Series and Parallel Circuits 3: Capacitors

  1. Series and Parallel Circuits 1: The Basics
  2. Series and Parallel Circuits 2: Resistors
  3. Series and Parallel Circuits 3: Capacitors (this article)
  4. AC Series and Parallel Circuits 4: Inductors and Capacitors
  5. Series and Parallel Circuits 5: More About Circuits

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Capacitance behaves differently from resistance in series and parallel circuits, as we discussed in the last post.  Contrary to resistance capacitance is reduced when capacitors are placed in series, and increased in an additive manner, when placed in parallel as tabulated below.

So, when capacitors are placed in series, the overall capacitance is decreased proportionally to the inverse capacitances of the capacitors in series.  And the voltage drops (ΔV) across the capacitors are additive to create the overall voltage drop for the circuit (ΔVT).  Additionally, the current (when there is current (e.g., charging, discharging, AC, etc.)) is constant when capacitors are in series configuration. 

When capacitors are placed in parallel, the overall capacitance increases additively, and the current throughout the entire circuit is also the sum of the currents through each parallel leg of the circuit.  In this case, the voltage drop across all legs of the parallel circuit is also the same.

These phenomena are used in the design of multilayer ceramic capacitors (MLCCs).  For instance, capacitors in parallel are used to increase MLCC device capacitance.  And capacitors in series are used to increase device voltage rating (at the expense of capacitance) as illustrated below.

Similar to capacitance, battery capacities (Ampere hours (Ah)) are also additive when batteries are placed in parallel, and battery capacity (Watt hours (Wh)) is also increased since Ah x V = Wh.  But in the case of batteries, capacity (Ah) remains constant when batteries are placed in series.  Thus the capacity of batteries in series in Watt hours (Wh) increases while current capability remains the same with respect to a single battery cell.  This is also the case for photovoltaics (solar cells), fuel cells and the like.  In the next post, we will discuss AC properties of series and parallel RLC circuits.  Until then… 


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