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I'm in a lab and for some reason I cannot replicate my results on LTSpice.

I have gathered data from an experiment where I built the circuit shown in Figure 1. I then took that data, plotted it in Excel and found the polynomial trend line, see Figure 2. However when I try to replicate this experiment in LTSpice, the plot does not match, see Figure 3. I believe my circuit is wrong, but I'm not sure what to change. Any suggestions?

circuit built in lab

Figure 1: Circuit built in the lab

Recorded values of the ammeter and voltmeter. Data was plotted and given a polynomial trend line

Figure 2: Recorded values of the ammeter and voltmeter plotted showing polynomial trend line

ltspice circuit and incorrect plot

Figure 3: LTSpice circuit and incorrect plot

SamGibson
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sam
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  • You need to tweak your polynomial and nobody is going to do that except you. – Andy aka Nov 25 '20 at 18:32
  • I've ran the same data through matlab and received the same polynomial but I was mainly worried about the circuit. Thanks Andy! – sam Nov 25 '20 at 18:40
  • One thing I noticed is that the current source is upside down. This is a "reverse light bulb" that recharges the battery when you power it. – user253751 Nov 25 '20 at 18:41
  • I tried flipping the current source to see what it would change but it still gives me the same plot, thanks for the suggestion though user 253751! – sam Nov 25 '20 at 18:48

1 Answers1

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Your curve-fit coefficients are off. Not by a huge amount, but enough to change the curve shape. I get (for a least-square error fit):

-0.000172167
0.002980111
-0.01877186
0.071220342
0.012035623
Spehro Pefhany
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