Capacitor types & dielectrics

Although all capacitors work in essentially the same way, key differences in the construction of different capacitor types makes an enormous difference in their properties.
The main element of the capacitor that gives rise to the different properties of the different types of capacitor is the dielectric - the material between the two plates. Its dielectric constant will alter the level of capacitance that can be achieved within a certain volume.
Some types of capacitor may be polarised, i.e. they only tolerate voltages across them in one direction. Other capacitor types are non-polarised and can have voltages of either polarity across them.
Typically the different types of capacitor are named after the type of dielectric they contain. This gives a good indication of the general properties they will exhibit and for what circuit functions they can be used.

 Overview of different capacitor types
There are many different types of capacitor that can be used - most of the major types are outlined below:

• Ceramic capacitor:   The ceramic capacitor is a type of capacitor that is used in many applications from audio to RF. Values range from a few picofarads to around 0.1 microfarads. Ceramic capacitor types are by far the most commonly used type of capacitor being cheap and reliable and their loss factor is particularly low although this is dependent on the exact dielectric in use. In view of their constructional properties, these capacitors are widely used both in leaded and surface mount formats
• Electrolytic capacitor:   Electrolytic capacitors are a type of capacitor that is polarised. They are able to offer high capacitance values - typically above 1μF, and are most widely used for low frequency applications - power supplies, decoupling and audio coupling applications as they have a frequency limit if around 100 kHz.
• Tantalum capacitor:   Like electrolytic capacitors, tantalum capacitors are also polarised and offer a very high capacitance level for their volume. However this type of capacitor is very intolerant of being reverse biased, often exploding when placed under stress. This type of capacitor must also not be subject to high ripple currents or voltages above their working voltage. They are available in both leaded and surface mount formats. 
• Silver Mica Capacitor:   Silver mica capacitors are not as widely used these days, but they still offer very high levels of stability, low loss and accuracy where space is not an issue. They are primarily used for RF applications and and they are limited to maximum values of 1000 pF or so. 
• Polystyrene Film Capacitor:   Polystyrene capacitors are a relatively cheap form of capacitor but offer a close tolerance capacitor where needed. They are tubular in shape resulting from the fact that the plate / dielectric sandwich is rolled together, but this adds inductance limiting their frequency response to a few hundred kHz. They are generally only available as leaded electronics components.
• Polyester Film Capacitor:   Polyester film capacitors are used where cost is a consideration as they do not offer a high tolerance. Many polyester film capacitors have a tolerance of 5% or 10%, which is adequate for many applications. They are generally only available as leaded electronics components
• Metallised Polyester Film Capacitor:   This type of capacitor is a essentially a form of polyester film capacitor where the polyester films themselves are metallised. The advantage of using this process is that because their electrodes are thin, the overall capacitor can be contained within a relatively small package. The metallised polyester film capacitors are generally only available as leaded electronics components.
• Polycarbonate capacitor:   The polycarbonate capacitors has been used in applications where reliability and performance are critical. The polycarbonate film is very stable and enables high tolerance capacitors to be made which will hold their capacitance value over time. In addition they have a low dissipation factor, and they remain stable over a wide temperature range, many being specified from -55°C to +125°C. However the manufacture of polycarbonate dielectric has ceased and their production is now very limited. 
• Polypropylene Capacitor:   The polypropylene capacitor is sometimes used when a higher tolerance type of capacitor is necessary than polyester capacitors offer. As the name implies, this capacitor uses a polypropylene film for the dielectric. One of the advantages of the capacitor is that there is very little change of capacitance with time and voltage applied. This type of capacitor is also used for low frequencies, with 100 kHz or so being the upper limit. They are generally only available as leaded electronics components.
• Glass capacitors:   As the name implies, this capacitor type uses glass as the dielectric. Although expensive, these capacitors offer very high levels or performance in terms of extremely low loss, high RF current capability, no piezo-electric noise and other features making them ideal for many performance RF applications.

How To Test a Capacitor

 

In this article, we will go over different tests that we can use to tell whether a capacitor is good or not, all by utilizing the functions of a digital multimeter.

There are many checks we can do to see if a capacitor is functioning the way it should. We will use and exploit the characteristics and behaviors that a capacitor should show if it is good and, in thus doing so, determine whether its is good or defective.

So let's start:

Test a Capacitor with an Ohmmeter of a Multimeter

A very good test you can do is to check a capacitor with your multimeter set on the ohmmeter setting.

By taking the capacitor's resistance, we can determine whether the capacitor is good or bad.

To do this test, We take the ohmmeter and place the probes across the leads of the capacitor. The orientation doesn't matter, because resistance isn't polarized.

 o do this test, We take the ohmmeter and place the probes across the leads of the capacitor. The orientation doesn't matter, because resistance isn't polarized.

If we read a very low resistance (near 0Ω) across the capacitor, we know the capacitor is defective. It is reading as if there is a short across it.

If we read a very high resistance across the capacitor (several MΩ), this is a sign that the capacitor likely is defective as well. It is reading as if there is an open across the capacitor.

A normal capacitor would have a resistance reading up somewhere in between these 2 extremes, say, anywhere in the tens of thousands or hundreds of thousand of ohms. But not 0Ω or several MΩ.

This is a simple but effective method for finding out if a capacitor is defective or not.

Test a Capacitor with a Multimeter in the Capacitance Setting

Another check you can do is check the capacitance of the capacitor with a multimeter, if you have a capacitance meter on your multimeter. All you have to do is read the capacitance that is on the exterior of the capacitor and take the multimeter probes and place them on the leads of the capacitor. Polarity doesn't matter.

This is the same as the how the setup is for the first illustration, only now the multimeter is set to the capacitance setting.

You should read a value near the capacitance rating of the capacitor. Due to tolerance and the fact that (specifically, electrolytic capacitors) may dry up, you may read a little less in value than the capacitance of the rating. This is fine. If it is a little lower, it is still a good capacitor. However, if you read a significantly lower capacitance or none at all, this is a sure sign that the capacitor is defective and needs to be replaced.

Checking the capacitance of a capacitor is a great test for determining whether a capacitor is good or not.

Test a Capacitor with a Voltmeter

Another test you can do to check if a capacitor is good or not is a voltage test.

Afterall, capacitors are storage devices. They store a potential difference of charges across their plate, which are voltages. The anode has a positive voltage and the cathode has a negative voltage.

A test that you can do is to see if a capacitor is working as normal is to charge it up with a voltage and then read the voltage across the terminals. If it reads the voltage that you charged it to, then the capacitor is doing its job and can retain voltage across its terminals. If it is not charging up and reading voltage, this is a sign the capacitor is defective.

To charge the capacitor with voltage, apply DC voltage to the capacitor leads. Now polarity is very important for polarized capacitors (electrolytic capacitors). If you are dealing with a polarized capacitor, then you must observe polarity and the correct lead assignments. Positive voltage goes to the anode (the longer lead) of the capacitor and negative or ground goes to the cathode (the shorter lead) of the capacitor. Apply a voltage which is less than the voltage rating of the capacitor for a few seconds. For example, feed a 25V capacitor 9 volts and let the 9 volts charge it up for a few seconds. As long as you're not using a huge, huge capacitor, then it will charge in a very short period of time, just a few seconds. After the charge is finished, disconnect the capacitor from the voltage source and read its voltage with the multimeter. The voltage at first should read near the 9 volts (or whatever voltage) you fed it. Note that the voltage will discharge rapidly and head down to 0V because the capacitor is discharging its voltage through the multimeter. However, you should read the charged voltage value at first before it rapidly declines. This is the behavior of a healthy and a good capacitor. If it will not retain voltage, it is defective and should be replaced. 

So there you have it, 4 strong tests that you can do (all or either/or) to test whether a capacitor is good or not.

A capacitor is composed of two conductors separated by an insulating material called a DIELECTRIC. The dielectric can be paper, plastic film, ceramic, air or a vacuum. The plates can be aluminium discs, aluminium foil or a thin film of metal applied to opposite sides of a solid dielectric. The CONDUCTOR - DIELECTRIC - CONDUCTOR sandwich can be rolled into a cylinder or left flat.

 In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy.

  HOW A CAPACITOR WORKS

When the circuit is switched on, the LED emits light and the capacitor charges up. When the switch is turned off the LED stills emits a light for a few seconds because the electricity stored in the capacitor is slowly discharged. When it has fully discharged it's electricity the LED no longer emits light. If a resistor is introduced to the circuit the capacitor charges up more slowly but also discharges more slowly. What will happen to the light ?

 

 Ceramic Capacitor

-is a fixed value capacitor in which ceramic material acts as the dielectric.

Electrolytic capacitor is a type of capacitor that uses an electrolyte to achieve a larger capacitance than other capacitor types.

 Epoxy Capacitor

                                               Typically the coupling capacitors are connected at the line terminal of motors and generators and in switch gear.

Capacitors are components that are used to store an electrical charge and are used in timer circuits. A capacitor may be used with a resistor to produce a timer. Sometimes capacitors are used to smooth a current in a circuit as they can prevent false triggering of other components such as relays. When power is supplied to a circuit that includes a capacitor - the capacitor charges up. When power is turned off the capacitor discharges its electrical charge slowly.


TYPES OF CAPACITORS






There are many different types of capacitors and they each vary in their characteristics and each have their own advantages and disadvantages.