Posts Tagged ‘alternator’

Shakeable Dynamo Part 4: Building the bridge rectifier

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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

Shakeable Dynamo Part 2: Building the initial dynamo

[ad#Google links]Shakeable Dynamo Part 1: Why bother?

Firstly, there is no such thing as ‘free energy‘ you have to always put something in to get something out. I call this free energy because it comes from your own movements rather than having to pay cash for a battery or the juice to charge it, I guess it’s better to call it ‘financially free energy’. Also when you look at this, some of you may point out that this isn’t a dynamo because it generates AC current, but I call it a dynamo because of the bridge rectifier built in to that converts this to DC.

Basically like all alternators and dynamos it works on the principle of converting mechanical energy into electrical energy by inducing current in a conducting medium, such as copper wire, using a magnetic field. Typically this is done by rotating a magnet inside coils of wire.

My alternator works in much the same way – we move a magnet through a coil of wire to induce a current, only we do this in a linear motion rather than circular. There are lots of crazy equations out there that state how much current you will get from a magnet of certain strength, a certain number of coils of wire of a certain thickness etc…

Mine is much much simpler – I first did a very small test to check that the principle worked, with only a few coils I got a current. Then I just kept winding until I got to a certain thickness and invariably got bored! My windings weren’t at all neat and were all over the place, so if my bodge job worked a more precise version will work better (probably).

So the main question arises – how much current can I get out of the smallest amount of wire and magnets. My aim was to build something to the thickness of an AA battery.

Ok, lets look at all the parts you’ll need, it’s actually not that many and for your magnets and wire – get it off ebay, you’ll get far more for far less than from buying them from a retailer.

What you need to build a simple dynamo / alternator

Parts

  • 1 biro or piece of tubing with a 6mm diameter cut to roughly 10cm in length, the magnets will need to slide freely down the tube
  • At least 3 neodymium (rare earth, super strong) circular magnets with a diameter of 6mm – you can buy a set of 50 for not very much – these are really strong so be careful
  • Magnet/ winding wire around a 32-42 AWG, thinner wire (42 AWG) means more coils
  • 4 ‘N’ series rectifier diodes – any will work fine for our low voltage most of the 1n series have the same voltage drop – I used 1n004’s
  • Some hookup wire – around 18-22 AWG (any wire will do really) for soldering the magnet wire to and building the circuit.
  • An LED (for testing)

Tools

  • Soldering iron & solder
  • Breadboard – useful to build the bridge rectifier and test the dynamo
  • Cutters & wire strippers
  • Also handy to have a multimeter to check the output and a couple of screwdrivers or sticks to help spool the wire

Other materials

  • Some clingfilm and electrical tape

So lets build it step by step with my photos, at the end of this you’ll have the basic dynamo, Step 4 at the bottom will show you how to build the rectifier and the theory behind that.

How to build the alternator

First check that your magnets slide easily through your tube, you may need a few connected together to stop them spinning inside or getting stuck.

Now get your tubing or pen and cut it to size, about 10cm in length

Shakeable dynamo: Cut the biro

Next we need to add some ‘guides’ so that we can keep our coils in place on the pen, I used a square of cardboard from a box taped on the ends

Shakeable dynamo: Add a guide for the coils

Now the fun part, winding the coils. First don’t bother taping down the end of the wire, instead make a small cut in one of the guides and use this to hold the wire in place as you wind – you need to be able to get to both ends of the wire later on! You’ll need to save about 5-10cm.

The easiest way to coil the wire would be do use a drill or something to spin the tube, taking wire off the reel, but this wire is so thin that if it gets snagged it will snap and you have to start all over again. Best to do it by hand and watch some TV as you do it, it doesn’t take that long just stick your tube over the a screw driver so you can spin it and stick the reel onto something like a drum stick.

With the reels stick on your lap, the reel between your legs, you can now hold the tube and spin it on the screwdriver to wind the coils and keep a fairly good tension. If you want to be precise then you can wind the coils accurately or like me just wind away in any fashion.

Shakeable dynamo: Spool the magnet wire on to the biro

I kept winding until my coils got to the thickness of an AA battery, so a diameter of about 12mm – took a while but after a while it gets easy, especially if you’re not fussed on how well it’s wound.

Next we take 2 pieces of our hookup wire, remove the casing on either end and then wrap one end of the copper magnet wire to one end of each wire, you’ll need several coils around this wire.

Shakeable dynamo: Wrap the ends of the magnet wire on to some thicker wire

Now get out that soldering iron and get it heated up, the heat of the solder on the ends of the wire will melt away the very thin varnish on the copper magnet wire while it also binds it to the hook up wire. Be careful as the thin wire will snap very easily and you’ll need to repeat this step.

Shakeable dynamo: Solder the wires

Before we go further you may want to check that the connections are good with a multimeter set to measure continuity. As long as there is some fluctuation in the initial reading all is good. You can see that I’ve temporarily secured my magnet wire to the guides. This is also a good time if you want to measure the current generated when your magnets pass through the tube / pen.

Shakeable dynamo: Test for continuity

And thats it, shake the magnets inside the tube to generate a current the basic alternator is built, you can hook that up to a breadboard to play with, if you add an LED and shake the generator you’ll see the LED light up, it’ll be quite dim and no matter how fast you shake the magnets, the LED doesn’t remain consistantly powered, this is because the current is alternating and an LED require direct current instead.

Once you’re happy and understand whats happening we can proceed to step 3 which improves up on the blinking LED and gives you a current you can actually use.

Shakeable Dynamo Part 3: How electromagnetic induction works
Shakeable Dynamo Part 4: Building the bridge rectifier