As you have seen, the Thevenin Equivalent of a circuit can be obtained by calcul

Question

As you have seen, the Thevenin Equivalent of a circuit can be obtained by calculating/
measuring two I-V values: voc and isc. Often, it is not practical to measure the short
circuit current. Can you imagine trying to measure isc for a car battery? Suppose you
wanted to obtain the Thevenin Equivalent of a circuit by making two measurements,
neither of which involves measuring isc. You measure voc and then place a 1 kW
resistor across the terminals and measure the voltage drop across the resistor. Do you
have enough information from these two measurements to obtain the Thevenin
Equivalent circuit? Justify your answer in detail.

Explanation / Answer

no, the 1 kW resistor may not match the equivalent resistance seen by the terminals of the battery. To identify the equivalent resistance, one you must find the voltage drop across those terminals. This can simply be done by measuring the voltage at terminals of the battery while it is connected and the car running. Next, to find the equivalent resistance of the car. Disconnect the battery and connect a small known voltage source, a 12 V battery for instance. Measure the current that flows. The ratio of the 12 V source divided by this current is the equivalent resistance of the car. Isc can be found using source transformation. (Isc)=(Vth)/(Req). The Req is still the equivalent resistance for the norton circuit. The only difference is that it is in parallel to this transformed voltage source.

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