Help with electric motor power calculations

[gotoluc]

Hi everyone,

I need some electric motor power information that I can't find or don't know how to calculate.

What I would like to know is how many grams of pull force would an 80% efficient electric motor have per Watt in stalled position.

Thanks for your time

Luc

[fritz]

Unless you don´t have a rated stall torque from a datasheet or torque/amps/rpm curves it might be pretty difficult to calculate.
If you have a motor with few poles - ths stall torque might be additional position dependent.
If you have the rating for 80% efficiency - than this will be given in a narrow rpm/load band.
For motors with few poles - there would be the need for a gearbox to get a useful stall torque.
If you provide more details on type of motor / model I could help out with assumptions / comparisons.
rgd.

[gotoluc]

Hi fritz,

thanks for your reply.

What I'm trying to find is a reference of what's the best known score (in grams of pull per watt) of an electromagnet (with air gap) like in an electric motor scenario.

A solenoid data could be used as it's the same principle of an electric motor but it must have an air gap to compare it with an electric motor.

Why I need this?... it's to test the pull force per watt of a new build I have of my mostly permanent magnet motor design. I want to see if the pull force of my design can beat what has already been accomplish.

I have looked around and found a solenoid can pull 20 grams per watt. However, I don't know if that's the best score?

Is there a way to convert inch or foot pounds to pull pound?... if so, then maybe we could convert a known motor stall torque from inch pounds to pull pounds. The only thing I don't understand is, if a motor stall torque is in inch or foot pounds but the shaft is not turning (stalled) how can that work?

Thanks for you time and offer to help

Luc

[Low-Q]

I think you are confusing torque with energy. Torque must be measured at a known radius. Only then you can figure out the "grams of pull" it can do.
You can have two motors with the same Watt rating and the same efficiency, but one can have 100 times more torque than the other. However, the higher torque is on expence of lower rpm's in order to conserve energy.


Vidar

[gotoluc]

I think you are confusing torque with energy. Torque must be measured at a known radius. Only then you can figure out the "grams of pull" it can do.
You can have two motors with the same Watt rating and the same efficiency, but one can have 100 times more torque than the other. However, the higher torque is on expence of lower rpm's in order to conserve energy.


Vidar

Hi Vidar,

thanks for your reply. I do agree with what you say. I am not knowledgeable in motor power calculations. This is why I started this topic, to get help from the more knowledgeable.

What I'm trying to do is find a way to measure the work force in watts of my mostly magnet motor design I came up with some years ago compared to the work force of a conventional electric motor.

Maybe I should compare it with the pull force of a solenoid as my design is more like that principle. But where to find the data of the most efficient solenoid pull force?  to see if my design can pull more per watt.

What I find interesting in my design is, there is not sticky spot as the magnets are fixed. Only the coil moves within the magnetized core area and the coils Inductance remains the same throughout the power stroke. But the most interesting thing is, the more the permanent magnets are powerful and the more core surface area there is, the more the coils pull force is without increasing power.

If you are not familiar with my motor, please have a look at the 2 video to get a better idea of how the motor works:
http://www.youtube.com/watch?v=GYoXmDvFqQs
http://www.youtube.com/watch?v=KnAeIE_NWjU

I've just finished building a new version and this one uses 4 of 1 inch cube N52 magnets instead of the tiny hard drive magnet I used in the video demo.

I'm just trying to see if my design has any more pull force than a standard coil and core. But for that I need some data and method of calculating it without going through the time and expense of building a flywheel for the new one I built just to convert the push pull action to rotation and build a dyno to test it. There must be a way I can just use a hook scale that will measure the pull force in grams, oz. or pounds and compared that to the watts consumed.

Can you or anyone help?

Thanks for your time and help

Luc