# Understanding electric motors and alternators!



## Coolio (Oct 29, 2010)

Hey guys. I am a student in mechanical engineering who is very interested in electric motors. I have been trying on my own to learn how they work and tried to come up with ways of improving them or finding new ways of using them. so far...nothing!
Well, I have some questions I would like to ask you guys (I saw some very interesting posts on this forum):
-how do you determine the torque required to rotate an alternator?
-is that torque formula the same as the one used to determine the torque output of an electric motor?
-do you have any idea of the coefficient factor of influence of a load on an alternator or motor? I mean is there any way to 'predict' the response of a motor/alternator under load?
-do different load have different impact on the alternator? I mean is there less current resistance or something when I plug in a bulb on a battery or if i plug in a fan?
these questions will most definitely help me have a better vision on this electricity world as I am almost 100% blind right now. Thank you all!

-Joe


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## tomofreno (Mar 3, 2009)

> -how do you determine the torque required to rotate an alternator?
> -is that torque formula the same as the one used to determine the torque output of an electric motor?


 Yes. The mechanical work done per unit time by a motor, or electrical work done per unit time by an alternator, is the shaft power, product of torque and shaft angular velocity. In the first case some electrical source of energy is used to excite the magnetic flux and electrical current in the rotor, which interacts with the rotating flux of the stator to convert electrical to mechanical energy, and in the second case mechanical work is done to spin the rotor and induce magnetic flux and current in the stator to convert mechanical to electrical energy.



> I mean is there any way to 'predict' the response of a motor/alternator under load?
> -do different load have different impact on the alternator?


 Yes. The work per unit time plus losses such as windage and bearing friction must equal the shaft power. Larger power dissipation in a load requires more work be done per unit time, more mechanical power input to the alternator, so more torque and/or higher rpm.

You might also try the Aussie group. They have some people who are knowledgeable in electrical/mechanical conversion devices:
http://www.aeva.asn.au/


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## major (Apr 4, 2008)

Coolio said:


> Hey guys. I am a student in mechanical engineering who is very interested in electric motors. I have been trying on my own to learn how they work and tried to come up with ways of improving them or finding new ways of using them. so far...nothing!


Hi Joe,

Why not sign up for a course in energy conversion or electrical machinery in the EE department?

There are plenty of books on the subject. See the library on campus.

The load questions you ask are most often found on the performance characteristic graphs supplied as the specifications with the motor, generator, or alternator. However, these quantities can be calculated if you have the parameters for the machine.

Regards,

major


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