Why do bill of materials and schematics always recommend 16 V or 25 V capacitors in circuits that are powered by only 12 V and even less? Would not it be right for the capacitors to have the same voltage as the circuits?
The voltage of a capacitor is not the voltage at which it must operate in a circuit. The voltage marked on a capacitor is the maximum voltage that it supports without damaging itself, that is, without its dielectric breaking and burning. Thus, it is good practice to always use a voltage capacitor larger than the one on which the circuit it is in. For example, at a 12 V source, the peak voltage after rectifying may reach 16 V, so it is recommended that the capacitors be 16 V or more. A good recommendation is always to use a capacitor with a working voltage at least 50% higher than what we will find at most in the circuit.