Engineering Solve Motor Coil Current at Startup & Full Speed

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SUMMARY

The discussion focuses on calculating the coil current for a motor with a resistance of 10 Ω powered by 120 V. When starting, the coil current is determined using Ohm's Law, yielding a current of 12 A. At rated speed, with an induced emf of 70 V, the coil current is calculated to be 5 A using the equation E = V - Ri. These calculations are confirmed as correct for an unloaded motor operating at design speed.

PREREQUISITES
  • Understanding of Ohm's Law
  • Familiarity with electromotive force (emf) concepts
  • Basic knowledge of electric motor operation
  • Ability to manipulate algebraic equations
NEXT STEPS
  • Study the principles of electric motor starting currents
  • Learn about the impact of load on motor coil current
  • Research the differences between unloaded and loaded motor performance
  • Explore advanced motor control techniques and their equations
USEFUL FOR

Electrical engineers, motor control specialists, and students studying electrical machinery will benefit from this discussion.

Lucas123
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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?
 
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You must make the attempt (rules of the website) . The difficult part is to decide which equations apply. What are likely candidates and why?
 
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
 
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.
 
I get the same answers you do.

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

Cheers,
Tom
 

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