VFD 3 phase Motor settings

[minilathe22]

I have my wood lathe setup with a VFD. With the default settings, I found I could vary the speed smoothly, but it had very little power, and I could stop the chuck easily with my hand unless it was running at 40Hz or above. I have improved this now but mostly through guesswork of the many settings on the VFD.

I now find that down to 10Hz or so the torque is reasonable, and I can get 100RPM if I have the pulleys also set on the slowest speed. However if I set the pulleys on the highest speed, I cannot go above about 1600RPM. If I push the speed dial above this "peak" point, the RPM falls. If I set the max frequency to 120Hz, as I increase the speed the motor falls, and at 120HZ it stops completely and just makes a high pitched noise. It is as though the motor can't keep up with the supplied frequency. However if I disconnect the belt then it reaches 120Hz ok.

The motor is a fairly old 3 phase Newman motor that came with the lathe:

0.75 HP 1425 RPM
220 Volts 2.2 AMPS 50Hz
380/440 Volts 1.25 AMPS

I have a 230 page setup manual for the drive, however any of the "constant torque" profiles they describe seem to have very low torque. Any ideas? I would like to increase the max speed if I can, but still keep the torque at low speed.

 

[Paul Hannaby]

If the motor was the original one, wouldn't the pulley gearing be set up to give you whatever the designed top speed was at 50hz? In which case, do you really need to try to achieve 120Hz? The motor was designed to run at 50Hz so you may not be able to go a great deal above that before you get strange things happening.

I think the constant torque profiles will increase the current at lower revs to compensate for the loss of power at lower frequencies.

 

[flh801978]

I’ve seen this on graduates before and it was the grease in the bearings...too much and old and coagulated..
Strip out and fit new sealed bearings Job done

Ian

 

[minilathe22]

I would like to go a little higher for attaching a buffing wheel. Ideally 3000RPM or so. I cannot even reach 2250RPM which as you say with the standard motor and pulley arrangement I should be able to.

I had not considered the bearings restricting it. Feels easy to turn by hand but at higher RPM could be significant. I may try to clean out the bearings in place, I don't fancy replacing them, I believe its a bit of job!

 

[Duncan A]

Most motor manufacturers of "standard" induction motors recommend around 75Hz as a max frequency. In your case, that would equate to around 2100 rpm which, with suitable pulleys should easily give you 3000 rpm.
Basic VFD's use a voltage/frequency curve and usually incorporate motor protection algorithms which may I suspect are causing your problem, reducing voltage and possibly also speed as your desired frequency is raised too high.
I suggest you turn off the fancy constant torque stuff and run it as a simple V/f VFD, and make sure that the motor parameters are set correctly, for a standard motor (not a variable frequency motor).
What inverter do you have, and what rating is it?
Duncan

 

[flh801978]

You can't clean them in situ at all and it's an hours job to replace
Ian

 

[minilathe22]

I do get a bit of a grumbling noise now and again - further evidence that my bearings are the issue here!

 

[CHJ]

I would like to go a little higher for attaching a buffing wheel. Ideally 3000RPM

What diameter and construction (stitched or loose leafed) are your mops.
Are you sure the mops you have are safe to operate at that rpm.
Most 200mm loose leaf mops are not intended to operate above 12-1500 rpm. for instance.

 

[minilathe22]

I have a 6" dia loose leafed mop that I have previously used with success on a bench grinder which I believe was a 2 pole motor, so 3000RPM approx.

I assume you meant 1,500 RPM not 15,000 :shock:

 

[minilathe22]

The VFD is a Yaskawa J1000 rated at 1.1kW. It has a heatsink but no fan, I have bolted it to the base of the casting inside the leg, so hopefully it will not get too hot. Until I have sorted the bearings, I think I will leave the settings as they are.

 

[minilathe22]

I did some investigation, and was wondering how to know what amount of load the (potentially) restrictive bearings were putting on the motor. I realized the VFD has a setting to display the current being used by the motor, and sure enough as it reached the peak rpm, the current was 2.5 amps, the current limit set in the vfd. Once past the peak, the current did not increase. I put some 3 in 1 oil in the grease cups while it was running at 1600rpm and the current went down to 2.2amps, allowing an increase in speed up to 2000rpm before the current limit was reached. Some really thick black grease has started coming out of the spindle at both ends, presumably softened up by the oil.

Definitely bearing replacement time, although its nice to be able to prove this was the problem before spending money and time on the bearing replacement.

 

[minilathe22]

I have pulled out the existing bearings this evening. Bit of fiddling around to get my bearing puller to line up and pop the bearings out. They are full of nasty looking grease, but I cannot detect any play in them. I don't know if they are truly worn, or if it was only the old grease that was the problem. As I have ordered new sealed ones, and I have it in bits I may as well fit the new ones anyway. They are rated to 5000RPM so plenty of headroom for my plans.