Right, so we’ve built the initial alternator/ dynamo and it works, not amazingly, but it works and we need to make this is a little bit more robust and protect all those lovely windings as well, at the same time we also need to convert our alternating current (AC) and convert that to direct current (DC), so that we can use this to power a small circuit/ LED without it turning on and off all the time. First I should probably explain how this all works… (feel free to correct me if I am wrong in my assumptions)
How do magnets work?
Every magnet creates a magnetic field due to the arrangement of the atoms in the material, in very simple terms, the atoms are spun so that most of the electrons are on one side of the atom, creating a negative charge on one side, while the lack of electrons on the other side of the atom exposes the positive charge of the protons in the nuclei. In the very simplified diagram to the left, the nuclei are blue and the electrons are orange and their arrangement produces the different overall charges with more electrons flowing to one end of the magnet. This also explains why when you cut a magnet in half you will get 2 magnets, not a separate south and a north pole. This then creates the polarisation effect we see in magnets and this is also where naming conventions jump into confuse matters! So first of all magnets are referred to has having a ‘north’ and a ‘south’ pole due to this polarisation effect from the different atomic charges. This is because when suspended freely, the magnets ‘north end’ will spin to point to the Earths magnetic north, which if you think about it makes no sense, since magnets attract the opposite pole (North attracts South). What is really happening is the ‘north’ pole of a magnet has a negative charge due to the arrangments in the atoms and it’s attracted to the positive charge of the Earths magnetic north – so either the north end of our magnet is actually south or the Earths magnetic north is actually magnetic south.
How does electromagnetic induction work?
Electromagnetic induction essentially is where a magnetic field or flux causes the flow of electrons in a conductive material. This is actually important to us in explaining what’s happening in our alternator, our north pole of the magnet is negatively charged, the south has a positive charge. This means that they will always try to attract an opposite charge, so when a magnet passes through or near an object with good electrical conductivity, the electrons in the conductor will be attracted to the south pole of our magnet, while the north pole will repel the electrons. This creates a movement in the electrons, essentially creating a flow of current, some materials will have a better conductivity as the electrons are able to move more freely. You can see in my basic diagram above how the magnet will attract and repel the electrons (orange circles) in the wire thus creating the alternating flow of electrons or current – without getting too complicated alternating means the current flows in 2 different directions which produces a sine wave.
Now, what happens as our magnet passes through our coils is that the electrons are pushed and pulled creating our alternating current, so the current switches directions based up on whether the electrons in the coils are being attracted or repeled. This then means that at either end of our coil there is an intermittent electrical charge switching between positive and negative, so an LED attached to one end will only light up when the magnets push/ pull the electrons in one direction.
Whats the difference between alternating current (AC) and direct current (DC)?
We want to get all the power of the alternator and not just half of it so we need a way to create a constant flow of current/ charge/ electrons so that our LED will always light up no matter which way the magnets are moving. This is where our rectifier comes in, converting or AC to DC (Direct Current). Direct current is where the current flows in only one direction, classically this is described as going from positive to negative and in most electronics this is the model that is used, however, in physics it’s considered the other way around!
Now that’s all understood we can move on to building our rectifier for the generator…