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What Is Dielectric Absorption?

K. Hamilton
K. Hamilton

Dielectric absorption occurs when a capacitor that has been charged for long time retains a small amount of voltage after being briefly discharged. The capacitor will have this small amount of voltage even if an attempt was made to fully discharge it. This effect usually lasts a few seconds to a few minutes.

Under ideal circumstances, a capacitor should be at zero volts after going through the discharging process. Capacitors, however, often retain a small amount of voltage through dielectric absorption, which is also known as soakage. The effect of dielectric absorption occurs because of polarization in the material used for insulation, which is also considered to be independent of the capacity of the capacitor.

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Man with a drill

The amount of voltage that remains is not necessarily substantial. In certain dielectrics, this voltage might be only about 1 percent of the original amount. This amount often depends on the type of dielectric used. For instance, materials such as polymer films typically have about 1 percent remaining after discharging, but supercapacitors and electrolytic capacitors might have as much as 25 percent of the original voltage.

Dielectric absorption is considered a bane in the field of electronics. When the amount becomes so excessive, it will affect the operation of a particular electronic device. A person can relieve a capacitor of the excess charge by testing it for voltage and rechecking its value. It is easily done using a device called a capacitor analyzer. This gadget will analyze dielectric absorption and recheck its value until the capacitor has no voltage remaining.

When dielectric absorption occurs on electronic devices, it usually can be left alone, because most have only a small amount of voltage remaining, and it often dissipates within a short period of time. A capacitor analyzer might be necessary, however, for certain devices that are believed to have supercapacitors, which have a tendency to have excessive charging that might damage circuit operation. One can often test for dielectric absorption in capacitors provided that safety measures are applied. Improper use could harm the user and the capacitor as well.

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