I am experiencing serious reduction in torque when using PWM to reduce speed - I'm temporarily resorting to 10Hz, and even then, 50% mark-space gives me (at most) half the torque of fully on. I'm assessing the torque by seeing what weight can be lifted via a worm gear. I've tried up to 1kHz and it gets worse with higher frequencies. Yet supposedly PWM should give the full torque.
What in theory could be causing this? I bumped into something mentioning inductance of windings, but inductance, when driving a 6000 RPM dc motor with 10Hz PWM shouldn't have any effect on torque?
If it is the inductance, then I suppose I'll need to drive the motor with a constant current source, which I suppose will mean driving the motor above its rated voltage for low speeds, assuming it won't die.