Human Powered Gym: Elliptical Team Fall 2012 Report Jodi Loo Eric Mao Rajith Jayaratne Steven Frangos Danny Namkyu Chang Dr. Alice Agogino Dr. George Anwar
Human Power Generation: Elliptical Team Fall 2012 Semester Report Jodi Loo, Eric Mao, Rajith Jayaratne, Steven Frangos, Danny Namkyu Chang Introduction Continuing from the previous Spring 2012 semester, the elliptical team was in the process of implementing the retrofit design involving the Vinfinity DC-‐DC converter and Enphase microinverter. However, while testing during the summer and beginning of the fall semester, we faced an impedance problem with the designed system, which resulted in a mid-‐semester redesign. At the end of the semester, we successfully demonstrated a new design system similar to that of a solar panel charging station. Testing During the summer, we created a test setup in preparation of connecting the elliptical machine and retrofit implementation to a grid system in the RSF. We created a circuit panel configuration with circuit safety components. We were almost ready to test the new system after finding out that the Vinfinity DC-‐DC converter successfully put out 28V using the elliptical as an input. However, when connecting the Enphase as the output load of the DC-‐DC converter, we found that there was not enough powerd to turn on the enphase. We came to this conclusion after some testing using a 20V 10A power supply. We could turn on and drive the Enphase with the power supply which was demonstrated by 5 flashing green lights on the Enphase followed by a continuous red flashing light. After talking to Enphase representatives, this light pattern indicates that the Enphase is ready to output 208V AC when connected to the grid. However, when connecting the Enphase to the output of the DC-‐DC converter (which is driven by the elliptical), the enphase did not turn on. We tried to isolate this problem by testing each component with the power supply and concluded that there was not enough current being drawn by the DC-‐DC converter from the elliptical to supply enough power for the enphase microinverter. It was concluded that there was an impedance matching issue. The following diagrams summarize the tests we performed. 5<!'
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Figure 1 – Using a 23V power supply to the DC-‐DC and microinverter setup. This demonstrates that at this voltage, the DC-‐DC pulls 50mA and Enphase pulls 11mA to turn on.
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Figure 2 – Using the 23V power supply and replacing the enphase with a 10-‐ ohm resistor, we see that the DC-‐DC pulls more current (4.4A) than with the enphase microinverter. 89!''
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Figure 3 – Using the elliptical as the power source (instead of the power supply) and using resistance level 10 at a constant 100 strides per minute which generates 30V, the DC-‐DC and enphase setup pulls only 14mA. The enphase does not turn on. We suspect this is because there is not enough power in this setup. Redesign We could either research and test different DC-‐DC converters in hopes of finding one that would work with the Enphase and solve the impedance matching problem, or we could start with a new approach to the design of the system. We essentially wanted to keep the Enphase microinverter in our system because of its built-‐in capability to track each elliptical’s power output through an EMU unit. Therefore, we chose to redesign the system by implementing a battery system. The elliptical output would charge rechargeable batteries, which would supply power to the Enphase. We accomplished this by using a charge controller that monitors and directs how much power would be going towards charging the batteries, and two
12V batteries in series to produce 24V that would be the input to the Enphase. We purchased the Xantrex C35 because of its wide voltage range input (0-‐55V) and 2 12V lead acid batteries. This replaced the DC-‐DC converter in our system and therefore avoided the issue of impedance matching. The following diagram demonstrates the charge controller and battery setup we implemented.
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Figure 4 – Charge Controller Setup We found that the elliptical was able to charge the batteries by measuring a net current out of the charge controller and directed towards the batteries. We hope that this new redesign will allow for a seamless implementation for producing power to a grid system. Implementation The goal of the elliptical team in Human Power Generation is two fold: increase use of ellipticals which generate electricity and decrease usage of treadmill machines which consume large amounts of electricity. From our research we believe this can lead to a 5% decrease in the Recreational Sports Facility’s (RSF) electricity consumption. To generate electricity from the elliptical machines we are using two main components -‐-‐ a DC/DC converter to convert the varying DC voltage to a constant output and an AC/DC microinverter which will be connected back to the grid. To accomplish the second goal of the HPG team, increasing use of ellipticals, we are building a website to uncover the data about user power generation. Gym goers who use elliptical machines would be able to track how much electricity they are producing over time and also compete for prizes by generating the most electricity. We predict that this gamification of elliptical usage will drive up usage and generate even more electricity. Future Work Although we would like to eventually design this retrofit to be able to produce power back to the grid, we acknowledge the fact that the system to grid is a complicated power system and will take more time to solve. For now, our system demonstrates that we can produce power and our short-‐term goal is to implement
this system in a micro-‐grid or a charge station system. Through this, we hope to implement this in the RSF and also promote this system as an educational opportunity for gym users while promoting steps towards a sustainable gym, which includes lessening the use of treadmills, as treadmills are one of the main consumers of power in a gym. Acknowledgements We would like to thank Professor Alice Agogino and Professor George Anwar for their advisement and support regarding this project. In addition, we thank Tom Clark from the Mechanical Engineering department for his help and knowledge in electrical systems as well as Professor Pister, Professor Sanders, and Professor Alon in the Electrical Engineering department for their knowledge and advice on debugging the power system. Lastly, we thank The Green Initiative Fund for continuing to provide funds for this project.
Appendix
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Figure A – Block Diagram of Precor EFX546 Elliptical Circuit Board
Figure B – Xantrax C35 Datasheet
Figure C – Enphase M215 Datasheet