1.5 - 2.2 kW VFD comparisons

[BobL]

I'm just going through and testing some of my 3 phase motors that I have picked up on gumtree/ebay in the last couple of years.

I have a "supposedly never used" 1.5 kW GMC motor that I have reconfigured as ∆ and connected it up to the 1.5kW VFD.
Another thing that suggests it has never been used is the shaft also came with a sort of transparent gummy coating holding the keyway onto the shaft and jot had to be scraped/peeled off to get a pulley onto it.

It's not that free running a shaft, being stiffer than any of my other motors, but I thought I give it a whirl anyway.
At 50Hz it starts up and runs no worries and it emits a very faint high frequency sound about the same amplitude as the 1HP Fasco motor I have on my MW lathe.
It has a small amount of vibe, enough for me to want to lightly clamp it down to a bench because it looks like it may eventually walk its way off the edge of the bench.
When I turn the frequency down to less than 30Hz the vibe disappears but I can hear what sounds like a faint ticking/clunking inside the motor , the clunking is loudest at 25Hz and then it dies away as at lower rpms.
The clicking sound may still be there at higher RPMs but maybe I just can't hear it above the fan
I also noticed the shaft was quite warm (48ºC inside the shaft near the front bearing) after running it at 50Hz for ~20 minutes.
The frequency of the "clunk" ( maybe 2-3 clicks per sec @ 25 Hz) is too low to be directly related to the RPM but I decide to open up the motor and it clearly is new (or at least near new) because it is very clean inside.
I look for signs of anything touching or scraping inside the motor but there is nothing obvious.

Before assembling everything I lubed the bearings and repeated the exercise, no difference.
I also tried it briefly without the fan so I could hear the clicking more clearly - Its definitely below my hearing threshold at above 35 Hz.
I should get SWMBO on the job as she has extremely good hearing - her weak point is her eyes.
I assumed that because the shaft was getting hot that maybe the bearings have a problem but that seems unusual for a brand new motor.

I also tested another 1HP Fasco motor on the 1.5 kW VFD - all good, no vibe or rattles etc, this one has less HF sound coming from it that my other Fasco motor.

Then I decided to try out the GMC with a 2.2kW VFD.
No vibe, no clunking but the shaft still gets just as warm.
The motor also puts out slightly more high pitch sounds than with the 1.5kW - not irritating enough to be a bother but definitely more there that with 1.5kW.

I've heard about different VFD/motors combinations behaving differently but does anyone have any ideas what might be happening?

[jhovel]

Bob,
the shaft heating up is more likely a dried up/hardened seal. I've had that issue puzzle me a while back. To test the idea I removed the seal and all stayed cool.I then soaked the seal in 'Rubber magic' which I already have (Google it) and smeared the lip with moly grease. After refitting it all was well.

[Bob Willson]

Hi Bob

On the old GMC motor, is it possible that the capacitor has lost some of its capacitance over time?

This is suggested in the sure and certain knowledge that I really don't know what I am talking about here. :)

[Big Shed]

Didn't know that GMC made 3 phase motors:?

[NCArcher]

Hi Bob

On the old GMC motor, is it possible that the capacitor has lost some of its capacitance over time?

This is suggested in the sure and certain knowledge that I really don't know what I am talking about here. :)

No capacitor on a 3 phase motor Bob.

[NCArcher]

The vibration and the shaft getting warm could mean a slight imbalance. Try rotating the end caps and see if frees it up.
Theoretically they should be symmetrical but ....:shrug:. Could also be a faulty bearing. Doesn't cost much to swap the bearings if it's a problem.

[A Duke]

Didn't know that GMC made 3 phase motors:?GMC didn't make any thing, just put their name on it and sold it.
Regards

[Big Shed]

GMC didn't make any thing, just put their name on it and sold it.
Regards

Yes, you're right, I should have said "I have never come across a GMC branded 3 phase motor":;

[BobL]

Thanks for all the info guys - much appreciated


Bob, the shaft heating up is more likely a dried up/hardened seal. I've had that issue puzzle me a while back. To test the idea I removed the seal and all stayed cool.I then soaked the seal in 'Rubber magic' which I already have (Google it) and smeared the lip with moly grease. After refitting it all was well.
Thanks I will give that a go.


Didn't know that GMC made 3 phase motors:?

Sorry that should be, CMG.
I have two CMG motors a 2 and a very nice 1/4HP unit - they were spares from a mining company that no longer needed them.
Both are what CMG call SLA motors; http://www.aemgroup.net.au/electric-motors/three-phase-motors/sla-series-electric-motor
From their website
"Standard terminal connections for motors 3kW and belowis 240V Delta / 415V Star. These motors are suitable foroperation with 240V three phase Variable FrequencyDrives or 415V DOL starting. "


The vibration and the shaft getting warm could mean a slight imbalance. Try rotating the end caps and see if frees it up.
Theoretically they should be symmetrical but ....:shrug:. Could also be a faulty bearing. Doesn't cost much to swap the bearings if it's a problem.
What's weird is there is no vibe if I drive it with the 2.2kW VFD.

Thanks again.

[BobL]

Bob,
the shaft heating up is more likely a dried up/hardened seal. I've had that issue puzzle me a while back. To test the idea I removed the seal and all stayed cool.I then soaked the seal in 'Rubber magic' which I already have (Google it) and smeared the lip with moly grease. After refitting it all was well.

I opened up the motor and pulled the bearing seals off but they seems nice and flexible, although perhaps a little dry so I smeared the lips with a little moly. I also notice the thrust spring was very dry so I smeared that with a little moly as well. All back together and it runs about 5 degrees cooler (was 49ºC after running for about 30 minute) and now reaches 44ºC - none of my other motors run this hot.

This motor (2HP) also draws 0.9A just free running at 50Hz which seemed high at first but then when I checked my other motors perhaps not.
The 1HP Fasco on my Hercus draws 1.2A free running, the Leeson 1.25HP draws 0.5A and the 1HP Crompton on my WW lathe draws between 0.1 and 0.2 A.
I can't make any sense of those figures.

[soundman]

A lot of motors and power tools are let down by cheap or poorly lubricated bearings.

Back in the day of GMC....( Global Machinery Company...the cheap power tool vendor that folded)....a lot of people baught their routers knowing the bearings where rubbish, noisy, prone to failure and runout in the shaft ( many baught as waranty returns).
A trip to the bearing shop for some name brand bearings ( about $5) and they where a different machine.

CMG motors..a formerly Australian owned manufacturer of motors...(not to be confused with CMG Brisbane ( Claus Meinking) a former manufacturer of "interesting" guitar amplifiers)....used to make a range of fair induction motors.....but these days they are well outclassed by some of the quite nice stuff comming out of europe.
It seems that the CMG brand has been under price pressure.....would not be surprised if the bearings have got cheaper.

ANYway.
Bearings in motors and power tools fail....I have changed plenty....quite often that failure is due to lubricant failure.....grease does not last forever either in storage or in use......the oil sepeartes from the mud and the bearing is left with no lubrication.....on the way there the grease stiffens and becomes far less effective.

A bloke I knew who was an engineer and metal fabricator, used to build some machines for arduous duty......he reconed that most bearings where under lubricated, so he routinely took brand new beraings, picked the seals out and added more grease....he reconed this reduced he in service failure rate considerably.

So......its worth either replacing those bearings or pulling them appart and re-lubing them while the motor is not bolted down.

cheers

[BobL]

.
.
.
ANYway.
Bearings in motors and power tools fail....I have changed plenty....quite often that failure is due to lubricant failure.....grease does not last forever either in storage or in use......the oil sepeartes from the mud and the bearing is left with no lubrication.....on the way there the grease stiffens and becomes far less effective.

A bloke I knew who was an engineer and metal fabricator, used to build some machines for arduous duty......he reconed that most bearings where under lubricated, so he routinely took brand new beraings, picked the seals out and added more grease....he reconed this reduced he in service failure rate considerably.

So......its worth either replacing those bearings or pulling them appart and re-lubing them while the motor is not bolted down.

Pulled the motor apart this afternoon and looked at the bearings. The grease was clean as new (this is supposed to be a new motor) but it looked a little stiff so I cleaned out the grease and repacked the bearings with new grease. No difference in the current (0.9A) drawn by the motor and a slight reduction in the shaft temperature (42º compare to 44ºC) after running for 30 minutes.

I pulled the motor apart again and couldn't see anything. This time I noticed that the bearing fit in the end cap with the greased thrust washer was a touch looser than the bearing fit on the other end. This suggested to me that when I tightened up the end caps the thrust washer may have been crushed down before the bearing at the other end was properly seated inside its end cap and could result in the bearings running with a higher side loading than usual.

This time I put the motor back together and with a few taps from a wooden malled on the shaft I made sure that when everything was finally tightened up the thrust washer was not completely crushed.

WHALA!!!!!!!!!!!!!!!!!

Shaft temp was 28º before testing, and after running for ~30 minutes the shaft temp was only 31º.
Free running current draw is slightly less at 0.8A.

I 'm pretty happy with that.

[soundman]

Ya just cant get good help these days.

Yeh slap it together..as long as it goes..she'll be right.

If you would not have spotted that....a few hundred hours down the track you would have had a failure.

This is yet another thing we can blame for premature bearing failure....careless assembly at the factory.

These induction motors should run for a very long time.....no wonder so many don't.

cheers