Capacitor Current Calculator

Electrolytic capacitor

Capacitor current formula

Voltage V

Example Voltages To Enter

This Capacitor Current Calculator calculates the current which flows through a capacitor based on the capacitance, C, and the voltage, V, that builds up on the capacitor plates.

The formula which calculates the capacitor current is I= Cdv/dt, where I is the current flowing across the capacitor, C is the capacitance of the capacitor, and dv/dt is the derivative of the voltage across the capacitor.

You can see according to this formula that the current is directly proportional to the derivative of the voltage. Since the derivative of a constant is equal to 0, if the voltage is a DC voltage, the current across the capacitor will be equal to 0. So if the voltage is a DC voltage, the current flowing through the capacitor will always be 0. This, again, is because the derivative of a constant is always equal to 0. A constant does not change. So if a user simply enters in a voltage such as 10V or 20V or 30V, the current will be 0, for all values. This shows that no current can flow through a capacitor connected to a DC power source. Current only flows through a capacitor when it is connected to an AC source.

Now that this is proven by the equation, you can see that only AC voltages can have current flowing through the capacitor. Because the AC voltage is constantly changing, it is not constant. Therefore, the derivative will not be equal to 0. The dv/dt value will always produce a result. Thus, the answer will not be 0. Normally, AC voltages are usually sine or cosine waves. When using AC voltage from a source such as a wall outlet, the voltage is a sine wave. The wave is a cycle. It goes from low to high, low to high, low to high. It keeps changing every moment. Thus, sine or cosine waves perfectly reproduce what a voltage signal would look like.

So, when using this calculator, for the voltage value, the input should be a sine or cosine value, such as sin(60t), 4cos(60t), 5sin(120t), etc. These type of voltage values simulate actual real voltage signals such as those you would use in electronic circuits. Again, entering DC voltage values, will yield a different result, because the derivative of a DC voltage is 0. Thus, current will be 0.

To use this calculator, a user enters in the voltage (in volts), the capacitance (in coulombs), and then clicks the 'Calculate' button. The resultant capacitor current value in unit amperes (A) will then be automatically computed and displayed.


What is the current across a capacitor if the voltage is 6sin(60t) and the capacitance is 0.5F?

I= Cdv/dt= (0.5)d/dt(6sin(60t))= 180sin(60t)

So the current flowing across the capacitor is 180sin(60t) amperes (A).

What is the current across a capacitor if the voltage is 5cos(120t) and the capacitance is 0.2F?

I=Cdv/dt= (0.2)d/dt(5cos(120t)= -120cos(120t)

So the current flowing across the capacitor is -120cos(120t)

Related Resources

Capacitor Impedance Calculator

Capacitive Reactance

How to Calculate the Current Through a Capacitor

How to Calculate the Voltage Across a Capacitor