The Capacitor

Capacitors are among the most commonly used components in electronics. Their construction is fairly simple, two metal plates and a dielectric layer separating them. Capacitors are very similar to batteries since they store electrical charge. However, capacitors must be charged with electricity, unlike batteries which produce their own using chemicals.

The storage rating of a capacitor is based on the Farad unit. A capacitor with a capacitance rating of one Farad is capable of storing one coulomb of charge (6.25 x 10 ^ 18 electrons) at 1 volt. Although that many electrons seems like a lot, it can only power an average incandescent light bulb for about a minute.

The reason capacitors are used is often because of their quick discharge ability. A chemical reaction in a battery takes time, while the capacitor requires no chemical reaction to discharge electricity. This makes the capacitor a lot faster when it comes to discharging. That is why capacitors are used in cameras and lasers to create a bright flash, rather than batteries.

Capacitors are also used to make DC voltage constant. In power supplies, the voltage can vary. With a capacitor included, it makes up for a lack of voltage and absorbs the excessive voltage. This is necessary in sensitive electronic devices that require constant voltage supplies.

Capacitors are also used to block direct current. Since a capacitor connected in series with a power source is essentially a broken circuit, current cannot flow, once the capacitor is charged. However, alternating current can still flow when connected to a capacitor, since the voltage shifts and the capacitor charges and discharges. When capacitors are connected in parallel the total capacitance in the network is the sum of all the capacitance, Ct = C1+C2…+Cn. For example if C1 was 10uF and C2 is 47uF the total capacitance is 57uF.



When capacitors are connected in series the capacitance is given by 1/Ct = 1/C1+1/C2…+1/Cn.



Capacitors are usually connected in series to increase the total voltage that can be connected between them; this is common with Tesla Coil Circuits as finding a capacitor with the exact capacitance and voltage would be almost impossible to find.

Special care must be taken with high voltage capacitors, such as capacitors where mains voltages (110-120v and 220-240) or the capacitors used in microwaves and TV sets and they can store enough charge to kill. Capacitors can store a charge for years after the power supply has been disconnected and the terminals should be shorted to remove the charge, some high voltage capacitors have ‘bleed resistors’ in them to drain the charge when the power is disconnected.

The different types of capacitors are generally named by the dielectric used in them, and have different purposes.

Aluminium electrolytic capacitors consist of one plate that is a chemical electrolyte and a dielectric that is an oxide on one side of the other metal plate. Aluminium electrolytic capacitors store the most charge in the smallest space with respect to other types of capacitors due to the oxide dielectric's amazing properties as an insulator. There are two main types of capacitor structural designs that you will run into when working with electronics. The two types are radial and axial. The radial design has both leads coming out of the same side of the capacitor. The axial design has one lead coming out of the center of each side, creating an axis.