How to Test a Capacitor

A capacitor is an electronic component that consists of two conducting plates bearing opposite electronic charges. These two plates have a dielectric (insulator) medium as their separator. Different capacitors may make use of different dielectric. Common ones include air, paper, plastic, polyester and polystyrene.

Now, a potential difference across the conducting plates causes the formation of a static electric field in the dielectric. This electric field is where the capacitor stores energy between the two conductors. The process which allows the capacitor to store energy is known as charging.

The capacitor has a wide range of application in electronic circuits with the purpose of restricting direct current (DC) and allowing alternating current (AC) to pass through. Also, it finds applications in filter networks, in resonant circuits, etc.

The device is basically built for storing energy and for releasing all the energy at once. The capacity of this device to hold an electrical charge is termed as 'capacitance' and it is measured by Farads.

A capacitor discharges into whatever both of its leads touch, at the same time. This implies that if you happen to touch both the leads at the same time, the capacitor discharges into your body. Those with low value may not create any concern, but be careful with the large ones. They may seem harmless, but have the potential to do severe damage to the body.

So before you know how to test a capacitor, you must know how to discharge it. To discharge a low capacitance capacitor, you need nothing more than a metal screwdriver. First you have to de-solder the device to be tested, from the unit, lest it may damage other components.

Now short both the metal terminals of the capacitor with the metal end of the screwdriver. Ensure you do not touch any of the metal parts, so as to avoid getting an electric shock. In case you are working with a high-voltage capacitor, it is better to seek guidance from an expert.

You must make a note of the reading that the meter shows before you begin the testing. Thereafter, touch the capacitor terminals (keeping the red lead on the left and the black lead on the right). Now watch what does the multimeter show.

The needles must move away from the infinity (which probably would be on the left side) and proceed slightly towards the right side and come back to infinity. Now if you reverse the leads, the needle of the multimeter must move away from infinity further to the right side before falling back again where it started from.

So, all such observations infer that the capacitor is in good working condition. On the other hand, if the needle moves away from the infinity and goes to the right and stays there, then it indicates that the device has shorted out.

To conclude, it is always safe to seek instructions about testing a capacitor in an AC unit or microwave, from a professional. This is because in such appliances, capacitors hold a high amount of charge within them and this might risk your safety, unless you are a professional yourself.