I am trying to optimize a 24V DC motor ( the permanent magnet field type ) driver using the PWM option in the 89c51RD2. The maximum motor current is 3 Amps. I do not have the value of the winding inductance.

Could anyone tell me as to what is the right PWM frequency for optimum control? I vaguely know that the frequency is kind off related to the time constant of the winding. But I would be glad if anybody can indicate an empirical formula for this.

Idea is to get a good torque characteristic over the full control span. Currently I have tried from about 1Khz to 5 Khz but unable to come to any conclusion in the absence of torque measuring sensors.

Thanks

Raghu