Fan motor question

[supersurgilator]

Does anybody know anything about portable fan motors? Reason I ask is because I have always heard that if you run the motor without the blades, it would overheat, as it relies on the air blowing through to cool the motor. One of my friends says that a relative of hers has slept with a fan motor since college (just the motor, no blades) She puts it on her nightstand and turns it on for white noise. The scary thing is this motor is quite old and I am really surprised that it has never overheated and caught on fire. Maybe that was just a myth, but I always thought fan motors could overheat being operated without blades.

 

[qsd-dan]

"The scary thing is this motor is quite old and I am really surprised that it has never overheated and caught on fire."

That doesn't surprise me. The older stuff was designed to take a beating. I know an older gentleman who has been running a 68 year old Emerson fan in his shop continuously 24/7/365 for over 30 years without a repair. Oh yeah, I forgot to mention he pulled it out of the trash in the 70's!! He says he oils it monthly. I sure love my 1940 Emerson 77648 fan!

 

[yogitunes]

many motors have a little fan blade built in to help cool the coils, some do and some don't....

 

[supremewhirlpol]

How old is the fan? Is it newer? It really depends on what duty the motor is rated for. I lot of smaller table fans have what are called shaded pole motors, capacitor-run motors and Permanent Split capacitor motors (PSC). Most of them are shaded pole and capacitor-run. Some of the motors do have internal blades for cooling, while others are cooled by the surrounding air. Motors that are cooled by the air may have a rating of "Air Over Struts". Do you have a picture of the motor? If you have a picture I can tell you what the motor is most likely rated for.

 

[tolivac]

Supremewhirlpol is correct here-there is a class of motors for fan and blower duty that are termed "air over " cooling they use the airstream from the fan or blower blades for cooling-these motors DON'T usually have an internal fan or fan blades cast into the rotor short rings.New fan and blower motors of this type have an internal thermal switch to shut off the motor if it overheats-like a curtain sucked into the fan grill or the fan falls over.A running fan laying on its face or back will have no airflow to cool the motor.Yes try to show a picture of the motor-I WOULD NOT recommend running the motor without the fan blade on the shaft-esp if it is an older motor.Older motors DON'T have the Thermal switch!You could start a fire.I have run a fan while I am sleeping for years even winter to shut out ext noise-in this case a neighbors barking dogs.Earlier years it was apartment living-all kinds of noises there.

 

[tristarcxl]

Well...

Let's be sensible here...... Most fan motors only pull a few watts! Whether or not they're cooled is really pretty inconsequential. The mass of the iron in the field windings and the turbulence created by the laminations in the rotor will usually cool the motor sufficiently to allow it to operate indefinitely.

Consider this....most bathroom vent fans have the same motors that table fans do. The motor is stuck up inside the cabinet with no fan, no vents, and no cooling. They last for years and years being run 24/7.

You also have to remember....a fan motor without a blade pulls far less current than a fan motor with a blade.....therefore it runs cooler than with a load.....

 

[supremewhirlpol]

You do bring a good point tristarcxl. If it is a standard shaded pole motor, it should be fine, but i'm not sure what type of motor it is. I wanted to see it to identify what type it was first. But it will probably be ok, just try to monitor the motor for changes in operation, such as burning smells, or the motor being hotter than normal, or locked rotor condition.

 

[davek]

Oh yeah, I forgot to mention he pulled it out of the trash i

Everything would last a lot longer if it got fresh oil monthly. Nothing today is made to accept any oil. At best, they have bearings of oiled bronze.

 

[tolivac]

There are some fan and blower motors that are "air over" cooled that are not shaded pole and draw more than a few watts.They may be as large as one half HP-your furnace-AC fan could be air over if its direct drive.Also some large floor fans-they even have a warning label on the motor not to run it unless a fan propeller is mounted on the motor shaft-Yes-shaded pole motors are current limited-they will run fine with or without a fan blade-some even have their own small fans attached to the motor shaft or built into the rotor.The motor in your bathroom or kitchen vent fan-blower has an air over motor.these will be fine.If the motor has bearings you can lube--so much the better for motor life.