The time constant When a capacitor is charging or discharging, the amount of charge on the capacitor changes exponentially. The graphs in the diagram show how the charge on a capacitor changes with time when it is charging and discharging. Graphs showing the change of voltage with time are the same shape.
The time it takes for a capacitor to discharge 63% of its fully charged voltage is equal to one time constant. After 2 time constants, the capacitor discharges 86.3% of the supply voltage. After 3 time constants, the capacitor discharges 94.93% of the supply voltage. After 4 time constants, a capacitor discharges 98.12% of the supply voltage.
After 2 time constants, the capacitor discharges 86.3% of the supply voltage. After 3 time constants, the capacitor discharges 94.93% of the supply voltage. After 4 time constants, a capacitor discharges 98.12% of the supply voltage. After 5 time constants, the capacitor discharges 99.3% of the supply voltage.
Capacitors will lose their charge over time, and especially aluminium electrolyts do have some leakage. Even a low-leakage type, like this one will lose 1V in just 20s (1000 μ μ F/25V). Nevertheless, YMMV, and you will see capacitors which can hold their charge for several months. It's wise to discharge them.
The Capacitor discharging cycle that a capacitor goes through is the cycle, or period of time, it takes for a capacitor to discharge of its charge and voltage. In this article, we will go over this capacitor discharging cycle, including:
For the equation of capacitor discharge, we put in the time constant, and then substitute x for Q, V or I: Where: is charge/pd/current at time t is charge/pd/current at start is capacitance and is the resistance When the time, t, is equal to the time constant the equation for charge becomes: