Piezoelectric Wheel Battery Charger For Sustainable Power Generation

Project Activities

Title: Piezoelectric wheel battery charger

Power generation is one of the most crucial elements in helping 21st century society and economic system. World energy consumption is about 23,000 TWhr of electricity annually and the number increases by the day. Much of this energy continues to be generated with risky and old technologies characterized by burning of fossil fuels. Continued reliance on fossil fuels impacts catastrophically on the earth and humanity as a whole, for instance the impacts of global warming. The mitigation of this hazard can be done through the use of clean, innovative techniques of electricity generation. In the process of electricity generation, Faraday’s law of magnetic induction is one process that has been applied in many occasions. The operation of Faraday’s law is illustrated in figure 1.1 below?. As the magnet is rotated, a time-varying magnetic field is applied to the coil inducing a voltage across the coil. This technique can also be reversed with the coil varying and the magnet being stationary. 

 

Fig 1.1: Faraday’s electromagnetic induction law

If our energy consumption continues this reliance on fossil fuels, at this rate without us looking for more aggressive and consumer friendly alternate forms of energy, such as our device, our planet will face serious environmental impacts. You can see from Figure 1-2 that most of the energy consumed in 2013 is produced with the use of fossil fuels, while a very small portion is created from renewable or nuclear options. The current reliance on fossil fuels, as shown in Figure 1-2, indicates a daunting task. The technology that we are trying to develop, and many other forms of energy-harvesting technologies, are trying to increase the share of renewables to reduce greenhouse gases produced by energy production. This technology could also be implemented in rural areas around the world. It is estimated that 1.2 billion people today do not have access to electricity. A simple technology like this could allow for some devices to be powered on command without the need for an expensive electrical grid or power plant.

If our energy generation keeps this over reliance on fossil fuels, at this rate without us looking for extra competitive and environmental friendly trade ways of energy generation for our daily uses including for our gadgets like mobile phones, our planet will face extreme environmental impacts. It is evident from figure 1.2 that power consumption according to the data of 2013 was generated from fossil fuels, at the same time as a totally small portion generated from renewable or nuclear options. The modern-day dependence on fossil fuels, as illustrated in figure 1.2, exhibits a daunting task. The technology being developed currently, and lots of other kinds of power-harvesting technologies, are seeking to raise the percentage of renewables to reduce emission of greenhouse gases in the name of energy generation. This generation may also be applied in rural regions across the globe. Data show that over 1.2 billion people in the world currently lack electricity access. A simple power generation technology like the Piezoelectric wheel battery charger will allow for some gadgets to be powered on command without the need for a costly power plant and electrical grid.

Status of Power Generation Today

 

Figure 1.2: energy consumption by the world (2013)

Global power generation has been on the upward trend over the last three decades. In 1985, the world was using just under 10,000 TWhr. In the year 2014, the global power generation was over 23,000 TWhr of electricity. The trends for consumption of electricity across the globe is graphically illustrated in figure 2.1. 

 

Figure 2.1: electricity consumption over the last three decades

The interesting thing about this graph is the relatively constant trend of generation of electricity in Europe and North America. Besides, the huge increase in electricity production in the Asia Pacific indicates the economic growth displayed by the Far East Asian countries like China, Japan, South Korea, to mention but a few. The worrying truth about this trend is that China’s energy generation majorly is connected to non-renewable sources such as coal and crude oil. The entire global usage of coal is illustrated in Figure 2.2. As shown, China is using 2.8 Million tons of oil equivalent (Mtoe) whereas the rest of the world uses 1.0 Mtoe with many countries like Germany, UK and France shutting down their coal plants.  

 

Figure 2.2: world coal consumption

Methods of electricity generation depend on the fuel being used. Fossil fuel electricity generation apply natural gas, coal, and oil and the method is through burning the fuel, and turning a steam turbine generator. But other forms of electricity generation also exist that do not involve burning fossil fuels. Some of these alternatives that are known as the non-conventional methods include solar, wind, hydroelectric, nuclear and geothermal, biofuel amongst others.

Solar electricity generation utilizes the sun’s light waves to generate an electric current. Wind and hydroelectric both use turbines to generate electricity through the wind or flowing water respectively. Nuclear power is similar to how fossil fuels generate electricity. Water is turned into steam to power a turbine but the heating process for nuclear is free from CO2 release. The same can be said for geothermal and biofuel generation technique that also utilize the steam turbine for electricity generation. These are the main forms of large scale energy production around the world with all types of forms being integrated into the grid.

Small scale electricity generation has also become a large industry. One of these methods is using a crankshaft to turn a magnet through a coil of wire to induce a voltage. This same technique is used in many applications including a shake flashlight that utilizes a magnetic and a coil to generate a voltage. As the magnetic moves back and forth through the coil, an alternating current can be generated. Small-scale solar has also been increasingly used on the roofs of houses and business, but also in the realm of electricity generation for personal devices.  

Methods of Electricity Generation

The goal of this project is to design an environmentally friendly and user friendly portable rechargeable battery capable of interfacing with small electronic devices, such as cell phones, mp3 players and tablets, via standard USB connections. The design of this project will be to build the most user friendly and intuitive device to minimize possible user errors and enable its use as easy as ABC. The Piezoelectric wheel, utilizes Faraday’s Law of Induction which states that by passing a magnet through a coil of wire, a small electrical current is created and then stored then used to power the USB device. The purpose here is to provide an innovative, user friendly, environmentally safe way to provide battery power for various devices.  

This project is centered around the design of a self-sustaining battery charging system that can be implemented on a wide range of bicycles. The system must be durable due to the widely-varying weather conditions that this device will be subjected to. This device must be able to provide enough current drive to power the internal circuitry of the system as well as provide current to the battery for charging purposes. In addition to providing a usable output current, the device must also be capable of charging USB powered electronics via the output USB hub located on the battery and power the lighting system on the bike.

The primary constraint for this system is the physical size and weight. The system must be portable and light so attachment to the bike frame is simple. This presents some difficulties due to the environment this device will be used. It will be exposed to a variety of weather conditions, and will need to be weatherproof to protect the sensitive electronics inside the package. In addition to these constraints, other difficulties will come from the design process where optimization is critical. To be competitive, minimum hardware is critical to lower overall cost.  

To develop a piezoelectric battery charger.

• To find out the possible sources of renewable energy
• To find ways of tapping the untapped sources
• Use the technology to convert mechanical rotation and vibration to electrical energy
• To transform the electrical energy to a form that can be used by gadgets like mobile phones

Figure 3.1: block diagram of a high level system

The block diagram shown in Figure 3-1 describes the input and output of the proposed Piezoelectric wheel and Battery System. The input to the kinetic energy harvesting device will be created by the bike user physically pedaling. This will result in a fluctuating sinusoidal wave. The wave then needs to be passed through a rectifier to make the signal a constant DC voltage. A constant DC voltage is needed to charge the battery and output from the USB. Since the required output needs to work with a USB connection the output voltage must be 5V. This will require the boosting of the output of rectifier which can be achieved using a boost converter. That boosted voltage will then be stored in a battery for future use via the USB output connection.  

Small Scale Electricity Generation

The completed system will have two available inputs. The main input is the alternating current signal produced from the kinetic energy harvesting block. The kinetic energy will be generated by the user through pedaling a bicycle or accelerating in a car. This will provide the power from the rest of the circuit to operate. A secondary input can be found on the removable battery. This battery can be recharged through a MicroUSB port when the battery is not present in the bicycle system. There are three outputs of the system. The first output is from the battery to the USB port where electronic devices can be charged. Another output powers the on-board lighting system. Since the lights will primarily be used at night time, there will be a switch controlling whether the lights are on or not. This gives the user flexibility when using the system. The last output is to the battery itself. If the user is not using the lighting system and not charging an external USB powered device, the system will only charge the battery for use at a later time. This gives the system an extraordinary amount of flexibility as the battery can be used to power the lights when riding alone isn’t enough. Table 3.1 shows each design requirement as well as the engineering specification that this design will follow. The requirements for this device is developed with careful consideration of the need out there and how this design could be made as robust as possible. Table 3.2 indicates the functional inputs and outputs of the system.  

Requirement	Engineering Specifications	Justification
Compact for ease of use	Small and portable  ? Box containing circuitry (7.5 inch. tall, 3 inch. wide, 1.2 inch. deep) ? Average initial setup time should not exceed 30 minutes	Based on competitor device packaging size and estimated installation times
Able to withstand outdoor weather conditions	Weatherproof casing and hermetic sealing	Product needs to be protected from weather and other possible external damage
Universally configurable for different bike frames	Attachment system based on either clips or magnet	Must be able to be moved from one bike to another,
Output provides 500mA of current	Regulated 5V USB output and capable of charging a 3.7V Lithium Ion Battery	Able to charge using USB connection

Table 3.1: engineering specifications and requirements

Input/Output	Type	Description
Input	Power	Kinetic Energy from the rotation of the wheel will generate an alternating current.
Input	MicroUSB Power	Power input to the battery from an external source.
Output	USB	Connection from battery to external USB-powered device.
Output	LED	Connection to front and rear LEDs
Output	Battery	Connection for charging battery through kinetic energy conversion.

Table 3.2: top level functionality of the piezoelectric wheel battery charger

The first step of this design was to figure out the correct chips to harvest energy at low voltages. After researching the different techniques for energy harvesting, piezoelectric energy harvesting was the method chosen. This method allows for mechanical kinetic energy to be converted into electrical energy through electromagnetic induction. It was noticed that the only chips that we were able to use were from the IC distributor Linear Technology. Specifically, LTC3588-1/2, were the chips chosen because they contain an internal full wave bridge rectifier. I decided that I wanted the chips to have an internal rectifier as opposed to making one myself to allow me to keep the size of my overall package down. The first chip, LTC3588-2, would have the best chip to use due to its selectable output voltage of 5V which is needed for the USB output. However, it required an input voltage in the 14-20V range. The second chip, LTC3588-1, could also be used due to its selectable output voltage of 2.5V which we would have needed to double. This chip’s input voltage range was a bit larger from 2.7-20V which gave me more flexibility if my piezoelectric device outputted a low voltage.

Project Goals and Constraints

An important factor in the design phase was to make the system compact. The system diagram shown in Figure 4-1 indicates the different subsystems used. The human user is the input to the piezoelectric device, once the mechanical energy has been converted to electrical energy, the device is inputted to the LTC3588-1 demo board. The utilization of this device reduced the component from two independent integrated circuits into one package. The output of the board is varying output at 1.8, 2.5, 3.3 or 3.6V.  

Figure 4.3: Simulated 5V Output of (LTC3588-2) 

The next step was to simulate these two chips using LTspice to see the theoretical minimum input voltage required for turn on. Due to the use of an LT chip it was possible to use the Test Fixture feature on LTspice to test the chip. As shown in Figure 4.2 minimum required input voltage for the LTC3588-2 is 17V and Figure 4.3 shows the desired 5V output. Figure 4.4 shows the minimum required input voltage for the LTC3588-1 is 9V and Figure 4.5 shows the desired 2.5V output.

Thus, it is prudent to order both chips just in case the input voltage from the piezoelectric device wasn’t as high as expected. When the chips are ordered, the packages of the integrated circuits must be MSOP-10. The ICs are very hard to deal with due to the small package size, flat pins and a ground plane on the bottom of the chip that is inaccessible to the dual inline package adapter. This can be remedied by ordering the demo board version of the LTC3588-1.  

Figure 4.5: Simulated 2.5V Output (LTC3588-1)

Once the energy harvesting circuitry is designed and simulated, the next step is to design the piezoelectric device that will convert mechanical energy into electrical energy. The preliminary design uses Faraday’s law of induction. This law states that if a time-varying magnetic field is applied to a coil of wire, an electromotive force (EMF) will be produced across the coil. The faster the magnetic field changes through the coil, the higher the EMF that will produced. The EMF can also be increased by increasing the number of coils that the magnet passes through. This limits the design variables to two.

Since the time-varying magnetic field will change at a very high number of rates, changing the number of coils is the only real choice for the design. The next step in this device is the choice of magnet. Since the intensity of the magnetic field is a determiner for the output EMF, neodymium magnet is chosen. The dimensions of the magnet is also given by the casing for the coil and magnet. The inner diameter of the housing for the magnet is 1 inches. This gives an upper limit for the diameter of the magnet. With this in mind, a neodymium magnet with 36pounds of pull and having a diameter of ¾inches and 1 inches long. This will allow the magnet to fit inside the housing as well as slide back and forth with relative ease. The final device is shown in Figure 4.6.

Project Objectives

Figure 4.6: Piezoelectric Device 

Figure 4.7 shows the individual components of the device. The device consists of the following parts: plastic cap with rubber stopper, tube with coil, and neodymium magnet. The plastic cap is used to contain the neodymium magnet inside the plastic tube during testing. During the design process it was realized that the magnet would occasionally get stuck in the cap. To prevent this it is necessary to glue rubber stoppers inside the cap to not only prevent the magnet getting stuck but to also increase the speed that the magnet would move through the coil. The coil is then made by putting two pieces of tape one inch apart in the center of the tube and then looping over 2000 coils to produce the desired voltage.

Figure 4.7: Individual Components of Piezoelectric Device

Once the design is completed and implemented, it is necessary to do a test. Firstly, the testing of the device should be done with no load. Figures 5.1 and 5.2 show the two different no load tests. Figure 5.1 was captured when the device was shaken with a constant frequency to get an indication of the output voltage. This output ranged from 1821 Vpp. on the other hand, figure 5.2 was captured when the device was shaken much more vigorously to simulate the rotation of a wheel. The output with the increased shake speed resulted in an increased voltage range of 30-36Vpp.

Next the testing of the LTC3588-1 demo board followed with a function generator and no load. Figure 5.3 shows the 2.5V output option from the demo board. The input sine wave was tuned to 1.5Hz because in previous test trials, the human shaking of the device was at a rate of about 1-2 cycles per second.

 

Figure 5.3: Chip Output 2.5V 

Once the demo board was properly initiated and tested to confirm it was functioning properly, a resistive load was applied to the output. Figure 5.4 below shows the output with a 100Ω resistive load. This capture shows the complete cycle of the magnet passing in and out of the coil in the device. As the magnet passes through, the voltage is spiked above the threshold of the LTC3588-1 where it is rectified and then regulated to output around 2.5V. Figure 5.5

shows the similar discharge but with a load of 1kΩ. The discharge is caused by the large capacitance at the output of the demo board.  

System Input and Output

Figure 5.4: 100ohm load output

 

Figure 5.5: 1kiloohm load output

The next test setup is to test the actual device on a rotating bike wheel to mimic real conditions. The issue that would arise is the magnet fall through the tubing as the wheel rotates and become attracted to the metal spokes around it. The pull strength of the magnet is stronger than the force of gravity causing the magnet to not flow through the coil in turn not generating voltage. This setup can be seen in Figure 5.6 with the piezoelectric device positioned between the spokes of the rim.

 

Figure 5.6: bicycle wheel set up for test

Since the bike rims’ spokes are magnetized, the neodymium magnet would interact with the spokes, a different test setup needs to be designed. As shown in Figure 5.7, the output from the system is set at 2.5V. The output is then connected to a resistor and LED in series. As the magnet passes through the coil of the device, the rectifier sets the output voltage to 2.5V. In turn, current would pass through the load causing the LED to turn as seen in Figure 5.8.

Figure 5.7: schematic for test

 

 Figure 5-8: LED Load Test Setup

Table 5.1 summarizes the important parameters for both the device and the LTC3588-1 Demo Board. As shown in the table the device outputs 18-30Vpp, a high enough voltage to be input into the next part of the system. Then it was verified that the next part of the system, the LTC3588-1 Demo Board, had an input range of 2.6-20V and outputs a range of 1.8-3.6V. The next step is to double the voltage in order to be used with a USB port.

Piezoelectric Device	LTC3588-1 Demo Board
Input	Output	Frequency	Input	Output	Frequency
Kinetic Energy	18-30 Vpp	1-5Hz	2.6-20V	1.8-3.6V	DC

Table 5.1: Component Parameters

Table 5-2 shows a comparison of the original design requirements and what the final design would end up being. The first requirement, compact for ease of use, is achieved; however, in the original design it was necessary to make a box containing all the circuitry. But as the design progressed there was less circuitry than anticipated which allows for not using a box in the final design. The last requirement, output provides 500mA of current, was also achieved..

Requirement	Engineering Specifications	Final Design
Compact for ease of use	Small and portable  ? Box containing circuitry (7.5 inch. tall, 3 inch. wide, 1.2 inch. deep) ? Average initial setup time should not exceed 30 minutes	Piezoelectric  Device Dimensions- 7.5”  Demo Board Dimensions- 2.5”x2.5”
Able to withstand outdoor weather conditions	Weatherproof casing and hermetic sealing	No longer required
Universally configurable for different bike frames	Attachment system based on either clips or magnet	Does not work on bike wheels
Output provides 500mA of current	Regulated 5V USB output and capable of charging a 3.7V Lithium Ion Battery	2.5V output, 50mA Max

Table 5.2: Comparison of Original Design Requirements and Final Design

If developed, this device can create jobs for engineers, manufacturers, marketers, and sales personnel. Profits will me made and price savings will be transferred to the consumer via their energy bills. This device uses such material as silicon, plastic, a magnet, and a battery. A large portion of the cost will come from the individual component prices. The projected payback in the long run will be seen by the consumer in the form of lower energy bills.

Item	Quantity	Company	Cost
Neodymium Magnet	1	Amazon	$11
Magnet Wire	1	Amazon	$18
LTC3588-1 Demo Board	1	Amazon	$200
Lithium Ion Battery	1	Amazon	$4
USB Connector	1	Amazon	$0.50

Table b.1: total estimated cost

Primary and Secondary Inputs

It is evident from the Table b.1 above that the total estimated costs for this device if implemented will be around $33.0 with a retail price between $35-$50.

If the production of this device would be rolled out on a large scale, the cost per component would be less due to pricing from manufacturers generally decreases with the number of products ordered. The approximated cost of production can be seen in Table b.2 below.

Manufacturing Estimation	Estimated Cost
Estimated Purchase price for each device	$30
Estimated number of devices to be sold per year	1,000
Estimated Manufacturing cost for each device	$12
Estimated Profit per year	$18,000

Table b-2: long-term analysis

This device has beneficial impacts onto the environment. It taps energy that would otherwise be lost and transforms it into usable electric energy. The electric energy realized from the device is clean and renewable. The electricity that is used from this system to charge devices such as cell phones will decrease the demand for electricity supplied from the power grid, and in turn reduce carbon emissions from power plants that normally would have to supply this electricity and transmit it across longer distances of power lines just to reach the final consumer. All manufacturing processes, require certain materials as prerequisites for production. In this process, the fabrication of materials such as silicon, printed circuit boards and other materials will require energy.  

This design incorporates some pre-fabricated components such as ICs. The cost and manufacturability of these components will have a direct effect on the consumer if rolled out for commercial purposes. The availability of these products will partially determine the rate and longevity of the manufactured product. The manufacturability also relates to the optimization of the design. If the design is not optimized, the product will require more components which will cause the manufacturing process to be more costly and complicated.  

This system aims at building an environmentally conscious gadget which means the device must be long lasting and durable. Since manufacturing is an energy intensive process and involves generation of a lot of wastes, this gadget was designed to last longer to reduce the environmental impacts of the manufacturing processes. A major constraint to increasing the device’s lifespan is weather conditions that this device will be subjected to throughout its lifespan.

The major ethical issues for this product come from the sustainability of the product itself. Some people design their products to have a limited lifespan to increase the sales of a product, but this design is long lasting since its aim is not primarily to make fraudulent profits but to solve the problem of energy crisis. One design consideration taken to improve the durability of this device is to use an hermetic seal to block water and moisture from entering the gadget.

System Outputs

The rechargeable system has very little health concerns associated with it. The power generated is of low voltage and low power, thus poses no harm of electrocution. The major safety hazard connected to this device is the hazard that comes with riding a bicycle, and not the device itself. On the contrary, this device produces clean, sustainable energy instead of having electricity generated from a coal plant that pollutes the atmosphere and is known to cause respiratory disorders, heart attacks and even death.

Over the last decade, there has been a dynamic change from the usual conventional energy generations methods to the non conventional ones that are renewable in nature. This technology is just a continuation of this trend. The clean electricity that is generated from this device may prevent pollution coming from coal power plants to enter the atmosphere because the electricity no longer needs to be produced for that device. It may seem insignificant, but if thousands of these devices were implemented, the power grid would have to produce a lot less power reducing the overall carbon emissions emitted from these plants.

The development of the piezoelectric rechargeable battery gadget enabled the examination of some new strategies regarding power electronics. Since the device input is based on a wheel rotating the input is an AC signal, the device circuitry will require the use of a rectifier to convert the output from AC voltage to DC voltage. In the field of power electronics rectifiers are used to transform alternating current (AC), which reverses direction periodically, to direct current (DC), which does not periodically reverse direction. DC-DC converter is another power electronic device that was applied in this project. The DC-DC converter was needed to boost the output of the rectifier to allow for storage in a battery for a later use via USB connection.

Conclusion  

The project design, layout and specifications ultimately met a number of the necessities and needs that were defined earlier on. The magnet’s magnetic pull proved to be more potent than the gravitational pull. This will be remedied through the use of a distinct kind of tubing that insulates the magnetic field from the rim’s steel spokes. This would allow the magnet to slide back and forth as the wheel rotated. Another issue with this design was the ability to attach the entire system to the wheel. Since the wheel is constantly rotating, the entire system has to be contained on the wheel so the reference frame stays constant. As a result, the ability to charge a phone while the bike wheel turns proved to be difficult. Another complication was the coefficient of friction of the tubing. The magnet would slide slowly at times causing the voltage at the demo board to be too low to rectify properly rendering the system non-functional. Next, the final design could not be outputted via USB since the system currently can output a voltage of 3.6V whereas USB requires 5V to operate properly. There exist two ways of curbing the problem. The first would be to get the LTC3588-2 which opts an output range to 5V. The other possibility would be to use a DC-DC boost converter. The LTC3588-2 demo board would be the best option because it would save space on the wheel instead of having an additional integrated circuit for the boost converter. The finished design would drive a maximum current of 50mA and operates solely from human kinetic energy which is clean, green and environmental friendly.

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