Posts Tagged ‘generator’

Playing with Peltier Elements

Something I’ve been continuously dabbling in is producing electricity. I figure that it’s not enough just to use it and I should look at ways in which I can produce and scavenge it to understand it better.

This is a simple exercise in which we look at Peltier elements and the Seebeck effect. By running electricity through a Peltier element you can make a device which can either heat or cool something. Not only that but by heating or cooling one side of the Peltier element you can generate electricity from something either hot or cold – note that this isn’t free energy and this is only useful for recovering waste energy.

And if you doubt any of this, then give it a go for yourself.

For this project you’ll need the following items (shown above):

  • Heat sinks – I ripped them out of an old computer, from the CPU and the graphics cards – basically you’re looking for anything aluminium or copper based, sheet or section metal will also work just as well.
  • Batteries – I’m using 3 AAA batteries to generate about 100ma / 3.5 V
  • Breadboard – not essential but useful for a quick circuit
  • Low power LED – I’ve added a couple of short leads to mine
  • Electrical tape (just in case) – balanced the heat sink on above the candle and also taped the multimeter probes to the peltier
  • Candles + lighter/matches
  • Thermometer – this is a medical one, use anything you have to hand (get a proper one, mine was rubbish)
  • Multimeter
  • Toothpaste – Yes! This is correct, it’s not a mistake.
  • A Peltier element

You should be able to find everything you need around the house for free, you don’t need anything fancy except of course the Peltier. To get one of these, they are used in some computers to help cool the CPU but probably, like me, you’ll just have to buy one. I got mine from Farnell Electronics – they have a good range of them on the site between £11 and £125, they also ship worldwide which is handy. The one I chose is a bit pricey at about £20, but it has a good temperature differential, low internal resistance and fairly low voltage/current at maximum temperature differential – meaning I won’t need to use a huge power supply to see it working. This is the Peltier element I used and here’s more Peltier elements listed.

Ideally after doing this experiment, I want to get a few more and you may also want to do that as well once you realise what you can do with them. Anyway, I guess I should actually explain what a Peltier Element is…

What is a Peltier Element

In 1821, Seebeck found by using two different metals that are connected by two separate junctions, they will develop very small voltage if the two junctions at maintained at different temperatures.

In 1834, Peltier discovered the opposite of this, he found that if you apply a voltage to the same setup that it caused a different temperature at each junction, allowing you to generate both heat and cold from the voltage. Although what’s actually happening is heat transfer, the heat is transferred from one side to the other, making this a solid state heat pump.

You may also find they are referred to as TEC’s – ThermoElectric Coolers or in some cases TEG’s – ThermoElectric Generators. Essentially the Peltier Element is a combination of lots of very small thermocouples, junctions between 2 different metals or semi conductors and these are sandwiched between 2 ceramic plates and then encased in silicon.

They are in no way as efficient as regular refrigeration and are used for the benefit that there is no maintenance, no moving parts and they can occupy a much smaller space. They are used when the rapid heating or cooling or something is needed – typically lab work.

So if they’re so inefficient why do we care?…

Energy Scavenging with Peltiers

OK, so you can’t get a lot out of these, but the point is by combining them in systems that produce a lot of wasted heat, we could minimise the waste and reclaim this. Granted, this is not going to amount to much, but scale it up and you can see why car manufacturers such as BMW are beginning to combine them around the exhaust – some of that wasted heat from the engine can be converted to electricity. So if you’re going to waste heat, why not get the most out of it?

Imagine an oven lined with these, or a device that could cook your food and chill something at the same time. Of course, it’s much harder than that, unfortunately Peltiers aren’t able to transfer much heat and because they work by creating a temperature differential, you need a way extract the heat and keep the other side cool at the same time. So just sticking them out in the sun or on the side of your oven isn’t going to generate electricity, it works on a car exhaust because of the air flow when the car moves cools one side.

OK, enough talk, on with the demonstration…

Generating temperatures with Peltier Elements

This circuit is really simple, we’re just going to connect the Peltier to the battery cells and measure the voltage. You can see from the picture above, I’m using the breadboard to connect the two, but this is just me being lazy. Be very careful when you connect this to the battery – one side is going to get very hot. For safety I’m resting this on one of the heatsinks. These temperatures are generated from a 3.5v source and to show room temperature I’ve added another thermometer.

Here’s the hot side giving out 42.6 degrees C

And the cold side was too cold for my thermometer to read – need to get a better one but it felt much like something fetched from the fridge

What I did find is that when I had the heatsink on the hot side, I got a much better result, also there was no notable heat from the hot side, however much more heat off the batteries! It seems these are much better at cooling that heating.

Generating electricity from heat

Still a simple circuit, but this time no batteries! the LED is going to be powered by the Peltier (hopefully), it’ll be really dim and if you can’t see anything, use the multimeter to measure the voltage and current – I did warn you not to expect much! The trick of course is to remember basic physics, heat rises, so ideally you want your peltier to the side of the heat source so that only one side is heated, otherwise you’re not creating the optimum temperature differential – this is what the metal is for – conducting heat to the peltier. First time and I get 0.5volts and 260 mA, not enough to light the LED.

Oh and the toothpaste? So, the surface of the heat sinks and the peltier are going to have lots of imperfections and because of this, they won’t transfer as much heat in between the element and the heatsinks. You could use thermal paste but I don’t have any to hand – I found using toothpaste (seriously!) works just as well for a short time, however, under heat it soon dries out. It’s also much much cheaper to use as you experiment. Basically I think any kind of paste will do, whatever you have to hand. I found that with this, I got additional voltage and current generated (0.67V and 350mA), as below – also just to prove I really did use toothpaste, I added in the picture of the nice striped toothpaste being applied.

I also increased the heat source to 2 candles which proved to substantially improved the readings to 1.05 volts and just over 520 mA!!. Still not enough to fully power my LED and I have a feeling that prolonged temperatures like this even with my toothpaste additive is shortening the life of this Peltier.

If I could generate airflow over the heatsink on the non-heated side, I suspect I could further improve the temperature differential and create more electricity and also further distance the heat source, it was still much too close but Idid the best with what I had.

In conclusion

So there you have it, from 2 candles I very inefficiently generated over a volt of electricity, I could really refine this and improve it but unless I’m using candles anyway, then there’s no point other than for demonstration. I’d be interested in adding in multiple elements to generate more, which I may do in the future, but I’d have to run this from something where there is wasted heat – maybe my motorcycle engine block.

Anyway if you want to get some energy back from the heat you’re wasting, want to heat something, want to cool something then have a look at these. They’re probably not that efficient used to cool electronics, such as computers but there are plenty of niche uses that can be found for them and they’re definitely worth playing with if you get the chance.

I was also surprised that the elastic band holding this all together didn’t snap off! :)

One top tip – to remove the toothpaste, the best thing to use is… a toothbrush! And unlike thermal paste, it leaves your heat sink smelling minty fresh.

I now have visions of a candle powered Arduino!!

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

shakeable-dynamo-part2

[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

Shakeable Dynamo Part 1: Why bother?

brother-battery

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First of all I have to start by condemning Brother Industries for what ultimately motivated me to build this basic prototype, allow me to explain and I apologise for the rant, the good stuff follows…

I read an article on the BBC news website (Vibration packs aim to replace batteries for gadgets) about a new type of battery developed by Brother that would require no external power source to charge it, just vibration from shaking it a few times. The aim being to replace batteries in low power applications such as TV remotes etc… thus removing alot of these batteries from the environment and ultimately saving energy.

A really nice, clean and elegant solution which could really benefit not only the developed world but for people in the developing countries. What a great company Brother Industries is until you read at the bottom of the article “There are no plans to commercialise the batteries as yet, according to Brother.”

Wait… So you’ve invented, or rather figured a way to not only replace millions of batteries in the common household, cutting down on waste and pollution providing free energy. But also a way to provide cheap portable power sources to people who can’t afford batteries, giving us as near as you’ll get to an ‘ever lasting battery‘!

And instead of rushing this to market, you do what… Nothing! Absolutely nothing. What a shame and a waste, I can’t help but feel that people at Brother have an interest in Duracell etc… as they obviously wouldn’t appreciate a battery that you don’t need to replace. It’s that kind of mindset of greed and ignorance that ruins the planet for the rest of us.

So this is leading somewhere, I assure you! I thought, how hard can this be to build my own – wouldn’t it be great to build a set of batteries that I could use to power my remote, wait wouldn’t it be even cooler to use this to power my Arduino? or even better build an interactive TV remote that you used like a wand to change channel with no power source needed. When you start imagining the potential applications and how this could revolutionise electronics and interactivity, its even more of a shame on Brother for doing nothing with this. Imagine Nintendo using this in their Wii remotes for instance? Imagine this being used to build a simple water tester… etc.

Anyway, here’s the start of it I’m going to show you how to build a basic dynamo with a bridge rectifier that converts our AC current to DC, and the size of it is not much bigger than an AA battery – it’s my first attempt and it turned out pretty well. It generates enough electricity to power an LED – doesn’t sound like much but when I figure out a condensing and charging circuit that’s when the fun starts – for which I’m hoping that you fine people of the web will help me out! :)

Ready to learn a bit about electro-magnetism and inductance?

Shakeable Dynamo Part 2: Building the initial dynamo
Shakeable Dynamo Part 3: How electromagnetic induction works
Shakeable Dynamo Part 4: Building the bridge rectifier