3 ms·

So all efficient (switching) voltage conversion involves AC. Your stock plug-in DC power supply is actually a AC->DC->AC->DC device yet it's trivial to get abov

by coryrc 3y ago

So all efficient (switching) voltage conversion involves AC. Your stock plug-in DC power supply is actually a AC->DC->AC->DC device yet it's trivial to get above 97% and miniscule quiescent (minimum) load. High-frequency AC isn't a problem for efficiency. What's NOT easy is efficiently making 60 Hz AC at low quiescent power. Most inverters always burn 2-5% of maximum power with no load, while 1% would be considered far excessive if the output was DC (maybe 0.1% would be generally okay?). Part of this is lack of regulation; consumer devices have low-quiescent power supplies originally because of government mandates and, now, economies of scale. The government mandate didn't apply to inverters so there isn't an initial push to shift to low-quiescent topologies and prevent the first movers from being undercut. So just for that reason, lower-voltage DC distribution can overall be more efficient if you are off-grid, even if some other portions of the system have increased losses. 120Vdc distribution would be superior from an efficiency standpoint in every way, but you're going to spend a lot on switches and protection equipment.

calamari4065 3y ago
> Your stock plug-in DC power supply is actually a AC->DC->AC->DC device That is actually not at all how switching converters work. Pulsed DC is not AC. Those are two very different things.
- coryrc 3y ago
  I'm not even sure how to reply to how wrong you are. You could only argue that with flyback topology (I'd still say you are wrong) but try a standard full-bridge and tell me the current isn't alternating. Then check out some ZCS variants and tell me which of those current waveforms don't look like Alternating Current.
- nine_k 3y ago
  Pulsed DC is not DC,:) Since all such power supplies prominently feature transformers, they can't operate on DC alone. But the frequency they use is high (a few kHz), the transformers are small, unlike the huge beasts in traditional 50/60 Hz power supplies.
- dreamcompiler 3y ago
  AC can mean "sinusoidal" or it can more generally mean "any non-constant voltage [or current]." It was clear from the context that the parent meant the latter.

by coryrc 3y ago

calamari4065 3y ago

> Your stock plug-in DC power supply is actually a AC->DC->AC->DC device That is actually not at all how switching converters work. Pulsed DC is not AC. Those are two very different things.

coryrc 3y ago
I'm not even sure how to reply to how wrong you are. You could only argue that with flyback topology (I'd still say you are wrong) but try a standard full-bridge and tell me the current isn't alternating. Then check out some ZCS variants and tell me which of those current waveforms don't look like Alternating Current.
nine_k 3y ago
Pulsed DC is not DC,:) Since all such power supplies prominently feature transformers, they can't operate on DC alone. But the frequency they use is high (a few kHz), the transformers are small, unlike the huge beasts in traditional 50/60 Hz power supplies.
dreamcompiler 3y ago
AC can mean "sinusoidal" or it can more generally mean "any non-constant voltage [or current]." It was clear from the context that the parent meant the latter.