Maximum time for a capacitor to charge?

Question

Maximum time for a capacitor to charge?

Answer 1

Current into a capacitor is a decaying exponential.  Rule of thumb is that a capacitor is essentially fully charged in 5 RC units or 5 times the resistance (Ohms) times capacitance (Farads) will yield time in seconds.  As you see, a larger resistance will increase the charging time.

Answer 2

David P is essentially correct, but he does not explain well what he means with resistance.  When you connect the capacitor directly to a battery, then the resistance in question is just the leakage resistance of the capacitor.  This acts like an external resistor connected in parallel to an ideal capacitor.  In an actual circuit containing other elements the actual charge time will vary. A simpe example is if you connect a resistor in parallel to the capacitor, which lowers the effective resistance (because you increase the "leakage" by giving the current another path to bypass the capacitor), and thus reduces the charging time.  In this example adding resistance actually has the opposite effect of David's statement- it all depends on how you connect the additional resistance.