On Sat, 9 Feb 2008 19:46:04 -0600, "Robert Swinney"
wrote:

This whole discussion reminds me of the old saw about giving a monkey a loaded gun and wondering how
long it will be before he shoots you in the ass with it.

Bob Swinney


Bob, you can do what you want of course, but I'll reiterate:

I doubt you're going to find the data on a non-vfd rated motor,
so personally I'd be hesitant to run over 4800.

I doubt the numbers are valid for your motor, but the trend
should hold.

I know inverter duty motors are insulated better due to the issues of
cooling at low speeds and high voltage transients from the VFD. It is
also entirely possible that the rotors in inverter duty motors are
built to withstand overspeed conditions, given the likelihood they'll
get used that way. Also, your application involves the side load of a
belt, although that would only relate to bearing failure.

The overspeed failure normally includes unwrapping of the rotor with
consequent sudden stoppage, and in big motors, likelihood that the
motor is going to wind up in a different location. I heard of one
instance in one of our plants in Texas of a 100 Hp. motor making it
clear across the ground level of the plant when the pump it was
driving seized. Yikes!

I personally would be cautious. Like one of the posters said, a
failure can be catastrophic.


"Bob Engelhardt" wrote in message
...
Pete Keillor wrote:
...
Below is a link to the manual for Marathon Black Max motors, ...
Table 3.4 for the recommended
maximum for those motors. ...

Thanks - good link! A couple of interesting things the
- for *belted" loads, their limit is 125% of rated speed. I'd guess
that's because of the radial bearing load. I'm going to go ahead and
ignore that.
otherwise (direct load), for my frame:
- a 3600 rpm motor has a 7200 (120 Hz) limit
- a 1800 rpm motor has a limit of 5400 (180 Hz)

I think that I'll compromise between the 125% limit and the 200/300% and
limit the 3600 to 150% (90 Hz, 5400 rpm) & the 1800 to 200% (120 Hz,
3600 rpm).

Thanks,
Bob