Test capacitor with an oscilloscope?

Discussion in 'Homework Help' started by GregJ7, Jul 15, 2015.

  1. GregJ7

    Thread Starter New Member

    Jun 7, 2014
    I'm trying to figure out how to use a simple oscilloscope to show me a curve so I can determine if a capacitor is working as it should or not (and then calculate its Farad rating). First I want to make sure I have set the non-oscilloscope portion up correctly. My goal was to use a switch that discharges the cap in one position and applies power to the cap in another position, which in theory will trigger the oscilloscope when the voltage becomes non-zero. Can anyone verify that my schematic will do that? Does the voltage on the hot ("+") end of the cap rise as the cap charges and then stay constant when it is fully charged?

  2. crutschow


    Mar 14, 2008
    You need a resistor in series with the Charge line so that you can see the charge curve on the oscilloscope and calculate the capacitance from the RC time-constant (in one time-constant it charges to 0.636 of the input voltage).
    Note that you may need some small resistance in the Discharge line to keep the peak discharge current to a safe level for the switch you are using.

    Yes the voltage rises exponentially to the supply voltage and stays there.
    GregJ7 likes this.