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How capacitors work

How capacitors workCapacitors are devices that can store energy using two plates and an isolating substance in between. This means that the energy cannot go true from one side to the other, but electricity can be stored that way because positive and negative electrons attract each other. Capacitors seem to be simple devices, but there are a lot of parameters to be measured to see if they are of good quality or not. Testing these parameters gives you a very good indication of the quality of the products that are being tested.

Capacitance: This is relatively easy to measure with a LCR meter, and shows the amount of electrical energy that can be stored in the capacitor.

ESR  (equivalent series resistance): A High ESR rating means that the capacitor will get hot very quickly at high ripple current, this causes the boric acid in electrolytic capacitors to heat up and evaporate,  causing malfunction.

Dissipation factor: The ratio of the power loss in a dielectric material to the total power transmitted through the dielectric, the imperfection of the dielectric.  The loss of power true the dielectric, unfortunately no material is 100% perfect an isolator, so there Is always some power that can go true the isolation inside a capacitor.

Quality factor: The quality factor describes the ability for the capacitor to be used in oscillation circuits and is closely connected to the Dissipation factor parameter.

Dielectric strength: This describes the isolative properties of a capacitor,  the middle layer in between of the plates as shown in fig one. The insulation properties decide the maximal voltage that we can put on a capacitor.

Direct Current Leakage or DCL: measures the amount of current passing through the dielectric during application of maximum rated DC voltage.  Ideally, capacitors should not pass DC current through its plates, however imperfections during manufacturing allows a very small amount to pass.  When a higher than rated DC voltage is applied to the capacitor, the dielectrics breakdown and causes high leakage current.  A counterfeit capacitor with a lower rated voltage can be detected by DCL test.

Insulation Resistance: This parameter is directly related to DCL and is a measure of the ability of the dielectric to pass DC current through itself.  Depending on capacitor type and manufacturer, insulation resistance is specified instead of DCL.  Like DCL, insulation resistance is also tested by applying the maximum rated DC voltage and measuring the resistance between the plates.



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