General comments – I've not used that particular brand of VFD.

There is usually some option to set the motor power – used when running a motor smaller than the converter nominal rating. The exact details of how this is done vary – it will involve setting parameters.

You may be able to set up different sets of motor parameters and switch between them using a digital input (maybe a spare contact on your lathe/mill selector switch).

There can sometimes be vibration issues at specific frequencies – it is often possible to program VFD to 'skip' over a range of frequencies if this is the case. That isn't ideal if you want continuous range of speed available.

If the VFD can be set to 'Vector' mode, that should give better speed control on a load like a machine tool compared to V-F mode for example.

Is the VFD set for the motor nominal speed / number of poles?

There is usually a group of parameters that relate to the motor (power, number of poles etc.). Some may be used just to make display of speed correct, some may actually affect behaviour of the inverter/motor or any external speed signal. You may get away with just setting a couple of parameters, and the inverter will 'optimise' the rest after measuring the motor electrical characteristics itself – you'd have to check the manual to see what is supported.

If your two motors are a long way from being similar, you may always have issues unless the inverter does support multiple motor parameter sets.

Inverter friendly, or inverter duty motors may well have higher rated insulation to cope with various side effects of using a VFD. Some inverter friendly motors may offer a separately powered cooling fan (the standard fan doesn't do much cooling when motor is running at low speed).

It's still worth making sure the VFD parameters match the motor rating plate (if for nothing beyond making sure the motor protection function of the inverter is set correctly).

Without knowing model of inverter, it's difficult to find a manual on-line and point you to the parameters.

I presume you already know to always make sure a motor is connected before running the VFD, and not to switch motors when VFD is active.

[EDIT – Sensorless Vector Control is a more advanced method of controlling the VFD, it'll hold speed better and cope with varying loads.  V-F follows a fixed voltage profile (either linear or quadratic, depending upon type of load the motor is driving).  Terminology may vary between manufacturers. ]

Edited By David Jupp on 25/05/2016 11:11:10

I have a Huanyang vfd on my Harrison but haven't noticed any vibration. Before blaming either the vfd or the motor I'd be tempted to look at a mechanical reason – it sounds as though it is a sort of resonance issue.

You've already hinted at this with comments about the drive belts and the motor mount. Maybe beefing up the motor mount would be the answer, or at least changing its' mass significantly. For a test try bolting or clamping a big lump of steel to it (a spare chuck for instance) – that might change the resonant frequency so it's out of your working range of speeds.

I have always had a similar problem with my Startrite bandsaw – it only happens at very low speeds just before it slows to a stop, when the whole machine shakes and shudders for a brief moment.

I can't imagine the motors rotor is out of balance, unless it's been physically damaged in some way. That wouldn't happen electrically. Even cheap import motors run smoothly in my experience. It is possible the bearings need replacing but you'd probably hear rather than feel the symptoms of that problem. However, bearings are fairly cheap so it might be worth changing them if you want to eliminate that possibility.

If you want to check the settings on the vfd, there is a post by Mark C with some suggested parameters which I found very useful (near the bottom of page 3 of this thread **LINK**&nbsp. Like you, I ran my motor on the default settings of 1440 and 4 poles for a while before realising they needed to be changed to 2880 2 pole, with no apparent change in how it performed. Also like you, my belts are long, maybe a bit longer than yours – you might want to check they are not too tight as that can cause them to whip just as much as if they are too slack. Also check the pulleys run concentrically and haven't suffered from corrosion in the vee – mine had in one spot because it had been stood idle for a long time.

David Jupps suggestion of running the motor on the bench should be your next step, via the vfd so you can check it at 22-39 Hz.

One other thought re the rubber bushings you tried out – if the motor was at fault the vibration should have been damped before it got transmitted to the rest of the machine. The fact that they didn't do much indicates that it is the machine vibrating rather than the motor. To me anyway!

Bernard,

I do live across the Humber, north bank, just outside of Hedon.

Not sure how we are aquainted…maybe another John you know?

I am not alone..