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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Failure mode of a small PM motor
My students are having the following experience with small permanent-magnet
DC motors: After some kind of misfortune (overload? nobody knows), the motor starts drawing much more current than it should. For example, a damaged motor will draw 1 amp at 3 volts, while the undamaged one will draw only 200 mA at that voltage. (Normal voltage is much higher, about 10 V.) Both motors turn easily; the damaged one seems to run fine except for requiring excessive current; and both have a resistance of about 1.5 ohms measured with an ohmmeter. This has happened to several motors. Are the permanent magnets getting demagnetized? How? Or what else could be going on? My electronics background is analog and digital but not much about motors! Many thanks, Michael A. Covington - Artificial Intelligence Ctr - University of Georgia "In the core C# language it is simply not possible to have an uninitialized variable, a 'dangling' pointer, or an expression that indexes an array beyond its bounds. Whole categories of bugs that routinely plague C and C++ programs are thus eliminated." - A. Hejlsberg, The C# Programming Language |
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