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DC Motors and Nameplate Ratings

by strgt
Tags: motors, nameplate, ratings
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Mar3-13, 11:14 AM
P: 3
I picked up a DC variable speed treadmill motor for a project that I am working on and I am having a hard time finding the information that I need. I need to drive a secondary pulley through a range of RPM up to a specific point. In order to pick the right size pulley, I need to be able to determine the operating speed range that I want the motor to run at. The only information I can get about the motor is whats listed on the faceplate. It shows:

3.0 hp continous duty

I am first trying to analyze the torque it could output on the drive pulley. My assumptions are that the rated RPM is the maximum RPM where the motor runs with no load on it. By assuming a linear torque vs. speed curve (which is characteristic of a dc permananent magnet motor), I can then assume the rated hp would occur at 50% of the maximum rpm. In this case I can then draw the rest of the torque curve and analyze the torque output at each rpm.

The problem with this idea is that if that RPM is where the motor outputs 3hp, then that changes the torque curve. Another problem would be if that rpm is a mechanical limit, IE the safe rpm limit where the motor may mechanically be safe and not necessarily the maximum no load speed. In this case it would give me no information about the motor or what range to run it at.

I need to be able to maximize the amount of torque on the secondary pulley through the specific RPM range. The more the better in this case and the secondary pulley is something that im having machined so its going to cost a bit of money. If anyone knows much about the ratings on these motors I would appreciate any info you can give. Thanks.
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