Voltage vs. RPMs

By: John Hensley

 

Background Information .:. Method .:. Pictures .:. Graphs .:. Conclusion .:. Bibliography .:. Go Out

 

Background Information

All electricity generating systems that exists consists of something spinning to generate that electricity except solar panels. Hydroelectric dams harness the kinetic energy of falling water by making the water pass through turbines, which makes the turbines spin. Similarly, wind turbines spin from air passing by. There are even turbines in nuclear and coal power plants that spin when steam, heated up from fission or combustion, rises. The faster these things spin the more volts they produce, and in an electric motor, the more volts that are pumped in, the faster the motor should spin, as long as the load is constant. Voltage can be described as the water pressure of electricity. If the water pressure in a pipe increases, the water will come out of the pipe with more force. So if the voltage is increased, the motor has to put in more work faster. For a fixed voltage, the speed of the motor is proportional to the torque load applied to the motor. The motor’s torque is proportional to the applied current, no matter what the voltage. The purpose of this experiment is to find out the relationship between voltage and rotations per minute. I believe that as the voltage increases, the RPM’s will increase as well. This will happen because of the law of conservation of energy.

Method

            To do this I connected a small dc motor to a rotary motion sensor and routed the power supply to the motor through a voltage manipulator. The rotary motion sensor sent the data it collected to a computer which organized the data into two line graphs using Lab Quest Mini and Logger Pro. One graph for velocity in revolutions per second and one graph for angle in revolutions for 300 seconds. I did this three times per voltage and did three voltages. I used the voltage manipulator in the picture to the left to alter the voltage and used the meter to the left to measure voltage and the meter to the right to measure amperes.

Pictures

https://lh5.googleusercontent.com/1uWYLK1k0wM10siff0HO4CYVj_qvQJQPJ82cyEf9gZXDsuswNBtOOF5Mxhbb41u77SSTWXGiOg-y691T3azC_YiL9wyblLxVAXcH_Xs3c7xpfnwXWe0zBCL7SBJGYQeKxA4ioZajhttps://lh3.googleusercontent.com/SwqGRDeDJkXfXgreqkjs03DhDvpVR7m6ZszEHtJCn8Dk8RN5vXudA2BfRBYaUTLbxs6expdGonO_c0R-HuETXQqHMITC6waDO_dzAHPezc22Iak821YtA4UzcZULiKkozI7ef7ze

            The voltmeter has an uncertainty of ±0.1V and the ammeter has an uncertainty of ±0.01A. The actual data collected (velocity) has an uncertainty of about ±3.4 rev/s. This is mostly because of the lack of stability is this setup and the rotary motion sensor’s max velocity (wouldn’t compute velocities over about 24 rev/s).


Graphs   Go Up

Potential @ 0.87 volts                                                                                                                                                                                    Raw Data

                                                                                                                                                                                                Data File: Text1 .:. Text2 .:. Text3 .:. Excel

https://lh5.googleusercontent.com/348frjefMGzrqji2MAy7SySyIU8sJZDJc1_7rv575fYcVOk4AsjQ65E6zAm0jYCbUF6c4So7DvO_LxrPHwOckkcmcEqdSfZbxfIJtIg-oZBffXAUnG7gzO92ZcAtBxMpiR6u-KsB

Potential @ 1.22 volts

https://lh5.googleusercontent.com/UXoehJmpHRjZEvsxf3FkQhtsPCQzNhodul6Rejbk1mIK9c_YUxcNgNImzP2-tsdlDLp40MJ3-TjjO-LSaqiNv1LecIIgHpMzu1BvtEXLHUikwWKHsF_iPieQjk6UJHDMe_qfwqAW

Potential @ 1.2 volts

https://lh5.googleusercontent.com/r7J9JK0Z9LIYfq5srzOHLl2RNChyrEXMT36HcORESiUIEw7bxIhQF36GIgROStyLVhiuB5sMNpdtxe_k-iRF0Ax_zUEE6SF-52kEPlKtx5gm9v10xETKP6EzVbkpTbAOOqJp_b7M

Conclusion

The change in stability from graph one to graph three is due to a change in the set up. I found a much more stable set up after taking the data for graphs one and two and before taking the data for graph one. This could be why it took much less voltage in graph one to get the same trend in velocity as graphs two and three.

            This data did not support my hypothesis, in which the RPM’s would increase as the voltage increased. However if I had either a slower motor or a much better rotary motion sensor I believe my hypothesis would’ve been correct. Using equations from simplemotor.com/calculations/ I found that RPM=(2πτIV)/(60η) where RPM is rotations per minute, τ is torque (Newton-meters), I is current (amperes), V is potential flowing into the motor (volts), and η is efficiency of the motor (no units). If I wanted to do further and better research I would use something more stable than a ring stand, three clamps, a block of wood, and duct tape. I would also try to find a rotary motion sensor that could compute higher velocities.

 

Bibliography/Related Websites   Go Up

https://www.precisionmicrodrives.com/tech-blog/2015/08/03/dc-motor-speed-voltage-and-torque-relationships

 

simplemotor.com/calculations/

http://www.me.umn.edu/courses/me2011/arduino/technotes/dcmotors/motor-tutorial/

https://www.researchgate.net/figure/Graph-of-DC-Voltage-v-s-Speed-in-RPM_fig7_305683710