Mike Henderson
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- 1,405
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- Villa Park, CA
Earlier in this thread Jeff Horton mentioned the R/I motor. I did not know what the R/I abbreviation stood for and PM’ed Jeff to ask. He was very kind to explain that it stood for “Repulsion/Induction” motor. This lead me to research how an R/I motor worked and how it compared to a capacitor start motor, since Jeff reported that he perceived his R/I motor was more powerful than a modern capacitor start motor of the same HP rating.
After enough research to understand the theory of operation of the R/I motor, I simply could not find any reason that an R/I motor would perform better than a capacitor start motor. The only difference between the two motors is in the starting mechanism. Once they are running at operating speed they are identical – they are both induction motors. The R/I motor has greater startup torque but this does not play any part once the motor is at operating speed – no more than a couple of seconds after power-on for woodworking applications.
This next led me to think of ways that the motors could be tested to see if the R/I motor did indeed produce more power than an equally rated capacitor start motor but testing HP is not easy and requires specialized equipment.
Then it occurred to me that there’s an indirect way to test the power of a motor. An electric motor is an energy conversion device. If one motor puts out more power than another motor, it must take more power from the lines. Efficiency could play into this, but almost all motors are of equal efficiency, with the modern motor being likely to be more efficient because of improvements in the magnetic properties of the metal and the layout of the electromagnets.
So to test whether an R/I motor is more powerful, you can measure the power into the motor while cutting a certain sized board, then replace the motor with a capacitor start motor of the same HP, and cut the same board while measuring the power into the motor.
My expectation is that the power would be about the same for the two motors but I’d welcome test results from anyone who has two motors and would carry out the tests.
Mike
After enough research to understand the theory of operation of the R/I motor, I simply could not find any reason that an R/I motor would perform better than a capacitor start motor. The only difference between the two motors is in the starting mechanism. Once they are running at operating speed they are identical – they are both induction motors. The R/I motor has greater startup torque but this does not play any part once the motor is at operating speed – no more than a couple of seconds after power-on for woodworking applications.
This next led me to think of ways that the motors could be tested to see if the R/I motor did indeed produce more power than an equally rated capacitor start motor but testing HP is not easy and requires specialized equipment.
Then it occurred to me that there’s an indirect way to test the power of a motor. An electric motor is an energy conversion device. If one motor puts out more power than another motor, it must take more power from the lines. Efficiency could play into this, but almost all motors are of equal efficiency, with the modern motor being likely to be more efficient because of improvements in the magnetic properties of the metal and the layout of the electromagnets.
So to test whether an R/I motor is more powerful, you can measure the power into the motor while cutting a certain sized board, then replace the motor with a capacitor start motor of the same HP, and cut the same board while measuring the power into the motor.
My expectation is that the power would be about the same for the two motors but I’d welcome test results from anyone who has two motors and would carry out the tests.
Mike