Hi Lady s and Gentlemen,

I am struggling with one of the question from coursework sheets, could you help me please?
A permanent magnet DC motor has an armature resistance of 0.5  and when a voltage of 120 V is applied o the motor it reaches a steady-state speed of rotation of 20 rev/s and draws 40 A. What will be (a) the power loss in the armature and (b) the power input to the motor?

Hopefully some one will give me a clue. I am not sure if the current given is the armature current or the real current of motor.

Many thanks

 

It depends, what motor model are you using?

This may be of assistance...

 

Well it does not say in the question...might it be the problem for solving it?

 

the kind of motor doesnt matter if it says its a permanent magnet motor. (that is the motor). You have all the information in the question to answer it. I don't want to give you the answer, but just dont get caught up in the model of motor nonsense.

 

the kind of motor doesnt matter if it says its a permanent magnet motor. (that is the motor). You have all the information in the question to answer it. I don't want to give you the answer, but just dont get caught up in the model of motor nonsense.

Really? What equations do you apply then? This is highly dependent of the motor model used. A simple series resistance can be used, or a whole 2nd order system. The solution depends on the model.

 

Think: What windings does a permanent magnet motor have besides the armature winding?

 

Think: What windings does a permanent magnet motor have besides the armature winding?

You are asking me?

 

No. I am replying to the original poster.

 

A quick search gave me these models:
http://engineeronadisk.com/V2/book_modelling/engineeronadisk-439.gif

http://www.rcgroups.com/articles/ezonemag/2003/feb/inside/motor_model.jpg

http://www.maplesoft.com/SizedImages/image.ashx?file=42f07ca18bce9ea2a26be91b0dc4996d_364_280.gif

http://www.eece.ksu.edu/~starret/589/man/Jfig2.gif

http://ars.els-cdn.com/content/image/1-s2.0-S0959152406001296-gr12.jpg