Re: rod-mill project - "mains" electric motor advice

"Richard Smith"  wrote in message news:m1iklhuoo1.fsf@void.com...
50% faster would generally be without unsought thrills?
YOu could go a bit faster as a test with everything out of the way, then
settle on what you want?
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That's a question to ask the motor manufacturer. More speed gives greater iron loss heating and greater centrifugal force on the rotor assembly components. I haven't yet abused motors; measuring the frequency response of Variacs showed me that they were closely designed for their rated frequency, losses rose and efficiency dropped rapidly above 60Hz, even at low voltage. I had considered using them in speaker crossover networks. Also applying more than the rated voltage to Variacs and transformers increases the iron loss by increasing the magnetic field strength above its design limit. The loss is visible as an increase in no-load current, which is proportional to voltage below the design limit and rises sharply above it.
For example I saw twice the no-load loss in a welding transformer at 130V as at 120V. At 140V 750W out required around 1000W in. 140V could come from a motor speed regulated gasoline generator set to deliver 110V at full load.
https://www.portescap.com/en/newsroom/whitepapers/2022/10/how-iron-losses-directly-influence-the-selection-of-a-bldc-motor
https://darwinmotion.com/blogs/what-is-v-hz-control-mode-for-ac-drives
The reason is because the current through the winding inductance rises with increasing AC voltage but falls with rising frequency. The V/Hz ratio controls the current which produces useful torque and damaging heat.
A motor's rotation makes it a generator whose voltage output opposes the power supply and thus limits the current to what the load requires. As the load slows the motor it generates less "back" voltage and allows more current, which permits the motor to drive the load, within design limits.
The 220V grinder motor I tested drew 4A, twice the rating, when stopped with 120V applied. When it reached full speed the current into the Variac driving the grinder was around 0.3A.
A simple analog current meter is enough to watch for excessive current draw when experimenting. Measuring the power consumed requires a more sophisticated meter that separates "real" from "apparent" power, Watts from Volt-Amps.
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-11/true-reactive-and-apparent-power/