Anyone familiar with electric motors?

[Boomyal]

Pictured is an exhaust fan motor that is about 40 years old. I have two of these in service and the most used one works perfectly. The one pictured is out of a bathroom that has had, easily, 1\5th of the use, of the working one.

This one is lazy. When you turn it on it spins very slowly. When installed in the fan unit, it doesn't initially have enough poop to keep the assembly's trap door all the way open so it sounds like a real bucket of bolts as the little door keeps opening and closing.

If you leave it on for a little while it picks up speed and everthing quiets down. First I thought that it might need to be oiled. It made no difference. The other night I had it out on the workbench in the garage (very cold) and plugged it in. It was super lazy. I brought it in and warmed it up and it started with a little more poop but still lazy.

I then thought maybe the motor was full of goo so I popped it apart. It is as clean and dry as the day it left the factory.

What gives? What could be wrong? Is there anything I can test? This motor is pristine inside.

I would just change out the assembly but that would be a real pain. I also thought that Grainger might have a suitable replacement motor but could not find one. Apparently both the motor manufacturer and the fan assembly manufacturer are out of business.

 

[foodfisher]

Re: Anyone familiar with electric motors?

wd 40 while running

 

[99yam40]

Re: Anyone familiar with electric motors?

Did you notice the wording on the case that says oil every 3 months? no one ever does that. Usually the oil gums up like you said and the bearing/bushings bind up and drag the rpms down
my guess is it never received any oil over the years and may have bound up some and over heated the windings and some have shorted together. Or the armature has gone bad.

Did you oil both bushings?

If the other one is identical you could pull it and test the ohms of its windings and compare the two, Or swap some parts to see what is going on.

It may not be easy but you should be able to find a motor the same size,specs, and mounting abilities if you look hard enough

 

[Boomyal]

Re: Anyone familiar with electric motors?

Hey, that macro photo function is pretty good, huh? Yeah, I saw that but it was kind of cryptic. If you look closely, it says 'auto oil every three months'. What could that refer to? None the less, there was never any resistance, whatsoever, when manually spinning the squirrel cage or subsequently, just the shaft itself. There is also absolutely no sign of any part of the motor having gotten hot. Needless, I will remove the other one and oil it, just in case.

As far as testing the Ohms, would I just put a multi meter on the two leads that lead to the plug?

For looking for a replacement motor, do you have any clue as to what kind of motor that is? Looking in the Grainger catalogue, there is a dizzying array of motor types.

 

[dvandsm64]

Re: Anyone familiar with electric motors?

bad bearings and or bushings

 

[dvandsm64]

Re: Anyone familiar with electric motors?

Hey, that macro photo function is pretty good, huh? Yeah, I saw that but it was kind of cryptic. If you look closely, it says 'auto oil every three months'. What could that refer to? None the less, there was never any resistance, whatsoever, when manually spinning the squirrel cage or subsequently, just the shaft itself. There is also absolutely no sign of any part of the motor having gotten hot. Needless, I will remove the other one and oil it, just in case.

As far as testing the Ohms, would I just put a multi meter on the two leads that lead to the plug?

For looking for a replacement motor, do you have any clue as to what kind of motor that is? Looking in the Grainger catalogue, there is a dizzying array of motor types.

as long as u ring both motors from the same leads, should give u similiar resistances through the brushes, windings,etc...

 

[PiratePast40]

Re: Anyone familiar with electric motors?

Might want to try a local motor rebuild shop to see what they can do. I've had a couple of motors that had problems and the guy at a shop in town could either fix it or get a replacement at a really good price. Grainger isn't known as a low price source, they usually list at MSRP.

BTW - from the picture, it looks like the right side and upper windings have burn marks on them.

 

[Tim Frank]

Re: Anyone familiar with electric motors?

Hey, that macro photo function is pretty good, huh? Yeah, I saw that but it was kind of cryptic. If you look closely, it says 'auto oil every three months'. What could that refer to? None the less, there was never any resistance, whatsoever, when manually spinning the squirrel cage or subsequently, just the shaft itself. There is also absolutely no sign of any part of the motor having gotten hot. Needless, I will remove the other one and oil it, just in case.

As far as testing the Ohms, would I just put a multi meter on the two leads that lead to the plug?

For looking for a replacement motor, do you have any clue as to what kind of motor that is? Looking in the Grainger catalogue, there is a dizzying array of motor types.

I think it says W20 auto oil. 20 weight automobile oil?

You could probably replace the bushings...or soak them in hot oil for an hour.

 

[bigdee]

Re: Anyone familiar with electric motors?

If the bushings feel OK with no lateral play and the shaft turns freely check for end play...sometimes the thrust washer or thrust bearing wears out causing the armature to slide partially out of the stator. If these conditions are OK chunk the motor for a new one.

 

[Boomyal]

Re: Anyone familiar with electric motors?

Might want to try a local motor rebuild shop to see what they can do. I've had a couple of motors that had problems and the guy at a shop in town could either fix it or get a replacement at a really good price. Grainger isn't known as a low price source, they usually list at MSRP.

BTW - from the picture, it looks like the right side and upper windings have burn marks on them.

I thought about stopping by my local starter repair shop to see what he had to say.

I checked re the burn marks. It is just the foto. One of the marks is a little bit of bubbled paint, like there was an air bubble when it was painted. No evidence of heat.

Both lateral and endplay are very good. All shaft, bearing and washer surfaces are pristine.

I'll have to do a more extensive electric motor search. It is correct that Graingers is no bargain. I guess they have to pay for that humongus catalogue somehow.

 

[j_martin]

Re: Anyone familiar with electric motors?

What you describe is how a squirrel cage motor runs when a bushing is worn and the armature lightly touches the stator. If the bushings are tight and turn freely, the motor (tin) frame might be bent a bit. If you can look at the stator and see where it's rubbing, you can "adjust" the metal a bit with a hammer and make it run in the center.

0.001 inch is the difference between running good and locked up. They get stupid like that when they get dropped as a baby.

hope it helps
john

 

[generator12]

Re: Anyone familiar with electric motors?

I see no sign of an armature or brushes. If not, there is probably a starting winding on this unit. Since it's trying to turn, that winding is probably okay. My guess is the running winding is OK also.

Usually a winding problem will do two things:

1. Overheat a shorted winding or, in the case of an open one, overheat the "good", unshorted winding paired with the open one.
2. Fail due to that overheating and/or the resultant short circuit.

I'd bet that your problem is either bearing wear, end play, or misalignment between the front and rear bearings. These very small fractional motors usually fail due to one or more of these than anything else.

If possible, loosen the bolts that hold the end caps on - just release the tension on them - and try to start it. Rotate each end cap very slightly to see if there is a "preferred" position, in which it operates more freely. If so, try to capture that position as you tighten the bolts.

If you can't find a postion in which it works acceptably, copy the nameplate information and do an internet search. You'll find one.

 

[DJ]

Re: Anyone familiar with electric motors?

WD-40 has NO lubricating qualities.

I would force some PB Blaster into the lube points followed by new grease. Old electric motors seem to last forever.

I wouldn 't be thinking "rebuild" until I got some lube to the bearings.

I'll bet it will be fine with lube getting to the bushings/bearings.

 

[Boomyal]

Re: Anyone familiar with electric motors?

Thanks for all your inputs but I have given up on it. Even my local electric motor shop has moved clear across town. I'll keep looking for a replacement motor.

This problem is either due to windings or magnets, none of which has taken any abuse from heat or mis-alignment. All of the rotor and stator surfaces are pristine with no sign of contact. The original case spray paint is undisturbed on the surfaces of the stator.

From the beginning, the rotor shaft spun easily and smoothly even not having been lubricated all these years. All the shafts, bushings and thrust washers are shiney clean and there does not seem to be any lateral slop or undue endplay.

Just for fun, again, I put it back out on the cold workbench in the garage. After an hour, the rotor just barely moved when I plugged it in. After it warmed up, it ran with more alacrity but was still somewhat anemic.

It will probably end up being a mystery unsolved.

btw, this motor is most likely called a shaded pole motor.

 

[generator12]

Re: Anyone familiar with electric motors?

I believe you're right. A shaded pole motor is probably what it is.

The shaded pole is used to simulate a rotation in the electric field, which is how the thing starts. And low starting torque is a constant with that type.

 

[dockwrecker]

Re: Anyone familiar with electric motors?

This is a bathroom exhaust fan? Looks bigger than that, or maybe you sized it larger for personal gas emmissions. We can wonder. New one with a light is between 60-90 bucks at Desperate Depot or Lowes.

 

[Boomyal]

Re: Anyone familiar with electric motors?

This is a bathroom exhaust fan? Looks bigger than that, or maybe you sized it larger for personal gas emmissions. We can wonder. New one with a light is between 60-90 bucks at Desperate Depot or Lowes.

Commercial size, I think.

My whole object was to keep from having to change all the ductwork, ceiling panel etc.