Build Your Own Mini Home Wind Turbine Generator-An Introduction
Wind power is seen as a very good source of renewable electricity.Wind power generation is a fairly simple process, and some people have had great success in building a home wind turbine from scratch.An ordinary stepper motor can be used instead of a complex and expensive ac power generator(alternator) to make a very simple home wind turbine generator. Stepper motors can be bought new quite cheaply, but they can also be cannibalised out of old computer printers, floppy disk drives, and other sources.Stepper motors generate ac power at low rates of rotation ,far lower than similarly sized dc motors for example. Therefore small wind turbine blades can be mounted directly onto the motor shaft rather than through a noisy and complicated mechanical gearing unit.Besides, stepper motors can be used in conjunction withhomemade pvc wind turbine blades to make a very affordable small wind turbine generator.
Stepper Motor Selection & Lead Identification
On the side of most stepper motors technical specifications will be labelled. The important parameters are the maximum voltage (Vmax), the current per phase (A/Ph), and the number of steps or degrees per step. A 3.6 degree stepper motor for example has 360/3.6 = 100 steps, a 1.8 degree stepper motor has 360/1.8 = 200 steps. A typical stepper motor based wind turbine generator will operate at around 200 rotation per minute(RPM).A motor rated at 50 volts for example could be used to charge a 12 volt battery at low speed, whereas a 15 volt stepper motor could only charge a 12 volt battery when up at its full speed!In principle,the higher the number of steps in the motor, the lower the RPM required to generate a decent voltage. So, if you had to choose between two motors with identical voltage and current characteristics then you should choose the motor with maximum steps.
Most stepper motors have 6 leads, however there are motors with 4, 5, or 8 leads also. Each of the four coils is made up of one length of wire with two ends. One end is called live and the other end is called common. In a five-lead stepper motor all four commons are joined together, in a six-lead stepper motor two pairs of common wires are joined together.But in an eight-lead stepper motor none of the four common wires are joined together.
For lead identification,systematically use a good quality digital multimeter(DMM) to measure the resistance between different pairs of wires. All four coils will have near identical resistances . If they did not the motor would not function properly.If the pair of wires being measured are both live, the resistance measured will be double that measured if one of the wires is a common. When you have identified the common wires, be sure to label them.Having identified the leads emerging from the stepper motor, it is now very easy to rectify the multi phase alternating current output into more useful direct current.
Rectifiers & Voltage Doublers
Note that the electricity generated by a stepper motor is usually in multiple phase ac. To convert this into direct current (dc) for battery charging (or lighting LEDs), you need to use a suitable bridge rectifier assembly. An optional voltage doubler enables a useful voltage to be output at low rotational speeds . Working principle of the rectifier and voltage doubler setup is simple.The ac voltage from each of the two pairs of stepper motor coils is rectified by the bridge rectifier into dc voltage and the two output voltages are then added together by the doubler giving a total output of double the original voltage, but with a current equivalent to that generated by just one pair of coils.Suitably rated electrolytic capacitors can also be used to smooth the output voltage to keep it fairly constant so it can be used directly in electronic applications as well as in battery charging. Add one capacitor in parallel with the positive and negative outputs of the first bridge rectifier, and then connect the second capacitor across the outputs of the next bridge rectifier.
A charge controller is crucial for a wind turbine used to charge a battery bank.A typical wind turbine charge controller constantly monitors the battery voltage. If the voltage reaches a set value, ie the float voltage , then the controller turns on a shunt(dump) load which dissipates excess power to prevent it from overcharging the batteries.When the battery voltage is measured to have fallen back below a set threshold ,typically 0.2V-0.5V below the float voltage, the shunt load will be switched off and battery charging will start again. An ordinary battery charge controller cannot be used with a wind turbine generator since the wind turbine controller must ensure that the wind turbine is constantly under load to prevent it from spinning out of control and being damaged in strong winds by overspeed.
Making suitable blades for your home wind turbine is really a nightmare . Wind turbine blades go through enormous stresses and must be made to quite tight tolerances if they are to balance and not send destructive vibrations through your wind turbine.Typically blades are carved from wood, but this is very time consuming, difficult, and requires a wide range of tools.Pvc pipe cut to size is a powerful alternative. In strong winds the flexibility of the pvc blades is useful as it takes some of the energy out of the wind preventing the wind turbine generator from spinning too quickly and being damaged. Obviously you need to take care to ensure that the blades cannot bend back far enough to hit the wind turbine mast.Best of all, if your wind turbine generator is damaged in a storm it is very cheap and quick to put together another set of turbine blades.The raw material( pvc pipe) is easy to find and work with.PVC wind turbine blades can simply be bolted onto the stepper motor. The performance is more than acceptable for a home wind turbine generator.
This article provides practical guidance for readers who need to design their own mini home wind turbines.The types of components available, and their applications, are so varied that only general guidelines can be provided. A more complete appreciation of their capabilities,and limitations, is only gained through experience and experimentation.