Capacitor basic: How it works & its working principle

  Hey guys Knowledge Amplifier here from lazyengineer123.blogspot.com . 

In this Article, we're going to be looking at capacitors to learn 

• What is a capacitor ?
• How they work ?
• Where we use them ?
• and Why they are important ?

(Remember, electricity is dangerous and can be fatal. You should be qualified and competent to carry out any electrical work. Do not touch the terminals of a capacitor, as it can cause an electric shock.)

What is a capacitor?

     A capacitor stores electric charge. It's a little bit like a battery, except it stores energy in a different way. It can't store as much energy as a battery, although it can charge and release its energy much faster. This is very useful, and that's why you will find capacitors used in almost every circuit board.

A capacitor is a device that is used to store charges in an electrical circuit.

How does the capacitor work? 

    A capacitor works on the principle that the capacitance of a conductor increases appreciably when an earthed conductor is brought near it. Hence, a capacitor has two plates separated by a distance having equal and opposite charges.

I want you to first think of a water pipe with water flowing through it. The water will continue to flow until we shut the valve, then no water can flow, however, if after the valve, we first let the water flow into a tank, then the tank will store some of the water but we will continue to get water flowing out of the pipe. Now when we close the valve, water will stop pouring into the tank but we still get the steady supply of water out until the tank empties. Once the tank is filled again, we can open and close the valve as many times as we like. As long as we do not completely empty the tank, we will get an uninterrupted supply of water out of the end of the pipe. So, we can use a water tank to store water and smooth out interruptions to the supply. 

In electrical circuits, the capacitor acts as the water tank and stores energy. It can release this to smooth out interruptions to the supply. If we turned a simple circuit on and off very fast without a capacitor, then the light will flash, but if we connect a capacitor into the circuit, then the light will remain on during the interruptions, at least for a short duration, because the capacitor is now discharging and powering the circuit. 

    Inside a basic capacitor, we have two conductive metal plates, which are typically made from aluminium or aluminum, and these will be separated by a dielectric insulating materials such as ceramic. 

    Dielectric means the material will polarize when in contact with an electric field, and we'll see what that means shortly. One side of the capacitor is connected to the positive side of the circuit, and the other side is connected to the negative. On the side of the capacitor, you will see a stripe and a symbol. This will indicate which side is the negative. 

    If we were to connect a capacitor to a battery, the voltage will push the electrons from the negative terminal over to the capacitor. The electrons will build upon one plate of the capacitor, while the other plate, in turn, releases some electrons. The electrons can't passthrough the capacitor because of the insulating material. Eventually, the capacitor is of the same voltage as the battery and no more electrons will flow. There is now a buildup of electrons on one side. This means we have stored energy and we can release this when needed. 

Because there are more electrons on one side compared to the other, and electrons are negatively charged, this means we have one side which is negative and one side which is positive, so there is a difference in potential, or a voltage difference, between the two, and we can measure this with a multimeter. 

Voltage is like pressure. When we measure pressure, we're measuring the difference or potential difference between two points. If you imagine a pressurized water pipe, we can see the pressure using a pressure gauge. The pressure gauge is comparing two different points, also: the pressure inside the pipe compared to the atmospheric pressure outside the pipe. When the tank is empty, the gauge reads zero because the pressure inside the tank is now equal to the pressure outside the tank, so the gauge has nothing to compare against; both are the same pressure. 

The same with voltage, we're comparing the difference between two points. If we measure across a 1.5 volt battery, then we read a difference of1.5 volts between each end, but if we measure the same end, then we read zero because there's no difference and it's going to be the same. 

Coming back to the capacitor, we measure across and read a voltage difference between the two because of the buildup of electrons. We still get this reading even when we disconnect the battery. If you remember, with magnets, opposites attract and pull towards each other. The same occurs with the build-up of negatively charged electrons. They are attracted to the positively charged particles of their atoms on the opposite plate. They can never reach each other because of the insulating material. This pull between the two sides is an electric field, which holds electrons in place until another path is made. If we then place a small lamp into the circuit, a path now exists for the electrons to flow and reach the opposite side. So, the electrons will flow through the lamp, powering it, and the electrons will reach the other side of the capacitor. This will only last a short duration, though, until the buildup of electron equalizes on each side. Then the voltage is zero. So, there is no pushing force and no electrons will flow. Once we connect the battery again, the capacitor will begin to charge. This allows us to interrupt the power supply and the capacitor that will provide power during these interruptions. 

Where do we use capacitors? 

They look a little bit different but they're easy to spot. In circuit boards, they tend to look something like this, and we see them represented in engineering drawings with symbols like these. We can also get larger capacitors, which are used, for example, on induction motors, ceiling fans, and air conditioning units. We can get even larger ones, which are used to correct poor power factor in large buildings. On the side of the capacitor, we will find two values. These are the capacitance and the voltage. We measure capacitance of the capacitor in the unit of Farads, which we show with a capital F, although we will usually measure a capacitor in microfarads. With microfarads, we just have a symbol before this, which looks something like a letter U with a tail. The other value is our voltage, which we measure in volts, with a capital V. On the capacitor, the voltage value is the maximum voltage which the capacitor can handle. We've covered voltage in detail in a separate video. Do check that out, link's down below. As I said, the capacitor is rated to handle a certain voltage. If we were to exceed this, then the capacitor will explode.

Why do we use capacitors? 

    One of the most common applications of capacitors in large buildings is for power factor correction. When too many inductive loads are placed into a circuit, the current and the voltage wave forms will fall out of sync with each other and the current will lag behind the voltage. We then use capacitor banks to counteract this and bring the two back into alignment. We've covered power factor before in great detail. Do check that out, link's down below. Another very common application is to smooth out peaks when converting AC to DC power. When we use a full bridge rectifier, the AC sine wave is flipped to make the negative cycle flow in a positive direction. This will trick the circuit into thinking it's getting direct current, but one of the problems with this method is the gaps in between the peaks. But as we saw earlier, we can use a capacitor to release energy into the circuit during these interruptions, and that will smooth the power supply out to look more like a DC supply. We can measure the capacitance and the stored voltage using a multimeter. Not all multimeters have the capacitance function. 

    You should be very careful with capacitors. As we now know, they store energy and can hold high voltage values for a long time, even when disconnected from a circuit. To check the voltage, we switch to DC voltage on our meter, and then we connect the red wire to the positive side of the capacitor and the black wire to the negative side. If we get a reading of several volts or more, then we should discharge that by safely connecting the terminals to a resistor and continue to read the voltage. We want to make sure that it's reduced down into the millivolts range before handling it, or else we might get a shock. To measure the capacitance, we simply switch the meter to the capacitor function. We connect the red wire to the positive side and the black wire to the negative side. After a short delay, the meter will give us a reading. We will probably get a reading close to the stated value but not exact. For example, this one is rated at 1,000 microfarads, but when we read it, we get a measurement of around 946. This one is rated at 33 microfarads, but we measure it, we get around 36. Okay, guys, that's it for this Article, but to continue your learning, then check out one of the Articles on-screen now and I'll catch you  here for the next lesson. Don't forget to follow us