On 2009-04-04, Karl Townsend wrote:


Others have said "Check with the manufacturer" - I'll tell what they'll
say: "Don't do it, it's not rated for it". But you won't know if they're
just covering themselves or if they mean it. If you ask "Why", you won't
know whether you've gotten a straight answer to that, either.

Ya, I'm not going to bother.

I thin that you are making wrong assumptions. Whenever I would ask VFD
companies or motor manufacturers I would get a straight answer such as
"do not do it because..." or "you can do it".

i




I can see 2 effects of higher that rated RPM: centrifugal forces on the
rotor windings (do 3 ph motors have rotor windings?) and bearing
overheating. Now, many motors have a rated speed of 3600 rpm & I doubt
that there's much difference between their designs (rotor & bearings) and
1200 rpm motors. I doubt that there would be enough cost savings to
justify different "technologies".

So, you gots to ax yourself "Do I feel lucky?". IOW, are you willing to
risk that motor to find out? I hope you do, 'cause I'd like to know. So
be sure to follow up if you do.


I've run a 1800 RPM 7 1/2 HP at 3600 for 100s of hours. (CHNC spindle). As
no one seems to know, I'm just going to guess that it is better to find an
1800 RPM motor - pretty sure that will work. These are fairly easy to find.

Karl