23 Aug
2015
23 Aug
'15
5:46 p.m.
Guess I'm too used to thinking in simple ohmic
terms, with Watt & Kirchhoff
always looming large. Something told me that, in the end, there was no way
Well, Kirchhoff's laws do apply in AC circuits, but you have to be careful
how you apply them, given that voltages and currents need not be in phase.
around dealing with the E^2/R heat - anything else
seemed like a
thermodynamic "cheat".
Not so. There are many ways of reducing a voltage without generating that
much heat. For AC an obvious one is a transformer. Trivial example, if you
had to run a string of valve heaters totalling, say, 25.2V from 240V AC mains you
could use a dropping resistor (which would consume almost 90% of the incoming
power, overall efficiency around 10%)) or you could use a transformer, overall
efficiency around 80%+. Are you suggesting a transformer is a 'thermodynamic
cheat'?
For AC or DC, chopper type devices (switching regualtors, triac-type lamp dimmers, etc
-- depending on the type of supply, etc) are another way which is a lot more efficient
than a resistor. Are those 'thermodynamoic cheats'?
-tony