Changing out large old mill motor for vfd install?

[Net30]

I have a supermax clone with an old rather large dual speed motor. Or multiple pole motor or whatever their called. I want to run a vfd. I can see how that might complicate the install. The motor is rather huge for its 2 HP rating, probably double of most motors its HP. I'm wondering how essential that size is, considering I have a much smaller three horsepower baldor I'd love to swap in its place. Is it providing a considerable amount of rigidity? I mean it's ran from a belt so I'm not sure how much it would matter?

It's a 100L motor i have a 143c. I would certainly have to make an adapter plate. I am sure the original motor is probably 40 years old. The new motor looks relatively recent.

 

[derf]

It would be less complicated to wire up the vfd to the high speed side of the old motor.

 

[cathead]

I would at a minimum consider using the existing motor with the VFD and give it a try. That would involve minimum work and you could at a later time change out the old motor if you wanted to.

 

[Ironman2]

You do not state whether the 2 speed multipole motor is single or 3 phase. I chucked my single phase 2 hp motor on the lathe and installed a vfd and 3 ph five hp motor last year this time.
It sat beside the lathe for 7 years and I sure regret not doing this sooner. I activated the electric brake feature in the VFD and put in a braking resistor. I just love it.

 

[Chip Hacket]

Understanding cost is always a factor with us hobby guys, I would still consider a VFD rated motor. They have insulation better suited to handle thermal and electrical stress created by a VFD. If you decide to stick with the existing motor, I would suggest using the low speed windings as that should provide more torque.

 

[Ulma Doctor]

There is no reason why you couldn’t use a 2 speed motor with a sufficiently rated vfd. With the addition of a 3 pole switch, both the speeds can be utilized. The motor speed can be switched only in the motor off condition, but both windings can be used.
It is also possible to use either the high or low speed windings depending on your needs

 

[Ulma Doctor]

I have run inverter rated and non-inverter rated motors for vfd service. While it is true that inverter rated motors are better at handling the waveform from the vfd, it doesn’t necessarily mean that a non inverter rated motor cannot be utilized in the same service .
If the non inverter motor is used in the 30 to 90Hz envelope for moderate loads and reasonable periods of time, there is little consequence

 

[epanzella]

I replaced my 2 hp mill motor with a 2 hp 3 ph Baldor that was given to me when I installed the VFD. The motor is great but you suffer an efficiency loss with the VFD setup. I use heavy duty belts on my machine (I kept the step pullies) and sometimes at the higher belt settings and lower VFD setting (30hz) the overcurrent limit will trip. The solution is to start the runup at 60hz and the drop to 30hz when it's up to speed. 3 hp would be better but once running the 2hp has plenty of power.

 

[slow-poke]

I have run inverter rated and non-inverter rated motors for vfd service. While it is true that inverter rated motors are better at handling the waveform from the vfd, it doesn’t necessarily mean that a non inverter rated motor cannot be utilized in the same service .
If the non inverter motor is used in the 30 to 90Hz envelope for moderate loads and reasonable periods of time, there is little consequence

I completely agree, especially if this is a 240V motor. I read an article where they are using VFDs for an entire plant on motors, many that are 50+ years old and they actually have less failures because they had larger transient voltages when the motors were powered by really long lines and the ringing associated with those long lines. I have been running non VFD rated motors with VFDs for years without issues, I don't typically run them at really slow speeds for a long time so cooling is also a non issue.

If the motor requires > 240V , I would be more inclined to look for a Inverter rated motor.

 

[Net30]

240v 3ph motor.