Portable Savonius Wind Turbine With Deflectors

If someone asked me which green energy device I prefer the most, without any hesitation I would answer that Solar Panels are at the top of my list. Although it is known that they still lack of an outstanding efficiency, there is no way to ignore the fact that their size is relatively small for the powers they are capable to develop, that they do not contain moving parts prone to failure or wear and it is relatively easy to calculate their average energy contribution in a certain place, are aspects that attract me to this technology.

In life nothing is absolute and everything has limitations and for Solar Panels this “law” is also applicable. They are conditioned by direct solar radiation hitting them all over their area so that they can contribute with their full potential. This has always led to a simple question: What happens with Solar Panel´s energy at night or when is it cloudy? Answer: They do not produce energy or their energy production is very limited. It should be added into that answer that in certain areas of our planet the incidence of Solar Radiation is poor as so this technological choice is not possible. On the other hand, technologies that take advantage of the wind for energy production do not have this limitation (unless there is no wind at all). In reality, Wind and Photovoltaic technologies may be seeing as a perfect complement, as generally on cloudy or stormy days the wind speed is higher. The wind blows even at night when Solar Radiation is not available.

Considering all of these facts and looking for an extra support on the days that I cannot count on the presence of the Sun for my solar panel, I thought about using the wind´s help to get an extra energy contribution. What is more, even if there is Solar Radiation, the extra contribution that a Wind Turbine could provide shouldn´t be missed.

Before launching to invest time and effort in the construction of a Wind Turbine or buying a Commercial one capable of providing me with practical electrical powers from the energy point, I decided to build a small Wind Turbine to experiment with around the house and “study” the areas with the best winds. Since I do not want the installation of large towers and considering that there are trees around the place that "block" part of the wind, making the flow somehow erratic and turbulent with variable directions and with not so high speed; I decided on a Savonius type Wind Generator. They are of low efficiency, however they can operate with higher torque at low wind speeds. The fact that it is a Vertical Axis Wind Turbine (VAWT), is indifferent to the direction of the wind and sudden changes in direction. Another of my design requirements is that it should be portable and I wanted it to contain wind deflectors to “attenuate” the negative torque inherent in this type of Wind Turbine improving its efficiency a bit.

In this Instructable I present the steps for the construction of a small Savonius type generator, portable and capable of capturing the energy of the wind to recharge small electronic devices through a USB port and light some LED lamps. Its power is limited, around 3 or 4W of use but it is an excellent starting point for experimentation with this type of technology.

Supplies

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Materials:

PVC pipe 30 cm in length and outer diameter 11cm

1950 cm2 of Plexiglass 4.5mm thick

Eight Wind Deflectors made from rectangular boards 40cm long by 10cm wide and 5mm thick

A Circular Wooden Base, 32 cm in outer diameter and 20 mm thick

42cm long M4 threaded rod (option A)

Two 6cm long M4 screws (option B)

Eight M4 nuts

Four 35mm long M3 screws (to lengthen the ones included in the Stepper motor)

Four 20mm long Wood Screws, no more than 4mm outside diameter

Four bearings 608RS

A piece of Flexible Silicone Hose, 4mm inside diameter and about 6cm long

A Nema 14 or 17 Stepper Motor (https://amzn.to/3gyUdgA )

Two Full Bridge Rectifier Module (https://amzn.to/3f9om5I )

A USB Female Connector (https://amzn.to/31TDj8r )

An Electrolitic Capacitor (https://amzn.to/2CivuOz )

An LV7805 Linear Regulator (https://amzn.to/3gyVvrW )

TO-220 Encapsulation Heat Sink (Optional) (https://amzn.to/2CqzQUc )

A pair of cables for electrical connections (approximately 30cm)

Sandpaper number 120

Instant glue

PVC glue

Hot Silicone Glue

Permanent marker

Soldering iron and tin

Tools:

CNC Machine, Laser Cutter, 3D printer or Contracting this Online Service

Jigsaw

Belt Disc Sander

Table Saw

Angle Grinder

Ruler and Measuring Tape

Two M10 metric wrenches

Electric cable stripper-cutter

Multimeter

Step 1: Obtain the Halves of the PVC Pipe That Will Make Up the Savonius Rotor

It is necessary to cut a length of 30 cm from the PVC pipe so that the cuts are straight with respect to the surface of the pipe. If you have a flexible tape, arrange it so that it fits perfectly to the surface of the pipe, with a marker draw a line that covers the entire perimeter of the PVC pipe using the outline of the flexible tape. A sheet of paper can also be used for this operation.

Note: If the pipe is new and has a factory cut end, take advantage of it.

Taking the previous line as a reference, measure 31-32 cm longitudinally and make a new mark (line) in that position. Using an angle grinder and a PVC-appropriate cutting disc, make the cuts on the lines drawn above. The cuts should be as straight as possible. Don't worry if they have minor blemishes. The extra centimeter will allow us to sand possible imperfections until they are 30 cm long.

Using a ruler or 90-degree angle section, snap it to the contour of the pipe and draw a horizontal line along the pipe section you just cut. From this line measure 172.7mm across the contour of the pipe and make a new mark on each end of it. Draw a line that goes through these new marks. Cut the pipe at these marks. At the end of this step you should have two halves of the PVC pipe. Finally sand possible imperfections in the cuts.

Step 2: Cut and Paste the Pieces That Will Make Up the Savonius Rotor

Based on vector drawings or files for 3D printing, cut or print these parts. In my case I designed them specifically to be cut on my CNC machine, which is quite small (300mm * 200mm) in working area. That is why I had to design several pieces by pieces and then assemble and glue them together with PVC glue. Yes I know, it is a bigger complication but I had to find a solution!!!!

In the particular case of the cut pipe sections, these should be well attached to their support bases and in the correct position. Help yourself with the clefts created for this purpose. An important aspect, these bases must be parallel to each other once glued. Use the threaded rod and nuts to firmly secure the entire assembly.

Something important I must clarify, for the design of the Rotor Savonius I based mainly on two scientific articles that summarize the experimental activity and theoretical results of several researchers in this type of VAWT. The spacing, the width-height ratio of the Rotor, the decision that the bases of the sections of the PVC pipes were closed, the angle of inclination of the wind deflectors among others are not arbitrary or random decisions, there is a certain scientific basis in it. Here I leave the articles in case you want to delve into these aspects.

https://www.sciencedirect.com/science/article/pii/S187661021735453X

http://www.akademiabaru.com/doc/ARFMTSV55_N1_P126_135.pdf

Step 3: Condition the Circular Base and Deflectors

A circular hole of 19cm in diameter should be made to the circular wooden base declared in the list of materials. Make a mark with a compass or similar and with the jigsaw make the cut. Leave a margin to finish with a round sander or similar.

Using the support parts that you cut at the CNC or 3D printed as a template, make the marks where the Deflectors will rest vertically. Use the table saw to make grooves 5mm thick and 6mm deep. This circular piece will be the base of the whole set of this generator so pay special attention to its construction.

You can round some of the vertices of the wooden rectangles if you prefer. Only make the coupling grooves to the deflector parts at the end when you have the semi-assembled set, this will avoid possible coupling errors.

To facilitate the understanding of the assembly process of these parts, see the associated video.

Step 4: Considerations About Electrical Wiring

As you can see in the connection diagram, interconnecting the elements that will make up the electrical generator set is quite simple. If you are tempted to use only one Full Bridge Rectifier instead of two, I don't recommend it. There may be mismatches between the induced voltages in these cables and this will cause problems (low efficiency). You can use a Schottky diode array to improve efficiency, but having these two rectifier modules will make wiring easier.

If you ask me what the most appropriate type of electric motor to be used as a generator I recommend, I would honestly answer "the best generator should be created for that only purpose", however after trying various configurations, the Stepper Motor was the one with the best results. Keep in mind that the torque you are going to get with this type of machine at this scale is quite limited, the Revolutions per Minute are also low and depend directly on the speed and "quality" (degree of turbulence) of the wind you have in your area.

Since the variations in the wind speed will have a direct impact on the induced voltage, the output must be regulated to a constant voltage, in my case I used a linear regulator of the type 7805 that provides 5V at the output. I know what you are thinking, "linear regulator?, you are wasting energy in the form of heat" hahaha!!, it certainly is, but at least I don't burn my USB devices. On this particular topic I have been doing several experiments with Buck-Boost Converters and you know what? I damaged two in my experiments, I think they didn't get along very well with the Stepper Motor, and to be honest, I do not think that the cause of these damages is an excess of the current value, which is intrinsically limited by the Stepper Motor in my case around 600 mA, but by the voltage spikes and BEMF. See the photo of the oscilloscope (80Vpp in a simple turn with the hand). However the linear regulator has not given any problem to date. What do you think of this? Let me know in the comments.

I also think that a very appropriate solution would be to connect 18650 cells after the capacitor protected by a Battery Management System (BMS) circuit. Taking into account that the current is low I don't think there is any problem. However, once these batteries are fully charged and the BMS circuit interrupts its charging, a Dummy Resistor will have to assume consumption if we don't want the RPM to get out of control. I did not include batteries on my design since I did not want to worry about them later on.

Step 5: Electrical Connections

The Stepper Motor that I use was recycled from an old printer and it came with a pulley which I had to remove with the help of two wrenches as shown in the photo. These Stepper Motors are likely to come with multiple cables. To identify which cables to choose, you must measure the electrical resistance between them and select two pair of cables with the highest electrical resistance. In my case the windings were 20 ohm and each pair had a central tap that I did not use in this design.

To reduce the complexity for the manufacturing of this generator the electronic components were soldered together directly as shown in the connection diagram above. Before connecting the linear regulator, it is recommended to perform certain performance tests. I tested that I was able to turn on a parallel array of LED lamps when turning the Stepper Motor at low revs.

Solder the conductors to the linear regulator also as shown in the diagram. In my case I did not have excessive heating that would compromise this regulator, but if you have doubts, use a heat sink attached to it.

Solder the USB connector to the regulator outlet. BE VERY CAREFUL IN THIS OPERATION AND RESPECT THE ESTABLISHED PINOUT. If you have doubts, check here: https://components101.com/connectors/usb-type-a-female

Only 2 (Vcc + 5V and Ground) wires will be soldered to the correct pins. To avoid compatibility issues with certain devices that need connections to the data pins, sandwich this device and you're done! (https://amzn.to/2APInQ0)

Step 6: Attach the Electronic Components to Its Support Plate and Screw It to the Base of the Wind Turbine

It is necessary to change the M3 screws that make up the Stepper Motor for slightly larger ones to be able to fix it to its support plate as shown in the image. The rest of the components can be glued with hot silicone, taking care not to obstruct the rotation of the motor shaft.

For the connection of the motor shaft and the Savonius Rotor, it was convenient for me to use a small piece of flexible silicone hose of approximately 4mm internal diameter and about 6cm long.

The 7805 regulator I fixed it to the base also with glue and I glued the USB port with hot silicone so that it was easily accessible from the outside.

Step 7: Endnotes and Conclusions

If you have followed each step in the construction of this Wind Turbine you should already have your own version of this generator. It is portable and will not only serve you to take advantage of the energy of the wind in the surroundings of your house but to any place with favorable wind conditions. I think it may last for many years if handled with caution and although its power is limited, it is always a good choice if you go outdoors and do not have an electric source to charge your phone or power bank or even turn on a light in the darkness (as examples).

I have noticed something curious, on cloudy days the wind speed (at least in my area of residence) is higher, also at night. I think this is common in several places, which emphasize to me that: technologies for harnessing the energy of the wind could be an excellent complement to the technologies of Solar Panels.

Luckily if you only want to experiment at home and get energy from the wind you can create your own wind turbine and thereby predict if you want and “need” a bigger one.

The knowledge and experiences derived from its construction have enabled me to learn a lot about this type of Vertical Axis Wind Turbines (VAWT). Having incorporated wind deflectors in order to increase its efficiency a little bit, I also think it was a good idea.

I hope you enjoyed it as much as I did. I am looking forward to hearing from you!.

Good luck!!!