What am i doing wrong here ?

[Adam S]

Dear all,

I am new to electronics and would appreciate some guidance on an issue I'm encountering. When I close the switch, the first multimeter shows 12V. However, the second multimeter, which is connected to the electrolytic capacitor, shows no reading. Could you please check my setup and let me know what I might be doing wrong?

Thank you for your help.

 

 

 

Design3.ms14

[Viktor Nikolov]

The connection I highlighted on the schema connects the ground to the junction PR1. So, the capacitor has ground from both sides and thus, there is no voltage across it.

What are you trying to achieve? What shall this design do?

[Adam S]

34 minutes ago, Viktor Nikolov said:

The connection I highlighted on the schema connects the ground to the junction PR1. So, the capacitor has ground from both sides and thus, there is no voltage across it.

What are you trying to achieve? What shall this design do?

What I'm trying to achieve is to observe the behavior of the capacitor when charging and discharging in the circuit. The goal is to see the voltage change across the capacitor when the switch is closed and then opened. Ideally, I want to monitor this process using the multimeter (or an oscilloscope) to understand how the capacitor stores and releases energy.

Could you please advise on how to modify the design to achieve this?

 

[Viktor Nikolov]

I suggest replacing the trace I highlighted with a resistor. To discharge the capacitor, you need a resistor parallel to it.

The resistor will also "isolate" junction PR1 from the ground. Just be aware that the voltage across the capacitor will be less than 12 V because the two resistors create a voltage divider. You can play with the values of the resistors to see the voltage divider's effect.

When you connect the switch S1, the capacitor charges. You will see a short spike of voltage across the resistor R1 because current flows through it until the capacitor charges (you will observe a so-called voltage drop on the R1). When you disconnect S1, the capacitor discharges through the new resistor, which you put in parallel.  The capacitor won't discharge into the ground; the circuit must be between the plus and minus pads of the capacitor.

I would replace multimeters with oscilloscopes because the process is dynamic and happens only shortly after the S1 is connected or disconnected.

[Adam S]

Thank you for the detailed suggestions! I've made the changes by adding a resistor and replacing the multimeters with oscilloscopes to better observe the process. Could you please confirm if the adjustments I’ve made align with your recommendations?

Also, is there a way to enable legends for time and voltage on the oscilloscope graph? It would help me better interpret the results. I tried right-clicking on the graph and looked for available options, but that didn’t work.

I have also attached the project file below.

Thanks again for your guidance!

 

Design3_Resistor_added.ms14

[Viktor Nikolov]

Yes, this is what I meant. You see the proper capacitor discharge curve on the oscilloscope. 👍

I'm unfamiliar with Multisim, so I can't advise on legends in the oscilloscope.

On Windows, I would take a screenshot using the Snipping Tool and then add the text to the picture in Paint. Or export the data from the oscilloscope in a text file (I see "Save" button), import it into Excel, and create a chart with proper legend in Excel.