier to step the voltage up for power transmission. It used to be much easier to step the voltage up with AC, but now we have advanced enough power electronics to make the inherent increased efficiency of HVDC be actually worth it.
  - caf 10y ago
    High voltage AC switches and breakers are also cheaper to make for arc-suppression reasons.

mulmen 10y ago

This is exactly the type of response I was hoping for, thank you. Is this a similar reason to why long distance power lines are of a much higher voltage?

lutusp 10y ago
> Is this a similar reason to why long distance power lines are of a much higher voltage? Long-distance power conductors use the highest practical voltage to avoid what are called "I squared R" losses, so named because the power dissipated in a resistance (like a transmission line) is equal the the square of the current times the resistance. For a given power level, one can obtain that same power with a very high voltage and a proportionally lower current, thus greatly reducing resistive losses in the lines. This is why a million volts is by no means out of the question for long power transmission lines.
euyyn 10y ago
Correct. And why AC won over DC: It's much easier to step the voltage up for power transmission.
- zkms 10y ago
  > It's much easier to step the voltage up for power transmission. It used to be much easier to step the voltage up with AC, but now we have advanced enough power electronics to make the inherent increased efficiency of HVDC be actually worth it.
- caf 10y ago
  High voltage AC switches and breakers are also cheaper to make for arc-suppression reasons.