Question About Motors

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Little Bill

Little Bill

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Semi-Retired Electrician
I'm not a motor guy so I know little about the different types. I know some that require start & run capacitors for single phase. My question is what type of single phase does not use the capacitors, and how do they start?

I have a small motor for a bath fan that has started stalling, or not starting. Sometimes it will come on full and just stop after a minute or so. Then sometimes it won't start at all. You can leave the switch on and it will eventually start. I've ruled out the switch and wiring. I would rather just replace the motor and not have to tear out the whole fan. The tag on the motor is faded so I don't know the size or type motor to buy.

I guess I'm asking if there is any way to fix the motor, or what type motor would be needed for replacement?
 
Most likely a shaded pole motor.

Like any single phase induction motor, you need some energy storage to create a proper rotating field. Instead of using capacitors, you have some wire turns shorted around a bit of the stator area, creating an inductance which stores energy and creates the rotating field.

See https://www.supplyhouse.com/Supco-SM552-Vent-Fan-Motor

My guess: the electromagnetic parts of the motor are just fine, but the bearings are shot or there is crud in the airgap. The bearings are probably simple oil soaked bushings, and adding new oil might be sufficient.

For replacement you mostly need to match mechanical sizes.

-Jon
 
winnie said:
Most likely a shaded pole motor.

Like any single phase induction motor, you need some energy storage to create a proper rotating field. Instead of using capacitors, you have some wire turns shorted around a bit of the stator area, creating an inductance which stores energy and creates the rotating field.

See https://www.supplyhouse.com/Supco-SM552-Vent-Fan-Motor

My guess: the electromagnetic parts of the motor are just fine, but the bearings are shot or there is crud in the airgap. The bearings are probably simple oil soaked bushings, and adding new oil might be sufficient.

For replacement you mostly need to match mechanical sizes.

-Jon
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Thanks, I will look for areas that I might could oil. Then try to find out the motor size.
 
What are the odds you fan was not made by Broan or Nutone?
I have bought the Broan replacements motors at big box stores. They fit into old fan housing, if you are slightly handy. They had some selectIon assistance on their website.
 
I have found replacements available at the big box or online. Usually comes with the motor & blower wheel already mounted and a new intake grill. You just pull the guts out and leave the same can. The bath fans at my condo are cheap builders models but they work ok. It was built in the 80s and the motors etc are still available
 
jim dungar said:
What are the odds you fan was not made by Broan or Nutone?
I have bought the Broan replacements motors at big box stores. They fit into old fan housing, if you are slightly handy. They had some selectIon assistance on their website.
Click to expand...
Eddie702 said:
I have found replacements available at the big box or online. Usually comes with the motor & blower wheel already mounted and a new intake grill. You just pull the guts out and leave the same can. The bath fans at my condo are cheap builders models but they work ok. It was built in the 80s and the motors etc are still available
Click to expand...
It is a Nutone, but it is very old. It's not like the tiny motors on the newer ones. I have replaced lots of those for customers. I haven't been able to find anything from Big Box or my SH for this one. I haven't been to the website, but will check it out.
 
Little Bill said:
I'm not a motor guy so I know little about the different types. I know some that require start & run capacitors for single phase. My question is what type of single phase does not use the capacitors, and how do they start?

I have a small motor for a bath fan that has started stalling, or not starting. Sometimes it will come on full and just stop after a minute or so. Then sometimes it won't start at all. You can leave the switch on and it will eventually start. I've ruled out the switch and wiring. I would rather just replace the motor and not have to tear out the whole fan. The tag on the motor is faded so I don't know the size or type motor to buy.

I guess I'm asking if there is any way to fix the motor, or what type motor would be needed for replacement?
Click to expand...
FYI, most resi fart fans are "universal motors" here is an explanation. https://byjus.com/physics/universal-motor/#:~:text=When fed with an AC,are in the same phase.
 
Little Bill said:
Thanks, I will look for areas that I might could oil. Then try to find out the motor size.
Click to expand...
Disassemble it and clean it thoroughly, especially the bearing surfaces inside & out.
Use the right kind of oil. Sewing-machine oil or turbine oil. Do not use automotive engine oil; it's intended for use at 125ºC and its viscosity is much too high at room temperature.
 
Here is some pics of the ones I did this weekend.
Had to clean and oil three, replace two motors with one bought at big box. Just took new out of new fan and replaced into old motor housing.

New fan was 21.00
Replacement motor was 31.00
So bought new fans and removed motors fan wheels.
 

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Tulsa Electrician said:
Here is some pics of the ones I did this weekend.
Had to clean and oil three, replace two motors with one bought at big box. Just took new out of new fan and replaced into old motor housing.

New fan was 21.00
Replacement motor was 31.00
So bought new fans and removed motors fan wheels.
Click to expand...
I believe Bills are somewhat older. Remember, he belongs to the OTD group.
 
Also, make note of how the motor comes apart and be sure to reassemble it the same way.
If you install the armature of a shaded-pole motor upside down, (this is easy to do; they're usually symmetrical) it will turn the other way and the fan will be less effective, less efficient, and probably noisier.
 
Seven-Delta-FortyOne said:
You do it from the bottom side.

Pull the cover, usually one or two screws and the entire housing comes down, unplug the connector, and it’s out. 👍
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I've took enough down to know that you can't always get them from below. Especially if they used the arms to attach to the joists. I always thought I had won the lottery when I could remove/install a fan from below.
 
If you can't find an upgrade/retro kit, try a new fan and mounting the new motor to the old plate.
 
LarryFine said:
If you can't find an upgrade/retro kit, try a new fan and mounting the new motor to the old plate.
Click to expand...
I found this on Ebay. Not sure yet if it is the one, but my motor is similar. It's not the tiny little motors that come in the newer fans in the lower sones category.

1703743701376.jpeg
 
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