Originally Posted by NC Cams  Whatever speed you run at, you'll cut service life of the motor bearings by a factor that EASILY EXCEEDS the inverse of the ratio of the new speed versus the previous rated speed.
Reason: the bearings will run at a much higher velocity and thus tend to heat up the grease therein much more. Thus, grease life can/will be drastically shortened.
Keep in mind that whatever factory imbalance tolerance that is allowed, will greatly be amplified by overspeeding. Thus, whatever was "tolerable" before, could become intolerable now. Result: drastically shortened life potential.
You also won't know if the motor is able to cool itself properly at the higher speed potential. Elevated temps geometrically tend to cut life expectancies.
A well epoxied armature should not toss windings. However, overheat one and run it DRASTIALLY above the rated speed, you could toss windings, balance weights or even other components that are not speed rated for the new ultraspeed.
The ultimate speed potential of the bearings is dependant on the size of the bearing. Simply specifying 'ball bearing' doesn't assure that the speed of the bearing can arbitrarily be doubled. This is especially true if the armature runs thru a range where it could go into an imbalance due to bizarre magnetic vectoring issues that can develop (saw it happen).
Geof's method is as good as any.
Unless someone has already run the same motor you're using at the speeds/loads you're going to encounter, a "generic" yes/no or maybe answer to the viability of the planned overspeeding effort is not something that I personally would count on. |
Are you talking about a dc motor or ac, ac induction rotors are laminated, they don't have armature coils to toss, they normaly have a aluminum end capped with fins onto it each end(no epoxy), its possible for them to become unlaminated from overheating, but I have never seen it. More likley they will shift or warp hitting the stator coil lams, this can happen from both locked rotor for excsive times and over speeding from bad bearings. Balancing is done on that end plate, typicaly if needs to be balanced they remove wieght via drilling not adding, tweaking the end casting can also happen dependant upon design as some have fins that stick out away from the lams.
Also most motors with ball bearings will have 5k rpm top end unless specially fitted, thats your typical 62xx series bearings which almost everyone uses.
Loesch
Friction and windage from the fan on the back end of that motor will cut its ablity to overspeed quite a bit, I would be impressed if you got 120 Hz on one HP, its entirely possible to go higher but the motor more then likely just won't.
At low RPM the motor will become hotter then normal, baldor seemst to better here then most others, you will have to call them and find out but I would that an inverted rated insulation motor should be able to handle 25Hz for cont. duty at FLA(full load amps) and less Hz for shorter periods. Just remember you loose torque with speed loss and and it flat lines above namplate speed the motor will preform the best at or near namplate speed. So boring that big hole won't be as easy with the drive only putting out 15Hz, if geared or belted correctly it should not be a problem. Even when you go to vector/sensorless control, the gains in torque are still not outstanding when using a regular motor.
chris