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Where does current go?

  1. Oct 16, 2016 #1


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    Hi I am trying to do a DIY with a servo and I was wondering...

    If I have a power source (e.g. 4V with 50 mAmps) connected to a 4V servo with a running current requirement of 200 mAmps...where will the current from the power source go? Will it just heat the motor of the servo? Or if there was a capacitor will the capacitor collect the current and then periodically discharge it to the motor?

    I have been taught that voltage is akin to the 'height' of the electron and current is the amount of electrons that are flowing. So if the voltage is correct will the electrons compile in the capacitor like a dam until it 'bursts' or discharge?

    thank you for any help!
  2. jcsd
  3. Oct 16, 2016 #2


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    Homework Helper
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    If your servo requires 200 mA, and you picked a power supply that can only deliver 50 mA, then you could be under-serving your servo. What little current your power supply is providing will still go into the servo. Have you tried it yet? Please report on what happens.

    If your servo is always doing something, a capacitor will not help. If your servo is only active, say less than 25% of the time, yes a right-sized capacitance will help (depends on how long the servo is continuously active).

    Why use with an undersized power supply to begin with?
  4. Oct 16, 2016 #3


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    Gold Member

    The circuit should not over-voltage the capacitor, capacitors have max voltage ratings. A capacitor voltage will rise at it charges, and it will accumulate less and less charge as the voltage at the terminal connected to the charging voltage source rises. The capacitor should not burst or overcharge, it will just get full and then current will stop flowing because the voltage at the input terminal of the capacitor will equal the voltage at the output of the power supply.

    The below is more elaborate / formal / better explanation.

  5. Oct 16, 2016 #4


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    Staff: Mentor

    In general, current just goes around and around the circuit. Using the water analogy, it's like a circular piping loop.
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