Lets assume I have a supercapacitor rated for 5v at 200F. That's 2500 joules of energy. My wall socket outputs 120V at a maximum of 15A, which is 1800 watts (or joules per second). If I hook up my capacitor to 120V DC at 15 amps for 1 second, I would expect my capacitor to be charged up to 1800 joules, or about 4.2 volts.
My expectation is that since the voltage across the capacitor is never above 5v, it should be fine.
Will this work in practice, or would my capacitor blow up in my face if I tried this? And if not, why?
Best Answer
Draw out your circuit and do the analysis.
Assuming you mean 120VAC -> rectifier -> resistor -> supercap, and you've got magic hands to unplug the cap when it reaches a certain voltage, it's theoretically possible- the voltage rating of the cap only "cares" about the actual voltage across the cap, and in this case the line voltage is across both the cap and the resistor. However, it's a horrible idea. Please don't hurt yourself.