AC Fan Motor Behavior

Is the fan blade pitch different or are the speed reduction ratios different?

Is the outgoing air flow restricted or limited?

Trying to spin a 4 ft dia fan only a little bit faster than what it was designed for can take a lot more power. As I recall doubling a fans speed can take about 4 times more power to run it. I may be wrong on that though, its been a while since I did any large fan work.

Both the Currently operating fan drive motor, and the one in question are the same?

Try disconnecting both belt assemblies, and turn each fan by hand, notice any difference?

Do the same with each component in the system. Compare the amount of resistance of each component on the "Non operating" system with the same component on the operating system.

"I have changed the bearings on the fan already" -Was this before or after the problem began?

Are you sure you have the motor wired to run on the full 220V?

It will spin on 110V, but lack the torque to operate as designed for 220V use. Double check how it is wired compared with the system that is normally operating.

I suppose thats enough to get a start on it... keep us updated.

Yes, I changed the bearings in response to friction that the fan was experiencing. The motors are not completely identical in that the currently operating one is rated at 1430rpm at 110V and 1725 at 230V. The 2 motors that I have currently have the same HP/Amp/rpm ratings but don't make that distinction. I did wire it to Hi voltage, even switched it to low just to see what would happen and it's definitely less happy!

The fan is a 3 aluminum blade one that is pretty beat up. I'm sure that the angle of the blades at this point is not anywhere near the mfr specs.

I just ordered some new motors (for back up purposes, I have 16 fans total and with hot weather they all need to be working) and got 1.5HP this time.

"Yes, I changed the bearings in response to friction that the fan was experiencing."

So.. this problem is the same before and after the bearing replacement? Did changing the bearing in the fan make any difference?

You have 16 of these units?

The one in question is the only one giving you grief?

Are the rest of the fan blades in the same shape as the one in question?

Yes the problem is the same, although I have a sneekiy suspicion that the old bearings did contribute to the original motor going out

This is the only one out of 16 exhibiting this issue. 4 have 3-blade galvanized metal props, the others are 3-blade fiberglass props, no belt tensioner but same motor.

This is probably the worst prop of the 4 with the same set-up

I think you may be onto something here... You could probably identify the problem as the prop... swap out the prop with the one operating correctly next to it... if the problem follows the prop its the prop... probably need to invest in a few more.

If the problem doesn't follow the prop its another factor in the system, but at least you will have crossed the prop off the list of possibilities.

So you have 16 more or less identical fans, one of which fails. RV has hit most of the points. But you mentioned "This is the only one out of 16 exhibiting this issue. 4 have 3-blade galvanized metal props, the others are 3-blade fiberglass props, no belt tensioner but same motor." Is this the only one with a tensioner? Maybe the tensions off.

Keep those chickens cool !!

Try to reduce the belts tensioning. If the belts tensioning is too tight, it will cause your motor to loss the torque due to the motor and the fan shaft is "pulling" each other.

We have the same experience in here. When I try to tighten the belts tensioning slightly higher, the motor having problem to ramps up the fan speed to normal speed and caused the motor in overcurrent trip.

Tightening belts does not make any meaningful difference to the motor load. What you are experiencing is that when you start the fan the belts slip allowing the motor to get up to speed fast enough not to trip. With the belts "correctly" tensioned they try to turn the fan during start up with no slip and trip the motor.

Typical example of a poorly desinged system. Your motors are under sized.

Yeah, I have a feeling that (as I've seen in other instances) that things aren't spec'd to what they should be and fail prematurely. Now whether that is to sell parts and make money that way, or they're trying to keep the upfront cost low is a discussion for another day. The way it stands right now I'm basically rebuilding the whole unit except for its housing. New motor, new tensioner, new prop. Overall consensus appears to be that the prop is the most likely culprit. I will have the parts in from Chicago next week (we're in OR) and will let you know about my progress.

Thanks so much to everyone responding. This is my first time using this forum and I'm very impressed. Hopefully I can be of help some day too...

...may not be of help, but is a simple solution...perhaps you need to throw in Starter Capacitor to get that baby up an running at the proper RPM's without overloading it when you start it.

Would be curious to know if you experience loss of power to other electrical devices when you start the problem motor, which would point to needing a cap to kick the motor in at the right RPM.

One motor I tried (the brand new one) is a cap-start/cap-run type. The other one was a cap-start type. I can almost audibly hear the start capacitor hand over the job to the run capacitor after which it gives up in only a short while. I do not notice any noticeable loss of power to other devices (usually my lights dim if I have that happen, like when my water pumps come on at the same time). I have 200amp coming in to the panel.

Do determine line voltage drop too

You are in Oregon eh?

You in Cresswell?

Mystery solved! It was the prop. In anticipation of my new prop coming I messed with the blades and reduced the pitch simply by twisting them. Now the fan runs continuously! I would have never given that any thought. One more reason to go back to engineering school....

And no, we're not in Creswell. The plant there has been shut down for some time but there is still a grower left close to the old plant. We're about 45 minutes NW from there in Junction City.

Ahh yes Junction City. I grew Up in cottage grove, and Eugene. I knew a bunch Of people out there at the place in Cresswell.

Good job on the Blades...