In this lab, we explored the concepts of power transfer through a circuit. We attempted to maximize power transfer to a load by modifying the source resistance, and then by modifying the load resistance. We should (hopefully) find that modifying source resistance does not result in maximum power transfer. We began by drawing what we should expect a power graph to look like, which contains a parabolic component along with a linear (i^2 * R).
According to this equation, the max power will be produced when the load resistance is equivalent to the Thevenin resistance. This can by shown by simply setting the derivative equal to zero.
We were asked to set up a simple circuit which contained a source resistor R_s = 2.2 kOhms, as well as a variable load resistor R_l in the form of a 10k potentiometer.
After setting up the circuit (which we apparently forgot to take photos of), we were instructed to measure the voltage V_out, and use this value to calculate the power delivered to the load. We then created a table of power vs. R_l and graph the data curve.
The table next to the graph shows, from left to right, the values of R_l, V_out, and P that were found from taking our measurements.
In Class Exercises:
1. (a) For the circuit given, obtain the Thevenin equivalent at terminals a-b.
(b) Calculate the current in RL = 8 Ω
(c) Find RL for maximum power
(d) Determine that maximum power.
1. (a) For the circuit given, obtain the Thevenin equivalent at terminals a-b.
(b) Calculate the current in RL = 8 Ω
(c) Find RL for maximum power
(d) Determine that maximum power.
2. In this example, we determined the internal resistance of 1 electric brushless DC motor and 2 CIM motors all in parallel using the spec charts for each motor.
3. Find the value RL for maximum power transfer in the circuit shown below:
4. The terminal voltage of a voltage source is 12 V when connected to a 2-W load. When the load is disconnected, the terminal voltage rises to 12.4 V. (a) Calculate the source voltage v s and internal resistance R s . (b) Determine the voltage when an 8-Ohm load is connected to the source.
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