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I would like to simulate process of capacitor charging. Basically I would like to see current drop as capacitor gets charged. I used multisim.com. Here is me circuit.

capacitor

Unfortunately, it only shows constant current of 12 pA. Is 12pA initial charging current or average? Is this normal or am I am missing something?

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Since you measure 12 V the capacitor is already charged, which is as expected because the simulator tries to find the steady-state solution. The 12 pA shown is likely a leakage current, either artificially introduced by the simulator to make the calculations easier, or a tiny parallel resistance in the capacitor model.

To see the charging current you have to modify two things:

  1. Create a transient simulation.
  2. Make sure that the capacitor is discharged at time=0

Both of these are specific to the simulator you are using.

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With a capacitance of 1 F and a resistance of 1 MΩ, your circuit's time constant is

$$ \tau = RC = 1\,\mathrm{F}\cdot 1000000\,\mathrm{Ω} = 1000000\,\mathrm{seconds}. $$

You would need to simulate the circuit running for many days to see significant charging or discharging, regardless of applied voltage. Instead, you should use much smaller values for either the capacitor or the resistor: try 1 kΩ and 1 μF as realistic component values for a time constant of 1 millisecond.

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Probably Multisim has a similar setting, but in LTspice you need to check te "Start external DC supply voltages at 0 V" to see the capacitor charging. enter image description here

And then you will be able to see the curves:

enter image description here

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  • \$\begingroup\$ Thank you! Found it! I had to set initial conditions to user-defined. \$\endgroup\$ – user1700890 Jul 17 at 23:27

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