Slow variation of spindle RPM under Mach3 control

My spindle RPM slowly goes up and down. from 10000 up to 13000 and back to 10000 in 5 - 6 seconds period. Tachometer measurements coinside with VFD.
Set up: Mach3 - Huanyang VFD (110V, 2.2 kW) and 110 V 2.2 kW spindle.
If I set J1 jumper to VR position - RPM fluctuation disappear (some variation on the level of 100 RPM at set value of 15000 is tolerable)
With jumper in VI position (PWM control from RNR USB breakout board) RPM fluctuates within 20% of the set value.
There are also difference between set value and real average RPM value: At 10000 RPM set on Mach3 spindle RPM fluctuates around 12000 RPM.
I check PWM signal on VI terminal with oscillopscope - it is fairly clean.

Any help is highly appreciated.

What PWM freq. rate are you using?
Does it vary much according to the 'scope trace?

I had this issue years ago, the solution was to get larger gauge wire that went from the analogue control to the VFD.

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Originally Posted by chromvis

My spindle RPM slowly goes up and down. from 10000 up to 13000 and back to 10000 in 5 - 6 seconds period. Tachometer measurements coinside with VFD.
Set up: Mach3 - Huanyang VFD (110V, 2.2 kW) and 110 V 2.2 kW spindle.
If I set J1 jumper to VR position - RPM fluctuation disappear (some variation on the level of 100 RPM at set value of 15000 is tolerable)
With jumper in VI position (PWM control from RNR USB breakout board) RPM fluctuates within 20% of the set value.
There are also difference between set value and real average RPM value: At 10000 RPM set on Mach3 spindle RPM fluctuates around 12000 RPM.
I check PWM signal on VI terminal with oscillopscope - it is fairly clean.

Any help is highly appreciated.

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This can be expected when running this 2.2Kw spindle on 120v single phase supply there is more than just the PWM at play with this setup, lack of power supply is your biggest problem

1.5Kw is the limit if you want a spindle to run half decent on a 120v single phase supply

If you live in NA, you don't have a 110v supply it is 120v :)

For anybody coming lately to this issue, I want to just post the solution I got. I just changed my PWM frequency from 5000Hz to 4500Hz and the harmonics problem disappeared magically. So, it must be resonating with career frequency of AC as I feel. I am in India and we use 50Hz AC mains that might got resonated with pwm frequency.
Anyway, just change your pwm frequency and see if it solves your case too!