Course work help

Daniel S Robinson:

. . .

I'm stuck on the 1st question, I have found two formulas   I= Tω/V   and  Ea = 2πNT/Ia   re aranged   Ia = 2πNT/Ea

Both give different answers and don't take into account the back EMF.


. . .

 

Hello Daniel. You have had some useful replies and I don't propose to enlarge on any of these. However I would give you a general tip for when you tackle questions like this.


Always be sure of the units you are dealing with.


In the first formula, I = Tω/V, the ω  refers to speed in radians per second. It is important that you convert from revs per minute. Likewise in the second formula, Ea = 2πNT/Ia, N represents revolutions per second, and the 2π performs the conversion to radians per second. If you do not use the correct units you can expect different answers.


Some of the other replies demonstrate this.


We seem to be lacking some information in the  question. Is this a shunt wound motor (whose speed varies little with torque) or a series wound motor (whose speed varies a lot with torque)? I would guess from the data that it is shunt wound but we should not use guess work with  calculations like this.


Zoomup's calculator includes a hash constant to do the conversion of non-SI units. This can be a useful cross-check, but in the work you submit you will be expected to explain your calculations.

Daniel S Robinson:

. . .

I'm stuck on the 1st question, I have found two formulas   I= Tω/V   and  Ea = 2πNT/Ia   re aranged   Ia = 2πNT/Ea

Both give different answers and don't take into account the back EMF.


. . .

 

Hello Daniel. You have had some useful replies and I don't propose to enlarge on any of these. However I would give you a general tip for when you tackle questions like this.


Always be sure of the units you are dealing with.


In the first formula, I = Tω/V, the ω  refers to speed in radians per second. It is important that you convert from revs per minute. Likewise in the second formula, Ea = 2πNT/Ia, N represents revolutions per second, and the 2π performs the conversion to radians per second. If you do not use the correct units you can expect different answers.


Some of the other replies demonstrate this.


We seem to be lacking some information in the  question. Is this a shunt wound motor (whose speed varies little with torque) or a series wound motor (whose speed varies a lot with torque)? I would guess from the data that it is shunt wound but we should not use guess work with  calculations like this.


Zoomup's calculator includes a hash constant to do the conversion of non-SI units. This can be a useful cross-check, but in the work you submit you will be expected to explain your calculations.