Motor Input Power: Does Load Affect Performance?

[firavia]

If I have a designed gear box that needs a motor to run , and according to my calculations the input power for the gear box must be 10 Kw at 10 r.p.s must I chose a motor with the same input specifications ?
when I buy a motorwith certain specifications like : 10 kw 3000 R.P.M , does these specifications change when the motor has a certain load ??



and is it right to say that when a motor run at no-load it runs freely at its specifications rates and when we put a load on the motor the specifications decreases

example , we have a motor that run at 10 kw and 1000 r.p.m at no load , when we attach it to a complex gear box would the motor deliver a power that is less than 10 kw and it will rotate the input shaft of the gear box at less than 1000 r.p.m? or the motor must run at the same specifactions at no load ?

 

[Cyrus]

A motor is rated for a certain speed and power output under load. You may or may not need to know the inertial load the motor can take before the speed controller cuts itself off (if it runs off of a speed controller). This has been a problem I've seen in the past.

 

[FredGarvin]

You have to do one of two things.

1) get a torque curve for the specific motor you are looking at. It will tell you the characteristics of the motor, i.e. how much torque at how much rotational speed. From there you can determine if the motor will suit your needs. I can say from personal experience that the rating on the data plate is nowhere near the whole story for a motor.

2) Definitely the easiest...talk to a local electric motor rep. They can size them on the spot in most cases and also have in depth knowledge of the controller required as well. You have to know the operating parameters, of course, but that should be a no brainer. Things can get complicated when you look at things like constant power vs. constant torque vs. variable torque.

If you want to start educating yourself, Baldor has a nice set of papers they put together called the Cowern Papers. Do a search on that term and you should be able to download a PDF of it.