Capacitor Charge and Time Constant Calculation, Formula, Example

Capacitor Charge and Time Constant Calculator

This calculator is designed to compute for the value of the energy stored in a capacitor given its capacitance value and the voltage across it. The time constant can also be computed if a resistance value is given. Note that the input capacitance must be in microfarads (μF).

The time constant of a resistor-capacitor series combination is defined as the time it takes for the capacitor to deplete 36.8% (for a discharging circuit) of its charge or the time it takes to reach 63.2% (for a charging circuit) of its maximum charge capacity given that it has no initial charge. The time constant also defines the response of the circuit to a step (or constant) voltage input. Consequently, the cutoff frequency of the circuit is defined by the time constant.

Diagram:

Formula:

Where:

$$V$$ = Applied voltage to the capacitor (volts)

$$C$$ = Capacitance (farads)

$$R$$ = Resistance (ohms)

$$\tau$$ = Time constant (seconds)

Example:

Example 1

Let’s consider capacitance C as 1000 microfarad and voltage V as 10 volts.

Let’s apply formula

E=CV²/2

E= 1000*10₂ /2

E= 0.0500 joules

Example 2

Let’s consider capacitance C as 2000 microfarad and reactance R as 10000 ohms.

Let’s apply formula

τ=RC

 τ = 2000*10000

 τ = 20 seconds