The facit says that a resistor with resistance 274 Ohms should be connected in series with the pedal and a resistor with a resistance of 554 Ohms should be connected parallell with the pedal. Does that make sense to you?

 

The facit says that a resistor with resistance 274 Ohms should be connected in series with the pedal and a resistor with a resistance of 554 Ohms should be connected parallell with the pedal. Does that make sense to you?

Yes in principle it would make sense, although the values I obtained are different to suit my starting assumptions. I had 367Ω in parallel with the 550Ω controller and 330Ω as the series element.

The facit solution suggests that a series value of 274Ω would result in the 50% power or 40W condition. Which is of course different for my solution. I'll take a final look at my numbers but doubt I can offer any other ideas.

Until we see the teaching solution, it's difficult to comment further.

 

Clearly 274Ω for the series element won't give 40W at the motor with 230V source. Get back to the forum if & when you have the answer from your teacher.

 

The effective resistance at the ends of pedal travel are now 274Ω and 274Ω+(550Ω||554Ω)=550Ω, so it matches at the low speed end.

It looks as if they are running from the assumption that "half power" will occur with a resistance that is half the size of the low speed resistor. But this doesn't make a whole lot of sense. The only basis that it would remotely make sense is under the assumption that the motor always draws the same current regardless of speed and that with 550Ω it is just barely turning and so has 0V across it and so the full voltage appears across the resistor. But that would require that the circuit as a whole draws a constant 80W but that doesn't jive with the 80W spec.

So I, too, am curious to see what their reasoning is for their answer.

 

The effective resistance at the ends of pedal travel are now 274Ω and 274Ω+(550Ω||554Ω)=550Ω, so it matches at the low speed end.

I suggested that should be the answer back in post #8.
I guess nobody reads anymore.

 

I guess nobody reads anymore.

One of the hazards of being a contributor. Sometimes it seems one's efforts are of no consequence.

If the confusion surrounding the problem statement was eliminated by ignoring any reference to speed and effort concentrated on dealing only with the source power vs series resistance issue then we would have said bravo you're right. The reference to source voltage and motor rated power would also be unnecessary information. Unless one had to also specify the resistor power ratings as part of the solution.

Then the problem is quite simple.

Don't feel too bad you'll more than likely prove correct. I believe you are.