Human Power Generation at the Recreational Sports Facility at UC Berkeley

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Human Power Generation at the Recreational Sports Facility at UC Berkeley Jodi Loo*, Kyle Zampaglione, Eric Mao, Frances Yan, Rajith Jayaratne*, Danny Namkyu Chang, Matthew Roeschke, Dr. Alice Agogino University of California, Berkeley Department of Mechanical Engineering Berkeley, CA, USA rsfenergy@gmail.com**

Introduction As energy usage across the world continues to rise, there is a strong need to develop new methods for energy conservation and power generation, particularly with approaches that have less environmental impacts. There is an untapped potential for harnessing human power at most fitness facilities. The Human Power Generation in Fitness Facilities research project is currently studying the technical feasibility and social benefit of harnessing human power at the University of California, Berkeley Recreational Sports Facility (RSF), which averages over 2,800 patrons per day.

The overall goal of our project is to create a human power generation center at the RSF by retrofitting the elliptical machines such that they can generate usable energy.

Additionally, our project aims to educate members of the RSF on the energy usage of various machines, the potentials of human power, and additional ways to lead more sustainable lifestyles. This goal will be accomplished by posting the energy usage statistics of various machines, installing an interactive display of the energy generation statistics at the RSF, and retrofitting a recumbent bicycle with a pedal-powered display station that teaches users about alternative energy and sustainability as they exercise.

Currently, we have developed a retrofitted prototype of the Precor C546 Elliptical Crosstrainer that acts as a charging station for individuals to plug in their mobile devices or portable media devices and charge them as they exercise. We also plan to add a user interface display in order for the user to track their usage. We have also retrofitted a Tectrix Bike Max-R recumbent stationary bike to also act as a charging station and plan on implementing an interactive display to act as an educational kiosk promoting sustainability.

*Corresponding team members: jodi.loo@berkeley.edu (Jodi Loo), rajithjayaratne@berkeley.edu (Rajith Jayaratne) ** Team e-mail: rsfenergy@gmail.com

Precor C546 Elliptical Crosstrainer Modifications

Figure 1 - Precor C546 Modification Schematic The general modifications to the Precor C546 Self Powering Elliptical Machine will not tamper with the circuitry of the elliptical machine, nor will it include any modification to the motor and display provided by the original manufacturer. The method at which the user operates it will not be changed in any way, nor will there be any movement of parts on the elliptical machine. The parts being added are a Xantrex C40 Charge Controller, its housing and internal components of the housing, and a USB charger.

Xantrex C40 The main modification to the Precor C546 Self Powering Elliptical Machine is directing current from two resistors coils into the Xantrex C40 charge controller. The original design of the Precor Elliptical Machine consists of current being dumped into two 20ohm resistor coils in parallel to create a resistance that the user feels. The Xantrex C40 charge controller, which takes in some current generated from the elliptical machine, is wired in parallel to the two resistor coils. The addition of this unit does not create a drastic change to the resistance that the user feels, nor does it create a sudden surge of resistance as the charge controller operates. There is a safeguard between the power generated by the Precor C546 and the Xantrex in the form of a 20A circuit breaker (PB531-ND ) which will automatically shut down the power generation system if there is too much current generated; this safeguard will only shut down the Xantrex but will keep the actual elliptical machine operating. The output current on the Xantrex goes into charging a 12V rechargeable battery, which is also located in the housing.

Xantrex C40 Housing The resistor coils will remain in the original position, as designated by the manufacturer, and will also be covered by the housing of the original manufacturer. Two wires will run into the housing of the resistor coils from the front of the elliptical machine where they will connect to the Xantrex C40 charge controller, which is located in its housing unit. The wires connecting these

Figure 2 - Component Housing

two components (the resistor coils and the charge controller), will be directed along the underside of the elliptical machine to prevent any hazards to the user. The housing of the Xantrex C40 is a Plexiglas rectangular cube located below the incline ramp of the elliptical so it does not interfere with the usage of the elliptical machine. The housing’s dimensions are measured to have a clearance at the lowest incline setting to prevent collision.

The housing is attached to the elliptical machine using industrial strength Velcro Tape so it can be removed and reattached. The strength of the tape will prevent dislocations due to motion of the elliptical machine under regular operation conditions as well as any tremor caused by earthquakes or collision from external objects. The housing itself also has one side that can be opened to grant access to the actual components inside. The housing is also well covered to prevent any water entering due to spilt drinks and perspiration from the user. All components in the housing are secured in place by Industrial Strength Velcro tape so they can be removed and reattached if necessary.

VInfinity DC-DC Converter LED Light System The V-Infinity DC-DC (102-2314-ND) converter is located inside the Xantrex housing as well. The DC-DC converter is wired in parallel with the Xantrex C40 and is protected by a TVS Diode (SA110CA-ND) for overvoltage protection. The DC-DC converter is used to power two LED light strips (WFLB-xx-DL) that are also located inside the Xantrex C40 housing.

USB Charger Two wires connected to the terminals 12V Battery will run out of the Xantrex Housing where they will be connected to a USB charger, which will be mounted onto the display of the elliptical machine for access by the user.

User Interface Future modifications would include adding a graphic user interface (powered by the rechargeable battery) by mounting an iPad or any other tablet computer onto the front of the elliptical machine, by the actual display of the elliptical machine, to display power production to the user. The goal of such interface would be to notify the user of the current progress of his/her workout in terms of energy saved. As well, further website enhancement would allow a secure, personalized report for every registered user.

Figure 3 - Retrofitted Precor Crosstrainer (Note: Currently the website is integrated with Cosm and the Exposed wiring is for Arduino Data Acquisition Device in order to track the overall testing and will be power being generated at any given time. The graph and concealed in final design to user-friendly data, such as number of light bulbs saved and be implemented) bowls of ramen made with the current power being generated are updated real-time for maximum interactivity. The data is

gathered from the HPG account on Cosm using the REST API, and cosm.js, which allows for us to post GET requests for the current power and voltage being generated.

From there, we embed the graph on our website and use a script to convert the values to user-friendly units as well as pull from the JSON feed to relay the data back to the site.

Arduino Data Acquisition Device In order to track power production, we are using the Arduino Uno R3 microcontroller with an Arduino Wi-Fi shield mounted on top and a 30A Hall Effect current sensor (ACS714 Current Sensor Board).

These components allow us to connect to the campus Wi-Fi network and broadcast in real time the power production to our servers using Cosm’s and Arduino’s APIs. Our data will be hosted on Cosm, which is an online platform that allows us to host our data and Figure 4 - Arduino Data provides customizable visuals for that data. Now that Acquisition Device our data is hosted in the cloud, we are able to query the data from our web services and present the data in any form that we see fit. The Arduino setup will be located next to the Xantrex charger controller within the housing. The Arduino itself measures 2.7in x 2.1in x 1.5in (l x w x h) so it is quite compact. It will be wired in series with the positive output of the charge controller in order to measure the current flowing into the batteries. Power is supplied into the Arduino data acquisition device from the 12V batteries which are located within the housing already. Using the Arduino microcontroller gives us the flexibility and extensibility that other power tracking devices don’t provide.

Tectrix Bike Max-R Modifications

Figure 5 - Tectrix Max-R Modifications Schematic

Figure 6 - Tectrix Bike Max-R

This recumbent bicycle is selfcontained; it does not have to be plugged into the wall to function its display.

After research, it was decided that the system would have four basic components: a generator, a DC charge controller, a lead acid battery, and a hub for transferring charge to standard adapters. The choice of generator was arbitrary; a basic high torque DC motor was used as a generator.

Rectifying Diode Between the DC motor and charge controller, a rectifying blocking diode was inserted.

Later in the process it was observed that the charge controller would dump excess power back into the motor, thus turning it the opposite direction and drawing high amperage. To remedy this problem, a diode used for wind turbines was placed into the circuit.

Xantrex C35 Charge Controller The DC controller is a complex electrical component. The controller used was a Xantrex C35 DC controller for use with solar, wind, and hydropower. The controller takes in a wide range of voltages and currents and converts them to a necessary output for charging different types of batteries. The controller has dials that allow the user to choose the voltages used for different stages of battery charging. The controller also has feedback that allows it to stop charging at a specified potential across the battery; a useful safety feature for an unregulated system like this.

12V Lead Acid Battery The battery chosen for this system was a 12V lead acid battery. Aside from high storage capacity, lead acid batteries are known for their flexible input ranges of charging in both current and voltage. These batteries can also be stored for long periods of time without

needing to be recharged; the slow discharge rate creates a lower service system. Finally, lead acid batteries can be cycled many times in charging without reducing their capacity.

The charging hub used in this prototype was not a universal one. For simplicity and cost, a generic Apple charger was used. These simple chargers take in 12V DC and convert it to the 5V 1A needed to charge apple devices.

LED Display The LED display system consists of rows of LEDs along the bottom edges of the drive unit and up the length of the handlebar pillar. The LEDs serve as visual feedback to the user of how much power he or she is generating. As the user pedals faster, the LEDs brighten. This simple system shows to the user real-time results of their working out and bathes the exercise machine in a bright blue aurora. The LED lighting system operates on a similar system to the charging system. The major difference between these systems is the lack of battery in the LED system. The Xantrex C-35 in the charging system requires a battery to start the DC/DC conversion process. The LED system uses a much smaller Orion 24/12-5 DC/DC converter.

Charge Switch A switch was added to allow the user to turn the charging system on and off. With the switch off, the user can simply observe the LEDs variable brightness. When the switch is turned on, the battery connection to the Xantrex is completed. The user can now charge his or her phone from the Apple charging attachment. While the user charges his or her phone, the LEDs still maintain their variable brightness. The switch is important because it prevents the Xantrex from pulling charge from the battery while the bike is not in use.

Future Additions In the future, we plan on implementing a universal charger to charge phones with mini USB connections and Apple connections. In addition, we plan on adding a user interface display that will have facts and applications about sustainability and the Human Powered Generation project to promote environmental consciousness.

Figure 7 - Retrofitted Tectrix Bike Max-R

Acknowledgments We would like to acknowledge our sponsors The Green Initiative Fund and Community Assessment of Renewable Energy and Sustainability (CARES) for funding this project in addition to the project’s advisors Prof. Alice Agogino and Prof. George Anwar from the Mechanical Engineering department at the University of California, Berkeley. We thank the Spring 2013 Human Power Gym class project groups of ME110 and ME290H for their help in designing a user interface prototype. We also thank Michael Neuwald, Devin Wicks, and Mike Weinberger at the RSF for their support throughout this process.

Appendix Figure A1 - Xantrex C40 Charge Controller Data Sheet

Figure A2 - VInfinity DC-DC Converter Data Sheet

Figure A3 - Orion DC-DC Converter Data Sheet