Looking to buy a used 3ph baldor motor to hook up to a VFD for a machine build. Advertised as working, are there any things to be weary of buying a motor that was likely used in industry? Do nothing and send it? Replace bearing and send it? Thanks.
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Buying a used 3ph motor.
- Thread starter Roju1985
- Start date
fatfillup
Well-known member
Well I would certainly want to see it work and ask why it was available for sale. I sell a few used motors that I take off pressure washers that have been traded in. It typically know the history of the machine and can have confidence in the motors. The ones I won't sell are ones that were drawing too high of amps, but you can only test that under load.
I don't think I have ever had one come back.
3 phase motors normally don't command much money used as the demand is low. And I also don't remember replacing too many 3 phase, good ones normally hold up well.
As to the bearings, if it ain't making a noise, I wouldn't bother though they normally aren't hard to replace.
Good luck
I don't think I have ever had one come back.
3 phase motors normally don't command much money used as the demand is low. And I also don't remember replacing too many 3 phase, good ones normally hold up well.
As to the bearings, if it ain't making a noise, I wouldn't bother though they normally aren't hard to replace.
Good luck
tool_scrounge
Well-known member
VFDs can be hard to the motor windings. Some folks have issues with older motors, so do not. New motors have "inverter rated" markings on the motor plate for VFD use. Or research the motor part number. Per the vfd entry on wikipedia:
Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 of NEMA Standard MG-1.
Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 of NEMA Standard MG-1.
VFDs can be hard to the motor windings. Some folks have issues with older motors, so do not. New motors have "inverter rated" markings on the motor plate for VFD use. Or research the motor part number. Per the vfd entry on wikipedia:
Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 of NEMA Standard MG-1.
Thank you for the reply. It's a baldor cm3546, which according to the baldor website is inverter rated.
matt_i
Well-known member
There is not much to go wrong other than the shaft getting rusty.
If you can test it under power, even better.
I've run motors from the ~1940s on VFDs and they seem just fine. Not for extended periods like fan duty but on and off for drilling holes and its all good.
If you can test it under power, even better.
I've run motors from the ~1940s on VFDs and they seem just fine. Not for extended periods like fan duty but on and off for drilling holes and its all good.
ClappedOutBport
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Never had a three phase motor get even slightly warm even pushing 100% hard under VFD duty. But these are on machine tools, not a 100% load situation. If the bearings are acceptably quiet, cool, otherwise replace and go on with your life.
jar944
Well-known member
I've run motors from the ~1940s on VFDs and they seem just fine. Not for extended periods like fan duty but on and off for drilling holes and its all good.
This.
There are lots of us running vintage 3ph motors and more modern (but still not inverter rated) without any issues.
Just dont run a motor at low hz rate for a extended time period.
dutchgray
Well-known member
Also dont run to far over rated frequency either, just because the drive will do 400Hz doesn't mean a motor will not fly apart.
seber
Well-known member
VFDs can be hard to the motor windings. Some folks have issues with older motors, so do not. New motors have "inverter rated" markings on the motor plate for VFD use. Or research the motor part number. Per the vfd entry on wikipedia:
Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 of NEMA Standard MG-1.
VFDs do not shove higher voltage than normal. Motors tend to overheat when run on them because they are used to lower the frequency and therefor the rpm. Motors normally are cooled by moving air. Lower the speed and you have less air movement. That causes the motor to overheat. VFD rated motors are made more heat tolerant. In fact, Every VFD I have been aquainted with allows for soft start which lowers the stress on the motor.
tool_scrounge
Well-known member
From what I have seen it is not the high voltage that is the issue, it that the voltage is pulse width modulated at a high frequency that can cause issues.
I used VDD's when needed. My hearing is pretty good, so the biggest annoyance of VFD's is the whine.
Here is a link to a good article in Electrical Construction and Maintenance magazine titled:
Mating New Variable Frequency Drives to Existing Motors
https://www.ecmweb.com/design/article/20897062/mating-new-variable-frequency-drives-to-existing-motors
I used VDD's when needed. My hearing is pretty good, so the biggest annoyance of VFD's is the whine.
Here is a link to a good article in Electrical Construction and Maintenance magazine titled:
Mating New Variable Frequency Drives to Existing Motors
https://www.ecmweb.com/design/article/20897062/mating-new-variable-frequency-drives-to-existing-motors
marinusdees
Well-known member
Smell it. Burned windings stink. Pretty hard to miss.
open the peckerhead, take a whiff. burned is burned.
make sure the wires aren't stiff like theyve been overheated.
take a meter and ohm out phase to phase and phase (L1 to L2, L1 to L3, L2 to L3), they should be equal. also check phase to case ground and make sure it's completely open. you could put a megger on it to be sure the insulation is in good order as well if you wanted to go farther.
bearings are pretty much a lifetime thing. if a bearing went out, then it likely took the motor with it. just make sure they feel decent.
other than that, 3 phase are pretty simple.
what size motor was this going to be?
make sure the wires aren't stiff like theyve been overheated.
take a meter and ohm out phase to phase and phase (L1 to L2, L1 to L3, L2 to L3), they should be equal. also check phase to case ground and make sure it's completely open. you could put a megger on it to be sure the insulation is in good order as well if you wanted to go farther.
bearings are pretty much a lifetime thing. if a bearing went out, then it likely took the motor with it. just make sure they feel decent.
other than that, 3 phase are pretty simple.
what size motor was this going to be?
ClappedOutBport
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open the peckerhead, take a whiff. burned is burned.
make sure the wires aren't stiff like theyve been overheated.
take a meter and ohm out phase to phase and phase (L1 to L2, L1 to L3, L2 to L3), they should be equal. also check phase to case ground and make sure it's completely open. you could put a megger on it to be sure the insulation is in good order as well if you wanted to go farther.
bearings are pretty much a lifetime thing. if a bearing went out, then it likely took the motor with it. just make sure they feel decent.
other than that, 3 phase are pretty simple.
what size motor was this going to be?
Great advice except for that last bit imo. Between the two of us, dad and I have replaced a pile of motor bearings.
Great advice except for that last bit imo. Between the two of us, dad and I have replaced a pile of motor bearings.
just my experience working in industrial plants since i got out of the navy. rarely ever had to replace bearings because people let them go so long they toast the motor insulation while they overwork for months on end.
but yeah, you could easily replace bearings.
ClappedOutBport
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just my experience working in industrial plants since i got out of the navy. rarely ever had to replace bearings because people let them go so long they toast the motor insulation while they overwork for months on end.
but yeah, you could easily replace bearings.
That's fair. I guess it's different in industrial use where you can't hear anything and no one cares. I respect your experience there.
marinusdees
Well-known member
Chinese motors have a different stink. It's the varnish on the windings.Smell it. Burned windings stink. Pretty hard to miss.
Firebrick43
Well-known member
VFDs do not shove higher voltage than normal. Motors tend to overheat when run on them because they are used to lower the frequency and therefor the rpm. Motors normally are cooled by moving air. Lower the speed and you have less air movement. That causes the motor to overheat. VFD rated motors are made more heat tolerant. In fact, Every VFD I have been aquainted with allows for soft start which lowers the stress on the motor.
This is false. Inverters absolutely do have high voltage spikes especially at lower Hertz. That is why inverter rated motors have a higher rating of insulation on the wires. I have personally seen several motors (older standard duty)destroyed by running an inverter at low hertz, high voltage spikes blow holes in the insulation.
Older non inverter rated motors have a 1:10 turn down ratio meaning you should not turn an 1800 rpm motor lower than 180 rpm or 10 hertz.
There are several classes of motors now, most every three phase industrial class currently made from baldor, Leeson, or SEW are “inverter rated” which means they have the higher class insulation only(class F). These are typically shaft mounted fan cooled and there fore should not run at low speeds for extended time at high loads. Even at low loads they typically have a 1:20 turn down ratio. 1800 rpm motor should not be below 90 rpm or 5 hertz.
An “inverter duty” have class H insulation and either have no fan or have a back mounted blower driven by a separate motor. They can have a 1:1000 turn down ratio. Or 2 rpm. They also in smaller size (sub 1 hp) have a 6000 rpm limit.
Then there are vector motors which can be use in sub rpm or positioning like a low resolution servo if they mount an encoder.
I have 3 idnm3542 motors mounted on my personal equipment and have paid no more than a George Washington each including shipping on eBay. I roll a new set of skf for nachi bearings and have great performance out of them. I also have a pair of lesson 1.5hp standard motors on my powermatic jointer and sander but other than ramp up and down run them at 60 hertz.
manwithtools
ALLIANCE MEMBER
There are many applications of FVD's without inverter rated motors that work just fine. It's not uncommon to see article after article written about how VFD's will destroy motors, just as it's common to have real world installations that have run for years or even decades with no problems.
I've deployed thousands of VFD's over the years (from 1/4 hp to 1200 hp), every application is specific and needs evaluation.
It comes down to application. Don't run the motor extremely slow and at high load and you'll likely never have problems.
As stated, there's not a lot to go wrong with three phase motor. If it turns smoothly and has windings with similar resistance and no burnt smell you should be good to go.
I've deployed thousands of VFD's over the years (from 1/4 hp to 1200 hp), every application is specific and needs evaluation.
It comes down to application. Don't run the motor extremely slow and at high load and you'll likely never have problems.
As stated, there's not a lot to go wrong with three phase motor. If it turns smoothly and has windings with similar resistance and no burnt smell you should be good to go.