All capacitors have a maximum voltage rating and when selecting a capacitor consideration must be given to the amount of voltage to be applied across the capacitor. The maximum amount of voltage that can be applied to the capacitor without damage to its dielectric material is generally given in the data sheets as: WV, (working voltage) or as WV DC, (DC working voltage).
If the voltage applied across the capacitor becomes too great, the dielectric will break down (known as electrical breakdown) and arcing will occur between the capacitor plates resulting in a short-circuit. The working voltage of the capacitor depends on the type of dielectric material being used and its thickness.
The DC working voltage of a capacitor is just that, the maximum DC voltage and NOT the maximum AC voltage as a capacitor with a DC voltage rating of 100 volts DC cannot be safely subjected to an alternating voltage of 100 volts. Since an alternating voltage that has an RMS value of 100 volts will have a peak value of over 141 volts! (√2 x 100).
Then a capacitor which is required to operate at 100 volts AC should have a working voltage of at least 200 volts. In practice, a capacitor should be selected so that its working voltage either DC or AC should be at least 50 percent greater than the highest effective voltage to be applied to it.
Another factor which affects the operation of a capacitor is Dielectric Leakage. Dielectric leakage occurs in a capacitor as the result of an unwanted leakage current which flows through the dielectric material.
Generally, it is assumed that the resistance of the dielectric is extremely high and a good insulator blocking the flow of DC current through the capacitor (as in a perfect capacitor) from one plate to the other.
However, if the dielectric material becomes damaged due excessive voltage or over temperature, the leakage current through the dielectric will become extremely high resulting in a rapid loss of charge on the plates and an overheating of the capacitor eventually resulting in premature failure of the capacitor. Then never use a capacitor in a circuit with higher voltages than the capacitor is rated for otherwise it may become hot and explode.
Basic Notes for Application of Capacitors
a. Rated voltage and working voltage
In view of the electric capacity characteristic, we generally advocate not surpassing the electric capacity rated voltage when using, even if electric capacity oneself can recover the function to some extent. When used with the rated voltage surpassed, even if in the short time not penetrate, the product itself dielectric resistance can reduce, thus very easy to create this electric circuit burning. Therefore before using, it is necessary to strictly take charge of the product specification book.
b. Electric current
Electric capacity when work is easy to produce the very big electric-current. And repeatedly sufficient electric-discharge of the electric capacity can bring certain quantity of heat, which is a challenge to the electric capacity service life, sometimes directly penetrates. Different type of product has different electric-current to plant, so it must be confirmed the most suitable type before application.
c. Application temperature
The electric capacity material quality has decided its heat resistance. When working under the high temperature, the electric capacity loss will increase, therefore the application environment and time also needs to be considered.
Post time: Aug-11-2020