Proof of common sense when maths is lacking concept

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SUMMARY

The discussion centers around the power consumption of electric appliances, specifically comparing electric fans and kettles. Participants clarify that while a fan has a lower wattage than a kettle, it does not necessarily mean it has lower resistance. The correct formula for calculating power at a constant voltage is (I^2)*R, and the distinction between resistance and impedance is crucial, especially in AC circuits. The conversation emphasizes that a fan, being an inductive motor, can have higher resistance than a heater while consuming less power.

PREREQUISITES
  • Understanding of electrical power formulas, specifically (I^2)*R and (V^2)/R.
  • Knowledge of the difference between resistance and impedance in AC circuits.
  • Familiarity with the concepts of inductive motors and their behavior under AC voltage.
  • Basic comprehension of DC motor operation and back EMF.
NEXT STEPS
  • Research the principles of AC power and the significance of phase relationships in power calculations.
  • Explore the differences between DC and AC motors, focusing on their efficiency and power consumption.
  • Learn about the role of impedance in AC circuits and how it affects power dissipation.
  • Investigate the characteristics of inductive loads and their impact on electrical systems.
USEFUL FOR

Electrical engineers, students studying circuit theory, and anyone interested in understanding the intricacies of power consumption in electrical appliances.

  • #61
TB1,

So you're saying I could force it into that form after partial fractions, interesting.
THOUGH it would take ages to even get to (1) if you didn't have a computer to aid in expanding and simplifying the fraction, wouldn't it?
Yep, lots of work without a computer. But you can see that eq(6) is the same equation as eq(1).
Also, I don't quite see where H came from when you introduced it.
After rationalizing the left side, I multiplied the numerator by what it took to make it look like the right side. The multiplier was "H". Of course, I also had to multiply the denominator by the same multiplier to balance the fraction out.

Ratch
 
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  • #62
milesyoung said:
I'm not quite sure what you mean. I can't see how you could argue that the induced voltage from flux cutting the rotor windings could be attributed to self-inductance.

'Equivalent Circuits' don't always make physical sense, I know, but when you start a motor, a lot of energy goes in. The rate of current reduction will be exponential with a time constant. That can be modeled with a CR series circuit across a parallel resistor. It's a simplification but it even works as the supply volts are reduced.
 

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