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