Spec a 3PH motor 1

[ihopeitworks]

I currently have a 2HP, 3PH, 60Hz AC motor, that is connected directly to a 12" dia drum. In the past, I would pull a cable that is wrapped around it with 2 lbs of tension (torque of 1 ft-lb). I have a new project that I am working on that requires a 10.75" dia drum pulling a cable that will have 25 lbs of tension (torque of 11.2 ft-lb). My current motor is not adequate to handle this task so I am now looking for a new motor and VFD to swap out. The kicker is I'll need to be able to apply 11.2 ft-lb of torque at both 120 RPM and 1400 RPM. The reason for the different RPM is that I need to pull this cable at two different speeds, but at the same tension.

How would I go about spec'ing in a motor for this sort of application? I would hope I can get to both RPM within 10 seconds or so. I have a panel wired to step up 120 VAC to run at ~230 VAC. It seems very difficult to find a motor's torque curve for the entire RPM range, it seems that they're only included for the high RPM end.

Looking for any guidance. Thanks.

 

[Skogsgurra]

All cases where I have seen this happen were in ventilator applications where the fans were running at maximum speed because of hot weather. The combined influence of maximum load and high ambient temperature may not happen very often. But it happens and may need some consideration.
I think that I will (carefully) rig such a situation and do some measurements. Stay tuned!

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.