00:00:05
Hey, there, guys.
00:00:06
Paul here from TheEngineeringMindset.com.
00:00:08
In this video, we're going
to be looking at capacitors
00:00:10
to learn how they work, where we use them,
00:00:12
and why they are important.
00:00:14
Remember, electricity is
dangerous and can be fatal.
00:00:17
You should be qualified and competent
00:00:19
to carry out any electrical work.
00:00:21
Do not touch the terminals of a capacitor,
00:00:23
as it can cause an electric shock.
00:00:25
So, what is a capacitor?
00:00:27
A capacitor stores electric charge.
00:00:30
It's a little bit like a battery,
00:00:31
except it stores energy
in a different way.
00:00:34
It can't store as much
energy as a battery,
00:00:36
although it can charge and
release its energy much faster.
00:00:40
This is very useful, and that's
why you will find capacitors
00:00:43
used in almost every circuit board.
00:00:45
So, how does the capacitor work?
00:00:47
I want you to first think of a water pipe
00:00:49
with water flowing through it.
00:00:51
The water will continue to
flow until we shut the valve,
00:00:54
then no water can flow,
however, if after the valve,
00:00:58
we first let the water flow into a tank,
00:01:00
then the tank will store some of the water
00:01:02
but we will continue to get
water flowing out of the pipe.
00:01:05
Now when we close the valve,
00:01:07
water will stop pouring into the tank
00:01:09
but we still get the steady supply
00:01:10
of water out until the tank empties.
00:01:13
Once the tank is filled again,
00:01:14
we can open and close the
valve as many times as we like.
00:01:18
As long as we do not
completely empty the tank,
00:01:20
we will get an uninterrupted
supply of water out
00:01:22
of the end of the pipe.
00:01:24
So, we can use a water tank to store water
00:01:26
and smooth out
interruptions to the supply.
00:01:29
In electrical circuits, the
capacitor acts as the water tank
00:01:32
and stores energy.
00:01:34
It can release this to
smooth out interruptions
00:01:36
to the supply.
00:01:37
If we turned a simple
circuit on and off very fast
00:01:40
without a capacitor, then
the light will flash,
00:01:43
but if we connect a
capacitor into the circuit,
00:01:46
then the light will remain
on during the interruptions,
00:01:48
at least for a short duration,
00:01:50
because the capacitor is now discharging
00:01:52
and powering the circuit.
00:01:54
Inside a basic capacitor,
00:01:56
we have two conductive metal plates,
00:01:58
which are typically made
from aluminium or aluminum,
00:02:01
and these will be separated
00:02:02
by a dielectric insulating
materials such as ceramic.
00:02:05
Dielectric means the
material will polarize
00:02:07
when in contact with an electric field,
00:02:09
and we'll see what that means shortly.
00:02:11
One side of the capacitor is connected
00:02:13
to the positive side of the circuit,
00:02:15
and the other side is
connected to the negative.
00:02:18
On the side of the capacitor,
00:02:19
you will see a stripe and a symbol.
00:02:21
This will indicate which
side is the negative.
00:02:24
If we were to connect a
capacitor to a battery,
00:02:26
the voltage will push the electrons
00:02:28
from the negative terminal
over to the capacitor.
00:02:31
The electrons will build up
on one plate of the capacitor,
00:02:34
while the other plate, in
turn, releases some electrons.
00:02:38
The electrons can't pass
through the capacitor
00:02:40
because of the insulating material.
00:02:42
Eventually, the capacitor is
the same voltage as the battery
00:02:45
and no more electrons will flow.
00:02:47
There is now a buildup
of electrons on one side.
00:02:50
This means we have stored energy
00:02:52
and we can release this when needed.
00:02:54
Because there are more
electrons on one side compared
00:02:56
to the other, and electrons
are negatively charged,
00:02:59
this means we have one
side which is negative
00:03:01
and one side which is positive,
00:03:03
so there is a difference in potential,
00:03:05
or a voltage difference, between the two,
00:03:07
and we can measure this with a multimeter.
00:03:10
Voltage is like pressure.
00:03:11
When we measure pressure,
we're measuring the difference
00:03:14
or potential difference
between two points.
00:03:17
If you imagine a pressurized water pipe,
00:03:19
we can see the pressure
using a pressure gauge.
00:03:22
The pressure gauge is comparing
two different points, also:
00:03:25
the pressure inside the pipe compared
00:03:27
to the atmospheric
pressure outside the pipe.
00:03:30
When the tank is empty,
the gauge reads zero
00:03:32
because the pressure inside
the tank is now equal
00:03:35
to the pressure outside the tank,
00:03:37
so the gauge has nothing
to compare against;
00:03:39
both are the same pressure.
00:03:41
The same with voltage, we're
comparing the difference
00:03:44
between two points.
00:03:46
If we measure across a 1.5 volt battery,
00:03:49
then we read a difference of
1.5 volts between each end,
00:03:53
but if we measure the same
end, then we read zero
00:03:56
because there's no difference
and it's going to be the same.
00:03:59
Coming back to the
capacitor, we measure across
00:04:01
and read a voltage
difference between the two
00:04:03
because of the buildup of electrons.
00:04:05
We still get this reading
00:04:07
even when we disconnect the battery.
00:04:09
If you remember, with magnets,
00:04:11
opposites attract and
pull towards each other.
00:04:13
The same occurs with the build-up
00:04:15
of negatively charged electrons.
00:04:17
They are attracted to the
positively charged particles
00:04:20
of their atoms on the opposite plate.
00:04:22
They can never reach each other
00:04:24
because of the insulating material.
00:04:26
This pull between the two
sides is an electric field,
00:04:29
which holds electrons in place
until another path is made.
00:04:33
If we then place a small
lamp into the circuit,
00:04:35
a path now exists for
the electrons to flow
00:04:37
and reach the opposite side.
00:04:39
So, the electrons will flow
through the lamp, powering it,
00:04:42
and the electrons will
reach the other side
00:04:44
of the capacitor.
00:04:45
This will only last a
short duration, though,
00:04:47
until the buildup of electrons
equalizes on each side.
00:04:51
Then the voltage is zero.
00:04:52
So, there is no pushing force
and no electrons will flow.
00:04:55
Once we connect the battery again,
00:04:57
the capacitor will begin to charge.
00:04:59
This allows us to
interrupt the power supply
00:05:01
and the capacitor that will provide power
00:05:03
during these interruptions.
00:05:05
So, where do we use capacitors?
00:05:07
They look a little bit different
but they're easy to spot.
00:05:10
In circuit boards, they tend
to look something like this,
00:05:13
and we see them represented
in engineering drawings
00:05:16
with symbols like these.
00:05:17
We can also get larger capacitors,
00:05:19
which are used, for example,
on induction motors,
00:05:21
ceiling fans, and air conditioning units.
00:05:24
We can get even larger ones,
00:05:25
which are used to
correct poor power factor
00:05:27
in large buildings.
00:05:28
On the side of the capacitor,
we will find two values.
00:05:31
These are the capacitance and the voltage.
00:05:34
We measure capacitance of
the capacitor in the unit
00:05:37
of Farads, which we show with a capital F,
00:05:39
although we will usually measure
a capacitor in microfarads.
00:05:43
With microfarads, we just
have a symbol before this,
00:05:45
which looks something like
a letter U with a tail.
00:05:48
The other value is our voltage,
00:05:49
which we measure in
volts, with a capital V.
00:05:52
On the capacitor, the voltage
value is the maximum voltage
00:05:55
which the capacitor can handle.
00:05:57
We've covered voltage in
detail in a separate video.
00:05:59
Do check that out, link's down below.
00:06:02
As I said, the capacitor is rated
00:06:03
to handle a certain voltage.
00:06:05
If we were to exceed this, then
the capacitor will explode.
00:06:09
Let's have a look at that in slow motion.
00:06:13
Eh, pretty cool.
00:06:15
So, why do we use capacitors?
00:06:17
One of the most common
applications of capacitors
00:06:19
in large buildings is for
power factor correction.
00:06:23
When too many inductive loads
are placed into a circuit,
00:06:26
the current and the voltage
waveforms will fall out of sync
00:06:29
with each other and the current
will lag behind the voltage.
00:06:32
We then use capacitor
banks to counteract this
00:06:35
and bring the two back into alignment.
00:06:37
We've covered power factor
before in great detail.
00:06:39
Do check that out, link's down below.
00:06:41
Another very common application
is to smooth out peaks
00:06:44
when converting AC to DC power.
00:06:47
When we use a full bridge rectifier,
00:06:49
the AC sine wave is flipped
00:06:51
to make the negative cycle
flow in a positive direction.
00:06:55
This will trick the circuit into thinking
00:06:56
it's getting direct current,
but one of the problems
00:06:59
with this method is the
gaps in between the peaks.
00:07:03
But as we saw earlier,
we can use a capacitor
00:07:05
to release energy into the circuit
00:07:07
during these interruptions,
00:07:08
and that will smooth the power supply out
00:07:10
to look more like a DC supply.
00:07:13
We can measure the capacitance
00:07:14
and the stored voltage using a multimeter.
00:07:17
Not all multimeters have
the capacitance function,
00:07:20
but I'll leave a link down below
00:07:21
for the model which I personally use.
00:07:24
You should be very
careful with capacitors.
00:07:26
As we now know, they store energy
00:07:27
and can hold high voltage
values for a long time,
00:07:30
even when disconnected from a circuit.
00:07:33
To check the voltage, we switch
to DC voltage on our meter,
00:07:36
and then we connect the red wire
00:07:37
to the positive side of the capacitor
00:07:39
and the black wire to the negative side.
00:07:42
If we get a reading of
several volts or more,
00:07:43
then we should discharge that
00:07:45
by safely connecting the
terminals to a resistor
00:07:48
and continue to read the voltage.
00:07:50
We want to make sure
that it's reduced down
00:07:52
into the millivolts
range before handling it,
00:07:54
or else we might get a shock.
00:07:56
To measure the capacitance,
we simply switch the meter
00:07:59
to the capacitor function.
00:08:01
We connect the red wire
to the positive side
00:08:02
and the black wire to the negative side.
00:08:05
After a short delay, the
meter will give us a reading.
00:08:07
We will probably get a reading
close to the stated value
00:08:09
but not exact.
00:08:11
For example, this one is
rated at 1,000 microfarads,
00:08:14
but when we read it, we get
a measurement of around 946.
00:08:18
This one is rated at 33 microfarads,
00:08:20
but we measure it, we get around 36.
00:08:23
Okay, guys, that's it for this video,
00:08:25
but to continue your learning,
00:08:26
then check out one of
the videos on-screen now
00:08:28
and I'll catch you there
for the next lesson.
00:08:30
Don't forget to follow us on
Facebook, Twitter, Instagram,
00:08:33
and of course, TheEngineeringMindset.com.
