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Induction motor is shaking on low RPMs with a VFD

Frigzy

Aluminum
Joined
Apr 26, 2018
Hi all,

I'm rebuilding an old Abene mill. I took apart the main motor, replaced bearings and put it back together. Now I'm testing it with a cheap import VFD and the motor is shaking violently at low RPMs. The vibration is reducing with higher frequency and it completely disappears at 60 Hz.

What could be the reason for this vibration/shaking? Did I messed up something during the assembly? Or it's just a problem with the cheap VFD? I triple checked all the windings and connections. There are no shorts, everything appears to be in order. I don't have any excessive experience with induction motors/VFDs. I tried to run 2 other motors with that VFD and they spin smoothly at any frequency. Those motors are much smaller though.

I'm not planning on using a VFD with this mill. I have a legitimate 3-phase circuit in the garage and I want to keep everything original. I only use the VFD for testing. VFD is powered off a single phase 240v if that matters.

Specs for the motor/VFD are attached and here is a short video for your entertainment:

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You need to get into your menu and make some other adjustments, v/hz and others to calm your motor down...Phil
Thank you! At this point I'm not interested in making this motor work with this particular VFD. I only want to make sure the motor is assembled correctly and working properly because it's a lot of a hassle to take it off/on the machine. I will play with the parameters a little bit though.
 
VFD must be programmed for the correct number of motor poles. Not sure if that is the issue though...
 
Phil is right I think. The V/Hz curve is way off at the low end of the frequency range. I had similar problems running a 5 HP motor until I boosted the curve at the low end. It acted much the same way as yours is. If you have an auto-tune function, use it. If not, you'd need to boost the curve at the low end probably.
 
VFD must be programmed for the correct number of motor poles. Not sure if that is the issue though...
This may very well be the issue - thank you. Can I deduct the number of poles from the spec'd RPMs? Assuming ~6% slip, 120*60/3600 = 2 poles?
 
Phil is right I think. The V/Hz curve is way off at the low end of the frequency range. I had similar problems running a 5 HP motor until I boosted the curve at the low end. It acted much the same way as yours is. If you have an auto-tune function, use it. If not, you'd need to boost the curve at the low end probably.
Thank you for the information - will play with all these parameters today. Anyway, the motor seems to be alright. I can probably move on to the remaining 95% of work on this machine :)
 
Unless you just want to find answers for you own satisfaction, it seems like you have everything you need. You say it runs smoothly at 60 Hz. It sounds like that's alright then if you're running the machine on straight 3 phase. And you say you've got 3 phase in the shop, so that should take the VFD out of the equation altogether. You can wire it up on the floor or bench to test once more before installing it in the machine.
 








 
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