Alright, let's jump in here. This is Al from als electronic classroom. And right now we're going to talk about inductance and inductance reactance. In this in this course, just mentioned here, right there in duction. Dense is the ability of a conductor to produce induce voltage when current varies, and we'll see how that's done as we progress here. All right.

Now, some of some of these bullets may not make any sense, and maybe you don't know a lot about them, but that's what this course is about. So right now we're going to talk about induced voltage and how it's produced by alternating current. We're going to talk about self induced voltage. We're also going to discuss how l which is inductance opposes change in current. We're going to talk about transformers. And we're going to talk about troubles and coils and how to check for troubles in cold coils.

So let's start our journey in this course by going to the next slide. l here at Al's electronic classroom. All right now in this in this course here, we're going to talk about inductors. And actually inductors are actually coils. That's why I put a little parenthesis there, around coils. And let's look at here, okay, and at the bullet points here, okay.

Inductors are conductors wound around a core All right, and I'm showing you some right there in this in this photo. All right. And, for instance, right here, if you look at that inductor that's wound around what I some it's it's actually a doughnut form. Alright, and the, the wire or the conductors around a wound around this way. All right. Over here we have another coiler inductor.

And this is a form. That's actually some type of, Oh, it looks like a column of some sorts. And the cabling is wound around that way. These two here are variable inductors Okay, he has an adjustment here and this one has some type of screwdriver adjustment where you you will place your screwdriver in there and you can make an adjustment All right, ah there are different types of core materials, the three main ones are air and ferrite okay and when I change the adjustment on the coil, I can change the inductance or the value of the inductance in the coil and inductance or inductors are measured in Henry's. Alright, so, let me stop here and clear the slide off So we have some schematic symbols for an inductor and we show them right there. This is fixed with the arrow through it, it's variable.

Alright. And we got to fix But that also means it's an air core core just like this. Alright, even though we're winding that on some type of form, the form is non metal. So therefore it does not add to the inductive properties. That could be air that could be some type of plastic, rubber, glass wood. So if I take my coil on my on my wire that I want to create a coil with by wrapping it around some form.

If that form is non metal, again, glass, wood plastic, it's not going to add add anything to the inductance properties. The reason they do that is golf, that some type of solid form to hold the wire. I mean, that's it. All right. So over here we have an iron core. And that part of the schematic denotes iron core.

And right here we have a ferrite. Core core. ferrite is a different type of metal. And you'll notice that those two lines are dotted. All right. So this is an introduction to coils right on this slide, what they look like how they're made.

And the following slides will give us how to determine the properties again, inductors are measured in Henry's, and how do we determine the value of the inductance and those are rough? Those are the things we're going to talk about in the in the episode slides. All right in this slide here where we're looking at a well, it's a sine wave, but if you can see it's varying current. Alright, so it's not a voltage, but it's current. And it has the same characteristics as a sine wave, all right. So as this varying current flows through a conductor, all right, what happens is we set up a magnetic field.

All right, and this magnetic field will have lines of force that either go counterclockwise or clockwise. And you'll notice what we're trying to show here in this illustration is, this is my peak, positive peak amplitude. And this is my maximum negative peak amplitude. And you'll notice that as my current varies from zero to some peak level, what we're trying to show here to here is that my, my magnetic lines of force become greater. And as it decreases here, my magnetic lines of force decrease, and then we kind of repeat this over here, but you'll notice that my magnetic lines of force go clockwise, and then when I go through zero, and actually my current is is in reverse directions. Okay, reverses direction, my lines of force go clockwise, all right.

So what happens is is if and let me see Stop here. And let me clear the slide off. All right, so here's my, here's one conductor. And then here's another conductor. All right. All right.

And in this conductor, this is where I have my, my current source. All right? My I could be that sine wave. Okay? And what happens is, if you remember those lines of force that we saw in the previous slide, will since these conductors are very close, even though I'm showing here, let's say they're rough, they're point one millimeter. The distance between here that magnetic force We'll cut through this conductor here, we'll also induce a current flow which will induce a voltage.

The difference is or not the difference, but it'll be out of phase. So for instance, if current is flowing this way, and this conductor, when I induced current flow in this conductor here, my current flow will be in the opposite direction. You may heard here that calling mutual inductance All right, where if I have two conductors, in a close that are very close to each other, when I induce a varying current in one of them, it will induce current flow into that conductor that that's actually the action of a transformer which we'll talk about a few more slides. But that's it. point I'm trying to make here. All right, that if I have Let's stop here and go back again going back here, so if I have my varying magnetic field that is generated by this waveform here which is varying current in one conductor, I will induce a current in my second conductor, this would be my first second here, all right, that would be the current will be in the opposite direction.

So, if I'm here then this one will flow this way. So, looking at at at my bullet points here, one Henry is the amount of inductance that allows one volt to be induced when the current changes at the rate rate of one ampere per second. All right. So if you look at my formula here, we're looking for L, that would be the value of the coil, in Henry's. All right, where L is the voltage, and dI dt is the current change per second. All right, again, this is my varying current, it's a sine wave.

So how much does the current vary in one second? All right. So let's we've got some problems. And some more illustrations on the next slide where we do some problems. So let's stop here, clear this slide off and go to the next one. And look at those problems.

Alright, on this slide here, we're still talking about this formula, right? They're L equals e L over dI dt. So, again, dI dt is a change of current over a change of time. All right, so let's look at this example here. Current inductor changes from 12 to 16 amps in one second. What is the DI change between the change?

Okay, so it would be the difference between 16 amps and 12 amps. So the ampere would be we get a change of four amps per second. All right. Okay, so let's stop here and I'm going to do the second one. All right, this one here. Current in an inductor changes by 50 milliamp hours in two microseconds.

How much is dI dt? Well, we we basically Basically, we just divide 50 milliamp hours by two micro micro seconds and we get 25 times 10 to the third, I do the conversion, and so that change would be 25,000 amps per second. All right here, Ken. Now we get into a little bit of the meat here on this, on this equation here. Basically what what the first two did is they want they wanted to make sure that you understood dI dt I, which which we know is a change of current over a change of time. But let's let's look at this this other example here.

All right, how much is the inductance of a coil? that induces 40 volts when its current changes at the rate of four amps per second. And again, we have we use this section equation L equals L over dI dt, where L is 40 volts. And we have a change per second of four amps per second. We just do the math and we get 10 Henry's. Alright, so looking looking at this circuit here, all right, what will happen is if this is 40 volts and we get a change of four amps per second here, we'll get a voltage.

And if this is I'm sorry, if this is a, this has to be a 10. Henry choke for me to develop 40 volts on this coil and the coil and I mentioned it down here. l will be a back or a Conner volt voltage or counter EMF voltage. All right. What that means is is this is going positive, this will go positive All right. So, when I enter again from the previous slide, when I induce a voltage in a coil by varying current, that current will create a counter EMF depending upon the rate of current change and the value of the coil right just by what we say here all right.

So, if I transpose this this formula we get L equals L dI over d t Alright, so the voltage across the coil is the factor of L, which is the value of the coil in Henry's times a change of current, over a change of time, dI dt. All right. That's the point. Now this circuit here is just used to demonstrate that and I put it up there. Is this a real circuit? Ah, sort of, okay.

And that's all I'm going to say here, because I don't want to go off on a tangent. So I'm going to say, sort of, alright, you'll see as we build upon this, that that would be the primary of a transformer. And I'm going to leave it at that at that point now. All right, so let me just stop this clear the slide. I cleared the slide. So let's do this last one here.

How much is the inductance of a coil that induces 100 volts when it's current changes at the rate of 50 milliamp hours in two seconds. And again, you can do the math when all is said and done, it's zero dot zero for Henry's or 40 milli Henry's, okay? And if I move my decimal point, three places that way, we get Milly Henry's and I'm not going to again, I'm not going to spend a lot of time on how I do that I've done at the beginning. And there's a there's a course up on my website, how to do that where I go into much detail. So here it is 40 million Henry's. This is just the beginning.

All right, and so I'm going to clean this fly off and we're going to go on. And on the next slides, we're going to see what determines the value of the inductor in Henry's. Alright, on this slide, we're going to talk about L, which as you know, L is the value of the inductor or coil in parentheses. And that's measured in hen Henry's, as we said in the previous slide. So let's look at this formula. We have u r times n squared times a over L. And right here, this is a constant.

All right, but let's look at this right here. Okay, n equals the number of turns, that's the number of turns right here where we got n is 100. So that would be the number of turns. Okay. We put a bullet here where it says more area per return more h. So this is the answer. area of the coil right there all right, and the permeability you are is increased L is increased permeability is the property where if I have a metal core it will allow more lines of flux okay.

More magnetic a larger or more forceful magnetic field All right. So, air is one which this is here, but if I have metals and if you remember it on the previous slide we talked about iron and ferrite they have a larger permeability. So, if I have the same number of turns okay and one has an air core One has a metal core, the metal core is going to have a higher inductance. Alright, so let me stop here, clear off the slide, we're going to go over that formula a little bit. All right, if I look at the equation, the number of turns there is 100. So we square that we get 10 to the for the area is right here we go.

And my length of the coil is right here that's measured in meters. I just go through the math, again, I stated that this is a Constance. So when I do the math, this meter is 12.6 micro Henry's. Alright. So again, this, what determines the inductance the turns, number of turns off that the coil has, the length, the area and the chord type that Determine L. Alright, so we're going to talk about back voltage your back emf and up. EMF stands for electro motive force, it's the fancy word for voltage.

But we've got a sine wave here, right? And you know from from previous discussions, current flows in one direction from from here and then reverses direction from here. So, if I'm, if I look at my circuit here, and I've got an AC wave form, and where we're going from zero to some positive point, what happens is, current increases, all right, current increases. And you know from previous courses that I've given, we talked about electron flow. So from here to here, If this is negative, I have electron flow this way. All right?

So when it enters my passive component, because a coil is a passive component there is no it's not like an IC where I have an integrated circuit where I have a separate voltage source on there where I'm I'm kind of, I need a voltage source for that component to manipulate voltage or current or to do something. This is passive, it sits in the circuit. And it has a specific property by the external voltage that it's attached to it. So what happens is, we increase current, and we create what we call a back emf. All right, because in this portion if this is negative, that is plus on that side. All right, what, what is that voltage doing?

Well, it's opposing this basically what I have is two voltages, all right, with the same polarity, what do I have? I've got two voltages that are opposing itself if you remember from some of the earlier courses that I gave, if I go around a closed loop ohms law or purchase law, the sum of the voltage should be zero. So, if you look at this instant here, when current for slows this voltage this voltage here will equal this voltage there. So if this is 10 volts AC at the very instance, this will be 10 volts AC. So at that, at that Exact second instant. All right?

If I put a meter across here and measure that voltage, it's gonna measure my supply voltage, in this case 10 volts AC, we're going to have no or it's going to try to oppose current flow for an instant for a microsecond for a micro micro micro microsecond. All right, it's all right. And what happens? Okay, what happens? Well, if I look at my waveform, right, it's gonna go to some peak, but then what's going to happen? The voltage are the current is going to start decreasing if more Count starts decreasing, my back emf gets smaller, because my current flow through the inductor starts decreasing, and it goes to zero.

And then we start the whole thing over again. All right, we're now my polarities are reversed. And I go here. And what I'm saying is as current decreases, this point becomes less negative. That's what we mean by back emf. So for instance, alright, for a very, very short instant and I'm stressing that.

All right, okay, the back EMF equals the source voltage. All right, and it opposes current flow, but that only lasts again for a very, very short answer. And then as my back emf care starts to decrease, okay, my source voltage starts to supply current. That's what we mean by back emf. That's why when we have a transformer, and you'll see in the next slide, I don't shut out the winding, you'll see what I mean. All right, I'm gonna leave it there.

Let's go to the next slide. Okay, here's, here's my transformer. Here's the graphical or the schematic representation of a transformer right there. And, for now, we can have more than two windings. But for this discussion, we have two windings. They're labeled primary and secondary.

Alright, I put my voltage source usually on the primary even though I don't show it that would be my voltage source and that would be my sine wave generated by the voltage list. So what happens is if you remember we have inductance to pi FL. Okay, that equals X sub l. And that's one of the reasons why when we put a voltage source on the primary, it's it's an AC circuit. And if we keep this alternating voltage going it sets up two things, it sets up XML which we will talk about in the in the coming slides, which is the opposition to two AC current in an inductive circuit in a pure inductive circuit, all right, plus we have if you remember on the previous slide, we have a back emf so what we have a back emf F on my primary which prevents this voltage from actually overwhelming the watt winding and again, you know, creating a lot of heat and burning it up and so forth.

Even though a transformer does get hot, alright, because of this back emf and this inductive reactance was safe. Okay. Because of the magnetic coupling that we spoke about at the beginning, we have a magnetic force that's created in the center of the transformer. If you remember correctly, if we have one conductor, very close to the other conductor and I induce a current, what happens is because of the magnetic properties, or what they call the mutual inductance, it creates a voltage and a current flow in my adjacent winding in this case, we'll call that the secondary, all right. And the only deal is that the voltage that is that is that is created on the secondary winding of the transformer is 180 degrees out of phase with the voltage source, alright, which is no big deal, we can take care of that. So that's really not a problem.

We can take care of that. But just be aware that there is a phase reversal. All right. Now, let me Okay, let me stop here, clear the slide we're going to go on. Now over here. We have what we call a turns ratio, and it's an ns number of turns in the secondary over NP, which is the number of turns on the primary.

All right, this happened To be a one to one transformer, which means the number of currents in my primary equals the number of turns in my secondary. Alright? So what will happen is the voltage if it's a one to one transformer, the the value or a voltage that's created or applied to my primary winding equals the voltage, I'll get my secondary. So if this was like 100 volts AC, if it was a one to one transformer, I would get 100 volts AC out on my secondary. That's what it means. All right.

We've give you some examples here. If we got 500 turns in my secondary and 50 turns in my primary that would be what we even though I didn't put it on there. That's called a step up and it's 50 to one So now, if I had 100 volts in my primary, I would multiply that by 50. And we would get 50 times 100, which would be 5000 volts. So let me just do this. So right here, this would be 5000 volts, because I'm multiplying it by 50.

And if we have 100, let me let me stop here and clear the slide. So I gave you a little bit of a formula here, s over EP equals ns over NP. What that mean is, voltage in the secondary over voltage in the primary equals the number of turns in the secondary over the number of turns in the primary right there. That's what that means. All right. So what we can do here is we can I can cross multiply here, I want to know what the voltage is in my secondary and I can just cross multiply here, do my math.

And I get 720 volts AC. All right, I'm not going to go. And again, I'm not going to go step by step on some of these math problems, because I've done them at the beginning and there's a whole course up or it also you should, you should know how to do cross multiplication and solve for a variable. That's what we're doing here. So when all is said and done EFI have 100 turns here 600 returns there. I'm putting 120 volts AC here on my primary, what's my secondary voltage?

720 Volts AC and that's what that means. All right. All right, so what would what I'm saying here is we will continue our talks in Transformers when we discuss diode rectifiers and power supplies. And I'll talk about power in power out the efficiency of the transformer. Actually, I'm actually going to go through the steps with you guys on how to design a linear power supply. All right, so we're going to stop here and Transformers will pick that up.

I think it's in a module or two that I'm going to develop. Alright, it's gonna be called linear power supplies, diodes and linear power supplies. All right, and we'll pick that up there. All right, let's stop here and go to the next slide. All right, basically, on this slide here we have a coil, and it's a transformer but the only thing that could really go wrong with a coil is weak. It could Being open, or it can be a shot.

So if it's an open I put a meter across, they're gonna read infinite resistance. And we know that's not good either. I'm doing it on the primary, but I could have also done it on the secondary too. All right. The other thing is the coil could be shorted. So if I go and I read the continuity of the coil, and it looks a little low, what I may have to do is go to the manufacturer and get the spec, the manufacturer will give me the resistance readings.

Will give me the resistance readings of the coil. And then I can I can just measure it. All right, if it's if it's, you know, shot it's gonna show Something that's less than what they publish, you know. And if it's open, it's going to read infinity. So that's, that's, that's pretty much it with a coil. I mean, I can check it with an ohm meter again, and measure the resistance, it's going to be open, or it's going to be shotted.

And that's pretty much it. So with that said, we, we ended this section here. This was a long one. It's over 30 minutes, I should have stopped it around 15 to 20 and broken up but I didn't. So we'll go on. We've got a little bit more here to go.

So Well, we'll see you on the next section.