Leakage Current
This is the residual current which continues to flow when the capacitor has been charged up to a set voltage. At this voltage its magnitude is determined by the thickness (forming voltage) and degree of perfection of the dielectric oxide and foil surface area. The value of leakage current will continue to fall, whilst voltage is applied, until a very low steady state value is reached. Its value will increase both with voltage and temperature. The longer capacitors are stored with no applied voltage, the higher the initial leakage current. More details are given under shelf life.
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Equivalent Series Resistance
The equivalent series resistance (e.s.r.) is made up of several resistive components within the capacitor , including electrolyte, tissue separators, foils etc. The method of construction also plays an important role. For example, the e.s.r. can be significantly reduced in some cases by making multiple connections to the anode and cathode foils. The e.s.r. is both temperature and frequency dependent, increasing either will cause a reduction in e.s.r., as exemplified by the graph below:

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Impedance (Z)
The impedance is govemed by the capacitance(C), e.s.r. and inductance(L) of the capacitor and is given by the formula:



Where and

The impedance is dominated by the capacitive reactance at low frequencies and by the inductive reactance at high frequencies. Series resonance occurs when at which point Z = e.s.r.

The impedance is clearly frequency dependent and is temperature dependent due to the capacitance and e.s.r. terms.
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Inductance
Some inductance is present in all wound aluminium electrolytic capacitors as a result of the construction of the winding and the tabbing. The value is usually not more than a few tens of nano-henrys and is more or less constant with changes in temperature and frequency.
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