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Using Multisim 14.2 to simulate a capacitor's charge cycle , I've noted that when the simulation starts for the first time, even if the SPST switch is OFF, the capacitor starts fully charged. Any idea?

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  • \$\begingroup\$ In simulators this may be called "ic" or initial condition. Some allow you to set this as a part parameter, such as 220uF and ic=0. I am not familiar with MC but perhaps it is similar. \$\endgroup\$
    – rdtsc
    Dec 2, 2022 at 20:22
  • \$\begingroup\$ In LTspice, S1 might toggle between two resistor values: one very large value, simulating the "open" condition, the other a very small value simulating the "closed" condition. In both cases, the initial steady-state voltage of C1 would by +12V due to that resistive path through the switch. Perhaps Multisim simulates switches similarly? \$\endgroup\$
    – glen_geek
    Dec 2, 2022 at 20:27

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Most (if not all) simulators "try and help out" by calculating all the steady-state DC conditions first then, the simulation is run so, your capacitor has already been forced into the steady-state situation.

In micro-cap there is a tick-box called "operating-point" and if I uncheck it, the simulation begins right from the very start without calculating steady-state DC conditions.

The same will be true of multisim but, I can't help you find that "checkbox" because, I don't use multisim.

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we assign our parameters to the switch model (these are the limits for Multisim)

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The program supports values 1e308 1e324 1e-308 1e-324 In each specific case, you need to slip them in, and the program itself will sort out what it cannot do

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