Why is my new 1ph AC motor overheating?

[tmoore624]

Hello all,

I'm about at my wits end with this project, so maybe someone with a little more knowledge can help me out? I recently bought a 30" Patterson air cannon fan that came with a Dayton 1hp 3ph ac motor. The whole unit needed to be reconditioned, and the motor needed to be replaced. After reconditioning the housing, I purchased a Leeson 1hp 1ph ac cap start motor to replace the 3ph motor, since we do not have 3ph power. Assembled everything, and wired the motor for 115V per the diagram stamped on the motor. The motor ran great for about 2 hours, then we noticed a burning smell, and found the motor to be extremely hot and smoking a little bit. Let it sit for several hours to cool down. Came back to find the motor locked. Had the motor replaced with an identical unit. After wiring in the new motor, it ran for 20 minutes before it started to get pretty warm. Shut it down before any serious damage occurred. When I contacted the company we purchased the motor from initially, they were stumped, and said this motor should be well suited for this application.
The motor is on it's own dedicated circuit. It is on a 30A 1 pole breaker, 10-2 solid copper wire, ending in a 30A receptacle. The fan has a 30A rated switch, and 12 ft 20A rated cord. I felt the cord was ok, seeing as how the full load amps of the motor is 13.6A. I know the power coming in is fine, but I'm at a loss as to why after 2 motors, this problem persists? The rated rpm of the motor is 1725. The old motor was 1175. Could it be the motor is spinning too fast since there is very little load? Any help would be greatly appreciated.

 

[Asymptotic]

The rated rpm of the motor is 1725. The old motor was 1175.

That's it right there.

For most fans and blowers, power requirement changes as the cube of speed (see affinity laws). You'd need a bit more than 3 HP to operate at 1725RPM versus the original motor's 1HP at 1175 RPM.

 

[tmoore624]

I learn something new every day. So would a 5 hp motor with the same specs be fine, or would I be better off just going back with something in the 1100 rpm range? Thank you so much much for your reply.

 

[Asymptotic]

I learn something new every day. So would a 5 hp motor with the same specs be fine, or would I be better off just going back with something in the 1100 rpm range? Thank you so much much for your reply.

If it uses pulleys and a V belt power transmission (and if there is enough room to fit a larger fan pulley) it should be possible to increase fan pulley diameter enough to drop fan RPM into a usable speed range.

If it is a direct drive (fan blades are mounted directly onto the motor shaft) then a 1 HP, 1 Ph, motor in the 1100-1200 RPM range is your best bet, and may be your only move. Standard single phase, 120V power range is limited to 3 HP, and in any event, the increase in overall motor frame size and shaft diameter may require a lot of mechanical rejiggering to get it installed (if it is even possible).

Good luck!