3 phase lathe conversion, motor question

[daved20319b]

The bearings went out in the motor on my older Grizzly lathe, so I decided to replace it with a 3 phase motor and VFD. Got a Westinghouse/TECO VFD and a Leeson 1.5 HP IEC motor. My question is on the motor. The nameplate says it's inverter rated, but it also lists a speed range of 3-60 Hz. I know the VFD can run it faster, but am I going to have issues if I run the motor faster than the base frequency? Kind of kills the whole reason for using a VFD. Later.

Dave

 

[matthewsx]

You'll probably be fine running over 60Hz.

Most of these motors are used in applications where they're running constantly, driving fans or pumps, not intermittent use like in a hobby machine shop. You will want to make sure your spindle bearings are good for whatever speed you plan on running.

There are numerous articles on the internet regarding running motors over their rated speed with VFD's so you can explore the question in depth if you like but I'm fairly confident the simple answer is running 1.5x to 2x the rated speed is acceptable.

John

 

[bulgie]

The bearings went out in the motor on my older Grizzly lathe, so I decided to replace it with a 3 phase motor and VFD. Got a Westinghouse/TECO VFD and a Leeson 1.5 HP IEC motor. My question is on the motor. The nameplate says it's inverter rated, but it also lists a speed range of 3-60 Hz. I know the VFD can run it faster, but am I going to have issues if I run the motor faster than the base frequency? Kind of kills the whole reason for using a VFD. Later.

Dave

What's the nameplate speed? I'm no expert but it's my understanding that a 4-pole motor will be listed as some small amount less than 1800 rpm at 60 Hz (e.g. 1750 or thereabouts), and those can usually (?) be run at double-speed or more. I've seen a number of people saying they run theirs at 130 Hz or more, though I usually stop at 120 myself, from an abundance of caution.

If it's a 2-pole (~3450 rpm) motor, we're outside my experience zone, I don't have any of those. Someone here knows for sure.

 

[slow-poke]

I have used non inverter rated motors with VFD's for years with no issues. When you read all the hoopla about using non-inverter rated motors with a VFD it helps to keep in perspective the HP and voltage ratings. For small motors 2HP and less especially running on 240V I would not worry at all.

The two main issues are:
1) Cooling at low frequency (less fan speed = less cooling), but my motors run cool as a cucumber and I often run at small fractions of nominal speed.
2) VFD output is square wave instead of sinewave so there is some transient voltage overshoot, however this is often a non issue with a 240V motor because the non-inverter rated insulation is well up to the overshoot when used with 240V, now if this is a 600V motor, It might be wise to use an inverter rated motor.

FWIW I read an article where a guy stated that they had many hundreds of old ( some a old as from the 20's and 30's) non inverter rated motors running on VFD's and they actually live longer, because the VFD is placed near the motor, and when non VFD driven the cable can be long causing ringing and even higher transient voltages.

 

[Ulma Doctor]

FWIW,
The bearings used in most modern electric motors are rated for at least 3450 rpms, so there is little chance of over-speeding the bearings.
The motor in question can certainly run for short periods of time, at moderate loads, above the 60Hz threshold. 90 Hz or 120 Hz is also possible.
I wouldn’t recommend operation above 90 Hz unless it’s a momentary situation, nor would I recommend operating below 30Hz unless it’s a momentary condition.
The cooling fan is insufficient for very low or very high speeds for extended periods of time.
Inverter rated motors have windings that are better suited for VFD service, but I have tested and run very old motors (20’s and 30’s vintage) in the 30 to 90 Hz envelope without consequence.

I have read that there is potential for bearing damage from very low frequency operation, but I have not run across the phenomenon personally.