The idea of a Capacitor and what it does, although intimidating to comprehend, isn’t at all that far-fetched. A capacitor is used to temporarily store an electrical charge and inevitably release that built up charge, quite rapidly (often within seconds or less). Why is this beneficial you may ask? Capacitors are an essential part to the operation of the electrical devices and machines which we rely on. Whether it be Dr. Emmett “Doc” Brown’s fictional DeLorean flux-capacitor or even a storm cloud above our very own heads, chances are it is quite possible that you’ve seen the concept of a capacitor in one form or another.
Types of capacitors. Image courtesy of Eric Schrader.
What is capacitance?
The amount of electrical energy a capacitor can hold is referred to as capacitance. Think of capacitance as a box: the bigger the box, the more it can store; the bigger the capacitance, the more electrical charge it can store. Capacitance is measured in units of farads, named after the English electrical pioneer, Michael Faraday (1791-1867). Considering one farad is a huge amount of capacitance, most capacitors we see on a daily basis are just fractions of a farad—typically microfarads (uF or a millionth of a farad). In some instances capacitance can be measured in smaller amounts with nanofarads (nF or a thousand-millionths of a farad) or even picofarads (pF or a millionth millionths of a farad).
How do capacitors work?
Capacitors come in a variety of shapes and sizes but they usually contain the same basic components which include two electrical conductors, (referred to as plates) separated by a non-conducting insulator (referred to as a dielectric). These two plates inside the capacitor are wired to two electrical connections, called terminals, (the two or three connections that wire to an electrical circuit). When the capacitor is properly connected and the power is turned on, an electric charge gradually builds on the plates; this is referred to as charging. As voltage is applied it is unable to penetrate the insulator resulting in new electrons gathering on one plate creating a positive charge while the other plate repels electrons creating a negative charge. In turn, this dielectric in the middle of the two charged plates stores energy. When the power is disconnected, the capacitor still holds a charge but over time the charge slowly leaks away; this is referred to as discharging.
A great way to describe how a capacitor works is the clouds drifting through the sky. Inside these clouds are small ice particles which rub against the air and gain static electrical charges, (similar to rubbing a cloth on a PVC pipe). The top of the cloud becomes positively charged when smaller ice particles swirl upwards and the bottom of the cloud becomes negatively charged when heavier ice particles gather lower down. As the cloud moves, the electrical charge within it also affects the ground below. The bottom of the cloud pushes negative charge downwards ultimately creating a positive charge on the ground. In a sense, the atmosphere from the bottom of the cloud to the ground becomes an insulator (dielectric). As giant electrical charges build inside the cloud, air is transformed from an insulator into a conductor as the voltage reaches a peak. Thus a giant spark or, “bolt of lightning” is shot out and if we’re lucky, strikes the Courthouse Clock Tower sending our timeless beloved fictional character, Marty McFly back smoothly through the space-time continuum to October 1985.
Why are capacitors important?
When most devices are initially started, they have some sort of inrush current and those electronic devices use capacitors to regulate the voltage and current. A capacitor in essence is a, “background superhero” which assists in the operation of sign ballast lighting, HID lighting, air conditioners, digital cameras, televisions, radios, and a surprisingly endless list. In HID lighting a lower light output, lower power factor, and overall reduced efficiency can be the result of a failed capacitor. There are a few factors to consider on why capacitors fail including shorts, mounting location, and environmental conditions. Shorts usually occur due to deterioration of the dielectric which is the aging process of time, temperature, or sustained damage from excess amounts of power. The “open” condition is the result of separation of proper connection to the terminals of the capacitor. By mounting the capacitor in a high vibration environment, there is a risk of malfunction in end termination resistance and heating, which could result in eventual failure. Environmental conditions must be taken into consideration in the life of the capacitor. Altitude may also play a key role while internal stresses due to pressure changes or even the dissipation of heat transfer at lead terminations can cause failure.
How do capacitors fail?
Exploded capacitor. Image courtesy of tml.
Capacitors can also, “partially fail” meaning it will not run at its full potential, which usually results in a lowering capacitance rating (unable to hold as much charge). This directly affects the performance of say for example, a HID lighting application. If a HID lamp does not seem to be producing its maximum brightness, evidence could suggest a partially failed capacitor may be at fault. In some instances a failing capacitor on an air-conditioning system could be more detrimental. A weakened capacitor connected to a compressor will lead to the unit struggling or, “hard starting” to turn the power on and off causing massive amounts of strain on the compressor. It is highly recommend regular maintenance is performed on the components that regulate the current and voltage on your electrical devices so that they perform at optimal levels.
Whether it is a lighting application or the successful operation of common household objects our, “background superheroes” take no breaks. Feel free to leave any questions, comments, suggestions, or puny jokes that you may have in the comment area below. For more information or innovative ideas on lighting, check back on our blog or our, Facebook, Twitter, Google Plus, LinkedIn, or Pinterest! As always, our staff at 1000Bulbs.com is up for the challenge of answering your everyday lighting questions.