Lab 9 - Capacitor Charging/Discharging

Objective:
- To test a charge/discharge system that uses a 12 V DC power supply
- Verify if the system charges within 20s with a  resulting stored energy of 2.5 mJ
- Verify if the system will discharge the 2.5 mJ in 2s.

Pre-Circuit Tasks:
The circuit below shows the simple schematic of the charging/discharging system on the capacitor.  To charge/discharge the capacitor, the connected to the positive side of the capacitor is placed in its respective positions.  Meaning the connected cable will be attached to the CHARGE position when the capacitor is to be charged and changed to the DISCHARGE position to discharge.  The rate at the which the energy is transferred is controlled by C, Rcharge, and Rdischarge.

Before determining the values of the components, the expressions for the Thevenin voltage and resistance for the charging and discharging circuits were calculated.

Calculation for Thevenin Expressions

Calculations for Charging/Discharging Circuit Components:

Charging Circuit Component 

Discharging Circuit Component 

The results for the component values:

C = 34.7 µF 

Rcharge = 121212 Ω

Rdischarge = 12121.2 Ω

The Circuit:

Schematic of the Actual Circuit

For each circuit, an oscilloscope was used to show the movement of energy within the circuit.  

Charging Circuit

Charging Circuit

The charging process for the capacitor was about 20 seconds.

The Vfinal obtained after 20secs was about 11.96V.

With the value of Vfinal, RLeak was determined to be 0.145 µΩ.

Discharging Circuit

Discharging Circuit

The discharging circuit did not completely dissipate all its energy within 2 secs. 

Follow up Question

Practical Question: