Bearing heating open-loop control system to reduce variability in BLDC motor tests

This paper presents an experimental study on the impact of the temperature of motor bearings on test results, in a dynamometer test rig for special motor performance testing. To evaluate the relationship between the variables, an automatic test rig capable of measuring small variations of electric power was developed, adapted with a heating system for the motor bearings. The tests were performed with low-power BLDC motors (electric power of about 10 W) and with grease lubricated metal ball bearings. The results show that raising the operating temperature of the bearings to a point above that they would naturally reach during operation guarantees a fixed condition for the tests, thus reducing the variability of electric power between tests from 0.82% to 0.04%. As a consequence, the use of the temperature control system for the bearings is capable of reducing the power variability within a test, as well as guaranteeing that tests performed in different time instants are under the same condition. Those characteristics enable the possibility of performing consecutive tests and improve the reproducibility of the test results.