How Transformers Work

How Transformers Work



in this video we're going to be looking at transformers and here's an example from my microwave Alton it consists of two coils a primary and a secondary and these are surrounded by a very substantial piece that I am their the iron actually goes through the middle of these two cores and this is something what we call an e core forms an e shaped with the land plate on it the primary is much thicker wire because it carries more current and the secondary has a lot more windings on it we'll see why later but basically this comes form has children 40 volts in and around 2000 volts out that's what we call a step-up transformer so what we'll do is have a look at how does this thing work transformer relies on two key physics principles electromagnetism an electromagnetic induction electromagnetism is when an electrical current generates a magnetic field electromagnetic induction is where a magnetic field causes an electrical current to flow as you can see one is just the reverse of the other the basic transformer construction consists of a primary coil magnetically linked via an iron core to a secondary coil the primary coil generates a magnetic field and the secondary coil converts that magnetic field back into a flow of current or a voltage so if we look at what goes on in a worm when we pass a current through it when we pass a current through a wire the red arrows representing the increasing current flow a magnetic field is formed to get a stronger magnetic field we float get more current to flow through the wire alternatively what we can do is use two wires doubling the Y's effectively doubles the current flow past a certain point and therefore it doubles the magnetic field strengths we can use this in a transformer to make some very strong magnetic fields by using a coil we can use it principle of multiple wires to greatly increase the strength of an electromagnet by looping a wire into a coil the same current carrying conductor passes the same point repeatedly the magnetic field from each wire effectively adds together and makes for a very strong magnet so if we look at what goes on in a transformer core we start with our coil of wire we now take a cropped section to the coil and only consider that wires going into and out of the screen by convention we represent objects going into and out of the page using dots and crosses and the mounting of our an arrow being fired from a bow if you can see the cross of the feathers of an arrow it's traveling away from you if you can see the point of the aisle it's heading towards you you can now add the magnetic field of each conductor as we have seen previously the magnetic fields actually add together creating one larger magnetic field and we can represent this with field lines showing the combined or the resultant magnetic field what we can then do is wrap this coil around an iron core instead of a loop of iron now when we do this because magnetism passes through wine much much better than this through air we actually find that a magnetic field is constrained within the iron core it permeates the iron core permeates just means travels through basically iron can be several thousand times better at conducting a magnetic field and air so if we now look at the primary side of the transformer and we can see how we generate this magnetic field which passes through the secondary coil what will now look up is induction in the secondary coil principle of induction involves moving a magnetic field past a conductor in this view as we move the magnet through the wire some electrons move we move the magnet the other way and the electrons move in the opposite direction key thing is if I move the magnet faster more electrons move so the faster I move the magnet the greater the current flow or key to this is it's a moving magnetic field that causes the electrons to move in other words a changing magnetic field generates a current so let's have a look about inside the transformer first looking at the primary side of a coil the rebels represent the magnitude of the currents are bigger arrows bigger current I increase the voltage the current increases and I get a growing magnetic field but once the current is the same the magnetic fields is static it stays the same so let's look at again increasing voltage increase in current changing magnetic field voltage stays the same current stays the same magnetic field stays the same the key thing is the voltage is only induced in the secondary coil when the magnetic field is changing so as long as the magnetic field is changing we've got a voltage in the secondary coil but once the magnetic field stays the same there's no voltage induced so just watch that again changing magnetic field we have a voltage in the secondary but when there's no change in magnetic field we have no voltage so what we actually need is an input voltage that changes constantly and we can do this using a sine wave as you can see the sine wave constantly changes voltage which constantly causes a changing magnetic field which means we're always going to have a voltage induced on the secondary so we're now seen how a voltage and a current flow can be induced in the secondary the induced voltage depends on the strength of the magnetic field and the number of turns on the secondary coil more turns on the secondary will generate a larger voltage the strength of the magnetic field though depends upon the number of turns on the primary so the voltage output of the transformer depends on the relationship between the number of turns on the primary and the number of turns on the secondary so let's now have a look at that relationship this is the transformer formula and it's one that you need to know it simply tells us if we take the ratio of the voltages secondly divided by primary it's the same as the ratio of the terms secondary divided by primary easiest way is to go through some examples if we take ten turns on the pram in ten turns on the secondary we look at the ratio secondary divided by primary and it's 110 divided by ten is one if we put it into our formula and then rearrange the formula what we know is that the output voltage on the secondary is one times the voltage on the primary or but actually both voltages are equal so equal number of terms equal voltages 240 volts in would give us two than forty volts out ten volts in would give us 10 volts out if you look at different example where we have ten turns and five turns we now have less terms on the secondary if we take the ratio of that fire divided by ten is naught point five we pull that into our formula rearrange it and this tells us that the voltage on the secondary the output is half of the voltage on the primary in other words the voltage house stepped down it's a step-down transformer we have half the turns on the secondary so we have half the voltage on the secondary you can probably guess what happens when it's the other way around again work out the ratio put it in our formula rearrange the formula and this now tells us that when we have twice as many turns on the secondary we get twice the voltage on the secondary this is called a step-up transformer so in summary voltage causes electrons to flow flow of electrons is a current the current generates a magnetic field by looping the wire we could increase the strength of the magnetic field magnetic field passes easily through iron and changing magnetic field induces a current in a conductor therefore transformers have to use alternating currents that will not work if you just connect them to a battery the output voltage is equal to the ratio of the number of terms multiplied by the input voltage or in other words the ratio of the primary and secondary voltages is the same as the ratio of the primary and secondary coils

38 thoughts on “How Transformers Work

  1. that is one the best video i ever seen about explaining of very abstract and long complated that puts things that are easy to follow and a very simple way that is very simple to understand, comprehend. it almost gave me chills, almost a similar feeling that understand a half adder

  2. I don't speak English but I andertant everything. …this is the best video about how magnetic field produce a current in the secundary of transformer….1 like for you man

  3. Awesome video! This is by far the best video explaining how transformers work that I have seen so far. I now mostly get it. I'll watch it again probably more than once! 😜

  4. I don't understand why the current flow of second coil is in different direction. Does it mean that the second coil produce opposite magnetic field?

  5. Very clear story, nice!
    A question: In a regular, 1:1, 4 pin transformer, could you 'add' the 5th, centre tap, be just adding two equal resistors between positive and negative pin? I mean, at any given moment it's basically at V+ and V-, so by adding a Voltage Divider, could you 'hack' the ground pin to it?

  6. Excellent video and effectively explains how a transformer works. Question: What would happen if you had 10 windings on the primary, but 10 windings on the secondary side with a heavier gauge wire, would that step the voltage up?

  7. But if power is conserved, then a higher secondary-coil voltage produced by more coils would mean current is lower, as P=I*R. But more coils mean current is higher as they add up. So is current higher or lower?? How do these things not contradict each other??

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