Ceiling Fan rotates slower

[JFletcher]

It sure is.:thumbsup:

Now that is a ceiling fan.

Very cool looking fan!

When that fan is moving air up, I wonder how much extra force it is adding to its own weight - perhaps enough that it has to be taken into design considerations.

 

[jmellc]

This ^^^^^

Just repaired one a while back that the capacitor had burned out. Had to put a complete new control unit on it as the capacitor was built in to it.
But the same problem can happen on an external cap.

To the OP:
I would either tell them to replace the fan or pay you to take out the old cap and try to find a matching one. When they find out the charge for troubleshooting is close to the price of a new fan they might just opt for a new one!

The little I dealt with capacitors, a bad one caused the fan not to start but didn't affect running speed. I would have to spin the blades & then it went OK. Do they work differently with different motors?

 

[drcampbell]

...When that fan is moving air up, I wonder how much extra force it is adding to its own weight - perhaps enough that it has to be taken into design considerations.

At an airspeed of 400 feet/minute, about 0.00035 pounds per square inch, based on disc area, (the entire diameter of the fan) not blade area. (length x width of each blade x number of blades) For a 60-inch-diameter fan, one pound of force.

F = ½⍴v²A

F: Force
⍴: density of fluid
v: velocity of fluid
A: area

 

[kwired]

The little I dealt with capacitors, a bad one caused the fan not to start but didn't affect running speed. I would have to spin the blades & then it went OK. Do they work differently with different motors?

For the typical household ceiling fan they are what dictates speed. They are usually a two or three value capacitor and when you change the speed switch you are changing how much capacitance is in the motor circuit which will change how much torque the motor puts out. On low speed the motor "synchronous speed" is same as it is on high speed, there just is less torque and more slip then there is on high speed.

 

[JFletcher]

At an airspeed of 400 feet/minute, about 0.00035 pounds per square inch, based on disc area, (the entire diameter of the fan) not blade area. (length x width of each blade x number of blades) For a 60-inch-diameter fan, one pound of force.

F = ½⍴v²A

F: Force
⍴: density of fluid
v: velocity of fluid
A: area

surely tho an industrial fan like kwired linked several posts up would generate more than a pound of downforce? thanks for the equation tho!

(I'm still leaning toward loose blades causing a pitch and subsequent drag/speed change). Also, an out of balance fan would cause more motor load and less rpm, yes?

 

[ggunn]

surely tho an industrial fan like kwired linked several posts up would generate more than a pound of downforce?

Have you ever seen one of those BA (I heard they are changing their name from Big Ass to BA) fans in operation? They typically turn pretty slowly.

 

[ADub]

Have you ever seen one of those BA (I heard they are changing their name from Big Ass to BA) fans in operation? They typically turn pretty slowly.

And will blow away anything not nailed down when they're ran wide open. We have dozens of those in our building

 

[kwired]

Have you ever seen one of those BA (I heard they are changing their name from Big Ass to BA) fans in operation? They typically turn pretty slowly.

I have installed them before. Yes RPM is low, but there is a lot of blade and if you consider how far the outer edge is traveling per revolution there is possibly more velocity there then there is on a small fan running at a higher RPM.

Big Ass puts some engineering into maximizing performance of those blades they are not just a big hunk of metal randomly connected to a rotating hub.

 

[just the cowboy]

warped blades

warped blades

eta: as to why an existing fan turns slower than it used to; drag in bearings, loose blades causing more blade pitch and air drag, extremely dirty fan (air drag), could be many things not electrically related.

I had one that the blades drooped after twenty years of humidity,a good hunter. My sons old crayon looking fan worked the best, quiet and workedgreat.