I've always had a love for electronics, and a love for the things you can do with them. Being a university student however, money is not exactly something that I have in abundance. This has lead for me to try and find ways to create ways of building, and experimenting with multiple different devices within my very shallow price range.
I've always found the concept of using motors as electric generators extremely interesting, and since I had a spare stepper motor from a previous project I thought I would have a little fun with it.
Why did I choose a steppor motor? The cheapest and probably most commonly found type of electric motor is the small DC motor. These are ideal for projects such as remote controls cars/ helicopters etc, but are far from perfect for use as electric generators. Why is that? Well these DC model motors are designed so that the can produce the maximum number of rotations (or RPM) for as small a current as possible. For a kinetic generator however, we want to be able to produce as much current as possible from as little rotations as possible, a problem not shared as much by an AC motor. So yeah, try and stay away from the DC motors.
Straying away from DC motors does make this whole process a tad longer though I'm afraid. The great thing about DC motors is, well, that they're DC. This means that the voltage outputted from the motor (I suppose really I should be saying that you input to the motor) is constant, and hence does not fluctuate. A stepper motor however, is not. This means that the current produced from a motor of this type is alternating (follows the shape of a sine wave). This is not very useful if you hope to use your generator to power, or to charge most electronics or batteries. But have no fear for we have the wonder of rectifier diodes! I'm not going to go into too much detail as to what they are and how we use them now as that will come in later. All you need to know know is that we shall use 8 of them to create two diode bridges, which along with the capacitors and resistors, will hopefully turn the AC output, into a DC one.
This turbine is potentially powerful enough to power a series of LED's, to power a small bulb or even charge rechargeable batteries.
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Step 1: Materials
Especially if you're a frequent electronics hobbyist, most if not all of these materials can probably be found lying around. The material used in this project:
- 5 Wood Skewers
- 1 Cork
- 5 Paint Can Lids
- 8 Rectifier Diodes
- 4 Wire Stepper Motor
- Connector Leads
- 2 100uF Capacitors
- 2 100K Resistors
Step 2: Making the Turbine
For this step, you shall need:
- 1 Cork
- 5 Wooden Skewers
- 5 Spray Paint Can Lids
For the first step, take the 5 spray paint lids. You want to make two holes, on the opposite side to one another. I placed these hole two centimetres down from the rim of the lid, and made these holes using a 2.5mm drill.
Once these holes have been drilled, push the skewer through both sides. You want to have 8cm from the point of the skewer to the lid. Cut off any extra wood coming out of the other side of the lid.
Now you want to mark the centre of the cork, and draw five lines leading from the the centre to the edge. Each should be at 72 degrees to the next. Choose a set distance into the cork (I chose 2 cm's) and then push the skewers in, following the lines drawn on the base of the cork. Hey Presto you're done! Once the circuitry is finished it will be time to attach this to the motor.
Step 3: The Circuit
So now on to the part that really makes this project work, the circuit.
The stepper motor has four wires coming out of it, two correspond to one of the coils in the motor, whilst the other two correspond with the other coil. This is important as we basically have to create a different circuit for each coil.
So first of all we want to take four diodes, and with them construct a diode bridge. What this section of the circuit ensures is that the entirety of the AC current coming form the motor is positive, and hence can be used in DC electronics. For a graphical representation of this refer to the picture at the top of this step.
Finally we come across the resistor and capacitor in series with one another. This, for obvious reasons, is called an RC circuit. What this does is it basically smooths out the signal, effectively converting it from AC to DC, again as shown in one of the earlier pictures (The diode bridge is the diamond with the four triangles with lines on the point). When placing these diodes into the breadboard, make sure you place them the right way round. You should find that there is a light grey band on the end of the diode corresponding to the line across the triangle in the circuit diagram. Also do the same for the capacitor. Ensure that the positive (the longer of the two pins) is connected to the output of the diode bridge, and the negative (should have a great strip above the pin with a '-' sign) to the next part of the circuit.
OK brilliant! All that needs to be done now is to recreate this circuit for the other coil and that's the circuitry done! We have managed to generate a DC signal that can be used to power pretty much any small household electronics. Bare in mind whilst selecting your motor that these kind of project are all about the currents produced. The idea is that you want a motor that can produce maximum current for as little revolutions as possible. The values that I got from my system is an average current output of 6.89A and an average voltage of 1.12V.
Step 4: Finishing Up
Now that all the individual parts are finished, its time to put everything together and see if this works.
I used a box cutter knife and then a screwdriver to make the hole down the centre of the cork for the motor shaft to fit in. Once the hole was big enough I found that the motor stayed in by itself and hence I didn't need to use any glue etc to keep the cork attached.
Now find a powerful water source (I just used a tap) and try it out! For testing if it works, try attaching an LED to the positive and negative terminals. If everything works OK you should find that it lights up and stays on.
This is by no means the most practical of projects, but its definitely a good bit of fun and a great introduction to using electric motors as generators. I hope you've enjoyed this project, now its your turn to go out there and get building!