Got Motor? Got Generator! Can a Motor Act Like a Generator, and How Efficiently?

Overview

Objectives/Goals My objective was to determine if a motor could act like a generator, and its efficiency. Also, I wanted to find out how the efficiency is affected by the rotation speed. My hypothesis was that if I turned the shaft of a DC motor, it would produce voltage, just like a generator. I could then use this voltage to drive another motor. I expected the efficiency to be in the 60-75% range. Methods/Materials I decided to use DC motors from my robotics kit, because they had built-in rotation sensors with 1 degree accuracy. Also, the microcomputer in the kit could be programmed to vary motor speed and rotations using LabView software. I rotated the shaft of a DC motor so that it would generate voltage. This voltage was used to power a 2nd motor. The aim was to measure "rotations in" at the 1st motor (generator) and "rotations out" at the 2nd motor, to determine the efficiency. Two motors were then added: a 3rd motor to act as a rotation sensor, and a 4th motor to control generator speed. "Rotations in" were varied from 1 to 10, and speed was varied from 10% to 100%. "Rotations out" were measured for each step, and then efficiency was calculated. As a further study, the generator voltage was measured to see how it changed with rotation speed. I did research to see which wires in the motor cable powered the motor. Then I stripped the cable and soldered those wires so that I could measure generator voltage with a multimeter. Results My experiments showed that a motor could act like a generator. The measured average efficiency was 67.4%. For the initial rotation, however, efficiency was lower. Efficiency did increase with speed, but below 50% speed, the generator voltage was not enough to drive the motor. Voltage increased linearly with speed. Conclusions/Discussion My results supported my hypothesis, since average efficiency was in the 60-75% range as expected. Efficiency is less than 100% because of mechanical, electrical, and magnetic losses. Using a microcomputer helped me take measurements which were accurate and repeatable. I learned that it is very important to research ways to improve generator efficiency. My report describes many practical uses for "motor-acting-like-generator". I plan to do more experiments to identify other characteristics of my generator.

Awards (1)

• First Place

Competition history

• CSEF 2007 Electronics & Electromagnetics · Entry J0806

Resources

• CSEF project summary ↗

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