WINTURER: a Portable NP-F Battery Charger Wind Turbine

Hello everyone and welcome to the WINTURER project page, the Wind Turbine for your Adventures.

update notes:

• I have been contacted by several Mechanical Engineering students and others interested in the original design files. I just uploaded them to GRABCAD at this link. I have spent a lot of time creating these parts. I hope they will be of great help to you!
• A new DIY variant of "NP-F" battery for this wind turbine at this link

The creation of WINTURER was inspired to provide a backup solution to recharge my electronic devices, during my explorations away from conventional power sources. Normally on my trips I take with me a 10000mAh (37Wh) PowerBank and a small 10W portable Solar Panel. Generally, the Power Bank is more than enough for me and the Solar Panel is a backup in case I use up all the power from the Power Bank and need to recharge my devices.

It happened to me that during an expedition a little longer than expected, I tried to recharge my phone and Power Bank when it had run out and there was no sun light at all. There was wind, but I wasn't prepared to take advantage of it. Suddenly, my phone had turned off completely and with it all the advantages of having it on (GPS, maps, possibility of communication in case of emergencies if I approached an antenna, the camera to get an interesting photo, an LED, etc...).

No matter what size of Power Bank you decide to take with you, at some point it will run out if things go off the rails and the return to civilization stretches out in time.

Solar panels also have their drawbacks, they depend on the Sun as is evident and they need to be perpendicular to solar radiation to extract their full potential. Many people hang the panels on backpacks and the orientation towards the Sun is a bit random which hardly contributes to generating energy efficiently. What if in your adventure destination there are no guarantees of having access to energy sources to charge your devices? Another aspect is that generally during the day we are on the move or in some activities while fulfilling our objectives and not precisely recharging our devices. As soon as it starts to get dark, it's time to stop moving and it's a good time to recharge, but unfortunately the sun light is gone. If there is any usable wind, this project may be a solution. Prototype 1 was my first proposal to take advantage of the wind to recharge my devices.

I think there are many people in the World with similar needs. There are regions where access to conventional energy sources is very scarce and access to devices of this type could be a good alternative to keeping an LED lamp on at night or perhaps a small fan. There are also monitoring devices for meteorological variables, air quality, etc. that need energy sources for their operation where the sun is scarce. How about in disaster situations?

It is true that there is no wind everywhere and perhaps there is no other choice but to carry along 10Kg of Batteries and thereby have a certain “peace of mind”. But what if there is wind? Would you carry around a reasonably small, low-mass device that harnesses the kinetic energy of the wind to charge your most essential devices? If your answer is positive, then in this project you can find a solution.

What would be the drawbacks of a Portable Wind Turbine? Why apparently are there many people who are still not convinced to take one on trips? Why aren't there several proposals for cheap DIY solutions, free to modify, replicate, share without being subject to patents and all the restrictions on development that this entails?

The answers to these questions were the compass and the obstacles that I have had to face in this project. I summarize what I think below about the most common comments.

"A Wind Turbine that provides a "feasible" amount of energy needs to be relatively large and heavy. This is inconvenient if you have to carry it on your trips!" This is true, very small and very light devices will not provide enough energy . Even so, I believe that in this project I have found a balance between Volume-Mass-Generation Power so that it is practical and some may wish to take it on their trips. I think the folding Blades was a decisive step in the design.

"How do I install the Wind Turbine, is it required to carry heavy and complex structures?"

Not in this case. If you don't mind carrying a light and compact photo tripod there is no need for additional structures. In many cases, this type of equipment is already carried with you.

"I have to leave my device charging and while this is happening I can't use it"

Removable batteries are used here. If you have 2 you can leave charging one in the Wind Turbine while you use the other with you.

"Skills and workshop tools are required to make the Blades and other parts, this is very complex for me"

If you have a 3D printer and you know how to use a soldering iron you have everything very easy.

This project meets the following requirements:

-Easy to reproduce, industrially scalable and multi-application.

-Reasonably cheap

-Reduced in size, similar to a 2 liter soda bottle

-Relatively low mass

-Compact and easy to handle for transport (Folding blades towards the central body)

-Most of its 3D printed parts on a typical Ender 3 type printer (Hotend max temp 250 deg and hot bed temp 90 to 100 deg celsius and no part bigger than 22cm)

-Detachable battery that eliminates the problem of twisted cables and inefficiencies. You won't have to throw it away if the battery goes bad, the problem is the battery not the generator lol.

-Efficient.

-Generation capacity between 3W-15W depending on the speed of the wind.

-Compatible with tripods and camera support accessories (¼-inch mount with 20 threads per inch)

-Support USB QC output

-Splash and dust resistant

-Good mechanical resistance

-Easily repairable.

WINDTURER has been designed to accompany you on your adventures and to be easily transportable. It does not matter if you want to make an expedition in a remote part of the World or if you simply want to impress your friends and teachers at a Science Fair, you decide!

• 3D printed parts from attached STL files
• Three-phase AC Permanent Magnet Wind Generator (1 needed)
• 1 Kg Spool ASA Filament (1/2 needed)
• Three Phase Rectifier Option 1 (1 needed)
• Schottky Diodes Option 2 (6 units needed)
• 6203-2RS Bearing (1 needed)
• Retaining Clips 15mm and 40mm (2 needed)
• Screws Bolts Nuts Washers Assortment Kit
• Battery Pack with USB Output NP-F970 (Opcional)
• Lightweight Camera Mount Tripod (Opcional)
• 2 Part Epoxy Glue (1 needed)
• Paracord (Opcional)

In the previous video I show you a summary of how I executed the following steps for the construction of the WINDTURER-P4 Prototype

You can download the STLs from here in the FILES section below.

I have also included the files (STEP_3MF) in case you want to take a closer look at the assembly or change something, depending on your interests and needs. If you need any special type of file format let me know and I'll see if I can help.

I have printed my prototype on ASA filament, specifically from the manufacturer Polymaker https://amzn.to/3ryQKGe (affiliate link). It is recommended that the 3D Printer, print in a closed space without drafts and use a heated bed at least 90 degrees celsius with some glue or lacquer for printing. I printed my pieces at 250 degrees celsius. PETG will likely work as well, though I haven't tested it. PLA should be discarded because it has very low adhesion between layers and on very hot days the pieces can deform.

I have included my CURA-GCodes, in the files section for you to analyze how the pieces were printed. The layer thickness was 0.2 mm in all cases. I used a Longer LK4-PRO printer with a 0.4mm nozzle.

The propellers were printed one at a time. It took about 6 hours each. I used supports and the position was as shown in the video. The infill pattern was TRIANGLE and I used the CURA software as Slicer.

Additionally you may need some accessories to fix the tripod to the ground. I have printed some from thingiverse via these links

Tent pegs: https://www.thingiverse.com/thing:2758339

Tent cord fastener: https://www.thingiverse.com/thing:3676148

How to use the tent cord fastener : (https://youtu.be/w34OC063BQA)

FILES

STEP, IGES and X_T files here: https://drive.google.com/file/d/1rMAIs99t_-0hSEGARhomb7LORKDwRoOJ/view?usp=sharing

Bill of Material: https://docs.google.com/spreadsheets/d/1aMOJwC7pS_DCuWPCbJbpmcdg3yCmRCFX/edit?usp=sharing&ouid=109023932284365279388&rtpof=true&sd=true

G-CODE FILES: https://drive.google.com/file/d/18l1un2bf9ErvrFCtGkQgvTXwFRAoUGFH/view?usp=sharing

It is recommended to sand the pieces in the places where the supports were created. Also to smooth out any bumps that could affect performance or cause damage to hands when handling.

Be careful with the sharp edges of the plastic, they can cut your skin.

All the holes in the designed parts are for M4 screws. Install the bolts and nuts as shown in the video, but do not over-tighten. The ends of the blades shall be free to articulate 90 degrees. Then install a locknut so there is no chance of them coming loose.

note: Why was it necessary to make these blade terminals? Wasn't it easier to integrate the blades with these parts in one piece?

For several reasons it was designed this way:

-This makes it possible to change the angle of attack of the Blades for different scenarios and experiment for better performance.

-It makes it possible to make optimization changes to the blades from QBlade and would also result in blades compatible with the rest of the assembly. In Qblade you cannot model the Blades, the software creates them but you cannot freely create shapes.

-Also by doing it this way you can take advantage of the maximum height of common Ender 3 type printers.

Put some epoxy glue inside the cavities of the Blades ends, try to cover the inner walls. Insert the Blades as shown in the video, ensuring that they are inserted all the way.

Before the glue dries and immediately after executing this step, place the central HUB with its Blades installed on a horizontal surface, as shown in the video. When turning the Blades you must ensure that the pointed back of each Blade slightly touches the horizontal surface. Once this happens, let the glue dry for at least 5 hours.

Clean the external part of the rotor of the electric motor (generator) with alcohol or another degreaser.Once the rotor is clean and dry, place some epoxy glue on the surface of the rotor as shown in the video. Gently slide the generator into the Hub cavity for this purpose. Let dry for at least 5 hours.

There are two possibilities of Full Bridge Rectifier to use in this project. The first would be to use the circuit that I designed and that you can order directly from PCBWay.

With this Full Bridge Rectifier you will obtain better efficiency since it is based on Schottky diodes with lower conduction losses. However, it makes this project more expensive and requires you to buy the components separately and assemble them. You can order the assembly by https://www.pcbway.com/ and with this LINK.

A simple way to make a three phase full wave rectifier is shown in the picture above.

Another option is to buy a small size three-phase full bridge rectifier like this https://amzn.to/3CepTnI and with it you will get a DC output.

I have decided to test the Windturer-P4 with this last option to compare the results and draw conclusions about the advantages of using Schottky diodes instead of traditional ones.

The electrical connections are very simple and are drawn on the circuit board or body of the Full Bridge Rectifier. In the signs (+ and –) the positive and negative outputs to the NP-F battery pins are obtained and in the signs ~ are the inputs from the generator. Once these connections have been made, this module must be placed inside the cavity of the central body using a double contact tape.

You are probably wondering what is the reason for this Mounting Plate to be a separate piece from the central body. I decided to do it this way for 2 main reasons. The first is that it makes the 3D printing of the central body less complex by requiring fewer supports and second, it can be easily replaced in case of damage. This part in particular is subject to constant friction when installing and uninstalling the battery continuously and that it is a serviceable part, I think that is something positive.

Before performing this step you must first install the battery safety clip. First the spring is placed, then the clip is slid into its cavity and then the Mounting Plate is screwed on. At the end the button of the clip is glued and it is verified that the NP-F battery is held firmly when installed.

The battery contact pins I used in this project were taken from an old video monitor. I have tried to buy them separately but I have not found them in the common stores. I guess I have to search better but if anyone knows where to buy them please let me know.

To complete this step place a small amount of epoxy glue in each hole for this purpose of the central body. Then with a fine nose pliers install each one in its place and then place a battery to fix them in position until the glue dries completely.

It is likely that the part of the pin where the positive and negative wires from the Full Bridge Rectifier are to be soldered has been contaminated with glue. Try to clean this part of the pins before the glue dries. Then lightly file this part of the terminals and apply a little solder. Then solder the cables from the Full Bridge Rectifier in the correct position respecting the polarity of the battery.

Using the bolts declared in the material list, bolt this assembly to the generator. While performing this step, it is recommended to use some type of silicone sealant in the joints to ensure that no water enters the interior cavities of the central body.

The tail tube and associated components should be glued so that the tail is parallel to the lateral plane of the central body. The tail is fixed by 4 screws to the part (L) of the STL files. When folding and unfolding the tail should not interfere with the rest of the assembly.

Install part (I) inside the bearing. Insert this assembly inside the cavity for this purpose of the Central Body. Place the two Retaining Clips in their positions. Glue the plastic handle to the piece (I). This will make it possible to screw this Wind Turbine to a tripod or other device with a ¼ inch male thread.

note: In the video that I showed you above, the depth that I had designed to contain the bearing was incorrect. I noticed this doing the assembly. I decided to glue the bearing to the central body and didn't use the retaining clips :) In the STL file I uploaded for this piece this error is fixed.

I recommend making part (I) in metal at a local workshop or by yourself if you have the skills and tools. Although I don't think it can fail in the short term in plastic material, I do think that in metal it would be much more resistant over time.

Units in mm

In the above video I will show you how you can easily install Windturer and collect free energy. As you can see in the video, the installation was carried out at a low height with respect to the ground and the wind speed was not high. Despite this, Windturer was able to initiate his move!

I coupled the WINDTURER generator to a three-phase electric motor whose RPM was varied with a VFD (Variable Frequency Drive). Using an oscilloscope with a magnetic probe, I accurately detected the rotational frequency and thus the RPM at which the generator was rotating. Measurements of the relationship between open circuit voltage vs. RPM, short-circuit current vs. RPM, as well as charging current for 18650-type lithium batteries in 1S2P and 2S3P configuration, respectively, vs. RPM were made.

A DC Boost-Buck Converter type converter inserted between the generator and the batteries was also used to see if there was an increase in the charging current.

During the experiments and measurements carried out, the following questions were answered

1- What is the electrical resistance value of the motor windings?

2- At how many RPM of generator P4 is 1V (kV value) obtained?

3- What is the maximum short circuit current at the expected RPM in the rotor?

4- What is the best configuration of 18650 batteries (1S or 2S) for the storage of the energy generated in the wind turbine?

5- Does the use of DC-DC converters favor an increase in the charging current of the batteries with this generator and under the expected operating conditions?

The results presented below will influence the design of the Blades and the energy storage system.

The motor windings turned out to be approximately 6.5 Ohms. Recall that this generator was wound with 80 turns per pole in a star-shaped three-phase configuration. The wire gauge used was 0.35mm in diameter. In total there were 12 poles.

The motor turned out to be approximately 60kV, that is, for every 60 turns of the rotor, 1V is obtained. This graph shows the values obtained.

The maximum short circuit current was 1.7 (A) at 888 RPM. The results are shown below.

The charging current values in the single cell configuration are higher than those of 2 cells, however, the energy generated in both cases is very similar at the same RPM. I consider using the configuration of 2 18650 cells in series, since the resistance torque is less in the generator. It also makes it possible to obtain the necessary RPM for the rotor to work with good efficiency, at higher RPM. In addition, the resistance torque is less when the rotor begins to rotate.

The cells that were used are capable of storing 8.14Wh of Electric Energy each. In the case of the 2S3P battery, it has a total of 6 cells, which means that it is a 48.86Wh battery. If we divide this value by 7.4V, which is the nominal voltage value of two 18650 cells in series, we obtain that it is a 6600mAh battery. This Batt at a stable charge rate of 0.6 A would take around 11 hours (estimate) to fully charge. A Samsung Galaxy S22+ battery is 4500mAh, but at 3.7V, which translates to about 16.65Wh. Ignoring the energy losses, we can estimate that in 11 hours, you would be able to charge this phone at least approximately 3 times. About 3 hours and a half approximately for each charge of the phone.

There are several assumptions in this reasoning, but I think it gives an idea. Results may vary and charging current may be higher or lower on average, depending on wind speed.

A DC-DC (Boost-Buck) converter was also used in the experiments. At approximately 300 RPM in the generator, which corresponds to about 5V of voltage obtained, the converter begins to deliver an output at stable voltage. Through two potentiometers this value can be configured up to 35V. It is also possible to set the maximum delivery current of this module up to a maximum of 4A.

However, when the batteries to be charged are connected in both configurations (1S and 2S), it is not capable of regulating the output voltage. The voltage drops to similar values as if this converter were not connected. It seems that a much higher generation power is required to guarantee that this happens. It was concluded that it is better not to use it because there is no benefit in doing so, on the contrary, the efficiency decreases with its use.

From the beginning of this Project I always wanted to store the energy captured in lithium batteries, preferably in 18650 type cells. I consider that these cells are a proven technology, with a high energy density, with a high level of safety, accessible and with a not so high price.

NP-F batteries in their different configurations (330,550,750,970 etc…) have this type of cells inside in a 2S configuration, that is, two cells connected in series. In a previous Log, where the electrical characteristics of the generator were addressed, it was concluded that a 2S configuration with a voltage range of 6V-8.4V is recommended as a storage system and this type of battery has this configuration.

As a reference let's take the Samsung INR18650-25C, its technical data sheet can be consulted here: https://www.powerstream.com/p/INR18650-25R-datasheet.pdf

This type of cells can support a maximum of 4A of recharging current for each cell, this is a higher value than that delivered by the generator of our Portable Wind Turbine. We can extract from them a maximum of 20A of discharge current continuously. They have a capacity of 2450mAh, when discharged at a rate of 10A. After 250 charge and discharge cycles they offer only a 2Wh decrease in capacity from the initial 7.4Wh (4A charge current up to 4.2V and 20A discharge current down to 2.5V). At -20 degrees Celsius and a cycle of 10 A of discharge current and 4 A recharge current, they retain 96 percent of their original capacity.

I don't think that all NP-F battery manufacturers use this type of Samsung cells, although I think that the characteristics of the ones they use should be similar in several respects.

Also, NP-F batteries have a BMS circuit inside them that adds safety and protection functions to the cells. I took the job to disassemble one of these to see its internal structure and analyze its characteristics. Specifically, it was an NP-F970 with a charging circuit and USB output https://amzn.to/3SsQVih *affiliate link*

In the previous photo you can see that this battery is made up of (6)) 18650 cells in 2S3P configuration. The circuit that can be seen above these cells is a BMS (Battery Management System) and the one that can be seen below is the charging circuit, charge level indicator and USB output. You can charge this type of battery with a charger specialized in NP-F batteries or simply through a micro USB connector. You can also power your compatible USB devices directly from this battery.

These batteries also come encapsulated in a plastic case that, while I don't necessarily consider it waterproof, I do consider dust and splash resistant. If any of you know if there is any IP-X certification for this type of battery, could you tell me where to find it?

One of the main functions of the BMS is to prevent overcharging and overdischarging. In addition, these circuits protect against short circuits, limit the maximum charge and discharge current. To test these features, I ran several experiments trying to find answers to the following questions:

- Does this battery have short circuit protection?

- What is the maximum charging current supported?

- What is the maximum load current supported?

- What is the maximum voltage that the BMS allows to the cells?

- What is the minimum voltage that the BMS allows to the cells?

The battery has short circuit protection.

The maximum charging current supported in my experiments was around 4.75A as can be seen in the video. For this, a variable current source was used and the current value was increased until the BMS circuit interrupted the charging process. The experiment was repeated several times and the results were consistent.

To check the maximum discharge current a Load Tester was used like this https://amzn.to/3yd4HNM *affiliate link*

This battery exceeds the 5A discharge current of this module, triggering its overcurrent protections. I tried to use a 55W car bulb and the BMS trips the overcurrent protection. I managed to get the battery to operate at 4.5A continuously with no problems.

Using a variable current source set to deliver a maximum of 1.85A, it was possible to determine that the BMS cuts off the charging process once 8.62V is reached, or approximately 4.3V per cell, which is a bit high for my taste, I would have preferred about 4.15V to promote greater longevity of these cells. In the video you can see this.

In the case of the minimum voltage that the BMS allows, this is 4.7V, about 2.35V per cell, also very low.

I think this manufacturer here has tried to maximize the capacity value over the longevity of this battery.

To conclude, I wish to express that this type of battery is offered as compatible and convenient for the characteristics of our Portable Wind Turbine Winturer-P4.

The Blade P4 is based on the NACA 6409 airfoil.

One of the frequent problems in this type of fixed pitch wind turbines is starting at low RPM. In order for the Blades to do their job efficiently they must operate at relatively high rotational speeds. This type of profile has proven to be effective at low RPM and guarantees higher lift forces during starting. It is also a narrow profile that results in thinner Blades and lower mass which contributes to less material being spent when printing them and lower forces being generated during rotation.

In the image above it can be seen that this profile reaches its maximum Lift coefficient (Cl) around 12 degrees of pitch, however we are interested in the angle for which the relationship between the lift and drag coefficients is maximum. The angle for which this occurs is around 5 degrees. When assembling the propellers with the rest of the set, the Blades must be rotated around this angle. All the simulations were made considering a Turbulent Flow (Reynolds Number 100000). This is due to the typical operating conditions of this wind turbine at very low height from the ground.

In the image you can see the position, chord length, angle of attack and type of profile data obtained after the Betz optimization for a Tip to Speed Ratio of 3. Knowing these values and the type of profile chosen, the Blades can be modeled in the 3D design programs. The Blade was sectioned into 11 parallel planes with a separation distance of 22mm between each. In the Files section, the analysis and design file of the Prototype 4 Blade is included.

QBlade is a public source, cross-platform simulation software for wind turbine Blade design and aerodynamic simulation. https://qblade.org/

This simulation tells us that at wind speeds of 30km/h a maximum generation power of approximately 40W is obtained. At lower speeds and more common at low altitude, say 20 km/h we get about 12W. Although it could be stated that we have designed a 40W Power wind turbine, this statement is really not very transparent and only in exceptional cases could we obtain those values.

In this LLT (Lifting-line theory) simulation, the three-dimensional behavior of the designed Rotor is appreciated when it faces a wind flow of 6m/s (21.6 km/h), obtaining about 26.3W of power. In real conditions and considering the losses, a use of about 12-15W of power is estimated.

The QBlade file can be downloaded directly from the Files section of this Project. You can analyze it carefully from QBlade, you could even make new optimizations and generate your own Blades which you can then export and use with the rest of my STL files. As long as you keep the two 20mm diameter circular profiles in the Blade design, you can experiment as much as you want and the project will still be compatible with your own Blades.

I have been thinking of a simple methodology to correlate the data obtained from the generator, with the behavior of Windturer in normal operating conditions. I have had some accuracy difficulties with certain manual tachometers. I'm still looking for a quality one.

My first idea was to try to place optical sensors and multimeters on the Windturer while it was operating, but placing all that equipment can be cumbersome and time-consuming. Also recording the data can be challenging with the conditions and equipment that I have. Recreating a variable wind, similar to that of Windturer operation under normal conditions, is also another challenge.

The results that I show you below have limitations, but it can be a method of estimating performance.

With the battery installed and under the influence of the wind generated by a fan created with a BLDC drone motor, I was able to generate a wind of around 10.5km/h as seen in the anemometer placed in front of the Windturer.

By shooting with a slow video camera capable of 240 frames per second and using TRACKER software, a free video analysis and modeling tool built on the Open Source Physics (OSP) Java framework, I was able to make certain measurements, in particular the linear speed of the tip of the Blade for a short period of time.

Averaging the values in m/s and converting them to RPM, I was able to conclude that with a value of 10.5 km/h of wind, the rotor rotated at approximately 670 RPM. Correlating this value to those obtained in the generator measurements, it can be inferred that the battery charging current at that time was 0.3A or 300mA. At first glance it might seem like a low value, but keep in mind that 10 km/h of wind is not a high value, and in this case it is very turbulent.

There are complete guides to learn how to use this software and I think it may be appropriate for your measurements. Thanks for following me here, See you!