My motor hums or whistles, how do I stop the noise?
The most common cause of a constant-pitch hum is a switching frequency that stays inside the audible band; switching above 20 kHz makes this noise inaudible. If the noise only appears under load and at a varying pitch, the cause is mechanical: look for bearings, gear backlash, misalignment or loose mounting.
First classify the noise:
- Noise at a constant pitch that does not change as the speed changes: It is electrical in origin and related to the switching frequency. This kind of hum is typically inaudible on a driver running above the audible band.
- Noise whose pitch changes with speed: It is mechanical. It comes from a bearing, coupling, gear or an unbalanced load.
- A rattle that appears only under load: Gear backlash or a loosened fastener.
- A buzz coming from the driver: It may originate from a capacitor or an inductor; in these components mechanical vibration produces sound.
What can be done:
- Mount the motor and the gearbox on elastic pads; if a sheet-metal panel is in direct contact, the panel amplifies the noise like a loudspeaker.
- Reduce start and stop jolts, and therefore mechanical noise, by lengthening the ramp time (soft start/stop on the KS250, the RMP pot on the PT500).
- Avoid running the motor continuously at very low speed; at low duty cycle the current ripple and vibration become pronounced.
- Check the supply cable cross-section; excessive voltage drop makes the motor run at a higher current and more noisily.
Full topic: DC Motor Driver Selection Guide