Mill Motor Runs on Line Power 3P/240VAC But Not on VFD - Why???
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    Default Mill Motor Runs on Line Power 3P/240VAC But Not on VFD - Why???

    my mill (Tree 2UVR) motor (Fairbanks Morse 1-1/2HP) runs fine on 3p/240VAC line power but not from a VFD??? thinking the VFD was bad, i bought a new one and got the same results. running on the VFD there is almost no torque. the spindle will stop with light cuts but runs fine off line power. how is this possible? the motor doesn't care or know that it is a VFD, or does it...

    _mg_7286-copy.jpg

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    it's the motor, despite what my motor shop has been telling me... the motor is bad.
    it is pulling the amps when connected to line power source, but there is no torque.
    bad motor.

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    You probably should have put this in the forum dedicated to this type of issue.

    I doubt it is the motor. If all the windings have the same resistance and there is no path to the case and all windings draw the same current then I bet the motor is good.

    Is the motor a dual voltage motor? If so, is it wired for 240V? If it is wired for 480 then it would run at speed with reduced power.

    Bill

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    which forum is that? cncz0ne?

    the motor has been running for ~7-yrs on a VFD then started to slow with cuts.
    assuming the motor was bad i sent it to a motor rebuild shop. they did a minor rebuild w/o a rewind (bearing, baked to remove moisture, etc...)
    i reinstall the motor and its not great but usable?
    then recently it had no torque and not able to make a cut.
    so, i assume the VFD is bad. buy, new VFD and get same results.
    this whole time the motor was bad...

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    The forum about transformers and electrical stuff.

    Sent from my SM-G973U using Tapatalk

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    yeah, got it. but, which forum. there are a lot of electrical forums.
    just thought this would be a good place because its a mill and plenty of users have decent electrical skills.

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    That is not a typical motor failure but it is possible.

    So it ran fine on a vfd for 7 years? No paramater changes in the drive?

    Could be potential bad connection somewhere.

    Really need to do some troubleshooting. Measure voltage to the drive, measure DC bus voltage (or read off the drive interface), measure the individual motor voltages, look at all 3 motor phase currents, read the drive torque or kilowatts off the drive interface, etc. All of these types of tests are quick and can tell you what is happening.

    To test the motor the shop should of done a surge test (to validate the phase to phase/coil to coil/turn to turn insulation), DC high voltage (500 volts DC) ground insulation test to determine if groundwall insulation is good and a phase to phase resistance imbalance test using a high current low resistance meter (look for no more than 2 - 3% imbalance).

    It could be as simple as a bad lug on the motor or elsewhere.

    But a drive does have the capability of phasing back (slowing down) to react to some motor insulation failures. The most blatant one I saw was the a 10 hp motor was shorting phase to phase because a braze joint was sharp and was digging through the insulation into another phase. Found it with a resistance imbalance test.

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    Quote Originally Posted by everettengr View Post
    yeah, got it. but, which forum. there are a lot of electrical forums.
    just thought this would be a good place because its a mill and plenty of users have decent electrical skills.
    https://www.practicalmachinist.com/v...rters-and-vfd/

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    Quote Originally Posted by markz528 View Post
    That is not a typical motor failure but it is possible.

    So it ran fine on a vfd for 7 years? No paramater changes in the drive?

    Could be potential bad connection somewhere.

    Really need to do some troubleshooting. Measure voltage to the drive, measure DC bus voltage (or read off the drive interface), measure the individual motor voltages, look at all 3 motor phase currents, read the drive torque or kilowatts off the drive interface, etc. All of these types of tests are quick and can tell you what is happening.

    To test the motor the shop should of done a surge test (to validate the phase to phase/coil to coil/turn to turn insulation), DC high voltage (500 volts DC) ground insulation test to determine if groundwall insulation is good and a phase to phase resistance imbalance test using a high current low resistance meter (look for no more than 2 - 3% imbalance).

    It could be as simple as a bad lug on the motor or elsewhere.

    But a drive does have the capability of phasing back (slowing down) to react to some motor insulation failures. The most blatant one I saw was the a 10 hp motor was shorting phase to phase because a braze joint was sharp and was digging through the insulation into another phase. Found it with a resistance imbalance test.
    the motor is bad. after a lot of testing i discovered the VFDs are good and the motor is bad.
    opposite from what the motor shop told me.
    that was the confusion, i assumed the motor was good when i got it back from service.
    not so...

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    PM Forum?
    same forum... different section.
    fell free to move this post, i don't how to do that.

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    So what's wrong with the motor?

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    Quote Originally Posted by markz528 View Post
    So what's wrong with the motor?
    It doesn't work

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    Quote Originally Posted by markz528 View Post
    So what's wrong with the motor?
    no torque. it is pulling the amps but is so weak i can stop the spindle with my hands.
    i think the motor shop just check the amps and did not put a load on the motor???
    if they did it would have stopped, almost...
    therefore, assuming the motor was good i bought new VFD, checked wiring, etc...
    wasted a lot of time and money :-(
    all along it was a bad motor.

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    From your comments you said motor ran fine for ~7 years on VFD but started to decline. You took it to a motor shop, they tested it on true line 3 phase power (yes?) and said the motor was fine. You replaced the VFD with the same results as before. Conclusion the motor shop doesn't know what they are doing, professionals are required to know what they are doing, and so the motor is bad.

    Let me guess what is going to happen next. You are going to replace the motor and the will come back crying that after all that has been done that it still doesn't work. Then the smart asses here will say get a new mill. Seen it before.

    Let's avoid all this and attack the real problem. The drive line in your mill. Bad bearing, lubrication, whatever.

    Tom

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    Quote Originally Posted by TDegenhart View Post
    From your comments you said motor ran fine for ~7 years on VFD but started to decline. You took it to a motor shop, they tested it on true line 3 phase power (yes?) and said the motor was fine. You replaced the VFD with the same results as before. Conclusion the motor shop doesn't know what they are doing, professionals are required to know what they are doing, and so the motor is bad.

    Let me guess what is going to happen next. You are going to replace the motor and the will come back crying that after all that has been done that it still doesn't work. Then the smart asses here will say get a new mill. Seen it before.

    Let's avoid all this and attack the real problem. The drive line in your mill. Bad bearing, lubrication, whatever.

    Tom
    ??? odd comment, but ok.
    gear box was just rebuilt and works great. both main drive and back gear as well as the lube pump. new belts installed, bearings, etc...
    the motor is bad and yes, the motor shop made a mistake, IMHO.
    no crying, just a new motor. already ordered. not the end of the world. it will be up and running soon.

    _mg_6397-copy.jpg

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    Where I come from we call it bulldozer troubleshooting (replace everything) instead of actually troubleshooting the problem and fixing or replacing only what was bad.........

    The tests I pointed out give a pretty clear picture of the health of the motor. Did the shop run the tests? If not it could of been taken back to them and in 15 minutes got the answers.

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    Quote Originally Posted by markz528 View Post
    Where I come from we call it bulldozer troubleshooting (replace everything) instead of actually troubleshooting the problem and fixing or replacing only what was bad.........

    The tests I pointed out give a pretty clear picture of the health of the motor. Did the shop run the tests? If not it could of been taken back to them and in 15 minutes got the answers.
    i appreciate your input and suggestions for troubleshooting the problem. i'm not going back to the motor shop and don't know of another good shop locally to try out. i also don't want to take the time and spend the $$ for another motor shop to check it out. i'm not getting rid of the motor and can investigate further another day, maybe get it fixed and keep as a spare. i just need the mill running to complete some projects.

    i purchased another motor for ~$390. it is a machine tool specific VFD rated motor with a 10:1 turndown rating. it is also 2HP vs. the old 1-1/2 HP. the new motor is free shipping and no tax. i will cnc out a adapter plate and have it ready to go when the motor arrives. this is the quickest for-sure method to get the mill running.

    when i started this post, i was assuming the motor was good based on the work the motor shop did.

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    Quote Originally Posted by everettengr View Post
    i appreciate your input and suggestions for troubleshooting the problem. i'm not going back to the motor shop and don't know of another good shop locally to try out. i also don't want to take the time and spend the $$ for another motor shop to check it out. i'm not getting rid of the motor and can investigate further another day, maybe get it fixed and keep as a spare. i just need the mill running to complete some projects.

    i purchased another motor for ~$390. it is a machine tool specific VFD rated motor with a 10:1 turndown rating. it is also 2HP vs. the old 1-1/2 HP. the new motor is free shipping and no tax. i will cnc out a adapter plate and have it ready to go when the motor arrives. this is the quickest for-sure method to get the mill running.

    when i started this post, i was assuming the motor was good based on the work the motor shop did.
    Please let us know how it works out.

    My 66 Bridgeport mill came with a Fairbanks Morse 1 hp motor. I replaced it with a Siemens aluminum frame 3 hp motor and dumped the multistep pulley - by over-sizing the motor by a factor of 3, I maintained good torque without having to change belt position. Worked out real well. The aluminum frame motor was much more easy to handle (install so high up) than the cast iron frame - only reason I went with aluminum.

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    Is this a case where the VFD carrier frequency caused movement in the windings that resulted in random wire to wire shorts through the wire varnish insulation?

    That would be consistent with near normal amp draw with a decrease in motor torque.

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    Quote Originally Posted by CalG View Post
    Is this a case where the VFD carrier frequency caused movement in the windings that resulted in random wire to wire shorts through the wire varnish insulation?

    That would be consistent with near normal amp draw with a decrease in motor torque.
    Was thinking a "similar" thing, more perhaps Corona damage, "pinholed" insulation, given the OEM motor was probably NOT "inverter duty".

    IIRC, Mark acquired a Rigol 'scope off the back of his Parker-SSD 10EE conversion project?

    I could be wrong.... But if so, it would be interesting to see what the output waveform and its bleeding edges show off the older VFD.

    Hopefully, the new VFD has cleaner output AND the new motor IS rated inverter duty?

    If not both, a salvaged dv/dt filter could be a sound investment.


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