DIY windmill for $150

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Recently, I had the idea to generate my own electricity for the house. It was not a great need, but my interest in this topic increased when I read an article about assembling a windmill with a motor from a treadmill and PVC pipes. Having previously estimated the costs, it turned out to be about $ 150-200 for a windmill that could generate approximately 50-250 watts of electricity (this comes out much cheaper than using solar panels at the same output power). And in this article I will share with you my experience of making a windmill with my own hands.

How does a windmill work?

Any windmill, regardless of its size and purpose, operates according to the following principles:

1. A constant wind blows.
2. A weather vane (windmill tail) turns in the wind.
3. The blades connected to the generator (directly or through a gearbox) under the force of the wind make it rotate.
4. Due to rotation, the generator generates electricity.

Doesn't sound so difficult, does it? So let's get down to specifics.

Tool

To make a windmill, you do not need any specialized tool. I have used the following tools:

- hacksaw
- drill and drills for it
- roulette
- wrench
- gas key
- protractor
- sandpaper (different grit)

Required details

My task was to make a windmill at the lowest possible cost (because I am a student and have limited finances). So, I took a ready-made solution for making a simple windmill from the Internet and simplified it even more. All the necessary spare parts can be bought at any construction market or in a store. Many will probably end up in your garage or shed.

So here's what I used:
- metal sheet 25x35cm
- 1/4" x 25 cm tubing
- 1/4" flange
- 20-25 mm square tube L=1m
- saw blade (for hub)
- pin (for connecting the disk to the motor axis)
- two car clamps
- 8" x 4" PVC pipe
- 30" x 8" PVC pipe
- DC motor (generator)
- bolts, washers, nuts
- metal screws
- diodes for current 10-40A (more possible)

There are no problems to get these spare parts, except for the motor. From the Internet, the most popular option is to use the Ametek motor from old tape recorders. When choosing a generator (motor), choose those with the highest number of volts per revolution. For example, the "Ametek" motor that I use puts out 30V at 325 rpm, so it is great for using it as a generator in a windmill. Also keep in mind that you need a motor of at least 12V to power the inverter or charge the battery. In my design, with good wind, the speed easily reaches values ​​​​of 300-400 rpm.

Blade manufacturing

The most important part of a windmill is probably the blades. Most make them from wood or composite materials (fiberglass and epoxy). But I think that it is realistic to make them from an ordinary PVC water pipe (in terms of efficiency, they will be no worse). Before continuing, a little theory about windmill blades...
- the longer the blades, the easier they spin in light wind, but they will have a slow rotation speed.
- at the ends of the blades, the rotation will be greater than at the base, so it is necessary to calculate the ratio of the rotation speed of the blades to the wind speed (TSR) during their manufacture (for example, old windmills rotate at a constant speed of 40 rpm all year round.)
- the power that can be obtained from wind energy is equal to the wind speed to the third power. Those. P=k*v^3, where k is the wind turbine constant, v is the wind speed.
- according to Betz's law, only ~59.3% of the energy can be obtained from the wind. Those. in reality, our formula will take the form: . P=0.593*k*v^3, where k is the loss in the wind turbine due to mechanical friction, etc.
- the higher the windmill is installed above ground level, the more power can be extracted from wind energy (recommend 6-15 meters, but I installed it at a height of 4 meters).

The blades themselves are very easy to make from a pipe. It is necessary to cut the PVC pipe into 3 sections: two of 150 degrees each. and one section 60 deg. (I tried to draw this very roughly in my favorite CAD program - MS Paint :) ). The red lines are the cut lines. To make it more convenient to see the cut line along the entire length, I recommend sticking tape, tape or just paper. From a piece of pipe 150 deg. you will get wide blades that will spin easily in a light wind, but slowly. Empirically, you yourself can choose the optimal angle, based on practice, it is somewhere between 75-150 degrees. To begin with, cut out wide blades, and then, if necessary, trim them to make them narrower. And remember: "Measure seven times - cut once."

After everything is cut, I rounded the edges. If you follow the aerodynamics, then you need to round the main edge and align the back, but in practice, when using PVC pipe, I did not see any difference. In general, you can make blades like these (see pic.) ...

Manufacturing of the attachment point of the blades (Hub)

The next task is to manufacture the attachment point for the blades (propeller hub, hub). There are many different manufacturing methods. I recommend making it from a saw blade, it's easy to find and easy to drill. Using a drill, drill 3 groups of holes (2 per each) with a 120 degree offset (you may need a protractor here). The distance in the group between the two holes is 1 inch (see picture).

If you also plan to use a saw blade as a hub, then do not forget to grind off all the teeth on it, otherwise if it comes off for any reason, it can harm you and others.

After everything is drilled and we are confident in the reliability and safety of the hub, you can screw the blades to it with bolts and nuts. Be sure to fit a lock washer or use a seal nut.

Making a weather vane and a hinge for turning

Now we must make a turntable on which our generator will be installed. To do this, we use a square pipe, a piece of PVC pipe, a flange and a small sheet of metal. In the picture below, you can see a rough sketch of how it will look.

First of all, it is necessary to cut the tail of the windmill (weather vane) from a piece of iron. The shape is not very important and serves mainly to give an aesthetic appearance.

Further, along the square pipe we make a cut (it is easier to do this with a grinder). The length is not very important, I recommend 20-25 cm. Then we insert our weather vane into the slot and drill through holes in the pipe and sheet. Fasten with bolts.

It is also necessary to provide some kind of cover for the generator, from bad weather. For this we also use a plastic pipe. In the figure below, I think it is clear how it will look (the side hole serves for electrical outlets).

Then we paint everything and collect it to the heap. We attach the motor and the cover for it to the pipe with clamps. From the bottom of the pipe, closer to the motor, we install the flange and fasten it with self-tapping screws.

Mast making

Any windmill needs a mast (tower). I made it from PVC pipes and various fittings for plastic pipes. For my mast, I needed: 1" PVC pipe, a coupling for it, 3 T-branches.

The mast is easy to make and it looks like this:

Next, we plant our entire structure on the resulting mast.

Windmill is ready

It remains only to put our hub with blades on the motor shaft and our homemade windmill is ready!

In the picture below you can see an experimental design with six blades. It rotates almost in calm, but the speed does not exceed 100 rpm.

In the battery compartment, power is supplied in parallel with the solar panels. I am using 2 batteries. You can use regular car batteries. Do not forget to solder the diodes between the batteries and the windmill generator, otherwise the current from the batteries will go to the generator.

During the experiments, it turned out that thinner blades work better in my wind conditions. Therefore, I used large white blades (see previous photos) and trimmed them a bit. The result is increased rotation speed.

Author: Koltykov A.V.; Publication: cxem.net

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