What are Capacitors?
A capacitor is an electrical component that stores energy in the form of electrical charge like an electric battery [2][3]. The difference between a capacitor and a battery is that a capacitor cannot produce new electrons while a battery can [3]. All capacitors contain at least two metal plates called electrical conductors. In between these plates, there is an insulator known as a dielectric [1][2]. Capacitors are commonly known as caps [2] and were formerly referred to as condensers [1].
A capacitor's ability to store charge is known as its capacitance [4] and it is measured in Farads [2][3]. One Farad holds a lot of electrical charge, so capacitors tend to have capacitance values that are measured in quantities as small as Picofarads and Microfarads [2][4]. The amount of charge stored by a capacitor can be calculated according to the equation Q = CV, where Q is the total charge, C is the capacitor's capacitance, and V is the voltage being applied to the capacitor [2].
Materials and Types
The dielectric of a capacitor can be made from various different materials including [5][6][7]:
- Aluminum
- Ceramic
- Glass
- Niobium oxide
- Paper
- Plastic
- Silver mica
- Tantalum
Capacitors can be broken down into two categories: fixed and variable. Fixed capacitors have unchangeable capacitance values, while variable capacitors have capacitance values that can be changed. Capacitors can be further classified by the material that makes up their dielectric [6].
Fixed Capacitors
Lifetime Expectancy
The end of a capacitor's life is usually defined as the point when the characteristics of the capacitor (ex. capacitance) change by a specific percentage [18]. A general rule of thumb is that the lifetime of a capacitor doubles for every 10°C decrease in temperature [19][20][21].
The shelf life of a capacitor is heavily determined by the conditions in which it is stored. Environmental factors such as humidity, temperature, and atmospheric pressure can greatly affect the shelf life of a capacitor. If capacitors are stored in harsh conditions, they will degrade much faster. Thus, it is important to follow storage instructions specified by the manufacturer of the capacitor. In addition, make sure to check the receipt time before using a capacitor. It is not advisable to use capacitors that have been in the store for a long time [20].
For aluminum electrolytic capacitors, make sure they are not exposed to moisture, UV rays, ozone, oil, and radiations while they are stored. They should be stored at around room temperature. If stored properly, modern day aluminum electrolytic capacitors have a shelf life of around 2 years [20].
The lifespan of an electrolytic capacitor can span anywhere from 1000 hours to 10000 hours or more [19]. Aluminum electrolytic capacitors have a rated lifespan, but this lifespan is typically on the lower end because it is calculated for cases of high stress. If the capacitor will be used in a lower stress environment, its lifespan can be de-rated. By taking into account the effect of certain stresses on the capacitor (heat, current, and voltage), the actual lifespan of an aluminum electrolytic capacitor can be much longer than its rated lifespan [18].
Tantalum capacitors are more stable than aluminum electrolytic capacitors and their capacitance value does not decrease with time, so they tend to have a longer shelf life. However, they should still be stored at low temperatures [20].
The shelf life of ceramic capacitors depends a great amount on how they are packaged and stored. They don't deteriorate much when stored for short periods of time but they can degrade a lot when stored for a long time, especially if they are stored in open air or are exposed to chlorine gas or sulfur dioxide [20].
A calculator that gives a rough estimate of the lifespan of a capacitor's lifespan can be found at illinoiscapacitor.com [21].
Safety Considerations
Capacitors can build up and hold dangerous charge for some time even when de-energized (power is turned off). They can discharge current which may result in electric shock if one comes into physical contact with the power supply. As a result, capacitors should be discharged before working with them. This can be done using bleeder resistors, which are permanently connected resistors that force capacitor discharge if the equipment is powered off [22][23]. The safety discharge of a capacitor can be calculated, with the website DigiKey having an online calculator [24].
Applications
Contributors:
User | Last Update |
---|---|
Mayurakhi Khan | 1075 days ago |
Former user (Deleted) | |
Former user (Deleted) | |
Former user (Deleted) |
Faculty Advisors: Allyson Giannikouris, Michael Lenover, Kim Pope, John Thistle