Should motor be replaced?
Should motor be replaced?
(OP)
We have a 7.5 hp 460 VAC 3ph motor on a gantry crane w/ nameplate FLA of 11.5. During operation the motor pulls approx 15.5 A. The motor is about 50 yrs old, but doesn't get used very often. Operation is critical when called upon. During operation they lift gates at a spillway, runs about 15 min per lift. Is 15.5 A too high for this application or is motor ok for short durations and infrequent use.





RE: Should motor be replaced?
I'm not sure about the current. I would be surprised if the OEM had misapplied the motor. Is it a 11.5A continuous or momentary rating? Is there anything on the nameplate that indicates the motor is suitable for short time overload? Is it possible that mechanical changes (binding) have caused increased load?
RE: Should motor be replaced?
RE: Should motor be replaced?
In many cases it is unwise to run any motor at a sustained 35% overload, particularly with insulation of advanced age.
Have you determined if overcurrent is from a mechanical or electrical problem? Have your determined if the motor-overload relay is correctly sized and indeed operational?
What does loss of production cost if the motor fails at an inopportune moment?
RE: Should motor be replaced?
Your motor is an old timer and like most old timers ,you cannot stress it too much.You don't mention the nameplate SFactor, but even at 1.15 SF it should only run at no more that 13.2 Amps for the type of cycle you experience.
If this motor has to run for 15 minutes drawing 15.4 amps, it is possible that motor overload protection is non existent.If it has never ben overhauled,perhaps it is time to refresh the bearings,clean windings and double dip same.If you do that, it may last a good number of years
once again.As you say, your motor is critical whenever it is needed.Just for some peace of mind I think I would do an overhaul.This motor has paid its dues many times over.
I do believe in condition monitoring but there are extenuating circunstances and I think this is on of them.
Thanks
GusD
RE: Should motor be replaced?
Thanks again.
RE: Should motor be replaced?
RE: Should motor be replaced?
RE: Should motor be replaced?
It is possible for some reason the load required for the motor has increased in the last 50 years, although most that come to mind are because of inadequet mechanical maintenance.
RE: Should motor be replaced?
RE: Should motor be replaced?
Considered rewinding at a better insulation class?... Then the motor will have no problems if she still gets warm in those 15 minutes! You may be hard pressed to find an exact replacement for that motor!
RE: Should motor be replaced?
RE: Should motor be replaced?