Ceiling fan issue

[eeprom]

I know this isn't the obvious forum to post this, but I'm pretty sure someone here can answer it.

A house ceiling fan makes a humming noise when it's on. Sounds like the motor would normally sound while it's coming to speed.

The fan spins and changes speed with the different switch positions, but there's a constant hum, even when the fan is at speed. Then I turn it off and the hum continues until the blades come to a full stop. But then while it's off I spin the blades by hand and the humming comes back. Any rotation of the blades causes the hum.

Then I turned off the breaker to the fan and spin the blades by hand and there is no hum.

The fan has a capacitor. I'm not sure that's related.

I'm sure the fan is dead, and I will replace it. But
any idea what this could be?

 

[racookpe1978]

Since it occurs when the fan is turned by hand, I would discount electrical or speed control interference or resonance.
Gotta be mechanical/bearing problem.

 

[waross]

Or it may be a fsulty speed control.

 

[eeprom]

It doesn't happen when there is no power to the circuit. It can't be bearings.

The speed switch (3 spd) is brand new.

The humming happens when the fan is off if the blades are spun by hand. It doesn't happen if the circuit breaker to the fan is open, and the fan is spun by hand.

 

[FacEngrPE]

A house inspector offers a list of causes of house ceiling fan
https://timbersill.com/light-fixtures/ceiling-fans/ceiling-fan-humming/

Ceiling Fan Uses A Dimmer Switch​

Loose Or Faulty Wire Connectors​

Loose Light Covers​

Loose Ceiling Fan Housing Screws​

Vibrating Light Bulbs​

Older Ceiling Fan Needs Lubricating Oil​

Unbalanced Fan Blades​

Ceiling Fan Is Past Life Expectance​

Small Piece of Metal Or Plastic Inside of Housing​

Loose Fan Blades Or Blade Screws Create Clicking​

This seems like a reasonable troubleshooting list.

 

[eeprom]

Thanks. I agree. The fan is past it's lifespan. But I would still like to know as an engineer why it hums when the switch is off and the blades are spun by hand. That makes me think it's not really off.

 

[waross]

A Wild Assumption Guess:
Control is wired in the neutral.
A small part of the winding is shorted to ground.

 

[eeprom]

Wouldn't the winding burn up if it the fan wasn't spinning and there was current in the winding?

 

[TugboatEng]

What do you mean the power is off? Is the dimmer set to zero or is there actually a switch that breaks the circuit? A diac/triac type dimmer does not completely break the circuit. Traditional dimmer knobs have a detent and switch near the zero position. Fans are usually shaded pole motors. Turning it maybe causes some amount of increased current and audible buzzing. I never needed to know anything about the low power characteristic of a shaded pole motor.

The diac/triac dimmer is a wave shaping device. It still passes 60hz , it just clips the waveform to reduce average voltage. It uses an RC circuit to time the trigger.

 

[davidbeach]

Yea, off as in not moving or off as in no applied voltage? They may look very similar...

 

[ewh]

It doesn't happen if the circuit breaker to the fan is open, and the fan is spun by hand