1.5 - 2.2 kW VFD comparisons
I'm just going through and testing some of my 3 phase motors that I have picked up on gumtree/ebay in the last couple of years.
I have a "supposedly never used" 1.5 kW GMC motor that I have reconfigured as ∆ and connected it up to the 1.5kW VFD.
Another thing that suggests it has never been used is the shaft also came with a sort of transparent gummy coating holding the keyway onto the shaft and jot had to be scraped/peeled off to get a pulley onto it.
It's not that free running a shaft, being stiffer than any of my other motors, but I thought I give it a whirl anyway.
At 50Hz it starts up and runs no worries and it emits a very faint high frequency sound about the same amplitude as the 1HP Fasco motor I have on my MW lathe.
It has a small amount of vibe, enough for me to want to lightly clamp it down to a bench because it looks like it may eventually walk its way off the edge of the bench.
When I turn the frequency down to less than 30Hz the vibe disappears but I can hear what sounds like a faint ticking/clunking inside the motor , the clunking is loudest at 25Hz and then it dies away as at lower rpms.
The clicking sound may still be there at higher RPMs but maybe I just can't hear it above the fan
I also noticed the shaft was quite warm (48ºC inside the shaft near the front bearing) after running it at 50Hz for ~20 minutes.
The frequency of the "clunk" ( maybe 2-3 clicks per sec @ 25 Hz) is too low to be directly related to the RPM but I decide to open up the motor and it clearly is new (or at least near new) because it is very clean inside.
I look for signs of anything touching or scraping inside the motor but there is nothing obvious.
Before assembling everything I lubed the bearings and repeated the exercise, no difference.
I also tried it briefly without the fan so I could hear the clicking more clearly - Its definitely below my hearing threshold at above 35 Hz.
I should get SWMBO on the job as she has extremely good hearing - her weak point is her eyes.
I assumed that because the shaft was getting hot that maybe the bearings have a problem but that seems unusual for a brand new motor.
I also tested another 1HP Fasco motor on the 1.5 kW VFD - all good, no vibe or rattles etc, this one has less HF sound coming from it that my other Fasco motor.
Then I decided to try out the GMC with a 2.2kW VFD.
No vibe, no clunking but the shaft still gets just as warm.
The motor also puts out slightly more high pitch sounds than with the 1.5kW - not irritating enough to be a bother but definitely more there that with 1.5kW.
I've heard about different VFD/motors combinations behaving differently but does anyone have any ideas what might be happening?