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Re: Internal resistance



Ludwik Kowalski wrote:
>>... r ... was found to decrease
>>monotonically from 1.4 ohms, at I=0.85 A,
>>to 1.0 ohms at 3.8A. .... (V1-V2)/I

The question is ill-posed.

In the key formula, V1 is not measured "at"
3.8A so the quotient (V1-V2)/I cannot be called
the resistance "at" (V1-V2)/I.

If I were doing it, I would express the results and
the questions in conventional Thevenin terms, i.e.
impedance and open-circuit voltage.

Also, since this appears to be a double-regulated
power supply, in the current-limited regime it
would be natural to switch to the Norton equivalent
circuit, i.e. an impedance and a short-circuit current.
The impedance in the current-limited regime should be
enormous.

We would expect grossly nonlinear behavior in the
regime where voltage-limiting crosses over to
current-limiting.