Hey, there, guys. Paul here from TheEngineeringMindset.com. In this video, we're going
to be looking at capacitors to learn 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. So, 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. So, how does the capacitor work? 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 up
on one plate of the capacitor, while the other plate, in
turn, releases some electrons. The electrons can't pass
through the capacitor because of the insulating material. Eventually, the capacitor is
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 of
1.5 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 electrons
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. So, 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. Let's have a look at that in slow motion. Eh, pretty cool. So, 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
waveforms 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, but I'll leave a link down below for the model which I personally use. 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 video, but to continue your learning, then check out one of
the videos on-screen now and I'll catch you there
for the next lesson. Don't forget to follow us on
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