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Old question about fan

S

Stan in Oly, WA

Well-known Member
I asked this question, or a related version of it, years ago, but since I don't remember the answer, I'm going to ask again. I have a small utility bathroom which we rarely use. There is a ceiling exhaust fan which does not start running as soon as the switch is turned on. It will start immediately if it has been used earlier the same day, pretty quickly if it has been used a day or two previously, and can take up to several minutes to begin running if it hasn't been used in a while. My question is, what's happening to the fan motor when it is on but not turning? If an electric power tool binds up in use, I have to get my finger off the trigger quickly or it will be damaged, so how has the bathroom fan managed to perform this way for years and still seem perfectly fine once it gets going?

Stan
 
Hello Stan in Oly WA,

Most likely just build up moist-dirt around the motor shaft. Most of those motors are the shaded pole type. Have pretty much zero torque. Even with the fan blade not turning the will not burn up or trip the breaker. look and see if the armature is visible.
If it is you will see a wire embedded in the outer fields. that would make it a shade pole motor. That's my guess

Guido.
 
Very simply it is dirty and when it takes a bit to start spinning it is getting hot and once hot enough the bearing/Bushing expand enough to free things up and then it spins up. It need to be pulled out and then cleaned up real good and the bearing/bushings lubed up good
 
Thanks for the quick and clear replies Guido, Bob, Dave, and Rich. Sounds like I ought to be able to get it running normally, God willing and the levee don't break.

Stan
 
Just another thought, if the fan is on a separate switch than the light it could be the switch sticking internally. If they are on the same switch then disregard.
 
Those fan motors are most of the time a very simple motor with brass bushings. I have taken many of them apart over the years and cleaned them and lubed them up with well you guessed it I use ATF on them. I keep a little squeeze bottle in the house full of ATF for things like that
 
Good suggestion---you never know where the problem will lie. The fan and the light are on separate switches, but the fan's current and previous switches were timers I put in. The timer I just replaced was fully functional, but was missing the knob. When I put it in, I expected to find a knob for it eventually (without making a specific effort to get one), but when that never happened and a spare timer came up from a different location, I changed it out again. I wish it was as simple as a malfunctioning switch, but I'm afraid it's the fan itself.

Stan
 
Just buy a new one of the same brand and change out the fan and motor. Most bathroom vent fans are real cheap. I used to pay around 10 dollars for the cheap fan. Installed 100s of them. most of them 1 screw and you can remove the motor and blade assembly. Could be the light sw but I doubt it.
 
I use ATF for both. I use it in a pumper oil can for freeing thing up and also in many places you need simple oil for a lube. I also use it as a gun cleaning oil and lube. I have found it works well as a universal oil
 
Guido has it right. Shaded pole motors have very little starting torque, so if there's any resistance they won't turn. But once the motor gets going, the "stiction" in the bearings will go away and it will work for a while.

If you can get a replacement, change out the fan and motor. But if it's an oddball brand for which parts aren't available and it's not practical to replace the whole unit, you can probably get a few more years out of it by lubricating the bearings with a drop of light oil.

Electric power tools use "universal" (AC/DC brush) motors that have full torque at zero RPM. If the motor is stalled it will draw tremendous current. A stalled shaded-pole motor, on the other hand, doesn't draw much current and is operating at almost zero power factor, so it will heat up just a little bit.
 
I have several house fans that I have picked up that people were throwing out, cleaned and lubed the bearings and they work fine.
 
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