Hot Laminations to Exhaust Fan Motor

Discussion in 'General Electronics Chat' started by David Babbitt, Dec 21, 2010.

  1. David Babbitt

    Thread Starter Member

    Oct 8, 2010
    I'm wondering why the steel laminations in a residential bathroom exhaust fan motor got so hot, so hot it slowed down and stoped. Within 5 minutes of running they got to 40 degF above ambient temperature. I compared to a similar motor and it rose to 20 degF in 5 minutes, acceptable, satisfactory.

    I compared the resistance and inductive reactance of both motor stators that encircle the laminations. They were essentially the same, 26 ohms resistive, inductive too small to measure using a resistor in series and computing the reactive. I didn't examine the squirrel cage rotors, assuming no fault there. They both run at 3400 RPM per photo tachometer.

    Any ideas? See photograph.
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    Dust, humidity, corrosion, toxic fume exposure? Bad bearings?

    The fans in my bath have operated for more than 30 years without service. Besides, 40°F above an ambient of 70°F is only 43°C. Many motors are rated to run hotter than that. If it stops at that temp, there is probably something wrong with the motor.

  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
    A drop or two of 3in1 oil on the motor bearings will help. How long since they were oiled? Line John said the bathroom environment, especially the humidity is hard on them, but oil should make them all better.
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    Toxic fumes...heheh :D
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Most likely the bearings failed. As they are typically sintered, there's not much to do but replace it.

    The motor created more heat because it was overloaded "trying to spin the fan", in layman's terms. Essentially, the windings looked more like a resistor to dissipate heat instead of the inductive load the spinning rotor provided.