DC motor+chopper: armature current falls to zero, speed not! why?
DC motor+chopper: armature current falls to zero, speed not! why?
(OP)
Im using chopper with 50Hz frequency. But my DC-motor has time constant L/R=1ms and thats much smaller then 20ms (chopper period). Because of that, armature motor current isnt constant, and with every "chopp" armature current falls to zero and goes up again (exponential-like)... and so all the time.
But, when chopper works, my motor has smaller speed (proportional to average motor armature voltage) but this speed has CONSTANT VALUE (motor doesnt move with "steps", he moves with CONSTANT speed).
i thought: motor will be moving with (smaller) CONSTANT speed ONLY IF:
(L/R)>(chopper period)=(1/chopper frequency)
I want to know: if armature current falls to zero, why my motor doesnt stop in this moment? what is the condition for stopping the motor? why is motor working with CONSTANT speed with chopper with TOO SMALL frequency?
am i wrong? when not, whats wrong?
thanks
P.S. when i say constant, i think aprox. constant (i cannot see any speed-change "with my own eye")
But, when chopper works, my motor has smaller speed (proportional to average motor armature voltage) but this speed has CONSTANT VALUE (motor doesnt move with "steps", he moves with CONSTANT speed).
i thought: motor will be moving with (smaller) CONSTANT speed ONLY IF:
(L/R)>(chopper period)=(1/chopper frequency)
I want to know: if armature current falls to zero, why my motor doesnt stop in this moment? what is the condition for stopping the motor? why is motor working with CONSTANT speed with chopper with TOO SMALL frequency?
am i wrong? when not, whats wrong?
thanks
P.S. when i say constant, i think aprox. constant (i cannot see any speed-change "with my own eye")





RE: DC motor+chopper: armature current falls to zero, speed not! why?
RE: DC motor+chopper: armature current falls to zero, speed not! why?
The speed is probably varies a little but is smoothed by the inertia of the motor. Your eye is not exact enough.
If your comparing motor speed to armature voltage average, which I assume you measure with a voltmeter, remember that the voltage you measure is CEMF+IR drop of the motor. So your speed with be slower by the factor of the IR drop.
The motor is not an instantaneous device. Neither the current, because of the various motor time constants, nor the speed because of the inertia.