There is virtually only one way to burn a Motor out that is as Gerry says is to pass too much current, with a DC motor that is free to move and no load it should not happen,
If you were to accidentally or on purpose, supply max voltage and the motor is free to move it should rapidly accelerate to a rpm where the back EMF equals the applied voltage, =non, or rather very little current depending on motor inertia etc . i.e. the high current should only occur very briefly at start and not normally enough time to do any damage.
As it accelerates, the current gradually diminishes, now if you lock the armature or place an extremely high load, then this can cause enough current to burn it out.
If your drive is rapidly reversing or is passing any kind of AC, a similar result will occur.
Also it does not seem that your drive current limit is working or adjusted way too high?
If I had to hazard a guess, I would say your armature is getting locked up periodically.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.