Can any 3 phase motor be run with a VFD?

[tootalew]

I want to ask this question in general before going into specifics. Can any 3 phase motor be run with a VFD or does the motor need to be "Inverter Class"?

[CalG]

Inverter rated motors include design features to minimize "iron losses" and the breakdown of insulation due to high voltages and high frequencies. Considerations for cooling at low shaft speed (rpms) are also part of inverter rated design.

For 99% of "home shop" applications any poly phase motor will do just fine.

YOUR specific application is the exception you must realize ;-)

CalG

[Al_The_Man]

I have installed quite a few VFD's on standard motors.
Apart from the 'supposedly' vector rated insulation, vector rated motors often have a higher rpm rating than should be used with a standard motor.
With an older motor, I generally restrict the rpm to around 3600 rpm, whether 4 pole or 2 pole.
Al.

[tootalew]

Thanks for the quick replys. I thought this was the case when I bought my VFD a few years ago. Its an Hitachi L100M. 1/2 HP 120V 10Amp Single Phase In 220V 3 Phase Out.

It will be used to power a small bench lathe.

Have found a few motors on Ebay, although I can't tell how many poles a paticular Motor has, even going to baldors site and looking at specs they don't list how many poles a motor has.

[Al_The_Man]

It can be obtained from the base rpm of the motor.
For a 60 hz 4 pole motor the rpm is in the high 1700's if 2 pole then it will be in the 3500's.
Al.

[tootalew]

Are there any benifits or drawbacks from either a 2 pole or four pole motor?

If my questions are starting to sound like Motors 101, is there any good reading material you could point me to?

[Al_The_Man]

If you already have a 4 pole motor in place, it essentially doubles the potential speed in the application it is in.
Al.

[zephyr9900]

Rather than start a new almost-identical thread, I'll piggyback onto this existing one.

My Feeler (Hardinge-clone) lathe has a 2-speed spindle motor of 860 and 1720 rpm, and a 6:1 ratio variable speed transmission, giving an overall speed range of 270 to 3440 rpm. There is a considerable overlap in the speed ranges--270 to 1720 in "low" and 540 to 3440 in "high"--a 1:3 reduction to a 2:1 increase of the motor RPM in each case. I'm creating fixed 60-hz 3-phase for the motor using a TECO FM-50 VFD.

I'd really like to remove the VST (big yoke, pulleys, two v-belts, motor-driven leadscrew actuator for varying the speed, electromagnetic brake) and use the VFD to control the spindle speed directly.

Since the motor is not inverter-rated I'm leery of running it faster than 1720, so that means I would put a timing belt with a 2:1 increase from the motor to spindle, wire the motor with the high-speed windings, and then use the existing VFD to vary the speed down from 60hz max.

I would plan to put a 120V fan with ducting to circulate cooling air through the motor because I've read that cooling of the windings is the main limitation of non-inverter-rated motors when slowed down by VFD's.

But am I reading you correctly, Al, that "regular" motors can be run faster than their nameplate ratings? What I don't know is how conservatively the motor and spindle are designed. I'd like to get maybe 4500 rpm at the spindle. (Most of my work is 1/2" and smaller brass and plastic.) With a 2:1 pulley ratio that would be 2250 rpm at the motor. But I'd only do that if the thing was reliable.

And then, in your experience, is there a limitation to the low-end RPM's of the motor assuming I provide decent air circulation?

Thanks,

Randy

[Al_The_Man]

I would think that manufacturers would make their 2 pole and 4 pole motors identical in mechanical construction, so I have always run a 4 pole motor up to around 120hz.
~ 3600-4000 rpm.
Although some VFD's such as made by WEG will produce 100% torque down to 1 rpm without the need for cooling fan (WEG motor), the HP will drop as it is dependant on rpm.
Al.

[zephyr9900]

I would think that manufacturers would make their 2 pole and 4 pole motors identical in mechanical construction,

Thanks, Al, for the logic behind your statement. Unfortunately I can't find any information on ToYang, other than they apparently now make treadmills and other small consumer goods. So I don't know if they made a 2-pole version of this motor.

I wouldn't be going anywhere near 1 rpm! If I kept the same low-end rpm as stock it would be more than fine (I think I've only gone into low range on the motor once.)

Randy

[Al_The_Man]

I would think that you should be able to run it in the 4 pole mode up to 120hz.
Al.

[Larken]

I would think that you should be able to run it in the 4 pole mode up to 120hz.

This would double the HP since HP=TQ x rpm.

As long as the motor isn't vibrating and the bearings are rated at the higher rpm it should be ok.