Squealing noise from 7 hp motor

Hmmmmmmm.....

• A bearing in need of lubrication?
• A drive belt slipping?
• A fan blade dragging on a cooling cowl?

Thanks for the reply, It does not have any belts, the bearings are sealed pre lubricated as best as I can tell, the fan inside the motor cowl is not dragging, I have the cowl off and it is still squealing. I guess the next step would be to replace the bearings, I just wanted to ask before I tore it all down.

pipewelder

When you turn it by hand, Put a screwdriver on the casing and the other end in your ear! (seriously!) Is there any fine grating sounds coming from the motor or around the bearing seal behind the fan?

LOL By "seriously" I'm guessing you mean, do it alone where no one else is watching. Being seen applying stethoscope to machine can lead others to think one is a nut case--something I learned all to painfully (and expensively) when trying to isolate defect noise in an IC rating branding machine while supervising a production line. A clear case of "too much knowledge can be a dangerous thing," especially in USA.

A third "manufactured" phase, created by capacitors, might not be exactly 120 degrees from the other phases and may be the source for the noise.

Is this "balanced output current" you mentioned under full load conditions? Usually this type of converter has unbalanced output.

If you have not noticed any excessive heat rise and can live with the noise, it will probably be OK.

If the output of the motor is connected tightly by a set screw, confirm that it is not loose.

May be 2 X line frequency noise. Did you check the motor for "soft foot" before wrenching the foot bolts down?

Thanks for all the replies. I will check all of these out as soon as I can. The current measurements are without a load on the motor. My buddy looked at the motor and told me that all the Baldor motors he buys have a grease fittings for the bearing lubrication. After looking at my motor it has a set screw plug on each end where the grease fitting usually is he was talking about. I don't know if there is a channel to lube. the bearing and it just didn't have a factory shipped grease fitting or if maybe the bearing is not able to be lubricated. I had assumed it was a sealed bearing because it did not have a grease fitting. I didn't think about checking for soft foot because the motor does not have anything attached to it that I would normally consider needing alignment. The frame is not extremely heavy though so I would think it would give enough to eliminate a soft foot.

pipewelder

maybe give it a few drops of 20WT? See if that helps?

The motor most likely has 4 foot bolts. Forget about coupling or belt alignment. If the motor does not sit true to the base and you tighten the bolts, this could cause motor frame distortion. Consequently, the bearings could then become misaligned. If the distortion is severe enough, it can cause vibration at 2 times the shaft turning speed. It may also preload the bearings and could cause a squeel. An other issue that can develop is an un-even air gap between the rotor iron (magnet) and the stator iron (magnet). The un-even air gap can cause a high 2 times line frequency vibration and that sometimes promotes a loud noise at 120 hz. The industry standard soft foot tolerance is .003". A quick way to determine if soft foot is the problem is to (with motor running) loosen one bolt and retighten before going to the next. if you hear the noise go away while loosening a bolt, you will need to shim that foot accordingly.

Thanks for your reply, I will check it out. It does have 4 foot bolts but it has nothing hooked to it such as coupling or belts as it is being used for a rotory phase converter.

pipewelder