Posts Tagged ‘direct current’

Shakeable Dynamo Part 4: Building the bridge rectifier

shakeable-dynamo-part4

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Shakeable Dynamo Part 1: Why bother?
Shakeable Dynamo Part 2: Building the initial dynamo
Shakeable Dynamo Part 3: How electromagnetic induction works

Lets start off by securing our coils on our alternator by removing the cardboard guides and then getting some clingfilm and wrapping a piece around your coils and then wrap a bit of tape around it to secure it all. Now we know it works, we don’t want to risk our coils moving or our connections breaking.

What’s a rectifier?

Diode

So what is a rectifier? A rectifier converts AC current to DC current, so we convert the current that changes direction to flowing in one direction. That means we’ll then get the full benefit of the electricity we’re creating rather than only half of it. Rectifiers use a series of diodes to achieve this. A diode (pictured left) is essentially a valve, it lets the flow of electricity through only one way, shown by the green arrow in my diagram, the silver band indicates the cathode  (-). By arranging a few of these together we can then convert our current by forcing current to flow one way.

How does a bridge rectifier work?

In the diagrams to the right, the flow of electricity is shown, red arrows for positive, black for negative. In the top diagram the current flows across the top diode from the alternator to the output, negative is flowing across the bottom from the green wire, back through the diode to the alternator. When the magnet changes direction and the current reverses, the bottom diagram shows that the flow is blocked and can only flow to the same positive output. So no matter which way the magnets move or whichever direction the current moves in the diodes always divert the flow to the same points.

How to build a bridge rectifier circuit

With that understood we can then plug in our hook up wire from our alternator into a breadboard to build the basic rectifier circuit which we can then check that it works and solder it to our leads. You can see in the series of photos below that we take the 2 leads from our alternator, connect them to the diodes as per the circuit diagram, then we attach another 2 leads to the 2 remaining ‘corners’ of our bridge rectifier – and remember these now are direct current and one lead will be positive and the other negative so it will matter which way you attach the LED or any other component.

Shakeable dynamo: Build a bridge rectifier

Cut and solder the diodes and leads together.

Shakeable dynamo: Solder the bridge rectifier

Then ‘wrap’ the circuit over the end of the tube.

Shakeable dynamo: Trim and wrap the rectifier around the end of the biro

And finally secure it into place with some electrical tape.

Shakeable dynamo: Tape over the connections

You can see that I’ve also soldered on an LED to the new DC power supply, also remember to mark out which wire is positive and which is negative. Here’s the final result again working…

Coming up – improving the alternator and charging a battery with it…

Shakeable Dynamo Part 3: How electromagnetic induction works

Atoms of a magnet

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Shakeable Dynamo Part 1: Why bother?
Shakeable Dynamo Part 2: Building the initial dynamo

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?

Atoms of a magnetEvery 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?

how electromagnetic induction works

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

Shakeable Dynamo Part 4: Building the bridge rectifier