H-Bridge frequency?

[Robotics Guy]

I'm trying to use an H-Bridge (similar to the L293D) and I want to use a PWM signal to control the speed of a motor. My question is, what should the frequency of the PWM signal be?

[Webbot]

Above 10kHz is best - otherwise you may get motor hum

[Soeren]

Hi,

I have to disagree. Hum/whine is a minor thing compared to efficiency IMO and this will depend on the motor, so takes some experimenting. Anyway, to make the PWM frequency inaudible to all, it would have to be at least 25kHz.

Good quality motors should be better wound and sometimes lacquer dipped, which will more or less cure the whining. If the motor comes apart for service, it's not hard to apply some lacquer (of the right type) yourself.

[Webbot]

Hi,

I have to disagree. Hum/whine is a minor thing compared to efficiency IMO and this will depend on the motor, so takes some experimenting. Anyway, to make the PWM frequency inaudible to all, it would have to be at least 25kHz.

Good quality motors should be better wound and sometimes lacquer dipped, which will more or less cure the whining. If the motor comes apart for service, it's not hard to apply some lacquer (of the right type) yourself.

And so your recommendation is .......?

[Soeren]

Hi,

And so your recommendation is .......?

Sorry, seems I forgot to write it down (could have sworn I did, perhaps the browser is still playing tricks on me).
Usually small(ish) DC motors are most efficient with 3..5 kHz when PWM'd, but it depends on the specific motor (or rather it's inductance) of course, so takes a little experimenting to get it perfected, but going with eg. 3kHz should work quite fine.

For max. torque, 100% (i.e. DC) could be used until (close to) the desired speed is reached, but that takes a more advanced controller.