# Voltage Drop across Capacitor?

1. Jul 28, 2008

### simoncastle

Hi all,

Here's the problem!

I am attempting to create a leakage current test suite. Basically it centers around cutting the voltage reference supply to a capacitor and measuring the voltage drop. Similar to the one in the attachment.

I figured that to determine the drop it would be a simple case of V at start minus V after time delay.

However a colleage told me that because of the exponential decay of capacitors this simple equation wouldn't be enough to accuratly determine the voltage drop.

Any ideas?

Thanks!

- Si

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2. Jul 28, 2008

### Redbelly98

Staff Emeritus
I'm assuming you want to measure the parallel resistance (which causes the charge to leak) of the capacitor.

You can use an exponentially decaying function for the voltage:

$$V_t = V_{ref} \ e^{-t/(RC)}$$
where Vt is the voltage after t seconds. Solve the equation for R after measuring all other quantities (Vt, Vref, t, and C)