I'm still making this project, so i'll be updating this as I proceed. Feel free to think along!
The pictures above started it all. A rainy sunday and some scrap wood, a file and a saw. These propellers were the result. Might as well put them to good use!
Step 1: Safety and Precautions
First of all there are some safety measurements you should take when building/installing a windmill generator.
As you get better wind high in the sky, you'll want to put the generator on a pole. Attach a lightning rod(before going outside)!
A non loaded generator will have no resistance, so in stormy weather your props may spin wild and disassemble.
So always provide a load or a tilting mechanism!
High voltages may kill you, so watch out with high voltage ac!
Step 2: Propeller Research
I saw that many people make their props out of PVC tubes cut in 3, but PVC has the tendency to get brittle in sunlight, couple that with rapid rotation and... no thanks.
Commercially available props can be obtained, but they can get rather pricey. Have I mentioned that I want this to be next to free?
So wood was the way to go. I will not go into great detail about the prop shaping. But in general: keep the angle greater near the centre than near the tips. This is because the tips rotate faster and would otherwise create drag! This can be seen in the picture above (not my propeller).
If you want to be sure of maximum output, go for a professionally designed propeller.
Note that professional turbines use lift based blades rather than drag based blades. The lift based blades are pointed towards the wind, while drag based ones are perpendicular to the wind.
Step 3: Generating Power
So what ways are there to convert the kinetic energy of the propeller to electrical energy?
We can generate AC or DC.
A Magneto: This is is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current.Also known as Permanent Magnet Generator (PMG).
An Alternator: While a magneto is a kind of alternator, in general alternators need to have power applied to a field coil to generate magnetic fields.
Dynamo: An electrical generator that produces direct current with the use of a commutator. DC motors used as generators fall into this category.
I first tried using an electric scooter motor (24v,150w,1500rpm). They are readily obtainable but since they're low voltage,high rpm, not much voltage will be generated at the 300rpm a wind turbine delivers. I tested and confirmed this.
A treadmill motor might be used, but in Belgium I can't easily get them.
Now I'm going for another option: Adding permanent magnets to a 4-pole 30 watt induction motor(see picture). These can be found in damn near everything! The rotor is a squirrel cage rotor. I've ordered 20 8 by 8mm cilinder neodynium magnets(1,3T), and will be placing them into the rotor. I'll try to write down all measurements, as a lot of the generator projects on here don't post their final Wattage or kWh/day average compared with wind speeds.
Step 4: Electrics
First of all, I already have a solar array going into 24v lead acid, so i'm aiming for 27v for charging. When the batteries are full, a relay will connect the generator to a water heater in an indoor water tank.
As I'm planning on having an AC output, I might be able to use a transformer to step up or step down the voltage.
Let's assume the propeller rotates at 300 rpm. That means it's spinning at 5Hz. Since the squirrel cage motor has 4 poles, and i'm planning on using 4 magnets in the rotor, that means I'll have an AC frequency of 10Hz (as the magnets are arranged in pairs of N N and S S,opposite to each other, each coil sees 2 increases and 2 decreases in flux per rotation).
This might not be enough for ordinary line transformers. Gearing for higher speed will add friction so we're not doing that. The Inductance will have to be very high to deliver any power at such low frequencies, maybe a Microwave transformer can be rewired.
Another option to get higher voltage is to use a voltage doubler circuit.
The squirrel cage motor delivered only 12v at max rpm of my drill, so not at all suited for wind power. Maybe with bigger magnets or an induction motor with more windings.
I've now wound 8 61 turn coils, and wired them for a 2 phase output . I Use 4 magnet groups of 3 2,5kg lifting force neodynium magnets for the rotor.
Update on squirrel cage: i've doubled the magnets, now I'm getting a 30v max output with the drill at 3000 rpm, but only at 50mA. This might be due to the fact that the wire of the windings is thin as it's only rated 30W.
I've stumbled upon some DC wheel motors from old electric bikes. Many manufacturers are going 3 phase ac now with their bike motors. The motor is a direct drive motor. If I short the output wires while i'm spinning the motor manually, it really STOPS. This motor can output 300 watts, so I'm expecting 150 watts generation.
Since this generator does not need much RPM to produce charging voltage of 24v, I will be using this generator.
Step 5: Mounting the Propeller to the Generator
We need to mount the propeller to a shaft, add a gear to said shaft and a chain to the generator gear.
For ease of assembly and lack of tools, I decided to use mainly bike parts.A rear axle has threads on it for a gear. You can use this gear directly or mount a bigger gear and use the small gear as a tension nut.