Capacitors or supercapacitors are typically wired in series when the voltage exceeds the limit of an individual capacitor. It is best to use as close to equal value capacitors as possible, as the current is the same for series components, and smaller value capacitors charge faster (seen as voltage rise) for a given current than larger value capacitors.

  • Caps/Supercaps connected in series should be equal value for safety reasons. This also helps simplify the math.
  • Series caps/supercaps are primarily used to increased voltage beyond individual capacitor max voltage.
  • Total capacitance of series caps/supercaps is a fraction of the value of the individual capacitors (which should all be of equal value). 2 series caps/supercaps = 1/2 total capacitance. 3 equal value series caps/supercaps = 1/3 total capacitance.
  • Series caps/supercaps won’t stay equally charged forever. The more differences they have (actual capacitance difference, leakage etc.) the worse they will unbalance. A short circuit can quickly discharge one capacitor while the other one(s) will stay charged and can easily cause a serious imbalance that can cause a lot of damage quickly. Effective over and reverse voltage protection circuitry is a must have feature of series caps/supercaps.

Care must be taken to prevent any capacitors/supercapacitors from overcharging or reverse charging if they are polarized. It is easy to accidentally overcharge/reverse charge while capacitors are in series, so it is best to have protection circuitry and to carefully monitor the behavior of the capacitors/supercapacitors.

Total capacitance of series capacitors actually goes down to a fraction of their rated value. Since series capacitors should be equal value, it is safe to assume that 2 series capacitors have 1/2 of their rated value. 3 series capacitors have 1/3 of the rated value, and so on.

Of course, capacitors aren’t perfect (ideal) and therefore their actual properties must be taken into account while predicting how they will behave in series.

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