I am told that when you move up to a decoder that drives the motors at 16 kHz pwm there is a certain amount of "tuning" that might be required (possibly based on specs of the motor within your specific loco) to get it to perform correctly. Can someone please give me some information on what sort of parameters 16 kHz decoder makers typically give you that allows you to do any per-loco tuning? I'm trying to get a better understanding of this topic, so any info is appreciated.
I believe earlier decoders drove their motors in to 200-500 hz range which gives you smooth operation, but can cause audible vibration within the range the ear can hear (in certain chassis). Eventually most decoder makers have moved to higher frequency decoders (16 kHz and up) which are "silent running" (operating at a frequency only dogs can hear) but it is harder to get smooth slow-speed operation at these higher frequencies. So they usually give you certain CV variables you can adjust that tune the PID on a per-loco basis so you can get smooth operation. I understand the goal is to tune the PID, and that the decoder makers give you specific CVs you can adjust. What I'm interested in understanding is what it is that these CV variables are adjusting, and perhaps an understanding of the calibration process.
The PWM frequency is a separate issue from back EMF, but decoders that support higher frequency drive will often have more tuning on the back EMF than more basic decoders. If you are tuning you need to get the PWM frequency correct (if it needs adjusting) before you try and adjust the back EMF. If the system does not have sufficient torque before you start adjustment the back EMF will not be able to function correctly. The big advantage of higher frequency PWM is that you do not get the motor 'growl' associated with older low frequency decoders. The higher frequency is usually above the limit of most people's hearing hence the popular name often used of 'silent drive'. The disadvantage of higher frequency is that you will sometimes get a reduction in torque due to the inductance of the motor windings causing a phase shift between the current and voltage being applied to the motor, this will often result in low performance and heating in both the motor and decoder. 'Pancake' and Coreless motors can be affected. Some decoders are self-tuning and will identify the motor type and set the parameters accordingly, but sometimes you might need to adjust the PWM frequency which is often in CV9. As a rule of thumb it is usually best to put the decoder in and see how it works. If you are seeing poor torque (won't pull as much as it should) or notice things getting excessively warm when under apparent light load then it is worth considering reducing the PWM frequency to see if things improve - especially if you have a loco with a pancake or coreless motor. If you need to adjust the PWM frequency (which is most unlikely) you should find that there is a sweetspot where the there is a tradeoff between torque and growl noise. Suzie x
