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Re: Internal resistance



that's your supply.

Obviously your supply is electronically regulated; in that case it may
be designed to get any reasonable internal resistance and variation with
load one could wish. Mine (just checked) is rather more constant.
But then it's an HP precision P/S # 6115A 0=>50 V. 0.8 A.; to 100
V., 0.5A

i.e. (@ ~ 7 V.)

current (Ampères) internal resistance (Ohms)
0.206 0.602
0.263 0.614
0.364 0.574
0.528 0.494
0.767 0.569


I used two 4 1/2 digit DMM's (Data Precision # 2480R)

As an example of lack of planning, I miss-wired, so the internal
resistance of the current DMM and it's wiring are included. (one A.
scale internal R is 0.1 Ohm in addition as much as 0.4 from the wires,
AND may vary because of connection resistance.)

an I-V plot is linear: R^2 = 0.999

bc

p.s. you method appears to give the R for only one point?

Ludwik Kowalski wrote:

The following results were obtained in a
lecture-demonstration today. They show
that the internal r of a power supply is
not a constant. It was found to decrease
monotonically from 1.4 ohms, at I=0.85 A,
to 1.0 ohms at 3.8A. Any comments?

938 AC/DC power supply from LabVolt

We used the DC output (designed for
0-36 V and up to 5A). First we measured
V1, the DOP between the terminal when
there is no current. Then our resistor of
2.8 ohms (Imax=12 A) was connected to
the DC terminals. Both the current I and
the DOP across the 2.8 ohm resistor, V2,
were measured at room temperature. The
internal r was calculated as (V1-V2)/I.
Ludwik Kowalski