Motor Over Current Help Needed

[larry_g]

Larry - with no shims I could manually move the shaft 5/64" and it was a bit noisy. With one shim I could move it about 1/32 and the non shimmed end was still giving some noise. With a shim in each end I could not move the shaft manually and most of the noise was gone. This is going to be mounted vertically if that matters at all.

Speaking of mounting - is there a convention or best practice regarding whether the fan should be up with the pulley or down?

My point on shimming was to get the rotor in the proper position in the stator. I don't know if your shims are moving the rotor into the optimum position or pushing it further out of position. If you measure when running as described above you should be able to measure distance from optimum to each end of the end play and select shims for each end based on that measurement. You have already learned that rotor position affects current draw by putting it in backwards.

Are you working with new bearings? The noise you are hearing may be worn bearings with excess clearance. I do know that some motors use an angular contact bearing if intended to be used in the vertical orientation.

As for the fan, someone else will have to advise on that.

lg
no neat sig line

 

[Rick_Br]

I got the motor assembled correctly this time and ran it for 40 minutes. Amp draw stayed around 2.1 with no appreciable heat build up.




For those who may have an interest I measured how far the rotor was off center to the stator when inserted backwards - 5/8". Good guess mm08822

Regarding the fan and motor orientation - based on a number of examples I placed the fan up when the motor is mounted on the drill press. I also only used one wavy washer in the fan end.

Thanks for all the help!

Rick

 

[mm08822]

This fixed problem is good reason to remind me of the old practice of marking both end bells with 1 & 2 scribe marks at the end bell/center tube interfaces.

Scribe or use the corner of a file. Re-assemble to the matching marks.

 

[Cruzan80]

That only works if you insert the same rotor end into the same endbell it came out of...

IIRC, the OP (either here or OWWM) said he did put witness marks on the endbells, hence the humor.

In seriousness, glad you got it worked out, and back to life again!

 

[fitter30]

Pull the washers ,put motor back together, run it mark the shaft where the shaft is running. Rotor and stator now is centered. Putnit back together.

 

[Rick_Br]

yes both end bells were marked to identify which end of the stator they went on. I use a small drill bit and put some matching dimples to insure the end bells are on the right end and oriented properly. as indicated above - what that doesn't do is identify rotor end goes where. I normally keep a note - for example end bell 1 is the fan end. My experience is also that the fan goes away from the electrical end of the stator. I didn't do either of those things this time and I can now add a check for rotor centering.

Rick

 

[mm08822]

That only works if you insert the same rotor end into the same endbell it came out of...

IIRC, the OP (either here or OWWM) said he did put witness marks on the endbells, hence the humor.

In seriousness, glad you got it worked out, and back to life again!

Very true for a double-ended shaft motor! Most aren't. So add a corresponding hash mark on the shaft.

 

[Innovate1]

Many thanks to JLanciani for the tip on rotor orientation. I took the whole motor apart again. The stator is not symmetrical in the casing.



I have been testing with the fan end of the rotor inserted in the stator from the wide side (first picture) - thinking that was wider to accommodate the fan. I turned it around and the operating amps dropped to 2.1 to 2.2 - well under the 2.8 FLA. This was cold - I have not let it run for more than a few minutes yet. I'm hoping as it warms up the amps will drop a little more. I was initially concerned because I could hear a faint tick - further investigation revealed a bent fin on the fan - straightened that and tick disappeared. On my last test I had a wavy washer in each end of the rotor. Not sure that is right as there is no end play that I can feel at this point.



The end bells are identical and are numbered 400146



However one of them has a 1 and one has a 2



I'm guessing that is an indicator of which end they go on - I did mark them when disassembling so I feel comfortable that 1 is the shaft end and 2 is the fan end.

I think at this point the problem may be resolved but am interested in any comments/cautions folks might have

Rick

I would guess the 1 and 2 may be what cavities in the die they came out of. Dies often have cavity marks so if any issues come up they can tie the parts back to the cavity.

 

[Rick_Br]

So I thought I was done with this problem but it has been suggested on another forum that 2.2 amps is still too high for an unloaded 3/4 HP 3 phase motor. Internet reading indicates that the unloaded amps should be 30 to 35 percent of FLA. In my case that would be about 1 amp.

Any thoughts/suggestions?

Rick

 

[PCustoms]

So I thought I was done with this problem but it has been suggested on another forum that 2.2 amps is still too high for an unloaded 3/4 HP 3 phase motor. Internet reading indicates that the unloaded amps should be 30 to 35 percent of FLA. In my case that would be about 1 amp.

Any thoughts/suggestions?

Rick

What does it run loaded?

That's likely a less efficient motor compared to anything more modern

 

[Rick_Br]

What does it run loaded?

Not sure what the loaded amps are - by loaded do you men with a belt on it or actually drilling? That may be a while - this is going on a 17" VS drill press. I still need to get it assembled and adjusted.

Rick

 

[Rick_Br]

I would guess the 1 and 2 may be what cavities in the die they came out of

Good point - you are probably correct

Rick

 

[PCustoms]

Not sure what the loaded amps are - by loaded do you men with a belt on it or actually drilling? That may be a while - this is going on a 17" VS drill press. I still need to get it assembled and adjusted.

Rick

Loaded means doing 3/4 HP of "work".

 

[Rick_Br]

Loaded means doing 3/4 HP of "work".

Thanks for that but some one is going to have to explain to me howto determine what 3/4 HP of Work actually is and how you determine that

Rick

 

[Rick_Br]

It has been suggested to run the motor with out any spring washers - this would result in the rotor being centered in the stator. Mark the rotor while running. Put the spring washer back in - maybe more shims - to get the at rest rotor in the same position.

I did this and marked the rotor shaft while running. The no load amps barely changed. I put the spring washer back in and the mark on the rotor shaft was, indeed, moved about an 1/8".



However given that the no load amps barely changed (maybe from 2.2 to 2.1) I wonder how critical that actually is. Also when running with the spring washer the marked shaft did not move.

Rick

 

[micromind]

No-load amps will usually be higher with a VFD than with line power.

The reason is line power is pretty close to a true sine wave while a VFD is more of a pulsed wave.

Inductive devices (motors and transformers) like true sine waves but will operate on distorted waves, just not as well.

 

[Rick_Br]

Micromind - I like what you are saying. I have been leaning towards just accepting what it is and moving on

Rick

 

[Rick_Br]

John (Jlanciani) has the exact same motor on a drill press running from a VFD. He tested all 3 phase and found the amps to be the same as mine - 2.1. I think I am moving on with this project.

Rick

 

[micromind]

Micromind - I like what you are saying. I have been leaning towards just accepting what it is and moving on

Rick

it'll work just fine!

 

[American Locomotive]

John (Jlanciani) has the exact same motor on a drill press running from a VFD. He tested all 3 phase and found the amps to be the same as mine - 2.1. I think I am moving on with this project.

Rick

Fractional horsepower motors are not efficient - that motor is probably 60-70% efficient at best. Older motors are even less efficient. I find that these older motors tend to draw 60-70% of their rated current when they're unloaded.