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Old 10-16-2014, 03:29 PM   #1215 (permalink)
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Um, yes, that's what I posted above. Look at graph 2 and 3; that's basically what you are describing. Paul has been very successful within the base speed range of performance. Beyond the base speed (which has a LOT to do with the input voltage, which Paul is wisely keeping low for now) things get non-linear. To make full use of a motor's capability, it's good to make full use of the "constant power" part of the performance curve.

The problem is that we are not starting with a complete VFD. We are making one. Ive done many motor control applications where one starts with a servo motor and a controller, which will have some performance curve like graph 2. No understanding of the motor or controller is necessary in this case to make an application (like a CNC machine) work. However, since we are actually making the controller, an understanding of what is physically happening underneath the nice control may be helpful in actually making a nice control. All of the CNC's I've owned have had seperate controllers: 1 for the overall machine and 1 for each servo. We are making the motor controller, not the overall control.

- E*clipse

Originally Posted by CrazyRick View Post
E*clipse, when an induction motor is driven by its correct V/Hz ratio, the torque will remain constant and horsepower increases the faster you go, when the Hz moves beyond the maximum voltage, the motor is in what's refered to as "constant horsepower" mode because the RPM will increase but the torque decreases since the V/Hz ratio is not met.

It would be very easy to run a 240V 60Hz motor on 480V 120Hz have the same torque and double the horsepower!

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