Engineering Solve Motor Coil Current at Startup & Full Speed

[Lucas123]

Homework Statement

electric machines

Relevant Equations

I do not know

The question I'm in doubt about is

The motor coil has a resistance of 10 Ω and is powered by a voltage of 120 V. When the motor is operating at rated speed, its emf is 70 V. Thus, it is questioned:

a) What is the coil current when the motor is started?
b) What is the coil current at rated speed?

What equations can I use to solve it?

 

[hutchphd]

You must make the attempt (rules of the website) . The difficult part is to decide which equations apply. What are likely candidates and why?

 

[Lucas123]

I thought about solving it like this:
a) V = Ri -> 120 = 10i -> i = 12 A

b) E = V - Ri -> 70 = 120 - 10i -> i = 5 A

But I don't know if it's correct

 

[hutchphd]

If I remember correctly (I do not do motors regularly) that will be true for an unloaded motor running at its design speed. Somebody will correct me as required... please.

 

[Tom.G]

I get the same answers you do.

[But your equations look funny here (odd characters), I can't sort them out.]

Cheers,
Tom